Homeostasis Flashcards
What is the concept of homeostasis?
Homeostasis is the maintenance of a constant state factors being controlled have receptors which detect changes from the normal. A corrective mechanism is brought about to restore it to normal. Coupled with this is a negative feedback system, once the normal has been restored the corrective mechanism is stopped to prevent over correction.
What is excretion?
Removal of waste products from metabolic processes nitrogen containing compounds (urea) from the breakdown of excess amino acids and nuclei acids in the liver as well as creatine a waste product from the breakdown of creatine phosphate (ATP synthesis)
What is osmoregulation?
Control of the water potential within the blood, controls the volume and concentration of urine produced under the influence of the antidiuretic hormone
What is the functional unit of the kidney?
The nephron
How is blood brought to the bowman’s capsule?
The afferent arteriole brings blood under high hydrostatic pressure to the bowman’s capsule the blood then leaves through the efferent arteriole which joins to a network of capillaries called the vasa recta, Within the cup of the bowman’s capsule the afferent arteriole branches to form a highly coiled knot of capillaries called the glomerulus.
What is the structure of the nephron?
The bowman’s capsule extends into what is called the proximal convoluted tubule which consists of cuboidal epithelium cells. The PCT then extends to the loop of henle in the Medulla, the loop of henle has a descending limb which is permeable to water and an ascending limb which is impermeable to water, they are both made up of cuboidal epithelium cells. Back in the Cortex is the distal convoluted tubule which then goes onto form the collecting duct. These both consist of cuboidal epithelium cells. The collecting ducts converge at the end of the pelvis and empty urine into the ureter.
What is the structure of the filter (bowman’s capsule)
The filter has 3 layers. The first layer is the squamous (thin flattened) endothelial cells of the blood capillaries in the glomerulus that have small pores which allow substances to pass. Podocytes wrap around the capillaries and have spacious gaps called filtration slits which allow substances through they are in the wall of the bowman’s capsule. In Between both of these layers is the effective filter which is called the basement membrane, it controls what enters the bowman’s capsule and prevents large proteins and blood cells entering. The 3 layers are either porous or a filter.
What are the factors which create the high hydrostatic pressure?
hydrostatic pressure is the main driving force for filtration. Factors which create this high hydrostatic pressure are; the afferent arterioles being wider in diameter to the efferent arterioles, the renal arteries being close to the heart and the coiling of the arteries in the glomerulus increases pressure
What else needs considered in ultrafiltration?
The blood in the capillaries have a lower solute potential and the filtrate has a higher solute potential, this opposes filtration, but the pressure potential highly promotes filtration as the blood is under a high hydrostatic pressure and the filtrate is under a lower pressure. There is resistance to further filtration due to the low back pressure of the filtrate in the nephron. The blood must have a higher water potential then the filtrate for filtration to occur.
Which components of the blood are filtered and why?
The only components of the blood which moves across are a certain size and they are amino acids, salts, water, urea, small plasma proteins and glucose however larger components do not filtrate through as they are too large to pass into the nephron they are blood cells and large plasma proteins.
What is the mechanism of selective reabsorption?
in the proximal convoluted tubule as you move along it glucose, amino acids and salts are selectively reabsorbed and move across by facilitated diffusion. Small plasma proteins are reabsorbed by pinocytosis. This causes a lower solute potential within the cuboidal epithelium cells and the blood capillaries of the vasa recta system, this osmotic gradient results in the bulk of the reabsorption of water. When the concentration gradient no longer permits the facilitated diffusion of components, active transport occurs to ensure all amino acids and glucose are reabsorbed as they are too valuable to lose
What are the adaptions of the cuboidal epithelium in the PCT?
carrier proteins, microvilli to increase the surface area for reabsorption, numerous mitochondria to provide ATP for active transport, basal invaginations of the membrane to increase SA and the vasa recta system being within close proximity to the cuboidal epithelium cells.
What is the role of the loop of henle?
the descending limb is permeable and thin where the ascending limb is impermeable and thicker. Sodium and chloride ions are moved out of the ascending limb into the interstitial fluid in the medulla by active transport, ATP is supplied for this from the mitochondria within the cuboidal epithelium cells of the ascending limb. This creates a low solute potential within the medulla and by osmosis water moves out of the descending limb into the medulla and is then absorbed by the vasa recta system. this concentrates the filtrate at the apex of the loop. The low solute potential of the interstitial fluid in the medulla also facilitates the osmotic removal of water from the collecting ducts and the DCT which is dependent on the permeability of the collecting duct walls which in turn is dependent on the level of ADH within the blood.
What is the benefit of a longer loop of henle for species?
The longer the loop of henle the more water can be reabsorbed this is because the longer loop allows the medulla to become even more concentrated. Therefore you can concentrate the urine and conserve water in a species.
What is osmoregulation?
Osmoregulation; control of water potential within the blood. ADH is produced within the hypothalamus and is then secreted into the posterior lobe of the pituitary body. ADH is synthesised when the osmoregulators in the hypothalamus detect a change in the solute potential of the blood, the synthesis of ADH variates. When ADH is released into the bloodstream it increases the permeability of the walls of the collecting duct and the distal convoluted tubule.
