Chapter 16 Digestive System Flashcards
Abdominal cavity tract layers
*Serous membrane: outer layer, connective tissue
*Muscaris- Smooth muscle tissue
* Submucosa
* Mucosa
Absorption of All Nutrients
Macronutrients - digestion is required
Micronutrients – nutrient molecules so small that no digestion is required before being absorbed
*Vitamins
* Minerals
* Water
Animals Groups Based on Stomach Anatomy
Monogastric
*Simple, single stomach
* Dogs
* Cats
* Horses
Ruminant
* Complex stomach consisting of 4 chambers
* Cattle
* Goats
*Sheep
* Deer
*Antelope
* Moose
Basic Function of the GIT
Digestion of macronutrients (there are 3)
Absorption of all nutrients (there are 6)
Elimination of wastes
Steps:
Prehension—Grasping food with the lips or teeth
Mastication—Mechanical grinding and breaking down of food (chewing)
Digestion—Chemical breakdown of food
Absorption—Movement of nutrients and water into the body
Elimination—Removal of waste materials
Basic Structure of the GIT
Tube that runs from oral cavity to the anus
Structures included
* Oral cavity – food swallowed
*Esophagus - Dorsal to the trachea**
*Stomach – food becomes chyme
*Small intestine
* Large intestine – chyme becomes feces
Side note- food changes chemically twice -Food to chyme, chyme to feces
Classification of Teeth
Brachyodont teeth
* Carnivores, humans, pigs
*Also ruminant incisors
*Small crowns, well-developed roots
* Do not grow continually
Hypsodont teeth
* Horse’s incisors and cheek teeth, boar’s canine teeth, rodents, lagomorphs
* Large reserve of crown beneath gingiva
* Grow continually
Composition of Saliva
Mainly water
Protein
Electrolytes
Antibodies
Glycoproteins
Salivary bicarbonate
Enzymes
* Lysozyme
* Amylase - beginning of carb digestion
Deciduous Teeth
= Milk Teeth = Baby Teeth
All domestic species have 2 sets of teeth
* Deciduous and permanent (adult teeth)
Deciduous teeth
*Smaller and whiter
*Present in the jaw at birth
*Erupt through gums at different times, depending on species
Dental Formula
Represents typical number of each type of tooth found on one side of the upper and lower jaws
Puppy: I3/3, C1/1, P3/3 = 28
Dog: I3/3, C1/1, P4/4, M2/3 = 42
Feline kitten I3/3, C1/1, P3/2 = 26
Feline: I3/3, C1/1, P3/2, M1/1= 30
Equine Adult: 13/3, c1/1. P3-4/3, M3/3= 40 or 42
Porcine I3/3, C1/1, P4/4, M3/3 = 44
Bovine: I0/3, C0/1, p3/3, M3/3 = 32
Digestion
Think Macronutrients
The part of the process where large molecules are broken down into their smaller components
When small enough, molecules enter the body
Breakdown processes
* Mechanical digestion
– GI tract movements
* Chemical digestion
– Chemical reactions cronutrients - Carbohydrates, Lipids (Fats), Proteins
Digestion of Macronutrients
Definition – large nutrient molecules that require breakdown into smaller molecules before being absorbed
*“Energy” nutrients (Calories)
** Carbohydrates
** Lipids (Fats)
**Proteins
Elimination of Wastes
Food –
Chyme –
Feces – waste product from animal’s digestive tract expelled through the anus during defecation
* Water (75%)
*Bacteria
* Fiber
* Undigested/unabsorbed nutrients
* Waste products
Functions of the Liver –
Manufacturing Plant, Warehouse, Detox Facility
Secretes substances essential for digestion and absorption of nutrients
Synthesizes nutrients and regulates their release into the bloodstream
Stores glycogen
* Where else in the animal body is glycogen stored?
