GCSE Homeostasis and response

Define homeostasis

The maintenance of a constant internal environment

Define negative feedback

when a change from normal conditions is detected and prompts a response to return to normal

Give three procedures that homeostasis maintains

Temperature, blood glucose levels (BGL), water balance

What are the two communication systems in the body

hormonal and nervous system

How does the hormonal system send signals

via hormones in the bloodstream

How does the nervous system send signals

via electrical impulses in neurones

define stimulus

a signal to which an organism responds

give the stimulus for smell

chemicals

describe the coordination pathway

stimulus - receptor (PNS) - coordinator (CNS) - effector

give examples of stimuli

pressure, temperature, sound, light, chemical

give examples of receptors

skin, eyes, ears, nose, tongue

give examples of coordinators

brain + spinal cord

give examples of effectors

muscles and glands

what are glands?

organs that secrete hormones or fluids such as tears and sweat

what are nerves?

bundles of neurons in the PNS

where are electrical impulses generated?

receptor

what are the three types of neurones?

sensory, relay and motor

where are sensory neurones found?

receptors to CNS

Where are relay neurones found?

CNS

where are motor neurones found?

CNS to effectors

What does the reflex arc do?

rapid automatic response to stimuli to protect the body

what part of the CNS do reflexes go through?

the spinal cord (usually closer than brain)

what is a synapse?

the gap between neurons

how do synapses work?

The nerve signal is transferred by neurotransmitters which diffuse across the gap and set off a new electrical signal in the next neuron.

describe how electrical impulses are transmitted across synapses

when the electrical impulse reaches the end of a neuron, vesicles move to the join to the cell membrane to release neurotransmitters into the synapse, which *diffuse* across the synapse, binding to receptors on the next neurons membrane and begins a new impulse.

give an identifying feature of a sensory neuron

cell body sticking out of the axon

give an identifying feature of a relay neuron

short

give an identifying feature of a motor neuron

cell body attached to the dendrites + effector on the end

what is the eye?

a sensory organ that detects light and converts light energy into electrical impulses.

what are rods responsible for?

black and white vision in low light

what are cones responsible for?

coloured vision in high light

what do radial and circular muscles do?

radial muscles contract, circular muscles relax

What is accommodation?

the process by which the eye's lens changes shape to focus near or far objects on the retina

how does accommodation work for distant images?

Ciliary muscles relax, suspensory ligaments contract, lens is long and thin (less refraction needed)

how does accommodation work for close images?

Ciliary muscles contract (bulge), suspensory ligaments relax, lens is short and fat (more refraction needed)

Why does the lens become fatter to see close objects?

the divergent rays are shining on the ends of the lens, so it makes it bulgy to focus the rays into the retina.

What is myopia?

short sightedness - unable to see distant objects - eye is too long / lens is too convex - image forms in front of retina

What is hyperopia?

long sightedness - unable to see close objects - eye is too short / lens is too concave - image forms behind the retina

what are the treatments for myopia and hyperopia?

concave for myopia, convex lens for hyperopia

What part of the brain controls homeostasis?

hypothalamus

What is the thermoregulatory system made up of?

receptors that monitor body (blood) temperature

What is negative feedback?

A response to a change in the body that reverses the change

What effectors do the thermoregulatory system use?

sweat glands, blood vessels in skin and skeletal muscles

What is the body's negative feedback loop to being too cold?

stimulus - too cold / receptor - thermoreceptors in the skin / coordinator - hypothalamus (brain) / effector - sweat glands, skeletal muscles, blood vessels, erector muscles / response - vasoconstriction, shivering, sweat glands stop, piloerection / core body temperature rises

Why does the body use vasoconstriction/dialation?

vasodialation allows heat to be lost by radiation. vasoconstriction stops heat from being radiated.

Why does the body shiver?

rapid skeletal muscle contraction - high rates of respiration, which is an exothermic reaction.

Why does the body use piloerection when cold?

to trap warm air between hairs.

Why does the body sweat?

cool skin through evaporation

What is the endocrine system?

a group of glands that secrete hormones directly into the blood

What are hormones and what do they do?

Hormones are messenger proteins that travel to their target organ in the blood. They create a response in the target organ

What is different about hormones?

They are slower than the nervous system but have longer-lasting effects.

What is the pituitary gland?

The master gland - it loosely controls other glands

What is thyroxine action an example of?

