3.4 - homeostasis + the kidney Flashcards
what’s homeostasis
maintenance of state of dynamic equilibrium in body despite fluctuations in internal + external conditions
why is homeostasis important
to ensure optimum conditions for enzymes + cellular processes in the body
define negative feedback
self-regulatory mechanisms return the internal environment to the optimum when there is a fluctuation
define positive feedback
fluctuation which triggers changes that result in an even greater deviation from normal level
what’s the set point
desired value or range of values determined by a coordinator
describe receptors + effectors
receptors - specialised cells located in sense organs that detect specific stimulus
effectors - muscles/glands which enable a physical response to a stimulus
describe the role of the coordinator
coordinated information from receptors + sends instructions to effectors
state the components of a negative feedback system
- set point
- receptors
- coordinator
- effector
what’s the mammalian kidney
one of a pair of organs in abdomen that has a role in osmoregulation + nitrogenous excretion
what’s osmoregulation
regulation of water potential of body fluids (eg: blood, tissue fluid, lymph) by the kideny
why is osmoregulation important
- prevents cells bursting or shrinking when water enters or leaves by osmosis
- cellular reactions occur in aqueous solution, water levels affect conc + rate of reactions in cells
define excretion
process of removing metabolic waste from an organism
describe how excess amino acids are excreted
- amino acids deaminated in liver (removal of amino group) forming ammonia
- ammonia converted to urea (less toxic)
- urea transported into blood plasma + eliminated by kidneys
what’s the function of the renal artery
supplies blood to kidneys
what’s the function of the renal vein
drains blood from kidneys
what’s the function of the ureter
takes urine to bladder from kidneys
what’s the function of the ureter
takes urine to bladder from kidneys
what’s the function of the urethra
releases urine from bladder, out of body
describe the gross structure of a mammalian kidney
fibrous capsule - protects kidney
cortex - outer region consists of bowman’s capsules, convoluted tubules, blood vessels
renal pyramids - cone shaped subdivisions
renal pelvis - funnel shaped dilation section of ureter
medulla - inner region consists of collecting ducts, loops of henle, blood vessels
what’s a nephron
functional unit of mammalian kidney
where are nephrons found within kidneys
part of nephron located in medulla + part in cortex
describe the blood vessels associated w/ a nephron
wide afferent arteriole from renal artery enters renal capsule + forms glomerulus, branched knot of capillaries which combine to form narrow efferent arteriole
efferent arteriole branches to form capillary network that surrounds tubules
define ultrafiltration
removal of small molecules, water + ions from blood in glomerulus of kidney at high pressure
describe the process of ultrafiltration
- occurs in bowman’s capsule
- high hydrostatic pressure in glomerulus forces small molecules (e.g: urea, water, glucose, ions) out of capillary fenestrations against osmotic gradient
- basement membrane acts as filter, blood cells + large molecules (e.g: proteins) remain in capillary
why is there a build up of pressure in glomerulus
afferent arteriole leading into glomerulus is wider than efferent taking blood from glomerulus
how are you cells of bowman’s capsule adapted for ultrafiltration
- fenestrations between epithelial cells of capillaries
- fluid can pass between + under folded membrane of podocytes
what happens in selective re absorption
- useful molecules from glomerular filtrate (glucose, some water, some ion) are reabsorbed into blood
- involves membrane transport proteins
where does selective re absorption occur
proximal convoluted tubule
how are cells in PCT adapted for selective reabsorption
- microvilli provide large SA for co-transporter proteins
- many mitochondria produce ATP for active transport of glucose in intracellular spaces
- folded basal membrane provides large SA
- tight junctions stop reabsorbed materials leaking back into filtrate
- peritubular capillaries extend into medulla enabling réabsorption of materials
by what mechanism are amino acids + filtered glucose selectively reabsorbed into blood
- secondary active transport
- uses co-transport mechanism involving Na+
by what mechanism are mineral ions selectively reabsorbed into blood
active transport
by what mechanism is water selectively reabsorbed into blood
osmosis
how are filtered protein (+some urea) selectively reabsorbed into blood
via diffusion
describe the loop of henle
loop consisting of descending limb (dips into medulla) + ascending limb (rises into cortex) surrounded by blood capillaries
what’s the function of the loop of henle
creates low water potential in medulla, enabling reabsorption of water
describe what happens in the loop on henle
- active transport of Na+ and Cl- out of ascending limb
- water potential of interstitial fluid decreases
- movement of water out of descending limb via osmosis (ascending limb is impermeable to water)
- water potential of filtrate decreases going down descending limb, lowest in medullary region, highest at top of ascending limb
- hair pin counter current mulitplier
what’s an endocrine gland
gland of endocrine system that secretes hormones directly into bloodstream
how is concentration + volume of urine controlled
controlled by secretion of anti-diuretic hormone (ADH)
explain the role of the hypothalamus in osmoregulation
- osmoreceptors in hypothalamus detect conc of blood plasma
- hypothalamus secrets ADH
explain the role of the posterior pituitary gland in osmoregulation
stores + secretes ADH produces by hypothalamus
describe how ADH affects the reabsorption of water from kidney tubules
- ADH causes insertion of aquaporins into plasma membranes of cells of DCT + collecting duct
- increases permeability of DCT + collecting duct
- more water reabsorbed
- more concentrated urine produced
describe the effects of kidney failure
- build up of toxic waste products (e.g urea) causes symptoms such as vomiting
- fluid accumulation leads to swelling
- disruption to electrolyte balance can make bones more brittle
- high conc of renin may lead to hypertension
- low conc of EPO can lead to anemia
outline the potential treatments for kidney failure
- low protein diet
- control of blood calcium + potassium levels using medication
- drugs to lower blood pressure
- renal dialysis
- kidney transplant
describe renal dialysis
- medical procedure that artificially filters blood
- relies on partially permeable membrane between patients blood + dialysis fluid
- 2 types: haemodialysis + peritoneal dialysis
what’s a transplant
medical procedure in which an organ or tissue in an individual is replaced
describe how animal excretory products can differ
- freshwater animal species excrete ammonia
- reptiles, birds + insects produce uric acid
- mammals excrete urea
how does length of loop of henle differ between mammals
- length of loop varies depending on availability of water in mammals environment
- longer loop in desert animals to allow greater time for reabsorption of water + salts
