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16. Digestive Physiology II
N/A
226
Physiology
Undergraduate 2
11/07/2012

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Term
What are the three types of exocrine glands?
Definition
apocrine, holocrine, and merocrine
Term
What kinds of digestive enzymes does the pancreas produce?
Definition
proteases, lipases, and amylases
Term
Where is the pancreas located in relationship to the stomach?
Definition
it is located just below the stomach next to the duodenum
Term
How does the pancreas know to secrete digestive enzymes?
Definition
the duodenum releases hormones
Term
What are the two types of exocrine cells in the pancreas?
Definition
duct cells and acinar cells
Term
What do duct cells in the pancreas secrete?
Definition
sodium bicarbonate
Term
What do acinar cells in the pancreas secrete?
Definition
digestive enzymes
Term
What is another name for the endocrine portion of the pancreas?
Definition
islets of Langerhans
Term
What are the endocrine secretions of the pancreas?
Definition
insulin and glucagon
Term
What type of cells secrete insulin?
Definition
beta cells
Term
What type of cells secrete glucagon?
Definition
alpha cells
Term
The pancreas has a mixture of ________ and __________ tissue.
Definition
endocrine, exocrine
Term
What are the four main enzymes produced by the pancrease?
Definition
  • proteolytic enzymes
  • amylase
  • chitinase
  • lipase
Term
What are three proteolytic enzymes?
Definition
trypsinogen, chymotripsinogen, and carboxypeptidase
Term
Trypsinogen is activated by ___________ into _________.
Definition
enterokinase; trypsin
Term
Cymotrypsinogen and carboxypeptidase are activated by __________.
Definition
trypsin
Term
What does pancreatic amylase do?
Definition
it converts polysaccharides into disaccharides
Term
What do pancreatic lipases do?
Definition
they convert triglycerides into fatty acids and monoglycerides
Term
What two things act as pH buffers?
Definition
water and bicarbonate
Term
How is the pancreas innervated? Explain.
Definition
It is innervated by the vagus nerve which applies a low level of stimulus to secretion in response to anticipation of a meal
Term
What is the most important stimulus for pancreatic exocrine secretions?
Definition
gastrin, secretin, and cholocystokinin
Term
How are pancreatic exocrine secretions regulated? What does this help maintain?
Definition
it is hormonally regulated to help maintain neutrality of the duodenal contents and to optimize digestion
Term
What was the first hormone discovered?
Definition
secretin
Term
The _________ secretes secretin in the presence of _______.
Definition
duodenum, acid
Term
How does secretin work?
Definition
it is transported to the pancreas by the blood and it stimulates secretion of bicarbonate into the duodenum by the pancreas
Term
What is the abreviation for cholocystokinin?
Definition
CCK
Term
What stimulates the secretion of CCK? What secretes it?
Definition
the duodenal mucosa secretes CCK in the presence of fat and protein
Term
What is the function of CCK?
Definition
it stimulates the secretion of pancreatic digestive enzymes
Term
What does gastrin act on?
Definition
the stomach and the intestine
Term
Where are secretin, CCK, and gastrin synthesized?
Definition
in the duodenum
Term
Explain the process that occurs whn there is acid in the duodenal lumen?
Definition
  • secretin is released by the duodenal mucosa
  • it is carried to the pancreas by the blood
  • it stimulates duct cells to secrete bicarbonate into the duodenal lumen which neutralizes the acid
Term
Explain the process that occurs when there are fats and proteins in the duodenal lumen?
Definition
  • CCK is released from the duodenal mucosa
  • CCK is carried to the pancreas by the blood
  • CCK stimulates acinar cells to secrete pancreatic digestive enzymes into the duodenal lumen which digest the proteins and fats
Term
What is the function of glucagon?
Definition
it plays a major role in maintaining normal concentration of glucose in the blood by increasing blood glucose levels  when necessary
Term
What is the function of insulin?
Definition
  • it is a key player in the control of intermediary metabolism
  • it has profound effects on both carbohydrate and lipid metabolism, and significant influences on protein and mineral metabolism
Term
What is another endocrine hormone that is secreted by the pancrease aside form glucagon and insulin?
