Ch 23: The Digestive System

• Ingestion (eating)
• Propulsion
• Mechanical digestion
• Chemical Digestion
• Secretion
• Absorption
• Defecation
• LOOK AT FIGURE 23.2

• movement of food thru GI track

• chewing
• churning and segmentation
• emulsifying (bile salts)

• HCl (stomach acid)
• enzymes
• H2O

• the release of chemicals into the GI track
• Adding:
• enzymes
• H2O
• HCl
• to take to the GI track

• from GI track into blood vessels
• have to be in blood to be in the body

• "POOP"
• eliminating solid wastes

• Mesenteries
• Greater omentum
• Lesser omentum
• Mesentery proper
• Mesocolon

• entire wrapping of abdominal region
• sheets of serous membrane that supports portions of the digestive tract

• lies anterior to the abdonimal viscera (positions stomach anteriorly)
• provides padding, protection, insulation, and energy reserves

The majority of mesenteries

• from liver to lesser curve of the stomach
• positions stomach to posterior

• maintains folds of small intestines

• secures large intestines to parietal peritoneum

• Mucosa
• Submucosa
• Muscularis externa
• Serosa

• lines digestive tract (inner most layer- secretes mucus= goblet cells)
• snot helps movement
• mucus huge microbial
• traps microorganisms
• moistened by glandular secretions
• lamina properia and epithelium form mucosa

• Submucosal plexus- stimulates contraction (food getting into GI tract)
• layer of dense irregular connective tissue

• smooth muscle arranged in circular and longitudinal layers
• adventitia
• Menteric plexus = real movement of getting things out of GI tract
• Local reflexes:
• 1 layer = circular
• 2 layer = longitudinal layers

• serous membrane covering most of the muscularis externa (outer most layer)

• Viceral smooth muscle shows rhythmic cycles of activity
• Peristalis
• Segmentation

• Pace setter cells
• under their own control
• "heres food pushed against whole..i better get going"

• waves that move a bolus

• churn and fragment a bolus

LOOK AT!!

• a) Peristalis
• pinch off back route so 1 direction to flow
• b) Segmentation
• long, muscles shorten
• mix together
• complete mix together
• ** how mater gets in the and mixes it all up

• Neural has 2 major intrinsic nerve plexuses:
• Submucosal nerve plexus
• Myenteric nerve plexus
• Segmentation and peristalsis are largely automatic involving local reflex arcs that respond to changes in pH or chemical stimuli
• Hormones can enhance or inhibit smooth muscle contractions

• regulates glands and smooth muscle in the mucosa

• major nerve supply that controls GI tract mobility

• analysis of material before swallowing
• mechanical processing
• lubrication
• limited digestion

• teeth
• roof of cavity = hard and soft palates
• floor of cavity = tongue
• salivary glands
• uvula guards opening to pharynx

• mastication of bolus (chewing)
• contact of occlusal surfaces

• enamel covering crown (similar to bones)
• dentin forms basic structure (inside enamel)
• root coated with cementum
• Periodontal ligaments hold teeth in alveoli

• 20 primary teeth (deciduous teeth) = baby teeth
• 32 teeth of secondary dentition = adult

• mechanical processing
• assistance in chewing and swallowing
• sensory analysis by touch, temperature, and taste receptors

• extrinsic and intrinsic tongue muscles
• innervated by the hypoglossal nerve

• lubrication, moistening, and dissolving
• initiation of digestion of complex carbohydrates
• carbohydrate digestion
• salivary analysis = polysacaraides and breaks them into trisacarides and disacarides

• watery solution containing electrolytes, buffers, glycoproteins, antibodies, enzymes → amylase, lipase (immediatly functional)

• parotid
• sublingual
• submandibular

(shares a common pathway with the respiratory system)

• common passageway for food,liquids, and air
• lined with stratifies squamous epithelium
• pharyngeal muscles assist in swallowing
• pharyngeal constrictor muscles
• palatel muscles

• muscular tube going from the laryngopharynx to the stomach
• travels thru thr mediastinum and pierces the diaphragm at esophageal hiatus
• joins the stomach at the cardiac orifice
• esophageal mucosa
• muscularic changes from skeletal (superiorly) to smooth muscle (inferiorly)

• nonkeratinized stratified squamous epithelium

• Coordinated activity of the tongue, soft palate, pharynx, esophagus, and 22 separate muscle groups
• Buccal phase
• Pharyngeal-esophageal phase
• Peristalis moves food thru the pharynx to the esophagus

• bolus is forced into the oropharynx (tongue forced into mouth)

• controlled by the medulla and lower pons (shutting off epiglottis = shutting off respiration)

• Bulk storage of undigested food (# 1 function)
• Mechanical breakdown of food
• Disruption of chemical bonds via acids and enzymes
• Production of intrinsic factor
• transport protein for fat soluble vitamins (vitamin B)

