GI Flashcards
What are the 4 functions of the GI tract
Digestion, Secretion, Absorption, and Motility
Structure of the GI tract wall
Apical layer is the Mucosa, then submucosa, then muscularis externa, then serosa
Layers of the Mucosa
Epithelium, lamina propria, muscularis muscoa
Function of lamina propria
Connective tissue through which small blood vessels, lymphatic vessels, and nerve fibers pass
Function of Muscularis Mucosa
Smooth muscle involved in movement of villi
What is the submucosa
It is the second connective tissue layer. Blood and lymph vessels that have branches that penetrate into BOTH the mucosa above and the muscularis externa below.
Also contains submucosal plexus - Network of neurons that innervate both the Muscosa and Muscularis Externa.
Describe muscularis externa
3 layers- the circular muscles, myenteric plexus, and the longitudinal muscle. These smooth muscles provide the forces for mixing and moving the GI content. The Myenteric plexus is innervated by ANS, have nerve fibers that project to submucosal plexus
Serosa
Thin layer of connective tissue that connects to Abdominal Cavity via thin sheets of connective tissue.
Goblet Cells
Interspersed between epithelial cells and secretes mucus
How is fat absorbed?
Blind-ended lymph vessels called LACTEALS - Eventually enters bloods through the thoracic duct
Digestion by numbers
Amount of fluid ingested - 1200 mL, FLUID SECRETIONS BY GI 7000 Ml, AMOUNT EXCRETED IN FECES 100ML
Carb absorption
250-300g - 2/3 starch rest lactose and sucrose
some digested by salivary amylase most digested by pancreatic amylaseto produce maltose and glucose polymers. Sucose and Lactose is only ingested
Sucrose Lactose and Maltose as well as well as slightly bigger polymers are broken down into monosaccharides by enzymes on brushborder
How is Fructose Absorbed
Facilitated diffusion via glucose transporters to both enter and leave epithelial cell
How is glucose absorbed
BY SECONDARY ATIVE TRANSPORT COUPLED WITH Na-Glu transporter
SGLT -
Leaves cell by GLUT
Proteins
60-90g/d
Digested by pepsin and pancreatic enzymes - trypsin and chymotrypsin
Peptide fragments can be broken at carboxyl terminal via pancreatic enzymes and at amino terminal at the brushborder
Di and Tri peptides are brought into the cell via secondary active transport coupled with H - peptide transproters
Specified transporter for each amino acid bring them in via Na- AA transporter
Small Peptides exit basolateral side via facilitated diffusion transporters.
How is fat absorbed
70-100g/d
Mostly digested by pancreatic lipase which breaks triglycerides to 2 free fatty acids and one monoglyceride
Fats must be emulsified
Diffused into the cell - Reporm to triglycerides in ER - aggregate and coated with amphipathic molecule.
After being processed by Golgi they are relased into interstitial fluid, called Chylomicrons
Requirements for emulsification
Mechanical disruption of large droplets into smaller droplets
An emulsifying agent such as phospholipids and bile salts secreted in bile
Form of fat that enters interstitial fluid from epithelial cells that synthesize the triglycerides
Chylomicrons - They are passed into lacteals
Fat soluble vitamins
A D E K
How are vitamin solublevitamins absorbed
Diffusion or mediated transport
How is B12 absorbed
Must bind to intrinsic factor made by parietal cells in stomach
Malabsorption
Decrease in ability to absorb fat soluble vitamins
Celiac disease
Autoimmune mediated loss of intestinal surface due to sensitivity of wheat proteins known as gluten
Pernicious anemia
Defficiency of b12 causes anemia - Caused by failure to produce intrinsic factor due to autoimmune attack of parietal cells of stomach, loss of part of stomach or small intestine
