Osmoregulation Flashcards
Ultrafiltration in the Renal Capsule.
High hydrostatic pressure in the glomeruls.
Afferent arteriole is wider than the efferent artieriole.
Bottleneck effect.
Fenstrations in the epithelial cells of the capillaries.
Basement membrane.
Finger-like processes on the podocytes.
Fenstrations and the Basement Membrane.
Tiny pores in the endothelial cells that make up the capillary walls are called fenstrations.
Basememt membrane is thin layer separating the capillaries and the podocytes, made of a mesh of fibres.
Thin layer, continuous barrier so it acts as a filter.
Red blood cells, platelets and plasma cells are to large to pass through.
Podocytes.
Podocytes are the cells that line the inside of the Bowman’s capsule.
Many finger-like processes with gaps between them.
Adjacent finger-like processes interdigitate.
Wrap around the capillaries to form the glomerulus.
This forms tiny filtration slits between the processes.
Selective Reabsorption.
Carried out by the cells lining the proximal convoluted tubule.
Many microvilli and many mitochondria.
Na+ K+ pump, N+ actively transported out from PCT into blood capillaries.
Decreases Na+ concentration in the epithelial cells.
Na+ now move, by facilitated down a concentration gradient into the epithelial cells, through carrier proteins.
Another molecule (glucose, amino acids, mineral ions) are carried along with the Na+.
Molecules move into blood by facilitated diffusion, valuable molecules are reabsorbed.
The Loop of Henle.
The cells of ascending limb are permeable to Na+ but impermeable to water.
Na+ moves out of the cells by active transport and intol the tissue fluid of the medulla.
Decreased water potential in the tissue fluid of the medulla, due to increased Na+ concentration.
The cells of the descending limb are highly permeable to water.
Water moves out of the filtrate by osmosis, down a water potential gradient, into the tissue fluid of the medulla.
The filtrate becomes more concentrated as it moves deeper into the medulla.
Water in the tissue fluid of the medulla is reabsorbed into the vasa recta by osmosis.
The DCT and Collecting Ducts.
The filtrate leaves the loop of Henle and moves into the distal convoluted tubule in the cortex and finally to the collecting duct which drops into the medulla.
The water potential of the tissue fluid decreases deeper into the medulla due to increasing Na+ concentration.
Depending on the water potential of the blood, this allows water to move out of the collecting ducts by osmosis into the medulla to be reabsorbed by the vasa recta.
Low blood wp = lots of absorption.
High blood wp = less absorption.
The role of ADH.
Low water potential of the blood:
Osmoreceptors in the hypthalamus detect this and send nervous impulses to the posterior pituitary gland.
Secrete more ADH into the blood.
Makes the epithelial cells that make up the wall of collecting duct more permeable to water (more aquaporins).
Water moves from the filtrate to the medulla by osmosis down a wp gradient and from there into the bloo via the vasa recta.
A small volume of highly concentrated urine is produced.
High water potential of the blood:
Detected by osmoreceptors in the hypothalamus and nervous impulses are sent to the posterior pituitary gland.
Much less ADH is secreted into the blood.
Epithelial cells beome less permeable to water (less aquaporins).
Far less water is reabsorbed by osmosis.
Large volumes of more dilute urine is produced.
Aquaporins.
ADH binds to complimentary shaped protein receptors in the cell-surface membrane of epithelial cells.
Activates phosphorylase enzymes within the cells.
Increased transcription of water channel proteins called aquaporins.
More aquaporins are inserted into the epithelial cells, making the cell-surface membrane of the colelcting duct more permeable to water.
