Homeostasis + hormones

what is homeostasis?

• the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal or external changes.

• maintains optimal conditions for enzyme action and cell function

what are some things homeostasis controls?

• body temperature

• blood glucose concentration

• water levels in blood

differences between endocrine system and nervous system?

• endocrine = hormones released into blood

• nervous = electrical impulses by neurons

• nervous = more rapid response, endocrine has longer lasting effect

what do all control systems include

1. receptors

2. co-ordination centre

3. effectors

what is the endocrine system

• glands which secrete hormones into blood stream

• blood carries hormones to target organ where it causes an effect

what are these glands called (+ one other)

A = pituitary

B = thyroid

C = Pancreas

E = Adrenal (on kidneys)

D = ovaries (women)

+ testes (men)

what is the pituitary gland?

‘master' gland, secretes several hormones into blood

these act on other glands stimulating other hormones

What is adrenaline? What does it do?

• produced by adrenal glands

• times of fear or stress

• increases heart rate, ++ oxygenated blood to muscles ++ rate of respiration ++ more energy released = faster muscle contraction

• fight or flight

what is thyroxine? what does it do?

• from thyroid

• stimulates basal (baseline) metabolic rate

• important in growth and development

• negative feedback

how does thyroxine negative feedback loop work?

• TSH (thyroid stimulating hormone) released from pituitary gland

• travels in blood

• TSH causes thyroxine to be released from the thyroid gland (acts on cells to increase metabolism)

• thyroxine travels in blood, inhibits tsh release

what is controlled by negative feedback?

• basal metabolic rate

• body temperature

• blood glucose concentration

• water concentration in blood

why is it important to maintain constant body temp

• optimum temp for enzymes which control reactions in our cells

what happens when temperature is too high?

hypERthermia

• over 40 degrees, enzymes denature, reactions slow down

what happens when temperature is too low?

hypOthermia

• below 35 degrees

• slows down reactions (enzymes DON’T denature)

• if respiration stops, cells start to die

how is temp controlled?

• stimulus = change in temp

• receptors = thermoreceptors found near surface of skin (external changes) AND in the thermoregulatory centre in the brain - detects changes in temp of blood flowing through it

• coordinator = thermoregulatory system (hypothalamus)

• effectors/response depend on whether too hot or too cold

Sweat glands - too high

• more sweat produced containing water and mineral ions to cover skin surfaces

• heat energy from skin is used to evaporate water/sweat

• skin is cooled

• blood flowing through the skin is cooled so core temp drops

muscle contraction - too high

no response

arteries - too high

VASODILATION

• muscles in walls of arteries relax, blood vessels dilate/widen

• more blood can flow near surface

• more heat lost by radiation

• skin looks redder, body temp down

sweat production - too low

less/no sweat production

muscles - temp too low

• contract and relax rapidly (shivering)

• extra respiration from muscle cells releases some heat energy

• respiration = exothermic reaction

arteries - too low

VASOCONSTRICTION

• muscles in walls of arteries contract - blood vessels constrict/narrow

• less blood flows near the surface

• less heat is lost by radiation

• skin looks paler (increased body temp)

what controls and monitors blood glucose levels?

pancreas

Why is glucose stored as glycogen?

glucose = small and soluble, impacts osmosis

glycogen = large and insoluble, no impact on osmosis

what does the pancreas do if blood glucose conc. is too high?

• produces insulin (hormone)

• causes glucose to move from blood into liver + muscle cells (target organs)

• glucose is stored as glycogen for storage

what does the pancreas do if blood glucose conc. is too low?

• produces glucagon (hormone)

• causes glycogen to be converted into glucose and released into the blood

• negative feedback as when glucose changes, the body opposes the change

what is type 1/type 2 diabetes?

Diabetes - body doesn’t respond correctly to changes in blood glucose

Type 1 - pancreas fails to produce enough/any insulin. characterised by uncontrolled high glucose, treated with insulin injections

Type 2 - body cells (liver/muscle) no longer respond to insulin from the pancreas. Controlled diet + exercise regime to treat, obesity is a risk factor

3 ways water leaves the body, loss controlled by, important why?

