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GI notes part 2
Lecture notes study book Focus on Adult Health of Linda Honan (GI) - ISBN: 9781496349286 (GI notes)
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NUR 110 GI 1 NotesAnatomy of the GI Tract
- GI tract is 23-26 ft long
Esophagus: hollow muscular tube (10 in long) that passes through the diaphragm to
diaphragm hiatus
- Location: in mediastinum
Stomach: hollow muscular organ w/ 1,500mL capacity, stores food during eating,
secretes digestive fluids, & propels partially digested food into small intestine
- Location: in upper left portion of the abdomen under the liver
- Has 4 regions: Cardia (entrance), Fundus, Body, Pylorus (outlet)
Small Intestine: 7,000 cm of surface area for absorption & secretion
- Duodenum: bile duct & pancreatic duct enter ampulla of Vater, allow passage of bile &
pancreatic secretions
- Jejunum & Ileum are middle & end of the small intestine
- Sphincter in the ileum controls that flow of digested material from the ileum into cecal
portion of large intestine (prevents bacteria reflux into small intestine)
Large Intestine: ascending segment, transverse segment, descending segment
- GI tract gets blood from portal venous system made of: Superior Mesenteric, Inferior
Mesenteric, Gastric Mesenteric, & Cystic Mesenteric→ form vena portae in liver
- O2 & nutrients supplied to stomach by gastric artery & to intestine by mesenteric arteries
- Internal abdominal cavity is lined w/ peritoneum
- Mesentery: double layer of peritoneum that encircles internal organs & contains blood
vessels, nerves, & lymphatic vessels
- Omentum: fold of mesentery that passes from stomach to organs in abdominal cavity
(cushions organs & provides body heat)
Function of GI System
- Breakdown food particles into molecular form for digestion
- Absorption into bloodstream of small nutrient molecules produced by digestion
- Elimination of undigested unabsorbed foodstuffs & other waste products
Chewing & Swallowing
- Digestive process begins w/ chewing because it breaks down food into small particles,
that can be swallowed & mixed w/ digestive enzymes
- 1.5L of saliva is secreted daily from parotid, submaxillary, sublingual glands
- Swallowing starts voluntary & is regulated by swallowing center in medulla oblongata
(CNS)
- As food bolus is swallowed, epiglottis moves to cover tracheal opening & prevents
aspiration of food into lungs
Gastric Function
- Stomach secretes highly acidic fluid 2.4/day w/ pH of 1 & it derives its acidity from
hydrochloric acid (HCl)
- Gastric function is breaking down food into more absorbable components & aid in
destruction of ingested bacteria
Pepsin: end product of conversion of pepsinogen; enzyme protein for digestion
Intrinsic factor: combines w/ Vit B12 so it can be absorbed into ileum
, - Peristaltic contractions propel the food to pylorus & food remains in stomach for 30 min
to several hours depending on volume, osmotic pressure, & chemical composition
Chyme: partially digested food mixed w/ gastric secretions
Small Intestine Function
- Digestive enzymes secreted by the pancreas: Trypsin: aids in protein digestion,
Amylase: aids in starch digestion, Lipase: aids in fat digestion
- Hormones, neuroregulators, local regulators control the rate of intestinal secretions &
influence GI motility
- 2 types of contractions in small intestine are stimulated by chyme: Segmentation
Contraction: produce mixing waves that move intestinal contents back & forth in churning
motion
- Intestinal Peristalsis:propels contents of small intestine to colon
- Glucose is a tissue cell fuel, protein source of energy
- Chyme stays in small intestine for 3-6 hrs, allowing further breakdown & absorption
- Villi line the entire intestine & produce digestive enzymes & absorb nutrients
- Absorption is the primary function of the small intestine
- Starts in jejunum (active transport & diffusion across intestinal wall into
circulation)
- Nutrients are absorbed throughout the intestine
- Fats,proteins, carbs,sodium & chloride are absorbed in jejunum
- Vit B12 & bile salts are absorbed in ileum
- Magnesium, phosphate, potassium are absorbed throughout intestine
Colon Function
- Food is pushed into colon by peristaltic waves from small intestine thru ileocecal valves
- 300-500 different intestinal bacteria are in large intestine & maintain homeostasis
- Intestinal flora can be damaged by abx causing pt to be at risk for overgrowth of
pathogens
- Probiotics are live organisms that restore microbial balance to intestines
- Electrolyte solution acts to neutralize the end products formed by colonic bacterial action
- Mucus protects the colonic mucosa from intraluminal contents
- Slow transport along the colonic tract allows for reabsorption of water &
electrolytes
Waste Products of Digestion
- Poop consist of undigested food, inorganic materials, water, & bacteria
- 75% fluid & 25% solid material
- Brown color comes from breakdown of bile by intestinal bacteria, chemicals form odor
- Gases formed contain methane, hydrogen, sulfide, & ammonia
- GI tract contains 150mL of gases which are absorbed & detoxified in the liver/ expelled
- During pooping the sphincter voluntarily relaxes to allow poop to come out
- External anal sphincter is maintained in state of tonic contraction
- Pooping is seen as spinal reflex that can be stopped by keeping external sphincter
closed
- Contracting abdominal muscles promotes pooping
Liver
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