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Physiology (L09) Slides#58 + #59 : -The only site for exchange inside our body is the capillaries. -The amount of oxygen in pulmonary vein and in radial artery is the same, what differs is the amount of oxygen in the artery and the vein of one structure because between we have a capillary where exchange of materials occur. -Pre-capillary center is within the arteriol that comes from the heart. -The capillaries have no blood vessels and therefore they have no vasodilatation neither vasoconstriction. -There are about 12 billions of capillaries in our body. Cross sectional area for an individual capillary is small, but when we multiply by 10 or 12 billion it becomes massive. Surface area of capillaries is around 500-700 m² which is a very huge area and therefore the exchange occurs very fast within the capillary, the velocity of blood when passing through the capillary is very low to allow the efficient time for exchange. Slide#60: -Simple diffusion is for substances that pass through the wall of the capillary, such as: lipid soluble and hydrophobic substances (gases), it is passive and does not need energy. That is why anesthetics use gases instead of solid drugs for their work, another reason for using gases is that when you remove gases, they move according to their concentration gradient and this makes it easy to remove, and they leave via the respiratory system . When using substances, they bind to their receptors and will not be removed unless with urine which takes a long time. –The thicker the membrane, the slower rate of diffusion, as what happened with hypoxia patient when the membrane between the lung and alveoli gets thicker. -Facilitated diffusion occurs via receptors and when all receptors are occupied, the velocity reaches what is called a V𝒎𝒂𝒙 and a (K𝒎) when K𝒎 is high, the affinity is low and vice versa. Slides#61 + #63: -There are certain forces that affect the filtration and reabsorption, such forces are present in capillary such as: hydrostatic pressure, it is 35 mmHg in the arterial site of the capillary, the hydrostatic pressure tries to push the fluid outside the capillary (filtration). A second force is the colloid osmotic pressure (colloid means caused by proteins, since that: plasma and interstitial fluid have the same total osmotic pressure since they have the same amounts of ions, the only difference is in plasma proteins and that is why we deal with colloid osmotic pressure). Plasma proteins are: Albumin, globulin and fibrinogen. –The osmotic pressure depends on the number of molecules, not on the grams. For example: if we take 23 gm of Na+ and 39 gm of K+, they have the same number of molecules which is called Avogadro number. 1 mole of any substance has Avogadro number of molecules which is 6.23 x 10²³. (23 is the M𝒘 of Na ; whereas 39 is the M𝒘 of K). –When we take 1 gm of Na+ and 1 gm of K+, the Na+ will have a higher osmotic pressure because it has more number of molecules (#moles=weight/ M𝒘). –According to plasma proteins Albumin participates the most in the colloid osmotic pressure. -Plasma proteins cannot pass the capillary membrane, they only attract the substances to them, causing reabsorption. Slide#62: -The colloid osmotic pressure in the interstitial fluid is extremely low. The hydrostatic pressure in that fluid is responsible for the process of filtration. Slide#64: -If the net filtration pressure is positive, there is filtration. And if it is negative then there is reabsorption. -Normally filtration and reabsorption have to be equal. -Any protein that passes from the capillary into the interstitial fluid will be reabsorped in the lymphatics. -Edema is collection of fluid in the interstitial space, and may happen anywhere. An example: people who have cirrhosis in the liver, their liver which is responsible for protein synthesis becomes sick, therefore it stops synthesize Albumin (hypoalbuminemia) which decrease the colloid osmotic pressure leading to more filtration and accumulation of fluid in the abdominal cavity which is an edema. Slide#65: -The blood hydrostatic pressure in veins are higher than the arterioles in order to cause a flow according to pressure gradient in a direction from arteriole to vein. Slides#68 + #69: -Filtration rate: how much fluid is filterd? -Filtration coefficient is constant. -In hypertension and venous growth the P𝒄 becomes high and therefore there is an increase in filtration rate and therefore causing edema. -Lymphatic capillary which is responsible for reabsorption fluid, if it has been blocked for any reason, edema will occur. -A person with a kidney disease, his kidney causes leakage of Albumin with urine causing hypoalbuminemia causing edema. Slide#71: THANK YOU!