Lecture 30 Digestive

Question 1

GI Tract

Answer 1

mouth -stratified squamous epithelium 
pharynx 
esophagus 
stomach -simple columnar epithelium 
small intestine
large intestine

Question 2

Accessory Organs

Answer 2

salivary glands
liver
pancreas
gallbladder

Question 3

Functions of the Digestive System

Answer 3

digestion
absorption
secretion
motility

Question 4

digestion

Answer 4

chemical breakdown of food molecules by hydrolysis

Question 5

absorption

Answer 5

of nutrients, electrolytes and H2O

Question 6

secretion

Answer 6

mucus, digestive enzymes, acid, bicarbonate, electrolytes

Question 7

motility

Answer 7

muscular movements of GI tract to mix and propel food
peristalsis - moves material forward
segmental contractions - mix contents

Question 8

regional specialization (“assembly line”)

Answer 8

ingestion → mechanical breakdown → chemical digestion → absorption → waste processing

Question 9

GI tract structure: 4-layered tube

Answer 9

mucosa
submucosa
muscularis (externa)
serosa

Question 10

mucosa

Answer 10

mucosa - epithelium + lamina propria (areolar CT) + muscularis mucosae

Question 11

submucosa

Answer 11

submucosa - connective tissue, vascular

Question 12

muscularis (externa)

Answer 12

muscularis (externa) - smooth muscle

Question 13

serosa

Answer 13

• thin covering membrane (visceral peritoneum)

Question 14

Mouth, Pharynx and Esophagus

functions:

Answer 14

ingestion, mastication (chewing), deglutition (swallowing)

Question 15

salivary glands

Answer 15

secrete saliva: H2O, ions, mucus, enzymes: amylase, lipase

Question 16

amylase

Answer 16

begins chemical digestion of starch → disaccharides

Question 17

esophagus

Answer 17

swallowing (upper portion), peristalsis (lower portion)

lower esophageal sphincter controls entry into the stomach

Question 18

Stomach

functions

Answer 18

storage
mechanical breakdown of food → chyme
sterilization
chemical digestion: acid (HCl) and enzymes (pepsin)

Question 19

stomach structure

Answer 19

mucosa: simple columnar epithelium, gastric glands
- secrete acidic gastric juice (pH 1-2), 1-3 L/day
- mucous cells secrete alkaline mucus to protect stomach epithelium
muscularis: 3 layers thick
- pyloric sphincter controls passage of chyme from stomach to duodenum

Question 20

acid secretion

Answer 20

parietal cells secrete hydrochloric acid (HCl)
CO2 + H2O  H2CO3  H+ + HCO3-
H+ is active transported into the lumen, Cl- follows via diffusion through channels
HCO3- is transported back into ECF (countertransport with Cl-)

Question 21

chief cells

Answer 21

enzyme secretion
chief cells secrete pepsinogen (inactive), activated at low pH to form pepsin
pepsin digests proteins into smaller peptides

Question 22

Small Intestine, Liver and Pancreas Functions and SI regions

Answer 22

Small Intestine, Liver and Pancreas
functions: chemical digestion and absorption
SI regions: duodenum, jejunum, ileum

Question 23

Digestion

Answer 23

duodenum receives chyme from stomach, secretions from liver and pancreas

Question 24

Liver

Answer 24

processes absorbed nutrients (delivered via hepatic portal vein)
secretes bile, stored in gallbladder
bile salts

Question 25

bile salts

Answer 25

derived from cholesterol, function to emulsify fats → micelles

Question 26

bile pigments

Answer 26

(bilirubin, biliverdin) - waste products from hemoglobin breakdown

Question 27

Pancreas

Answer 27

acinar cells secrete digestive enzymes: trypsin, chymotrypsin, carboxypeptidase, amylase, lipase many enzymes are secreted in inactive form (zymogens), activated by trypsin in lumen

Question 28

duct cells

Answer 28

secrete bicarbonate (NaHCO3) to neutralize acid (pH → 8)

Question 29

SI (brush border)

Answer 29

enzymes complete digestion | complete digestion of starch

Question 30

exopeptidase

Answer 30

digests terminal peptide bonds to release amino acids

Question 31

endopeptidase

Answer 31

digests internal peptide bonds

Question 32

small intestine

Answer 32

has huge surface area, specialized for absorption (1) length > 3 meters (2) circular folds (3) villi - epithelium (enterocytes and goblet cells) + lamina propria (capillaries and lacteals) (4) microvilli - “brush border” membrane

Question 33

transport mechanisms of the small intestine

Answer 33

- Na+, Cl - , K+ absorbed via active transport and diffusion through channels - glucose & amino acids - cotransport with Na+ (secondary active transport) - H2O - via osmosis, follows solute transport

Question 34

water soluble nutrients

Answer 34

are absorbed into intestinal capillaries → liver (via HPV)

Question 35

chylomicrons

Answer 35

lipids are formed into chylomicrons and absorbed into lymphatic vessels (lacteals)

Question 36

Large Intestine | functions

Answer 36

fluid absorption, waste packaging and elimination - LI absorbs most remaining water and ions from chyme - intestinal microflora - bacteria in colon, produce some vitamins (K, B12) - defecation reflex

Question 37

Neural and Hormonal Control

Answer 37

``` enteric ns ans GI peptides hormones phases of digestion ```

Question 38

. Enteric Nervous System

Answer 38

- submucosal and myenteric plexuses | - local control within the GI tract (short reflex)

Question 39

Autonomic Nervous System

Answer 39

parasympathetic: vagus nerve - stimulates GI tract motility and secretion (long reflex) sympathetic division mostly inhibits GI tract

Question 40

gastrin

Answer 40

secreted by G cells in the gastric glands - stimulates gastric acid secretion; stimulates gastric motility and mucosal growth (- acid secretion is also stimulated by histamine secreted by ECL cells in gastric glands)

Question 41

CCK

Answer 41

(cholecystokinin) - secreted by endocrine cells in intestinal crypts - stimulates bile release from gallbladder and pancreatic enzyme secretion

Question 42

secretin

Answer 42

- stimulates bicarbonate secretion by pancreas

Question 43

GIP

Answer 43

(gastric inhibitory peptide) - stimulates insulin secretion by pancreas; - GIP, CCK and secretin all inhibit gastric acid secretion

Question 44

Phases

Answer 44

1. Cephalic Phase - sensory stimuli and thoughts of food activate autonomic NS (vagus n.) 2. Gastric Phase - vagus n., mechanical & chemical stimuli in stomach stimulate gastric secretion 3. Intestinal Phase - arrival of chyme in duodenum triggers SI endocrine and exocrine secretion; hormonal feedback inhibits gastric acid secretion and slows stomach emptying