9.3- homeostasis Flashcards
what is homeostasis
-maintenance of a state of dynamic equilibrium in the body, despite changes in internal or external conditions
osmoregulation
-maintenance of osmotic potential in the tissues of living organisms
-both kidneys and liver are involved
role of liver in deamination (breakdown of amino acids)
-hepatocytes (liver cells) deaminate excess amino acids
-they remove the amino group and convert it first to ammonia (toxic) then to urea (less toxic)
-ammonia produced is converted to urea by a series of enzyme controlled reactions called the ornithine cycle
what happens in the ornithine cycle
-purpose is to covert ammonia to urea
-by removal and addition of water
summary of what happens in the kidney
-kidney controls the water potential of the blood
-kidneys also filter the blood, removing unwanted or excess products as urine such as urea and excess ions and water
-reabsorb products which are needed; glucose, dissolved ions and some water
general structure of the kidney
-fibrous capsule (membrane which protects kidney)
-cortex (light coloured outer region)
-medulla (dark coloured inner region)
-ureter (carries urine to bladder)
-renal artery (supplies kidney with oxygenated blood)
-renal vein (returns blood from heart to kidney)
2 types of nephrons
- cortical- found in renal cortex, loop of henle only just reaches the medulla
- juxtamedullary- long loop of henle penetrates right through medulla, efficient at producing concentrated urine
basic structures of the nephron
-bowmans capsule (mass of blood capillaries)
-proximal convoluted tubule (links bowmans and loop of henle, surrounded by blood capillaries)
-loop of henle (extends into medulla of kidney, surrounded by blood capillaries)
-distal convoluted tubule (between loop of henle and collecting duct, surrounded by fewer blood capillaries)
-collecting duct (DCT empties into this)
first process in nephron- ultrafiltration
-between glomerulus and bowmans capsule
-afferent arteriole has larger diameter than efferent, creates hydrostatic pressure
-Water, glucose and mineral ions are squeezed out of the capillary to form glomerular filtrate.
-Blood cells and proteins are too large to pass through.
-Podocytes – specialised cells which line the inner layer of the bowman’s capsule.
-they have spaces between them where the filtrate passes through
-filtrate contains; , glucose, salt and urea
second process in nephron- selective reabsorption
-occurs in the PCT
-80% of glomerular filtrate is reabsorbed
-The cells in the PCT are adapted by:
Microvilli (large surface area)
Infoldings at their base to give large SA to reabsorb substances into blood capillary.
Lots of mitochondria to provide ATP for active transport
-glucose, amino acids, vitamins and hormones are moved back into the blood via active transport
-Sodium ions and chloride ions are also actively transported, which means water will follow passively down the concentration gradient.
-When the filtrate reaches the loop of Henle, it is isotonic with the tissue fluid surrounding the tubule.
third process in nephron- loop of henle
1.Na ions are AT out of the ascending limb using ATP.
2.Low water potential is created between limbs.
3.Water moves out of the descending limb from the filtrate into the interstitial space and then into the blood capillaries. (it doesn’t move out of the ascending limb because of the thick, impermeable walls).
4.Water is lost as the filtrate moves down the descending limb, meaning that the lowest water potential is at the bottom of loop of Henle.
5. Na ions diffuse out at the base of the ascending limb and then are actively pumped out (as you move further up).
6. This means that the water potential in the filtrate gets progressively higher.
7. In the interstitial space, there is a gradient of water potential, with the highest water potential at the cortex.
8. Water is lost from the collecting duct by osmosis into the blood vessels.
9. Water moves out of the collecting duct and of the interstitial space so the gradient is maintained.
features of the loop of henle
-extends into the medulla
-responsible for creating a water potential gradient between filtrate and tissue fluid in medulla
-this allows water to be reabsorbed from the collecting duct later in the nephron
-concentration of urine is related to the length of the loop of henle
-made up of 2 regions; descending limb (narrow, thin walls, permeable to water, not to Na or Cl ions) + ascending limb (wider, thick walls, impermeable to water very permeable to sodium and chloride ions)
stage 4 of nephron- DCT
-permeable to water
-permeability varies with ADH
-here where balancing of water in body occurs
stage 5 of nephron- collecting duct
-permeable to water
- permeability varies with ADH
-water moves out of collecting duct down water potential gradient
-fluid collects in kidney pelvis and then passes along ureters to bladder where it is sorted
what is ADH?
-Antidiuretic Hormone (prevents urine being passed, makes more reabsorbed)
