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