B5 - Homeostasis and Response

Synapse diagram, brain diagram, eye diagram, iris reflex diagram, accomodation diagram, reaction time practical, vision defects diagram, dialysis diagram, menstrual cycle diagram, phototropism diagram, gravitropism diagram

Define homeostasis

Maintaining a stable internal environment in response to changes in internal and external conditions

What four body conditions need to be regulated?

body temperature, blood glucose, water, salt

Describe a negative feedback system

1. Receptor detects stimulus (levels low)

2. Coordination centre processes information and organises response

3. Effector produces response to counteract change (levels increase)

4. Receptor detects new stimulus

Receptors

stimuli-detecting cells (taste, sound, light)

effectors

respond to impulses (muscles, gland)

Where is the Central Nervous System?

brain and spinal cord

Sensory neurones

send impulses from receptors to CNS

Motor neurones

carry impulses from CNS to effectors

Describe synapses

1. Electrical impulse reaches end of neurone A and triggers release

   1. Neurotransmitters diffuse across synapse and trigger electrical impulse on Neurone B

reflex

rapid, automatic response to stimuli which reduce chance of injury (pupil dilation, hormone release)

Describe the reflex arc (part 1)

1. Receptor detects stimulus

2. Send electrical impulse along sensory neurone

3. When the impulse reaches the end of the sensory neurone, neurotransmitters diffuse across the synapse to the relay neuroneDes

Describe the reflex arc (part 2)

4. Impulse passes along the relay neurone, then crosses the synapse to the motor neurone in the same way

5. Impulse travels along the motor neurone to the effector, when the reflex action is triggered

Cerebral cortex

consciousness, intelligence, memory, language

Cerebellum

muscle coordination

Medulla

unconscious activities

Brain damage

linking damaged area with affected function

Electrical stimulation

stimulating a particular part causes a particular effect

MRI (magnetic resonance imaging)

track brain activity during a particular activity

What are consequences to MRI, electrical stimulation etc.?

electrically stimulating the brain can treat Parkinson’s disease, can cause physical brain damage, disrupting function

Name the 8 parts of the eye

cornea, iris, lens, optic nerve, ciliary muscles, suspensory ligaments, retina, sclera

Cornea

transparent outer layer at front

Iris

controls size of the pupil

Sclera

tough, supporting wall

Lens

focusses light onto retina

Retina

contains light receptors

Optic nerve

carries impulses to brain

What is the iris reflex with bright light?

radial muscles relax, circular muscles contract

What is the iris reflex with dim light?

radial muscles contract, circular muscles relax

What is accomodation with near objects?

ciliary muscles contract, so suspensory ligaments slacken, lens thickens and refracts more light

What is accomodation with far objects?

ciliary muscles relax, so suspensory ligaments tighten, lens is thinner and refracts less

Hyperopia

not enough refraction, weak ciliary muscle or short eyeball (convex lens)

Myopia

too much refraction, thick lens or long eyeball (concave lens)

Contact lenses

lightweight, invisible lens which sit on the eyeball

Laser eye surgery

a laser is used to change the shape of the cornea

Replacement lens surgery

artificial, plastic lens transplant

Thermoregulatory centre

balances energy lost and gained to maintain constant body temperature, (processes information and organises response)

Temperature receptors

detect body temperature

Effector

Carries out response

What does your body do when hot?

sweat glands produce sweat, which transfers energy to the environment, vasodilation helps to transfer energy to the environment

What does your body do when cold?

hairs trap an insulating layer of warm air, vasocontriction stops energy transfer to the surroundings, shivering causes respiration, which releases energy

nerves

fast, short time, precise

hormones

slow, long time, general

hormones =

chemical molecules released by glands into the blood

Pituitary gland

many hormones which trigger the release of other hormones (brain)

Thyroid

produces thuroxine, regulates metabolism and temperature (throat)

Adrenal gland

produces adrenaline, prepares for ‘fight or flight’ (abdomen)

Testes

produces testosterone, controls puberty and sperm production (male reproductive system)