Excretes toxic substances
* Those originating within and from outside the body
Produces plasma proteins, cholesterol, and blood coagulation factors
Largest digestion gland in the body
Gastric Pits
Found on rugae
Different glandular cells, each with different secretions:
Mucus neck cells
Chief cells
Parietal cells
GIT
*Gastrointestinal tract, digestive tract, alimentary canal - all names for the same thing
-digestive tract, not accurate though because not all 6 nutrients require digestion
*tube that runs from mouth to anus; has accessory digestive organs
Glandular Portions of the Pancreas
Endocrine portion = pancreatic islets- Regulates sugar
* Contain several different cell types
* Beta cells secrete insulin
* Alpha cells produce glucagon
Exocrine portion = groups of acini - Aids in digestion
* Ducts merge to converge into pancreatic duct
* Excretions contain bicarbonate and digestive proenzymes
* Anticipation of food causes increase of secretions
* Neural and endocrine stimuli increase secretions
Glycogen Processing in the Liver
Excess glucose can be stored as glycogen
* In liver
* In skeletal muscle and adipose cells
Glycogenolysis
* Glycogen can be broken down to glucose when needed
Gluconeogenesis
* Synthesis of glucose from non-carbohydrate sources – amino acids, fatty acids
* Ketosis – Atkins diet, Keto diet BAD!
Heterodont Dentition
4 types of teeth of different shapes and sizes each has a different function
Incisor
Canine
Premolar
Molar
Hypsodont Teeth
Radicular hypsodont
*Apices of roots remain open for a long time
*Apices eventually close and stop growing
* Found in cheek teeth of horses
Aradicular hypsodont
* Lack a true root
* Grow continuously throughout life of animal
* Found in lagomorphs and some rodents
Lacteals and Blood Capillaries
Lacteals = lymphatic capillaries
* Carry absorbed lipids and fat-soluble substances to thoracic duct, and into vena cava
Blood capillaries
* collect some absorbed nutrients and transport them to the liver
Liver Overview
Mammalian liver consists of five lobes
Strategically placed to process blood leaving GI tract
* Prevents toxic substances from entering general circulation
* Area known as the triad
Hepatic artery and hepatic portal vein come together and empty their blood into sinusoids
* Kupffer cells engulf foreign objects
Proteins made by hepatocytes enter bloodstream through pores in adjacent sinusoids
Bile is excreted by hepatocytes into canaliculi
Lumen
Tube of a tract
More Functions of the Liver
Protein production
* Nearly all the plasma proteins, including albumin and blood clotting proteins
Conversion of amino acids into ketoacids
* Energy production
* Lipid synthesis
Nutrient Processing by the Liver
Vital role in keeping blood glucose levels normal
#1 Glucose absorbed from small intestine
* Enters hepatic portal vein
* Arrives in liver
* Metabolized to produce energy
#2 Fructose and galactose (milk sugar breakdown) can be converted to
glucose by the liver
omentum
A double layer Connects the peritoneum that links the stomach to abdominal wall or to other organs:
Lesser omentum
Greater omentum
Oral cavity anatomy
Lips
Tongue
Teeth
Salivary glands
Hard palate
Soft palate
Organs That Contribute Secretions to the GIT
SALIVARY GLANDS
PANCREAS
LIVER
Peristalsis
Pattern of muscle contraction that propels food through the GI tract
As soon as an animal swallows it begins a wave of peristalsis
Rugae
Transient folds in gastric mucosa
Allow stomach to expand when filled with food
Increase surface area for absorption
“have ridges”
Ruminant Stomach
4 chambers
First 3 chambers are the forestomachs: reticulum, rumen, and omasum
▪ The forestomachs are lined by stratified squamous epithelium and are non-glandular.