Definition
somatostatin
Term
What type of cell secretes somatostatin?
Definition
delta cells 
Term
Most of the circulating somatostatin appears to come from the ________ and the _______.
Definition
pancreas, GIT
Term
What is the basic function of somatostatin?
Definition
it inhibits the secretion of many other hormones 
Term
(Insulin/glucagon) concentrations are higher before a meal whereas (insulin/glucagon) concentrations are higher after a meal.
Definition
glucagon, insulin
Term
9
Definition
Term
What are the six general functions of the liver?
Definition
synthesis, activation, degredation, storage, detoxification, and excretion
Term
How is the liver related to metabolism?
Definition
it carries out metabolic processing of the major categories of nutrients 
Term
Why does the liver carry out detoxification and degredation?
Definition
to get rid of body wastes and hormones
Term
The liver synthesizes __________ and _________.
Definition
plasma proteins, ascorbic acid
Term
The liver stores _______, ________, _________, _________, and _______.
Definition
glycogen, fats, iron, copper, and vitamins
Term
What kind of vitamins does the liver store? Explain.
Definition
fat soluble vitamins; it can't store watersoluble vitamins
Term
The liver activates _________.
Definition
vitamin D
Term
The liver removes ________ and ________ by resident ______________.
Definition
bacteria, worn out RBCs, macrophages
Term
The liver excretes ________ and _______.
Definition
cholesterol, bilirubin
Term
What other process occurs in the liver with regards to carbohydrates?
Definition
gluconeogenesis
Term
What is another name for ascorbic acid? What is it?
Definition
vitamin C; it is a water soluble antioxidant 
Term
What vitmains are fat soluble?
Definition
A, D, K, and E
Term
What is the major product taht is secreted by the liver?
Definition
bile
Term
Bile is secreted by the ___________ into the ____________.
Definition
biliary tract, small intestine
Term
What is the function of bile?
Definition
They function in digestion and absorption of fats and fat-soluble vitamins in the small intestine
Term
Many __________ are eliminated from the body via bile secretions and elimination in the ________.
Definition
waste products, feces
Term
What are the two sources that the liver recieves blood from?
Definition
  • arterial blood from the hepatic artery which provides the liver's O2 supply and carries blood born metabolites for hepatic processing 
  • venous blood from the hepatic vein draining the digestive tract for processing and storag of newly absorbed nutrients
Term
Why can't many drugs be ingested?
Definition
because they can be inactivated by the acid in the stomach or in the liver
Term
What is the functional unit of the liver?
Definition
hepatocytes 
Term
13
Definition
Term
14
Definition
Term
The hepatocyte is a made up of ___________ liver cells.
Definition
parenchymal
Term
Hepatocytes make up ____ to ____% of the cytoplasmic liver mass.
Definition
70, 80
Term
What are hepatocytes involved in?
Definition
  • protein synthesis
  •  protein storage 
  •  transformation of carbohydrates
  • synthesis of cholesterol, bile salts, and phospholipids
  • detoxification, modification, and excretion of exogenous and endogenous substances
Term
The hepatocyte also initiates the formation and secretion of ______.
Definition
bile
Term
How are bile salts produced?
Definition
by the oxidation of cholesterol
Term
What happens to bile salts (acids) before they are stored in the gallbladder?
Definition
they are conjgated with taurine or the amino acid glycine, or with a sulfate or a glucuronide 
Term
How often is bile produced? Explain how this doesn't have negative side effects
Definition
it is produced continuously but is stored in the gall bladder between meals 
Term
How are bile salts recycled?
Definition
through the enterohepatic circulation
Term
Explain the enterohepatic circulation of bile salts?
Definition
  • bile is released from the gall bladder into the duodenum 
  • once it reaches the termianl ileum, it is reabsorbed before it enters the colon
  • it is returned to the liver via the portal circulation 
Term
What is the sphincter between the common bile duct and the duodenum?
Definition
sphincter of oddi
Term
How does bile help with the digestion and absorption of fats?
Definition
through their detergent action and micellar formation
Term
19
Definition
Term
20
Definition
Term
__________ is a waste product excreted in the bile.
Definition
bilirubin
Term
What is bilirubin?
