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117 Cards in this Set

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  • Back
What is intracellular digestion?
It is digestion that occurs within the cell
What is extracellular digestion?
It refers to the digestive process that occurs outside of the cell, within a lumen or tract
Do Mammals have a two or one way digestive tract?
It is one way
What is it known as?
The alimentary canal
Are mammalian digestive tracts complex or simple?
They are complex
What are they organized into regions specialized for?
They have regions for digestion and absorption of specific nutrients
Where does the digestive tract begin?
With the oral cavity
What is the path of the rest of the tract and where does it end?
It goes through the pharynx, the esophagus, the stomach, the small intestine, and the large intestine, ending in the anus.
What are the accessory organs involved with digestion?
Salivary glands, the pancreas, the liver, and the gall bladder, all have essential roles
What are epithelial cells?
They are the linings of most body surfaces
Are they loosely or tighly connected together?
They are tightly connected
What is the purpose of this?
To act as a barrier against mechanical injury, invading organisms, and fluid loss
Can the free surface of epithelium be exposed to air or liquid?
Is it ciliated?
It can be
What is the inner surface attached to underlying connective tissue by?
The basement membrane
How is epithelium classified?
According to the number of layers and the shape of its cells
What is simple epithelium?
It is a single layer of cells
What is stratified epithelium?
It has multiple layers of cells
What is pseudostratified epithelium?
It is single layered but appears stratified because its cells vary in height
What are the three types of cell shape?
Cuboidal, columnar, and squamous (scale-like)
Do epithelial cells absorb or secrete solutions?
Yes, some are specialized
What is an example of this?
Simple cuboidal cells in the small intestine absorb nutrients
What is a mucous membrane or mucosa?
It is a specialized epithelium that lines most body cavities
Where does mechanical digestion take place?
It takes place in the oral cavity
Does mechanical digestion lead to changes in the molecular composition of food?
What does it do?
It increases the surface area of the food, allowing for faster and more efficient enzymatic action
What is chemical digestion?
It is the enzymatic breakdown of macromolecules into smaller molecules
Where does it begin?
It actually begins in the mouth when salivary glands secrete saliva
What is the purpose of saliva?
It has several purposes such as facilitating swallowing through lubrication, and it provides a solvent for food particles
Saliva is secreted why?
In response to a nervous reflex triggered by the presence of food in the oral cavity
What enzyme does saliva contain that hydrolyzes starch into simple sugars?
Salivary amylase (ptyalin)
During swallowing, what does the epiglottis do?
It covers the opening of the trachea, thereby preventing food particles from going down the wrong passageway
What is peristalsis?
The rhythmic waves of involuntary muscular contractions
What is the ring of muscle in the lower esophagus that opens during peristalsis?
It is called the lower esophageal sphincter or cardiac sphincter
Do sphincters normally remain open or closed?
What are the walls of the stomach lined by?
Thick gastric mucosa, which contains the gastric glands and pyloric glands
How does the brain stimulate the gastric glands?
It responds to the sight, taste, and or smell of food, stimulating nervous impulses
What are the three types of gastric glands?
They are mucous cells, chief cells, and parietal cells
What do mucous cells do?
They secrete mucous, which protects the stomach lining from the low pH (2) present in the stomach
What is gastric juice comprised of?
It is composed of the secretions of the chief cells and the parietal cells
What do chief cells secrete?
What is pepsinogen?
It is the zymogen of the protein-hydrolyzing enzyme pepsin
What do parietal cells secrete?
They secrete HCl
What does HCl do in the stomach?
It kills bacteria, dissolves the glue holding food tissues together, and facilitates the conversion of pepsinogen to pepsin
What does pepsin do?
It hydrolyzes specific peptide bonds to yield polypeptide fragments
What do the pyloric glands secrete?
They secrete the hormone gastrin
Why do they secrete gastrin?
In response to the presence of certain substances in food
What does gastrin do?
It stimulates the gastric glands to secrete more HCl, and also stimulates muscular contractions of the stomach
What does this churning produce?
What is at the junction of the stomach and small intestine?
The pyloric sphincter
What is its purpose?
It regulates the passage of chime from the stomach into the small intestine via alternating contractions and relaxations
What can be absorbed into the bloodstream through capillaries in the stomach wall?
Alcohol and certain drugs such as aspirin
Where is chemical digestion completed?
In the small intestine
What are the three sections of the small intestine?
The duodenum, the jejunum, and the ileum
Why is the small intestine so long?
In order to maximize the surface area available for digestion and absorption
Why are villi in the stomach?
They extend out of the intestinal submucosa even further
Do they have projections off of them too?
Yes, microvilli project from the surface of individual cells lining the villi
Where does most digestion occur in the small intestine?
Within the duodenum
Where do the secretions of the intestinal glands, pancreas, liver, and gall bladder mix together with the acidic chyme?
In the duodenum
What does the presence of chyme in the duodenum trigger?