Last chamber and “true stomach”: abomasum
Saliva
Deposited into oral cavity via ducts
Production varies depending on species
Composition: watery or viscous or mixed
Saliva Physiology
Secreted by 3 main paired glands
* Parotid, mandibular, and sublingual
Lubrication
Antibacterial action
pH regulation
Thermoregulation
Enzymatic digestion
Small Intestine adaptions
Adaptations help increase surface area
* Organ is long with many loops and coils
*Plications (folds) in mucosal lining
*Villi in mucosa contain microvilli
*Brush border
*Intestinal crypts (crypts of Langerhans)
Stomach anatomy
On the left side
Mucosal lining (rugae)
Mechanical digestion
Chemical digestion of protein
* HCl
* Protease (pepsin)
Pylorus (pyloric valve) - 1 wave valve
Structure of
the Tooth
Crown covered by enamel
*Enamel
* Dentin
–Dentin forms bulk of tooth
— Pulp cavity that contains blood and nerves
Gingiva - gums
Root - cemented in gingiva
* Dentin
* Pulp
* Cementum- thin bone that cements
* Periodontal ligament
Surfaces of a Tooth
Named by direction the outer surface faces:
Buccal
Labial
Lingual
Palatal
Teeth
The Teeth Embedded in upper maxilla bone and lower mandible bone Parts of a tooth:
Parts of tooth- Crown, Root, Apex, Neck
The Cecum
Blind diverticulum at beginning of colon
*Inconspicuous in carnivores – whipworms in dogs
* Large blind tube in ruminants
* Huge in equines
3 parts
*Base, main body, apex
Ileum opens into cecum, colon, or both (depending on species)
The Esophagus (GI physiology)
Muscular tube connecting pharynx to stomach
Lined with folded mucosa
Tunica muscularis
* 2 layers (circular and longitudinal) needed to move food
The Exocrine Pancreas
Enzymes are vital to digestion
* lipase, amylase, nuclease, protease
Proenzyme (or zymogen)
* All proteolytic enzymes secreted in inactive form
* Trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B
* CCK starts the activation process
The Gallbladder
Concentrates and stores bile until needed
* Bile enters duodenum to emulsify fat - makes fat water soluble
Provides means for liver to excrete waste products even when animal is not eating
Composition of bile
* Bile salts
* Phospholipids
* Cholesterol
* Bile pigments
The Large Intestine
Components
* Cecum – blind sac at ileocecal junction
* Colon
* Rectum
* Anus
Species variation in structure
Primary functions
* Recover fluid and electrolytes
* Store feces until they can be eliminated
The Monogastric Stomach
C-shaped, located just behind diaphragm
Glandular portion with gastric pits:
* Cardia
* Fundus
*Body
Distal portion
*Pylorus
The Oral Cavity
= Mouth = Buccal Cavity
Entrance to the GI tract
Contains everything in the mouth
2 parts
*Vestibule
*Space between lips and cheeks, and outer surface of teeth
* Oral cavity
*Bordered by inner surface of teeth, and hard and soft palates
The Pharynx (GI physiology)
= Throat/common passageway
Part of both GI and respiratory tracts
Swallowing sends food from the oral cavity to the esophagus
Structures found here
*Eustachian tube
* Tonsils
Structure of Small Intestine
Tube that carries chyme away from stomach and deposits it in the large intestine
Suspended from the body wall by mesentery
Duodenum
* Receives chyme through pyloric sphincter
* Pancreatic duct opens here
* Common bile duct opens here
Jejunum
* Longest part
* Most chemical digestion and absorption occur here
Ileum
* Prominent Peyer’s patches
* Empties into large intestine at cecum (horse), at colon (dog and cat), or at cecum and colon (ruminant and pig)
The Stomach physiology
Functions
*Storage of ingested food
* Mechanical and chemical breakdown of food
*Beginning of protein digestion
*Production of intrinsic factor for Vitamin B12 absorption in small intestine
Food leaves stomach in semi-liquid form = chyme
The Stomach
Functions
*Storage of ingested food
* Mechanical and chemical breakdown of food
*Beginning of protein digestion
*Production of intrinsic factor for Vitamin B12 absorption in small intestine
Food leaves stomach in semi-liquid form = chyme
The Tongue
Muscular structure on ventral surface in oral cavity
3 parts
*Apex, body, and root
Papillae on dorsal surface
* Mechanical functions
* Grooming and moving food into pharynx
*Specialized functions
* Taste sensations, pain, temperature, touch, and thermoregulation through panting (dogs)
4 types of taste buds
– sweet, sour, salty, bitter
Functions of Pancreas
Only gland in body with both exocrine and endocrine functions!!!
