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Small and Large Intestines
Parts of the Small Intestines
How do the parts of Small intestines Vary?
• Duodenum: secretes mucous enzymes and hormones and is a site of entry for bile and pancreatic juices
• Jejunum: nutrient absorption
• ileum: central portion of the abdominal cavity; pH 7-8; absorbs B12 and bile salts
Intestinal Wall• Mucosa contain:
absorptive cells aka: enterocytes
• 2 layers of smooth muscle– Circular and
longitudinal aid in intestinal mobility
• Serosa: supportive CT
Function of villi and microvilli
• Specialized absorptive units– Microscopic units with layers of epithelial cells
• 200m2 for nutrient absorption
• desmosomes and tight junctions prevent microbes b/t cells
Regulator of absorptive units
• Absorption occurs by active transport, facilitated diffusion, Na/K pump
• Actin (protein)
• Filaments regulated by autonomic nerve fibers
• Fats and water soluble nutrients take different paths
Movement Patterns
• Segmentation: circular muscle contraction
• Peristalsis: movements by circular and longitudinal muscles
Large Intestines
• Colon
• 6 cm wide and 1.5 meets long (6 feet)
Movement of chyme
• Chyme enters the colon thru ileocecal valve
• Located b/t ileum and colon
• Gastroileal reflex regulates ileocecal valve by the peristaltic waves
Major segments of Lg intestines• Transverse
• Ascending– Sites of water and Na absorption and mucus
secretions
• Descending
• Sigmoid– Storage of fecal matter
Process that allows for water absorption
• Osmosis
• …following the Na/K pump which is what type of cellular transport??
Important to replenish electrolyte balance
• Homeostasis
• K is secreted into large intestines
Stool massWhat’s in your Poo?
• Dietary fiber (pectin and cellulose)
• Fruits and vegetables
• Indigestible substances
Movements of colon
• Segmentation: circular muscle contraction
• Peristalsis: movements by circular and longitudinal muscles
• Mass movement: force of feces along the colon through the anal canal
Mass movements
• Defecation
• Rectal distention triggers defecation reflex, which then forces feces out of anal canal
• Control? Other mechanisms– Internal and external valves (sphincters)– Pressure from abdominal cavity
Diseases/Disorders
• Diverticulitis– Fever, pain in
abdomin, diareherra
• Possibly caused from increase in intraluminal pressure.
• Indiv. With low dietary fiber intake at high risk
Crohn’s Disease
• autoimmune disease: caused by the immune system attacking the gastrointestinal tract and producing inflammation in the gastrointestinal tract
• may affect any part of the gastrointestinal tract from mouth to anus,
• Symptoms: abdominal pain, diarrhea (which may be bloody), vomiting, or weight loss
• Type of inflammatory bowel disease (IBD)• appears to be a genetic link • Mutations in the CARD15 gene