Digestive System Flashcards
Prehension
Taking a hold of food/water into the oral cavity
Mastication
Mechanical breakdown of food and mixing it with saliva in the oral cavity
True or false:
When you swallow food, it is considered to be INSIDE the body
False
Good remains OUTSIDE of the body until it is absorbed
Carnivores
Eats meat and no fibres
How much fermentation does a carnivore have going on
Little to none
Who is the one true carnivore
The cat
Herbivore
Eats mostly plant matter
How much fermentation is required for a herbivore
A lot
The will either have a large cecum (horses) or a rumen
What is cellulose
The most abundant plant sugar
True or false
There are mammalian enzymes that can break down cellulose
False
What is needed to break down cellulose
Fermentation
Omnivores
Eats both plants and meat
How much fermentation is needed for omnivores
Some fermentation in an enlarged colon
True or false
Dogs are considered omnivores
True
Monogastric
Have a single true stomach
Ruminants
Have one true stomach and 3 forestomachs including a large rumen/fermentation chamber
Cecal or hindgut fermenters
Have a large cecum and sometimes a big large intestine for a fermentation chamber
Name the 3 salivary glands and where they are
Parotid: below the ear canal caudal to the mandible
Mandibular: medial to the bones of the mandible
Sublingual: below the base of the tongue
What enzymes are in saliva
Amylase
Lipase
Lysozyme
What does amylase do
Breaks down amylose/starch
True or false
Amylase is present in omnivores but not in dogs, carnivores and ruminants
True
What does lipase do
Breaks down lipids
What does lysozyme do? And what is it considered?
Considered a antibacterial enzyme
Breaks down bacteria
AIDS in cleaning the food
A Function of saliva in dogs
Evaporative cooling (panting)
What does saliva help to do in ruminants
High amounts of sodium bicarbonate and phosphate buffers (with a high pH) help neutralize rumen acids from fermentation
What can cause acidosis in ruminants
Large amounts of carbohydrate feeds result in an increase in the process of fermentation and the build up of acids in the rumen
True or false
Salivary fluid and buffers are recycled in ruminants
True
A row of teeth is called an
Arcade
A tooth is embedded in a socket, a socket is called an
Alveolus
The crown is the part of the tooth
Above the gums
The root is the part of the tooth
Below the gum in the alveolus
Internal structure of the tooth:
Enamel is the____
Dentin is the____
Pulp cavity is the___ and contains ___
Enamel is the outer surface of the tooth
Dentin is the majority of the tooth
The pulp cavity is the central cavity and contains blood vessels and nerves
The soft palate separates
The oropharynx(throat) and the nasopharynx
Two orientations of muscle in the esophagus
Longitudinal and circular
Explain Deglutition (swallowing)
Starts a voluntary action (tongue moves food to o the back of the throat)
Relaxation of the esophagus and closure of the larynx
Peristalsis in the esophagus by contraction of the longitudinal muscles on aboral side
Contraction of circular muscles on the oral side and relaxation of circular muscles on the aboral side
Aboral
Away from the mouth
Cardiac sphincter prevents what
Reflux of stomach contents into the esophagus
True or false
Horse can vomit
False
The cardiac sphincter prevents this
Myasthenia Gravis or megaesophagus
Interference with muscles function and tone in the esophagus and causes muscle tone loss and dilation of the esophagus
Food cannot move down the esophagus and is often regurgitated
Normally mistaken for vomiting
Makes animal more prone to pneumonia
Vomiting (emesis) is controlled where
A centre in the brainstem
Emetics
Drugs that Stimulate the brainstem to induce vomiting
Antiemetics
Drugs that prevent vomiting
Process of vomiting (emesis)
Pyloric sphincter relaxes
Reverse peristalsis moves food from SI to stomach
Relaxation of cardiac sphincter
Inspiratory movements and contraction of abdominal muscles result in vomiting
Closed epiglottis prevents aspiration and the soft palate directs food out of the mouth
Rumination
Masticated partially digested food gets regurgitated and chewed on again, swallowed and re-digested
Called “chewing a the cud”
Why do ruminants ruminate their food
Efficient fiber digestion: mixed with saliva and chewed again to increase surface area exposed to microbes
How long does each rumination cycle last
About 1 minutes between regurgitation and swallowing
Where is the reticulum in ruminants
Most cranial compartment
What appearance does the reticulum have
