In a healthy individual, GFR is approximately 125 mL per minute, or about 180 litres per day.
Glomerular filtration rate is the amount of filtrate formed by the kidneys per minute.
JGA is formed by cellular modifications in the DCT and afferent arteriole at their contact point. A fall in GFR activates JG cells to release renin. Renin stimulates glomerular blood flow through the renin-angiotensin mechanism, restoring GFR toward normal.
GFR is autoregulated mainly by the juxta glomerular apparatus through renin release when GFR falls.
Micturition is controlled by a neural reflex. ADH promotes water reabsorption and makes urine more concentrated, not hypotonic. Glomerular filtrate is protein-free plasma filtrate. Henle's loop maintains medullary osmotic gradient. Glucose is actively reabsorbed mainly in PCT.
(a) True. (b) False. (c) True. (d) True. (e) True.
Filtrate flows in opposite directions in the two limbs of Henle's loop, and blood flows oppositely in the two limbs of vasa recta. NaCl is transported out of the ascending limb and exchanged with vasa recta, while urea recycles between collecting duct and Henle's loop. This maintains medullary osmolarity from about 300 mOsmol/L in cortex to 1200 mOsmol/L in inner medulla, allowing water reabsorption from collecting ducts.
Counter current mechanism maintains a high osmotic gradient in the renal medulla, enabling production of concentrated urine.
Lungs eliminate about 200 mL CO2 per minute and water vapour. Liver secretes bile containing bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs, which leave with digestive wastes. Sweat contains water, NaCl, small amounts of urea and lactic acid; sebaceous glands eliminate sterols, hydrocarbons and waxes.
Lungs remove CO2 and water; liver excretes bile pigments and other substances through bile; skin removes small wastes through sweat and sebum.
As the bladder fills, stretch receptors in its wall send signals to the CNS. The CNS sends motor signals that contract bladder smooth muscles and relax the urethral sphincter, releasing urine. This neural mechanism is called the micturition reflex.
Micturition is the process of releasing urine from the urinary bladder through the urethra.
Bony fishes are ammonotelic. Bowman's capsule is part of the renal tubule/nephron. Micturition involves the urinary bladder. Birds are uricotelic. ADH facilitates water reabsorption.
(a)-(iii), (b)-(v), (c)-(iv), (d) Uricotelism-(i), (d) ADH-(ii).
Excretory organs help maintain ionic concentration, fluid volume and acid-base balance. In humans, kidneys regulate water, salts and wastes through filtration, reabsorption and secretion.
Osmoregulation is regulation of water and solute concentrations in body fluids to maintain osmotic balance.
Water availability is limited on land. Urea is less toxic than ammonia and can be excreted with moderate water loss, while uric acid is least toxic and can be excreted as paste/pellets with minimal water loss.
Ammonia is highly toxic and requires large amounts of water for excretion, so terrestrial animals convert it to less toxic urea or uric acid to conserve water.
When glomerular blood flow, blood pressure or GFR falls, JG cells release renin. Renin activates the renin-angiotensin mechanism, increasing glomerular blood pressure and restoring GFR. It also promotes aldosterone release, increasing Na+ and water reabsorption.
JGA regulates glomerular filtration rate and blood pressure through renin release.
Protonephridia/flame cells occur in Amphioxus among chordates. The cortex extending between medullary pyramids forms renal columns called Columns of Bertini. The U-shaped capillary running parallel to Henle's loop is vasa recta.
(a) Amphioxus. (b) Columns of Bertini or renal columns. (c) Vasa recta.
The descending limb is water permeable, while the ascending limb is water impermeable. ADH increases water reabsorption from later tubules. Dialysing fluid lacks nitrogenous wastes so they diffuse out of blood. Average urea excretion is 25-30 g/day.
(a) impermeable; permeable. (b) ADH/vasopressin. (c) nitrogenous wastes. (d) 25-30.