Anatomy and Digestion Flashcards
What is the alimentary canal?
This is a tube beginning with the mouth and ending at the anus in which digestion and absorption of nutrients occurs.
It has a tubular structure.
Lumen (digesta) is exterior to the body (i.e. the inside of the canal)
What is the gastrointestinal tract (GIT)?
This is the region of the alimentary canal that runs from the stomach to the colon.
What are the layers of the alimentary canal from innermost to outermost?
mucosa, submucosa, muscularis, serosa
Describe the mucosa
This is the innermost layer of the alimentary canal.
It is the interface with the lumen.
Absorption and secretion occurs here.
Describe the submucosa.
Structural and immune cells are found here
Describe the muscularis.
This is a muscle for motility. It helps move the digesta.
Describe the serosa.
This is the outermost layer of the alimentary canal and is the interface with the body.
What are the pregastric functions?
prehension, mastication, ensalivation, swallowing
What is prehension?
Grasping food and bringing it to the mouth.
Its mechanisms vary with behavior and diet.
In some animals, the importance of incisor integrity is key.
What is mastication?
Mastication is the physical reduction of feed.
It is especially important in nonruminant herbivores.
Describe salivation and the glands associated with it.
Three main glands secrete fluids with different compositions. The relative size of these glands differs between species.
The three glands are: parotid, sublingual, and the submaxillary (aka submandibular)
Describe the parotid gland.
This gland secretes a serous (watery) mixture containing water, enzymes, and ions.
Describe the sublingual gland.
This gland secretes mucous, and mucus (mucin) is its main constituent.
Describe the submaxillary gland.
This gland secretes a mixed liquid comprised of mucus, ions, enzymes, and water.
What are the functions of saliva?
Salvia…
- moistens feed (via ions and water)
- lubricates food (aids in swallowing)
- aids in starch digestion (amylase)
- buffers rumen pH
- helps recycle nitrogen (urea) in ruminants
- other specialized functions
ex. Draculin, an enzyme secreted in vampire bats’ saliva, prevents blood from coagulating
Describe swallowing (deglutition).
Swallowing is a reflex initiated by the presence of food in the pharynx. The action stops respiration.
Propulsion of food to the stomach then occurs via esophageal peristalsis.
The reflex of swallowing is the most similar among species.
What are the major functions of gastric digestion in a nonruminant?
- mixed and mechanical breakdown of feed (further breakdown after mastication)
- hydrolytic digestion by acid enzymes (especially of protein)
- reservoir for controlled release of digesta to the small intestine
Describe the stomach.
The size and shape varies among species.
It is lined by nonglandular or secretory (aka glandular) epithelium that secretes acid and enzymes.
Its functions are storage, mixing, and partial digestion of food.
It has a limited absorptive capacity, and can absorb some things like drugs or alcohol.
Describe the four regions of the stomach.
Esophageal: nonglandular portion that connects directly to the esophagus
Cardiac: secretory or glandular portion that has mucus producing cells for lubrication and protection on the stomach lining from acid. It is the top portion of the stomach.
Fundus (aka Fundic): a secretory portion covered with gastric pits. These pits contain chief (peptic) cells with secrete proteolytic enzymes like pepsinogen, as well as parietal cells, which secrete HCl. HCl activates pepsinogen to pepsin and drops the stomach pH.
Pyloric: contains mucus secreting cells and endocrine G cells, which secrete the hormone gastrin. The gastrin stimulates HCl production by the parietal cells in the fundus.
What are the three phases of gastric secretion?
cephalic, gastric, intestinal
Describe the cephalic phase.
There is a vagal reflex, this phase is involuntary and is controlled by the brain.
There is increased gastric motility, enzyme secretion (pepsinogen), and HCl secretion.
Describe the gastric phase.
This phase begins when food enters the stomach.
It is a local reflex that depends on the presence of food in the stomach.
It is reinforced by gastrin, a peptide hormone secreted by the stomach.
The gastric phase sees the increase of HCl and pepsinogen secretion.
Describe the intestinal phase.
This phase begins with the presence of food in the small intestine.
It is stimulated by duodenal distension, which tells the brain to decreases stomach secretions to prepare for absorption.
It is also stimulated by H+, osmolarity, and nutrients.
There is a decrease in HCl secretion and gastric motility.
The enzymes secretin and CCK are released.
Describe gastric motility and the emptying of the stomach.
