Homeostasis Flashcards
Positive feedback
Deviation from optimum causes changes that result in greater deviation from the normal
Components of control mechanism
Optimum point
Receptor - detects deviation from optimum
Coordinator - coordinates info from receptor and sends to effector
Effector - brings about changes to bring system to optimum
Negative feedback
Stimulus causes corrective measures that turns off its own measures. Brings system to original and prevents overshoot
Mechanism of adrenaline
Binds to protein receptor on liver cell membrane.
Causes protein to change shape on inside of membrane.
Leads to shape change and activation of enzyme called adenyl cyclase that converts ATP to cyclic AMP that binds to and activates kinase.
This catalyses conversion of glycogen to glucose, which moves out of the cell via channel proteins to blood.
Glycogenesis
Conversion of glucose to glycogen
Glycogenolysis
Breakdown of glycogen to glucose.
Gluconeogenesis
Production of glucose from sources other than carbohydrate i.e amino acids and glycerol
How insulin brings about change of blood-glucose level
Combines with cell surface receptor. Change in tertiary structure of glucose transport carrier proteins so that more glucose enters cell via facilitated diffusion.
Increase in number of glucose carrier proteins in cell membrane (vesicles containing this protein fuse with cell surface membrane)
Activation of enzymes that convert glucose to glycogen and fat
How does glucagon change blood-glucose level
Binds to protein receptor on liver cell membrane.
Causes protein to change shape on inside of membrane.
Leads to shape change and activation of enzyme called adenyl cyclase that converts ATP to cyclic AMP that binds to and activates kinase.
This catalyses conversion of glycogen to glucose, which moves out of the cell via channel proteins to blood.
Type 1 diabetes
Body unable to produce insulin, auto-immune attack of beta cells of islets of Langerhans
Type 2 diabetes
Glycoprotein receptors on body cells being lost/losing responsiveness or inadequate supply of insulin from pancreas
Type 1 diabetes control
Injections of insulin, blood glucose monitored by biosensors
Type 2 diabetes control
Regulating intake of carbohydrate in diet and matching to amount of exercise.
Can also be supported by injections of insulin
Renal (Bowman’s) Capsule
Close end at start of nephron, surrounds mass of blood capillaries known as glomerulus, inner later made of podocytes
Proximal convoluted tubule
Series of loops surrounded by blood capillaries, walls made of epithelial cells with microvilli
Also cotransport
Loop of Henle
Long, hairpin loop that extends from cortex into medulla and back, surrounded by blood capillaries
Distal convoluted tubule
Series of loops surrounded by blood capillaries, walls made of epithelial cells
Collecting duct
Tune where distal convoluted tubules empty into, lined by epithelial cells
Afferent arteriole
Small vessel that arises from renal artery and supplies nephron with blood, enters renal capsule and forms glomerulus
Glomerulus
Branched knot of capillaries where fluid is forced out of blood
Efferent arteriole
Tiny vessel that leaves renal capsule, smaller diameter than afferent arteriole so increase of blood pressure in glomerulus, branches later on to form capillaries
Blood capillaries
Concentrated network of capillaries that surrounds proximal convoluted tubule, loop of Henle and distal convoluted tubule where mineral salts, glucose and water are reabsorbed, merge to form veins which merge to form renal vein
Contents of glomerular filtrate
Water, glucose, mineral ions
What factors resist movement of glomerular filtrate out of arteriole
Capillary epithelial cells and connective tissue
Epithelial cells of renal capsule
Hydrostatic pressure of fluid in renal capsule space
Low water potential of blood in glomerulus
How is glomerular filtrate formed
Despite resistance, podocytes on inner later of renal capsule allow filtrate to pass between their branches.
Endothelium also has spaces between cells so fluid can pass between and through basement membrane.
The hydrostatic pressure due to the decrease in diameter between afferent and efferent arteriole pushes molecules out between these gaps and through capillary basement membrane.
What happens in ascending limb of loop of Henle
Sodium ions actively transported out using ATP, creating low water potential in region of medulla between 2 limbs. Thick walls mean no water escapes. Increasingly higher water potential due to loss of Na+
What happens in descending limb of loop of Henle
Water passes out of filtrate by osmosis into interstitial space and is carried away be blood capillaries and Na+ diffuses in. Reaches lowest water potential at end of hairpin
Water potential in cortex and medulla
High water potential (low ion conc.) in cortex that gets lower when going further into medulla
What happens in collecting duct
Filtrate moves down and loses water via osmosis and is carried away by capillaries
What happens in DST
Concentration of ions and glucose and pH of blood controlled by reabsorption of molecules from filtrate by active transport .
How does body respond to fall in water potentia
Cells in hypothalamus lose water due to fall in water potential in blood.
Hypothalamus produces ADH and it secreted in capillaries via pituitary gland.
Passes to blood in kidneys, increases permeability of water of cell surface membrane in cells of DST and CD.
Receptors bind to ADH and activates phosphorylase that causes vesicles with aquaporins to bind to cell surface membrane.
Permeability of collecting duct to urea also increased, lowering water potential of fluid around duct.
How does body respond to rise in water potential
Osmoreceptors detect rise and increase frequency of impulses to pituitary gland to reduce release of ADH.
Decrease in permeability of cells of DST and CD to water and urea, less reabsorption, more dilute urine.
When water potential returns to normal, osmoreceptors make pituitary gland raise release of ADH again.
Why does longer loop of Henle result in high urine conc
Increase in sodium ion concentration in medulla.
More water absorbed from collecting duct and loop by osmosis.
