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- Zoology 2404
- Hanson
- Final Review
Final Review
Zoology 2404 with Hanson at Texas Tech University
About this deck
By: Morgann Hambright
Created: 2011-05-01
Size: 357 flashcards
Views: 82
Created: 2011-05-01
Size: 357 flashcards
Views: 82
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Typical Adult Kidney
Is about 10 cm long, 5.5 cm wide, and 3 cm thick (4 in. x 2.2 in. x 1.2 in.) Weighs about 150 g (5.25 oz)
Three Functions of the Urinary System
Excretion: Removal of organic wastes from body fluids Elimination: Discharge of waste products Homeostatic regulation: Of blood plasma volume and solute concentration
Kidneys
organs that produce urine
Urinary Tract
organs that eliminate urine
-ureters (paired tubes), urinary bladder (muscular sac), urethra (exit tube)
-ureters (paired tubes), urinary bladder (muscular sac), urethra (exit tube)
Urination or Micturition--Process of eliminating urine
contraction of muscular urinary bladder forces urine through urethra, and out of body
Five Homeostatic Functions of Urinary System
Regulates blood volume and blood pressure, regulates plasma ion concentrations, helps stabilize blood pH, conserves valuable nutrients, and assists liver in detoxifying poisons
Renal Pyramids
6 to 18 distinct conical or triangular structures in renal medulla Base abuts cortex Tip (renal papilla) projects into renal sinus
Nephrons
Microscopic, tubular structures in cortex of each renal lobe Where urine production begins Structural, functional units of kidneys >1million per kidney
Blood Supply to Kidneys
Kidneys receive 20–25% of total cardiac output 1200 mL of blood flows through kidneys each minute Kidney receives blood through renal artery
Segmental Arteries
Receive blood from renal artery Divide into interlobar arteries Which radiate outward through renal columns between renal pyramids Supply blood to arcuate arteries Which arch along boundary between cortex and medulla of kidney
Afferent Arterioles
Branch from each cortical radiate artery (also called interlobar artery) Deliver blood to capillaries supplying individual nephrons
Cortical Radiate Veins (also called interlobular veins)
Deliver blood to arcuate veins Empty into interlobar veins Which drain directly into renal vein
Renal Nerves
Innervate kidneys and ureters Enter each kidney at hilum Follow tributaries of renal arteries to individual nephrons
Sympathetic Innervation
Adjusts rate of urine formation By changing blood flow and blood pressure at nephron Stimulates release of renin Which restricts losses of water and salt in urine By stimulating reabsorption at nephron
The Nephron
Consists of renal tubule and renal corpuscle Renal tubule Long tubular passageway Begins at renal corpuscle Renal corpuscle Spherical structure consisting of: glomerular capsule (Bowman’s capsule) cup-shaped chamber capillary network (glomerulus)
Glomerulus
Consists of 50 intertwining capillaries Blood delivered via afferent arteriole Blood leaves in efferent arteriole Flows into peritubular capillaries Which drain into small venules And return blood to venous system
Filtration
Occurs in renal corpuscle Blood pressure Forces water and dissolved solutes out of glomerular capillaries into capsular space Produces protein-free solution (filtrate) similar to blood plasma
Three Functions of Renal Tubule
1.Reabsorb useful organic nutrients that enter filtrate 2.Reabsorb more than 90% of water in filtrate 3.Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus
Segments of Renal Tubule
Located in cortex Proximal convoluted tubule (PCT) Distal convoluted tubule (DCT) Separated by nephron loop (loop of Henle) U-shaped tube Extends partially into medulla
Organization of the Nephron
Traveling along tubule, filtrate (tubular fluid) gradually changes composition Changes vary with activities in each segment of nephron
Each Nephron
Empties into the collecting system: A series of tubes that carries tubular fluid away from nephron
Collecting Ducts
Receive fluid from many nephrons Each collecting duct Begins in cortex Descends into medulla Carries fluid to papillary duct that drains into a minor calyx
Cortical Nephrons
85% of all nephrons Located mostly within superficial cortex of kidney Nephron loop (Loop of Henle) is relatively short Efferent arteriole delivers blood to a network of peritubular capillaries
Juxtamedullary Nephrons
15% of nephrons Nephron loops extend deep into medulla Peritubular capillaries connect to vasa recta
The Renal Corpuscle
Each renal corpuscle Is 150–250 µm in diameter Glomerular capsule: is connected to initial segment of renal tubule forms outer wall of renal corpuscle encapsulates glomerular capillaries Glomerulus knot of capillaries
The Glomerular Capsule
Outer wall is lined by simple squamous capsular epithelium Continuous with visceral epithelium which covers glomerular capillaries separated by capsular space
The Visceral Epithelium
Consists of large cells (podocytes) With complex processes or “feet” (pedicels) that wrap around specialized lamina densa of glomerular capillaries
Filtration Slits
Are narrow gaps between adjacent pedicels Materials passing out of blood at glomerulus Must be small enough to pass between filtration slits
The Glomerular Capillaries
Are fenestrated capillaries Endothelium contains large-diameter pores
Blood Flow Control
Special supporting cells (mesangial cells) Between adjacent capillaries Control diameter and rate of capillary blood flow
The Filtration Membrane
Consists of Fenestrated endothelium Lamina densa Filtration slits
Filtration
Blood pressure Forces water and small solutes across membrane into capsular space Larger solutes, such as plasma proteins, are excluded
Filtration at Renal Corpuscle
Is passive Solutes enter capsular space Metabolic wastes and excess ions Glucose, free fatty acids, amino acids, and vitamins
Reabsorption
Useful materials are recaptured before filtrate leaves kidneys Reabsorption occurs in proximal convoluted tubule
The Proximal Convoluted Tubule (PCT)
Is the first segment of renal tubule Entrance to PCT lies opposite point of connection of afferent and efferent arterioles with glomerulus
Epithelial Lining of PCT
Is simple cuboidal Has microvilli on apical surfaces Functions in reabsorption Secretes substances into lumen
Tubular Cells
Absorb organic nutrients, ions, water, and plasma proteins from tubular fluid Release them into peritubular fluid (interstitial fluid around renal tubule)
Nephron loop (also called loop of Henle)
Renal tubule turns toward renal medulla Leads to nephron loop Descending limb Fluid flows toward renal pelvis Ascending limb Fluid flows toward renal cortex Each limb contains Thick segment Thin segment
The Thick Descending Limb
Has functions similar to PCT Pumps sodium and chloride ions out of tubular fluid
Ascending Limbs
Of juxtamedullary nephrons in medulla Create high solute concentrations in peritubular fluid
The Thin Segments
Are freely permeable to water Not to solutes Water movement helps concentrate tubular fluid
The Thick Ascending Limb
Ends at a sharp angle near the renal corpuscle Where DCT begins
The Distal Convoluted Tubule (DCT)
The third segment of the renal tubule Initial portion passes between afferent and efferent arterioles Has a smaller diameter than PCT Epithelial cells lack microvilli
Three Processes at the DCT
1.Active secretion of ions, acids, drugs, and toxins 2.Selective reabsorption of sodium and calcium ions from tubular fluid 3.Selective reabsorption of water: §Concentrates tubular fluid
Juxtaglomerular Complex
An endocrine structure that secretes Hormone erythropoietin Enzyme renin Formed by Macula densa Juxtaglomerular cells
Macula Densa
Epithelial cells of DCT, near renal corpuscle Tall cells with densely clustered nuclei
Juxtaglomerular Cells
Smooth muscle fibers in wall of afferent arteriole Associated with cells of macula densa Together with macula densa forms juxtaglomerular complex (JGC)
The Collecting System
The distal convoluted tubule opens into the collecting system Individual nephrons drain into a nearby collecting duct Several collecting ducts (not considered part of nephron) Converge into a larger papillary duct Which empties into a minor calyx
The Collecting System continued…
Transports tubular fluid from nephron to renal pelvis Adjusts fluid composition Determines final osmotic concentration and volume of urine
The goal of urine production
Is to maintain homeostasis By regulating volume and composition of blood Including excretion of metabolic waste products
Three organic waste products
1. Urea 2. Creatinine 3. Uric Acid