Negative feedback

What is thyroxine?

A hormone secreted by the thyroid when it detects TSH. It controls metabolic rate and targets almost all cells. It has nearly constant levels due to negative feedback

What is used to make thyroxine?

Iodine

How does thyroxine link to temperature regulation?

Because thyroxine controls metabolic rate, including respiration (an exothermic reaction), thyroxine production will be inhibited in high temperatures to reduce metabolic rate and slightly cool the blood. The reverse is also true.

What is adrenaline?

A hormone secreted by the adrenal gland that is stimulated by the nervous system at times of excitement/distress. It prepares the body for fight or flight.

What are adrenaline's target organs?

Vital organs like the heart and lungs

Describe the fight or flight response

Increased heart rate, increased breathing rate, dilation of airways, increased blood glucose levels, dilation of pupils

Describe the journey of glucose in the blood

glucose is eaten as sugar/starch/carb - digestive system uses carbohydrases to break down into glucose - glucose is absorbed into the bloodstream by the SI (villi)

Why can't blood glucose levels get too high?

The water concentration of the blood would fall. Water would leave the cells via osmosis and shrivel up.

Why can't blood glucose levels get too low?

The water concentration in the blood would rise. Water would enter the cells via osmosis and burst.

What would cause peaks in blood glucose levels?

Eating

Why might blood glucose levels peak at different rates?

Differences in food: simple and complex carbohydrates

What evidence might be in a graph to show that there's a mechanism to prevent blood glucose from falling too low?

Blood glucose levels never fall beyond a certain point - negative feedback might activate a mechanism to raise blood glucose levels like glucagon secretion or hunger

What is the function of the pancreas in the endocrine system?

Detects and controls blood glucose levels with insulin and glucagon.

What are the target organs for insulin and glucagon?

Liver and muscles

How does the pancreas respond to high blood glucose?

Secretes insulin

How does the pancreas respond to low blood glucose levels?

Secretes glucagon

What does insulin do?

Makes glucose into glycogen to be stored in the liver, reduced blood glucose levels.

What does glucagon do?

Breaks glycogen in the liver down to be released into the blood, increases blood glucose levels.

Define excretion

The removal of metabolic waste from the body.

How is carbon dioxide produced and how is it excreted?

Produced by the aerobic respiration of cells, diffuses from bloodstream into lungs to be exhaled

How is lactic acid produced and how is it excreted?

Produced by anaerobic respiration in muscles, oxidised in the liver

How is excess water produced and how is it excreted?

Produced by drink/food/respiration, urination through the kidneys

How are excess ions/salts produced and how are they excreted?

Produced by food/drink/chemical reactions, urination through the kidneys

From what source is the most water gained?

Drinking water

How is the most water lost?

Urination

Why must the body remain isotonic?

Cells will shrivel or burst if blood is too concentrated or dilute

What do the kidneys control?

How much urea, salt ions and water are released in urine

Which blood vessels carry blood to the kidneys?

The renal arteries off the aorta

Which blood vessels carry cleaned blood away from the kidney?

The renal vein off the vena cava

Name the tube that carries urine from the kidneys to the bladder.

The ureter

Where does ultrafiltration occur?

The capsule

How does ultrafiltration work?

The pores in capillaries seep tissue fluid etc into the gap between it and the capsule. Particles small enough to diffuse across the nephron's wall (water, glucose, salts, urea) into the nephron. Bigger particles like RBC's, WBC's and proteins cannot fit and don't get filtered out.

What is a nephron?

The small capillary-like tubules that filter metabolic waste out of blood.

What does the nephron reabsorb?

The glucose lost by ultrafiltration

What are the three main processes in the nephron?

Filtration, reabsorption, urine production

How does reabsorption work and what does it reabsorb?

Capillaries wound around the nephron diffuse all glucose particles back into the blood. It also diffuses some water back into the blood.

How does urine production work?

Controlled by ADH, contains urea, some water and some salt ions.

What is the problem with urea? How is it produced?

Proteins consumed in the diet will be broke down into amino acids to be turned into different proteins. Excess amino acids can't be stored, so they are deaminated into ammonia, and then urea. Urea is toxic.

What does deaminated mean?

Breaking down excess amino acids into ammonia and then urea.

Define osmoregulation

the control of the water and salt levels in the body. The correct water balance between the cell and the surrounding fluid must be maintained to prevent problems with osmosis.