Production of pancreatic amylase, proteases, and lipase (groups of acini) - Exocrine
Secretes bicarbonate into the duodenum
* Helps neutralize acidity of contents and maintains the pH in the duodenum needed for proper enzyme function
Produces insulin and glucagon
* Help regulate blood glucose levels
Adding secretions that enhance digestion
Trace a bolus of food
1 - Mouth
2- teeth
3 - tongue
4 - pharynx
5 -esophagus
6 -stomach
7 -duodenum (part of small intestine)
8 - jejunum (part of small intestine)
9- ilium (part of small intestine)
(Food doesn’t go in Cecum, but it’s next. Part of large intestine)
10 - Ascending Colon- 2nd part of large intestine
11 Transverse colon - large intestine
12 - Descending colon - large intestine
13- Rectum - large intestine
salivary glands, pancreas, liver contribute to “tube” but aren’t part of GI tube
14 Anus
What Animals Eat
Herbivores eat plant material
* Ruminants: cattle and goats
* Non-ruminants: horses
Carnivores eat meat
* Cats
Omnivores eat combination of plants and meat
* Humans, pigs, dogs
Small intestine adaptions
Adaptations help increase surface area
* Organ is long with many loops and coils
*Plications (folds) in mucosal lining
*Villi in mucosa contain microvilli
*Brush border
*Intestinal crypts (crypts of Langerhans)
Salivary Glands
Adding secretions that enhance digestion
Parotid- ventral to ear, very large
Mandibular- medial to mandible
Sublingual- below tongue
Zygomatic- cheek bone
acini
Pancreatic acinar cells synthesize and secrete almost all the digestive enzymes active in the lumen of the small intestine which are necessary for nutrient digestion
Lobes of the liver
left medial
left lateral
quadrate lobe
right medial
right lateral
Ruminants
Herbivores
* Cattle, sheep, goats, deer, reindeer, moose
* Require more food and more complex digestion process than carnivores
Forestomachs are non-glandular
* Microorganisms for fermentation in rumen and reticulum
* Complex carbohydrates (cellulose) broken down
Abomasum functions same as monogastric stomach
Rumen
Part of the Forestomachs
Each performs a different digestive function and has different anatomical features
Rumen = “the paunch”
Occupies most of left side of abdominal cavity
Microorganisms ferment carbohydrates, so they can digest fiber
Papillae in mucosa increase surface area for absorption
Pillars divide rumen
* Dorsal sac, ventral sac, and 2 caudal sacs
Reticulum
Part of the Forestomachs
Reticulum = “the
honeycomb”
Located cranial to the rumen
Contents easily enter and exit to rumen
*reticulorumen
Esophageal Groove
Part of the Forestomachs
Links esophagus with omasum in young ruminant
Milk for nursing ruminant bypasses reticulorumen
* Goes directly to omasum and abomasum
If groove didn’t close:
*Bacteria in reticulorumen would ferment milk
* Lactic acid produced would inhibit normal microbial action
Omasum
Part of the Forestomachs
Omasum = “many plies” or “book stomach”
Connects reticulorumen to abomasum
Folds of mucosa with papillae on surfaces
Absorption of water and salts here
The Abomasum
Elongated “true stomach”
Lined with glandular tissue
Released renin causes milk protein coagulation
*Prolongs time for pepsin to break down proteins
Functions like simple monogastric stomach
*Exception: abomasum is not a storage compartment
Continuous flow of ingesta into abomasum
Contractions in the Reticulorumen
Primary contractions = mixing contractions
Ensure content movements between reticulum and rumen
Separate particles based on size
Rumination
Rumination = “chewing the cud”
Ingesta moves from reticulorumen back into oral cavity for additional saliva and continued chewing
4-step process
* Regurgitation
* Re-insalivation
* Remastication
* Re-swallowing
secondary contractions
Eructation = belching = secondary contractions
Responsible for the release of gases
* Carbon dioxide and methane produced during
fermentation
Without gas release, develop condition of bloat
Area of brainstem controls reticuloruminal activity
Reticulorumen Ecosystem
Wide variety of bacteria, protozoa, and fungi in ruminants
Proper balance between types acquired after birth
* Controlled by diet and amount of food consumed
*Also by interactions between mother and young
Oxygen ingested along with food
Carbohydrate Digestion in Ruminants
Ruminants’ diet – herbivore
* Mostly grasses (roughage): complex carbohydrates
* Cellulose, hemicellulose, and pectin
*Some grains (concentrates): nonstructural carbohydrates
* Starches, fructosans, and simple sugars
Microorganisms use nutrients consumed for their own growth and development
Ruminant can digest microorganisms as source of protein
Complex carbohydrates
* Hydrolysis by catalase enzymes to simple sugars
Starches and soluble sugars
* Hydrolysis by amylolytic bacteria to monosaccharides and polysaccharides
