Digestion and Absorption Flashcards
(22 cards)
1
Q
What 3 locations does Digestion occur?
A
- Luminal digestion
- In the GI lumen
- Mediated by enzymes in salivary glands, stomach, and pancreas
- Membrane digestion
- Brush border enzymes
- a-dextrinase, maltase, sucrose, trehalase, and sucrose
- Synthesized by enterocytes that are inserted into the membrane
- Brush border on the luminal surfaces of the cells is permeable to both sodium ions and water.
- Intracellular digestion
* Mediated by cytoplasmic enzymes within enterocytes
2
Q
Where does Carbohydrates get absorbed?
A
- Proximal Small Intestines
3
Q
Where does Bile and Vitamin B12 get absorbed?
A
- Distal Ileum
4
Q
What does Lactose breakdown into?
A
- Glucose and Galactose
- Due to Lactase making it into a monosaccharide for it to be absorbed inot the intestinal mucosa
5
Q
What does Sucrose breakdown into?
A
- Glucose and Fructose
- Breaksdown by sucrase
6
Q
How are carbohydrates (starch) digested?
A
- Begins in the mouth by salivary a-amylase
- Most digestion occurs in the small intestines by Pancreateic amylase
- Breaksdown into disaccharides
- Disacchrides are broken down by Intestinal Brush Border Enzymes to monosaccharides
- a-dextrinase, maltase, sucrose, trehalase, and sucrose
7
Q
How is Glucose and Galactose Absorbed?
*Comes from Lactose
A
- Transported from intestinal lumen into the cells by SGLT 1 (Secondary Active transport-Cotransport)
- From cell to blood Glucose and Galactose transported by Facilated diffusion (GLUT 2)
- Clinical
- Oral Rehydration Solution
- Contains Na and Glucose for reuptake
- Restores body fluid volume
- Ex: Cholera
- NA and glucose are rapidly reabsorbed by intestinal epithelia via SGLT 1
8
Q
How is Fructose Absorbed?
A
- Transports by Facililated Diffusion (GLUT 5) across the brush-border membrane
- Clinical
- Patient can’t express Functional SGLT-1
- Unable to resabsorb glucose
- Alternate route
- GLUT-5 converts fructose to glucose in the Liver
9
Q
What is Lactose Intolerance?
A
- Absent Brush-Border Enzyme Lactase
* Lactase splits Lactose into Glucose and Galactose - Lactose can’t be brokendown without lactase and remains undigested in the intestinal lumen
- Nonabsorbable
- Holds water in the lumen causing Osmotic Diarrhea
- Lactose gets fermented by colonic bacteria
- Produces gases (hydrogen and carbon dioxide) and Lactic Acid
10
Q
How are proteins Digested?
A
- Begins in the stomach due to acidic pH and Pepsin
- Most digestion occurs in the Small Intestines by Pancreatic and Brush-border proteases
*Enterocytes cytoplasm site of peptide degradation which allows amino acids to enter portal blood
11
Q
How does Stomach Protein Digestion occur?
A
- Chief cells secrete Pepsinogen
- Parietal cells secrete HCl
- HCl converts Pepsinogen to Pepsin in Low pH
* Pepsin is denatured in the duodenum b/e pH is greater than 5
*Pepsin is not essential for protein digestion
- Pancreatic and brush-border proteases can digest proteins and pepsin is not necessary
12
Q
What is Cystinuria?
A
- Disorder in the transport of amino acids
- Cystine, Lysine, Arginine, and Ornithine (“COAL”)
- Absent in Small Intestines and Kidney
- No reabsorption of amino acids causing Excess CYSTINE EXCRETION
13
Q
What is Cystic Fibrosis?
A
- Mutation in CFTR (cystic fibrosis transmembrane conductance regulator)
- Thick mucus blocks ducts that prevent transport of enzymes to intestines for digestion
- Pancreatic enzyme deficiency
* leads to intestinal malabsorption
14
Q
How are Lipids digested in the Stomach?
A
- Lipid digestion begins in the stomach
* By Lingual and Gastric Lipases - Lingual and Gastric lipases hydrolyze triglycerides into Glycerol and 2 fatty acids
15
Q
How are Lipids digested in the Small Intestines?
A
- Digestion of lipid is completed in the Small Intestines
* By Pancreatic lipase, choleterol ester hydrolase, and phospholipase A2 - Pancreatic lipase Requires COLIPASE
- Hydrolyze fats
- Displaces bile salt to create binding site for pancreatic lipase
16
Q
What are Chylomicrons?
A
- Reesterfied lipids packed with Apoproteins
- Contains
- Triglycerids and Cholesterol at CORE
- Apoproteins on OUTSIDE
- Packaged in vesicles on the Golgi apparatus
* Chylomicrons too large to enter blood, which they enter the LACTEAL of the lymph
*Apoproteins synthesized by Enterocytes for absorption
17
Q
What is Abetalipoproteinemia?
A
- Failure in synthesizing Apo B (Beta-lipoproteins)
- Results
- Malabsorption of chylomicrons
- Dietary lipids
- Fat soluble vitamins
18
Q
How is Calcium Absorbed?
A
- Calcium enter enterocytes by calcium channels
- Binds to CALBINDIN
- Calcium in enterocytes transport by Ca2+-ATPase and 3Na+/Ca2+ exchanger
- Vitamin D induces Calbindin D-28 K in enterocytes
- Vitamin D-dependent Ca2+ binding protein
- Increase calcium absorption
- Calcium absorption depends on VITAMIN D3
19
Q
How is Iron Absorbed?
A
- Free iron bind to Apoferritin
- In Circulation, iron binds to transferrin
* Transports iron from the small intestines to the liver for storage (Stored as Ferritin) - Iron is transported from the Liver to Bone Marrow
* Released in bone marrow for Synthesis of Hemoglobin
20
Q
How are Electrolytes transported in the Jejunun?
A
- Na+ absorption occurs via (mutation in transport causes diarrhea)
- Na+-glucose cotransport
- Na+-amino acid cotransport
- Na+- H+ exchanger
- Carbonic anhydrase
- Converts CO2 and H2O into H+ and HCO3-
- HCO3- absorbed into blood
- Jujunum, Net absorption of NaHCO3
21
Q
How are Electrolytes transported in the Ileum?
A
- Contain all the same transporters as the Jejunum plus
- Cl--HCO3 exchanger in apical membrane
- Cl-transporter in basolateral membrane
- HCO3 is secreted instead of being absorbed into the blood as in the Jejunum
- Net movement of NaCl into the cell for absorption
22
Q
How are electrolytes transported in the Colon?
A
- Contains
- Na+-K+ channels (Stimulated by Aldosterone)
- Na absorption into cell
- K secretion into lumen