Organic Waste Products
Are dissolved in bloodstream Are eliminated only while dissolved in urine Removal is accompanied by water loss
The Kidneys
Usually produce concentrated urine 1200–1400 mOsm/L (four times plasma concentration)
Kidney Functions
To concentrate filtrate by glomerular filtration Failure leads to fatal dehydration Absorbs and retains valuable materials for use by other tissues Sugars and amino acids
Basic Processes of Urine Formation
1.Filtration 2.Reabsorption 3.Secretion
Types of Carrier-Mediated Transport
Facilitated diffusion (passive) Active transport (active) Cotransport (active/passive) Countertransport (passive)
Characteristics of Carrier-Mediated Transport
1.A specific substrate binds to carrier protein that facilitates movement across membrane 2.A given carrier protein usually works in one direction only 3.Distribution of carrier proteins varies among portions of cell surface 4.The membrane of a single tubular cell contains many types of carrier protein Carrier proteins, like enzymes, can be saturated
Transport maximum (Tm) and the Renal Threshold
If nutrient concentrations rise in tubular fluid Reabsorption rates increase until carrier proteins are saturated Concentration higher than transport maximum Exceeds reabsorptive abilities of nephron Some material will remain in the tubular fluid and appear in the urine: determines the renal threshold
Renal Threshold
Is the plasma concentration at which A specific compound or ion begins to appear in urine Varies with the substance involved
Renal Threshold for Glucose
Is approximately 180 mg/dL If plasma glucose is greater than 180 mg/dL Tm of tubular cells is exceeded Glucose appears in urine: glycosuria
Renal Threshold for Amino Acids
Is lower than glucose (65 mg/dL) Amino acids commonly appear in urine After a protein-rich meal Aminoaciduria
An Overview of Renal Function
Water and solute reabsorption Primarily along proximal convoluted tubules Active secretion Primarily at proximal and distal convoluted tubules Long loops of juxtamedullary nephrons and collecting system Regulate final volume and solute concentration of urine
Regional Differences
Nephron loop in cortical nephron Is short Does not extend far into medulla Nephron loop in juxtamedullary nephron Is long Extends deep into renal pyramids Functions in water conservation and forms concentrated urine
Osmolarity
Is the osmotic concentration of a solution Total number of solute particles per liter Expressed in osmoles per liter (Osm/L) or milliosmoles per liter (mOsm/L) Body fluids have osmotic concentration of about 300 mOsm/L
Other Measurements
Ion concentrations In milliequivalents per liter (mEq/L) Concentrations of large organic molecules Grams or milligrams per unit volume of solution (mg/dL or g/dL)
Filtration
Hydrostatic pressure forces water through membrane pores Small solute molecules pass through pores Larger solutes and suspended materials are retained Occurs across capillary walls As water and dissolved materials are pushed into interstitial fluids
Filtration
In some sites, such as the liver, pores are large Plasma proteins can enter interstitial fluids At the renal corpuscle Specialized membrane restricts all circulating proteins
Reabsorption and Secretion
At the kidneys, it involves Diffusion Osmosis Channel-mediated diffusion Carrier-mediated transport
Glomerular Filtration
Involves passage across a filtration membrane Capillary endothelium Lamina densa Filtration slits
Glomerular Capillaries
Are fenestrated capillaries Have pores 60–100 nm diameter Prevent passage of blood cells Allow diffusion of solutes, including plasma proteins
The Lamina Densa
Is more selective Allows diffusion of only Small plasma proteins Nutrients Ions
The Filtration Slits
Are the finest filters Have gaps only 6–9 nm wide Prevent passage of most small plasma proteins
Filtrate
Glomeruli generate about 180 liters of filtrate per day 99% is reabsorbed in renal tubules
Filtration Pressure
Glomerular filtration rate depends on filtration pressure Any factor that alters filtration pressure alters GFR
Hormonal Regulation of the GFR
By hormones of the Renin–angiotensin system Natriuretic peptides (ANP and BNP)
The Renin–Angiotensin System
Three stimuli cause the juxtaglomerular complex (JGA) to release renin Decline in blood pressure at glomerulus due to decrease in blood volume Fall in systemic pressures due to blockage in renal artery or tributaries Stimulation of juxtaglomerular cells by sympathetic innervation due to decline in osmotic concentration of tubular fluid at macula densa
The Renin–Angiotensin System: Angiotensin II Activation
Constricts efferent arterioles of nephron Elevating glomerular pressures and filtration rates Stimulates reabsorption of sodium ions and water at PCT Stimulates secretion of aldosterone by suprarenal (adrenal) cortex Stimulates thirst Triggers release of antidiuretic hormone (ADH) Stimulates reabsorption of water in distal portion of DCT and collecting system
The Renin–Angiotensin System
Aldosterone Accelerates sodium reabsorption: in DCT and cortical portion of collecting system
Increased Blood Volume
Automatically increases GFR To promote fluid loss Hormonal factors further increase GFR Accelerating fluid loss in urine
Natriuretic Peptides
Are released by the heart in response to stretching walls due to increased blood volume or pressure Atrial natriuretic peptide (ANP) is released by atria Brain natriuretic peptide (BNP) is released by ventricles Trigger dilation of afferent arterioles and constriction of efferent arterioles Elevates glomerular pressures and increases GFR
Autonomic Regulation of the GFR
Mostly consists of sympathetic postganglionic fibers Sympathetic activation Constricts afferent arterioles Decreases GFR Slows filtrate production Changes in blood flow to kidneys due to sympathetic stimulation May be opposed by autoregulation at local level
Reabsorption
recovers useful materials from filtrate
Secretion
ejects waste products, toxins, and other undesirable solutes
Reabsorption and Secretion at the PCT
PCT cells normally reabsorb 60–70% of filtrate produced in renal corpuscle Reabsorbed materials enter peritubular fluid And diffuse into peritubular capillaries
Five Functions of the PCT
1. Reabsorption of organic nutrients
2. Active reabsorption of ions
3. Reabsorption of water
4. Passive reabsorption of ions
5. Secretion
2. Active reabsorption of ions
3. Reabsorption of water
4. Passive reabsorption of ions
5. Secretion
Sodium Ion Reabsorption
Is important in every PCT process Ions enter tubular cells by Diffusion through leak channels Sodium-linked cotransport of organic solutes Countertransport for hydrogen ions
The Nephron Loop and Countercurrent Multiplication
Nephron loop reabsorbs about 1/2 of water and 2/3 of sodium and chloride ions remaining in tubular fluid by the process of countercurrent exchange
Countercurrent Multiplication
Is exchange that occurs between two parallel segments of loop of Henle The thin, descending limb The thick, ascending limb
Countercurrent
Refers to exchange between tubular fluids moving in opposite directions Fluid in descending limb flows toward renal pelvis Fluid in ascending limb flows toward cortex
Multiplication
Refers to effect of exchange Increases as movement of fluid continues
Parallel Segments of Nephron Loop
Are very close together, separated only by peritubular fluid Have very different permeability characteristics
The Thin Descending Limb
Is permeable to water Is relatively impermeable to solutes
The Thick Ascending Limb
Is relatively impermeable to water and solutes Contains active transport mechanisms Pump Na+ and Cl- from tubular fluid into peritubular fluid of medulla
Sodium and Chloride Pumps
Elevate osmotic concentration in peritubular fluid Around thin descending limb Cause osmotic flow of water Out of thin descending limb into peritubular fluid Increasing solute concentration in thin descending limb
Concentrated Solution
Arrives in thick ascending limb Accelerates Na+ and Cl- transport into peritubular fluid of medulla
Solute Pumping
At ascending limb Increases solute concentration in descending limb Which accelerates solute pumping in ascending limb
Countercurrent Multiplication
Active transport at apical surface Moves Na+, K+ and Cl- out of tubular fluid Uses carrier protein: Na+-K+/2 Cl- transporter
Na+-K+/2 Cl- Transporter
Each cycle of pump carries ions into tubular cell 1 sodium ion 1 potassium ion 2 chloride ions
Benefits of Countercurrent Multiplication
