Term
| What is the function of the gastrointestinal tract? |
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Definition
The function of the gastrointestinal tract is to reduce the consumed food stuffs to simpler molecules and to transfer them to the blood so that they can be delievered to the cells for metabolism. The gastrointestinal tract must also absorb other essential minor nutrient (e.g salts, vitamins) so that they are available to the cells of the body. |
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Term
| What are the characteristics of the gastro-intestinal tract? |
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Definition
Characteristics are: -Long smooth muscle tube extending from mouth to anus -The tube has two distinct layors: Circular and longitudinal -Lined with epithelia that function as selective barriers between the lumen and the body fluids
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Term
| What is gastrointestinal motility? |
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Definition
Gastrointestinal motility: is the ability for the smooth muscle in the gastrointestinal tract to force digesta to move through the tract.
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Term
| What are the three mechanisms that regulate gastrointestinal motility? |
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Definition
1. Autonomic Nervous System 2. Gastro-Intestinal Hormones 3. Enteric Nervous System
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Term
| What are Enteroendocrine cells? |
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Definition
Enteroendocrine cells are responsible for Gastrointestinal hormones that are released from endocrine cells in the epithelial lining of the gastrointestiinal tract and may stimulate or inhibit gastrointestinal smooth muscle
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Term
| Why are Gastro-Intestinal Hormones usually released? |
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Definition
Gastro-Intestinal Hormones are usually released in response to digesta in the lumen of the tract. These hormones are a means of local regulation that is coordinated with the ingestion and digestion of food.
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Term
| What does the enteric nervous system consists of? |
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Definition
The enteric nervous system consists of neural plexuses between layers of smooth muscle in the wall of the tract.
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Term
| What do the neural plexuses in the enteric nervous system consist of? |
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Definition
The neural plexuses contain complete neurons (dendrites, cell bodies, and axons) that can form complete neural and reflex circuits in the wall of the tract, so that nerual regulation can be independent of external innervation.
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Term
| What does the presence of food and distension of gastrointestinal tract segments act as? |
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Definition
The presence of food and distension of gastro intestinal tract segments act as stimuli to initiate activity of the enteric nervous system.
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Term
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Definition
| The act of bringing food into the mouth. |
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Term
| What does saliva consist of? |
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Definition
| Saliva consists of water, electrolytes, mucus, and enzymes. The water and mucus soften and lubricate the ingesta to facilitate mastication and swallowing |
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Term
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Definition
| Lysozyme is a salivary enzyme with antibacterial actions. |
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Term
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Definition
| The starch digesting ezyme that is present in the saliva of omnivores and to a limited degree in horses but absent in ruminants and carnivores. |
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Term
| About how many liters of saliva do adult cattle secrete each day? What does this large volume of fluid do for the ruminant? |
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Definition
Adult cattle may secrete up to 200 L of saliva per day. This large volume maintains the fluid consistency of the rumen contents, and components of the saliva may also prevent frothing of the rumen fluid. Ruminant saliva has a relatively high pH and contains high concentrations of bases (bicarbonate and phophate). These bases neutralize acids produced by fermentation in the rumen so that the pH in the rumen does not become too acidic. |
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Term
| What do the parasympathetic nerves do for the salivary glands? |
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Definition
Para Sympathetic nerves are the efferent limbs of neural reflexes that regulate salivary secretion. Afferent inputs that stimulate salivary secretion include sight and smell of food, presence of food in the oral cavity, and conditioned reflexes, were some event is associated with food and feeding.
