Homeostasis-Osmoregulation Flashcards
osmoregulation
the control of water potential in the blood via homeostatic mechanisms
structure of mammalian kidney and their functions
-fibrous capsule: protects kidney
-cortex: outer region, consists of Bowman’s capsule, convulated tubules, blood vessels
-medulla: inner/middle region, consists of loop of Henle, collecting ducts, blood vessels
-renal pelvis: funnel shaped cavity that collects urine into ureter
-ureter: tube that carries urine to the bladder
-renal artery: supplies kidney with oxygenated blood
-renal vein: returns deoxygenated filtered blood to the heart.
structure of nephron
-Bowman’s capsule: a cup shaped capsule that surrounds the glomerulus, inner layer made up of podocytes
-Proximal convulated tubule (PCT): series of loops surrounded by blood capillaries, walls are made up of epithelial cells which have microvilli
-loop of Henle: long hairpin loop that extends from the cortex into medulla, surrounded by capillaries
-Distal convulated tubule (DCT): series of loops surrounded by capillaries but fewer than PCT, walls are made of epithelial tissue.
-collecting duct: a tube into which multiple nephrons’ DCT empties. It’s epithelial cells become increasingly wide as it empties into renal pelvis.
blood vessels associated with a nephron
-afferent: wide vessel arising from renal artery, supplying the nephron with blood.
-glomerulus: arteriole forms a branched knot of capillaries from which fluid is forced (filtrate)
-efferent: narrow vessel that leaves renal capsule. smaller diameter-> increase in blood pressure in glomerulus.
-capillaries: concentrated network of capillaries that surrounds most structures in the nephron that reabsorb water, mineral salts and glucose.
general stages of osmoregulation
-ultrafiltration: formation of glomerular filtrate
-selective reabsorption-glucose, amino acids, water
-maintenance of a gradient of sodium ions in medulla by loops of henle
-reabsorption of water: DCT and collecting ducts
stages of ultrafiltration
-blood enters the Bowman’s capsule through the wide afferent arteriole which branches into smaller capillaries.
-this causes build up of hydrostatic pressure within the glomerulus.
-the smaller molecules carried in the blood to be forced out of capillaries into Bowman’s capsule.
-forms the glomerular filtrate.
3 layers through which ultrafiltration occurs
-1st cell layer: endothelium cells of capillary- contain tiny pores (fenestrations) between the cells, cells e.g. proteins & RBCs are too large to pass through.
-basement membrane: mesh like structure made up of network of collagen and glycoproteins acting as a filter
-2nd cell layer: epithelium cells of Bowman’s capsule-known as podocytes, have many finger-like projections that wrap around the capillary-> increases the surface area for efficient ultrafiltration. Podocytes have small gaps allowing small molecules to filter through
what are the main substances to pass out of capillary to form glomerular filtrate?
-amino acids, water, glucose, urea and inorganic ions (mainly Na+, K+ and Cl-)
-red blood cells ,white blood cells and platelets remain in the blood as they are too large to pass through the holes of capillary.
stages of selective reabsorption
-sodium ions are actively transported out of the PCT into the blood in the capillaries
-this lowers the conc. of sodium ions inside epithelial cells, sodium ions in the filtrate diffuse down conc. gradient from lumen of PCT to epithelial cells of PCT.
-co-transport takes place as the carrier protein that transports sodium ions carry glucose with it.
-glucose can then diffuse from PCT epithelial cell into bloodstream
-as these molecules are transported into blood, water potential in blood also decreases, water travels down water potential potential gradient from PCT into blood by osmosis.
adaptations of PCT for selective reabsorption
-microvilli: large surface area for transporter proteins
-many mitochondria: produce ATP to provide energy for sodium-potassium pump proteins in the basal membranes of the cell.
-infolding basal membrane: large surface area
2 regions of loop of Henle
-descending limb: narrow with thin wall, highly permeable to water
-ascending limb: wider, thick walls impermable to water
what happens in loop of Henle
-sodium ions active transported out of ascending limb
-this lowers water potential in the interstitial region of medulla
-water diffuses out of permeable walls of descending limb by osmosis into the interstitial space and then into the blood capillaries.
-at the base of ascending limb, sodium ions diffuse out of filtrate. As filtrate moves up the limb, ions are actively transported out, increasing water potential in the filtrate (more dilute due to less ions).
water potential lowest in medullary region, highest at top of ascending limb.
role of DCT and collecting duct
-filtrate from top of ascending limb into DCT and collecting duct have higher water potential than interstitial fluid.
-collecting duct is permeable to water so water moves out by osmosis through water channels called aquaporins
-permeability of walls is determined by ADH (antidiuretic hormone)- alters the no. aquaporins so can control water loss
-epithelial cells of DCT have mitochondria and microvilli that allows further substitution of ions via active transport
-walls can be influenced by various hormones
importance of maintaining an Na+ gradient
-countercurrent multiplier: filtrate in collecting ducts is always beside an area of interstitial fluid that has a lower water potential.
-maintains water potential gradient for maximum reabsorption of water
what can cause blood water potential to change
-level of water intake
-level of ion intake in diet
-level of ion used in metabolic processes or excreted
-sweating