Definition
(formerly referred to as hematoidin) it is the yellow breakdown of normal heme catabolism 
Term
How can you identify the digestive system of a human?
Definition
the large colon will have an ascending, transverse, and descending column
Term
How can you identify the digestive system of a ruminant?
Definition
it will have a huge stomach and the large intestine will be in a spiral shape
Term
How can you identify the digestive system of a horse?
Definition
it will have a small stomach and a large cecum
Term
Name the layers of a gut cross section starting with the outside and moving in. (Be general about the muscularis externa and mucosa).
Definition
body wall, peritoneum, mesentery, serosa, muscularis externa, submucosa, mucosa, lumen
Term
What are the layers of the muscularis externa starting with outside and moving in?
Definition
  • outer logitudinal muscle
  • inner circular muscle
Term
What are the layers of the mucosa starting with the outside and moving in?
Definition
  • muscularis mucosa
  • lamina propria 
  • mucous membrane 
Term
23
Definition
Term
What are the four layers of the digestive tract?
Definition
mucosa, submucosa, muscularis externa, serosa
Term
The mucosa is where ___________ takes place.
Definition
nutrient absorption
Term
What is the mucous membrane?
Definition
  • it is a protective surface
  • it also contains endocrine, exocrine, and epithelial cells for absorption
Term
What is the lamina propria?
Definition
small blood vessels, lymph vessels, and nerve fibers pass through it
Term
What are the two parts of the mucosa?
Definition
the mucous membrane and the lamina propria
Term
What is the submucosa?
Definition
it is a thick layer of connective tissue that rpovides the digestive tract with distensibility and elasticity
Term
What is the muscularis externa?
Definition
it is the major smooth muscle coat
Term
What is the function of the inner layer muscle of the muscularis externa?
Definition
it carries out circular contraction which reduces diameter
Term
What is the function of the outer layer of muscle in the muscularis externa?
Definition
it carries out longitudinal contraction which shortens the tube
Term
What is the function of the serosa?
Definition
  • it secretes a watery serous fluid for lubrication 
  • it is attached to the mesentery and suspends the digestive tract in position
Term
Once nutrients are dumped from the intestines into the capillaries, what is the next stop?
Definition
the liver
Term
What happens to lipids that are absorbed?
Definition
they enter the centarl lacteal and enter the lymphatic system
Term
What is the purpose of villi and microvilli?
Definition
they increase the surface area over which nutrients can be absorbed
Term
What is the function of segmentation in the small intestine?
Definition
it mixes and slowly propels the chyme
Term
What initiates segmentation?
Definition
pacesetter cells
Term
What does the intensity of segmentation depend on?
Definition
the number of action potentials reaching the threshold 
Term
How does segmentation start?
Definition
the duodenum distension by the presence of chyme 
Term
Explain how segmentation works?
Definition
there is a rate of segmentation difference between the duodenum and the terminal ileum which induces slow movement of chyme through the small intestine
Term
Chyme in the small intestine is pushed form the segment that is moving (slower/faster) to the segment that is moving (slower/faster).
Definition
faster, slower
Term
What sweeps the intestine clean between meals?
Definition
the migrating motility complex
Term
What prevents contamination of the small intestine by colonic bacteria?
Definition
the ileocecal juncture
Term
What is the most common bacteria in the colon?
Definition
E. coli
Term
Despite the ileocecal sphincter, sometimes bacteria still enters the small intestine. How is this fixed?
Definition
at the end of the small intestine is an area called the Pyer's patch which has a bunch of immune cells which kill the bacteria
Term
Do small intestine secretions in vertebrates contain digestive enzymes? Explain.
Definition
no, the small intestine synthesizes enzymes but they stay within the borders of the epithelial cells
Term
What are the sources of amylase?
Definition
  • salivary glands
  • exocrine pancreas
  • small intestine epithelial cells
Term
What are the sites of action for amylases?
Definition
  • mouth
  • body of stomach
  • small intestine
Term
What are five main enzymes that are meant to break down proteins?
