homeostasis and hormones Flashcards
what is homeostasis
the maintenance of a constant internal environment for the cells within a living organism e.g temperature, pH, blood glucose and salt levels
homeostasis is important because…
helps maintain optimal conditions for cellular reactions
gives organisms independence from the external environment whilst still living in it
how is homeostasis maintained
homeostasis is maintained through a combination of nervous and hormonal mechanisms such as negative feedback
negative feedback is…
whenever a factor moves away from the ideal/norm, a set of processes moves it back towards normal again
what are hormones
molecules that are released by the endocrine glands directly to the blood that travels to a target organ to produce an effect.
what are endocrine glands
a ductless gland that secrete hormones directly to the blood.
what are target cells/tissue
cells that have receptors on their plasma membrane that are complimentary in shape to specific hormone molecules
what is an exocrine gland
a gland that secretes substances to a duct
what is a duct
a tube lined with epithelial cells and conveys a secretion
what do kidneys do
excrete, the filter the blood removing nitrogenous excretions (urea and ammonium ions) to produce urine.
what does excretion mean
it is the removal of metabolic wastes from the body
how is urea formed
urea is formed by the deamination of amino acids in which occurs in the liver
what is osmoregulation
the control of water and solute composition of body fluids
what is a nephron
it is the functional unit of the kidney, there is about 1 million in each kidney
what are the two regions in a nephron
cortex and medulla
what is ultrafiltration
it occurs in the bowmans capsule, and it is the filtration of small soluble molecules from the blood plasma to the nephron under pressure.
how does the structure of the glomerulus and bowmans capsule allow ultrafiltration
the basement membranes of the capillaries form a selective barrier between the blood plasma and the nephron, it acts as a molecular sieve.
it does not allow large plasma proteins and RBC’s through the filtration membrane
molecules that pass through form the glomerular filtrate.
what causes filtration pressure
high pressure is created in the glomerulus due to the different diameter size of the afferent and efferent arterioles. High blood pressure comes from the renal artery and the resistance of capillaries in the glomerulus.
what is selective reabsorption
it occurs in the proximal convoluted tube (PCT), it is the reabsorption of ions, amino acids, glucose and vitamins from the nephron into the blood plasma
what molecules travel into the bowmans capsule
water, ions, amino acids, urea, glucose
how are chloride ions reabsorbed in the PCT
facilitated diffusion, down a concentration gradient from high to low, no energy is required.
how are water molecules reabsorbed in the PCT
through osmosis from a high to low water potential, no energy is required as it has a partially permeable membrane
how is sodium ions reabsorbed in the PCT
through facilitated diffusion into the cell from filtrate. a sodium-potassium pump may be used but this will require ATP
how are glucose and amino acids reabsorbed in the PCT
facilitated diffusion, they diffuse with sodium ions and they are active transported from the PCT into the blood.
what do the cells lining the PCT do?
1 - sodium is pumped out of cell whilst potassium is pumped in via active transport
2 - a higher concentration of sodium in filtrate than in blood is caused. so the sodium moves back in cell via facilitated diffusion
3 - BUT sodium can only travel back in if ‘coupled’ with glucose (which therefore shows why movement of sodium out provides a gradient bringing back glue from filtrate into cell)
4 - a pore protein then allows glucose to diffuse to the blood via facilitated diffusion down a concentration gradient.
5 - water travels from the filtrate to the blood via osmosis down a water potential gradient.
what does the loop of henle do
it is a shape of a hairpin, it is a counter-current multiplier. it actively concentrates salt in the medulla therefore much water is reabsorbed from filtrate into blood to produce concentrated urine.
how does the counter-current mechanism work?
the ascending limb is permeable to salts (Na+ and Cl-) and less permeable to water. the descending limb is more permeable to water and less permeable to salts. the salts are actively pumped out of ascending limb to tissue fluid in the medulla and is diffused back into the descending limb.
then the water enters the blood in the vasa recta and is returned to the body.
so what is a counter-current multiplier
counter-current means runs in the opposite direction. this allows multiplication of Na+ and Cl- in the medulla of the kidney due to ions being pumped out of ascending limb.
blood in capillaries (vasa recta) also run in opposite directions.
as a result, water leaves descending limb via osmosis and returns to the blood supply.
what is osmoregulation
it occurs in the collecting duct, it is the homeostasis control of water and solute composition of the blood under hormonal control.
what do osmoreceptors do
they are found in the hypothalamus of brain, it detects the fall in concentration of water in blood and it stimulates neurosecretory cells in the hypothalamus to synthesise and secrete hormone ADH (antidiuretic hormone)
what does ADH do?
ADH passes from the hypothalamus to the posterior pituitary where it is released into the blood. it increases the permeability of the collecting duct to water so more water is reabsorbed and urine volume decreases.
what are the common causes of kidney failure
diabetes high blood pressure auto-immune disease infection crushing injuries
what happens if both kidneys do not function well
treatment must reduce concentration of waste products and control volume of body fluids to regulate solute concentration
what is haemodialysis
haemodialysis uses ia dialysis machine
blood is taken from artery and the blood runs through thousands of long, narrow fibres made of selectively permeable dialysis tubing which is surrounded by dialysis fluid
pores in the tubing allow molecules in an out (in solution, out dialysis fluid) except large RBC or proteins
blood and dialysis fluid run through machine in opposite directions, enhancing diffusion out of blood by a counter-current mechanism.
blood is then returned to the vein.
what does heparin do?
thins the blood and prevents clotting
