Gastrointestinal Flashcards
What is included in the digestive system
The oral cavity and associated organs:
Teeth, tongue, lips, and salivary glands
Esophagus
Forestomachs in Ruminants
Reticulum, rumen, and omasum
The true stomach of all species (abomasum in ruminants)
The small intestine, liver, and pancreas
The large intestine, rectum, and anus
Major functions of the oral cavity
Prehension: taking hold of feed and water
Mastication: chewing to break down food and mixing with saliva
Major functions of the stomach
Sterilization and holding chamber
Major functions of small intestine
Digestion: chemical breakdown of food
Absorption: of food (nutrients) and water
Major fxns of the large intestine
Evacuation of waste
Ruminants def
have a large rumen (fermentation chamber)
Cecal or hind gut fermenters def
have a large cecum and/or large intestine for a fermentation chamber
Structures of the oral cavity include
Include lips (labia), tongue, teeth, salivary glands, hard and soft palate, and oropharynx
Salivary glands types
Parotid, Mandibular, sublingual
Parotid salivary gland is located
Below the ear canal; caudal to mandible
Mandibular salivary gland is location
Medial to the bones of the mandible
Sublingual salivary gland islocated
Under the base of the tongue
Enzymes in saliva
Amylase, lipase, lysozyme
Amylase in saliva
Present in omnivores (pigs)
Absent in dogs, cats and ruminants
Useful for breaking down amylose (starch)
Lipase in saliva
Present in some young animals while nursing
Breaks down lipids
Lysozyme in saliva
Not really digestive, has antibacterial action
Functions of saliva
Dog: evaporative cooling
Cattle: lots of sodium bicarbonate and phosphate buffers in saliva to help neutralize rumen acids
Produce up to 200 L of saliva per day!
Help prevent rumen acidosis
Salivary fluid and buffers are recycled from GIT
How are salivary glands controled
Salivary glands and other GI glands are controlled by autonomic nervous system
Primarily under parasympathetic stimulation
Sympathetic stimulation usually inhibits
The dry mouth of fear
Function of teeth
Mechanical breakdown of food
Defense and offense
Tongue is and function
a mass of muscle covered by a mucus membrane and papillae (most of which bear taste buds). It functions to prehend and move food within the mouth to position it for mastication and swallowing. Dorsal surface is covered in taste buds.
How do animals use there tongue to drink
Canine and Feline - tongue ladles water in
Others - tongue acts as pump to create a vacuum
Palate in the oral cavity is located
hard palate is the roof of the mouth
Becomes the soft palate caudally
The soft palate separates the oropharynx from the nasopharynx
Pharynx
The oropharynx connects the buccal cavity with the esophagus
Esophagus is and function
a muscular tube
Peristalsis moves food from oral cavity to stomach
Two orientations of muscles in the esophagus- longitudinal and circular
4 layers of the esophagus and what they look like
Mucosa: the epithelium, lines the organ wall
Submucosa: connective tissue supporting the mucosa
Muscularis: the smooth muscle layer, allow distensibility and propulsion of lumen contents
Serosa: the serous membrane layer on the outside of the organ
Steps of swallowing (deglutition)
Starts as a voluntary action (not present if anesthetized) – food is pushed by the tongue back into the pharynx
Continues as an involuntary action
Reflex contraction of pharynx, movement of epiglottis to cover glottis, relaxation of esophagus to allow entry of food bolus.
Followed by peristalsis – a wave of muscular contraction along a tubular organ
Contraction of longitudinal and relaxation of circular muscles to open the lumen on the aboral (away from the mouth) side of the bolus
Contraction of the circular muscles on the oral side
Once in the stomach, there is a natural fold and tone in the cardiac sphincter of the stomach to help prevent reflux
In horses – this sphincter prevents vomiting as well
Steps of emesis
Relaxation of pyloric sphincter (found at distal end of stomach)
Reverse peristalsis to move ingesta from the SI into the stomach
Relaxation of cardiac sphincter
Inspiratory movement against a closed glottis + forceful contraction of abdominal muscles = vomiting
Closed glottis prevents aspiration
The soft palate directs food out of the mouth
Cardiac of the mono gastric stomach
Area surrounding the opening of the esophagus into the stomach
Fundus of the mono gastric stomach
A distensible, blind pouch, which can expand as more food is swallowed
Body of the monogastric stomach
Distensible end in the middle stomach
Antrum of the monogastric stomach
Distal portion of stomach
Grinds up food
Regulates acid production
Produces mucus
Pylorus of the monogastric stomach
Muscular sphincter that regulates the movement of chyme (semi-digested stomach contents) into the small intestine
Prevents backflow from small intestine into stomach
Shape of the monogastric stomach
The stomach is shaped like a C
Inside curve of the C is called the lesser curvature of the stomach
Outside curve is called greater curvature of the stomach
The mucosal lining of the stomach occurs as longitudinal folds called rugae
Ruminants ruminate their food by
they masticate, swallow, mix and ferment food in the rumen,
regurgitate and chew again (also called chewing the cud), then swallow again.
