The system responsible for regulating the water balance, electrolyte balance and acid-base balance of the body, as well as the excretion of metabolic wastes
Kidneys
Homeostatic function: Regulation of the water balance, electrolyte balance and acid-base balance
Excretory function: Excretion of metabolic wastes, urea, creatinine, toxins, drugs, excess minerals, water
Endocrine secretory function: Secretion of renin, erythropoietin and prostaglandins
Endocrine metabolic function: Conversion of Vitamin D3 in active 1,25-dihydroxycholecalciferol
Urine formation
1. Filtration from glomerular capillaries into Bowman's capsule
2. Reabsorption of organic nutrients, ions and water
3. Secretion of waste products
Glomerular filtration rate
Volume of filtrate/min, 180 L/day
Nutritional substances are completely reabsorbed from the tubules and do not appear in the urine
Substances that must be cleared from the blood (e.g. urea, creatinine, uric acid) are poorly reabsorbed and excreted in large amounts in the urine
Tubular transport
1. Reabsorption and secretion of substances
2. In loop of Henle: Descending limb is permeable to water, ascending limb is impermeable to water but permeable to solutes
Urine concentration
1. Continuing to secrete solutes while increasing water reabsorption
2. Requires high level of ADH and highly osmolar renal medullary interstitium
Plasma osmolality
Measure of osmotically active solutes in plasma, normal range 282-295 mOsm/kg H2O
Alterations in plasma osmolality
Can cause swelling or shrinking of cells, leading to cell death
ADH mechanism of action
ADH acts on collecting duct cells, stimulating insertion of water channels (aquaporins) to promote water reabsorption
High plasma osmolality
Increases ADH secretion, leading to more water reabsorption and less water excretion
Low plasma osmolality
Decreases ADH secretion, leading to less water reabsorption and more water excretion
Blood pressure
The pressure blood exerts on the arterial walls, determined by cardiac output and total peripheral resistance
Kidneys regulate blood pressure
By regulating extracellular fluid volume through excretion of variable amounts of sodium and water
RAAS (Renin-Angiotensin-Aldosterone System)
1. Renin converts Angiotensinogen into Angiotensin I. ACE converts Angiotensin l into Angiotensin II->Aldosterone
2. Increases water and sodium reabsorption, leading to increased blood pressure
Anatomy of the renal system
kidneys
renal artery and vein
ureter
bladder
urethra
Anatomy of the kidneys:
capsule
cortex
medulla
calyx
renal pelvis
ureter
Urine in the kidneys:
Urine is formed from the arterial blood that enters the kidney via renal artery
Urine is collected in the calyx, leads to the renal pelvis and finally the ureter
Filtered blood leaves the kidney through renal vein