GI System Part 1 Flashcards
What are the tissues that make up the wall of the GI tract?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
The Mucosa is composed of three layers, what are they?
- Mucous membrane: epithelial cells
- Lamina propria: connective tissue and vasculature
- Muscularis mucosae: thin smooth muscle
What are the three cell types in the mucous membrane of the Mucosa?
- Absorptive cells-absorbing nutrients
- Exocrine cells-secrete digestive fluids
- Endocrine cells
All of which are Entercyote
The Lamina propria contains connective tissue. What else make up this layer?
Small blood vessels, lymphatic vessels, nerves, and lymphoid tissues (i.e.-lymph nodules and Peyer’s patches)
Which layer of the Mucosa is a thin layer of smooth muscle with both longitudinal and circular fibers that mix the lumenal contents?
Muscularis mucosae
Which layer of the GI wall is comprised of a thick layer of connective tissue with large blood and lymphatic vessels? It also has one part of the Enteric Nervous System called Submucosal plexus (Meissner’s plexus).
Submucosa
Which layer of the GI wall is comprised of two layers of smooth muscle in which the inner layer is circular to change diameter and the outer layer is longitudinal to change length? It also contains one part of the Enteric Nervous System called Myenteric plexus (Auerbach’s plexus).
Muscularis externa
Which layer of the GI wall is comprised of an inner layer of connective tissue and an outer layer of epithelial tissue? It is continuous with the mesenteries.
Serosa
What are the major organs of the GI tract and what are their functions?
Mouth-food breakdown starts here
Pharynx-passageway for food
Esophagus-passageway for food
Stomach-food storage, secretes gastric juices
Small Intestine-digestion and absorption of nutrients
Colon-concentration of wastes into feces, water absorption, and storage of feces
Rectum-storage of feces
Anus-wastes exit
What are the two major divisions of the Enteric Nervous System and where are they located?
Submucosal-in the Submucosa
Myenteric-in the Muscularis externa
Describe the brush border. Where is it located and what is its function?
The brush border is a layer of microvilli on the absorptive cells located on the Villi in the Duodenum. It increases surface area of epithelial cells.
Where does the most digestion and absorption occur in the GI tract?
The small intestine.
The lining of the stomach contains gastric pits. What is their purpose?
Gastric pits secrete products to aid in digestion.
Name the products secreted from the Gastric Pits and describe them.
Pepsinogen: secreted by chief cells, precursor to pepsin, which digests protein.
Hydrogen ions: secreted by parietal cells and maintain the acidic environment of the stomach
Intrinsic factor: secreted by parietal cells, necessary for the absorption of B12.
Gastrin: secreted by G cells (hormone)
Mucous: secreted from neck cells
What environment is necessary to activate Pepsin?
an acidic environment, pH 2
What is the purpose of the pancreatic juices entering the duodenum?
To neutralize the pH of chyme to 7
How do the Pancreas, Gall Bladder, and Liver connect to the small intestine?
The pancreas connects to the small intestine with the pancreatic duct. The gall bladder and liver connect to the small intestine with the common bile duct.
What are Crypts of Lieberkuhn?
The epithelia of the villi extend down into the lamina propria where they form crypts. The cells in these crypts secrete bicarb-rich fluids in the proximal small intestine and absorb bicarb in the distal small intestine.
What is the function of the Hepatic Portal System?
the vasculature delivers absorbed nutrients to the liver before they enter general circulation.
What are the four types of accessory glands and what are their functions?
- Salivary glands-secrete saliva
- Pancreas-secrete pancreatic juices
- Acini
- Liver-secretes bile
Name the characteristics of saliva.
Rich in bicarb, contains mucus, and contains salivary amylase and lysozyme.
The pancreas has both endocrine and exocrine capabilities. What does the EXOCRINE portion do?
It produces pancreatic juices that are rich in bicarb, secretes more protein than any other tissue, and contains enzymes: pancreatic amylases and lipase (breakdown carbs and fats), proteases (breakdown proteins), and nucleases (nucleic acid).
What does the liver do?
Secretes bile Processes nutrients Removes old blood cells Eliminates wastes and toxins Synthesis of plasma proteins Secretion and modification of hormones
How does bile get to the duodenum from the liver and gall bladder?
Liver secretes bile and the gall bladder stores it. To get to the duodenum bile goes through the common hepatic duct and the cystic duct to the common bile duct which connects to the duodenum.
What are the fundamental mechanisms involved in the absorption of carbohydrate digestion products?
Glucose and galactose are absorbed through secondary active transport on the apical membrane and facilitated diffusion on the basolateral membrane. Fructose is absorbed through facilitated diffusion on both membranes.
What are the fundamental mechanisms involved in the absorption of protein digestion products?
Amino acids cross the apical membrane by sodium-linked secondary transport or facilitated diffusion. They cross the basolateral membrane with facilitated diffusion. Dipeptides and tripeptides cross the apical membrane by active transport and then are broken down to amino acids.
What are the fundamental mechanisms involved in the absorption of lipid digestion products?
The major products of lipid digestion enter the enterocyte by simple diffusion across the plasma membrane.
Once inside the enterocyte, lipid digestion products are transported into the ER, where they are used to synthesize triglyeride. Beginning in the endoplasmic reticulum and continuing in the Golgi, triglyceride is packaged with cholesterol, lipoproteins and other lipids into particles called chylomicrons.
Chylomicrons are extruded from the Golgi into exocytotic vesicles, which are transported to the basolateral aspect of the enterocyte. The vesicles fuse with the plasma membrane and undergo exocytosis, dumping the chylomicrons into the space outside the cells.
Chylomicrons are transported first into the lymphatic vessel than into the blood.
How is lipid absorption related to the hydrophobic nature of fats?
Lipids are unable to go directly into the blood, since blood is mostly water. They need to be transported through the lymph system and then into the blood.
The digestion of carbohydrates is complete when they have been reduced to _________.
monosaccharides
The digestion of proteins is complete when _______.
they are broken down into amino acids that can be absorbed.
Can fats be transported directly to the bloodstream?
No, lipids are hydrophobic and blood is mostly water.
What are chylomicrons and what is their role in lipid absorption?
Chylomicrons are a small fat globule that help lipids enter the lymph system to be absorbed.
What is the role of bile salts?
Bile salts increase the surface area of droplets by breaking each large droplet into several small droplets: emulsification
How are vitamins A, D, E, and K absorbed?
Absorbed with lipids and go into the lymphatic system
How are water-soluble vitamins absorbed?
with special transport proteins
How is vitamin B12 absorbed?
It will only absorb if bound to intrinsic factor.
Tell me about sodium absorption….
solvent drag with water reabsorption.
actively absorbed in the jejunum, ileum, and colon
True or False: Chloride passively follows sodium absorption.
True
True or False: Potassium is passively absorbed and is secreted when lumenal concentrations are very low.
True
True or False: Bicarb ions are actively absorbed in the ileum and colon and secreted in the jejunum.
False. Bicarb ions are passively absorbed in the jejunum and secreted in exchange for chloride ions in the ileum and colon.