Definition
pepsin, trypsin, chymotrypsin, carboxypeptidase, aminopeptidases
Term
What are the sources of protein enzymes?
Definition
  • stomach chief cells
  • exocrine pancreas
  • small intestine epithelial cells
Term
What is the site of action for protein enzymes?
Definition
  • antrum of the stomach
  • small intestine
Term
What are the primary fat enzymes?
Definition
lipases and bile salts
Term
What is the source of fat enzymes?
Definition
  • exocrine pancreas
  • liver

 

Term
What is the site of fat enzyme action?
Definition
small intestine
Term
The small intestine is highly __________ for its primary role in absorption.
Definition
adaptable
Term
What happena when there is a prolonged carbohydrate diet?
Definition
there is an upregulation of glucose transporters 
Term
What characteristics of the small intestine are adaptable to diet?
Definition
length, types, and densities of intestine transporters
Term
Why do herbivores have longer intestines?
Definition
because vegetation is harder to digest than meat
Term
What increases the effectiveness of peristalsis?
Definition
the gastro enteric reflex
Term
How do the muscles that cause peristalsis work?
Definition
the longitudinal muscles contract first for a long stretch and then the circular muscle contract and relax
Term
What is the basis for peristalsis?
Definition
electrical activity: slow waves superimposed with spikes
Term
With ragards to the nervous system, there is ________ activity in the stomach and the duodenum. This rate is decreased in the _____________.
Definition
pacemaker, terminal ileum
Term
What is peristalsis like in the colon?
Definition
it is less frequent but more powerful
Term
Eructation is ________ peristalsis.
Definition
reverse
Term
What is a portion of food called?
Definition
a bolus
Term
What are the four factors in the duodenum that affect the rate of gastric emptying?
Definition
  • fat
  • acid
  • hypertonicity
  • distension
Term
How does fat affect the rate of gastric emptying?
Definition
it digests slowly so this slows down emptying 
Term
Hoes acid affect the rate of gastric emptying?
Definition
it must be buffered to to avoid damage to the gut
Term
What causes hypertonicity?
Definition
large amounts of amino acids and glucose molecules 
Term
How does distension affect rate of gastric emptying?
Definition
too much chyme slows gastric emptying
Term
In livestock, rate of passage is also affected by ___________.
Definition
particle size
Term
How many hormones have been identified in the gastrointestinal system?
Definition
over two dozen
Term
All of the hormones in the GIT are _________.
Definition
peptides
Term
Are the hormones found in the GIT only found in the gut? Explain.
Definition
no, many are found in other tissues, expecially the brain
Term
Explain how the hormones found in the GIT serve many different functions?
Definition
they can be neuro-, para-, auto-, and endocrine depending on the region where they act and where they are secreted 
Term
What is the importance of the GIT hormones to health? Explain. 
Definition
their importance to animal health is uncertain as no known deficiency disorders have been found for any of them except gastrin
Term
Salivary glands serve a (endocrine, exocrine) function.
Definition
exocrine
Term
What doe gastric glands secrete?
Definition
mucus, HCl, and pepsinogen
Term
The oancreas serves a (endocrine, exocrine) function.
Definition
both
Term
The liver and gallbladder serve a (endocrine, exocrine) function.
Definition
exocrine
Term
40
Definition
Term
40
Definition
Term
What enzyme breaks down starch and glycogen?
Definition
amylase
Term
What are the three major disaccharides?
Definition
sucrose, lactose, and maltose
Term
What is sucrose?
Definition
glucose and fructose
Term
What is lactose?
Definition
glucose and galactose
Term
What is maltose?
Definition
two glucose
Term
What enzyme acts on sucrose?
Definition
sucrase
Term
What enzyme acts on lactose?
Definition
lactase
Term
What enzyme works on maltose?
Definition
maltase
Term
What are the three main monosaccharides?
Definition
glucose, galactose, and fructose
Term
What proteases act on whole proteins?
Definition
pepsin, trypsin, chymostrypsin, and carboxypeptidase
Term
What protease acts on peptide fragments?
Definition
aminopeptidase
Term
Saliva and pancreatic amylase convert polysaccharides into __________.
