What is special about the smooth muscle of the GI tract?
It can self-initiate its contractions without any nerve stimulation because of pacemaker cells
Pacemaker cells in the GI have what type of potentials?
Slow wave potentials
What regulates the pacemakers in the GI?
The mechanical sensors
since smooth muscles of the GI are connected together by gap junctions, they can also be called?
What are the nerve plexuses of the GI?
Myentric plexus and the submucosal plexus
Where are the two nerve plexuses located?
Myenteric = between longitudinal and circular smooth muscle layers Submucosal = within the submucosa
The intrisic nerve plexus promote what functions ?
digestive tract motility, secretion of digestive juices, and secretion of GI hormones
Which portions of the GI tract have intrinsic innervation?
Everything from the esophagus to anus
What do both types of autonomic control do to the GI system?
parasympathetic = increases peristalsis and secretion Sympathetic = decrease peristalsis and secretion
GI hormones are secreted by what cells?
by enteroendocrine cells
Enetroendocrine cells secrete hormones due to what factors?
local changes in luminal content, such as presence of fats, proteins, or acids
What digestive process occurs at the mouth?
It is the first line of digestion, where mastication occurs;
What are the three functions of the mouth in digestion?
1. Mechanical breakdown of food into globs 2. Mix food with saliva 3. stimulate the taste buds
What do the taste buds do ?
when activated, they send signals that stimulate secretion of salivary, gastric, pancreatic, and bile secretions
How does mechanical digestion differ from chemical?
mechanical doesn't involve the breaking of chemical bonds while chemical does
What are the percentages of protein and water in saliva?
99.5% water, 0.5% protein
What are the salivary proteins and their functions?
Mucus - provides lubrication for deglutition Salivary Amylase - begins to digest carbs in the mouth Lingual Lipase - begins digestion of triacylglycerols in the mouth Lysozyme - enzyme that destroys bacteria
What type of receptors are the taste buds?
What are the two types of ways that salivary secretion can be stimulated and give examples of each.
1. Simple Reflex - chemoreceptors and pressurereceptors 2. Conditioned Reflex - sight of food, smells, thought of food
Explain the pathway of simple reflex.
Taste buds sense food, send signals to the salivary center in the medulla, which stimulates autonomic nervous system, and this stimulates the salivary glands to secrete saliva
What functions does the stomach provide?
food storage, initiation of digestion of proteins and short chain triacylglycerols, and move food into the small intestine as a pasty material known as chyme
What mechanical process occurs in the stomach that aids digestion? Why is this important?
Several minutes after eating food, peristaltic movements are initiated every 15-20 seconds; it helps mix gastric juices with the food to form chyme
Chemical digestion in the stomach... explain.
As food enters the stomach, it is broke down by lingual lipase and salivary amylase; soon after, gastric secretion of pepsinogen, HCl, and Mucus occurs which will inhibit salivary amylase and lingual lipase; pepsinogen will be activated and begin digesting proteins
Gastric secretions come from anatomical areas of the mucosa called?
What are the secretory cells in gastric pits called and what does each secrete?
1. receptors for sight, smell, and taste activate the cerebral cortex and hypothalamus 2. Cerebral Cortex and hypothalamus stimulate medulla 3. Medulla activates parasympathetic nerves (vagus nerves) that activate the submucosal plexus 4. submucosal plexus increases secretion of gastric juices, gastrin, and promotes gastric peristalsis
Explain the gastric phase of regulation of digestion.
1. Food enters stomach, raises pH, and distends the stomach wall 2. stretch receptors and chemoreceptors activate submucosal plexus 3. submucosal plexus stimulates increase in gastric secretions, gastrin, and also promotes gastric peristalsis
Describe the intestinal phase of digestive regulation.
1. increased gastric motility from cephalic and gastric phases move chyme into the SI 2. Stretch receptors respond to distension in walls and chemoreceptors detect fatty acids and glucose 3. enteroendocrine cells secrete CCK, GIP, and secretin that inhibit gastric secretions and peristalsis 4. enterogastric reflex via the medulla inhibits the gastric secretions and peristalsis
Chemical digestion in the SI depend on primarily what accessory structures?