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Term
| What is Deglutition and what are the three stages? |
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Definition
Deglutition is the act of swallowing. -The first stage is passage of food or water through the mouth -The second stage is passage through the pharynx -The third stage consists of passage throuh the esophagus into the stomach
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Term
| What happens in the first stage of deglutition? |
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Definition
-Swallowing is under voluntary control 1. the food is chewed and mixed with saliva and creates a bolus 2. The bolus is moved to the upper surface of the tongue 3. The tongue is raised against the hard palate to push the bolus toward the pharynx 4. At the same time, the soft palate is raised, closing the caudal nares 5. The base of the tongue acts as a plunger, forcing the bolus into the pharynx
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Term
| What happens in the second stage of deglutition? |
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Definition
1. The second stage is intitiated when the bolus enters the pharynx and stimulates pressure receptors in the walls. 2. Respiration is reflexively inhibited, and the larynx reflexively closes and pulls up and forward. 3. The base of the tongue folds the epiglottis over the laryngeal opening as it moves back 4. The pharynx shortens, and a peristaltic action of the pharyngeal muscles force the bolus into the esophagus.
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Term
| What happens in the third stage of deglutition? |
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Definition
In the third stage: 1. The presence of food in the esophagus initiates reflex peristalsis of the esophagus. 2. Peristalsis consists of alternate relaxation and contraction of rings of muscle in the wall coupled with regional contraction of longitudinal musles in the area of the bolus.
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Term
| What is Fermentative Digestion? |
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Definition
| The microbial digestion in the forestomach which occurs in an anaerobic environment. |
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Term
| How are volatile fatty acids produced? |
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Definition
| Volatile faty acids are produced by fermentation of carbohydrates consumed by ruminants, including carbohydrates produced by the actions of microbial cellulase. |
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Term
| What are the primary VFA's (volatile fatty acids) and how are they absorbed? |
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Definition
The primary VFA's are acetic acid, propionic acid, and butyric acid. The VFA's are absorbed directly from the forestomach and are the major energy source for ruminants. *VFA's are also used for synthesis of millk fat in lactating animals.
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Term
| How is Methane and Carbon Dioxide produced, and where does it accumulate? |
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Definition
Methane and Carbone Dioxide are produced by fermentative digestion and accumulate as a gaseous layer above the ingesta in the rumen and reticulum. |
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Term
What does this sequence of contraction do: -This contraction begins in the reticulum and spreads over both the dorsal and ventral sacs of the rumen |
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Definition
These series of contractions mixes the contents to promote fermentation and provide force to move liquified digesta out of the forestomach and into the abomasum.
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Term
What does this sequence of contraction do: -These contractions begin in the caudal portion of the dorsal sac and moves cranially. |
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Definition
These contractions move gases toward teh cranial part of the rumen for eructation.
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Term
| What does rumination permit? What does it involve? |
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Definition
Rumination permits an animal to forage and ingest food rapidly and finish chewing it later. It entails regurgitation of the food (returning it to the mouth), from the forestomach, remastication (rechewing), reinsalivation (mixing with more saliva), and finally reswallowing. |
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Term
| What is the only step in Rumination that clearly differs from the intial mastication, insalivation, and swallowing. |
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Definition
Regurgitation is the only step of rumination that differs markedly from the inital mastication, insalivation, and swallowing.
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Term
| What is regurgitation preceeded by? |
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Definition
1.Contraction of the reticulum 2. The Spincter at the junction of the esophagus and the forestomach (lower esophageal sphincter) relaxes as the bolus of food reaches it. An inspiratory movemet with closed glottis follows. 3. The negative pressure produced in the thorax by this movement is transmitted to the relatively thin walled esophagus, dilating the thoracic esophagus and cardia. 4. The lower pressure in the esophagus than in the rumen coupled with reverse peristalsis causes a quantity of material (semifluid ingesta) to pass through the cardia into the esophagus and up to the mouth.
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Term
| What does regurgitated material generally consist of? |
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Definition
Regurgitated material consists larely of roughage and fluid with little if any concentrate. *It is well known that whole kernels of corn may pass through the entire digestive tract with little change in physical appearance.
