(continuation) Digestive System Flashcards
Cells of Gastric Glands:
- Regenerative cells
- Parietal cells
- Chief cells
- Enteroendocrine cells
divide rapidly to produce new cells that migrate to surface
Regenerative cells
secrete HCl acid and intrinsic factor
Parietal cells
secrete pepsinogen
Chief cells
secrete hormones and paracrine messengers
Enteroendocrine cells
Gastric Secretions:
- 2 to 3 L of gastric juice/day (H2O, HCl and pepsin)
- Parietal cells contain carbonic anhydrase (CAH)
Functions of Hydrochloric Acid:
- Activates pepsin and lingual lipase
- Breaks up connective tissues and plant cell walls
- Converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+)
- Destroys ingested bacteria and pathogens
essential for B12 absorption by the small intestine. RBC production (lack causes pernicious anemia)
Intrinsic factor
secreted as pepsinogen (inactive). HCl converts it to pepsin (active)
Pepsin
lipase digests the butterfat of milk in infants. chymosin curdles milk by coagulating proteins
Gastric lipase and chymosin
hormones enter blood
distant cells
paracrine secretions
neighboring cells
signaling molecules produced in digestive tract and CNS
Gut-brain peptides
Swallowing center signals stomach to relax
Gastric Motility
when abdominal contraction forces upper esophageal sphincter to open
vomiting
lower esophageal sphincter to relax
retching
sight, smell, taste or thought of food; vagus nerve stimulates gastric secretion and motility
Cephalic phase
activated by presence of food or semi-digested protein
Gastric phase
duodenum regulates gastric activity through hormones and nervous reflexes
Intestinal phase
duodenum inhibits stomach
enterogastric reflex
Gross Anatomy of Liver:
- 3 lb. organ located inferior to the diaphragm
- 4 lobes - right, left, quadrate and caudate
Tiny cylinders found in the liver
hepatic lobules
________ and ________ bring blood to liver
hepatic portal vein and hepatic artery
Pancreatic Acinar Cells:
- Zymogens = proteases
- trypsinogen
- chymotrypsinogen
- procarboxypeptidase
- Other enzymes
- amylase
- lipase
- ribonuclease and deoxyribonuclease
- involve only mucosa and submucosa
- chyme flows in a spiral path causing more contact
Circular folds (plicae circularis) up to 10 mm tall
______ are fingerlike projections 1 mm tall
Villi
Gradual movement of contents towards colon
Peristalsis
Water is absorbed by ________ following the absorption of salts and organic nutrients
osmosis
Gross Anatomy of Large Intestine:
5 feet long and 2.5 inches in diameter in cadaver
Begins as cecum and appendix in lower right corner
Ascending, transverse and descending colon frame the small intestine
Sigmoid colon is S-shaped portion leading down into pelvis
Rectum - straight portion ending at anal canal
straight portion ending at anal canal
Rectum
muscle tone in longitudinal muscle fibers (concentrated in taeniae coli) form pouches (haustra)
Muscularis externa
Bacterial flora populate large intestine
- ferment cellulose and other undigested carbohydrates; we absorb resulting sugars
- synthesize vitamins B and K
- average person produces 500 mL per day
- most is swallowed air but hydrogen sulfide, indole, and skatole produce odor
Flatus (gas)
Absorption and Motility
Transit time is 12 to 24 hours
Anatomy of Anal Canal:
- 3 cm total length
- Anal columns are longitudinal ridges separated by mucus-secreting anal sinuses
- Hemorrhoids are permanently distended veins
Stretching of the rectum stimulates __________
defecation
Neural Control of Defecation:
- Filling of the rectum
- Reflex contraction of rectum and relaxation of internal anal sphincter
- Voluntary relaxation of external sphincter