Definition
maltose
Term
Monosaccharides enter the blood via ____________.
Definition
passive diffusion
Term
44
Definition
Term
How do amino acids enter the blood?
Definition
via Na+ and energy dependent active transport 
Term
Where are small peptides broken down?
Definition
epithelial cells
Term
47
Definition
Term
Fat globules (truglycerides) are ________ by bile salts.
Definition
emulsified
Term
How do fatty acids enter the blood?
Definition
via passive diffusion
Term
What happens to fatty acids once they enter the blood?
Definition
  • they are reformed into triglycerides (from monoglycerides and fatty acids)
  • they are then coated with lipoprotein and called chylomicrons which are extruded by exocytosis to the lymph vessels
Term
What kind of fatty acids are very easily absorbed into capillaries?
Definition
medium chain fatty acids; they are good for people who have a hard time absorbing fat
Term
Explain the process in which lipids are broken down up to when they are used by a cell?
Definition
  • bile salts emulsify dietary fats in the small intestine
  • intestinal lipases are degraded into triacylglycerols 
  • fatty acids and other breakdown products are taken up by the intestinal mucosa and converted into triacylglycerols
  • triacylglycerols are incorporated with cholesterol and apoproteins into chylomicrons
  • chylomicrons move through the lymphatic system and the bloodstream
  • lipoprotein lipase reelases fatty acids and glycerol
  • fatty acids enter the cell where they are oxidized to be used as energy
Term
Which four organs have the highest rate of blood flow from most to least?
Definition
  • kidney
  • liver
  • heart
  • small intestine
Term
What kind of digestive system do pigs have?
Definition
monogastric
Term
What is a monogastric?
Definition
an animal with a one chambered stomach
Term
What is the technical name of the stomach in a monogastric animal?
Definition
abomasum
Term
What does the abomasum do?
Definition
it secretes a strong acid and many digestive enzymes 
Term
What is the epithelial layer of the small intestine called?
Definition
the mucosa
Term
What is the connective tissue layer of the small intestines called?
Definition
submucosa
Term
What does the submucosa contain?
Definition
blood, lymph vessel, and nerve and muscle fibers
Term
The liver and pancreas empty into the ____________.
Definition
small intestine
Term
Most digestion and absorption occurs in the _______________.
Definition
small intestine
Term
Why is the large colon not involved in digestion to a great extent?
Definition
  • it does not have mucosal enzymes
  • it does not have any significant active transport mechanisms for sugars and amino acids 
Term
What is the large colo responsible for?
Definition
water reabsorption
Term
What are the four chambers of the staomach in a ruminant?
Definition
the rumern, reticulum, omasum, and abomasum
Term
In which chamber of the stomach is acid secreted?
Definition
abomasum
Term
Name the order in which food passes through the stomach of  ruminant and into the small intestines in a ruminant.
Definition
  • food enters the rumen form the esophagus
  • it then goes into the reticulum
  • from the reticulum it is regurgitated and rechewed in the mouth
  • it then goes back down the esophagus into the omasum
  • from the omasum, it goes into the abomasum and then into the small intestine
Term
What is the purpose of rumination?
Definition
it reduces particle size of fiber and exposes sugars to microbial fermentation
Term
Cows produces _____ to _____ liters of saliva while they chew ___ to ___ hours a day.
Definition
160, 180, 6, 8
Term
How much saliva does a cow produce if rumination is not stimulated (too much concentrate in the diet)?
Definition
30-50 liters
Term
What is the function saliva in the ruminant?
Definition
it consists of bicarbonate and phosphates which neutralize the acids produced by microbial fermentation to maintain a neutral acidity which favors fiber digestion and microbial growth in the rumen
Term
What are the two major sugars that are ingested as plant material?
Definition
amylose and cellulose
Term
What is cellulose?
Definition
it is the chief component of cell walls and consequently, the single most common, by mass, organic molecule on Earth
Term
What is the main similarity between amylose and cellulose?
Definition
they both have three glucose molecules
Term
What is the difference between amylose and cellulose?
Definition
the three glucose molecules are bonded differently: amylose has an alpha 1 to 4 glycosidic linkage whereas cellulose has a beta 1 to 4 glycosidic linkage
Term
What enzyme breaks down amylose? Does this enzyme work on cellulose?