A honey comb appearance to increase surface area
Reticulorumen contractions
Coordinated contractions to move food to the rumen
The rumenoreticular fold
Separates the rumen from the reticulum
Where is the rumen in ruminants
Occupies the left half of the abdominal cavity
True or false
the rumen is the largest forestomach compartment
True
What appearance does the rumen have
Pile rug appearance
Function of the rumen
Site of fermentation digestion
What separates the rumen into different compartments
Rumenal pillars -long muscular folds
Compartmentalization in the rumen
Contractions that assist in mixing of rumen contents controlled by the vagus nerve (parasympathetic NS)
What affects compartmentalization in the rumen
Distension of the rumen PH Presence of VFAs Consistency of contents And feedback from other areas
Eurctation
The expulsion of CO2 and methane gas from fermentation that accumulates in the rumen
Contractions of rumen and relaxation of the esophagus result in belching
Why is cellulose and pectin indigestible in monogastrics
Due to the fiber linkage of the molecules
Microbes convert saccharides into
Volatile fatty acids
3 most important VFAs in rumen
Propionic acid
Butyric acid
Acetic acid
VFAs are absorbed across the rumen wall and go to the liver for conversion to
Glucose (mostly propionic acid) to make adipose tissue or to be burnt for energy
True or false
Things are normally absorbed where they are created
True
Cellulase breaks down cellulose to _____, microbes convert this to _____, liver of ruminants converts VFAs back to _____
Glucose
Propionic acid
Glucose
Proteases break down protein into
Amino acids
Amino acids are used to
Make proteins
Or converted to VFAs and ammonia
Some ammonia is absorbed and ends up in the liver to be converted to___
Urea
What happens to urea
Secreted back into the salivary glands and eventually the rumen to provide microbes with a nitrogen source
Or secreted in urine after the digestion process
Why do farmers add chicken waste to cattle feed
To add urea/ammonia to aid in protein synthesis
Microbes from fermentation sometimes slip into the small intestine as ingests moves, what happens to them
They provide an important source of protein for the ruminant when they get digested
Where are vitamins B and K made
In the rumen
Any alteration in balance of microbes, feed, pH and gas production can cause
Bloat
Acidosis
Death
The omasum
The third chamber
Appearance of the omasum
Large surface area due to large mucosal folds “many piles”
Looks like leaves or pages of a book
Omasum has strong muscular walls for
Mechanical break down
Absorptive function of the omasum
VFAs, water and bicarbonate
To prevent neutralization of the abomasal acid (a change in the acidity can inhibit function)
The abomasum
The true stomach in ruminants similar to the stomach of a monogastrics
A milk diet does not require fermentation so young nursing calves have underdeveloped ____ , ___and ___ and have a presence of a _____
Rumen, reticulum, and omasum
A reticular/esophageal groove
What does the reticular groove do for nursing cattle
Allows milk to Bypass the rumen, reticulum and omasum into the abomasum
5 parts of the monogastric stomach
Cardia (cardiac sphincter) Fundus Body Antrum Pylorus (pyloric sphincter)
The cardia (cardiac sphincter)
The area around the opening of the esophagus into the stomach
The fundus
Area that forms a distensible pouch that expands as food enters
What allows the fundus to expand the way it can
The Rugae (folds) flatten out as it distends
The body
Also distensible, middle portion of the stomach
The antrum
Distal portion of the stomach that grinds food, regulates acid production, and produces mucus
The pylorus
Muscular sphincter that regulates the movement of chyme into the SI
Prevents back flow from SI to the stomach
The inside curve of the stomach is called
The lesser curvature of the stomach
The outside curve of the stomach is called
The greater curvature of the stomach
Pepsinogen is secreted by
Chief cells in response to gastric stimulation
Pepsinogen is the precursor for
Pepsin
Made my cleaving Pepsinogen with HCL (in the stomach)
Pepsin catalyses _____ into smaller amino acids called____
Protein
Peptides
Pepsin is inactivated by the more ____ pH in the duodenum
Alkaline
Mucus is a mixture of mucin, water and bicarbonate ions, what does this help with
Assists in mucus’ ability to neutralize stomach acid
Mucus is important in the stomach, to protect it from
Autodigestion due to pH of 2-3
Why must mucus be continuously secreted in the stomach? What can happen if it doesn’t?
