Summary: Medical Physiology

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• 68 Metabolism of carbohydrates and formation of Adenosine Triphosphate

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• What are the 3 final products of carbohydrate digestion and which one is the most important one?

  Glucose is the most important one (80%), fructose and galactose

• How is glucose transported through the cell membrane of most tissue cells? And how is it transported through the gastrointestinal membrane and through the ephitelium of the renal tubules?

  Through most tissue cell membranes glucose is transported by faciliated diffusion, moving from high concentration to low concentration. Glucose carrier proteins are present on the membranes to make the diffusion of the large glucose molecules possible. 
  
  For the gastrointestinal membrane and the epithelium of the renal tubules the mechanism of active sodium-glucose-co-transport is used, in which active transport of sodium provides energy for absorbing glucose against a concentration difference. 

• What happens immediately upon entry of glucose into the cells, that can only be reversed in liver cellls, renal tubular epithelial cells and intstinal epithelial cells? And why does this happen?

  Upon entry glucose phosphorylates into glucose-6-phosphate, which is promoted by the enzyme glucokinase (liver) and hexokinase (other cells). The phosphorylation serves to "capture" the glucose.

• During the breakdown of glucose a total of 38 ATP molecules are formed. Which steps are taken and how many ATP molecules are gained per step?

  1 - glycolysis: phosphorylation of glucose. 2 ATP needed, 4 formed --> net gain of 2 ATP 
  2 - citric acid cycle: happens twice, because one glucose gives two pyruvic acid molecules. --> gain 2 ATP 
  3 - During step 1 and 2, 24 hydrogen ions are released. 20 of those are oxidized with conjuction. Per 2 hydrogen atoms metabolized 3 ATP molecules are gained. --> adding 30 ATP
  4 - Remaining four hydrogen atoms are released by their dehydrogenase. Two ATP molecules are usually released for every two hydrogen atoms oxidized. --> gain 4 ATP 

• How can anaerobic glycolysis be a lifesaving measure for up to a few minutes when oxygen becomes unavailable?

  During anaerobic glycolysis lactid acid is formed out of pyruvic acid, NADH and H+, which are the glycolytic end products. Therefor lactic acid represents a type of sinkhole into which the glycolytic end products can dissappear, thus allowing glycolysis to proceed far longer than would otherwise be possible. Supplying extra ATP to the body. 
  
  When oxygen is available (again) the heart muscle especially will use the lactic acid by converting it back to pyruvic acid and using it for energy. 

• What is the pentose phosphate pathway?

  A mechanism for the breakdown and oxidation of glucose, which is responisble for 30% of the glucose breakdown in the liver and even more than that in fat cells. Can provide energy without using enzymes.

• 69 Lipid Metabolism

• 69.1 Transport of lipids in the body fluids

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• How are all the fats absorbed from the intestines?

  While passing through the intestinal epithelial cells the monoglycerides and fatty acids are resnthesized into lipoproteins called chylomicrons. Chylomicrons are composed of 87% triglycerides, 9% phospholipids, 3% cholesterol and 1% apoprotein B. The chylomicrons move from the intestines to the intestinal lymph and eventually enter the blood circulation through the vena cava.

• How long does it more or less take to remove most chylomicrons from the circulation after a meal?

  After around 5-8 hours after a meal there is almost no chylomicrons left in the circulation, because they have a half-life < 1 hours

• What are lipoptroteins? Also name the 4 substances they are composed of and their "normal" concentration in plasma.

  Lipoproteins are small particles, much smaller than chylomicrons, that contain triglycerides, cholesterol, phosolipids and protein.
  
  Cholesterol: 180 mg/dl of plasma 
  Phospholipids: 160 mg/dl of plasma 
  Triglycerides: 160 mg/dl of plasma 
  Protein: 200 mg/dl of plasma 

• Name the four major types of lipoprotreins, classified by their densities, from large to small molecules and what is their primary function?

  VLDLs (very low density lipoproteins)
  IDLs (intermediate-density lipoproteins)
  LDLs (low density lipoproteins)
  HDLs (high density lipoproteins) 
  
  (see notes knowdlegde klip week 21) 
  
  
  Primary function: tranport their lipid components in the blood