Liver, gallbladder, and the pancreas
List the 8 major functions of the liver.
- production/secretion of bile - carbohydrate metabolism - lipid metabolism - protein metabolism - detoxification of drugs and hormones - Chemical storage - phagocytosis - Vitamin D activation
What is bile made of? Whats its pH?
water, bile salts and acids, cholesterol, lecithin, bile pigments, and ions ; 8.0
What gives poop its brown color?
RBC's are broken down into iron, globin, and bilirubin, and bilirubin is broken down into constituents that have a brown color
What does the term glycogenolysis mean?
Carbohydrate metabolism in the liver is important because...
It regulates blood-glucose levels;
Low blood glucose will result in?
glycogenolysis, gluconeogenesis, and isomerization of fructose and galactose into glucose
Describe how lipid metabolism is aided by the liver.
lipoproteins that transport fatty acids, triacylglycerols, and cholesterol in the blood are synthesized, and cholesterol is also synthesized to be used in bile
Explain protein metabolism in the liver.
Plasma proteins such as albumins, globulins, prothrombin, and fibrinogen are synthesized here, transamination and deamination of amino acids, and conversion of ammonia into urea for urine secretion
What is stored in the liver?
glycogen, Vitamins A, D, B12, E, and K, and also ferritin
What is phagocytized in the liver?
worn out RBC's and WBC's by the Kupffer Cells , and also some bacteria
What is the function of the gallbladder?
its function is to store and concentrate bile until needed in the SI
What causes the gallbladder to release bile?
CCK will stimulate smooth muscle contractions and this forces bile into the ducts
The pancreas secretes pancreatic juices which are composed of?
bicarbonate ions which increase pH of chyme entering the SI, and also digestive enzymes
So again, how do CCK and secretin affect digestive function related to the pancreas?
As acidic chyme moves into the SI, CCK and secretin are going to be secreted, which travel through the blood and stimulate the pancrease to release bicarbonate and digestive enzymes
Identify the ways which CCK is involved in digestion.
Stimulates secretion of pancreatic enzymes, stimulates contraction of the gallbladder, and decreases gastric peristalsis
Describe all digestive functions of secretin.
increases the secretion of bicarbonate ions in pancreatic juices, increases secretion of bicarbonate into the bile, and decreases gastric secretions
What are the enzymes secreted in pancreatic juice and what do they do?
trypsinogen - cleaves internal peptide bonds chymotrypsinogen - cleaves internal peptide bonds proelastase - cleaves internal peptide bonds procarboxypeptidase - cleaves C-terminal amino acids prophospholipase - cleaves fatty acids on phospholipids lipase - cleaves fatty acids from glycerol amylase - digests starch to short glucose polymers cholesterolesterase - frees cholesterol from other molecules
What are brush-border enzymes?
They are enzymes found in the microvilli of the SI that participate in digestion of carbohydrates, proteins, and nucleic acids
Explain the activation of the protein digesting enzymes in pancreatic juice for use in the SI.
Trypsinogen will be activated into trypsin by enterokinase, and then trypsin will activate chymotrypsinogen, proelastase, and procarboxypeptidase
What are the 4 families of brush-border enzymes?
Disaccharidases, peptidases, phosphatases, and nucleosidases
What are the disaccharidases, whats their substrate, and whats their products?
Sucrase - hydrolyzes sucrose into fructose and glucose Maltase - hydrolyzes maltose into two glucose molecules Lactase- breaks down lactose into glucose and galactose
What are the peptidases, whats their substrate, and their products?
Aminopeptidase - cleaves the N-terminal amino acids of a polypeptide Enterokinase - activates trypsin
What do phosphatases and nucleosidases do?
Phosphatases - cleaves phosphate groups from nucleotides Nucleosidases - cleaves bases from ribose or deoxyribose sugars
What are the two processes of mechanical digestion in the SI?
Segmentation - localized contractions in areas of SI with food which mixes chyme and juices Peristalsis - minor form compared to segmentation; propels chyme through the intestinal tract
How are carbohydrates broken down in the SI?
By pancreatic amylase and brush border enzymes
What are the substrates and products of the carbohydrate enzymes of SI?
pancreatic amylase - takes starches and makes disaccharides and dextrin brush-border enzymes - take disaccharides and dextrin and make monomer sugars
What are the protein enzymes in the SI, and differentiate between them.