Because it is broken down by HCL and can cause gastritis and ulcers
Hydrogen and chloride ions (HCl) are secreted by
Parietal (oxyntic) cells as separate ions
What does HCL do in the stomach
Sterilizes the food and protects GIT from infections and aids in denaturation of proteins
Secretion of HCl is controlled by receptors on parietal cells for
Gastrin
Acetylcholine
Histamine
(Need all 3 receptors to be stimulated for optimal HCL release)
When the pH of gastric contents drops below 3, gastrin is inhibited, what does this do to the release of HCl
Inhibits it
Can inhibit the release of HCl by the use of Drugs that block the
Histamine receptor
Acetylcholine receptor
The proton pump
Stomach Contractions stimulated by the parasympathetic nervous system
Relaxes the fundus and increases antrum and body contractions
Prepares the stomach to accept food
Stomach contractions stimulated by the sympathetic nervous system
Decreases stomach motility and can result is gastric atony (decreased muscle tone)
Stomach contractions stimulated by gastrin
Produced by G cells in the antrum in response to filling and peptides
Increases HCl production and Pepsinogen in the fundus
Causes muscular relaxation in the fundus to allow filling
Muscle contractions stimulated by secretin
Produced in the duodenum in response to excess stomach acid in SI
Causes relaxation of the fundus
Inhibits peristalsis to delay movement of ingesta into the SI
Stomach contractions stimulated by cholecystokinin (CCK)
Produced in response to fats and proteins in the duodenum
Inhibits gastric contractions and slows gastric emptying
Carnivore stomachs empty within
A few hours
Horse and pigs stomachs take about __ hours to empty
24
Duodenum
First part of the SI, extends from the pylorus to the jejunum
The duodenum receives 3 things
Ingesta from the stomach
Bile from the liver
Pancreatic secretions
Jejunum and ileum are
Indistinguishable from each other
The ileum connects to the colon of the large intestine by the
Ileocecal sphincter
What 4 things increase surface area of the SI
Folded walls
Intestinal crypts (depressions)
Intestinal villi
Microvilli on the villi
The microvilli cells have enzymes for digestion and ___ for absorption in/on the cell membrane
Carrier molecules
All parts of the SI are divided into 3 major layers
The luminal mucosa with microvilli
An outer serosa which is continuous with the visceral peritoneum
Segmental contractions in the SI
Mixing and churning of food
Increases exposure of food to the villi
Slow movement of ingesta through the GIT
more random than peristalsis and compartmentalization
Amylase in carbohydrate digestion
May be present in saliva, always secreted by the pancreas into the duodenum
Converts starch to disaccharides
Sucrase, Maltase, isomaltase, and lactase in carbohydrate digestion
Enzymes in the microvilli cell membrane
Convert disaccharides to monosaccharides
Proportion of these enzymes depend on diet, age and species
True or false
Young animals often have a lot of lactase to digest milk, but may lose it as adults if not fed milk continuously
True
Glucose is absorbed by using transport proteins on the cell membrane of the brush border by secondary active transport, explain
Na-K ATPase maintains a low sodium level inside of cells
Glucose and sodium are co-transported into the cell using the concentration gradient of sodium
Glucose leaves the cell for the blood by diffusion through the basement membrane
Examples of proteases produced by the pancreas that further break down proteins in the small intestine
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase
The pancreatic proteases are secreted as inactive precursors and are activated in the lumen of the GIT, why?
To prevent autodigestion
Luminal digestion of proteins yields
Free amino acids and small peptides
Fat is digestion by
Emulsification
Explain emulsification of fats
Fats are warmed and mixed in the antrum to change to an oil/liquid
Bile salts are added in the SI (secreted by the liver through the bile duct into duodenum)
The bile salts are bipolar, they bond to the fat with their hydrophobic head and hold onto water with their hydrophilic tail
Emulsification makes fats into small droplets with large surface area, this allows
Fat soluble vitamins to attach to the fats
Pancreatic lipases to digest the fat
Main dietary fat
Triglycerides (3 fatty acids and 1 glycerol)
Triglycerides are hydrolyzed by lipase into free fatty acids and monoglycerides, what do the bile salts do?
