16 - Homeostasis Flashcards
homeostasis
the maintenance of an internal environment within restricted limits in organisms
conditions which need to be maintained in mammals
temperature, pH, water potential (osmoregulation), blood glucose concentration, cholesterol
negative feedback mechanisms
the change produced by the control system leads to a change in the stimulus detected by the receptor, and turns the system off
the stimulus causes the corrective measures to be turned off
hormones
produced in glands which secrete the hormone directly into the blood
carried in blood plasma to their target cells
are effective in very low concentrations
usually have widespread and long-lasting effects
role of adrenaline in conversion of glycogen to glucose
- adrenaline approaches transmembrane protein
- adrenaline fuses to the receptor causing it to change shape on the inside of the membrane
- this activates enzyme adenyl cyclase inside the membrane
- the activated adenyl cyclase converts ATP to cyclic AMP, which acts as a secondary messenger
- the cAMP activates the protein kinase enzymes
- the active protein kinase enzyme catalyses the conversion of glycogen to glucose
islets of Langerhans
groups of hormone producing cells in the pancreas
contains alpha cells (produce glucagon), and beta cell (produce insulin)
glycogenesis
conversion of glucose to glycogen
when blood sugar levels are higher than normal the liver converts glucose from the blood into glycogen and stores it
glycogenolysis
the breakdown of glycogen into glucose
when blood sugar levels are lower than normal
gluconeogenesis
production of glucose from sources other than carbohydrates (eg. from glycerol and amino acids)
when an insulin molecule binds with a receptor it causes:
- the tertiary structure of the glucose transport carrier to change, meaning they change shape and open allowing more glucose into cells by facilitated
- an increase in the number of carrier proteins responsible for glucose transport across membranes
- activation of the enzymes that convert glucose to glycogen
effect of glucagon
glucagon attaches to specific protein receptors on the cell membrane of liver cells
activates enzymes that convert glycogen to glucose
activates enzymes involved in gluconeogenesis
type 1 diabetes
autoimmune condition, often inherited
immune system attacks and destroys beta cells, prevents sufficient insulin from being produced
without insulin blood glucose levels get too high
treated with insulin injections
type 2 diabetes
not an autoimmune disease
body doesn’t produce enough insulin to deal with high blood glucose levels, or body’s cells do not respond
can be controlled with diet or tablets
renal fibrous capsule
outer membrane for protection
renal cortex
lighter coloured outer region consisting of renal capsules, convoluted tubules and blood vessels
renal medulla
darker coloured inner region consisting of loops of Henle, collecting ducts and blood vessels
renal pelvis
funnel shaped cavity which collects urine into the ureter
renal artery
supplies kidney with blood from the heart
renal vein
returns blood from the kidney to the heart
renal Bowman’s capsule
cup shaped, surrounds a mass of blood capillaries known as the glomerulus
proximal convoluted tubule
a series of loops surrounded by blood capillaries, walls made of epithelial cells which have microvilli
loop of Henle
long, hairpin loop that extends from the cortex into the medulla, surrounded by blood capillaries
distal convoluted tubule
series of loops surrounded by blood capillaries, walls of epithelial cells
collecting duct
a tube into which several DCTs from a number of nephrons empty
becomes increasingly wide as it empties into the renal pelvis
afferent arteriole
arteriole from the renal artery and supplies the nephron with blood
forms the glomerulus in the renal capsule
glomerulus
knot of capillaries from which fluid is forced out the blood
efferent arteriole
tiny vessel that leaves the renal capsule
smaller diameter than the afferent arteriole
formation of glomerular filtrate
- blood enters the kidney via the renal artery
- this then divides into the afferent arteriole and glomerulus
- water and all soluble components are forced out of the glomerulus
- the pressure to do this is aided by the efferent arteriole leaving the glomerulus being narrower than the afferent arteriole entering
- filtrate passes BETWEEN podocyte cells to enter renal capsule
reabsorption of glucose
- all glucose in the glomerular filtrate must be reabsorbed into the blood, however waste products like urea don’t need to be
- glucose is reabsorbed in the process of co-transport from the epithelial cells of the proximal convoluted tubule to blood capillaries
- sodium ions are actively transported from the epithelial cells into the blood, creating a low concentration of sodium ions in the epithelial cells
- sodium ions therefore move in from the lumen of the proximal convoluted tubule by facilitated diffusion, carrying glucose with it
- the glucose then diffuses into blood capillaries
reabsorption of water in loop of Henle
- in the ascending limb, Na+ are actively transported out into the interstitial space in medulla
- this lowers water potential in interstitial space
- ascending limb is impermeable to water, so water moves out permeable ascending limb by osmosis into medulla
- water moves into capillaries in medulla by osmosis
- at base of loop, Na+ diffuse out into medulla naturally lowering water potential of medulla further
- water moves out DCT and collecting duct into low water potential medulla by osmosis
loop of Henle as a countercurrent multiplier
Na+ leaving ascending limb increases down ascending limb because Na+ diffuses out of base of loop
water potential in interstitial space increases further down medulla
therefore interstitial fluid in medulla always has lower water potential than collecting duct
