Kidney Functions

Kidney function:

1.  Removes foreign compounds from body. Medium for this urine.
2. The maintenance of the extra-cellular fluid in homeostatic state.
3. Regulation of the rate of production of RBC’s.
4. Activation of vitamin D.

Two major components in each nephron:

1. renal corpuscle: fluid is forced out of the capillaries (as blood passes through the glomerulus) and into Bowman’s capsule
2. tubule: filtered fluid is processed to urine on its way through the tubule

Urine formation:

1.glomerular filtration: filtration of fluid from the glomerular capillaries into the renal tubules

2. tubular reabsorption: return of solutes from the tubules back into the blood

3.reabsorption of the bulk of the water via osmosis

4. tubular secretion: movement of solutes into the tubules

Filtration of glomerulus:

1. Fluid and small solutes are forced under pressure to flow from the glomerulus into the capsular space of the glomerular capsule.
2. The Bowman's capsule is the filtration unit of the glomerulus. Blood entering the glomerulus has filterable and non-filterable components.
3.  Filterable blood components include water, nitrogenous waste, and nutrients and will be transferred into the glomerulus to form the glomerular filtrate.
4. Non-filterable blood components include blood cells and platelets and remain in the arteriole

Glomerular Filtration Rate (Gfr)

• Total surface area available for filtration is about 6 m2
• 10% of plasma delivered to kidneys enters the tubules
• GFR = the amount of filtrate produced by the kidneys/minute
• 120-125ml/min (180 L /day): (cf the total volume of blood in your body)
• GFR is a significant clinical determinant.
• Notably renal failure is staged based upon the degree of reduction in GFR as this is indicative of nephron loss

Creatinine clearance:

Exercise

•24h urine sample: 1500 mL

•plasma creatinine: 0.1 mmol/L

•urine creatinine: 10 mmol/L

 = 10 mmol/L x (1500/(24*60)) mL/min  divided by 0.1 mmol/L

 = 104 mL/min

Cystatin C is a cysteine-protease inhibitor that is produced by all nucleated cells in the body at a constant rate .

• It is readily filtratable in the glomerulus and it is catabolised in the PCT, there is no secretion and thus minimal urinary excretion
• Unlike creatinine, plasma cystatin C levels do not vary with muscle mass, gender or dietary protein intake and release remains relatively stable after 2 years of age

Blood Urea Nitrogen (BUN):

•Urea is freely filterable by the glomerulus and is excreted in the urine . Elevated BUN (azotaemia) is characteristic of renal failure. This is linked with a number of complications of renal failure: pruritis, encephalopathy, impaired cardiac function, anaemia .

The greater the level detectable in the urine then the less has been the degree of reabsorption

Diabetes/Glucose

• Glucose is the most important source of energy for all tissues being utilised for both glycolysis and the TCA cycle.
• Hypoglycaemia: blood glucose concentration below the fasting range (< 4.0 mM).
• Hyperglycaemia: blood glucose above the normal range. Elevation of fasting plasma glucose levels over 7.0 mM on more than one occasion is diagnostic of diabetes mellitus.

• glucose that is not immediately required for energy production is stored as glycogen and triglyceride via insulin-mediated processes. In the fasting state the plasma glucose level is maintained by glycogen breakdown or glycogenolysis and gluconeogenesis. The main controllers of these processes and ultimately the plasma glucose level are insulin, glucagon, adrenalin and cortisol.

• Glycolysis- this is the oxidation of glucose through glucose-6-phosphate with the formation of ATP.
• Glycogenesis- formation of glycogen from glucose; stimulated by insulin.
• Glycogenolysis- breakdown of glycogen to glucose-6-phosphate stimulated by glucagon and adrenalin and inhibited by insulin.
• Gluconeogenesis- formation of glucose from amino acids, lactate and triglyceride-derived glycerol.
• Lipogenesis- formation of triglycerides from glucose; stimulated by insulin.
• Lipolysis- liberation of glycerol and fatty acids from triglycerides, and conversion of glycerol to glucose.

Glucagon: Increases

enzyme carnitine acyl transferase (CAT) . CAT activity by mobilising carnitine which is a cofactor of the enzyme