digestive part C Flashcards
what is the small intestine structure?
- The Small intestine is the major organ of digestion and absorption
- 2–4 m long (7–13 f t) from pyloric sphincter to ileocecal valve, point at which it joins the large intestine
- Small diameter of 2.5–4 c m (1.0–1.6 inches)
what is a duodenum?
– Duodenum: mostly retroperitoneal; ~25.0 c m (10.0 in) long; curves around head of pancreas
Has most features
– Jejunum: ~2.5 m (8 f t) long; attached posteriorly by mesentery
– Ileum: ~3.6 m (12 f t) long; attached posteriorly by mesentery; joins the large intestine at ileocecal valve
what is the blood supply in the small intestine?
– 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
what is the nerve supply in the small intestine?
– Parasympathetic innervation via vagus nerve, and sympathetic innervation from thoracic splanchnic nerves
what are the modifications of the small intestine for absorption?
– Small intestine’s length and other structural modifications provide huge surface area for nutrient absorption
Surface area is increased 600 × to ~200m2 (size of a tennis court)
– Modifications include:
Circular folds
Villi
Microvilli
– Circular folds
Permanent folds (~1 c m deep) that force chyme to slowly spiral through lumen, allowing more time for nutrient absorption
– Villi
Fingerlike projections of mucosa (~1 m m high) with a core that contains dense capillary bed and lymphatic capillary called a lacteal for absorption
– Microvilli
Cytoplasmic extensions of mucosal cell that give fuzzy appearance called the brush border that contains membrane-bound enzymes brush border enzymes, used for final carbohydrate and protein digestion
what is the histology of the small intestine?
– Modifications of mucosa and submucosa of the small intestine reflect its function in digestion
– Intestinal crypts: tubular glands scattered between villi
– Five main types of cells found in villi and crypts
what are enterocytes?
make up bulk of epithelium
– Simple columnar absorptive cells bound by tight junctions and contain many microvilli
– Function
* Villi: absorb nutrients and electrolytes
* Crypts: produce intestinal juice, watery mixture of mucus that acts as carrier fluid for chyme
what is goblet cells?
mucus-secreting cells found in epithelia of villi and crypts
what is enteroendocrine cells?
source of enterogastrones (e.g.: C C K and secretin)
– Found scattered in villi but some in crypts
what are pentad cells?
found deep in crypts, specialized secretory cells that fortify the small intestine’s defenses
– Secrete antimicrobial agents (defensins and lysozyme) that can destroy bacteria
Stem cells that continuously divide to produce other cell types
– Villus epithelium renewed every 2–4 days
– Mucosa-associated lymphoid tissue protects intestine against microorganisms and includes:
Individual lymphoid follicles
what are Peyer’s patches?
Peyer’s patches (aggregated lymphoid nodules), located in lamina propria
– Found in great numbers in distal part of the small intestine, where bacterial numbers increase
Lamina propria also contains large numbers of plasma cells that secrete I g A
– Submucosa consists of areolar tissue
Duodenal glands of duodenum secrete alkaline mucus to neutralize acidic chime
Homeostasis imbalance for small intestine
- Chemotherapy targets rapidly dividing cells, such as cancer cells
- Negative side effect is that it also targets rapidly dividing G I tract epithelium
- Reason why many patients undergoing chemotherapy have symptoms of nausea, vomiting, and diarrhea
what is intestinal juice?
- 1–2 L secreted daily 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
– Mucus is secreted by duodenal glands and goblet cells of mucosa
what is the digestive process in the small intestine?
- Chyme from stomach contains partially digested carbohydrates and proteins and undigested fats
- Takes 3–6 hours in the small intestine to absorb all nutrients and most water
what is t source of enzymes for digestion?
– Substances such as bile, bicarbonate, and digestive enzymes (not brush border enzymes) are imported from liver and pancreas
– Brush border enzymes bound to plasma membrane perform final digestion of chyme