*Saccharides absorbed by microvilli and further metabolized to pyruvate and converted to volatile fatty acids (VFAs)
* VFAs are main source of energy for the ruminant
Lipid Digestion in Ruminants
Lipids found in grasses and plants:
* Triglycerides, glycolipids, free fatty acids
Lipids constitute small portion of diet
* Too many lipids: decreased appetite, reduced motility of reticulorumen, decreased fermentation of cellulose
Microorganisms in reticulorumen hydrolyze triglycerides
*VFAs produced, used to produce energy or stored
*Acetic acid (acetate), propionic acid (propionate), and butyric acid (butyrate)
Protein Digestion in Ruminants
Fermentation process occurs before enzymatic digestion
Nutrients in food first available to microbes in reticulorumen
* Microbial peptidase breaks down proteins to peptide chains
* Microbes can synthesize amino acids from ammonium, and by converting non-protein nitrogen
(NPN) compounds
Further broken down in small intestine by enzymatic action and transported to liver
* Amino acids are metabolized
* Urea is produced; goes back to rumen (and then saliva) for reuse in making microbial proteins
Glucose Production in Ruminants
Ruminal microbes process carbohydrates before they are exposed to intestinal enzymes
* potential glucose deficiency
Gluconeogenesis
* Occurs in liver from non-carbohydrate sources
*Propionate, butyric acid, acetate, absorbed amino acids
Conservation of glucose
Large Intestine Comparative Anatomy
Carnivores: simple, tubular colon; poorly developed cecum
Nonruminant herbivores: very large colon and cecum (hindgut)
* Fermentation site
VFA
Volatile fatty acids are the main energy source for ruminants, providing approximately 70% of the total energy requirements. They are used primarily by the microorganisms for reproduction and growth, with the excess production being used by the ruminant itself.
Ascending Colon in various species
Equine- Large Colon
Bovine- Coiled Colon
Porcnie - Spiral Colon
Elimination of Wastes
Food –
Chyme –
Feces – waste product from animal’s digestive tract expelled through the anus during defecation
* Water (75%)
*Bacteria
* Fiber
* Undigested/unabsorbed nutrients
* Waste products
Digestion in the Oral Cavity and Pharynx
Prehension
Chewing = mastication
Salivary secretion
* Regulated by nervous system
*Also triggered by conditioned responses
Swallowing = deglutition
*Voluntary
*Pharyngeal stage
*Esophageal stage – initiates peristalsis
Pepsin
A proteolytic enzyme
Essential in the digestive process
*Begins the chemical digestions of proteins
Activated in the fundus
*Pepsinogen secreted by chief cells
*Pepsinogen converted to pepsin in presence of HCl
Pyloric Gland Region of Stomach
Last glandular portion of the stomach
Regions:
* Pyloric antrum
* Pyloric canal
* Pylorus
Opens into duodenum through pyloric sphincter
Cells found here
* Mucous-secreting cells
* G cells secreting gastrin
Stimulation of Stomach Secretions
3 substances stimulate secretions by glandular cells
*Acetylcholine from cholinergic neurons
* Gastrin released by G cells
* Histamine secreted by enterochromaffin-like cells
(ECL-cells) in gastric mucosa
Cephalic phase of secretion – thinking about food!
*Anticipation of eating a meal
Gastric phase of secretion
*Begins when food enters stomach
Cephalic Phase of Secretion
Begins in anticipation of eating
*Enteric nervous system is stimulated
*Acetylcholine is released and binds to receptors
* Parietal cells secrete H+ and Clions
* Chief cells secrete pepsinogen into stomach
* G cells secrete gastrin into bloodstream
Gastric Phase of Secretion
Begins when food enters stomach
* Glandular cells stimulated by stretching of stomach wall
*Peptides formed by protein breakdown
* Local enteric reflexes, and vagal reflexes to and
from brain
*Stomach can be as acidic as pH 2.0
Digestion of protein, carbs and fats start where
Carbs- mouth
Protein - stomach
Fats- small intestine
Monogastric Stomach Motility
Muscle contractions of stomach wall help break down food particles
Gastric contents released at controlled rate
*Specialized smooth muscle pacemaker cells
* Fluctuations in resting membrane potential lead to muscle contraction
*Acetylcholine elevates resting potential
*Entry of Ca++ ions into muscle cell initiates contraction
Each part differs in degree of movement based on its function
Fundus expands to accommodate large volumes of food
Body is a large mixing chamber
Pyloric antrum acts like a pump
Peristaltic Contractions
Movements
* Fragment food into small particles
*Influence rate of gastric emptying
Weak in fundus and body
Progressively stronger as food moves toward pylorus
* Larger particles prevented from leaving stomach
* Retropulsion
Segmentation
Grinding of food.
