homeostasis Flashcards
describe how ultrafiltration occurs
hydrostatic pressure
small molecules (glucose, ions) and liquids (water) pass through capillary endothelium
- through basement membrane
- into renal capsule
where does ultrafiltration occur
glomerulus
what does homeostasis mean
involves physiological control systems that maintain the internal environment within restricted limits
what is homeostasis important for
- maintaining core body temperature
- maintaining blood pH in relation to enzyme activity
what does negative feedback mean
any deviation from normal value, there are mechanisms put in place to bring conditions back to original level
what detects changes in blood glucose levels
pancreas - beta cells (when levels are high) and alpha cells (when levels are low) in islets of Langerhans
- ISLETS OF LANGERHAN release insulin/glucagon to bring glucose levels to normal
when is insulin released
BGL to high
when is glucagon released
BGCtoo low
when is adrenaline released
when body anticipates danger
= more glucose released from hydrolysis of glycogen in liver
what happens after insulin is released
liver cells become more permeable to glucose
- enzymes activated to convert glucose to glycogen
- glucose removed from blood and stored as glycogen in cells
- normal BGC
what occurs after glucagon and adrenaline are released
second messanger model occurs to activate enzymes to hydrolyse glycogen into glucose
- glucose released back into blood
- BGC normal
what is the role of insulin in lowering BGC
- attaches to receptors on surfaces of target cells (liver/muscle) which changes tertiary structure of channel proteins in cell membrane = more glucose absorbed (facilitated diffusion)
- more protein carriers incorporated into cell membranes so that more glucose is absorbed from blood into cells
- activates enzymes to convert glucose into glycogen (glycogenesis)
what is the action of glucagon which increases BGC
- attaches to receptors on target cells (liver/muscle)
- causes protein to be activated into adenylate cyclase
- ATP converts to cAMP
- cAMP activates protein kinase (hydrolyses glycogen into glucose)
- activates other enzymes to convert glycerol from lipids and AA from proteins into glucose
explain the second messenger model
- glucagon binds to receptors on cell membrane
- changes shape to adenylate cyclase
- adenylate cyclase activates the conversion of ATP to cAMP (second messenger)
- cAMP activates protein kinase which converts glycogen into glucose
what is gluconeogenesis and where does this occur
creating glucose from other molecules (amino acids and glycerol in liver)
occurs in liver due to enzymes found there
what is glycogenesis and where does it occur
converting glucose into glycogen
occurs in the liver and catalysed by enzymes there
what is glycogenolysis and where does this occur
hydrolysis of glycogen to glucose
occurs in liver due to second messenger model
what is type 1 diabetes and its treatment
body doesn’t produce insulin
- starts in childhood
- result of autoimmune response
- treated with injections
what is type 2 diabetes and its treatment
receptors on target cells lose responsiveness to insulin
- adulthood due to obesity and poor diet
- treated with good diet and exercise
what does hypotonic mean
blood with too high a water potential
- too must water will move into cells from blood by osmosis and cells will burst (lysis)
what does hypertonic mean
blood with too low water potential
- too much water will leave cells into blood and cells shrivel (crenation)
what is the corrective mechanism for hypertonic blood
more water reabsorbed by osmosis into blood from tubules of nephron
- urine is lower in volume + more concentrated
what is the corrective mechanism for hypotonic blood
- less water reabsorbed into the blood from the tubules of the nephron
- larger volumes of urine produced which are more dilute (more water is lost in urine)
where does osmoregulation occur
within the nephrons of the kidneys
what are the nephrons
long tubules surrounded by capillaries
- where the blood is filtered to remove waste + selectively reabsorb useful substances back into blood
what happens to the filtrate after ultrafiltration
passes through the proximal convoluted tubule
- selective reabsorption occurs (back into blood)
what does the Loop of Henle do
maintains sodium ion gradient so water can reabsorb back into blood
- ascending limb (losing lots of ions = lowers water potential of surrounding area of loop of henle)
= water moves out by osmosis as travels down descending limb
what happens as the filtrate reaches the distal convoluted tubule
lost a lot of water and ions = more water moves out by osmosis
- at collecting duct more water moves out and back into blood
- collecting duct carries remaining liquid away to form urine
where are the nephrons found
medulla
why are proteins and blood cells never found in urine
too large to be filtered out of the blood
why is glucose never found in the urine
glucose is filtered out but reabsorbed by active transport in proximal convoluted tubule (selective reabsorption)
what occurs at the proximal convoluted tubule and how are PCT cells adapted to this
selective reabsorption
- 85% filtrate reabsorbed back into blood
- PCT cells (epithelial cells) have lots of microvilli = large SA for maximised absorption
- lots of mitochondria in cells = provides energy for active transport
how does selective reabsorption occur
concentration of NA ions in PCT cells decreases (NA ions are actively transported out of PCT into bloodstream)
- due to conc gradient, NA ions diffuse down gradient from lumen of PCT into cells lining it (via cotransporter protein- NA ions carry glucose in with them)
- large conc of glucose within PCT cell = glucose diffuses down from PCT cell into bloodstream
- all glucose reabsorbed
how is the Loop of Henle structures
ascending limb
- walls are impermeable to water (no water can move out)
- thicker walls
- NA ions actively transported out
descending limb
- filtrate moving down the Loop of Henle
- thinner walls
- walls are permeable to water (water out by osmosis into blood)
what occurs at the Loop of Henle
- mitochondria within walls of ascending limbs (energy for active transport of NA ions - out of filtrate into interstitial space)
- accumulation of NA ions in interstitial space in medulla = low water potential)
- water in descending limb moves out by osmosis into interstitial space and reabsorbed into blood
- base of ascending limb has very dilute solution (low conc NA) = some NA ions move out by diffusion
what occurs at the distal convoluted tubule + collecting duct
- filtrate which enters DCT is at low con (dilute)
- even more water diffused out
- remaining filtrate forms urine
suggest how and why the length of Loop of Henle differs for a desert animal compared to a human’s
longer Loop of Henle
= larger SA for NA ions to be ACTIVELY transported out
- water potential decreases further
- more water moves out by osmosis
- more water reabsorbed into the blood
= very conc urine (essential for desert animals)
what is the role of the hypothalamus
where changes in water potential is detected by osmoreceptors
- where the ADH is produced
what releases ADH
posterior pituitary gland
what occurs when there is an increased water potential
water enters osmoreceptors by osmosis
- stimulates hypothalamus to produce less ADH
- less ADH is released
- DCT and collecting duct walls become less permeable to water
- less water reabsorbed
- large volumes of dilute urine
what occurs when water potential is too low
water leaves osmoreceptors by osmosis (shrivel)
- stimulates hypothalamus to produce more ADH
- posterior pituitary released ADH into capillaries and blood
- travels through blood to target organs
- DCT and collecting duct walls become more permeable to water
- more water reabsorbed into blood
- concentrated urine
what is the role of ADH
- causes increase in permeability of walls of PCT and DCT
- more water moves out by osmosis
- more water reabsorbed
- concentrated urine
