Digestion and Absorption Flashcards Preview

Physiology 1 Block 2 > Digestion and Absorption > Flashcards

Flashcards in Digestion and Absorption Deck (22):
1

What 3 locations does Digestion occur?

1. Luminal digestion

  • In the GI lumen
  • Mediated by enzymes in salivary glands, stomach, and pancreas

2. 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.

3. Intracellular digestion

  • Mediated by cytoplasmic enzymes within enterocytes

 

2

Where does Carbohydrates get absorbed?

1. Proximal Small Intestines

3

Where does Bile and Vitamin B12 get absorbed?

1. Distal Ileum 

4

What does Lactose breakdown into?

1. Glucose and Galactose

2. Due to Lactase making it into a monosaccharide for it to be absorbed inot the intestinal mucosa

5

What does Sucrose breakdown into?

1. Glucose and Fructose

2. Breaksdown by sucrase 

6

How are carbohydrates (starch) digested?

1. Begins in the mouth by salivary a-amylase

2. 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

How is Glucose and Galactose Absorbed?

 

*Comes from Lactose

1. Transported from intestinal lumen into the cells by SGLT 1 (Secondary Active transport-Cotransport)

2. From cell to blood Glucose and Galactose transported by Facilated diffusion (GLUT 2)

3. 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

How is Fructose Absorbed?

1. Transports by Facililated Diffusion (GLUT 5) across the brush-border membrane

2. Clinical

  • Patient can't express Functional SGLT-1
    • Unable to resabsorb glucose
  • Alternate route
    • GLUT-5 converts fructose to glucose in the Liver

9

What is Lactose Intolerance?

1. Absent Brush-Border Enzyme Lactase

  • Lactase splits Lactose into Glucose and Galactose

2. 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

How are proteins Digested?

1. Begins in the stomach due to acidic pH and Pepsin

2. 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

How does Stomach Protein Digestion occur?

1. Chief cells secrete Pepsinogen

2. Parietal cells secrete HCl

3. 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

What is Cystinuria?

1. Disorder in the transport of amino acids

  • Cystine, Lysine, Arginine, and Ornithine ("COAL")
  • Absent in Small Intestines and Kidney

2. No reabsorption of amino acids causing Excess CYSTINE EXCRETION

13

What is Cystic Fibrosis?

1. Mutation in CFTR (cystic fibrosis transmembrane conductance regulator)

2. Thick mucus blocks ducts that prevent transport of enzymes to intestines for digestion

3. Pancreatic enzyme deficiency 

  • leads to intestinal malabsorption

14

How are Lipids digested in the Stomach?

1. Lipid digestion begins in the stomach

  • By Lingual and Gastric Lipases

2. Lingual and Gastric lipases hydrolyze triglycerides into Glycerol and 2 fatty acids

15

How are Lipids digested in the Small Intestines?

1. Digestion of lipid is completed in the Small Intestines

  • By Pancreatic lipase, choleterol ester hydrolase, and phospholipase A2

2. Pancreatic lipase Requires COLIPASE

  • Hydrolyze fats
  • Displaces bile salt to create binding site for pancreatic lipase

16

What are Chylomicrons?

1. Reesterfied lipids packed with Apoproteins

2. Contains

  • Triglycerids and Cholesterol at CORE
  • Apoproteins on OUTSIDE

3. 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

What is Abetalipoproteinemia?

1. Failure in synthesizing Apo B (Beta-lipoproteins)

2. Results

  • Malabsorption of chylomicrons
    • Dietary lipids
    • Fat soluble vitamins

18

How is Calcium Absorbed?

1. Calcium enter enterocytes by calcium channels

2. Binds to CALBINDIN

3. Calcium in enterocytes transport by Ca2+-ATPase and 3Na+/Ca2+ exchanger

4. Vitamin D induces Calbindin D-28 K in enterocytes

  • Vitamin D-dependent Ca2+ binding protein
  • Increase calcium absorption

5. Calcium absorption depends on VITAMIN D3

19

How is Iron Absorbed?

1. Free iron bind to Apoferritin 

2. In Circulation, iron binds to transferrin

  • Transports iron from the small intestines to the liver for storage (Stored as Ferritin)

3. Iron is transported from the Liver to Bone Marrow

  • Released in bone marrow for Synthesis of Hemoglobin 

20

How are Electrolytes transported in the Jejunun?

1. Na+ absorption occurs via (mutation in transport causes diarrhea)

  • Na+-glucose cotransport
  • Na+-amino acid cotransport
  • Na+- H+ exchanger

2. Carbonic anhydrase

  • Converts CO2 and H2O into Hand HCO3-
  • HCO3- absorbed into blood 

3. Jujunum, Net absorption of NaHCO3

21

How are Electrolytes transported in the Ileum?

1. Contain all the same transporters as the Jejunum plus

  • Cl--HCO3 exchanger in apical membrane
  • Cl-transporter in basolateral membrane

2. HCO3 is secreted instead of being absorbed into the blood as in the Jejunum

3. Net movement of NaCl into the cell for absorption

22

How are electrolytes transported in the Colon?

1. Contains

  • Na+-K+ channels (Stimulated by Aldosterone)
    • Na absorption into cell
    • K secretion into lumen