Motility aids in mixing, mechanical, and hydrolytic reduction of feed to chyme.
Emptying is stimulated by distension of the antral wall (the region near the pylorus) and the presence of liquid chyme.
What does the pancreas secrete and what is its function?
The pancreas secretes enzymes and bicarbonate.
The bicarbonate’s function is to neutralize HCl entering the small intestine from the stomach. It is a pH buffer that allows pancreatic enzymes to function without being denatured by the low stomach pH.
The enzymes function to digest carbs, fats, proteins, and nucleic acids.
The functions of the pancreas are exocrine functions.
What does the liver secrete and what are its functions.
It secretes bile salts, bicarbonate, and organic waste products.
The bile salts function to solubilize water-insoluble fats.
Bicarbonate neutralizes HCl entering from the stomach.
Organic waste in eliminated in feces.
Describe bile salts.
Bile salts are made in the liver from cholesterol, but they are stored in the gallbladder.
They help solubilize fats.
Discuss the small intestine.
The small intestine varies in length among species.
The majority of digestion in the GIT occurs here, and lots of absorption happens here as well.
It adds secretions to the digesta.
The portions of the small intestine are the duodenum, jejunum, and ileum.
Describe the cells found in the small intestine.
The types of cells in the lumen of the small intestine include:
- absorptive
- mucus secreting
- endocrine
- stem cells
Like the stomach, there are glandular and non-glandular cells.
There is a very fast turn over rate of cells that occurs every 3-6 days.
What does the duodenum do?
This is the site of addition of many digestive juices.
- secretions from enterocytes (ex. lactase, sucrase)
- pancreatic juices (enzymes and bicarbonate) from common bile duct
- bile secretions (biles salts) from common bile duct
Define enterocyte
cells of the intestinal lining
What does the jejunum do?
The jejunum is where most of the absorption occurs.
The compounds must be simple enough to be absorbed.
Further digestion occurs here if needed.
The jejunum is filled with folds, villi, and microvilli which increase the absorptive surface area of the small intestine.
What occurs in the ileum?
Less absorption happens here, but there is an absorptive capacity present if needed.
The ileum contains gut associated lymphoid tissue (GALT).
Describe GALT
Gut Associated Lymphoid Tissue
This is the intestinal immune system present in the ileum.
It is responsible for the formation of Peyer’s patches.
Peyer’s patches: immunological tissue which samples contents of the GI tract and protects the host. It is an aggregation of lymphoid tissue.
Describe the large intestine.
Consists of the cecum, colon, and rectum.
The size and shape of the large intestine varies among species.
Herbivores have more total capacity than omnivores or carnivores. This is especially true in regards to non-ruminant herbivores.
The ratio of the cecum to colon is variable.
In humans, the cecum is a blind pouch called the appendix.
What are the functions of the large intestine?
The large intestine has a high capacity for water absorption.
Little enzyme of hormone secretion occurs here.
In non-ruminant herbivores that are hindgut fermenters, there is considerable bacterial fermentation in the cecum and colon. This leads to the absorption of volatile fatty acids (VFA’s), but not protein and vitamins produced by bacteria.
Define nutritional ecology.
The adaptation of animals to their environments by development of dietary habits and physiological mechanisms that allow them to exploit available food sources in their habitats.
ex. Darwin’s Galapogos finches
Differentiate between herbivores, omnivores, and carnivores.
These are examples of dietary habit.
Herbivores: consume only plant matter (ex. cows)
Omnivores: consume plant and animal material (ex. pigs)
Carnivores: consume only animal material (ex. lions)
Discuss the sub-categories by dietary habit.
a. obligate vs. facultative (ex. cats are obligate carnivores)
b. digestive anatomy or physiology (ex. ruminants vs. nonruminants)
c. specified food source (ex. frugivore, folivore, insectivore)
d. way in which they eat (ex. selector vs. non-selector, browser vs. grazer)
Give some examples of pregastric adaptations to food sources.
Prehensile adaptations
- forelimbs, snouts, tongues, lips
Masticatory adaptations
- large canines and incisors, specialized molars, relative toothlessness of endentates (anteater, sloth, armadillos)
Deglutition
- varies little with diet, but quantity and composition of saliva varies considerably
How does gastric capacity and structure vary among species?
a. capacity is greatest in pregastric fermenters (stomach=reservoir)
b. small stomach in carnivores related to nutritive density of diet
c. distribution and composition of epithelial lining varies between species and dietary adaptations