Flashcards in Test yourself ?s Chpt. 11 The Digestive System Deck (48):
How do diets differ among herbivores, carnivores, and omnivores? To which group would cats, horses, cows, and humans belong?
Herbivores: Plant-eating animals, such as cattle, sheep, and goats
Carnivores: Meat-eating animals, such as cats
Omnivores: Plant- and Meat-eating animals, such as pigs and humans)
What are the "lower arcade" and the "upper arcade" in reference to teeth? What bones of the skull are associated with each of these?
Upper arcade: Teeth in the upper part of the mouth contained by the MAXILLA and INCISIVE BONES of the skull
Lower arcade: Teeth in the lower part of the mouth contained by the MANDIBLE
What are the four types of teeth? Where are they located, rostral to caudal?
1. Incisors: Most rostral teeth of the upper and lower arcade
2. Canine teeth (when present): Located at the corners of the incisors
3. Premolars: Rostral cheek teeth
4. Molars: Caudal cheek teeth used for grinding
Define lingual, palatal, labial and buccal surface of teeth
Lingual: "inner" surface of lower arcade facing towards the tongue
Palatal: "inner" surface of upper arcade facing towards the hard palate at roof of mouth
Labial: "outer-facing" surface of upper and lower arcade at front of mouth
Buccal: "outer-facing" surface more caudal in mouth
What are deciduous teeth?
Why do ruminants have a dental formula that has a zero after the I and the C?
They do not have any upper incisors or canine teeth. Instead, they have a dental pad, which is a flat, thick, connective-tissue structure on the maxilla opposite the lower incisors and canine teeth
Where are the apex, root, pulp, cementum, dentin, and enamel of a tooth located? What is the gingiva?
Apex: At the bottom or root of the tooth, where the blood and nerve supply enter
Root: At the bottom of the tooth
Pulp: In the center of the tooth made up by the blood and nerve supply
Cementum: Covers the root of the tooth, it's a hard connective tissue helps fasten the tooth securely in its bony socket
Dentin: Surrounds the tooth pulp inside the tooth
Enamel: Covers the crown, it's the hardest, toughest tissue in the body
Gingiva: Epithelial tissue forming the gums around teeth
What are amylase and lipase? From where in the mouth do they come? What do they do?
They are both enzymes that digest and/or break down.
They are found in saliva produced by the salivary glands.
Amylase: Breaks down amylose, a sugar component of starch
Lipase: Digests lipids
What effect does the parasympathetic nervous system have on the mouth? The sympathetic nervous system?
Parasympathetic: Stimulation of this results in increased salivation (e.g. anticipation of eating?
Sympathetic: Stimulation of this (either through fear or preanesthetic drugs e.g.) produces "dry mouth"/decrease in saliva production
What is peristalsis? How does it differ from segmentation?
Peristalsis: Smooth muscle contraction moves contents along the digestive tract
Segmentation: Smooth muscle contraction mixing the GI tract contents, thus aiding digestion and absorption, and slowing movement through tract
What are the cardia, fundus, pyloric antrum, and pylorus of the stomach? What are each of their functions?
Cardia: Located at the top of the stomach where the esophagus and stomach meet. Surrounded by a weak sphincter of smooth muscle. Aids as a natural valve to prevent reflux.
Fundus: Section of the stomach that forms a distensible, blind pouch that expands as more food is swallowed.
Pyloric antrum: Distal part of the stomach that grinds up swallowed food and regulates the hydrochloric acid that is produced by the fundic and body parietal cells
Pylorus: Muscular sphincter regulating movement of chyme (digested stomach contents) from stomach into duodenum (first part of small intestine) and prevents backflow of duodenal contents
Describe what each of these cells produces and what their products do:
1. Parietal cells
2. Chief cells
3. Mucous cells
4. G cells
1. Parietal cells: produce hydrochloric acid
2. Chief cells: produces an enzyme precursor called pepsinogen
3. Mucous cells: produce protective mucus
4. G cells: secrete hormone gastrin, this stimulates the release of hydrochloric acid from the parietal cells
How does motility differ in the fundus versus the body or pyloric antrum?
The proximal part of the stomach (fundus and body) relax with swallowing of food, allowing stomach to distend and fill (act as reservoir). Body of stomach also contracts to help mix food.
