Homeostasis and Hormones

Question 1

Endocrine Glands

Answer 1

Group of cells that are specialised to secrete hormones eg the pancreas releasing insulin

Question 2

Hormones

Answer 2

These are chemical messengers and many of them are are proteins or peptides such as insulin and some are steroids such as progesterone. They are secreted when a endocrine simulated and can be done by a change in conc of a substance or an electrical impulse

Question 3

Hormone response

Answer 3

Stimulus – Receptor – hormone – Effectors – Response
Low glucose Receptors Pancreas Target cells Glucose is released into the
levels in pancreas releases the in liver detect blood so glucose conc inc
detect the hormone glucagon ​ low level Glucagon convert glycogen
into glucose

Question 4

How hormones trigger the response

Answer 4

1) Hormone carriers messenger molecule from endocrine gland to receptor on the target cells when the hormone binds to its receptor it activates an enzyme in the cell membrane. 2) The enzyme catalyses the production of a molecule inside the cell called a signalling molecule and signals to other parts of the cell to change how the cell works.
3) Signalling molecule is called a second messenger as it carries the chemical message the second part of the way from the receptor to other parts of cells
4) Activates a cascade inside of the cell

Question 5

Adrenaline response

Answer 5

it is the first messenger binds to specific receptors in the cell membrane of many cells eg liver cells. When Adrenaline binds it activates an enzyme in the membrane called adenylyl cyclase and when activated it catalyses the production of a messenger called cyclic AMP (cAMP) inside the cell and this activates a cascade to male glucose more available by catalysing breakdown of glycogen into glucose.

Question 6

Cortex

Answer 6

Secretes steroid hormones eg cortisol and aldosterone when your stressed both have short and long term responses. Stimulates the breakdown of proteins and fats into glucose. This increases the amount of energy available so the brain and muscles can respond to the simulation

Question 7

Medulla

Answer 7

Secretes catecholamine hormones eg it secretes adrenaline and noradrenaline. These act to make more energy available in the short term by increasing heart and breathing rate causes cells to break down glycogen to glucose

Question 8

Pancreas

Answer 8

Areas with endocrine tissue are called the islets of Langerhans and are found in clusters around blood capillaries. The islets secrete hormones directly into the blood and made up of of two type of cells Alpha cells secrete glucagon and beta cells secrete insulin and these hormones help control blood glucose conc

Question 9

How does insulin lower blood glucose

Answer 9

Binds to specific receptors on cell membranes of liver and muscle cells and increases permeability of cell membranes to glucose so cells take up more glucose. Insulin activates enzymes that convert glucose to glycogen and cells store glycogen in their cytoplasm and is called glycogenesis and insulin increases the rate of respiration of glucose

Question 10

Action potentials- stimulus

Answer 10

Excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium so the ions diffuse into neurone down the electrochemical gradient makes the inside of neurone less negative.

Question 11

Action potentials- depolarisation

Answer 11

If the potential difference reaches the threshold voltage gated sodium ion channels open- more sodium ions diffuse into the neurone- positive feedback

Question 12

Action potentials- repolarisation

Answer 12

At a potential difference of around +30 mV the sodium ion channels close- voltage gated potassium ion channels open - membrane is more permeable to potassium so they diffuse out of the neurone down the potassium ion concentration gradient- Starts to get the membrane back to its resting potential. Negative feedback.

Question 13

Hyperpolarisation

Answer 13

Potassium ion channels are slow to close so there’s a slight overshoot- too many potassium ions diffuse out of the neurone- The potential difference becomes more negative than resting potential

Question 14

Resting potential

Answer 14

The ion channels are reset- sodium potassium pump returns the membrane to its resting potential and maintains it until excited again

Question 15

Refactory period

Answer 15

The recovery period between the membrane getting excited after a action potential as the ion channels are recovering.

Question 16

Myelin sheath

Answer 16

The myelin sheath is an electrical insulator which speeds action potentials up

Question 17

What type of cell is the myelin sheath made off?

Answer 17

Schwann cell

Question 18

Nodes of ranvier

Answer 18

Tiny patches of bare membrane between each Schwann cell- sodium ion channels are concentrated at these nodes

Question 19

Saltatory conduction

Answer 19

This is when the neurones cytoplasm conducts enough electrical charge to depolarise the next node- impulse jumps from node to node

Question 20

Synapse

Answer 20

Junction between one neurone and another one or between a neurone and a effector cell

Question 21

Presynaptic neurone

Answer 21

Neurone before the synapse has a swelling called a synaptic knob - Contains synaptic vessels filled with chemicals and neurotransmitters

Question 22

What happens when a action potential reaches the end of a neurone?

Answer 22

Causes neurotransmitters to be released into the synaptic cleft - diffuse across to the postsynaptic membrane and bind to specific receptors.

Question 23

How nerve impulses are transmitted between neurones

Answer 23

An action potential triggers a calcium influx- Action potential arrives at the synaptic knob of the presynaptic neurone- the action potential simulates voltage gated calcium ion channels to open in the presynaptic neurone- Calcium ions diffuse into the synaptic knob pumped out afterwards by active transport.

Question 24

Calcium influx causes neurotransmitter release

Answer 24

Influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane then fuse with the membrane
- The vesicles release the neurotransmitter into the synaptic cleft by exocytosis.

Question 25

Neurotransmitter triggers an action potential in the postsynaptic neurone

Answer 25

• Neurotransmitter diffuses across the synaptic cleft and binds to the specific receptors on the postsynaptic membrane.
• Causes sodium ion channels in the postsynaptic neurone to open- influx of sodium ions into the postsynaptic membrane causes depolarisation. A action potential on the postsynaptic membrane is generated if the threshold is met
• The neurotransmitter is removed from the synaptic cleft so the response doesn’t carry on happening.

Question 26

Excitatory synapse

Answer 26

Neurotransmitters depolarise the postsynaptic membrane making it fire an action potential if the threshold is reached.

Question 27

Inhibitory synapse

Answer 27

Neurotransmitters bind to receptors on the postsynaptic membrane, they hyperpolarise the membrane preventing an action potential from being fired.
Hyperpolarisation- makes the potential difference more negative.

Question 28

Synaptic divergence

Answer 28

When one neurone connects to many neurones information can be dispersed to other parts of the body.

Question 29

Synaptic convergence

Answer 29

When many neurones connect to one neurone information can be amplified.

Question 30

Spatial summation

Answer 30

• When neurones converge the small amount of neurotransmitter released from each neurone can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action potential.
• If some neurones release and inhibitory neurotransmitter than the total effect of all of the neurotransmitters may be no action potential.
• Stimuli may come from different sources. Spatial summation allows signals from many stimuli to be coordinated into a single response.

Question 31

Temporal summation

Answer 31

• Is where two or more nerve impulses arrive in quick succession from the same postsynaptic neurone- makes action potential more likely because more neurotransmitter is released into the synaptic cleft.