1. via the skin in sweat (can’t control)

2. via lungs in exhalation (can’t control)

3. via kidneys in urine (can control vol/conc)

controlled by kidneys

cells do not function properly if they gain/lose too much water by osmosis

how are excess proteins excreted

Amino acid -deamination→ammonia (in liver)

ammonia (toxic) → urea (safer, excreted) (in liver)

the urea is then transported to the kidneys via blood stream where it is filtered out of the blood and excreted in urine

what 3 things does urine contain

• urea

• excess water

• excess mineral ions

3 stages of kidneys…

1. filtration

2. selective reabsorption

3. urine

how does filtering work in kidney

• all water and dissolved substances pass into tubule (filtered out of blood)

• large molecules and blood cells are too large, remain in blood

how does selective reabsorption work - what happens to glucose, water, mineral ions, urea

• osmosis of water, diffusion/active transport of glucose/mineral ions (depending on conc gradients)

Glucose - ALL reabsorbed as needed for respiration (already at optimum)

Water - SELECTIVELY reabsorbed by osmosis (depends on ADH in blood)

Mineral ions - SELECTIVELY reabsorbed - those that body needs

Urea - NONE reabsorbed, remains in tubule to form urine along with excess water/mineral ions

how is water level controlled?

• Hormone ADH → released from pit gland

• acts on kidney tubule (more permeable to H2O)

what happens when blood to concentrated (low levels h2o)

• MORE ADH released

• MORE water reabsorbed back into blood

• smaller volume more concentrated urine

• controlled by negative feedback

what happens when blood too dilute (too much h2o)

• LESS ADH released

• less water to be reabsorbed by osmosis

• larger volume of dilute urine produced

what is kidney failure

2 diseased kidneys and would die without treatment due to build up of poisonous urea

2 treatments for kidney failure

• dialysis machine (keeps you alive, not a cure)

• kidney transplant

how does dialysis work?

• blood flows in a membrane that is partially permeable, dialysis fluid flowing past

IN FLUID

• same conc useful solutes (glucose/ions) and water as blood - no useful stuff lost from blood

• NO urea - diffuses into dialysis fluid

how do you prevent rejection of kidney

• match tissue type

• immunosuppressant

• patient kept in sterile conditions

pros of kidney transplant

• improved quality of life - no dialysis, normal diet

• high success rate - esp if live donor

• cheaper in long run

cons kidney transplant

• risk of surgery complications

• risk of rejection

• risk of infection

• difficult to find compatible donor

• stressful wait

solutions for shortage of kidney donors

• opt-out donor scheme

• GM animals e.g. pig kidney (ethical/religious)

• stem cell research, therapeutic cloning

what do hormones cause in puberty?

• secondary sex characteristics

• male - sperm production, deeper voice

• female - wider hips, breasts develop + menstrual cycle starts

what is main female reproductive hormone?

oestrogen, produced in ovaries

what is the main male reproductive hormone

testosterone, produced in the testes

four main hormones in menstrual cycle

1. FSH

2. Oestrogen

3. LH

4. Progesterone

what does FSH do

causes maturation of egg, stimulates oestrogen

what does oestrogen do

maintains uterus lining. stop FSH and release LH (pit gland)

what does LH do

stimulates release of the egg, causes progesterone to be released

what does progesterone do

maintain lining of uterus, inhibits LH + FSH

order of menstrual cycle

1. FSH (pit gland) causes maturation of egg in ovary, stimulates oestrogen

2. oestrogen maintains lining of uterus, stops FSH and starts LH from pit gland

3. LH stimulates release of egg, causes progesterone to be released

4. progesterone maintains lining of uterus, inhibits LH and FSH from pit gland

what happens if egg is not fertilised + implants

both unfertilised egg + uterus lining are released = menstruation

2 hormonal contraceptives

• oral contraceptives - pill

• implants, skin patches + injections

how does oral contraception work

inhibits FSH so no egg matures, inhibits LH so no eggs are released

e.g. progesterone + oestrogen in the pill

how do implants, skin patches and injections work

slow release progesterone to inhibit the maturation (FSH) and release of eggs (LH) for a number of months of years

possibly better than pill → can’t forget

5 methods of non-hormonal control

• barrier methods - condoms/diaphragms (stop sperm reaching egg)

• intrauterine devices that prevent implantation of embryo/release hormone

• spermicidal agents that kill/disable sperm

• abstaining from sex around day 14 - egg may be in oviduct

• surgical methods of sterilisation

how does a ‘fertility drug’ work

contains FSH and LH, woman may become pregnant normally

4 stages of IVF (what does it stand for)

In vitro fertilisation

• give mother FSH + LH to stimulate maturation + ovulation of several eggs

• eggs are collected and fertilised by sperm in lab (petri dish)

• fertilised eggs divide by mitosis to develop into an embryo

  one/two embryos inserted into mother’s uterus. should induce pregnancy

what happens to left over embryos from ivf

can be used in stem cell research

what makes ivf possible

improvement in microscope techniques

3 advantages of IVF

• allows pregnancy to occur for couples that are struggling naturally

• screen for genetic disorders (e.g. cystic fibrosis)

• can use spare embryos for stem cell research

3 disadvantages of IVF

• emotionally/physically stressful

• LOW success rate

• can lead to multiple babies (dangerous for mother + babies)