Efficiently reabsorbs solutes and water: Before tubular fluid reaches DCT and collecting system Establishes concentration gradient: That permits passive reabsorption of water from tubular fluid in collecting system: regulated by circulating levels of antidiuretic hormone (ADH)
Reabsorption and Secretion at the DCT
Composition and volume of tubular fluid Changes from capsular space to distal convoluted tubule: only 15–20% of initial filtrate volume reaches DCT concentrations of electrolytes and organic wastes in arriving tubular fluid no longer resemble blood plasma
Reabsorption at the DCT
Selective reabsorption or secretion, primarily along DCT, makes final adjustments in solute composition and volume of tubular fluid
Tubular Cells at the DCT
Actively transport Na+ and Cl- out of tubular fluid Along distal portions: contain ion pumps reabsorb tubular Na+ in exchange for K+
Aldosterone
Is a hormone produced by suprarenal cortex Controls ion pump and channels Stimulates synthesis and incorporation of Na+ pumps and channels In plasma membranes along DCT and collecting duct Reduces Na+ lost in urine
Natriuretic Peptides (ANP and BNP)
Oppose secretion of aldosterone And its actions on DCT and collecting system Parathyroid Hormone and Calcitriol Circulating levels regulate reabsorption at the DCT
Secretion at the DCT
Blood entering peritubular capillaries Contains undesirable substances that did not cross filtration membrane at glomerulus Rate of K+ and H+ secretion rises or falls According to concentrations in peritubular fluid Higher concentration and higher rate of secretion
Control of Blood pH
By H+ removal and bicarbonate production at kidneys Is important to homeostasis
Reabsorption and Secretion along the Collecting System
Collecting ducts Receive tubular fluid from nephrons Carry it toward renal sinus
Regulating Water and Solute Loss in the Collecting System
By aldosterone Controls sodium ion pumps Actions are opposed by natriuretic peptides By ADH Controls permeability to water Is suppressed by natriuretic peptides
Reabsorption in the Collecting System
1.Sodium ion reabsorption 2.Bicarbonate reabsorption 3.Urea reabsorption
Secretion in the Collecting System
Of hydrogen or bicarbonate ions Controls body fluid pH
The Control of Urine Volume and
Osmotic Concentration
Osmotic Concentration
Through control of water reabsorption Water is reabsorbed by osmosis in Proximal convoluted tubule Descending limb of nephron loop
Water Reabsorption
Occurs when osmotic concentration of peritubular fluid exceeds that of tubular fluid 1–2% of water in original filtrate is recovered During sodium ion reabsorption In distal convoluted tubule and collecting system
Obligatory Water Reabsorption
Is water movement that cannot be prevented Usually recovers 85% of filtrate produced
Facultative Water Reabsorption
Controls volume of water reabsorbed along DCT and collecting system 15% of filtrate volume (27 liters/day) Segments are relatively impermeable to water Except in presence of ADH
Osmotic Concentration
Of tubular fluid arriving at DCT 100 mOsm/L In the presence of ADH (in cortex) 300 mOsm/L In minor calyx 1200 mOsml/L
Without ADH
Water is not reabsorbed All fluid reaching DCT is lost in urine Producing large amounts of dilute urine
The Hypothalamus
Continuously secretes low levels of ADH DCT and collecting system are always permeable to water At normal ADH levels Collecting system reabsorbs 16.8 liters/day (9.3% of filtrate)
Urine Production
A healthy adult produces 1200 mL per day (0.6% of filtrate) With osmotic concentration of 800–1000 mOsm/L
Diuresis
Is the elimination of urine Typically indicates production of large volumes of urine
Diuretics
Are drugs that promote water loss in urine Diuretic therapy reduces Blood volume Blood pressure Extracellular fluid volume
Function of the Vasa Recta
To return solutes and water reabsorbed in medulla to general circulation without disrupting the concentration gradient Some solutes absorbed in descending portion do not diffuse out in ascending portion More water moves into ascending portion than is moved out of descending portion
Osmotic Concentration
Blood entering the vasa recta Has osmotic concentration of 300 mOsm/L Increases as blood descends into medulla Involves solute absorption and water loss Blood flowing toward cortex Gradually decreases with solute concentration of peritubular fluid Involves solute diffusion and osmosis
The Vasa Recta
Carries water and solutes out of medulla Balances solute reabsorption and osmosis in medulla
The Composition of Normal Urine
Results from filtration, absorption, and secretion activities of nephrons Some compounds (such as urea) are neither excreted nor reabsorbed Organic nutrients are completely reabsorbed Other compounds missed by filtration process (e.g., creatinine) are actively secreted into tubular fluid
The Excretory System
Includes all systems with excretory functions that affect body fluid composition Urinary system Integumentary system Respiratory system Digestive system
The body must maintain normal volume and composition of
Extracellular fluid (ECF) Intracellular fluid (ICF)
Water
Is 99% of fluid outside cells (extracellular fluid) Is an essential ingredient of cytosol (intracellular fluid) All cellular operations rely on water As a diffusion medium for gases, nutrients, and waste products
Fluid Balance
Is a daily balance between Amount of water gained Amount of water lost to environment Involves regulating content and distribution of body water in ECF and ICF
The Digestive System
Is the primary source of water gains Plus a small amount from metabolic activity
The Urinary System
Is the primary route of water loss
Electrolytes
Are ions released through dissociation of inorganic compounds Can conduct electrical current in solution Electrolyte balance When the gains and losses of all electrolytes are equal Primarily involves balancing rates of absorption across digestive tract with rates of loss at kidneys and sweat glands
Water Accounts for Roughly
60% percent of male body weight 50% percent of female body weight Mostly in intracellular fluid
Water Exchange
Water exchange between ICF and ECF occurs across plasma membranes by Osmosis Diffusion Carrier-mediated transport
Major Subdivisions of ECF
Interstitial fluid of peripheral tissues Plasma of circulating blood
Minor Subdivisions of ECF
Lymph, perilymph, and endolymph Cerebrospinal fluid (CSF) Synovial fluid Serous fluids (pleural, pericardial, and peritoneal) Aqueous humor
Exchange among Subdivisions of ECF
Occurs primarily across endothelial lining of capillaries From interstitial spaces to plasma Through lymphatic vessels that drain into the venous system
ECF: Solute Content
Types and amounts vary regionally Electrolytes Proteins Nutrients Waste products
The ECF and the ICF
Are called fluid compartments because they behave as distinct entities Are separated by plasma membranes and active transport
Cations and Anions
In ECF Sodium, chloride, and bicarbonate In ICF Potassium, magnesium, and phosphate ions Negatively charged proteins
Membrane Functions
Plasma membranes are selectively permeable Ions enter or leave via specific membrane channels Carrier mechanisms move specific ions in or out of cell
The Osmotic Concentration of ICF and ECF
Is identical Osmosis eliminates minor differences in concentration Because plasma membranes are permeable to water
Basic Concepts in the Regulation of Fluids and Electrolytes
All homeostatic mechanisms that monitor and adjust body fluid composition respond to changes in the ECF, not in the ICF No receptors directly monitor fluid or electrolyte balance Cells cannot move water molecules by active transport The body’s water or electrolyte content will rise if dietary gains exceed environmental losses, and will fall if losses exceed gains
An Overview of the Primary Regulatory Hormones
Affecting fluid and electrolyte balance: Antidiuretic hormone Aldosterone Natriuretic peptides
Antidiuretic Hormone (ADH)
Stimulates water conservation at kidneys Reducing urinary water loss Concentrating urine Stimulates thirst center Promoting fluid intake
ADH Production
Osmoreceptors in hypothalamus Monitor osmotic concentration of ECF Change in osmotic concentration Alters osmoreceptor activity Osmoreceptor neurons secrete ADH
ADH Release
Axons of neurons in anterior hypothalamus Release ADH near fenestrated capillaries In neurohypophysis (posterior lobe of pituitary gland) Rate of release varies with osmotic concentration Higher osmotic concentration increases ADH release
Aldosterone
Is secreted by suprarenal cortex in response to Rising K+ or falling Na+ levels in blood Activation of renin–angiotensin system Determines rate of Na+ absorption and K+ loss along DCT and collecting system
