Biology 3.5 Flashcards
(22 cards)
The urinary system
Excretion of harmful substances and osmoregulation that regulates osmotic pressure by controlling water and salt concentration. Blood filtered by kidneys makes using that goes through ureters and stored in bladder before excreted through the urethra.
Kidney structure
Outer layer is cortex. Inner layer is medulla. Nephrons are filtering units that begin in the cortex and makes urine. Urine travels through tubules in the medulla and then to renal pelvis where it is drained into bladder via ureter
The nephron
Tubular filtering unit closely associated with blood vessels. When blood is filtered at nephron, large molecules cannot enter the filtrate. Small molecules such as glucose, salts, urea, and water are reabsorbed in specific nephron structures to be returned to the body through closely associated vasculature to dispense of waste in concentrated urine. Consists of afferent arteriole, glomerulus, efferent arteriole, particular capillaries and vasa recta.
Afferent arteriole
Part of the nephron. Vessel that carries blood to the glomerulus.
Glomerulus
Part of the nephron. Tight, knot-like structure of vessels encapsulated by the bowman’s capsule. High pressure in glomerulus allows the blood to be filtered into the bowman’s capsule via bulk flow.
Efferent arteriole
Part of the nephron. Narrow vessel with remaining blood from glomerulus. Restricts blood flow and generates high pressure in glomerulus.
Particular capillaries
Part of the nephron. Low pressure capillary bed surrounding the convoluted tubules that absorb small molecules reabsorbed from filtrate
Vasa recta
Part of the nephron. Unbranched capillary network with similar shape to loop of Henlé. Absorbs materials reabsorbed from loop of Henlé.
Nephron structure
In the order of filtrate flow: Bowman’s capsule, Proximal convoluted tubule, loop of Henlé, distal convoluted tubule and collecting duct
Bowman’s capsule
Part of nephron structure. Cups the glomerulus with highly porous wall, located in cortex. Highly porous inner wall is a filter for blood passing through the glomerulus to make glomerular filtrate
Proximal convoluted tubule
Part of nephron structure. Highly twisted tubule extending from the Bowman’s capsule. All glucose, amino acids, vitamins, hormones, and most water and mineral ions are reabsorbed
Loop of Henlé
Part of nephron structure. Hairpin shaped tube extending into medulla. Descending limb carries filtrate deep into medulla of kidney and reabsorbs water from filtrate. Ascending limb carries filtrate back up to the cortex and reabsorbs salts from filtrate.
Distal convoluted tubule
Part of nephron structure. Highly twisted, located in cortex. Reabsorbs salt from filtrate.
Collecting duct
Part of nephron structure. Wide tube, travels from cortex to medulla to renal pelvis. Multiple nephrons drain into collecting duct which carries the filtrate through the cortex, medulla and renal pelvis. Site of urea, salt, water reabsorption which is controlled by ADH (Anti-diuretic hormone)
Nitrogen Waste
Produces ammonia NH3 that is toxic to animals.
- Aquatic animals/fish: excrete NH3+/NH4+ directly into the water
- Mammals: Converts NH3 to urea in the liver which conserves water and is less toxic
- Birds, insects, reptiles: Converts urea to uric acid crystals, conserves water, uric acid is insoluble
- Eggs: Special sac called allantois physically separates solid nitrogen toxic waste from the developing embryo
Urine filtration at the Nephron, 3 steps
Filtration, secretion, reabsorption
Filtration
1st step of urine filtration at the Nephron. When blood from afferent arteriole enters the glomerulus, the high pressure forces small molecules to exit the glomerular capillaries via small pores on the inner surface of the Bowman’s capsule. Produces glomerular filtrate that enters the Bowman’s capsule and travels to the proximal convoluted tubule
Secretion
2nd step of urine filtration at the Nephron. Additional fluids and substances secreted from the capillaries of efferent arteriole can be secreted into the convoluted tubule. Materials are selectively secreted via active and passive transport.
Reabsorption
3rd step of urine filtration at the Nephron. At proximal convoluted tubule, filtrate reabsorbs glucose, amino acid, vitamins, hormones, water and mineral ions. Loop of Henlé creates salt gradient in fluid surrounding tubule at medulla. The descending limb is permeable to water and impermeable to salts; ascending limb is impermeable to water and permeable to salts. Filtrate on descending limb, reabsorbs water and produces increasingly concentrated filtrate as it moves further down the loop. Filtrate on ascending limb, salt is transported out of filtrate and produces a decreasingly concentrated filtrate as it moves up the loop. Vasa recta surrounding the loop of Henlé flows in the opposite direction which carries away the reabsorbed water or salt in a process called counter-current exchange, results in salt gradient and increasing salt concentration as we move deeper into medulla. After the loop, filtrate goes to distal convoluted tubule where additional reabsorption of salts occur. Filtrate of several nephrons then drain into collecting duct which passes through the medulla and drains into renal pelvis and ureter. At the same time, hypertonic solution of the deep medulla draws water by osmosis to make highly concentrated urine
Kidney hormone influence
Water level of organism (osmoregulation) is controlled by regulating concentration of the filtrate using 2 hormones: antidiuretic hormone (ADH) and aldosterone
Antidiuretic hormone (ADH)
Aka “vasopressin”. Increases water absorption by the body, increases salt concentration in urine, increases water permeability of the collecting duct before it dumps into the renal pelvis
Aldosterone
Increases reabsorption of sodium which causes reabsorption of water via osmosis. Increases permeability of the distal convoluted tubule and collecting duct to Na+. Increases salt concentration using water to passively flow.