Usually graze, then lie down and ruminate
One rumination cycle lasting about 1 minute between regurgitation and reswallowing
Rumination allows relatively rapid food gathering (while watching out for predators), then later mastication (while safe and resting)
Very efficient fiber digestion: food is repeatedly mixed with saliva and ground to increase the surface area exposed to microbial activity in the rumen
4 stomachs of the ruminant stomach
Reticulum
Rumen
Omasum
Abomasum
Reticulum shape and function
Small
Most cranial compartment
Separated from rumen by rumenoreticular fold
Has honeycomb appearance to mucosa (increases surface area)
Coordinated contraction with rumen (reticulorumen contractions)
Rumen shape
Largest forestomach compartment
Occupies most of the left half of the abdominal cavity
Mucosa has a ‘pile rug’ appearance
Fermentation chamber (along the reticulum)
Separated into different compartments by rumenal pillars – essentially muscular sacs
Ruminal pillars do what
This assists mixing of rumen contents during contractions
Contractions occur in a synchronized manner
Controlled primarily by a vagus nerve of parasympathetic system
Also affected by rumen pH, presence of VFA in the rumen, consistency of the rumen contents, degree of rumen distension, and feedback degree from other areas in the GIT
Eructation is
is the expulsion of carbon dioxide and methane gas from fermentation that accumulates in the top of the rumen (gas cap).
Coordinated contraction of rumen and relaxation of esophagus
Rumen effects on starch and enzymes
During fermentative digestion, plant material is broken down by enzymes from microbes (bacteria, fungi and protozoa) in the rumen.
Cellulose convert cellulose to monosaccharides (simple sugars) and polysaccharides
Starch is also broken down into monosacchardies
Rumen fermentation
Microbes convert these saccharides to volatile fatty acids, methane and CO2
Protein is broken down by microbial proteases to amino acids
Amino acids are then used by microbes to make proteins, or are converted to VFA’s and ammonia (NH3)
Ammonia can be picked up by other microbes to synthesize new amino acids
Travels to liver, converted to urea, which is then used as a nitrogen source for rumen microbes
Can feed urea as another nitrogen source to boost protein made by microbes.
VFAs are absorbed where and do what
VFA’s = propionic acid, butyric acid, and acetic acid
VFA’s are absorbed across rumen wall and go to liver for conversion to glucose (mostly propionic acid) , to make adipose tissue and milk fats (dairy cattle) or are burnt for energy.
What happens to microbes after fermentation
Microbes eventually move with ingesta through the GIT and end up being digested in SI
These microbes provide an important protein source for the ruminant animal (microbial proteins!)
B vitamins and Vitamin K are also made in the rumen
What happens if the rumen is messed up
**It is extremely critical to maintain the correct balance of microbes, feed, pH, and gas production in the rumen
Any alteration can cause bloat, acidosis, and death
Includes sudden diet change, particularly more starch
Omasum shape and function
The third chamber of the ruminant stomach
Has lots of surface area due to presence of large mucosal folds – looks like leaves or pages in a book(often called the ‘butcher’s bible’)
Strong muscles in omasal wall – important for further mechanical breakdown
Also has absorptive function – VFA’s, water, and bicarbonate
Prevents neutralization of abomasal acid
The abomasum function and structure
The true stomach – similar to monogastric in structure and function
The young ruminant digestive tract
A milk diet does not require or lend itself to fermentation.
The rumen and reticulum of nursing calves are undeveloped and lack the microbial population necessary for efficient fermentation
Young ruminants have a reticular grooce or esophageal groove, which directs milk into the omasum when swallowed, bypassing the rumen and reticulum
Seems to work better if calf is suckling vs drinking from a bucket
How long the reticular groove functions depends on how soon the calf is introduced to grain and hay
Gastric secretions
Stomach submucosa contains gastric pits, glands which produce
Mucus
HCl
Enzymes
Hormones (gastrin)
Mucus secretions by the gastric system
Mix of mucin (produced by goblet cells in the gastric glands), water, and bicarbonate ions (secreted on the surface to neutralize stomach acid)
Necessary to protect stomach wall autodigestion due to pH of 2-3 in stomach
Is broken down by HCl so must be continuously secreted to prevent gastritis and ulcers