“Water Follows Salt”
High aldosterone plasma concentration Causes kidneys to conserve salt Conservation of Na+ by aldosterone Also stimulates water retention
Natriuretic Peptides
ANP and BNP are released by cardiac muscle cells in response to abnormal stretching of heart walls Reduce thirst Block release of ADH and aldosterone Cause diuresis Lower blood pressure and plasma volume
When the body loses water
Plasma volume decreases Electrolyte concentrations rise When the body loses electrolytes Water is lost by osmosis Regulatory mechanisms are different
Fluid Balance
Water circulates freely in ECF compartment At capillary beds, hydrostatic pressure forces water out of plasma and into interstitial spaces Water is reabsorbed along distal portion of capillary bed when it enters lymphatic vessels ECF and ICF are normally in osmotic equilibrium No large-scale circulation between compartments
Fluid Movement within the ECF
Net hydrostatic pressure Pushes water out of plasma Into interstitial fluid Net colloid osmotic pressure Draws water out of interstitial fluid Into plasma
Fluid Movement within the ECF
ECF fluid volume is redistributed From lymphoid system to venous system (plasma) Interaction between opposing forces Results in continuous filtration of fluid ECF volume Is 80% in interstitial fluid and minor fluid compartment Is 20% in plasma
Edema
The movement of abnormal amounts of water from plasma into interstitial fluid
Fluid Losses
Water losses Body loses about 2500 mL of water each day through urine, feces, and insensible perspiration Fever can also increase water loss Sensible perspiration (sweat) varies with activities and can cause significant water loss (4 L/hr)
Fluid Gains
Water gains About 2500 mL/day Required to balance water loss Through: eating (1000 mL) drinking (1200 mL) metabolic generation (300 mL)
Metabolic Generation of Water
Is produced within cells Results from oxidative phosphorylation in mitochondria
Fluid Shifts
Are rapid water movements between ECF and ICF In response to an osmotic gradient If ECF osmotic concentration increases Fluid becomes hypertonic to ICF Water moves from cells to ECF
Shifts
If ECF osmotic concentration decreases Fluid becomes hypotonic to ICF Water moves from ECF to cells ICF volume is much greater than ECF volume ICF acts as water reserve Prevents large osmotic changes in ECF
Dehydration
Also called water depletion Develops when water loss is greater than gain
Allocation of Water Losses
If water is lost, but electrolytes retained ECF osmotic concentration rises Water moves from ICF to ECF Net change in ECF is small
Severe Water Loss
Causes Excessive perspiration Inadequate water consumption Repeated vomiting Diarrhea Homeostatic responses Physiologic mechanisms (ADH and renin secretion) Behavioral changes (increasing fluid intake)
Distribution of Water Gains
If water is gained, but electrolytes are not ECF volume increases ECF becomes hypotonic to ICF Fluid shifts from ECF to ICF May result in overhydration (also called water excess): occurs when excess water shifts into ICF: distorting cells changing solute concentrations around enzymes disrupting normal cell functions
Causes of Overhydration
Ingestion of large volume of fresh water Injection of hypotonic solution into bloodstream Endocrine disorders Excessive ADH production Inability to eliminate excess water in urine Chronic renal failure Heart failure Cirrhosis
Signs of Overhydration
Abnormally low Na+ concentrations (hyponatremia) Effects on CNS function (water intoxication)
Juxtaglomerular Complex
An endocrine structure that secretes Hormone erythropoietin Enzyme renin Formed by Macula densa Juxtaglomerular cells
Hormonal Regulation of the GFR
By hormones of the Renin–angiotensin system Natriuretic peptides (ANP and BNP)
The Renin–Angiotensin System
Three stimuli cause the juxtaglomerular complex (JGA) to release renin Decline in blood pressure at glomerulus due to decrease in blood volume Fall in systemic pressures due to blockage in renal artery or tributaries Stimulation of juxtaglomerular cells by sympathetic innervation due to decline in osmotic concentration of tubular fluid at macula densa
Electrolyte Balance
Requires rates of gain and loss of each electrolyte in the body to be equal Electrolyte concentration directly affects water balance Concentrations of individual electrolytes affect cell functions
Sodium
Is the dominant cation in ECF Sodium salts provide 90% of ECF osmotic concentration Sodium chloride (NaCl) Sodium bicarbonate
Normal Sodium Concentrations
In ECF About 140 mEq/L In ICF Is 10 mEq/L or less
Potassium
Is the dominant cation in ICF Normal potassium concentrations In ICF: about 160 mEq/L In ECF: is 3.5–5.5 mEq/L
Rules of Electrolyte Balance
1.Most common problems with electrolyte balance are caused by imbalance between gains and losses of sodium ions 2.Problems with potassium balance are less common, but more dangerous than sodium imbalance
Sodium Balance
Sodium ion uptake across digestive epithelium Sodium ion excretion in urine and perspiration
Sodium Balance
Typical Na+ gain and loss Is 48–144 mEq (1.1–3.3 g) per day If gains exceed losses Total ECF content rises If losses exceed gains ECF content declines
Sodium Balance and ECF Volume
Changes in ECF Na+ content Do not produce change in concentration Corresponding water gain or loss keeps concentration constant
Na+ regulatory mechanism changes ECF volume
Keeps concentration stable When Na+ losses exceed gains ECF volume decreases (increased water loss) Maintaining osmotic concentration
Large Changes in ECF Volume
Are corrected by homeostatic mechanisms that regulate blood volume and pressure If ECF volume rises, blood volume goes up If ECF volume drops, blood volume goes down
Homeostatic Mechanisms
A rise in blood volume elevates blood pressure A drop in blood volume lowers blood pressure Monitor ECF volume indirectly by monitoring blood pressure Baroreceptors at carotid sinus, aortic sinus, and right atrium
Hyponatremia
Body water content rises (overhydration) ECF Na+ concentration <136 mEq/L
Hypernatremia
Body water content declines (dehydration) ECF Na+ concentration >145 mEq/L
ECF Volume
If ECF volume is inadequate Blood volume and blood pressure decline Renin–angiotensin system is activated Water and Na+ losses are reduced ECF volume increases
Plasma Volume
If plasma volume is too large Venous return increases: stimulating release of natriuretic peptides (ANP and BNP) reducing thirst blocking secretion of ADH and aldosterone Salt and water loss at kidneys increases ECF volume declines
Potassium Balance
98% of potassium in the human body is in ICF Cells expend energy to recover potassium ions diffused from cytoplasm into ECF
Processes of Potassium Balance
1.Rate of gain across digestive epithelium 2.Rate of loss into urine
Potassium Loss in Urine
Is regulated by activities of ion pumps Along distal portions of nephron and collecting system Na+ from tubular fluid is exchanged for K+ in peritubular fluid Are limited to amount gained by absorption across digestive epithelium (about 50–150 mEq or 1.9–5.8 g/day)
Factors in Tubular Secretion of K+
1.Changes in concentration of ECF: §Higher ECF concentration increases rate of secretion 2.Changes in pH: §Low ECF pH lowers peritubular fluid pH §H+ rather than K+ is exchanged for Na+ in tubular fluid §Rate of potassium secretion declines 3.Aldosterone levels: §Affect K+ loss in urine §Ion pumps reabsorb Na+ from filtrate in exchange for K+ from peritubular fluid §High K+ plasma concentrations stimulate aldosterone
Calcium Balance
Calcium is most abundant mineral in the body A typical individual has 1–2 kg (2.2–4.4 lb) of this element 99% of which is deposited in skeleton
Functions of Calcium Ion (Ca2+)
Muscular and neural activities Blood clotting Cofactors for enzymatic reactions Second messengers
Hormones and Calcium Homeostasis
Parathyroid hormone (PTH) and calcitriol Raise calcium concentrations in ECF Calcitonin Opposes PTH and calcitriol
Calcium Absorption
At digestive tract and reabsorption along DCT Is stimulated by PTH and calcitriol
Calcium Ion Loss
In bile, urine, or feces Is very small (0.8–1.2 g/day) Represents about 0.03% of calcium reserve in skeleton
Hypercalcemia
Exists if Ca2+ concentration in ECF is >5.5 mEq/L Is usually caused by hyperparathyroidism Resulting from oversecretion of PTH Other causes Malignant cancers (breast, lung, kidney, bone marrow) Excessive calcium or vitamin D supplementation
Hypocalcemia