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Term
| About how many hours a day to cattle ruminant for? |
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Definition
Cattle average about 8 hours a day ruminating, with periods of activity scattered through out the entire day. |
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Term
| About how long is one rumination cycle? |
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Definition
One rumination cycle required about 1 minute, of which 3-4 seconds is used for both regurgiation and reswallowing.
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Term
| What is the likely stimulus for rumination? |
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Definition
| Contact of roughage with the wall of the reticulum and near the cardia is likely the major stimulus for rumination. |
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Term
| In young ruminants, nursing and afferents from the pharynx appear to stimulate reflex closure of the groove, which causes ? |
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Definition
Which causes milk to bypass the rumen and reticulum and pass through the omasum directly to the abomasum. -The paunchiness of bucket fed calves usually is attributed to milk entering the rumen, where it is not properly digested. |
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Term
| What does the term gastic juice refer to? |
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Definition
The term gastric juice refers to the combination of substances secreted into the stomach lumen by gastric glands, also termed gastric pits becasue of their pit-like extension into the wall of the stomach, and epithelial cells of the stomach mucosa. |
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Term
| What does Gastric Juice contain, and how are gastric juice secretions regulated? |
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Definition
Gastric juice contains water, hydrochloric acid, mucus, intrinsic factor, pepsinogen (an inactive form of pepsin, a proteolytic enzyme), and the enzyme rennin. The regulation of gastric juice secretion has three phases: cephalic, gastric, and intestinal. |
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Term
| How are gastric secretions stimulated in the Cephalic phase and what does this induce? |
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Definition
Stimulation of gastric secretions during the Cephalic phase is in response to the sight, smell or taste of food. These induce a neural response that increases parasympathetic (vagal nerve) stimulation to the stomach, and this stimulates gastric secretions.
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Term
| When does the Gastric Phase begin? |
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Definition
The Gastric phase begins when food enters the stomach.
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Term
| How are Gastrin and Histamine hormones stimulated? What do they stimulate? |
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Definition
The presence of food, especially proteins, stimulates the secretion of the hormones gastrin and histamine form cells in the gastric epithelium. Gastrine and Histamine stimulate parietal cells in gastric glands to secrete hydrochloric acid.
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Term
| What parasympathetic nerotransmitter also stimulates pareital cells to secrete hydrochloric acid? |
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Definition
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Term
| What three regulators must be present for the most efficient hydrochloric acid secretion? |
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Definition
| Histamine, Gastrin, and Acetylcholine. |
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Term
| What hormones inhibit hydrochloric acid secretion? Where are they released? |
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Definition
The hormones cholecystokinin, gastric inhibitory peptide, and secretininhibit hydrochloric acid secretion. These hormones are released from the duodenal epithelium in response to the presence of food in the duodenum.
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Term
| The release of cholecystolkinin, gastric inhibitory peptide, and secretin that act to inhibit gastric function is part of what phase of gastric regulation? |
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Definition
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Term
| Why is the pH is gastric juice in mammals 2 or less? |
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Definition
The low pH is protective in that most foreign microbes ingested with food cannot survive such an acidic environment. The low pH inhibits hydrochloric acid secretion to prevent it from becoming too acidic. The low pH also promotes the activity of pepsin, because the most favorable pH range for its proteolytic activity is 1.3 to 5. |
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Term
| What do Chief or Peptic Cells do? |
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Definition
Chief or Peptic Cells secrete pepsinogen to begin protein digestion in the stomach, but protein digestion is completed in the small intestin by other digestive enzymes.
