Comparative Gastrointestinal Anatomy Flashcards
GI tract
The organ system, glands, and structures responsible for consuming, digesting, absorbing, and secreting/excreting
Another name for the GI tract
Alimentary or digestive tract
Chyme
Semi-fluid mixture of digestive secretions and semi digested food in the stomach
Diverticulum
Sac/pouch formed in wall of alimentary tracts
Sacculated
Formed of/divided into sac-like pouches
Prehension
Getting food in the mouht
Rumination
Controlled form of vomiting, allowing half-liquid materials to be brought back up the esophagus, swallowing the liquid and deliberate re-mastication of and swallowing of the bolus formed in the process
Foregut
The stomach + small intestin
Hindgut
Cecum, colon and rectum
Enteroendocrine hormone
Peptide that is synthesized primarily in cells of the digestive tract and influences the activity of organ digestives in a hormone manner
Hysodont teeth
Keep growing
Brachydont teeth
Are not replaced, do not keep growing
Three main functions of the GI tract
Digest/absorb Prevent entry of pathogens Eliminate waste (material and toxins)
Three classifications of animals based on their GI tracts
Simple nonruminants
Nonruminant herbivores
Ruminants
GI tract of simple nonruminants
Pouch-like, non-compartmentalized stomach, do not depend on microbial digestion in any part of the gut
Another name for simple nonruminants
Mono-gastric
GI tract of non-ruminant herbivores
Has modifications to facilitate microbial fermentation, many of the same functions performed as in the rumen
Three groups of nonruminant herbivores
Foregut fermenters
Colon fermenters
Cecal fermenters
Foregut fermenters GI tract
Compartmentalized stomach with one or more pouch where microbial fermentation occurs, it is separate from the glandular stomach
Colon fermenters GI tract
Have an enlarged colon for microbial fermentation
What is a disadvantage of colon fermentation
It is less efficient than rumen fermentation because of the anatomical location
Since the microbe’s in the hind gut get the stuff the animal cannot digest, it is a less favorable nutrient environment and the products are less available to the host animal
Cecal fermenters GI tract
Have a large, muscular blind pouch
What is cecotrophy
Small herbivores consume their soft feces which contain well-fermented material from the cecum rich in protein and vitamins, this results in normal hard pellets
What are the four basic layers/tunics of the GI tract
Tunica serosa
Tunica muscularis
Tunica submucosa
Tunica mucosa
What is the mesentery
The fusion of the tunica serosa in the abd cavity
What is the function of the mesentary
Houses vascular and nervous supplies to the digestive tract
What is the tunica serosa referred to as in the abdominal cavity vs esophagus and rectum
abd: visceral peritoneum
esophagus/rectum: tunica adventitia
What is the function of the tunica muscularis
Contraction (peristalsis)
What is the distinction between in the two layers of the tunica muscularis
The inner layer are circular fibers, the outer layer are longitudinal fibers
What is found between the two layers of the tunica muscularis
The myenteric plexus
What is the myenteric plexus
Controls the frequency and strength of contraction, part of nervous system
What does the tunica submucosa contain
Blood and lymphatic vessels, and the submucosal plexus
What is the function of the submucosal plexus
Provides nervous control to affect mucosal glandular secretions, motility and blood flow
What/where is the lamina propria
In the mucosa layer, houses blood vessels and lymphatics that supply the epithelium
What/where are the GALT
In the mucosa layer, important for immune functions
What/where is muscularis mucosae
In the mucosa layer, responsible for movement of villi in the small intestine
What are the two types of contractions in the GI tract
Segmental and peristaltic
Segmental contractions
Squeezing of the bolus so that it is always being mixed as it moves down the intestine
How is segmental contraction acheived
The contraction and relaxation of circular smooth muscles
Peristaltic contractions
Propel a bolus down the GI tract away from the oral cavity
How is peristaltic contraction achieved?