Exopeptidases - cleave external bonds and make AA's Endopeptidases - cleave internal bonds and produce small polypeptides
What enzyme destroys lipids in the SI? What does it do?
Pancreatic Lipase - hydrolyzes triacylglycerols into fatty acids and monoglycerides
What breaks down nucleotides in the SI?
Pancreatic enzymes ribonuclease and deoxyribonuclease, which breakdown the nucleic acids into nucleotides, but also brush-border enzymes nucleosidases and phosphatases which breakdown nucleotides into pentoses, phosphates, and nitrogenous bases
How do sugars, lipids, and proteins enter the luminal epithelial cells int eh SI?
Carbohydrates - glucose and galactose enter through secondary active transport with Na, and fructose through facilitated diffusion Proteins - enter as amino acids through active transport or secondary active transport with Na, and enter as tripeptides and dipeptides through secondary transport with H+ Lipids - all through simple diffusion
Describe how carbs, proteins, and lipids travel from the epithelial cells to blood stream in the SI
Carbohydrates - facilitated diffusion of monosaccharides Proteins - diffusion of amino acids Lipids - diffusion of short-chain FA's
How do fats enter the lymph system?
They become triacylglycerols in the epithelial cells and then are exported as chylomicrons into the lacteal of the lymph system
Describe the functions of the renal system.
- Regulate plasma ionic composition - Regulate plasma volume - Regulate plasma osmolarity - Regulate plasma pH - Remove metabolic waste products and foreign substances from body
What are the two types of nephrons and which are a majority?
Cortical and juxtamedullary; cortical
What is filtered out of plasma during glomerular filtration?
proteins and blood cells
How much of the original filtrate goes through the glomerulus into the bowman's capsule?
If MAP goes up, what happens to GFR?
It also goes up
how does one calculate for glomerular filtration rate?
Glomerular Filtration Rate =
How is the GFR intrinsically and extrinsically regulated?
Intrinsic - myogenic regulation, tubuloglomerular feedback, mesangial cell contraction Extrinsic - sympathetic nervous system via the Low-Pressure baroreceptors
When do extrinsic and intrinsic regulations of GFR occur?
intrinsic occurs when MAP is between 80 - 180 mmHg, and extrinsic with anything outside of that range
What is reabsorption?
selective transport of solute and water from lumen of renal tubule to the interstitial fluid
How does reabsorption occur?
solute is either actively or passively reabsorbed, and water is wicked up from osmolarity differences created by solute reabsorption
What is the transport maximum?
it occurs whenever all carriers and pumps are saturated, and the excess solutes are simply excreted in the urine; the plasma concentration that this occurs at is called the renal threshold
Differentiate between reabsorption in the proximal and distal convoluted tubules.
The proximal can reabsorb many more molecules than the distal, because the distal has tighter junctions, and the distal is more highly regulated, and also has fewer mitochondria and ATP for use in transport
How does secretion occur?
through carrier proteins, but also primary and secondary active transporters in the basolateral and apical membranes
What waste products and ions are secreted from the ISF to the renal tubule?
K, H, choline, creatine, and penicillin
How does one calculate excretion?
Excretion = Filtered + Secreted - Reabsorbed
What is Filtered Load?
The quantity of a solute filtered per minute;
FL = GFR x Plasma Concentration
How does one figure out excretion rate?
Excretion Rate = Urine Conc. x Urine Flow Rate
(E = U*V)
What is renal clearance and what is it used for?
It is the volume of plasma from which that substance is completely removed (cleared) per unit of time; measure of kidney function
Clearance = Excretion Rate / Plasma Conc. = U*V/P
What are the units of filtered load, excretion, and clearance?
FL = g/min E = g/day C = L/day
When doing calculations, what should one always remember to do?
convert the GFR to L/min values!!
What is inulin?
It is a polysaccharide that is NOT secreted or reabsorbed, and so all inulin filtered is secreted, so the clearance of inulin is = GFR
What is PAH?
Para-aminohippuric Acid; plasma containing PAH is completely cleared of PAH in the kindeys, so