Related Subjects:
|Metabolic acidosis
|Lactic acidosis
|Acute Kidney Injury (AKI) / Acute Renal Failure
|Renal/Kidney Physiology
|Chronic Kidney Disease (CKD)
|Anaemia in Chronic Kidney Disease
|Analgesic Nephropathy
|Medullary Sponge kidney
|IgA Nephropathy (Berger's disease)
|HIV associated nephropathy (HIVAN)
Glucose, Amino acids, organic acid and phosphate and sulphate are transported from the lumen coupled to a Na+ transport and driven by energy in the electrochemical gradient of Na+
Anatomy
- 11-14 cm length
- Located retroperitonealy
- Adjacent to T12 to L3
- Medially is the aorta and IVC
Functions
- Excretes urea, ammonia , creatinine, uric acid
- Excretes drugs and other toxins
- Manages water and salt balance and homeostasis
- Manages electrolytes
- Calcium and phosphate homeostasis
- Activates Vitamin D
- Erythropoiesis through erythropoietin release
Basics
- Each kidney has 1,000,000 nephrons
- This is the longest part of the nephron (1 cm) and consists of polar cells with different basolateral and apical surfaces covered with brush border and microvilli
- Basolateral surface contains many mitochondria providing ATP for Na+-K+-ATPase pump pumping N+ out of the cell into blood
- There is a huge 100m 2 of surface area absorbs huge amount of solutes
Uptake
- Tight junctions allow water and small ions such as Na, K, Cl and H2O to pass
- Active uptake by special co-transporters of D-Glucose/Na+ transporter, L-Amino acids/Na+ co transporter, Lactate, Sulphate, Phosphate, dicarboxylates
- Brush border peptidases break down oligopeptides into amino acids for uptake
- Albumin, lysozyme, alpha1-microglobulin, B2 microglobulin and other proteins taken up by receptor-mediated endocytosis
- Glucose is absorbed up to its tubular maximum with Na+ as a co-transporter - any excess glucose that exceeds this TM leads to glycosuria. Note that only D-Glucose is taken up this way.
- There are at least 5 different transporters for amino acids - (1)Imino acids (2) Neutral acids (3)Basic (4) Aspartate and Glutamate (5) Glycine and defects are seen - Check out Hartnup's disease
Secreted
- Organic acids: PAH, frusemide, ethacrynic acid, Penicillin, sulphonamide, salicylates - Where Penicillin excretion is a problem a competitive inhibitor such as probenecid can be given to reduce its urinary loss
- Organic bases: Tetraethylammonium ion, acetylcholine, Adrenaline [US Epinephrine] , histamine, riboflavin, thiamin, amiloride, morphine, quinine
- Ammonium ions which help to maintain pH. Ammonium is formed from Glutamine (produced in the liver) in the Proximal tubular cells which it enters by Na+ co-transport. Breakdown of the amino acid releases
Secreted and Reabsorbed
- Urate is both filtered and reabsorbed and secreted by proximal tubular cells - net reuptake can result in gout.
- Probenecid blocks urate reuptake
Others
- Magnesium which is free is filtered and most is taken up in the thick ascending limb (stimulated by PTH) and 25% in the PCT
- Calcium which is free is filtered and is absorbed in the ascending limbs of the loop of Henle and distal tubules and collecting ducts (Action of PTH)
- Phosphate - reabsorbed in PCT and is inhibited by PTH
- Sulphate - reabsorbed in PCT with Na cotransporter
- Bicarbonate - Filtered HCO3- with tubular excreted H+ forms H20 and CO2. For each H+ released a HCO3 is returned ot the plasma across basolateral membrane
- Amino acid + O2 ? NH4+ + HCO3-
- NH4+ + HCO3- ? urea + CO2 + H 2O
Physiology
- Kidneys
- Receive 20% of cardiac output
- Each nephron is supplied by an afferent arteriole which enters the glomerulus a sort of twisted look of blood vessels which is wrapped in a basement membrane and beyond that the foot processes of podocyte. Structural support is with mesangial cells.
- Glomerular filtrate
- Only 20% of renal blood flow becomes Glomerular filtrate
- Under control of the afferent and efferent arterioles.
- It is a passive process depending on hydrostatic pressure
- This depends on BP and efferent arteriole resistance
- Renal functional unit is the nephron
- 1,000,000 nephrons per kidney
- Consists of
- Glomerulus
- Proximal tubule
- Loop of henle
- Distal convoluted tubule
- Collecting ducts.
- Each part of the nephron has its own distinct and highly specialised role.
- Glomerular Basement Membrane
- Type IV collagen
- Negatively charged
- More resistance to negatively charged molecules than neutral
- The filtration barriers consists of
- Fenestrated endothelium 50-100 nm pore size
- The Glomerular Basement Membrane
- Podocyte foot processes within between slit pores of 5 nm
- Measuring Glomerular flow rate
- 130 ml/min per 1.73 m2 of surface area in men
- 120 ml/min per 1.73 m2 of surface area in women
- Inulin: freely filtered (M=5000) and is neither absorbed or excreted or metabolised on its way through the nephron.
- Chromium labelled EDTA
- Iohexol an iodine based non ionic water soluble compound
- Creatinine which is derived from creatine
- Used as a rough estimation of GFR. Typical GFR = 180 L/day
- Produced from muscle cells at constant rate
- Various factors can change creatinine levels