Hormonal release, which in turn stimulates and regulates the secretions of the small intestine and its accessory organs
What are some of the intestinal mucosa enzyme secretions that hydrolyze carbohydrates into monosaccharides?
Maltase, lactase, sucrase, and peptidases
What does the hormone secretin do and where does it come from?
It is released by the duodenum in response to the acidity of chyme, stimulating the pancreas to secrete pancreatic juice
Do the enzymes of the small intestine function better at an acidic or basic pH?
A basic pH
Is pancreatic juice acidic or basic?
What is its purpose?
It contains enzymes that neutralize the acidity of chyme and contains enzymes that digest carbohydrates, proteins, and lipids
What is trypsinogen?
It is a proteolytic zymogen secreted by the pancreas
What is its active form, and what converts it to the active form?
The active form is trypsin, which is converted by an enzyme called enterokinase
What does trypsin then convert?
Another pancreatic zymogen, chymotrypsinogen into chymotrypsin
What does each of these enzymes do?
They cleave specific peptide bonds within proteins, producing polypeptide fragments
What else does the pancreas secrete?
Carboxypeptidase, which is also secreted as a zymogen and converted by trypsin
It along with what digests polypeptides into amino acids?
It along with aminopeptidase digests polypeptides into amino acids
What is the hormone CCK (cholecystokinin)?
It stimulates the secretion of pancreatic enzymes and the release of bile
What secretes CCK?
The duodenum
In response to chyme
What is bile?
An alkaline fluid synthesized and secreted by the liver
Where is it stored?
It is stored in the gall bladder
Where is it released?
Into the duodenum
What is bile composed of?
Bile salts, bile pigments, and cholesterol
What are bile salts?
Molecules with a water-soluble region on one and a fat-soluble region on the other
What does this structure allow?
It allows bile salts to emulsify fat globules as well as surround and maintain these particles in finely dispersed complexes called micelles
What is this process known as?
The emulsification of fat
Why is it done?
To increase the surface area to the actions of lipases, which hydrolyze molecules of fat into glycerol and fatty acids
How much bile is released?
The amount released is proportional to the amount of fat ingested
If the chyme is fatty, what does the duodenum release?
A hormone called enterogastrone
What does it inhibit?
Stomach peristalsis
It slows down the release of chyme into the small intestine
In addition to hormonal regulation, what else are digestive processes stimulated and inhibited by?
They are stimulated by the parasympathetic nervous system and inhibited by the sympathetic nervous system
Where does the majority of nutrient absorption occur?
Across the walls of the jejunum and ileum
Does any absorption occur in the duodenum?
Yes, a very small amount
How are monosaccharides absorbed?
They are absorbed via active transport and facilitated diffusion into the epithelial cells lining the villi
How are amino acids absorbed?
They are absorbed into the epithelium via active transport
How do monosaccharides, amino acids, and small fatty acids diffuse directly into the intestinal capillaries and enter portal circulation?
Via the hepatic portal vein
Where do larger fatty acids, glycerol, and cholesterol diffuse?
Into the mucosal cells
What do fatty acids and glycerol recombine then?
They combine to form triglycerides
Triglycerides, which, along with phosphoglycerides and cholesterol, are packaged into protein-coated droplets called what?
Where are chylomicrons secreted?
Into tiny lymph vessels within the villi called lacteals
What do lacteals do?
They lead into the lymphatic system
Where does the lymphatic system converge with venous blood at the thoracic duct?
In the neck
Where are chylomicrons processed?
In the bloodstream
Where are they then delivered?
To the liver
Once there, repackaging allows their release into the bloodstream as what?
LDLs, VLDLs, and HDLs
Where are vitamins and minerals absorbed?
In the small intestine
How are the fat soluble vitamins such as A, D, E, and K absorbed?
They are absorbed along with fats
Most water soluble vitamins such as the vitamin B complexes and vitamin C are absorbed how?
Via simple diffusion into the circulatory system
How many liters of fluid enter the small intestine every day?
About seven
Where does most of it go?
Most is absorbed through the walls of the small intestine
How long is the large intestine, and what does it consist of?
It is about 1.5m long, and it consists of the cecum, the colon, and the rectum
What is the cecum?
It is the blind out pocketing at the junction of the small and large intestines
What is at the tip of the cecum?
A small finger-like projection called the appendix
What is the appendix?
A vestigial structure
What does it contain?
Lymphoid tissue that is often surgically removed if it becomes infected
How does the colon function?
It works in the absorption of salts and the absorption of any water not already absorbed by the small intestine
If digested matter moves through the colon too quickly, too litter water is absorbed, causing what?
Diarrhea and dehydration
What causes constipation?
When movement through the bowels is too slow, causing too much water to be absorbed
What does the rectum do?
It stores feces
What are feces?
Bacteria, particularly E. coli, water, undigested food, and unabsorbed digestive secretions like enzymes and bile
What is the anus?
It is the opening through which wastes are eliminated and is separated from the rectum by two sphincters that regulated elimination