Blood pressure

Question 1

Define blood pressure, it’s unit and how it’s measured

Answer 1

The pressure exerted by the blood flowing through the blood vessels
mmHg
measured via blood pressure cuff, sphygmomanometer or stethoscope

Question 2

Define systolic BP and diastolic BP

Answer 2

SBP-measured from the LV during contraction, highest BP
DBP- measured from LV at rest (diastole) lowest BP

Question 3

Define Pulse pressure (PP) and how to calculate it

Answer 3

PP is the difference between systolic and diastolic BP
PP=SBP-DBP

Question 4

Define means arterial pressure and how to calculate it

Answer 4

MAP- the pressure that propels blood through the tissues
MAP= DBP-1/3 of PP

Question 5

What are the factors that determine BP?

Answer 5

1. Cardiac output: HRxSV, more blood pumped out the higher the HR
2. Peripheral resistance: vessel diameter & length, (vasocon & vasodila)
3. Blood volume, an increase in BV will increase BP (hydration affects BV)
4. Blood viscosity: thickness of blood, thicker the blood, harder to push generating a greater pressure

Question 6

Define vascular tone

Answer 6

at rest this is the state of contraction, to the relative vessel that is maximally dilated state

Question 7

Intrinsic factors that affect BP:

Answer 7

Myogenic mechanisms

Hypoxia

Endothelial factors (nitric oxide)

Hormones (histamine)

Metabolic by-products

Question 8

Extrinsic factors that affect BP:

Answer 8

Sympathetic nerves

Circulating hormones (e.g., angiotensin)

Question 9

How is blood pressure regulated?

Answer 9

BP is detected in the blood via baroreceptors that detect pressure changes
(negative feedback mechanism)

Question 10

Define and explain the function of the medulla oblongata

Answer 10

An area of the brain responsible for controlling HR, CO & BP and more. It uses 2 pathways (sympathetic & parasympathetic)
It contains vasomotor centre, cardiac centre etc
Pathway uses neurons down the spinal cord
emotional centres of the brain can also influence HR & BP
Medulla oblongata responds to changes in O2, CO2 & H+ concentrations

Question 11

Define Marey’s law

Answer 11

There is an inverse relationship between HR & BP

Question 12

Define frank starlings law

Answer 12

The force of ventricular contraction is determined by the length of the cardiac muscle fibres

Question 13

Explain the Bainbridge reflex

Answer 13

It is a reflex that increases HR in response to increased stretching of wall of RA due to filling. HR increase to clear extra blood

Question 14

How does BP differ during excercise?

Answer 14

BP increases to meet body’ demands of O2 to respiring muscles.
Chest muscles and skeletal muscles squeeze veins during contraction pushing venous blood back to RA
HR & SV increases

To meet demands for oxygen during muscle contraction, remove waste of CO2 and delivery of oxygen and glucose needed for respiration

Increased muscle activity is detected by proprioceptors, stimulates a increase in HR & SV causing higher BP

Increased levels of CO2 cause acidosis, which lowers blood pH, this is detected by chemoreceptors, they stimulate an increase in respiratory rate, enables more CO2 to be removed (negative feedback mechanism)

Our bodies know when to stop exercising,

CO2 + H2O—> carbonic acid—> H+ and HCO3-

Question 15

Define stroke volume (SV) end diastolic volume and end-systolic volume

Answer 15

The volume of blood ejected from the heart during one ventricular contraction
SV=EDV-ESV
EDV- volume of blood left in the ventricle at the end of diastole
ESV- volume of blood left in the ventricle at the end of systole

Question 16

Define preload & afterload

Answer 16

Preload: The degree to which the cardiac muscle is stretched before contraction
Afterload: The pressure ventricles have to overcome to push blood through semi-lunar valves as the ventricles contract

Question 17

Describe the negative feedback mechanism that occurs when BP is low

Answer 17

BP falls and is detected by baroreceptors found in carotid sinus & aortic arch

Baroreceptors send signals to the vasomotor centre (medulla oblongata)

Sympathetic impulses to the heart cause an increase in HR, greater volume of blood is pumped out, contractability increases as well as cardiac output. Vasoconstriction occurs via stimulation of vasomotor fibres

Cardiac output & peripheral resistance increases, causing pressure to return to homeostatic range

Question 18

Describe the negative feedback mechanism that occurs when BP is high

Answer 18

Blood pressure in arteries rises above normal range and is detected by baroreceptors found in carotid sinus and aortic arch.

Impulses released from baroreceptors stimulate the cardioinhibitory centre and inhibits vasomotor centre

Parasympathetic signals reduce the cardiac output, HR and contractibility of the heart, the vessels vasodilate causing a drop in peripheral resistance

Cardiac output and Peripheral resistance return to homeostatic range