The distal part of the stomach (pyloric antrum) increases contractions with swallowing. It's responsible for most of the grinding activity in the stomach, moving food towards the pylorus.
Explain the effect that each of the following has on gastric motility:
2. Increased acidity in the duodenum
4. Cholecystokinin (CCK)
1. Gastrin: Upon swallowing food, gastrin signals the fundus to relax so that the food can be accomodated
2. Increased acidity in the duodenum: Inhibits stomach contraction and prevents the stomach from pushing its contents into the duodenum before the small intestine is ready to handle additional chyme. This is also known as the enterogastric reflex.
3. Secretin: It's a hormone released from the duodenum. Also causes fundus to relax, but can inhibit peristalsis of body and antrum of stomach as well, to slow gastric emptying.
4. Cholecystokinin (CCK): This hormone is released by the presence of large amounts of fat or protein in the duodenum. It decreases contraction of the antrum, body and the fundus.
What's the relationship between pepsinogen and pepsin? What does pepsin do?
Pepsinogen is secreted by chief cells and is a precursor for the enzyme pepsin.
Hydrochloric acid converts pepsinogen into pepsin, which is a protein-digesting (or proteolytic) enzyme in the lumen of the stomach.
Pepsin breaks down proteins forming chains of amino acids.
What is the difference between the terms mucus, mucous, and mucin? What role does bicarbonate play in the mucous layer?
Mucus is the noun, the substance.
Mucous is the adjective, the description of it.
Mucins are complex molecules produced by goblet cells in the gastric glands, and are the main constituent of the mucous coating.
Bicarbonate ion is secreted onto the surface together with the mucins. Bicarbonate makes the mucous coat more alkaline. Through this process, hydrochloric acid contacting the mucus is neutralized to some degree.
What are the three receptors on the parietal cells that stimulate hydrochloric acid production?
The receptors are for gastrin, acetylcholine and histamine on the "blood" side of the parietal cell.
Stimulation of all three results in the optimum amount of hydrogen and chloride secretion.
How does the stomach know when to stop producing acid?
When the pH of the stomach contents in the antrum drops below 3, gastrin release is inhibited. With this, one of the three key stimulants for hydrogen and chloride production is terminated, and hydrochloric acid production declines.
What effect do prostaglandins have on (1) mucus production, (2) gastric blood flow, and (3) the ability of the stomach to heal itself?
1. They stimulate cells in the gastric glands to produce the bicarbonate ion, which helps make the mucous layer capable of neutralizing the stomach acid to some degree.
2. They enhance blood flow to the stomach.
3. All of the above, plus the PGs stabilizing potentially destructive lysosomes within the gastric cells and regulating the activity of macrophages and mast cells, help the stomach to rapidly repair any damage to the stomach epithelial lining caused by a break in the mucous barrier.
Explain how NSAIDs produce side effects in the GI tract.
They block the production of PGs, which can result in a stomach ache.
What are the four compartments of the ruminant stomach? Which ones are forestomachs and which one is the true stomach?
The reticulum, rumen, omasum and the abomasum.
The abomasum is the true stomach, the other three are the forestomachs.
What is hardware disease? With which forestomach is hardware disease usually associated?
Swallowed, heavy objects (such as wire, metal fragments, stones, etc.) settle into the reticulum, due to its location. When the reticulorumen contractions occur, the objects may penetrate the wall of the reticulum, causing a condition known as hardware disease.
What is rumination versus eructation? What purpose do they serve?
1. Rumination: Partially digested plant food (cud) is regurgitated up to the esophagus, where it is chewed and reswallowed. This process facilitates the mechanical breakdown of tough plant material through multiple chewing cycles, resulting in a greater surface area on which the rumen microbes and digestive enzymes can act.
2. Eructation: Built-up carbon dioxide or methane gas is expelled from the rumen. This is essential for dispelling excessive gas created by fermentation, thereby reducing the risk of too much gas being trapped in the rumen (a condition called bloat).
What is fermentative digestion? How is it different from nonfermentative digestion?
Fermentative digestion: Found in ruminants. Rechewed (remasticated) plant material is fermented by bacterial and protozoal enzymes. Ruminants depend on these microbes for their nutritional needs.