• Cardiac region
• Fundus
• Body
• Pyloric Region
• The pylorus is continuous with the duodenum thru the pyloric sphincter (muscle aids in 1st part of small intestines)

• surrounds the cardiac orifice

• dome-shaped region beneath the diaphragm (major part of stomach)

• midportion of the stomach (surrounded by greater, lesser)

• made up of the antrum and canal which terminates at the pylorus

• Mucous neck cells
• Parietal cells
• Chief cells
• Enteroendocrince cells

• secrete acid mucus (responsible for making HCl)

• secrete HCl and intrinsic factor
• (parietal sounds like parent...parents are like acid - they ruin your social life) ↓
        secretes HCl (acid)

• produce pepsinogen

• HCl in the stomach
• Pepsin itself via a positive feedback mechanism
• Pepsinogen → Pepsin - enzyme responsible for breaking down proteins

                          ↑HCl

• Pepsin only break down to polypeptides
• Pepsinogen            ogen = inactive
• only protein in hydrochloric environment that becomes active

• secrete gastrin, histamine, endorphins (food is comfort, eat more to block all sadness), serotonin ("happy feel good", eat and feel good), cholecystokinin (CCK), and somatostatin

Food = gives you energy

• Neural and hormonal mechanisms regulate the release of gastric juice
• stimulatory and inhibitory events occur in 3 phases: (prepare, degest, or spit out food)
• cephalic (reflex) phase
• gastric phase
• intestinal phase

• prior to food entry (regulated by the brain)
• Function:
• prepare stomach for yhr arrival of food
• Duration:
• minutes
• Primary Mechanism:
• Neural: Vagus (x) nerve
• Resulting Action:
• stimulate submucosal plexus to secrete gastric juices

• once food enters the stomach
• Function:
• food processing
• increase gastric juice
• Duration:
• 3-4 hrs
• Primary Mechanism:
• Local Reflexes: ↑pH (chemo), stretch of wall
• Neural: Myenteric plexus, submucosal
• Hormone: Gastrin
• Resulting Action:
• peristalic contractions, segmentation, ↑gastric juice

• as partially digested food enters the duodenum (regulated by small intestines - helps control the rate of digestion)
• Function:
• controls the rate of gastric activity
• Duration:
• 4-8 hrs (depends on type of food you eat/diet)
• Primary Mechanism:
• Hormones: CCK, GIP, secreting, gastrin
• Neural: ↓pH, stretch receptors
• Resulting Actions:
• feedback inhibition of gastric secretion
• ↑ intestinal juice
• ↓in stomach motility

• realeased form small intestine
• targets the liver and galbladder to synthesize and release bile

• released from small intestine
• targets pancrease to release its juices

• released from small intestine
• targets stomach
• block (inhibit) gastric juice

• released from small intestin
• blocks stomach- tricks the body

• Pepsin: proteins broken down into plypeptides
• carbohydrates are broken down from salivary amylase

• very little of nutrients
• some drugs (aspirin)
• alcohol

• bacterial toxins
• excess drugs
• overdistention (Biggest issue- eats so much it causes stretching)
• high-order brain functions

• processed by medulla oblongata
• Degree of coloration indicates severity
• Green
• Red
• Black

• bile, breakdown of food

• blood
• rupture cappilaries
• any mucousal lining
• NEED HELP

• old blood
• inflammation of stomach
• tissue dying away
• NEED HELP

• Duodenum
• Jejunum
• lleum

• main function is buffering and digestion
• hepatopancreatic ampulla

largest

• most absorption occurs here
• increased abundance of plicae, villi, and microvilli (secretes enzymes breaks down)

small

• llioceal valve- opens to large intestines
• peyers patchs

keep liquid not a solid

• secreted by intestinal glands in response to distension or irritation of the mucosa
• slightly alkaline and isotonic with blood plasma
• helps buffer acidic pH from gastric juices
• Largely water, enzyme-poor, but contains mucus
• keeps digestive material in solution

• peristalsis
• segmentation
• gastroenteric reflexes - signals to duodenum that food is coming soon
• initiated by stretch receptors in stomach
• gastroileal reflex
• triggers relaxation of ileocecal valve

• secretes pancreatic juices which breaks down all categories of foodstuff -  enzymes for everything we eat
• Acini (clusters of secretory cells) contain zymogen granules with digestive enzymes - responsible for producing enzymes

• water solution of enzymes and electrolytes (primarily HCO3¯‾
• neutralizes acid chyme
• provides optimal environment for pancreatic enzymes
• Enzymes are released in inactive form and activated in the duodenum

• Trypsinogen is activated to trypsin (targets proteins)
• procarboxypeptidase is activated to carboxypeptidase (targets proteins)

• amylase
• lipases
• nucleases (target nucleotides)
• these enzymes require ions or bile for optimal activity
• have to have neutral pH to be functionable

