BIOLOGY TOPIC 5

Homeostasis and response

Homeostasis

the regulation of conditions inside the body and cells, it maintains the stable internal enviourment, with optimal conditions for enzyme action, in response to changes in internal and external conditions

Receptors

to detect stimuli

stimuli

changes in the enviourment

Coordination centres

To receive and process information from receptors and organise response

Effectors

to produce a response to counteract change, and restore optimal conditions

Automatic control systems use

nervous or chemical responses

Automatic control systems maintain

body temperature, blood glucose level, blood water content.

Central nervous system ( CNS )

Consists of brain and spinal cord, connected to body by neurones

Neurones

cells that carry information as electrical impulses in the nervous system

How does the stimulus turn into a response

stimulus → receptor → sensory neurone → CNS → motor neurone → effector ( muscle/gland ) → responce

Synapse

connection between two neurones, a nerve signal is transferred across the synapse by the diffusion of chemicals. neurotransmitters that bridge the gap between nerve cells.

Reflexes

Rapid, automatic responses to stimuli that don’t involve the conscious part of the brain, they help prevent injury.

Reflex arc

the passage of information in a reflex, from receptor to effector

How do reflexes work?

1) Stimulation of receptor

2) impulses sent along sensory neurone

3) impulses pass along relay neurone

4) impulses sent along motor neurones

5 ) impulses reach effector ( e.g. muscle contracts and arm moves )

( the neurones are connected by synapses which pass onto the impulse to the next neurone )

Brain

the organ in charge of complex behaviour, made up of billions interconnected neurones.

Label the brain

AT THE FRONT - the cerebral cortex controls consciousness, intelligence, memory and language

AT THE BASE ( PINK LONG THING ) - medulla, unconscious activities

AT THE BASE AT THE BACK - spinal cord

AT THE BACK - cerebellum, controls unconscious activities.

Ways to study which bits of the brain do what

• observe patients with brain damage

• Electrically stimulate different parts of the brain

• use MRI scanners to map brain activity.

Risk of studying the brain

the brain is complex and delicate, studying it is difficult and risky, but it has led to the development of treatments for nervous disorders.

Label the eye

check

Sclera

tough, supporting wall

Cornea

transparent outer layer at front

Iris

contains muscles controlling pupil size and determines eye color.

retina

contains cells sensitive to light intensity and colour

Optic nerve

carries impulses from receptor cells to the brain

Eye reflexes

bright light, pupil shrinks,

Dim light, pupil dilates

Accommodation

is a reflex where the lens changes is shape to focus light onto the retina

when an object is close

ciliary muscles contract

lens becomes thicker

suspensory ligaments react

light refracts more

When an object is distance

ciliary muscles relax
lens becomes thinner
suspensory ligaments tighten
light refracts less

Long sightedness`

hyperopia, image of near objects brought into focus behind retina, fixed using convex lens

Short sighted

myopia, image of distant objects brought into focus in front of the retina, fixed using concave lens

Treatments of myopia and hyperopia

glasses, contact lenses, replacement lens surgery, laser eye surgery.

When your too hot..

temperature receptors detect that core body temperature is too high, thermoregulatory centre receives info from receptors and triggers effectors automatically. effectors produce response and counteract the change.

when your hot ( physical )

blood vessels dilate ( vasodilation )

more blood flows close to skin

sweat glands produce sweat

when your temperature is too low

temperature receptors detect that the core body temperature is too low, thermoregulatory centre receives info from receptors and triggers effectors automatically, effectors produce response and counteract the change.

When your cold. ( physical )

blood vessels constrict

less blood flows close to skin

shiver as your skeletal muscles contract

no sweat produced

The endocrine system

is made up of glands that secrete chemicals called hormones into the blood, the bloodstream carries them to target oragans.

Pituitary gland

master gland, secretes hormones that stimulates other glands

Thyroid

produces thyroxine

Adrenal gland

produces adrenaline pan

pancreas

produces insulin

ovaries ( female )

produce oestrogen

Testes ( male )

produce testosterone

Hormones

act more slowly than nerves, but effects last longer

the pancreas secretes

the hormones insulin and glucagon, which controls blood glucose levels

5 steps to reduce blood glucose

1) too much glucose in the blood

2) pancreas secretes insulin

3) insulin makes glucose moves to cells

4) liver turns glucose into glycogen

5) glucose is reduced

5 steps to increase blood glucose

1) too little glucose in blood

2) pancreas secretes glucagon

3) glucagon in blood

4) liver turns glycogen into glucose and releases it

5) glucose levels increased

Type one diabetes

cause - pancreas does not produce enough or any insulin

effect - blood glucose can rise to dangerously high levels

treatment - insulin injections remove glucose from blood

Type two diabetes

cause - cells no longer respond properly to insulin

effect - blood glucose can rise to dangerously high levels

treatment - carbohydrate controlled diet, and regular excersize

risk - obesity

Where is adrenaline produced

adrenaline is produced by adrenal glands

why is adrenaline released

released in response to fear or stress → increases heart rate → increases o2 and glucose supply to muscles and brain → readies body for fight or flight

where is thyroxine produced from

thyroxine is produced by the thyroid gland

what does thyroxine do

helps regulate basal metabolic rate

stimulates protein synthesis for growth and development

levels controlled by negative feedback

what happens if there is wrong water or ion content

wrong water/ or ion content → too little or too much water enter cells by osmosis → cell damage