Nonfermentative digestion: Found in monogastric animals. The enzymes needed for digestion are produced by glands in and along the intestinal tract.
What is the relationship among cellulose, pectin, cellulase, glucose, and VFAs?
Cellulose and pectin are digested by cellulase enzymeson rumen bacterial surfaces and transformed into much simpler monosacchrides or polysacchrides.
The glucose derived from this process is converted biochemically to volatile fatty acids (VFAs).
These VFAs are rapidly absorbed into the bloodstream and the liver converts selected ones to glucose.
The other absorbed VFAs are used to produce adipose tissue, milk fat, and other essential components required by the ruminant body.
What is the relationship among proteases, peptides, and amino acids?
Proteases (enzymes that break down proteins) reduce the long proteins to short peptides (short chains of amino acids) and the amino acid building blocks of the peptides and proteins. The resulting amino acids and peptides are also used by the rumen's microbes.
What role does urea play in the rumen function? Which organ converts ammonia to urea?
The liver converts ammonia to urea.
Additional nitrogen, necessary for rumen microbes, comes from the production of urea by the liver. It gets there via the bloodstream and saliva.
How is the young calf's GI tract different from the adult's? What is the role of the reticular groove?
Rumen and reticulum are small at birth and essentially nonfunctional. Little or no fermentative digestion occurs while the animal is primarily receiving a milk diet (nursing).
The reticular groove, also called the esophageal groove, is a trough in the wall of the reticulum that extends from the esophageal opening to the opening of the omasum. When the calf nurses, the muscles associated with the groove contract and form a tubular structure that brings the liquid directly to the omasum, bypassing the rumen and reticulum.
What are the three segments of the small intestine? Which is usually the longest?
Duodenum, jejunum, and ileum, with the jejunum usually being the longest.
What does the ileocecal sphincter do?
Ileum and colon are separated by the ileocecal sphincter. It is an anatomical and functional muscle that regulates movement of materials from the small intestine into the colon or the cecum.
What are villi, microvilli, brush border, and crypts? How do they aid digestion and absorption of food?
Villi: Tiny, cylindrical, fingerlike projections.
Microvilli: Thousands of these can be found on the villi. They resemble short bristles on a brush.
Brush border: Layer of microvilli
Crypts: Invaginations in the intestinal mucosa surrounding each villus. They constantly produce cells that are pushed up the villus to replace the oldest cells, which are constantly shed at the tip of the villus.
All of these aid in digestion and absorption of food as they increase the absorption area for nutrients.
What is the role of segmental contractions in the small intestine? Why do animals get diarrhea if segmental contractions are decreased?
They mix the intestinal contents and slow their movement through the length of the intestine.
Peristalsis push ingesta forward, if segmental contractions decrease there is nothing slowing down the flow of ingesta and this results in diarrhea.
1. What is ileus? What causes it?
2. Why would antiparasympathetic drugs like atropine cause it?
1. Ileus happens when there is a decrease in peristaltic waves resulting in ingesta moving too slowly through the intestinal tract.
2. Because things like disease or stress (associated with the sympathetic nervous system) inhibit peristalsis, so antiparasympathetic drugs would do the same.
What do CCK and prostaglandins do to the small intestine?
They stimulate and/or increase intestinal motility and secretions.
What are polysacchrides, disacchrides, and monosacchrides? Give examples of each. What enzymes break down each of these?
Polysaccharides: Complex carbohydrates (Starch, Glycogen, ...). Amylase breaks down starch into disaccharides.
Disaccharides: Two sugars (Sucrose, maltose, isomaltose, and lactose). Sucrase, maltase, isomaltase, and lactase break down disacchrides into monosaccharides.
Monosacchrides: One sugar (Glucose, galactose, and fructose)
What are proteases? What protease is produced by the stomach? What effect do proteases have on polypeptides?
Proteases are protein-splitting enzymes.
The pancreas produces five basic protease enzymes: trypsin, chymotrypsin, elastase, aminopeptidase, and carboxypeptidase.
They break apart some of the protein chains into smaller chains called polypeptides for better absorption.
Explain how each of the following plays a role in digestion of fats: emulsification, bile acids, liver, pancreatic lipase, triglycerides, glycerol, fatty acids, monoglycerides, and micelles.
