GFR influenced by:• Blood pressure and blood flow• Obstruction to urine outflow• Loss of protein-free fluid• Hormonal regulation – Renin – angiotensin – Aldosterone – ADH – ANP 10
Juxtaglomerular apparatus• Juxtaglomerular cells lie in the wall of afferent arteriole• Macula densa in final portion of loop of Henle – monitor Na+ and Cl- conc. and water• Control blood flow into the glomerulus• Control glomerular filtration 11
• By end of proximal tubule have reabsorbed:• 60- 70% of water and sodium• about 100% of glucose and amino acids• 90 % of K+, bicarb, Ca++, uric acid• Transport maximum – maximum amount of a substance that can be absorbed per unit time• Renal threshold – plasma conc. of a substance at which it exceeds Tm. 19
Loop of Henle• Responsible for producing a concentrated urine by forming a concentration gradient within the medulla of kidney.• When ADH is present, water is reabsorbed and urine is concentrated.• Counter-current multiplier 20
Distal convoluted tubule and collecting ducts• What happens here depends on ADH• Aldosterone affects Na+ and K+• ADH – facultative water reabsorption• Parathyroid hormone – increases Ca++ reabsorption 22
Distal convoluted tubule and collecting ducts• Tubular secretion to rid body of substances: K+, H+, urea, ammonia, creatinine and certain drugs• Secretion of H+ helps maintain blood pH (can also reabsorb bicarb and generate new bicarb) 24
Homeostatic Functions of Urinary System1. Regulate blood volume and blood pressure: – by adjusting volume of water lost in urine – releasing erythropoietin and renin2. Regulate plasma ion concentrations: – sodium, potassium, and chloride ions (by controlling quantities lost in urine) – calcium ion levels
3. Help stabilize blood pH: – by controlling loss of hydrogen ions and bicarbonate ions in urine4. Conserve valuable nutrients: – by preventing excretion while excreting organic waste products5. Assist liver to detoxify poisons
ENDOCRINE FUNCTIONS… Kidneys have primary endocrine function since they produce hormones In addition, the kidneys are site of degradation for hormones such as insulin and aldosterone. In their primary endocrine function, the kidneys produce erythropoietin, renin and prostaglandin. Erythropoietin is secreted in response to a lowered oxygen content in the blood. It acts on bone marrow, stimulating the production of red blood cells.
Renin -the primary stimuli for renin release include reduction of renal perfusion pressure and hyponatremia. Renin release is also influenced by angiotension II and ADH. It is a key stimulus of aldosterone release. The effect of aldosterone is predominantly on the distal tubular network, effecting an increase in sodium reabsorption in exchange for potassium. The kidneys are primarily responsible for producing vitamin D3 from dihydroxycholecalciferol
METABOLIC FUNCTION• Kidney perform gluconiogenesis during periods of starvation.