• secretin and CCk are released when fatty or acidic chyme enters the duodenum
• CCK and secretin enter the bloodstream
• Vagal stimulation also causes release of pancreatic juice

• CCK induces the secretion of enzyme-rich pancreatic juice
• Secretin causes secretion of bicarbonate-rich pancreatic juice

• largest gland in the body
• superficially has 4 lobes:
• right
• left
• caudate
• quadrate
• the falciform ligament:
• separates the right and left lobes anteriorly
• suspends the liver from the diaphragm and anterior abdominal wall

• Composed of hepatocyte (liver cell) plates radiating outward from a central vein
• Portal triads are found at each of the six corners of each liver lobule

•  enlarged, leaky capillaries located between hepatic plates

• hepatic macrophages found in liver sinusoids

• Production of bile (metabolic function)
• Processing blood borne nutrients (all plasma proteins made by liver) - metabolic function
• storage of fat-soluble vitamins
• store glucose (glycogen) males all lipids (steroid hormones)
• Detoxification (kupffer cells) - alcohol

•    A yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes

•    Enterohepatic circulation recycles bile salts

•    The chief bile pigment is bilirubin, a waste product of heme

• **Emulsifys fats (physiacal/mechanical)
• ­­­­­­­­­­­­­­­­­­­­­­­­­­ Facilitate fat and cholesterol absorption
• Help solubilize cholesterol

* need to know stores bile!

•    Thin-walled, green muscular sac on the ventral surface of the liver

•  stores, modifies and concentrates bile by absorbing its water and ions

•    Releases bile via the cystic duct, which flows into the bile duct

• Acidic, fatty chyme causes the duodenum to release:
• Cholecystokinin = CCK (primary)  and secretin into the bloodstream
• Bile salts and secretin transported in blood stimulate the liver to produce bile
• Vagal stimulation causes weak contractions of the gallbladder

• Neural and hormonal mechanisms coordinate glandular secretion with intestinal motility
• **GI activity stimulated by parasympathetic innervation
• Inhibited by sympathetic innervation
• **Enterogastric (intestines goes to stomach), gastroenteric and gastroileal reflexes coordinate stomach and intestines
• 1st part of word = origin, where it starts
• 2nd part = motor, where it goes (whats happening

•    Cecum

•    Colon

•    Rectum

•    Anal canal

• Ascending
• transverse
• descending
• sigmoid

(controls defication)

• Internal and external anal sphincter

(where defication occurs)

• opens to the exterior at the anus

(absorption of water)

•    Other than digestion of enteric bacteria, no further digestion takes place

•    Vitamins, water, and electrolytes are reclaimed

•    Its major function is propulsion of fecal material toward the anus

•    Though essential for comfort, the colon is not essential for life

• Bacteria surviving the small intestine that enter the cecum
• Bacteria entering via the anus

–  Colonize the colon

–  Ferment indigestible carbohydrates

–  Release irritating acids and gases (flatus)

– **Synthesize B complex ( B12 needed for hemoglobin) vitamins and vitamin K (needed thru clotting process)

• Haustral contractions (mass movement)
• Presence of food in the stomach

–  Slow segmenting movements that move the contents of the colon

–  Haustra sequentially contract as they are stimulated by distension

–  Activates the gastrocolic reflex

–  Initiates peristalsis that forces contents toward the rectum

•    Distension of rectal walls caused by feces:

–  stimulates contraction of the rectal walls

–  relaxes the internal anal sphincter (involuntary smooth muscle)

•    voluntary signals stimulate relaxation of the external anal sphincter (voluntary skeletal muscle - can hold it or cant = conscious control) and defecation occurs

• Salivary and pancreatic amylase
• Disaccharides and trisaccharides (multase, lactose, sucrose)

•   Brush border enzymes (found in microvili)
•   Monosaccharides

• bile salts improve chemical digestion by emulsifying lipid drops

•    Lipid-bile salt complexes called micelles are formed so lipids can diffuse into intestinal epithelia (absorption)

•    Lipids coated w/ proteins (chylomicrons) enter lacteals of lymphatic vessels

•    Enters into blood via thoracic duct

•    Gastric juices (low pH) and pepsin (released by chief cells) destroy tertiary and quaternary structure

•    Pancreatic enzymes such as trypsin and chymotrypsin create polypeptides

•    Brush border enzymes liberate amino acids

•    Absorption of amino acids occurs across the intestinal epithelia into blood (b/c water soluable)

–  Nearly all that is ingested is reabsorbed via osmosis

•    Vitamins – 

• Water soluble vitamins are absorbed by diffusion
• Fat soluble vitamins are absorbed as part of micelles
• Vitamin B₁₂ requires intrinsic factor

(water follows solid)

•    Thinner, more fragile epithelium

•    Reduction in epithelial stem cells

•    Weaker peristaltic contractions (constipation issue)

•    Effects of cumulative damage

•    Increased cancer rates