Contraction of outer longitudinal muscles and inner circular muscles behind the bolus, and relaxation of these muscles ahead of the bolus
What are 5 functions of the oral cavity
Prehension, salivation, mastication, taste and formation of a bolus for swallowing
Three structures used for prehension
Lips, tongue, teeth
What is the chief prehensible organ in cattle
Tongue
What are the objectives of mastication
Reduce size, increase surface area, soften, lubricate
What has hypsodont teeth
Ruminants and horses
What has brachydont teeth
Dogs, cats and humans
The rostral two thirds of the tongue is sensitive to…
Temperature, touch, pain
The caudal one third of the tongue is…
Innervated by nerves that carry taste sensation from the taste buds
What are the 5 tastes
Salty, sour, sweet, bitter and umami
What is the composition of saliva
99% water, 1% mucin, salts digestive enzymes and lysozymes
Acini
Basic secretory units of salivary glands
What are the two types of acinar epithelial cells
Serous cells and mucous cells
What are some functions of saliva
Aids in bolus formation, keeps mouth moist, aids in taste, provides enzymes, control bacterial populations
What is an additional function of saliva in ruminants
Source of N, P and Na which are used by rumen microorganisms and aid in maintaining the pH of the rumen
What are three salivary glands, their locations, and their products
Submandibular (base of tongue) - mix of serous and mucous secretion
Sublingual (under tongue) - mostly mucous
Parotids (below ears) - mostly serous/watery
Muscle type in the esophagus
Striated (all in cattle and sheep), smooth muscle in some locations (in cats, horses and humans)
What controls salivary secretions
Parasympathic stimulation and secretin
Mucins prevent…
Foaming (bloat)
What binds the esophagus
Upper and lower esophageal sphincters
What keeps the lower esophageal sphincter shut
Gastrin and vagal parasympathetic stimulation
What causes the lower esophageal sphincter to relax
Response to the presence of a bolus
What is the esophagus lined with
Stratified squamous epithelium
4 functions of the stomach
Storage/release, mechanical breakdown, digestion, clotting of milk
4 glandular regions in the stomach
Esophageal, cardiac, peptic/fondus, pyloric
Esophageal area of the stomach
Extension of esophagus, no glands, alpha-amylase activity
Cardiac region of the stomach
Mostly mucus
Peptic region/fondus of the stomach
Covered with gastric pits, produce a mix of acid, enzymes, mucus and hormone, largest compartment
What are the 3 main cell types of the fondus and what to they produce
Chief/peptic cells (pepsinogen and renin)
Parietal/oxyntic cells (hydrochloric acid)
Mucous surface and neck cells (mucus)
Pyloric region of the stomach
Before entry to small intestine, lined by cells that produce mucus and buffer, has enteroendocrine cells that produce hormones
Pyloric sphincter
Controls the rate at which the stomach empties
What is an example of an entereoendocrine cell
G cells
3 factors that control acid secretion by parietal cells
Histamine production when pH gets too high - stimulates acid secretion
Gastrin in response to distension and rise in pH - stimulate acid secretion
Parasympathetic afferent vagal nerve
Stomach motility is increased when…
Gastrin and parasymp. vagus in response to distension
Stomach motility is decreased by…
Distension of duodenum
Increase in osmolarity in the duodenum
CCK (cholecystokinin) secreted in response to fats and amino acids in the duodenum
Release of secretin in response to reduction in pH in the duodenum
What is the crop
A diverticulum of the esophagus, holds food
Why is the crop a site of digestion
Continued action of salivary amylase and because of microbial activity
Proventriculus
Glandular stomach
Gizzard/ventriculus
Muscular stomach, grinds food
What is the koilin layer
Coats the muscular stomach, protects from gizzard erosion
What stimulates vagal efferent activation of stomach muscle contraction
Distension of the fundus
What is the function of the small intestine
Digestion and absorption of nutrients
What are the 3 parts of the small intestine
The duodenum, jejunum and the ileum duodenum
Villi
Projections of the tunica mucosa in the small intestine into the lumen
Crypts
Invaginations of the tunica mucosa of the small intestine (opposite of villi basically)
What are found at the tips of mirovilli
Glycocalyx
Brush border
Made up of the mircovilli and glycocalyx of each villus
Each villus contains…
Arteriole and venules, together with a drainage tube of the lymphatic system a lacteal
Where do the venules drain
Hepatic portal system
Where do lacteals drain
Thoracic lymphatic duct
What are 3 cell types in crypts
Enterocytes, goblet cells and enteroendocrine cells
How many cells slough off the normal villous tip each day
1400
The duodenal area is the site of….
Mixing and secretion
The jejunal area is the site of…
Absorption
What are Brunner’s glands and what are they controlled by
Produce alkaline secretion that acts as a lubricant in the duodenum to protect it from the HCl from the stomach
Controlled by secretin when the pH of the fluid falls too low (too acidic)
What are some functions of the enterocytes in the crypts
Sodium secretion provides an electrochemical gradient needed to allow absorption
Water secretion reduces osmolarity of digesta
What is the primary stimulus of contraction of the small intestine
Distension
What are the first contractions of the small intestine to occur
Segmental
What moves the bolus through the small intestine
Peristaltic contractions
What stimulates small intestine motility
Gastrin and CCK
What slows small intestine motility
Secretin
What is the function of the liver
Secrete bile to digest fats
What is the portal triad
Hepatic artery, portal vein and bile ducts in the liver
Where is bile secreted and what is it made up of
Into the duodenum through bile duct
Made of salts of bile acids, phospholipids, and bile pigments
What is bile production stimulated by (and contraction of gall bladder)
CCK
What are the small spaces between adjacent hepatocyte membranes
Canaliculus - where bile is secreted into
What happens with bile secretion in rats and horses
They do not have a gall bladder so bile flows into the duodenum continuously.
What is the exocrine function of the pancreas
Provide enzymes needed for digestion secreted from acinar cells (secreted in inactive form)
Function of the large intestine
Absorption of water, secretion of inorganic elements, microbial fermentation, VFAs production, B-complex vitamins, forms feces
What are the 3 parts of the large intestine
Cecum, colon and rectum
What is a benefit of bacterial action in the large intestine
Synthesis of B vitamins that can be used by the host
What species have an ileocolic sphincter and what is its function
Ruminants, cat and dog
Passage for material from the ileum to the large colon
What species have and ileocecal sphincter and what is its function
Horse, pig, rabbit, elephant and rats
Place where the ileum empties into the cecum
What causes the sphincters in the large intestine to relax
Distension of the ileum and gastrin
What contractions take place in the ascending colon
Segmental or peristaltic
Antegrade contractions
Move material forward
Retrograde contractions
Keep material in the cecum longer for more extraction
