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 mass
What’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