Digestive system-5 Flashcards
What are the 2 purposes of the small intestine? what are the 3 subdivisions? What is it’s blood supply? what is it’s nerve supply?
The major organ of digestion and absorption
▪ Duodenum (retroperitoneal)
-25.0 cm (10.0 in) long; curves around head of pancreas
-Has the most features
▪ Jejunum
-2.5 m (8 ft); attached posteriorly by mesentery
▪ Ileum
-3.6 m (12 ft) attached posteriorly by mesentery); joins
large intestine at ileocecal valve
▪ Blood supply:
– Superior mesenteric artery brings blood supply
– Veins (carrying nutrient-rich blood) drain into superior mesenteric veins, then into hepatic portal vein, and finally into liver
▪ Nerve supply
– Parasympathetic innervation via vagus nerve, and sympathetic innervation from thoracic splanchnic nerves
What are the 3 modifications of the small intestine for absorption?
o Circular folds
▪ Permanent folds (~1 cm deep) that force chyme to slowly spiral through lumen, allowing more time for nutrient absorption
o Villi
▪ Fingerlike projections of mucosa (~1 mm high) with a core that contains dense capillary bed and lymphatic capillary called lacteal for absorption
o Microvilli
▪ Cytoplasmic extensions of mucosal cell that give fuzzy appearance called the
brush border; contains membrane-bound enzymes brush border enzymes used
for final carbohydrate and protein digestion
What are intestinal crypts? What do they do?
▪ Intestinal crypts: tubular glands scattered between villi
▪Produce intestinal juice -watery mixture of mucus that acts as carrier fluid for chyme
What are the five major types of cells in the villi and crypts?
▪ Enterocytes: make up bulk of epithelium
-Simple columnar absorptive cells bound by tight junctions with many microvilli
Function
-Villi: absorb nutrients and electrolytes
-Crypts: produce intestinal juice, watery mixture of mucus that acts as carrier fluid for chyme
▪ Goblet cells: mucus-secreting cells in epithelia of villi & crypts
▪ Enteroendocrine cells: source of enterogastrones (CCK secretin) & GIP
-Found scattered in villi but some in crypts
▪ Paneth cells: deep in crypts, specialized secretory cells that fortify SI’s defenses.
-Secrete antimicrobial agents (defensins & lysozyme) that can destroy bacteria
▪ Stem cells that continuously divide to produce other cell types
-Villus epithelium renewed every 2–4 days
What is the submucosa?
▪ Submucosa
- areolar tissue
- Duodenal glands secrete alkaline mucus to neutralize acidic chyme
▪ Muscularis
- circular & longitudinal muscle
- Most of the duodenum (retroperitoneal) → adventitia
- Visceral peritoneum (serosa) covers the external intestinal surface
What are 4 key facts of intestinal juice? what are 2 sources of digestive enzymes for the small intestine?
▪ 1–2 L secreted daily by the intestinal glands in response to distension or irritation of mucosa
▪ Major stimulus for production is hypertonic or acidic chyme
▪ Slightly alkaline and isotonic with blood plasma
▪ Consists largely of water but also contains mucus secreted by duodenal glands and goblet cells of mucosa
▪ Substances such as bile, bicarbonate, digestive enzymes (not brush border enzymes) are imported from liver and pancreas
▪ Brush border enzymes bound to plasma membrane perform final digestion of chyme
What are 4 key facts of stomach chyme? What controls movement of food into duodenum?
▪contains partially digested CHO, PRO & undigested fats
▪ usually hypertonic; therefore, delivery has to be slow to prevent osmotic loss of H2O from blood
▪ low pH has to be adjusted upward
▪ has to be mixed with bile & pancreatic juice to continue digestion
Enterogastric reflex & enterogastrones control movement of food into duodenum to prevent it from being overwhelmed
What is the digestive process that happens after a meal? What process happens between meals?
▪ Segmentation is most common motion of SI
▪ Initiated by intrinsic pacemaker cells
▪ Mixes/moves contents toward ileocecal valve
▪ Intensity is altered by long /short reflexes & hormones
» Parasympathetic increase motility; sympathetic decrease
▪ Peristalsis increase, initiated by increase in hormone motilin in late intestinal phase
Motility of the Small Intestine (mixing)
Digestive Processes in the Small Intestine Wave every 90–120 minutes
▪ Each starts distal to previous one →Migrating Motor Complex (MMC)
▪ Meal remnants, bacteria & debris are moved toward large intestine
▪ Complete trip from duodenum to ileum: Wh~2 h
What are 4 things that the ileocecal sphincter does?
relaxes and admits chyme into large intestine when:
• Gastroileal reflex enhances force of segmentation in ileum
• Gastrin increases motility of ileum
▪ Ileocecal valve flaps close when chyme exerts backward pressure
• Prevents regurgitation into ileum