Exists if Ca2+ concentration in ECF is <4.5 mEq/L Is much less common than hypercalcemia Is usually caused by chronic renal failure May be caused by hypoparathyroidism Undersecretion of PTH Vitamin D deficiency
Magnesium Balance
Is an important structural component of bone The adult body contains about 29 g of magnesium About 60% is deposited in the skeleton Is a cofactor for important enzymatic reactions Phosphorylation of glucose Use of ATP by contracting muscle fibers Is effectively reabsorbed by PCT Daily dietary requirement to balance urinary loss About 24–32 mEq (0.3–0.4 g)
Magnesium Ions (Mg2+)
In body fluids are primarily in ICF Mg2+ concentration in ICF is about
26 mEq/L ECF concentration is much lower
26 mEq/L ECF concentration is much lower
Phosphate Ions (PO43- )
Are required for bone mineralization About 740 g PO43- is bound in mineral salts of the skeleton Daily urinary and fecal losses: about 30–45 mEq (0.8–1.2 g) In ICF, PO43- is required for formation of high-energy compounds, activation of enzymes, and synthesis of nucleic acids In plasma, PO43- is reabsorbed from tubular fluid along PCT Plasma concentration is 1.8–2.9 mEq/L
Chloride Ions (Cl-)
Are the most abundant anions in ECF Plasma concentration is 97–107 mEq/L ICF concentrations are usually low Are absorbed across digestive tract with Na+ Are reabsorbed with Na+ by carrier proteins along renal tubules Daily loss is small: 48–146 mEq (1.7–5.1 g)
Digestive tract also called gastrointestinal (GI) tract or alimentary canal
Is a muscular tube Extends from oral cavity to anus Passes through pharynx, esophagus, stomach, and small and large intestines
Functions of the Digestive System
1. Ingestion
2. Mechanical Processing
3. Digestion
4. Secretion
5. Absorption
6. Excretion
2. Mechanical Processing
3. Digestion
4. Secretion
5. Absorption
6. Excretion
Histological Organization of the Digestive Tract
Major layers of the digestive tract Mucosa Submucosa Muscularis externa Serosa
Lining of the digestive tract protects surrounding tissues against
Corrosive effects of digestive acids and enzymes Mechanical stresses, such as abrasion Bacteria either ingested with food or that reside in digestive tract
The Mucosa
Is the inner lining of digestive tract Is a mucous membrane consisting of Epithelium, moistened by glandular secretions Lamina propria of areolar tissue
The Digestive Epithelium
Mucosal epithelium is simple or stratified Depending on location, function, and stresses: oral cavity, pharynx, and esophagus: mechanical stresses lined by stratified squamous epithelium stomach, small intestine, and most of large intestine: absorption simple columnar epithelium with mucous (goblet) cells
The Digestive Epithelium
Enteroendocrine cells Are scattered among columnar cells of digestive epithelium Secrete hormones that: coordinate activities of the digestive tract and accessory glands
The Submucosa
Is a layer of dense, irregular connective tissue Surrounds muscularis mucosae Has large blood vessels and lymphatic vessels May contain exocrine glands Secrete buffers and enzymes into digestive tract
Submucosal Plexus
Also called plexus of Meissner Innervates the mucosa and submucosa Contains Sensory neurons Parasympathetic ganglionic neurons Sympathetic postganglionic fibers
The Muscularis Externa
Is dominated by smooth muscle cells Are arranged in Inner circular layer Outer longitudinal layer
The Muscularis Externa
Involved in Mechanical processing Movement of materials along digestive tract Movements coordinated by enteric nervous system (ENS) Sensory neurons Interneurons Motor neurons
The Movement of Digestive Materials
By muscular layers of digestive tract Consist of visceral smooth muscle tissue Along digestive tract: has rhythmic cycles of activity controlled by pacesetter cells Cells undergo spontaneous depolarization: triggering wave of contraction through entire muscular sheet
Pacesetter Cells
Located in muscularis mucosae and muscularis externa Surrounding lumen of digestive tract
Peristalsis
Consists of waves of muscular contractions
Moves a bolus along the length of the digestive tract
Moves a bolus along the length of the digestive tract
Peristaltic Motion
1.Circular muscles contract behind bolus: §While circular muscles ahead of bolus relax 2.Longitudinal muscles ahead of bolus contract: §Shortening adjacent segments 3.Wave of contraction in circular muscles: §Forces bolus forward
Control of Digestive Function
Neural mechanisms Control: movement of materials along digestive tract secretory functions Motor neurons: control smooth muscle contraction and glandular secretion
Long reflexes
Higher level control of digestive and glandular activities Control large-scale peristaltic waves Involve interneurons and motor neurons in CNS May involve parasympathetic motor fibers that synapse in the myenteric plexus: glossopharyngeal, vagus, or pelvic nerves
Hormonal Mechanisms
At least 18 peptide hormones that affect Most aspects of digestive function Activities of other systems Are produced by enteroendocrine cells in digestive tract Reach target organs after distribution in bloodstream
Esophagus
A hollow muscular tube About 25 cm (10 in.) long and 2 cm (0.80 in.) wide Conveys solid food and liquids to the stomach Begins posterior to cricoid cartilage Is innervated by fibers from the esophageal plexus
Major Functions of the Stomach
Storage of ingested food Mechanical breakdown of ingested food Disruption of chemical bonds in food material by acid and enzymes Production of intrinsic factor, a glycoprotein required for absorption of vitamin B12 in small intestine
Gastric Glands
Produce and secrete chemicals and enzymes that aid in digestion Extend deep into underlying lamina propria Each gastric pit communicates with several gastric glands Parietal cells Chief cells
Parietal Cells and Chief Cells
P cells-Secrete intrinsic factor and hydrochloric acid (HCl) Chief Cells-Secrete hydrochloric acid (HCl) Are most abundant near base of gastric gland Secrete pepsinogen (inactive proenzyme) Is converted by HCl in the gastric lumen to pepsin (active proteolytic enzyme)
G Cells
produce gastrin-stimulates HCl production by parietal cells
Regulation of Gastric Activity
Production of acid and enzymes by the gastric mucosa can be Controlled by the CNS Regulated by short reflexes of ENS Regulated by hormones of digestive tract
Digestion and Absorption in the Stomach
Stomach performs preliminary digestion of proteins by pepsin Some digestion of carbohydrates (by salivary amylase) Lipids (by lingual lipase) Stomach contents Become more fluid pH approaches 2.0 Pepsin activity increases Protein disassembly begins Although digestion occurs in the stomach, nutrients are not absorbed there
The Small Intestine
Plays key role in digestion and absorption of nutrients 90% of nutrient absorption occurs in the small intestine
Functions of Pancreas
1.Endocrine cells of the pancreatic islets: Secrete insulin and glucagon into bloodstream 2.Exocrine cells: Acinar cells and epithelial cells of duct system secrete pancreatic juice
Pancreatic Secretions
1000 mL (1 qt) pancreatic juice per day Controlled by hormones from duodenum Contain pancreatic enzymes
Pancreatic Enzymes
Pancreatic alpha-amylase A carbohydrase Breaks down starches Similar to salivary amylase Pancreatic lipase Breaks down complex lipids Releases products (e.g., fatty acids) that are easily absorbed
Pancreatic Enzymes
Nucleases Break down nucleic acids Proteolytic enzymes Break certain proteins apart Proteases break large protein complexes Peptidases break small peptides into amino acids 70% of all pancreatic enzyme production Secreted as inactive proenzymes Activated after reaching small intestine
Liver
Is the largest visceral organ (1.5 kg; 3.3 lb) Lies in right hypochondriac and epigastric regions Extends to left hypochondriac and umbilical regions Performs essential metabolic and synthetic functions
Hepatocytes
Are liver cells Adjust circulating levels of nutrients Through selective absorption and secretion In a liver lobule form a series of irregular plates arranged like wheel spokes Many Kupffer cells (stellate reticuloendothelial cells) are located in sinusoidal lining As blood flows through sinusoids Hepatocytes absorb solutes from plasma And secrete materials such as plasma proteins
Metabolic Regulation
The liver regulates: 1.Composition of circulating blood 2.Nutrient metabolism 3.Waste product removal 4.Nutrient storage 5.Drug inactivation
Composition of Circulating Blood
All blood leaving absorptive surfaces of digestive tract Enters hepatic portal system Flows into the liver Liver cells extract nutrients or toxins from blood Before they reach systemic circulation through hepatic veins Liver removes and stores excess nutrients Corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities
