b12 - homeostasis in action

what are the functions of the skin

• pathogen protection
  - touch/pain receptor
  - temperature regulation

what does our body do when we're too hot

• sweating
  - vasodilation
  - hairs lie flat
  - no shivering

what does our body do when we're cold

• no sweating
  - vasoconstriction
  - goosebumps
  - shivering

why do we sweat

energy is transferred as water evaporates off the skin

what is vasodilation

when blood passes close to the surface of the skin and thermal energy is transferred to the surroundings

what is vasoconstriction

when reduced blood flows near the surface and less energy is transferred to the surroundings

why do we shiver

higher rate of respiration. respiration is a process that is exothermic and releases heat, thus arming us up

why do we get goosebumps

forms a thin layer of air which acts as an insulator

what muscles cause our hair to stand on end

hair erector muscles

what part of the body regulates temperature

hypothalumus

how does hypothalumus do thermoregulation

• receives nerve impulses from heat and cold receptors in the skin
  - has receptors called central thermoreceptors (checks core body temp)

how does water leave the body

via exhalation

what is lost through sweat

water, mineral ions and urea

what do the kidneys filter out of the blood

excess water, mineral ions and urea

when is urea produced

when you eat more protein than necessary or when tissues are worn out

explain how urea is formed

excess protein is in the form of amino acids. liver removes the amino group from the amino acids. this makes ammonia. ammonia - highly toxic. ammonia is converted to urea to be excreted from body.

is urea toxic

yes, but not too much so it can be removed from the body safely

how can water be lost

urine or exhalation

what are the kidneys important for

excretion and homeostasis

how does a healthy kidney function

produces urine by filtering the blood. it then reabsorbs all of the glucose, mineral ions and vital water

the water balance is controlled by what

ADH

what is the effect of ADH

increases permeability of the kidney tubules by inserting aquaporins

what are aquaporins

water channels

what is ADH secreted by

pituitary gland

when is ADH released by the pituitary gland

when the blood is too concentrated and it causes more water to be reabsorbed back into the blood from the kidney tubules by making them more permeable

what is ADH release controlled by

negative feedback loop

what is filtered out the blood by the kidneys

• water
  - ions
  - glucose
  - urea

what is reabsorbed back into the blood in the kidneys

• all glucose
  - some water
  - some ions

what is in urine

urea, some water and some ions

what is not filtered out of the blood

• protein
  - cells (RBC, WBC etc;)

ADH

a hormone that controls blood water concentration by changing the permeability of the kidney tubules

ADH stands for

anti diuretic hormone

2 solutions to kidney failure

• kidney dialysis
  - kidney transplant

what does dialysis do

the concentration of dissolved substances in the blood is restored to normal levels

what is removed in dialysis

urea and excess mineral ions pass from the blood into the dialysis fluid

how does dialysis work

1. blood is removed from the body and mixed with anticoagulant to prevent clotting.
   2. blood flows through the dialysis machine past a partially permeable membrane.
   3. dialysis fluid contains normal levels of glucose and ions but no urea.
   4. urea, excess salts and excess water diffuse from the blood into the dialysis fluid.
   5. red blood cells and proteins stay in the blood because they are too large to pass through the membrane.
   6. clean blood is returned to the body

disadvantages of dialysis

• dieting
  - the sessions are long and regular
  - it can stop working over time

what does a kidney transplant do

a healthy kidney from a donor replaces the function of the diseased or damaged kidney

what do doctors do to try and minimise risk of rejection of donor kidneys

the tissue types of the donor and the recipient are matched as closely as possible as well as immunosuppressant drugs