Blood glucose

Eating carbohydrates puts glucose into the blood which is removed by cell metabolism (changes are monitored by the pancreas)

How does the pancreas monitor blood glucose

1. Pancreas detects high blood glucose and secretes insulin

2. Insulin stimulates liver to turn glucose into glycogen

3. Blood glucose is decreased

1. Pancreas detects low blood glucose and secretes glucagon

2. Glucagon stimulates liver to turn glycogen into glucose

glucose

sugar from carbs

glycogen

the way glucose is stored in the liver

Glucagon

secreted by pancreas when blood sugar is low

Type 1 diabetes

genetic, pancreas produces too little insulin, treated with insulin therapy, diet and exercise, transplant

Type 2 diabetes

caused by lifestyle factors, resistant to own insulin, treated with diet and exercise

Kidneys

Kidneys make urine by taking waste products from the blood

Urea

excess amino acids are converted into fats and carbs in the liver (deamination), ammonia (waste product) is converted by urea

Ions

ions come from food, ions lost in sweat, selectively reabsorbed

Water

lost in sweat and breathing, selectively reabsorbed

ADH

anti-diuretic hormone, pituitary gland (ADH down, then water reabsorption down)

Dialysis

done regularly to control concentration of waste products, dialysis machine becomes part of circulatory system, expensive inconvenient and unpleasant (dialysis fluid in, partially permeable membrane, dialysis fluid out)

Kidney transplant

from an organ donor, from a living donor, risk of rejection (immune-suppressants are used), cheaper long waiting lists

What are the stages of the menstrual cycle?

Stage 1: menstruation starts

Stage 2: uterus lining builds again

stage 3: ovulation

Stage 4: lining maintained until next cycle

FSH (follicle-stimulating hormone)

pituitary gland, causes egg to mature, stimulates oestrogen

Oestrogen

ovaries, grows uterine lining, stimulates LH, inhibits FSH

LH (luteinising hormone)

pituitary gland, ovulation

Progesterone

ovaries, inhibits FSH and LH, maintains uterine lining

The Pill

oestrogen (inhibits FSh release), progesterone (stimulating production of thick mucus (acts as a barrier), 99% effective w/ side effects, progesterone - only has fewer side effects

Contraceptive patch

oestrogen and progesterone

Contraceptive implant

constant progesterone

Contraceptive injection

progesterone

IUD

kills sperm and prevents implantation

Condoms

barrier method

Female condoms

barrier method

Diaphragm

used with spermicide

Spermicide

not very effective

Sterilisation

cutting or tying fallopian tubes or sperm ducts

Natural method

tracking menstruation, ineffective

Abstinence

only 100% effective method

FSH and LH for fertility

expensive, multiple births

IVF

1. collect eggs from ovaries (use FSH and LH)

2. fertilise in a lab with sperm

3. fertilised eggs grow into embryos in an incubator

4. one or two transferred to uterus

(ICSI used for low sperm count, micro-tools for genetic testing, time-lapse imaging

Pros of IVF

gives a couple a child

Cons of IVF

multiple births, low success rate, physically stressful, expensive, unused embryos are destroyed, genetic testing could lead to preferred characteristics

Adrenaline

adrenal glands, response to stress, increase oxygen and glucose supply (increase heart rate)

Thyroxine

thyroid gland, basal metabolic rate, protein synthesis

Describe thyroxine

1. thyroxine increase detected

2. pituitary gland inhibits TSH

3. thyroxine levels decrease

1. thyroxine decrease detected

2. pituitary gland stimulates TSH

3. thyroxine levels increase

Auxin

plant hormones which control growth near shoots and roots, stimulates shoot growth and inhibits root growth

phototropism

growth towards light

gravitropism/ geotropism

growth against gravity

What do auxins do?

kill weeds (used in selective weedkillers), grow cuttings (used in rooting powder), tissue culture (used in growth medium)

Gibberellin

stimulates seed germination, stem growth and flowering, controls dormancy (alters dormancy to stimulate growth year round), induces flowering (no need to alter environment), larger fruit

Ethene

stimulates fruit ripening (fruit picked while unripe and ripened on demand)