The Functions of Bile
Dietary lipids are not water soluble Mechanical processing in stomach creates large drops containing lipids Pancreatic lipase is not lipid soluble Interacts only at surface of lipid droplet Bile salts break droplets apart (emulsification) Increases surface area exposed to enzymatic attack Creates tiny emulsion droplets coated with bile salts
The Large Intestine
Is horseshoe shaped Extends from end of ileum to anus Lies inferior to stomach and liver Frames the small intestine Also called large bowel Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide
Functions of the Large Intestine
Reabsorption of water and some nutrients (less than 10%) Compaction of intestinal contents into feces Absorption of important vitamins produced by bacteria Preparation and storage of fecal material prior to defecation
Two Positive Feedback Loops
Short reflex: Triggers peristaltic contractions in rectum Long reflex: Coordinated by sacral parasympathetic system Stimulates mass movements
Rectal stretch receptors also trigger two reflexes important to voluntary control of defecation
A long reflex Mediated by parasympathetic innervation in pelvic nerves Causes relaxation of internal anal sphincter A somatic reflex Motor commands carried by pudendal nerves Stimulates contraction of external anal sphincter (skeletal muscle)
Essential Nutrients
A typical meal contains Carbohydrates Proteins Lipids Water Electrolytes Vitamins
Digestive system handles each nutrient differently
Large organic molecules Must be digested before absorption can occur Water, electrolytes, and vitamins Can be absorbed without processing May require special transport
Metabolism
Metabolism refers to all chemical reactions in an organism Cellular Metabolism Includes all chemical reactions within cells Provides energy to maintain homeostasis and perform essential functions
Essential Functions
Metabolic turnover Periodic replacement of cell’s organic components Growth and cell division Special processes, such as secretion, contraction, and the propagation of action potentials
Catabolism
Is the breakdown of organic substrates Releases energy used to synthesize high-energy compounds (e.g., ATP)
Anabolism
Is the synthesis of new organic molecules
is an "uphill" process that forms new chemical bonds
is an "uphill" process that forms new chemical bonds
Abundant Organic Compounds
Glycogen Most abundant storage carbohydrate A branched chain of glucose molecules Triglycerides Most abundant storage lipids Primarily of fatty acids Proteins Most abundant organic components in body Perform many vital cellular functions
Carbohydrate Metabolism
Generates ATP and other high-energy compounds by breaking down carbohydrates: glucose + oxygen ® carbon dioxide + water
Glycolysis
Breaks 6-carbon glucose Into two 3-carbon pyruvic acid Pyruvate Ionized form of pyruvic acid
Mitochondrial ATP Production
If oxygen supplies are adequate, mitochondria absorb and break down pyruvic acid molecules: H atoms of pyruvic acid are removed by coenzymes and are primary source of energy gain C and O atoms are removed and released as CO2 in the process of decarboxylation
Oxidative Phosphorylation and the ETS
Is the generation of ATP Within mitochondria In a reaction requiring coenzymes and oxygen Produces more than 90% of ATP used by body Results in 2 H2 + O2 ® 2 H2O
The Electron Transport System (ETS)
Is the key reaction in oxidative phosphorylation Is in inner mitochondrial membrane Electrons carry chemical energy Within a series of integral and peripheral proteins
ATP Generation and the ETS
Does not produce ATP directly Creates steep concentration gradient across inner mitochondrial membrane Energy released drives H ion (H+) pumps That move H+ from mitochondrial matrix Into intermembrane space
Summary: ATP Production
For one glucose molecule processed, cell gains 36 molecules of ATP 2 from glycolysis 4 from NADH generated in glycolysis 2 from TCA cycle (through GTP) 28 from ETS
Gluconeogenesis
Is the synthesis of glucose from noncarbohydrate precursors Lactic acid Glycerol Amino acids Stores glucose as glycogen in liver and skeletal muscle
Glycogenesis
Is the formation of glycogen from glucose Occurs slowly Requires high-energy compound uridine triphosphate (UTP)
Glycogenolysis
Is the breakdown of glycogen Occurs quickly Involves a single enzymatic step
Lipid Metabolism
Lipid molecules contain carbon, hydrogen, and oxygen In different proportions than carbohydrates Triglycerides are the most abundant lipid in the body
Lipid Catabolism (also called lipolysis)
Breaks lipids down into pieces that can be Converted to pyruvic acid Channeled directly into TCA cycle Hydrolysis splits triglyceride into component parts One molecule of glycerol Three fatty acid molecules
Lipid Catabolism
Enzymes in cytosol convert glycerol to pyruvic acid Pyruvic acid enters TCA cycle Different enzymes convert fatty acids to acetyl-CoA (beta-oxidation)
Beta-Oxidation
A series of reactions Breaks fatty acid molecules into 2-carbon fragments Occurs inside mitochondria Each step Generates molecules of acetyl-CoA and NADH Leaves a shorter carbon chain bound to coenzyme A
Lipids and Energy Production
For each 2-carbon fragment removed from fatty acid, cell gains: 12 ATP from acetyl-CoA in TCA cycle 5 ATP from NADH Cell can gain 144 ATP molecules from breakdown of one 18-carbon fatty acid molecule Fatty acid breakdown yields about 1.5 times the energy of glucose breakdown
Amino Acid Catabolism
Removal of amino group by transamination or deamination Requires coenzyme derivative of vitamin B6 (pyridoxine)
Transamination
Attaches amino group of amino acid To keto acid Converts keto acid into amino acid That leaves mitochondrion and enters cytosol Available for protein synthesis
Deamination
Prepares amino acid for breakdown in TCA cycle Removes amino group and hydrogen atom Reaction generates ammonium ion
Ammonium Ions
Are highly toxic, even in low concentrations Liver cells (primary sites of deamination) have enzymes that use ammonium ions to synthesize urea (water-soluble compound excreted in urine)
Five Metabolic Tissues
Liver Adipose tissue Skeletal muscle Neural tissue Other peripheral tissues
The Liver
Is focal point of metabolic regulation and control Contains great diversity of enzymes that break down or synthesize carbohydrates, lipids, and amino acids Hepatocytes Have an extensive blood supply Monitor and adjust nutrient composition of circulating blood Contain significant energy reserves (glycogen deposits)
Adipose Tissue
Stores lipids, primarily as triglycerides Is located in Areolar tissue Mesenteries Red and yellow marrows Epicardium Around eyes and kidneys
Skeletal Muscle
Maintains substantial glycogen reserves Contractile proteins can be broken down Amino acids used as energy source
Neural Tissue
Does not maintain reserves of carbohydrates, lipids, or proteins Requires reliable supply of glucose Cannot metabolize other molecules In CNS, cannot function in low-glucose conditions Individual becomes unconscious
Metabolic Interactions
Relationships among five components change over 24-hour period Body has two patterns of daily metabolic activity Absorptive state Postabsorptive state
The Absorptive State
Is the period following a meal when nutrient absorption is under way
The Postabsorptive State
Is the period when nutrient absorption is not under way Body relies on internal energy reserves for energy demands Liver cells conserve glucose Break down lipids and amino acids
Ketonemia
Is the appearance of ketone bodies in bloodstream Lowers plasma pH, which must be controlled by buffers Ketoacidosis is a dangerous drop in blood pH caused by high ketone levels In severe ketoacidosis, circulating concentration of ketone bodies can reach 200 mg dL, and the pH may fall below 7.05 May cause coma, cardiac arrhythmias, death
Calories
Energy required to raise 1 g of water 1 degree Celsius is a calorie (cal) Energy required to raise 1 kilogram
of water 1 degree Celsius is a Calorie (Cal)= kilocalorie (kcal) The Energy Content of Food Lipids release 9.46 Cal/g Carbohydrates release 4.18 Cal/g Proteins release 4.32 Cal/g
of water 1 degree Celsius is a Calorie (Cal)= kilocalorie (kcal) The Energy Content of Food Lipids release 9.46 Cal/g Carbohydrates release 4.18 Cal/g Proteins release 4.32 Cal/g
Energy Expenditure: Metabolic Rate
Clinicians examine metabolism to determine calories used and measured in Calories per hour Calories per day Calories per unit of body weight per day
Metabolic Rate
