Flashcards in Lecture 30 Digestive Deck (44)
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1
GI Tract
mouth -stratified squamous epithelium
pharynx
esophagus
stomach -simple columnar epithelium
small intestine
large intestine
2
Accessory Organs
salivary glands
liver
pancreas
gallbladder
3
Functions of the Digestive System
digestion
absorption
secretion
motility
4
digestion
chemical breakdown of food molecules by hydrolysis
5
absorption
of nutrients, electrolytes and H2O
6
secretion
mucus, digestive enzymes, acid, bicarbonate, electrolytes
7
motility
muscular movements of GI tract to mix and propel food
peristalsis - moves material forward
segmental contractions - mix contents
8
regional specialization (“assembly line”)
ingestion → mechanical breakdown → chemical digestion → absorption → waste processing
9
GI tract structure: 4-layered tube
mucosa
submucosa
muscularis (externa)
serosa
10
mucosa
mucosa - epithelium + lamina propria (areolar CT) + muscularis mucosae
11
submucosa
submucosa - connective tissue, vascular
12
muscularis (externa)
muscularis (externa) - smooth muscle
13
serosa
- thin covering membrane (visceral peritoneum)
14
Mouth, Pharynx and Esophagus
functions:
ingestion, mastication (chewing), deglutition (swallowing)
15
salivary glands
secrete saliva: H2O, ions, mucus, enzymes: amylase, lipase
16
amylase
begins chemical digestion of starch → disaccharides
17
esophagus
swallowing (upper portion), peristalsis (lower portion)
lower esophageal sphincter controls entry into the stomach
18
Stomach
functions
storage
mechanical breakdown of food → chyme
sterilization
chemical digestion: acid (HCl) and enzymes (pepsin)
19
stomach structure
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
20
acid secretion
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-)
21
chief cells
enzyme secretion
chief cells secrete pepsinogen (inactive), activated at low pH to form pepsin
pepsin digests proteins into smaller peptides
22
Small Intestine, Liver and Pancreas Functions and SI regions
Small Intestine, Liver and Pancreas
functions: chemical digestion and absorption
SI regions: duodenum, jejunum, ileum
23
Digestion
duodenum receives chyme from stomach, secretions from liver and pancreas
24
Liver
processes absorbed nutrients (delivered via hepatic portal vein)
secretes bile, stored in gallbladder
bile salts
25
bile salts
derived from cholesterol, function to emulsify fats → micelles
26
bile pigments
(bilirubin, biliverdin) - waste products from hemoglobin breakdown
27
Pancreas
acinar cells secrete digestive enzymes:
trypsin, chymotrypsin, carboxypeptidase, amylase, lipase
many enzymes are secreted in inactive form (zymogens), activated by trypsin in lumen
28
duct cells
secrete bicarbonate (NaHCO3) to neutralize acid (pH → 8)
29
SI (brush border)
enzymes complete digestion
complete digestion of starch
30
