Control of Blood Pressure

Question 1

Blood flow to the body is based on a ______ system. Brain and heart first.

e.g., If you are sitting down, blood vessels to the intestines dilate to allow for more digestion whereas blood vessels to the legs dilate as your legs are not in use.

e.g., If you start exercising, blood flow is constricted to the intestines whereas blood flow to the legs is
increased via vasodilation of the arteries

Answer 1

priority

Question 2

This change in blood flow is controlled by intrinsic + extrinsic factors

What are intrinsic factors?

Answer 2

Intrinsic (local) → decrease in O2, increase in CO2, increasing the cellular respiration rate. Chemoreceptors
identify these changes and change blood flow accordingly

Question 3

This change in blood flow is controlled by intrinsic + extrinsic factors

What are extrinsic factors?

Answer 3

Extrinsic (external) → hormones, neuronal inputs

Question 4

Extrinsic control
Neuronal control is regulated via the _______ nervous system.

Answer 4

sympathetic

Question 5

Arteries have sympathetic _____ fibres attached to them which allow them to change shape

Answer 5

nerve

Question 6

Vasoconstriction:

Answer 6

If these sympathetic nerve fibres increase their firing rate hence increasing number of action potentials, artery is constricted (diameter is reduced), decreasing blood flow

Question 7

Vasodilation:

Answer 7

If sympathetic nerve fibres decrease their firing rate hence decreasing number of action potentials, artery is dilated (diameter is increased), increasing blood flow

Question 8

These sympathetic nerve fibres act on thick ______ wall of the arteries.

Answer 8

muscular

Question 9

What is the function of the neurotransmitter nor-epinephrine? (2)

Answer 9

• The nerve fibres release a neurotransmitter called nor-epinephrine which works on an Alpha 1 receptor on the thick muscular wall of the artery which induces vasoconstriction of the blood vessel.
• On the inside of the blood vessel in lumen, you find Beta 2 receptors which respond to circulating
  catecholamines (things within blood like epinephrine → Hormone produced by adrenal medulla) which leads to vasodilation

Question 10

Different tissues have different combinations of receptors which allows for fine-scale control of where the blood flows in response to the body’s ______.

Answer 10

needs

Question 11

Can capillary walls change shape?

Answer 11

Unlike arteries, capillary walls are very thin so they cannot change shape. Capillaries have a ring of smooth
muscle at the beginning of the capillary → pre-capillary sphincter

Question 12

What happens when sphincters open?

Answer 12

When sphincter is open, blood can flow into capillary allowing for gaseous exchange when tissues are
metabolising.

When tissues are not metabolising, ring of smooth muscle contracts, closing the sphincter, reducing the amount of blood flowing into the capillaries.

Question 13

Local/intrinsic __________, CO2, O2, can influence if pre-capillary sphincters are open or closed.

Answer 13

metabolites

Question 14

Blood pressure (MAP) =

Answer 14

Blood flow (cardiac output) x Vessel resistance (total peripheral resistance)

Question 15

Cardiac output =

Answer 15

Question 16

What is Frank-Starling Law of the heart?

Answer 16

The energy of contraction is proportional to the initial length of the cardiac muscle fibre.

An increased blood volume in the ventricles will cause the muscle fibres of the myocardium to stretch more
which will increase the force with which blood is pumped out of the ventricles further increasing the
amount of blood pumped out.

Question 17

What happens as the blood bloom in the ventricle increases?

Answer 17

As the blood volume in the ventricle increases, your
actin filaments stretch more increasing the length of
sarcomeres which increasesthe length of muscle fibres
which increases the stretch of myocardium, increasing
the force with which blood is pumped out and further
increasing the amount of blood pumped out of the
ventricle (stroke volume).

Question 18

Increase in end ______ volume (amt
of blood returning to heart), Increase in _____
volume (amt of blood leaving the heart).

Answer 18

diastolic
stroke

Question 19

The cardiovascular centre in the medulla oblongata within brain stem has 2 parts:

Answer 19

Cardioinhibitory centre
Cardioacceleratory centre

Question 20

Cardioinhibitory centre:

Answer 20

Acts via parasympathetic system via the vagus nerve on the SA node to reduce the firing rate and acts on the AV node to decrease conduction to decrease heart rate via a neurotransmitter called acetylcholine.

Question 21

Cardioacceleratory centre:

Answer 21

Acts via sympathetic system on the SA node increasing the depolarization of the SA node to speed up firing rate and acts on the AV node to increase conduction and reduce delay. Also acts on cardiac muscle by increasing force of contraction to increase amt of blood pumped out of blood (stroke volume) via a neurotransmitter called norepinephrine/noradrenaline.

Question 22

What are baroreceptors? (4)

Answer 22

• Located within carotid sinus (carotid baroreceptor) → bulge were common carotid artery splits into
  internal and external carotid
• Located within aortic arch (aortic baroreceptor)
• Monitor blood pressure
• Have fine nerve endings in artery walls which react to blood pressure
• If blood pressure increases, nerve endings move apart due to stretch in artery wall, which increases firing rate of baroreceptors, sending message to brain to help counter increase in BP

Question 23

What are chemoreceptors? (4)

Answer 23

• Located alongside baroreceptors just outside the carotid artery and the aortic arch
• Monitor concentration of O2 CO2 and pH of blood
• To determine if there is sufficient oxygen in blood going to brain and body
• Sensitive to increase in CO2 and send message to brain to activate reflex to counteract increase in CO2

Question 24

What is the Baroreceptor reflex? (6)

Answer 24

• Increase blood pressure stretches the carotid arteries and aorta causing the baroreceptors to increase they rate of action potential generation.
• Action potentials are conducted via the glossopharyngeal nerve and vagus nerve to the cardio regulatory and vasomotor centres in the medulla oblongata in the brain stem.
• This increases parasympathetic stimulation into the heart which decreases heart rate.
• Cardio regulatory centre decreases the sympathetic stimulation which decreases heart rate + stoke volume.
• The vasomotor centre decreases sympathetic stimulation to blood vessels causing vasodilation.
• Vasodilation + decreased heart rate + decrease stoke volume bring blood pressure back to normal.

Question 25

What is the Chemoreceptor reflex? (3)

Answer 25

• In the carotid body and aortic arch monitor O2 CO2 and ph. Impulses from chemoreceptors are conducted to the cardio regulatory and vasomotor centre via the glossopharyngeal and vagus nerve. Chemoreceptors in
  medulla oblongata monitor blood CO2 and ph.
• Decrease O2, Increased CO2 and decreased pH decrease parasympathetic stimulation which increases heart rate.
• Decrease O2, Increased CO2 and decreased pH increase sympathetic stimulation which increases heart rate and stroke volume. Increase sympathetic stimulation of blood vessels increase vasoconstriction.