Definition
amylase; no
Term
Can ruminants break down cellulose? Explain.
Definition
no, not without microorgansims
Term
Why are chickens more efficient in pulling nuteints from feed than cows?
Definition
because they ingest lots of unsaturated fats whereas cows do also but the microorgansims saturate these fatty acids so they are harder to absorb
Term
extra credit- 61
Definition
Term
What are the general functions that occur in the rumen and reticulum?
Definition
  • retention
  • microbial fermentation
  • absoprtion
  • production and expulsion
Term
What are the two products of microbial fermentation?
Definition
  • volatile fatty acids (VFA) as end products of the fermentation of cellulose and other sugars
  • a microbial mass rich in high quality protein
Term
What happens with regards to retention in the rumen and reticulum?
Definition
there is retention of long forage particles which stimulate rumination
Term
What are the two products of microbial fermentation?
Definition
  • volatile fatty acids (VFAs) as end products of the fermentation of cellulose and other sugars
  • a microbial mass rich in high quality protein
Term
Where are volatile fatty acids absorbed?
Definition
through the rumen wall
Term
What are volatile fatty acids used for in cows?
Definition
  • they are used for the main energy source for the cow
  • they are also used for the synthesis of milk fat (triglycerides) and milk sugar (lactose)
Term
With ragards to production and expulsion, what happens in the rumen and the reticulum?
Definition
production and expulsion through belching of as many as 1000 L of gases (methane) per day
Term
What are the three main volatile fatty acids?
Definition
acetic acid (acetate), propionic acid (propionate), and butyric acid (butyrate)
Term
How much of volatile fatty acids is acetic acid?
Definition
65%
Term
How much of volatile fatty acids is propionic acid?
Definition
20%
Term
How much of volatile fatty acids is butyric acid?
Definition
15%
Term
How many carbons make up acetic acid?
Definition
2
Term
How many carbons make up propionic acid?
Definition
3
Term
How many carbons make up butyric acid?
Definition
4
Term
What is unique about propionic acid?
Definition
it is the only VFA that can be used to synthesize glucose
Term
Are the percentages of volatile fatty acids always the same? Explain.
Definition
no, diet can influence percentages as do ionophores like Rumensin
Term
What occurs in the omasum?
Definition
  • recycling of some nutrients: absorption of water, sodium, phosphorus, and residual VFAs
Term
What happens in the abomasum?
Definition
  • acid digestion:
  • secretion of strong acids and digestive enzymes 
  • digestion of feed fractions not fermented in the rumen (some proteins and lipids)
  • digestion of bacterial proteins produced in the rumen
Term
How many bacterial proteins that are produced in the rumen are digested each day?
Definition
.5 to 2.5 kg
Term
___% of the food that enters the small intestines comes from bacteria.
Definition
65
Term
Once the food passes through the stomach, what are the three other organs that produce digestive enzymes?
Definition
the small intestine, liver, and pancreas
Term
What types of nutrients are digested in the small intestine?
Definition
carbohydrates, lipids, and proteins 
Term
What is absorbed in the small intestine?
Definition
some water, minerals, and products of digestion: glucose, amino acids, and fatty acids
Term
In general, what happens in the small intestine?
Definition
digestion and absorption
Term
What happens in the cecum?
Definition
a usually small microbial population ferments the unabsorbed products of digestion
Term
What happens in the large intestine?
Definition
absorption of water and formation of feces
Term
Explain how the cecum in the horse is different from other animals?
Definition
the cecum is found in most animals but is not weel developed like it is in the horse
Term
What is a major source of energy for the horse and is produced in the cecum?
Definition
volatile fatty acids
Term
Can microbial proteins be utilized to a great extent in the horse? What does this mean?
Definition
no; this means that animals with a high demand for protein (foals, lactating mares, exercising horses) must be fed high quality protein
Term
Bacterial proteins synthesized in the rumen are digested in the small intestine and constitute the major source of amino acids for the cow. Why is this not the case in horses?
Definition
because their cecum is caudal to the small intestine
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