homeostasis

why is homeostasis necessary?

if internal conditions fluctuate too much:

enzymes denature and metabolic reactions stop

what are the regulated internal conditions?

• blood glucose conc

• body temp

• water levels

what does the CNS consist of

brain and spinal cord

2 diff responses from effectors

• is effector is a muscle = muscles contract

• if effector is a gland = glands secrete hormones

reflex arc

automatic and rapid response

doesn’t involve the conscious part of the brain

protects body from harm

reflex pathway

• stimulus detected by a receptor in the skin

• an electrical impulse detected by the sensory neuron

• sends an electrical impulse in the relay neuron

• sends an electrical impulse to the motor neuron

• the impulse travels to the effector

• muscle contracts/ gland secretes to move the hand away

synapses

• gap between neurons

• neurotransmitters (chemicals) are released here

how does an impulse cross the synapse

• neurotransmitters are released into the synapse

• it diffuses across the gap

• it binds to receptor sites on the membrane of the next neuron

• this triggers a new electrical impulse in the next neuron

why is reflex important

its rapid and automatic

minimises damage to tissues by bypassing the conscious brain

stimulus

change in environment

receptor

specialised cells that detect stimuli

endocrine system

composed of glands which secrete chemicals called hormones

into the bloodstream

blood carries the hormone to a target organ

endocrine vs nervous system

• nervous = electrical, fast, short lasting effects, along neurones, very precise

• endocrine = chemical, slower, longer lasting effects, in the bloodstream, general

master gland

pituitary gland

blood glucose too high

• detected by pancreas

• produces insulin

• insulin causes glucose to move from blood into cells

• excess glucose is converted to glycogen and stored in liver and muscle cells

• glucose levels fall back to normal

blood glucose is too low

• detected by pancreas

• produces glucagon

• glucagon causes liver to convert the glycogen back to glucose

• glucose released into bloodstream

• glucose level back to normal

negative feedback

insulin and glucagon work in a negative feedback loop to maintain a constant range

type 1 diabetes

• pancreas fails to produce enough insulin

• genetic/ early on in life

• treat with insulin injections

type 2 diabetes

• body cells no longer respond to insulin produced

• obesity/ old age

• treat = carbohydrate controlled diet and regular excess

reproductive hormones

oestrogen

testosterone

testosterone

male reproductive hormone produced by the testes

stimulates sperm production

4 hormones involved in the menstrual cycle

1. FSH

produced by the pituitary gland

causes an egg to mature in the ovary

stimulates the ovaries to produce oestrogen

2. Oestrogen

produced in the ovaries

causes the lining of the uterus to thicken

stimulates release of LH

inhibits further release of FSH

3. LH

produced by pituitary gland

stimulates release of the eggs

4. Progesterone

maintain the lining of the uterus

produced in the ovaries

inhibits both LH and FSH

progesterone if no pregnancy

• If no embryo has implanted

• the corpus luteum begins to break down

• drop in progesterone levels

• causes the uterus lining to break down

• period starts

• allows FSH to be produced again

progesterone if pregnant

• progesterone levels increase

• keeps the uterus lining thick

• stable to nourish the developing fetus

• inhibits FSH and LH production

adrenaline

• produced by the adrenal glands

• times of fear or stress

• increases heart rate

• boosts delivery of O2 and glucose to the brain and muscles

• prepares body for fight or flight

thyroxine

• produced by thyroid gland

• stimulates basal metabolic rate

• plays a role in growth and development

• controlled by negative feedback

combined pill

• contains oestrogen and progesterone

• oestrogen inhibits FSH so no eggs mature

• progesterone inhibits LH and creates a thick cervical mucus to stop sperm

progesterone only pill

fewer side effects

not as effective

combined pill = pros

• over 99% effective at preventing pregnancy

• reduces risk of some types of cancer

combined pill = cons

cause side effects = headaches, nausea, irregular periods

doesn’t protect against STDs

fertility drugs

mixture of FSH and LH is given to stimulate the maturation and release of eggs

cons of fertility drugs

• multiple eggs can me released resulting in multiple pregs

• might have to take too many injections for it to work = expensive

IVF

• mother given FSH and LH to stimulate egg release

• eggs collected and fertilised by sperm in a lab

• fertilised eggs develop into embryos

• embryo inserted into the womans uterus for birth

pros and cons of IVF

• pros = gives a couple a chance to have their own baby

• cons = emotionally and physically stressful. Low success rates.

4 stages of the menstrual cycle

1. day 1

uterus lining breaks down for about 4 days

2. day 4 - 14

lining of uterus builds up again into a thick spongy layer full of blood vessels

ready to receive a fertilised egg

3. day 14

egg released from the ovary

4. wall maintained until day 28

if no fertilised egg received the lining breaks down and u start the cycle again

thyroxine and negative feedback

• low thyroxine levels detected by brain

• pituitary gland releases TSH

• TSH stimulates the thyroid to release thyroxine

• as thyroxine levels rise, the high level is detected

• brain inhibits release of TSH

• levels fall back to normal

how water leaves the body

• lungs = during exhalation

• skin = through sweat

• kidneys = urine

why condoms over pills

• protect against STD’s

• no chemical side effects

IVF and ethical issue

• some embryos are destroyed or used for research which some ppl find ethically wrong

why is a computer better than a ruler

• higher res

• remove human error