health food makes me sick! -calvin trillin. ruminants only have one true stomach (abomasum), but...
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“Health food makes me sick!-Calvin Trillin
Ruminants and Complex Stomachs
Ruminants only have one true stomach (abomasum), but have 3 forestomachs (reticulum, rumen, and omasum).
Rumination The act of swallowing food, then regurgitating
it to chew it some more then swallow it again.
◦How does regurgitation differ from vomiting?
Reticulum Smallest and most cranial compartment. Separated from rumen by ruminoreticular fold. Interior is a honeycomb type arrangement to
increase absorption. Muscle wall is continuous with the rumen Rumen and Reticulum work together and produce
Reticulorumen contractions. Hardware disease is associated with the reticulum.
Rumen Series of muscular sacs
separated by pillars (long, muscular folds of rumen wall).◦ Sacs can close off to allow
more mixing to take place Fermentation takes place here Reticuloruminal contractions
allow:◦ Regurgitation to take place◦ Eructation-Expulsion of built
up carbon dioxide or methane gas If build up continues, may
cause bloat.
Gastric motility is controlled by:◦Vagus nerve primarily
◦Rate and strength of contractions is controlled by other factors: pH (ideal is 5.8-6.4)
Presence of volatile fatty acids
Consistency of foodstuffs
Stretch receptors
Rumen
Enzymes are produced by bacteria and protozoa.◦How does this differ from monogastric
animals?
Rumen bacterial surfaces produce cellulase◦Allows for the breakdown of plant cell
walls into simpler monosaccharides and polysaccharides.
Fermentative Digestion
Volatile Fatty Acids (VFA’S)-◦Produced when glucose is absorbed by
microbes and converted.◦VFA’s are by-products of the anaerobic
fermentation process◦They are rapidly absorbed by host animal◦In host animal, liver converts the VFA
propionic acid into usable glucose.◦Other volatile fatty acids can be used to
produce fat tissue, milk fat.
Fermentative Digestion
Proteases- breakdown proteins to amino acids and peptides◦ Then can be broken down farther to ammonia and
VFA’s.
Ruminant is dependent on microbes to digest nutrients.
Very delicate balance◦ Changes in diet can upset this balance
Fermentative Digestion
Omasum When reticulorumen
contractions occur, ingesta moves to omasum.
Omasum is muscular with interior full of parallel, longitudinal muscular folds.
Breaks down food particles and carry these particles to the abomasum.
Omasum abosrbs remaining VFA’s and removes bicarbonate ions
Abomasum Functions very similar to that of
mongastric stomach. Only glandular part of the stomach.
Young Ruminant Digestive Tract
Newborn’s stomach functions mainly as a monogastric digestive system.
Rumen and reticulum are small and non-functional◦ Development of rumen and reticulum is dependant on diet
Milk in rumen can disrupt fermentation process so is carried directly to omasum.◦ Reticular groove (Esophageal groove)- allows liquids
to be carried from esophagus to omasum.◦ Initiated by suckling, can not drink from pail ◦ As calf ages, groove disappears.
Where majority of nutrients are absorbed into the bloodstream.
Divided into:◦Duodenum
Short, first segment that leaves stomach.◦ Jejunum
Longest portion, makes up majority of small intestines.
◦ Ileum Short section that enters the colon (large
intestine). Separated from colon by ileocecal sphincter-
muscle that regulates movement of materials from small intestine into colon or the cecum (blind pouch of the large intestine).
Small Intestines
Similar to other segments of GI tract.
Thickness changes depending of area of GI tract.◦ Inner mucosal layer◦ Submucosal layer◦ Muscular layer◦ Serosal layer
Small Intestine Structure
Provides large surface area for absorbing nutrients.◦Folds in intestinal wall called villi are
present◦Villi- tiny, cylindrical, fingerlike
projections that help with absorption. Each villus contains very small villi
called microvilli (brush border). Crypts- small invaginations in the
intestinal mucosa that help with replenishing cells of villus.
Mucosa of Small Intestines
Vagus nerve and some sacral-vertebral nerves of parasympathetic system provide stimulation for motility, secretions, and blood flow.
Intestinal tract is constantly functioning and is never at rest.
Peristalsis◦ What type of contractions are associated with
peristalsis?◦ How does diarrhea occur?◦ Antidiarrheal meds decrease secretion and
increase segmental contractions.
Small Intestine Motility
Ileus- decreased movement of ingesta.◦ May be caused by disease or stress.
Cholecystokinin (CCK)◦ Stimulates intestinal motility (opposite of gastric
motility) Prostaglandins
◦ Increase GI motility and secretions.
