Lecture: Digestive System Flashcards

Question

How is gastric HCl formed?

Answer 1

bicarbonate reactions catalyzed by carbonic anhydrase

Answer 2

1) activates enzymes 2) liquefies food 3) converts iron 4) nonspecific resistance

Answer 3

high blood pH during digestion; HCl accumulates in stomach while bicarbonate ions accumulate in blood; b/c of bicarbonate, blood leaving stomach has higher pH when digestion is occurring than when the stomach is empty

Answer 4

pepsinogen = type of zymogen; HCl removes some of pepsinogens amino acids, converting it to pepsin; pepsin digests protein

Answer 5

inactive protein which can be converted to an active enzyme by the removal of some of its amino acids

Answer 6

``` digestive enzymes -gastric lipase -chymosin chemical messengers -hormones, including paracrine secretions -gut-brain peptides ```

Answer 7

1) VIP 2) GIP 3) NPY 4) secretin 5) CCK 6) Substance P

Answer 8

swallowing center of medulla signals stomach to react with a receptive-relaxation response; peristaltic contractions are governed by pacemaker cells in the longitudinal layer; the pyloric sphincter controls flow of chyme into small intestine

Answer 9

stomach's response to incoming food in which it briefly resists stretching but then relaxes to accomodate the arriving food

Answer 10

``` forceful ejection of stomach and intestinal contents; controlled by emetic center in medulla; caused by: -overstretching -chemical irritants -trauma or pain -psychological stimuli physiology -vomiting is usually preceded by nausea and retching ```

Answer 11

thoracic expansion and abdominal contraction create a pressure difference that dilates the esophagus; when combined with reverse peristalsis, becomes vomiting

Answer 12

nervous system and endocrine system collaboration; 1) cephalic: controlled by brain 2) gastric: controlled by stomach 3) intestinal: controlled by small intestine

Answer 13

hypothalamus responds to sight, smell, taste, and thought of food; in a parasympathetic response, vagus nerve fibers of the medulla stimulate increased gastric activity

Answer 14

bolus enters stomach: -stomach distention triggers short & long reflexes; -raised pH triggers stomach buffering; acetylcholine (ACh), histamine, and gastrin trigger release of HCl, intrinsic factor (IF), and pepsinogen

Answer 15

as dietary protein is digested, it breaks down into small peptides and amino acids, which directly stimulate the G cells to secrete more gastrin (positive feedback loop that accelerates digestion); small peptides buffer stomach acid; as digestion continues, pH drops lower and lower; with a pH <2, stomach acid inhibits the parietal cells and G cells (negative feedback loop that slows digestion)

Answer 16

chyme enters duodenum; stomach is stimulated by: -stretching of the duodenum which accentuates vagovagal reflexes -intestinal gastrin released in response to incoming chyme; gastric secretion and motility is inhibited by: -enterogastric reflex; -enteroendocrine (EE) cells' release of secretin, CCK, and GIP

Answer 17

shuts off release of gastrin from G-cells of the stomach, inhibiting gastric motility and the secretion of gastric acid

