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