3.7 Homeostasis and the kidney 5 Flashcards
What is homeostasis?
maintenance of a state of dynamic equilibrium in the body despite fluctuations in internal and external conditions
why is homeostasis important?
to ensure optimum conditions for enzymes and 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
a fluctuation which triggers changes that result in an even greater deviation from the normal level
what is the set point?
a desired value or range of values determined by a coordinator
describe receptors and effectors
receptors- specialised cells located in sense organs that detect a specific stimulus
effectors - muscles or glands which enable a physical response to a stimulus
describe the role of the coordinator:
coordinates info from the receptors sending instructions to the effectors
state the components of a -ve feedback system
set point
receptors
coordinator
effectors
what is the mammalian kidney?
one of a pair of organs in the abdomen that has a role in osmoregulation and nitrogenous excretion
What is osmoregulation?
the regulation of water potential of body fluids (e.g.blood, tissue fluid, lymph by the kidney)
why is osmoregulation important?
-prevents cells bursting or shrinking when water enters or leaves cells by osmosis
-cellular rctns occur in aqueous soln therefore water levels affect concs and the rate of rctn in cells
define excretion
the process of removing metabolic waste from an organism
describe how excess amino acids were excreted
-amino acids deaminated in the liver (removal of amino grp) to form ammonia
-ammonia converted to urea (less toxic)
-urea transported into blood plasms and eliminated by the kidneys
function of renal artery?
supplies blood to the kidneys
function of renal vein?
drains blood from the kidneys
function of the ureter?
takes urine to the bladder from the kidneys
function of the urethra
releases urine from the bladder out of the 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 dilated section of ureter
medulla - inner region consists of collecting ducts, loop of Henle, blood vessels
what is nephron?
the functional unit of the mammalian kidney
where are the nephrons found within the kidneys?
part of the nephron is located in the medulla and part in the cortex
describe the blood vessels associated with a nephron?
wide afferent arteriole from renal artery enters renal capsule forms glomerulus, knot of capillaries whiohc combine to for narrow efferent arteriole
efferent arteriole branches to form capillary network that surrounds tubules
describe ultrafiltration
the removal of small molecules, water and ion from the blood in the glomerulus of the kidney at high pressure
describe the process of ultrafiltration
-occurs in bowman’s capsule
-high hydrostatic pressure in glomerulus forces small molecules (urea, water, glucose, ions) out of capillary against osmotic gradient
-basement membrane acts as a filter, blood cells and large molecules (proteins) remain in capillary
why is there a build-up of pressure in glomerulus?
afferent arteriole leading into the glomerulus is wider than the efferent arteriole taking blood from the glomerulus
how are cells of the bowman’s capsule adapted for ultrafiltratioon?
-fenestrations bet epithelial cells of capillaries
-fluid can pass bet & under folded membrane of podocytes
what happens during selective reabsorption?
-useful molecules from glomerular filtrate (glucose, some water, some ions) are reabsorbed into the blood
-involves membrane transport proteins
where does selective reabsorption occur?
proximal convoluted tubule (PCT)
how are cells in the proximal convoluted tubule adapted for selective reabsorption?
-microvilli provide large surface area for co-transporter proteins
-many mitochondria produce ATP for active transport of glucose into intercellular spaces
-folded basal membrane provides a large sa
-tight junctions stop reabsorbed materials leaking back into the filtrate
- peritubular capillaries extend into the medulla enabling reabsorption of materials
by what mechanism are amino acids and filtered glucose selectively reabsorbed back into the blood?
secondary active transport
uses a co-transport mechanism involving Na+
by what mechanism are mineral ions selectively reabsorbed into the blood?
active transport
by what mechanism is water selectively reabsorbed into the blood?
osmosis
how are filtered proteins (and some urea) selectively reabsorbed into the blood?
via diffusion
describe the loop of Henle
a loop consisting of a descending limb (dips into the medulla) and ascending limb (rises into the cortex) surrounded by blood capillaries
function of the loop of Henle??
creates a low water potential in the medulla, enabling the reabsorption of water
describe what happens in the loop of 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 multiplier
what is an endocrine gland?
gland of the endocrine system that secretes hormones directly into the bloodstream
how is the conc and vol 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 secretes ADH
explain the role of the posterior pituitary gland in osmoregulation
stores and secretes the ADH produced by hypothalamus
describe how ADH affects the reabsorption of water from the kidney tubules
-ADH causes insertion of aquaporins into plasma membranes of cells of the DCT and collecting duct
-increases permeability of the DCT and collecting duct
-more water reabsorbed
more conc urine produced
describe the effects of kidney failure
-build up of toxic waste products(e.g. urea) causes symptoms like vomiting
-fluid accumulation leads to swelling
-disruption to electrolyte balance can make bones more brittle
- high conc of renin may lead to hypertension
- low concs of EPO can lead to anaemia
the potential treatments of kidney failure
-low protein diet
-control of blood calcium and potassium levels using medication
-drugs to lower blood pressure
-renal dialysis
-kidney transplant
describe renal dialysis
-medical procedure that artificially filters the blood
-relies on a partially permeable membrane between the patient’s blood and dialysis fluid
-two types: haemodialysis and peritoneal dialysis
what is a transplant?
a 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 and insects produce uric acid
- mammals excrete urea
how does length of the loop of Henle differ between mammals?
-length of the loop caries depending on availability of water in the mammal’s environment
-longer loop in desert animals (kangaroo rat) to allow greater time for reabsorption of water and salts
