Digestive Introduction
Table of Contents

Gut Overview

 Immunological role:
- unbroken mucosal epithelium
- mucus covering as a physical barrier and coats bacteria for easier mobility
- acidity of stomach
- glycocalyx layer over the epithelium
- bile
- IgA helps to prevent colonization
- Gut motility
- Peyer’s patches – lymph follicle
- GI flora of anaerobes can compete with pathogenic bacteria for resources
 Role of tract:
- mouth: food chewed and saliva added
- oesophagus: transportation of food to stomach
- stomach: food is stored, mixed with acid (2500mL gastric acid produced daily) and broken up
- intestine: nutrient and fluid are absorbed and waste excreted
 Protection from acid: mucus (stimulated by prostaglandin) and bicarbonate production
 Small intestine:
- divided into duodenum, jejunum and ileum and its walls is made up of mucosa and submucosa
- mucosa consisting of epithelium, lamina propria, muscularis mucosae
- Vili and crypt (glands) along with microvilli of the columnar epithelium further increase surface area. Goblet cells exists in between and secret mucus to protect against noxious substance. Paneth cells at the bottom of the crypt offer first line immune protection.
- Epithelial cells are renewed every 3 days
 Importance of small intestine:
- absorbs both food and liquid and its own secretion. Disruption can cause death by dehydration within 24 hours
- damage to small intestine by chemotherapy or radiation will produce malabsorption, diarrhea and loss of bacterial defense
 Large intestine:
- no villi are present but the crypts are much larger, more densely packed and numerous
- many more goblet cells to produce mucus
- no Paneth cells
- lots of lymphocytes, macrophages, plasma producing IgA for defense
 Importance of large intestine:
- receives unabsorbed constituents of diet-fibre, waxes, fat and dead bacteria and also 1-2 litres of isotonic fluid from the small intestine
- Will absorb all of fluid and Na+ except for 100mL and 4mmol but absorptive capacity is at 3 L.
 Salivary glands: 3 pairs of glands in mouth with each being parotid, submandibular and sublingual
- exocrine glands produce amylase to break down starch
- helps swallowing and cleans the mouth
- growth factor that helps heal wounds
 Liver: the largest visceral organ
- produces bile to help digestion and provides mechanism of excretion of protein breakdown products etc
- most absorbed food passes the liver to be stored, e.g. carbohydrates as glycogen
- synthesizes protein and break down toxin
 Pancreas:
- secrete enzyme for digestion and regulate endocrine function of insulin and glucagons for blood-sugar control
 Pathology of GI tract:
- coelic disease: duodenal and jejunal mucosa destroyed by hypersensitivity to gluten in diet and produce nutritional deficiency such as iron deficiency.
- Aspirin and NSAIDS: deplete prostaglandin in the gastric mucosa which leads to mucosal damage and ulcer
- Crohn’s disease: inflammation of the gut related to an imbalance between immunity, gut flora, and diet
- Ulcerative colitis: similar to Crohn but affects only the colon
- C. difficile toxin: overgrowth of the C difficile bacteria due to normal bacteria being killed off by antibiotics and results in severe diarrhea and colitis.
 Total Parenteral Nutrition (TPN): nutritional provision through injection into the body, i.e. instead of ingested. Venous access is very common (into vein that lie above superior vena cava)
- required when the gut is malfunctioning, obstructed, too short due to enterectomy (less than 3 meters), fistulated, needs resting, or food can’t be orally taken past 10 days
- components: glucose, amino acids, lipids, trace element, water and electrolyte
- problems: fluid overload, infection (sepsis), pneumothorax, trace element deficiency, hyperglycemia, pH changes, electrolyte disturbances

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