Emulsification and micelle formation: Breaking down fat globules into smaller pieces for adequate digestion.
Bile acids: Keep droplets (smaller pieces of fat) from forming back into globules.
Liver: Produces bile
Pancreatic lipase: Penetrates the bile acid coating and digests the fat molecules to produce glycerol, fatty acids, and monoglycerides.
Triglycerides: The fat molecules being digested by the pancreatic lipase
Glycerol, Fatty acids, monoglycerides: Produced by the digestion of fat molecules (triglycerides)
Why do some animals get diarrhea when their diet is changed suddenly?
This is caused by the changing needs for appropriate numbers and types of digestive enzymes to match the changing demands of the diets.
Changing diet suddenly can result in a greater amount of food being incompletely digested. The presence of this retains water within the lumen of the intestine, producing diarrhea.
What are haustra?
A series of lined up sacs inside the cecum
How do microbes in the colon and cecum use carbohydrates and proteins? How does this compare with how microbes in the rumen use them?
A significant percentage of ingested carbohydrates makes it through the small intestine to the cecum and colon. Proteins are digested in the horse's small intestine; thus less protein nitrogen is available to the colonic microbes than would be available to rumen microbes. However, like the ruminant, the nitrogen needs of the colonic microbes are supplemented by the liver's secretion of urea into the GI tract.
One of the differences between the rumen and the equine colon, however, is that acids must be buffered by the secretion of bicarbonate directly into the colon and cecum (the bicarbonate ions secreted in the saliva buffers the rumen).
What role do stretch receptors, internal and external sphincters, and receptors in the anal mucosa play in defecation?
As the rectum fills and distends, stretch receptors in its wall cause partial relaxation of the internal sphincter. This allows fecal contents to move briefly into the internal sphincter canal, where they make contact with the anal mucosa and stimulate mucosal receptors. This increases the sense or need for defecation. As the rectum distends further, the internal sphincter opens for longer periods, allowing more time for anal mucosa to contact fecal material, which further increases the conscious need for defecation. When defecation finally occurs, the voluntary motor impulses to the external sphincter are inhibited, allowing it to relax.
What does it mean to be fecally incontinent?
If the integrity of the anal sphincter is infiltrated or disrupted, the animal can be rendered fecally incontinent or unable to control defecation.
What are hepatic lobes and lobules? What is the hepatic portal system?
The liver is divided into several hepatic lobes, which are further divided into microscopic lobules.
The blood vessel system that transports blood from capillaries in the intestines to hepatic capillaries is called the hepatic portal system.
The liver plays an important role in filtering materials absorbed from the GI tract before they have a chance to reach the systemic circulation.
What produces bile? Where is it stored? How does it reach the intestine? What stimulates bile to be secreted into the small intestine?
Bile is produced by hepatic cells.
The gallbladder is a storage compartment for bile.
Stimulation of the gallbladder by CCK during digestion causes the gallbladder to contract, thereby forcing bile down the common bile duct into the duodenum.
In some species the common bile duct fuses with the pancreatic duct before entering the duodenum.
What is glycogenesis, glycogenolysis, and gluconeogenesis?Where do these occur? What is produced by each process?
The glucose absorbed from the GI tract may be stored in the liver as glycogen through a process called glycogenesis. There, the glycogen acts as a storage pool for glucose molecules.
If the body needs glucose, the glycogen is broken down by the liver (a process called glycogenolysis), and the glucose is moved into the blood.
Glucose also can be made in the liver from amino acids through a process called gluconeogenesis.
In addition to digestive enzymes, what else does the pancreas secrete into the duodenum? What is the role of this secretion?
It also secretes significant amounts of bicarbonate into the duodenum, which helps neutralize the acid contents coming from the stomach and maintains a pH in the duodenum at which the pancreatic enzymes can function.
What impact do insulin and glucagon have on blood glucose concentrations?
Insulin and Glucagon are two hormones secreted by the pancreas that help regulate blood glucose levels from food that has been digested and absorbed.
The combined effects of insulin and glucagon result in blood glucose being tightly regulated in a specific concentration range, despite varying demands for glucose by the body and changes in carbohydrate in the diet.