Water, ions and urea

water, ions and urea are filtered out of the blood as it passes through the kidneys ( filtration )

waste products are excreted by

unregulated amounts of water lost in exhalation

unregulated amount of water ions and urea lost through sweat

excess amino acids deaminated in lives, formed toxic ammonia converted to urea

Kidney filter urea from blood excreted in urine

Right amounts of water, glucose and ions reabsorbed into blood by kidneys after filtration, the rest is removed in urine

Anti - Diuretic Hormone

the brain monitors blood water content and instructs the pituitary gland to release ADH, ADH affects the permeability of the kidney tubules

Braid detects blood water content is too high

Brain detects blood water content is too high → pituitary gland releases less ADH → less water is reabsorbed from kidney tubules, more water is lost in urine → water content decreases

Brain detects water content is too low

brain detects blood water content it too low → pituitary gland releases more ADH → more water is reabsorbed from kidney tubules, less water is lost in urine → water content increases

Kidney failure treatment

people with kidney failure may have an organ transplant of dialysis treatment

Regular dialysis

keeps the concentration of dissolved substances in the blood at normal levels, removes waste substances

How dialysis works

the partially permeable membrane lets through ions and waste substances, but not big molecules like proteins, but not big molecules like proteins, dialysis fluid has same concentration of dissolved ions as healthy blood so these useful substances aren’t lost.

Puberty

the body starts releasing sex hormones and develops secondary sexual characteristics

Men

( testosterone ) sperm production, secondary = facial hair

Women

oestrogen, menstrual cycle, secondary = breasts

Four hormones control the menstrual cycle

oestrogen ( causes uterus lining to grown ) → luteinising Hormone ( LH ) triggers ovulation → follicle-stimulating hormone (FSH) stimulates egg growth → progesterone stabilizes the uterine lining.

stages of menstrual cycle

stage 1 - menstruation starts uterus lining breaks down

stage 2 - uterus lining builds up, ready to receive a fertilised egg

stage 2 - egg released from ovary ( ovulation )

stage 4 - lining maintains without fertilised egg, cycle starts

Contraception

reduces the likelihood of a sperm reaching an ovulated egg

Hormonal methods use

oestrogen to in inhibit FSH, so egg not released, and or progesterone to reduce fertility

Hormonal methods

oral contraceptive pills, skin patches, injections, contraceptive implants, intrauterine devices

Pros and cons of hormonal methods

very effective, doesn’t protect from STDS and side effects

Non hormonal ways

condoms and diaphragms, prevent sperm from reaching egg - ( protect from STDS, better with spermicide )

sterilisation - permanent procedure to make someone infertile - ( small change cut tubes can re-join )

natural, methods avoid fertile time of menstrual cycle, spermicides, disable/kill sperm - ( less effective )

abstain from sex - ( 100% effective )

Women who sturggle to get pregnant can take

fertitility drug, containing FSH and LH to stimulate ovulation. another option is in vitro fertilisation

IVF ( in vitro fertilisation )

women is given FSH and LH to stimulate maturation of several eggs, eggs are collected from ovaries, eggs are fertilised in lab using sperm, fertilised eggs are grown into embryos, once embryos are tiny balls of cells, one or two are transferred to the women’s uterus

Negatives of IVF

emotionally and physically stressful, low success rate, risk of multiple births

Phototropism

the growth of plant shoots in response to light exposure

Auxin

a plant hormone that controls growth near the tips of shoots and roots, when the shoot tip is exposed to light, auxin accumulated on the shaded sides, cell grow faster on shaded side so shoot bends towards the light

Gravitropism

the growth of plant shoots in response to gravity

auxin

a plant hormone that controls the growth near the tips of shoots and roots , influencing directional growth through differential cell elongation.

Shoots grow upward..

auxin accumulated on lower side of shoot, auxin makes lower side grow more quickly, shoot bends upwards

and roots grown downwards

auxin accumulates on lower side of root, gravity pulls down, auxin inhibits root growth on lower side, root bends downwards.

uses of Auxins

develop to selectively kill weeds, but not affect crops, added to rooting powders to boost root growth for cuttings, stimulate cell division in tissue culture for plant cloningU

uses of Givverelin

makes seeds germinate, induces flowers without need for specific conditions, makes fruit grow larger

Ethene uses

speeds up ripening of fruits, effects can be blocked to delay repining in storage. ( also controls cell division )