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Term
| What does the layer of mucus that covers the epithelial lining of the stomach do? How is it produced? |
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Definition
It protects the epithelium from the low pH of gastric fluids. The mucus is produced by cells in the gastric glands and is secretd form there onto the surface of the epithelium. |
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Term
| What is rennin? What is its function? |
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Definition
Rennin is an ezyme in gastric juice in the abomasum of young ruminants. Its function is to coagulate milk and reduce its rate of passage though the gastrointestinal tract. |
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Term
| What is Intrinsic Factor and what does it do? |
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Definition
Intrinsic factor is a carrier protein for vitamin B12. It binds to vitamin B12, and the resultant complex passes though the tract to the ileum, which absorbs the B12. |
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Term
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Definition
Chyme is ingesta that is forced though the pyloric sphincter. It is a mushy, semisolid, mixture of ood, water and gastric juice. |
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Term
| Similar to the regulation of gastric secretions, the regulation of gastric motility can be divided into: |
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Definition
-Cephalic Phase -Gastric Phase -Intestinal Phase |
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Term
| What are Gastric Slow waves? |
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Definition
Gastric Slow Waves: Waves of peristaltic contractions that may occur over the stomach as a slight ripple. These are produced by spontaneous electrical depolarizations, which sometimes induce action potentials, in the smooth muscle. These begin in the Cardia Region. |
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Term
| What are Hunger Contractions? |
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Definition
It is due to prolonged fasting, which makes the magnitude of the contractions to become greater. These are a response to an increase in parasympathetic input during prolonged fasting. -The intensity of hunger contractions is related to the level of blood sugar. As the blood sugar level decreases, the intensity of hungar contractions increases.
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Term
| The small intestine is the primary side of ? |
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Definition
| Chemical digestion and absorption of nutrients. |
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Term
| What do exocrine secretion so fhte pancreas contain? |
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Definition
The Exocrine secretions of the pancreas contain most of the enzymes for chemical digestion in the lumen of the small intestine. |
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Term
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Definition
Enterocytes are epithelial cells that line the small intestine whcih have enzymes in their cell membranes that participate inthe final steps of chemical digestion.
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Term
| What is the primary function of the liver? |
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Definition
| The primary function of the liver is to provide bile salts, which facilitate the enzymatic digestion of lipids. The liver is not a source of digestive enzymes. |
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Term
| What is intestinal juice derived from? What do these intestinal juices include? |
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Definition
Intestinal Juice is derived from intestinal glands in the wall of the small intestine. These include crypts or crypts of Lieberkuhm and duodenal glands.
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Term
| Where are Crypts of Lieberkuhn found? |
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Definition
| Scattered through out the entire small intestine |
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Term
| Where are duodenal glands found? |
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Definition
Duodenal glands are found only in the duodenum and they contribute mucus.
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Term
| What does the intestinal juice contain? |
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Definition
The intestinal juice contains salts and water derived from blood capillaries in the wall of the intestine.
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Term
| What are the two primary types of movement by the small intestine? |
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Definition
1. Segmentation 2. Peristalsis
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Term
| What are segmentation Movements and where do they occur? |
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Definition
Segmentation movements, which occur when food is in the small intestine, are characterized by alternating local areas of contraction and relaxation. These movements mix the digesta with intestinal juice and digestive enzymes and increase the contact between digesta and the epithelial surface of the small intestine. The increased contact provides more exposure to enzymes associated with epithelial cells and to the absorptive surface of the epithelial cells.
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Term
| What is the purpose of Peristaltic contractions of the small intestine? |
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Definition
Peristaltic contractions of the small intestine in fasting animals or several hours after a meal proper ingesta down the tract, presumably to clean the small intestine of undigested foodstuffs before the next meal.
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Term
| What do pancreatic exocrine secretions primarily consist of? |
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Definition
| A variety of digestive enzymes and sodium bicarbonate. |
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Term
| What are Pancreatic Acinar cells? |
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Definition
Pancreatic Acinar Cells secrete the enzymes, and cells tha tline ducts in the pancreas secrete the sodium bicarbonate. These ducts empty into the duodenum.
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Term
| What is a major stimulus for bicarbonate secretion? |
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Definition
The major timulus for bicarbonate secretion is the hormone secretin from the small intestinal mucosa. Secretin secretion increases in response to the acid chme entering from the stomach. |
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