B14 - coordinated response

Question 1

What is the ‘fight or flight’ response?

Answer 1

• when an animal considers a situation to be potentially dangerous
• Body triggers a series of physical responses to increase survival chance by preparing the body to run or fight fo life.

Question 2

How is the flight or fight response activated? (4)

Answer 2

1) threat detected by autonomic NS
2) Hypothalamus communicates with sympathetic NS and the adrenal-cortical system
3) Symp NS sends impulses to effectors and tells adrenal medulla to release adrenaline & noradrenaline into bloodstream.
4) At the same time, the hypothalamus stimulates pituitary gland to secrete ACTH, which travels in bloodstream to adrenal cortex.
5) ACTH activates adrenal cortex, so that it releases stress hormones such as cortisol (increases blood glucose and pressure for rapid response)

Question 3

What is the role of adrenaline? (2)

Answer 3

Increases blood glucose levels:
- Trigger liver cells to undergo glycogenolysis
- more respiration, so more energy for muscle contraction

Question 4

What type of hormone is adrenaline? (2)

Answer 4

• Non-steroid (protein) hormone
• hydrophobic so cannot pass through target cell membrane
• Binds to receptor on target cell & triggers chain reaction.

Question 5

Describe the steps of the action of adrenaline (second messenger model) (4)

Answer 5

1) adrenaline fuses with receptor site on target cell membrane
2) activates enzyme adenylyl cyclase inside the cell/other side of membrane.
3) adenylyl cyclase triggers conversion of ATP into cAMP
4) cAMP activates protein kinases which phosphorylate and hence activate other enzymes to trigger glycogen -> glucose.

Question 6

What is cAMP?

Answer 6

A secondary messenger which activates other enzymes that, in turn, convert glycogen to glucose.

Question 7

List some physical fight or flight responses and their purpose. (4)

Answer 7

• heart rate increases to pump more oxygenated blood around the body.
• pupils dilate to take in more light for better vision
• arterioles in skin constrict, so more blood travels to major muscle groups.
• Blood glucose levels increase = more respiration and provide more energy for muscle contraction.
• smooth muscles of airways relax to allow more O2 to lungs.
• non essential systems shut down to focus resources on emergency functions
• Difficulty focusing on small tasks so brain can focus solely on the threat.

Question 8

What us the hypothalamus responsible for?

Answer 8

detecting risks & activating mechanisms e.g. FOFR

Question 9

What is the medulla responsible for? And where is it located?

Answer 9

• cardioregulatory centre in brain
• monitors heart rate e.g. body needing more O2 due to exercise.

Located at the base of the brain. Near the top of the spinal cord.

Question 10

How does a heart beat occur?

Answer 10

• Initiated by SAN (sino-atrial node), causes atria to contract.
• Impulse travels down AVN. AVN delays impulse before stimulating the bundle of his. This ensures the atria fully contract before the ventricles.
• Impulse travels down Bundle of His (conducting tissue made of purkyne fibres), which penetrates the septum between the ventricles .
• Purkyne fibres at the apex of the heart conducts the wave of excitation, triggering the ventricles to contract.
• Ventricles contract at apex for more sufficient emptying of the ventricles.

Question 11

The medulla has two centres linked to the SAN. One is called the acceleratory centre which increases heart rate. How does it do this? (3)

Answer 11

• Increases heart rate by sending impulses along the sympathetic nervous system.
• Impulses are transmitted by accelerator nerve
• Noradrenaline secreted at SAN synapse
• causes SAN to increase frequency of electrical waves it produces.

Question 12

The medulla has two centres linked to the SAN. One is called the Inhibitatory centre which decreases heart rate. How does it do this? (3)

Answer 12

• Decreases heart rate by sending impulses along the parasympathetic nervous system.
• Impulses transmitted by the vagus nerve.
• Acetylcholine secreted at the SAN synapse
• Cause SAN to decrease frequency of electrical waves produced.

Question 13

What is a chemoreceptor and where are they located?

Answer 13

Detects changes in levels of CHEMICALS in the blood.

located: aorta, carotid artery(neck), medulla

Question 14

What is a baroreceptor and where are they located?

Answer 14

Detect changes in blood PRESSURE.

located: aorta, carotid arteries, vena cava

Question 15

Explain how blood pressure is returned back to normal after it increases. (3)

Answer 15

• Baroreceptors detect rise in blood pressure
• Impulse sent to inhibitatory centre in the medulla
• Impulse sent along parasympathetic nervous system to SAN (acetylcholine released at synapse)
• Decreases heart rate to return blood pressure back to normal.

Question 16

Explain how high CO2 levels are returned back to normal. (5)

Answer 16

• High CO2 lowers blood pH (water + carbon dioxide -> carbonic acid)
• chemoreceptors detect drop in pH
• Impulse sent to acceleratory centre in medulla.
• impulse sent along sympathetic nervous system to the SAN (noradrenaline)
• Increases heart rate
• Increased blood flow removes CO2 faster.
• CO2 exhaled and levels returned back to normal.

Question 17

Why is cardiac muscle myogenic?

Answer 17

Contraction of the heart is initiated by the muscle itself.
No external stmuli.