Is the sum of all anabolic and catabolic processes in the body Changes according to activity
Metabolic Rate
If daily energy intake exceeds energy demands Body stores excess energy as triglycerides in adipose tissue If daily caloric expenditures exceeds dietary supply Body uses energy reserves, loses weight
The Ovulatory Cycle
Causes temperature fluctuations
Pyrexia
Is elevated body temperature Usually temporary
The Male Reproductive System
Testes or male gonads Secrete male sex hormones (androgens) Produce male gametes (spermatozoa or sperm)
The Female Reproductive System
Ovaries or female gonads Release one immature gamete (oocyte) per month Produce hormones Uterine tubes Carry oocytes to uterus: if sperm reaches oocyte, fertilization is initiated and oocyte matures into ovum Uterus Encloses and supports developing embryo Vagina Connects uterus with exterior
The Testes
Egg shaped 5 cm long, 3 cm wide, 2.5 cm thick (2 in. x 1.2 in. x 1 in.) Weighs 10–15 g (0.35-0.53 oz) Hangs in scrotum
Histology of the Testes
Septa subdivide testis into lobules Lobules contain about 800 slender and tightly coiled seminiferous tubules Produce sperm Each is about 80 cm (32 in.) long Testis contains about 1/2 mile of tightly coiled seminiferous tubules: Form a loop connected to rete testis, a network of passageways
Spermatogenesis
Is the process of sperm production Begins at outermost cell layer in seminiferous tubules Proceeds toward lumen
Spermatogonia (stem cells)
divide by mitosis to produce two daughter cells: One remains as spermatogonium Second differentiates into primary spermatocyte
Primary spermatocytes
begin meiosis and form secondary spermatocytes
Secondary spermatocytes
differentiate into spermatids (immature gametes)
Spermatids:
Differentiate into spermatozoa
Spermatozoa:
Lose contact with wall of seminiferous tubule Enter fluid in lumen
Contents of Seminiferous Tubules
Spermatogonia Spermatocytes at various stages of meiosis Spermatids Spermatozoa Large nurse cells (also called sustentacular cells or Sertoli cells) Are attached to tubular capsule Extend to lumen between other types of cells
Spermatogenesis
Involves three integrated processes Mitosis Meiosis Spermiogenesis
Spermiogenesis
Is the last step of spermatogenesis Each spermatid matures into one spermatozoon (sperm) Attached to cytoplasm of nurse cells
Spermiation
At spermiation, a spermatozoon Loses attachment to nurse cell Enters lumen of seminiferous tubule Spermatogonial division to spermiation Takes about 9 weeks
Sperm Maturation
Spermatozoa Detach from nurse cells Are free in lumen of seminiferous tubule Are functionally immature: are incapable of locomotion or fertilization are moved by cilia lining efferent ductules into the epididymis
The Epididymis
Is the start of male reproductive tract Is a coiled tube almost 7 m (23 ft) long Bound to posterior border of testis Has a head, a body, and a tail
Functions of the Epididymis
Monitors and adjusts fluid produced by seminiferous tubules Recycles damaged spermatozoa Stores and protects spermatozoa Facilitates functional maturation
Spermatozoa Leaving Epididymis
Are mature, but remain immobile To become motile (actively swimming) and functional Spermatozoa undergo capacitation
Steps in Capacitation
Spermatozoa become motile: When mixed with secretions of seminal glands Spermatozoa become capable of fertilization: When exposed to female reproductive tract
The Ductus Deferens (or vas deferens)
Is 40–45 cm (16-18 in.) long Begins at tail of the epididymis and, as part of spermatic cord, ascends through inguinal canal Curves inferiorly along urinary bladder Toward prostate gland and seminal glands Lumen enlarges into ampulla Wall contains thick layer of smooth muscle
The Ductus Deferens
Is lined by ciliated epithelium Peristaltic contractions propel spermatozoa and fluid Can store spermatozoa for several months In state of suspended animation (low metabolic rates)
Seminal Fluid
Is a mixture of secretions from many glands Each with distinctive biochemical characteristics Important glands include Seminal glands Prostate gland Bulbo-urethral glands
4 Major Functions of Male Glands
Activating spermatozoa Providing nutrients spermatozoa need for motility Propelling spermatozoa and fluids along reproductive tract Mainly by peristaltic contractions Producing buffers To counteract acidity of urethral and vaginal environments
Vesicular (Seminal) Fluid
Has same osmotic concentration as blood plasma but different composition High concentrations of fructose: easily metabolized by spermatozoa Prostaglandins: stimulate smooth muscle contractions (male and female) Fibrinogen: forms temporary clot in vagina Is slightly alkaline To neutralize acids in prostate gland and vagina Initiates first step in capacitation Spermatozoa begin beating flagella, become highly motile
Vesicular (Seminal) Fluid
Is discharged into ejaculatory duct at emission When peristaltic contractions are underway Contractions are controlled by sympathetic nervous system
Erectile Tissue
In body of penis Located deep to areolar tissue In dense network of elastic fibers That encircles internal structures of penis Consists of network of vascular channels Incompletely separated by partitions of elastic connective tissue and smooth muscle fibers In resting state Arterial branches are constricted Muscular partitions are tense Blood flow into erectile tissue is restricted
The Corpora Cavernosa
Two cylindrical masses of erectile tissue Under anterior surface of flaccid penis Separated by thin septum Encircled by dense collagenous sheath Diverge at their bases, forming the crura of penis Each crus is bound to ramus of ischium and pubis By tough connective tissue ligaments Extends to neck of penis Erectile tissue surrounds a central artery
The Corpus Spongiosum
Relatively slender erectile body that surrounds penile urethra Extends from urogenital diaphragm to tip of penis and expands to form the glans Is surrounded by a sheath With more elastic fibers than corpora cavernosa Erectile tissue contains a pair of small arteries
Hormones and Male Reproductive Function
Adenohypophysis releases: Follicle—stimulating hormone (FSH) Luteinizing hormone (LH) In response to Gonadotropin-releasing hormone (GnRH)
Gonadotropin-Releasing Hormone
Is synthesized in hypothalamus Carried to pituitary by hypophyseal portal system Is secreted in pulses At 60–90 minute intervals Controls rates of secretion of FSH and LH Testosterone (released in response to LH)
FSH and Testosterone
Target nurse cells of seminiferous tubules Nurse cells Promote spermatogenesis and spermiogenesis Secrete androgen-binding protein (ABP)
Luteinizing Hormone
Targets interstitial cells of testes Induces secretion of Testosterone Other androgens
Testosterone
Is the most important androgen Stimulates spermatogenesis Promoting functional maturation of spermatozoa Affects CNS function Libido (sexual drive) and related behaviors Stimulates metabolism Especially protein synthesis Blood cell formation Muscle growth
Testosterone
Establishes male secondary sex characteristics Distribution of facial hair Increased muscle mass and body size Characteristic adipose tissue deposits Maintains accessory glands and organs of male reproductive tract
Testosterone and development
Production begins around seventh week of fetal development and reaches prenatal peak after 6 months Secretion of Müllerian inhibiting factor by nurse cells leads to regression of Müllerian ducts Early surge in testosterone levels stimulates differentiation of male duct system and accessory organs and affects CNS development Testosterone programs hypothalamic centers that control: GnRH, FSH, and LH secretion Sexual behaviors Sexual drive
Estradiol
Is produced in relatively small amounts (2 ng/dL) 70% is converted from circulating testosterone By enzyme aromatase 30% is secreted by interstitial and nurse cells of testes
Organs of the Female Reproductive System
Ovaries Uterine tubes Uterus Vagina External genitalia
Ovaries
Are small, almond-shaped organs near lateral walls of pelvic cavity Three main functions Production of immature female gametes (oocytes) Secretion of female sex hormones (estrogens, progestins) Secretion of inhibin, involved in feedback control of pituitary FSH
Oogenesis
Also called ovum production Begins before birth Accelerates at puberty Ends at menopause
The Ovarian Cycle
Includes monthly oogenesis Between puberty and menopause
Process of Oogenesis
Primary oocytes remain in suspended development until puberty At puberty Rising FSH triggers start of ovarian cycle Each month thereafter Some primary oocytes are stimulated to develop further