Small intestine motility
Absorbed intact into small intestinal wall are:◦ Sodium◦ Chloride◦ Postassium
The above are collectively known as electrolytes
◦ Vitamins
Small Intestine Digestion
Must be chemically broken down to absorb in small intestine are:◦ Carbohydrates◦ Proteins◦ Fats
Chemically digested in 2 steps:◦ Enzymes in lumen of intestine◦ Enzymes of microvilli
Once digested, a “unit” of foodstuff can be transported or diffused across intestinal tract membrane
Small Intestine Digestion
Amylase- converts starch into smaller sugar segments
Then sucrase, maltase, isomaltase and lactase found in cell membrane of microvilli convert sugar segments down further.
Finally, units of foodstuff are transported across microvilli into the body
Types of enzymes present is dependent on diet.◦ Changes in diet produce diarrhea because enzymes
necessary to digest new diet may not be present in sufficient quantities.
Carbohydrate Digestion
Gastric pepsin can help break apart some protein chains, but this is not sufficient for complete protein digestion.
Pancreas secreted 5 basic Proteases:◦ 1. Trypsin
Precursor is trypsinogen Trypsin activates other enzyme precursors Break apart bonds in middle of protein
◦ 2. Chymotrypsin Break apart bonds in middle of protein
◦ 3. Elastase Break apart bonds in middle of protein
◦ 4. Aminopeptidase Break apart proteins at amino `ends
◦ 5. Carboxypeptidase Break apart proteins at carboxyl ends
◦ Peptidases embedded in the cell membrane of brush border cells
Protein Digestion
Fats in water environment form globules. Globules are broken down by emulsificaton
(mixing of fat and water by agitation or shaking) and micelle (fat surrounded by hydrophilic molecules that allow it to readily move in small intestine) formation.
Bile acids (secreted by liver to make fat more water soluble) combine with droplets to keep from returning to globular state. ◦ Have a hydrophobic and hydrophilic end◦ Pancreatic lipases penetrate and digest fat◦ Fat soluble vitamins (A, D, E, and K), are
incorporated into the micelles and absorbed with them.
Fat Digestion
General functions are to recover fluid and electrolytes and to store feces until it can be eliminated.
Consists of:◦ Cecum
Blind sac at ileocecal junction Fermentation in horses Poorly developed in carnivores
◦ Colon◦ Rectum
Large Intestine
Consists of 4 sections:◦Cecum◦Ventral colon
Right and left halves◦Dorsal colon
Right and left halves◦Small colon
Horse Hindgut
Ingesta from small intestine passes through ileocecal sphincter and enters cecum.
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 haustra
Cecum is separated from colon by cecocolic orifice
Horse Hindgut
Ileocecal sphincter►Cecum►Right ventral colon►sternal flexure►left ventral colon►Pelvic flexure►left dorsal colon►diaphragmatic flexure►Right dorsal colon►small colon.
Colonic impaction is most common form of colic in horse
VFA’s absorbed from cecum and colon provide energy needs in animals with hindgut fermentation.◦ Guinea pigs, rats, rabbits, swine.
Ingesta flow in horse hindgut
Terminal portion of the large intestine Extension of colon Secretions similar to colon to help lubricate
feces as they pass through colon. Capable of more expansion than colon Has sensory receptors that detect stretching
or distention and stimulates defecation response.
Defecation- process of expelling feces
Rectum
Composed of:◦ internal sphincter
Under autonomic control Parasympathetic system causes relaxation Sympathetic system causes constriction
◦ external sphincters. Under voluntary control
When material makes contact with anal mucosa of internal sphincter, increases conscious need for defecation.
Anal abnormalities can result in fecal incontinence.
Anus
Produces bile acids that help to digest fat. Helps to filter materials absorbed from GI
tract before they reach blood. Hepatic portal system- is blood vessel system
that transports blood from capillaries in the intestine to liver.
Some nutrients are stored or metabolized by the liver.
Bile is produced in liver and leads to gallbladder.
Source of blood proteins◦ Albumin
Liver
Storage compartment for bile. Will force bile down bile duct to duodenum.
Gallbladder
Exocrine gland(secretes substances to outside of body through a duct) as well as Endocrine gland (secretes hormones directly into the blood without going through a duct).
Insulin and glucagon help regulate blood glucose◦ Beta cells (located in pancreatic islets or islets
of langerhans) produce insulin which lowers glucose levels in blood
◦ Lack of insulin leads to Diabetes mellitus◦ Glucagon produced by alpha cells in pancreas
dos the opposite insulin by working to increase blood glucose when the body is running low.
Pancreas
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