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Human Biology HB4 > homeostasis and hormones > Flashcards

homeostasis and hormones Flashcards

1
Q

what is homeostasis

A

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

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2
Q

homeostasis is important because…

A

helps maintain optimal conditions for cellular reactions

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

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3
Q

how is homeostasis maintained

A

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

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4
Q

negative feedback is…

A

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

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5
Q

what are hormones

A

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

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6
Q

what are endocrine glands

A

a ductless gland that secrete hormones directly to the blood.

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7
Q

what are target cells/tissue

A

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

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8
Q

what is an exocrine gland

A

a gland that secretes substances to a duct

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9
Q

what is a duct

A

a tube lined with epithelial cells and conveys a secretion

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10
Q

what do kidneys do

A

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

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11
Q

what does excretion mean

A

it is the removal of metabolic wastes from the body

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12
Q

how is urea formed

A

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

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13
Q

what is osmoregulation

A

the control of water and solute composition of body fluids

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14
Q

what is a nephron

A

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

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15
Q

what are the two regions in a nephron

A

cortex and medulla

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16
Q

what is ultrafiltration

A

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

17
Q

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

A

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.

18
Q

what causes filtration pressure

A

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.

19
Q

what is selective reabsorption

A

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

20
Q

what molecules travel into the bowmans capsule

A

water, ions, amino acids, urea, glucose

21
Q

how are chloride ions reabsorbed in the PCT

A

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

22
Q

how are water molecules reabsorbed in the PCT

A

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

23
Q

how is sodium ions reabsorbed in the PCT

A

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

24
Q

how are glucose and amino acids reabsorbed in the PCT

A

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

25
Q

what do the cells lining the PCT do?

A

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.

26
Q

what does the loop of henle do

A

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.

27
Q

how does the counter-current mechanism work?

A

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.

28
Q

so what is a counter-current multiplier

A

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.

29
Q

what is osmoregulation

A

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

30
Q

what do osmoreceptors do

A

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)

31
Q

what does ADH do?

A

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.

32
Q

what are the common causes of kidney failure

A 
diabetes
high blood pressure
auto-immune disease
infection
crushing injuries
33
Q

what happens if both kidneys do not function well

A

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

34
Q

what is haemodialysis

A

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.

35
Q

what does heparin do?

A

thins the blood and prevents clotting

Human Biology HB4 (9 decks)

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