Small Intestinal Wall

1
Small Intestinal Wall

• Mucosa, submucosa,muscularis, serosa
• Mucosa increased surface area due to many villi
• Each villus contains thousands of ___________
  (brush border)
• Microvilli have both digestive enzymes and
  carrier molecules for nutrients, vitamins, and
  minerals embedded in cell membranes
• _______- invaginations of mucosa around each
  villus. New cells are produced and pushed from
  bottom of crypt to replace cells of villus
• Goblet cells present. Mucus helps with flow of
  ingesta.

2
Nervous System and Small Intestines

• _____________ nervous system provides stimulation
  for intestinal motility, secretions, and blood
  flow.
• _____________ nervous system decreases
  circulation to the intestines.
• Intestinal tract is constantly functioning and is
  never at rest.

3
Small intestine Motility

• Peristalsis
• Circular contractions prevent backflow of
  ingesta, longitudinal muscles propel ingesta
  caudally
• Dilation of bowel with ingesta stimulates
  peristalsis
• CCK and Prostaglandins can both affect motility.
• Fats/protein in the intestine stimulate the
  mucosa to release CCK, which increases intestinal
  motility (opposite of the effect on the stomach)
• Prostaglandins can increase GI motility and
  secretions which can lead to colic.
• Segmental contractions slow the movement of
  ingesta to allow time for it to be both mixed
  with intestinal enzymes and absorbed through the
  intestinal wall.
• Many times diarrhea is caused not due to
  increased peristalsis, but lack of segmental
  contractions.

4
Small Intestine Digestion

• _____________, _____________, _____________
• Absorbed intact across SI wall
• _____________, _____________, _____________
• Chemically digested via enzymes in the lumen and
  enzymes on the microvilli b/c they are too large
  to pass through the mucous membrane

5
Carbohydrate Digestion

• Starch is broken into disaccharides by amylase
  found in the saliva and from the pancreas
• Disaccharides are broken down into
  monosaccharides by enzymes (lactase, sucrase, and
  maltase) in microvilli
• Monosaccharides can then be transported across
  microvilli and absorbed into blood
• Microvilli enzymes are dependent on diet
  (Lactose-intolerant animals/diarrhea)

Food Enzyme Source Broken into Fate
Starch Amylase Saliva, Pancreas Disaccharide
s lactose sucrose
maltose Lactase Brush border Monosaccharides
Sucrase glucose Absorbed Maltase
galactose Absorbed fructose Absorbed
6
Protein Digestion

• Protein chains are broken into smaller
  polypeptides by pepsin
• Polypeptides are broken down into peptides
  (several amino acids) by pancreatic proteases
• Peptides are broken down into amino acids,
  dipeptides, and some tripeptides by peptidases
  are then absorbed

Food Enzyme Source Broken into Fate
Protein Pepsin Stomach Polypeptides Protease
s SI (Pancreas) Peptides Peptidases Brush
border Amino acids Absorbed di-peptides
Absorbed tri-peptides Absorbed
7
Fat Digestion

• Agitation of the pyloric antrum emulsifies
  (breaks down) fat globules (triglycerides) into
  smaller droplets
• Bile acids from the liver coat the fat droplets
  in duodenum
• Keeps them from re-forming into globules again
• Arranges them to make them more water soluble
• Pancreatic lipases (fat-digesting enzymes)
  penetrate bile acid coating
• Digest triglycerides to form glycerol, fatty
  acids, and monoglycerides (micelles) which are
  absorbed through the microvilli
• Vitamins A, D, E, K are often absorbed with the
  micelles

Food Enzyme Source Broken into Fate
Lipids Bile acids SI (Liver) small fat
droplets Lipases SI (Pancreas) glycerol Absor
bed fatty acids Absorbed monoglyceride
s Absorbed
8
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9
Large Intestine

• Species variation in structure
• Components
• 1. ________ - blind sac at ileocecal junction
• 2. ________
• 3. ________
• Primary functions -
• Store feces
• Recover fluid and
• electrolytes
• Hindgut fermentation (non ruminant herbivores)
• Equine, guinea pigs, rats, rabbits, swine

10
Large Intestines

• ____________ simple, tubular colon poorly
  developed cecum
• __________ __________ very large colon and cecum
  (hindgut)
• Fermentation site
• Modifications of cecum and colon allow
  fermentative digestion in hindgut
• similar to rumen
• VFAs (produced by microbes) absorbed from cecum
  and colon for energy needs (similar to rumen)
• Possible areas of impaction
• Flexures, Small colon
• Cause of colic

11
Horse Hindgut

• Consists of 4 sections
• Cecum, Ventral colon (right and left halves),
  Dorsal colon (right and left halves), Small colon
• Cecum is composed of
• Base, Main body, Apex
• Cecum and dorsal and ventral colons have
  longitudinal bands that separate the structure
  into a series of sacs called ________
• The role of the small colon is to absorb
  electrolytes, water, and any VFAs that were not
  previously absorbed.

12
Rectum

• Terminal portion of the large intestine an
  extension of colon
• Capable of more expansion than colon
• Mucus-secreting glands ___________ feces to aid
  their passage
• Has sensory receptors that detect stretching or
  distention and stimulates defecation response.

13
Anus

• Internal sphincter under ________ control
• (Parasympathetic system causes relaxation,
  Sympathetic system causes constriction)
• External sphincters under __________ control
• As rectum distends, stretch receptors cause
  partial relaxation of internal sphincter. Fecal
  material moves into the Internal Sphincter Canal
  which stimulates more stretch receptors
  increasing urge to defecate.
• Stretching of Anal mucosal receptors increase the
  sense or need for defecation
• Surgery or disease in anal region can damage
  sphincter muscles and nerves, causing incontinence

14
Livers Role in the GI Tract

• ________, __________, and/or ___________
  materials absorbed from GI tract before they
  reach blood.
• Removes toxins, infectious agents, old blood
  cells that enter the body via the GI tract.
• Glucose, amino acids, and vitamins are stored or
  metabolized.
• Glucose absorbed by the GI tract can be stored in
  the liver as _____________ (glycogenesis). When
  glucose is needed in the blood, glycogen is
  broken down by the liver (glycogenolysis).
  _____________________ is the process of glucose
  being made in the liver by using amino acids.
• Major source of blood __________
• Albumin

15
Gallbladder

• The liver produces _______ which contains bile
  acids, cholesterol, and bilirubin
• Bile is secreted into bile ducts, which lead to
  the hepatic duct, which leads to the
  ____________for storage (not horse)
• The gallbladder stores bile until it is
  stimulated by CCK (due to fat in SI), causing it
  to contract.
• Contraction forces bile down the common bile duct
  into the duodenum, where it aids in the digestion
  of fat.

16
Pancreas Role in the GI Tract

• Exocrine and endocrine gland
• Exocrine functions
• Produces _________, _________, ___________
• Secretes _____________ (HCO3-)into duodenum
• Neutralizes acidity of stomach contents and
  maintains pH in duodenum needed for proper enzyme
  function
• Endocrine functions
• Produces ___________ _________
• Regulates blood glucose levels
• Insulin moves glucose from the blood to the
  bodys tissues. Glucagon stimulates
  gluconeogenesis and glycogenolysis in the liver.