Lecture 11 - circulation of blood

Question 1

The flow of blood: what is it dependent on?

Answer 1

The pressure difference and the resistant forces need to be supportive of forward flow (high pressure difference, low resistance)

Question 2

How vessel length affects resistance

Answer 2

Double length = double resistance

Question 3

How vessel radius affects resistance

Answer 3

Double radius = 16x less resistance

Question 4

How blood viscosity affects pressure and resistance

Answer 4

Increasing viscosity reduces flow and increases resistance

Question 5

Flow equation

(F = flow
R = resistance
ΔP = pressure change
L = vessel length
η = viscosity)

Answer 5

F = ΔP/R

R = 8Lη/πr⁴

F = (ΔP x πr⁴) / 8Lη

Question 6

Elastic arteries: how the elasticity helps with blood flow?

Answer 6

As the heart pumps the blood, the increased pressure causes the arteries to expand and, as the pressure decreases, the arteries return to their normal position and this pushes blood through the artery

Question 7

How is blood pressure measured?

Answer 7

Using a blood pressure machine to measure the difference between systolic and diastolic pressure

The top number is the maximum pressure the heart exerts while beating (systolic pressure). The bottom number is the amount of pressure in the arteries between beats (diastolic pressure)

Question 8

The nodes that contract the heart

Answer 8

Sinoatrial (SA) node: located in the posterior wall of the right ventricle, near the superior vena cava. This is called the cardiac pacemaker since it is the main pacemaker.

Atrioventricular (AV) node: located at the junction of the atria and the ventricles. Continues impulses sent from the SA node (essentially a backup SA node)

Question 9

The fibres that continue contraction of the heart after the AV node

Answer 9

Bundle of His (atrioventricular bundle) carry the electrical impulse to the Purkinje fibres which stimulate the contraction of ventricle muscle cells

Question 10

Tricuspid valve: what does it separate, what are some key features, and what are the other names?

Answer 10

Valve separating the right atrium and right ventricle

Three cusps and is connected to anterior, posterior, and septal papillary muscles

Also known as an atrioventricular valve

Question 11

Bicuspid valve: what does it separate, what are some key features, and what are the other names?

Answer 11

Valve separating the left atrium and left ventricle

It contains two cusps and is connected to anterolateral and posteromedial papillary muscles

Also known as an atrioventricular/mitral valve

Question 12

Aortic valve: what does it separate and what are the other names?

Answer 12

Separates the left ventricle and the aorta

Also known as a semilunar valve

Question 13

Pulmonary valve: what does it separate and what are the other names?

Answer 13

Separates the right ventricle and the pulmonary artery

Also known as a semilunar valve

Question 14

Chemoreceptors: what are they, where are they located, what do they do, and how do they maintain homeostasis?

Answer 14

Chemical receptors in the carotid bodies, aortic bodies, and the ventral surface of the medulla

They sense the chemical composition of blood (CO₂ and pH levels) and increase or decrease heart rate if CO₂ and pH levels are not in ideal ranges

Question 15

Isovolumetric contraction

Answer 15

Causes left ventricular pressure to rise above atrial pressure, which closes the mitral valve and produces the first heart sound

Question 16

Baroreceptors: what are they, where are they located, what do they do, and how do they maintain homeostasis?

Answer 16

Mechanoreceptors in the carotid sinuses and aortic arch

They sense the blood pressure and increase or decrease heart rate if BP levels are too low/high