Nutrient Components in a Meal
Macronutrients-
Carbohydrates
Proteins
Lipids
Micronutrients-
Vitamins
Minerals
Water
Digestion Completed in the Small Intestine
Mechanical digestion
*Essential to increasing amount of food surface area
Chemical digestion
* Digestive enzymes from exocrine pancreas responsible
* Carbohydrates – amylase
*Proteins – proteases
* Lipids (fats) – lipase
Absorption of All Nutrients
Macronutrients- requires digestion
Micronutrients – nutrient molecules so small that no digestion is required before being absorbed
*Vitamins
* Minerals
* Water
Carbohydrates
Starches
* Made of repeating glucose monosaccharides
Sugars
*Simple monosaccharides (glucose)
* Multiple monosaccharides linked together
* Disaccharides, sucrose and lactose
Cellulose
* Complex carbohydrate
Proteins
Proteins
Made of repeating amino acid units
Chain of >50 amino acids = protein
Chain of <50 amino acids = peptide
Lipids
Majority of fat found in animal’s diet
Made of a glycerol backbone and 3 fatty acids
Lipids
Majority of fat found in animal’s diet
Made of a glycerol backbone and 3 fatty acids
Chemical Digestion
Carbohydrate digestion
Begins with amylase in saliva
Continues in stomach and small intestine
Protein digestion
Begins in the stomach; continues in small intestine
Pepsinogen activated by HCl to pepsin
Mucosa
*Innermost layer of GIT
*made of epithelium, lamina propria and muscularis mucosae
-epithelium is made of stratified squamous and simple columnar epithelium
-mucosa is made of loose areolar connective tissue
-muscular mucosae is a thin layer of smooth muscle
Prostaglandins
*Hormonelike substances that regulate biochemical activities in the tissue they are formed.
*Produced from lipids (eicosanoids)
*Important role in controlling blood pressure and smooth muscle contraction
Serous Layer of GIT
–Visceral peritoneum
–Parietal peritoneum
–Mesentery
–Omentum
Non-fermentative Digestion
▪ Monogastric animals, including the dog, cat, and horse
▪ Muscle contractions of the stomach wall contribute to
the mechanical breakdown of food particles
▪ Mechanical digestion in the oral cavity and in the stomach is essential to increase the amount of food surface area that can be exposed to the digestive enzymes
▪ Digestive enzymes are responsible for the second phase of digestion, chemical digestion
▪ Luminal chemical digestion breaks down macromolecules being broken down through hydrolysis
▪ Hydrolysis is then repeated in membranous chemical digestion, where the short chain polymers are completely broken down into their most basic component parts
▪ In some animals, such as omnivores, chemical digestion begins with amylase (breaks down starch CHOs) in the saliva.
▪ In animals that do not have amylase in their saliva, the digestion of starch does not begin until the food has reached the small intestine and pancreatic amylase is released.
▪ Protein digestion, on the other hand, begins in the stomach.
Chemical Digestion Monogastric
▪ Chemical digestion is divided into two phases:
➢ Luminal chemical digestion
▪ Occurs in the lumen of the stomach or intestine
▪ Digestive enzymes mix with food and acid or alkaline fluids
to digest free-floating food particles in the lumen
➢ Membranous chemical digestion
Fermentative Digestion
▪ Mastication breaks larger food mixing them with saliva to create a rounded mass called a bolus that the ruminant swallows.
▪ Saliva is alkaline and contains both bicarbonate and phosphate which help buffer the rumen during fermentation
▪ As food leaves the forestomachs, it enters the fourth chamber or the “true” stomach, the abomasum
▪ The rumen and the reticulum are where the majority of cellulose is degraded.
*contain a large number of microorganisms (bacteria,
protozoa, and fungi) that are responsible for a fermentation
* During fermentation, complex CHOs such as cellulose and hemicellulose are broken down
▪ The omasum is where the absorption of water and salts take place.