Answer 18

``` largest gland (3 lbs); 4 lobes; digestive function: bile secretion; porta hepatis, which provides a point of entry for: -hepatic portal vein -hepatic artery -hepatic duct ```

Answer 19

on the posterior liver, point of entry for the hepatic portal vein and proper hepatic artery and a point of exit for the bile passages

Answer 20

interior of liver filled w/ tiny cylinders called hepatic lobules; a lobule contains: a central vein surrounded by hepatocytes, which synthesize bile salts from cholesterol; spaces between plates of hepatocytes called hepatic sinusoids; bile secreted into narrow channels called the bile canaliculi hepatic triad = distinctive structure consisting of an artery, vein, and bile ductule

Answer 21

function: concentrates and stores bile; neck leads into cystic duct, which converges with the hepatic duct to form the bile duct, which terminates in the duodenum; enterohepatic circulation enables bile to be reabsorbed from the small intestine to the liver

Answer 22

route of secretion (by hepatocytes of liver), reabsorption (in the ileum), and resecretion (by hepatocytes of liver) of bile; ~80% of bile acids are reabsorbed into the ileum

Answer 23

green fluid containing minerals, cholesterol, phospholipids, fats, and bile pigments; principal pigment = bilirubin, derived from the decomposition of hemoglobin

Answer 24

exocrine gland; secretory acinar cells have a high density of secretory vesicles called zymogen granules; acini secrete enzymes and zymogens; pancreatic ducts secrete sodium bicarbonate; pancreatic juice = alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes

Answer 25

1) neural parasympathetic (vagal) stimulation; sympathetic inhibition 2) hormonal cholecystokinin (CCK) & gastrin stimulate gall bladder contraction and pancreatic secretion; secretin stimulates hepatic and pancreatic bicarbonate secretion

Answer 26

chemical digestion and nutrient absortion; 1) duodenum (1st 10") 2) jejunum (next 8') 3) ileum (final 12')

Answer 27

circular folds made up of mucosa and submucosa force chyme to spiral through; villi in the intestine are tiny projections in the SI made up of 2 kinds of epithelial cells: 1) enterocytes (absorptive cells) -microvilli form a fuzzy brush border on the surface of each enterocyte, increasing surface area; they also contain brush border enzymes in the plasma membrane; 2) goblet cells; core of each villus contains a lymphatic capillary called a lacteal; between the bases of the villi are porous intestinal crypts, which house dividing stem cells; clusters of Paneth cells are clustered at the base of each crypt- they secrete defensive proteins that resist bacterial invasion of the mucosa; duodenal glands (in the duodenum) secrete bicarbonate-rich mucus

Answer 28

1) mix chyme with intestinal juice, bile, and pancreatic juice 2) bring chyme into contact with the mucosa for contact digestion and nutrient absorption 3) move residue towards large intestine

Answer 29

movement in which stationary ringlike constrictions appear at several places along the intestine and then relax as new constrictions form elsewhere; effect: mixing and contact digestion

Answer 30

successive, overlapping waves of peristaltic contraction; each wave travels partway down the intestine and milks the contents towards the colon

Answer 31

complex CHOs to sugars; in mouth, salivary amylase hydrolyzes starch to oligosacchrides; in stomach, the food is churned and mixed, and salivary amylase is exposed to lower pH which inactivates it; in small intestine, pancreatic amylase breaks down oligosacs to smaller oligosacs and disacs; brush border enzymes dextrinase and glucoamylase breaks down smaller oligosacs to disacs; brush border enzymes maltase, sucrase, and lactase break down disacs to monosacs

Answer 32

glucose & galactose both transported into enterocytes (absorptive cells) via the Sodium-Glucose Linked Transporter (SGLT), a secondary active transport mechanism coupled to sodium; fructose is transported via facilitated diffusion and converted to glucose inside the enterocyte; all are transported to the liver

Answer 33

in stomach, pepsin hydrolyzes any peptide bond between tyrosine and phenylalanine, leaving behind shorter polypeptides and free amino acids; in small intestine: -the pancreatic enzymes trypsin and chymotrypsin break polypeptides down into smaller oligopeptides; -3 brush border enzymes break down these oligopeps one AA at a time: 1) carboxypeptidase 2) aminopeptidase 3) dipeptidase

Answer 34

similar to monsaccharides; different sodium-dependent AA cotransporters; dipeptides and tripeptides are absorbed and then hydrolyzed to AAs within the cytoplasm of enterocytes; AAs leave cell via facilitated diffusion and enter the blood capillaries of the villus

Answer 35

duodenum receives small emulsification droplets from the stomach, which it promptly coats with lecithin and bile salts; pancreatic lipase converts triglyceride into 2 free fatty acids (FFAs) and a monoglyceride; micelles, coatings of bile acids, form to facilitate the transportation of the lipids to enterocytes

Answer 36

Micelles pass through microvilli of the brush border, where the lipids leave the micelles and diffuse into the enterocytes; lipids are transported to the Golgi complex, where chylomicrons, lipoproteins particles, are formed; chylomicrons are too large to enter capillaries, so they move into lacteals and are taken up by lymph vessels; some free fatty acids (FFAs) enter capillary blood; chylomicrons are hydrolyzed to FFAs and glycerol by lipoprotein lipase; these products are taken to the liver, where lipoproteins are made

Answer 37

pancreatic nucleases break nucleotides apart; brush border enzymes nucleosidase and phosphatase further break down nucleotides into pentose sugars (ribose & deoxyribose), nitrogenous bases, and phosphate ions

Answer 38

pentose sugars (ribose & deoxyribose), nitrogenous bases, and phosphate ions are transported across the intestinal epithelium by active transport mechanisms and enter the capillary blood of the villus

Answer 39

fat soluble vitamins (A,D,E, & K) are absorbed with other lipids; water soluble vitamins (B & C) are absorbed via simple diffusion; vitamin B12 is absorbed bound to intrinsic factor (IF) from the stomach: vitamin B12-intrinsic factor complex binds to specific mucosal receptor sites on enterocytes in the ileum and is absorbed by endocytosis

Answer 40

actively absorbed along length of small intestine; Na+ ions are contransported with sugars and AAs; Cl- ions are actively transported in the ileum by a pump that exchanges them for bicarbonate ions; K+ ions are absorbed by simple diffusion; iron and calcium are absorbed based on the body's needs (other minerals absorbed at fairly constant rates)

Answer 41

GI tract receives about 9L of water per day; most of this water consists of GI secretions; ~8L absorbed by SI, and ~0.8L absorbed by LI; moves across intestinal mucosa via osmosis, following the concentration gradient established by active transport of solutes; water uptake is coupled to solute uptake (solute uptake affects rate of water absorption)

Answer 42

colon: part of LI between the ileocecal junction and rectum; rectum: distal portion of LI in pelvic cavity; taenia coli: 3 strips of smooth muscle in the colon whose muscle tone contracts the colon lengthwise and causes its walls to bulge, forming pouches called haustra; bacterial flora produce intestinal gas

Answer 43

haustral contractions: segmentation that occurs every ~30 min; distension of a haustrum with feces causes it to contract; mass movements: stronger, occur 1-3 times a day, last ~15 min; triggered by filling of stomach and duodenum

Answer 44

anus contains an internal and external anal sphincter; stretching of rectum stimulates defecation reflexes: 1) intrinsic reflex: stimulated by myenteric nerve plexus; causes peristalsis that drives feces downward; 2) parasympathetic reflex: spinal reflex; intensifies peristalsis; external anal sphincter under voluntary control: you can poop when you want!