Oogenesis: Two Characteristics of Meiosis
Cytoplasm of primary oocyte divides unevenly Producing one ovum (with original cytoplasm) And two or three polar bodies (that disintegrate) Ovary releases secondary oocyte (not mature ovum) Suspended in metaphase of meiosis II Meiosis is completed upon fertilization
Ovarian Follicles
Are specialized structures in cortex of ovaries Where oocyte growth and meiosis I occur Primary oocytes Are located in outer part of ovarian cortex: near tunica albuginea in clusters called egg nests
Primordial Follicle
Each primary oocyte in an egg nest Is surrounded by follicle cells Primary oocyte and follicle cells form a primordial follicle
Ovarian Cycle
After sexual maturation A different group of primordial follicles is activated each month Is divided into Follicular phase (preovulatory phase) Luteal phase (postovulatory phase)
The Uterine Tubes
Fallopian tubes or oviducts Are hollow, muscular tubes about 13 cm (5.2 in.) long Transport oocyte from ovary to uterus
Uterine Tube and Oocyte Transport
Involves ciliary movement and peristaltic contractions in walls of uterine tube A few hours before ovulation, nerves from hypogastric plexus “Turn on” beating pattern Initiate peristalsis From infundibulum to uterine cavity Normally takes 3–4 days
The Uterus
Provides for developing embryo (weeks 1–8) and fetus (week 9 through delivery): Mechanical protection Nutritional support Waste removal
The Uterine Wall
Has a thick, outer, muscular myometrium Has a thin, inner, glandular endometrium (mucosa)
The Myometrium
The thickest portion of the uterine wall Constitutes almost 90% of the mass of the uterus Arranged into longitudinal, circular, and oblique layers Provides force to move fetus out of uterus into vagina
The Endometrium
Contributes about 10% of uterine mass Glandular and vascular tissues support physiological demands of growing fetus Uterine glands Open onto endometrial surface Extend deep into lamina propria
The Functional Zone
Contains most of the uterine glands Contributes most of endometrial thickness Undergoes dramatic changes in thickness and structure during menstrual cycle
The Basilar Zone
Attaches endometrium to myometrium Contains terminal branches of tubular endometrial glands
Cyclical Changes in Endometrium
Basilar zone remains relatively constant Functional zone undergoes cyclical changes In response to sex hormone levels Produce characteristic features of uterine cycle
The Uterine Cycle (or menstrual cycle)
Is a repeating series of changes in endometrium Lasts from 21 to 35 days Average 28 days
Uterine Cycle
Responds to hormones of ovarian cycle Menses and proliferative phase Occur during ovarian follicular phase Secretory phase Occurs during ovarian luteal phase
Menses
Is the degeneration of functional zone Occurs in patches Is caused by constriction of spiral arteries Reducing blood flow, oxygen, and nutrients Weakened arterial walls rupture Releasing blood into connective tissues of functional zone
Menstruation
Is the process of endometrial sloughing Lasts 1–7 days Sheds 35–50 mL (1.2-1.7 oz) blood
The Proliferative Phase
Is stimulated and sustained by Estrogens secreted by developing ovarian follicles Entire functional zone is highly vascularized Small arteries Spiral toward inner surface From larger arteries in myometrium
The Secretory Phase
Endometrial glands enlarge, increasing rate of secretion Arteries of uterine wall Elongate and spiral through functional zone Begins at ovulation and persists as long as corpus luteum remains intact Peaks about 12 days after ovulation Glandular activity declines Generally lasts 14 days
The Uterine Cycle
Ends as corpus luteum stops producing stimulatory hormones
Hormones and the Female Reproductive Cycle
Involves secretions of pituitary gland and gonads Forms a complex pattern that coordinates ovarian and uterine cycles
GnRH
GnRH from the hypothalamus regulates reproductive function GnRH pulse frequency and amplitude change over course of ovarian cycle Changes in GnRH pulse frequency are controlled by Estrogens that increase pulse frequency Progestins that decrease pulse frequency
Hormones and the Follicular Phase
Begins with FSH stimulation Monthly Some primordial follicles develop into primary follicles As follicles enlarge Thecal cells produce androstenedione
Androstenedione
Is a steroid hormone Is an intermediate in synthesis of estrogens and androgens Is absorbed by granulosa cells and converted to estrogens
Estradiol
Is most abundant Has most pronounced effects on target tissues Is dominant hormone prior to ovulation
Estrogen Synthesis
Androstenedione is converted to testosterone Enzyme aromatase converts testosterone to estradiol Estrone and estriol are synthesized from androstenedione
Five Functions of Estrogen
Stimulates bone and muscle growth Maintains female secondary sex characteristics Such as body hair distribution and adipose tissue deposits Affects central nervous system (CNS) activity Especially in the hypothalamus, where estrogens increase the sexual drive Maintains functional accessory reproductive glands and organs Initiates repair and growth of endometrium
Early in follicular phase of ovarian cycle
Estrogen levels are low GnRH pulse frequency is 16–24/day (1 per 60–90 minutes) As tertiary follicles form, concentration of circulating estrogens rises steeply and GnRH pulse frequency increases to 36/day (1 per 30–60 minutes)
In follicular phase
Switchover occurs When estrogen levels exceed threshold value for about 36 hours Resulting in massive release of LH from adenohypophysis
Sudden surge in LH concentration triggers: Completion of meiosis I by primary oocyte Rupture of follicular wall Ovulation Ovulation occurs 34–38 hrs after LH surge begins (9 hrs after LH peak)
Sudden surge in LH concentration triggers: Completion of meiosis I by primary oocyte Rupture of follicular wall Ovulation Ovulation occurs 34–38 hrs after LH surge begins (9 hrs after LH peak)
Luteal Phase
Progesterone levels remain high for 1 week Unless pregnancy occurs, corpus luteum begins to degenerate Progesterone and estrogen levels drop GnRH pulse frequency increases Stimulating FSH secretion Ovarian cycle begins again
Hormones and the Uterine Cycle
Corpus luteum degenerates Progesterone and estrogen levels decline Resulting in menses Endometrial tissue sheds several days Until rising estrogen stimulates regeneration of functional zone Proliferative phase continues Until rising progesterone starts secretory phase Increase in estrogen and progesterone Causes enlargement of endometrial glands And increase in secretory activities
Hormones and Body Temperature
Monthly hormonal fluctuations affect core body temperature During luteal phase: progesterone dominates During follicular phase: estrogen dominates and basal body temperature decreases about 0.3°C Upon ovulation: basal body temperature declines noticeably Day after ovulation: temperature rises
Male Sexual Function
Is coordinated by complex neural reflexes Using sympathetic and parasympathetic divisions of ANS Male Sexual Arousal Leads to increase in parasympathetic outflow over pelvic nerves, which leads to erection
Male Sexual Stimulation
Initiates secretion of bulbo-urethral glands Lubricates penile urethra and surface of glans Leads to coordinated processes of emission and ejaculation
Emission
Occurs under sympathetic stimulation Peristaltic contractions of ampulla Push fluid and spermatozoa into prostatic urethra Seminal glands contract Increasing in force and duration Peristaltic contractions in prostate gland Move seminal mixture into urethra Sympathetic contraction of urinary bladder and internal urethral sphincter Prevents passage of semen into bladder
Ejaculation
Occurs as powerful, rhythmic contractions In ischiocavernosus and bulbospongiosus muscles That stiffen penis Push semen toward external urethral opening Causes pleasurable sensations (orgasm) Followed by subsidence of erectile tissue (detumescence)
Female Sexual Arousal
Parasympathetic activation leads to Engorgement of erectile tissues Increased secretion of cervical mucous glands and greater vestibular glands Blood vessels in vaginal walls fill with blood Fluid moves from underlying connective tissues To vaginal surfaces
Female Orgasm
Is accompanied by Peristaltic contractions of uterine and vaginal walls Rhythmic contractions of bulbospongiosus and ischiocavernosus muscles
About this deck
By: Morgann Hambright
Created: 2011-05-01
Size: 357 flashcards
Views: 82
Created: 2011-05-01
Size: 357 flashcards
Views: 82
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