▪ The abomasum (” true stomach”) functions in the same way as the monogastric simple stomach. However, The flow of ingesta into the abomasum is continuous.
▪ CHO digestion – starch end product is volatile fatty acids (main source of energy for the ruminant)
▪ Lipid digestion – triglycerides are hydrolyzed producing VFAs
▪ Protein digestion – the end product are amino acids used to make microbial protein, ammonium to proAnuduce VFAs.
CHO
Carboydrates
Anus
The opening of the GI tract for elimination of stool
➢ At the junction of the rectum and anus, the mucosa changes from glandular villi to flattened squamous epithelial tissue
➢ Two large muscle sphincters surround the anus to help retain the stool before defecation
➢ The inner anal sphincter is under smooth muscle control while the outer anal sphincter is under skeletal muscle control.
Rectum
➢ When chyme passes through the large intestine much of
the water is absorbed, leaving a semisolid material called feces.
➢ When feces are transported to the rectum, sensory receptors are stimulated. This stimulates the defecation reflex ➢ The animal then perceives the need to defecate
Colon
- some microbial digestion
—Ascending
—Transverse
— Descending - most variety between species
*reabsorbs fluids and prepare wastes for elimnation
Carbohydrate digestion
▪ Majority of chemical CHO digestion occurs in small intestine
▪ Starches are one of the few CHOs broken down in the luminal phase
▪ In the membranous phase enzymes in the brush border:
–there are specific enzymes for each type of polysaccharide
– Sugars, such as sucrose and lactose, are degraded
Protein digestion
*Luminal protein digestion began in the stomach with pepsin and is completed in the small intestine.
*The pancreas releases proenzymes that are activated in the lumen of the small intestine.
— the endopeptidases and the exopeptidases
➢ Free amino acids are yielded
➢ Some peptide chains are incompletely hydrolyzed and form
dipeptides and tripeptides.
—-These are small enough to be absorbed into the intestinal wall
Luminal Digestion
*First phase of chemical digestion
*Large macromolecules broken into short polymers through hydrolysis
Membranous Digestion
*Second phase of chemical digestion
*Hydrolysis is repeated to completely break down the short chains of polymers formed through luminal digestion
▪ Fats and fat-soluble vitamins are also digested in and absorbed from the small intestine.
▪ Triglycerides are the primary dietary lipids; other lipids include cholesterols, phospholipids, and esters
▪ Lipids are not water soluble and cannot be dissolved in the watery medium of the GI fluids.
▪ In order to digest and absorb fats, a four-step process must occur:
➢ Emulsification
➢ Hydrolysis
➢ Micelle formation
➢ Absorption
Emulsification
Begins in the stomach where lipids are warmed to body
temperature and thoroughly mixed. This process helps
break lipids into smaller droplets. Emulsification is then
completed in the small intestine by the detergent action of
bile salts and phospholipids.
Hydrolysis of Lipids
▪ Bile salts coat the lipid droplets, causing them to repel one
another and remain small individual droplets. Decreasing
the size of lipid droplets increases the surface area
available for the hydrolytic pancreatic enzymes, lipase and
colipase, to break down each triglycerid
Micelle formation
▪ The monoglyceride and the two fatty acids are not yet
soluble in water, which again would cause a problem if it
were not for the bile salts forming micelles
▪ The micelles essentially act like tiny ferries, transporting the
fatty acids and monoglycerides to the enterocyte surface. At
this point the monoglyceride and fatty acids diffuse into the
cell and the bile salts do not. This keeps the bile salts
available to transfer other monoglycerides and fatty acids
Absorption of Lipids
▪ Inside the enterocyte, the monoglyceride and the two fatty
acids are reassembled into a triglyceride and packaged into
chylomicrons.
▪ Chylomicrons are spherical structures that are made up of
triglycerides, cholesterol, phospholipids, and proteins
▪ The Golgi apparatus packages the chylomicrons into
vesicles, which are transported to the cell membrane, from
which they are released into the interstitial fluid by
exocytosis.
▪ Chylomicrons cannot enter the capillaries because of their
large size; instead they are picked up by the lymphatic
system and transported to the
Bird stomachs
The stomach of birds consists of a glandular portion (proventriculus) and a muscular portion (gizzard). The process of chemical digestion begins in the proventriculus. The gizzard is comprised of bands of striated muscles that grind food.