With bile salts, these form small water soluble micelles that carry fat to the microvilli
Bile salts stay in the lumen and the free fatty acids and monoglycerides are reassembled into a triglyceride
These are excreted with protein as chylomicrons from the cell and transported in the lymphatics to the vena cava
Sudden diet changes can result in incompletely digested food, leading to
Diarrhea
That’s why diet changes should be gradual
Functions of the large intestine
Recover water and electrolytes
Store feces
Ferment fiber
The cecum
A blind diverticulum (sac) at the ileocecal junction
The cecum in carnivores, ruminants and hind gut fermenters
Carnivores: poorly developed
Ruminants: moderately sized
Hindgut fermenters: large and highly developed
3 portions of the colon
Ascending: most cranial
Transverse: courses from right to left
Descending: connects to the rectum
The colon has many mucus secreting glands to___ and uses ____ to control movement through it
Lubricate feces
Peristalsis and segmental contractions
The horse’s cecum and large colon
Where fermentation takes place (like the reticulum and rumen in a cow)
Ascending colon is usually called the large colon
Consists of 4 large banks stacked in pairs running cranially and caudally along the sides of the abdomen
The cecum and large colon in a horse are divided into sacculations called
Haustra
The longitudinal muscles that form prominent bands in the cecum and large colon of a horse are called
Tenia
In ruminants the ascending colon is called the spiral colon, why?
It is long and doubles into a spiral that runs in the mesentery supporting the small intestine
The difference between the layers of the large intestine and the small intestine are that the mucosa is
Not as extensively folded, and contains more mucous cells
Differences in fermentation from ruminants in hind gut fermenters:
Much of starch and protein digested and absorbed in the small intestine of hindgut fermenters (in the rumen for ruminants)
Microbial protein cannot be absorbed
Bicarbonate secreted directly to cecum and colon wall into the lumen
The rectum
Terminal portion of the colon which continues into the pelvic cavity
Stores feces prior to defecation
Has many mucus secreting glands for lubrication
Has sensory receptors for stretch -stimulates defecation response
The anus has an internal and external muscular sphincter to allow controlled passage of feces. Explain the nervous control for both
Internal sphincter:
Parasympathetic: causes relaxation
Sympathetic: causes constriction
External sphincter:
Voluntary control
What happens when the internal sphincter relaxes and allows fecal contents to contact the anal mucosa
Stimulates conscious need to defecate
What happens when muscles and nerve supply in the anus/rectum are damaged by perianal surgery, trauma and perianal tumours?
Can cause fecal incontinence (loss of control of defecation)
Exocrine functions of the pancreas for digestion
Secretion of proteases, amylase and lipase from acinar cells into the duodenum
Secretes bicarbonate into the duodenum to neutralize stomach acid
Second largest organ in the body
The liver
Hepatic portal system
System of veins that Drains the intestine and deliver blood to the liver to be filtered
What does the liver do to filter toxins
Has phagocytize cells in the hepatic sinusoids (blood filled cavities) to filter and remove toxins and other substances from the blood
What does the liver absorb
Trace Minerals
Fat soluble vitamins (also stores them)
Glucose (stored as glycogen)
The liver makes bile which contains bile acids/salts, cholesterol and bilirubin, it is collected in canaliculi, and drained into bile ducts, is stored in the gallbladder and can lead to the pancreatic duct into the duodenum. The gallbladder releases bile in response to what
Cholecystokinin which is released in response to fats and proteins therefore providing the bile for fat emulsification
How are bile salts reabsorbed
Through the hepatic portal system, they are removed from the blood and recycled by the liver to make more
The liver makes albumin, what is that
A blood protein that maintains blood oncotic pressure
Why do starving kids have pot bellies
Due to protein deficiencies that cause ascites
How is the liver important in glucose metabolism? What processes does it use?
Glycogenesis: makes glycogen from sugars to store in liver
Glycogenolysis: breaks down glycogen to maintain blood glucose
Gluconeogenesis: makes glucose from non carbohydrate substances such as amino acids (ruminants and true carnivores) or propionate (VFA) in herbivores
True or false
Horses have gallbladders
False
Cleft lip
Due to a disturbance of the process making the jaws and face during development
Cleft palate
Defect may involve the soft palate alone or extend rostrallu to the maxillary bones and lips
Salivary Mucocele
An excessive accumulation of saliva in or around the gland due to traumas or inflammation that occluded the duct/gland
Megaesophagus
Esophagus dilates proximal to a constriction
Congenital cause: persistent aortic arch
Choke
Obstruction in the esophagus of horses due to dry feed
Abdominal hernia
Protrusion of abdominal contents through an opening in the wall
Umbilical, inguinal and scrotal
GVD
gastric torsion or volvulus
Large dee chest animals
Exercise after a heavy meal
Distension due to gas