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