Lecture 9: The Digestive System Flashcards
what is the small intestine
-muscular tube, pyloric sphincter to ileocecal valve
-site of most digestion and absorption
describe the three segements of the digestive system
- duodenum: ~25 cm, “mixing bowl” receives chyme from stomach and digestive secretions from the pancreas and liver, mostly retroperitoneal
- jejunum: ~1 m, most chemical digestion and nutrient absorption occurs here
- ileum: ~2 m, ends at the ileocecal valve
what are the modifications of the small intestine for absorption
small intestine;s length and other strutural modifications provide hugh surface area for nutrient absorption
-modifications include: circular folds, villi, and microvilli
what are the circular folds of the small intestine
-transverse folds in intestinal lining
-allow chyme to spiral through the lumen
-they are permanent features that do not disappear when small intestine fills
what are the intestinal villi
-simple columnar epithelium
-core of dense capillary bed and lymphatic capillary called luteal for absorption
-transports chylomicrons that are too large to enter blood capillaries
what is the microvilli of the small intestine
-cytoplasmic extensions of mucosal cell
-gives fuzzy appearance-> brush border
-contains membrane-bound enzymes; brush border enzymes for final CHOs and protein digestion
what are intestinal glands (intestinal crypts or crypts of lieberkuhn)
-tubular glands scattered between villi
-extend deep into lamina propria
what are the 5 main cell types in the villi and crypts
stem cells, enterocytes, goblet cells, enteroendocrine cells, and Paneth cells
what are the three types of enteroendocrine cells in the small intestine
-S cells: secretin
-CCK cells: cholecystokinin
-K cells: glucose-dependent insulinotropic peptide (GIP)
what are the duodenal submucosal glands
-produce large quantities of mucus secretion when chyme arrives from stomach
-mucus protects epithelium from acidity of chyme; contains bicarbonate ions that raise pH to neutralize gastric acid in chyme
-MALT: protects intestine against microorganisms and includes: indivual lymphoid follicles, adn Peyer’s Patches (aggregated lymphoid nodules) within lamina propria (abundant in distal part of SI, where bacterial numbers increase)
-lamina propria also contain large numbers of plasma cells that secrete IgA
what is intestinal juice
-secreted daily in response to distension or irritation of mucosa
-major stimulus for productions is hypertonic or acidic chyme
-slightly alkaline; isotonic with blood plasma, assists in buffering acids
-consists largely of water but also contains mucus (which is secreted by duodenal glands and goblet cells of mucosa
-keeps digestive enzymes and products of digestion in solution
what enzymes of the small intestine mucosa are involved in chemical digestion
-brush border enzymes: break down materials in contact wtih brush border
-enteropeptidase: brush border enzymes; activates pancreatic trypsinogen
motility of small intestine between meals
-Peristalsis increases, initiated by rise in hormone motilin
-Each wave starts distal to previous wave; referred to as migrating motility complex (MMC)
-Meal remnants, bacteria, and debris are moved toward large intestine
-Complete trip from duodenum to ileum takes ~2 hours
motility of small intestine after a meal
-Segmentation is most common motion of small intestine
-Mixes/moves contents toward ileocecal valve
-Intensity is altered by reflexes and hormones
-Parasympathetic increases motility; sympathetic decreases it
what is peristalsis
adjacent segments of the alimentary canal organs alternately contract and relax
-food is moved distally along the tract
-primarily propulsive; some mixing may occur
what is segmentation
nonadjecent segments of the alimentary canal organs contract and relax
-food is moved forward, then backward
-primarily mixes food and breaks it down mechanically; some propulsion may occur
what are the primary functions of the small intestine
- segmentations: mix chymes with digestive juices and bring food into contact with mucosa for absorption; perstalsis propels chyme through small intestine
- completes digestion of carbohydrates, proteins, lipids; begins and completes digestion of nucleic acids
- absorb about 90% of nutrients and water that pass through digestive system
what is the large intestine
-extends from end of ileum to anus
-lies inferior to stomach and liver
-frames the small intestine
What are the primary functions of the large intestine
-Reabsorption – water, nutrients (< 10%), bile salts, organic wastes,
vitamins and toxins produced by bacteria
-Compaction of intestinal contents into feces
-Storage of fecal material prior to defecation
What are the 5 sub divisions of the large intestine
Cecum, appendix, colon, rectum, anal canal
What is the cecum
sack-like first portion
-Receives and stores food from ileum
-Compaction of materials begins
What is the appendix (vermiform appendix)
-Posteromedial surface of cecum
-Lymphoid nodules
What is the appendix (vermiform appendix)
-Posteromedial surface of cecum
-Lymphoid nodules
What is the colon and the three parts
has several regions, most which are retroperitoneal (except
for transverse and sigmoid regions)
-Ascending colon: travels up right side of abdominal cavity to
level of right kidney, Ends in right colic (hepatic) flexure
-Transverse colon: travels across abdominal cavity, Ends in left colic (splenic) flexure
-Descending colon: travels down left side of abdominal cavity
-Sigmoid colon: S-shaped portion that travels through pelvis
What is the rectum
three rectal valves stop feces from being passed with gas (flatus)
What is the anal canal
last segment of large intestine that opens to body exterior at anus
What are the two sphincters of the anal canal
- Internal anal sphincter: smooth muscle
- External anal sphincter: skeletal muscle
What are the unique features of the colon
larger diameter, and thinner wall than small intestine