homeostasis and hormones

Question 1

what is homeostasis

Answer 1

the maintenance of a constant internal environment for the cells within a living organism e.g temperature, pH, blood glucose and salt levels

Question 2

homeostasis is important because…

Answer 2

helps maintain optimal conditions for cellular reactions

gives organisms independence from the external environment whilst still living in it

Question 3

how is homeostasis maintained

Answer 3

homeostasis is maintained through a combination of nervous and hormonal mechanisms such as negative feedback

Question 4

negative feedback is…

Answer 4

whenever a factor moves away from the ideal/norm, a set of processes moves it back towards normal again

Question 5

what are hormones

Answer 5

molecules that are released by the endocrine glands directly to the blood that travels to a target organ to produce an effect.

Question 6

what are endocrine glands

Answer 6

a ductless gland that secrete hormones directly to the blood.

Question 7

what are target cells/tissue

Answer 7

cells that have receptors on their plasma membrane that are complimentary in shape to specific hormone molecules

Question 8

what is an exocrine gland

Answer 8

a gland that secretes substances to a duct

Question 9

what is a duct

Answer 9

a tube lined with epithelial cells and conveys a secretion

Question 10

what do kidneys do

Answer 10

excrete, the filter the blood removing nitrogenous excretions (urea and ammonium ions) to produce urine.

Question 11

what does excretion mean

Answer 11

it is the removal of metabolic wastes from the body

Question 12

how is urea formed

Answer 12

urea is formed by the deamination of amino acids in which occurs in the liver

Question 13

what is osmoregulation

Answer 13

the control of water and solute composition of body fluids

Question 14

what is a nephron

Answer 14

it is the functional unit of the kidney, there is about 1 million in each kidney

Question 15

what are the two regions in a nephron

Answer 15

cortex and medulla

Question 16

what is ultrafiltration

Answer 16

it occurs in the bowmans capsule, and it is the filtration of small soluble molecules from the blood plasma to the nephron under pressure.

Question 17

how does the structure of the glomerulus and bowmans capsule allow ultrafiltration

Answer 17

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.

Question 18

what causes filtration pressure

Answer 18

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.

Question 19

what is selective reabsorption

Answer 19

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

Question 20

what molecules travel into the bowmans capsule

Answer 20

water, ions, amino acids, urea, glucose

Question 21

how are chloride ions reabsorbed in the PCT

Answer 21

facilitated diffusion, down a concentration gradient from high to low, no energy is required.

Question 22

how are water molecules reabsorbed in the PCT

Answer 22

through osmosis from a high to low water potential, no energy is required as it has a partially permeable membrane

Question 23

how is sodium ions reabsorbed in the PCT

Answer 23

through facilitated diffusion into the cell from filtrate. a sodium-potassium pump may be used but this will require ATP

Question 24

how are glucose and amino acids reabsorbed in the PCT

Answer 24

facilitated diffusion, they diffuse with sodium ions and they are active transported from the PCT into the blood.

Question 25

what do the cells lining the PCT do?

Answer 25

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.

Question 26

what does the loop of henle do

Answer 26

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.

Question 27

how does the counter-current mechanism work?

Answer 27

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.

Question 28

so what is a counter-current multiplier

Answer 28

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.

Question 29

what is osmoregulation

Answer 29

it occurs in the collecting duct, it is the homeostasis control of water and solute composition of the blood under hormonal control.

Question 30

what do osmoreceptors do

Answer 30

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)

Question 31

what does ADH do?

Answer 31

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.

Question 32

what are the common causes of kidney failure

Answer 32

``` diabetes high blood pressure auto-immune disease infection crushing injuries ```

Question 33

what happens if both kidneys do not function well

Answer 33

treatment must reduce concentration of waste products and control volume of body fluids to regulate solute concentration

Question 34

what is haemodialysis

Answer 34

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.

Question 35

what does heparin do?

Answer 35

thins the blood and prevents clotting