haemodynamics

Question 1

what does haemodynamics mean

Answer 1

physical laws governing pressure/ flow relationships in blood vessels.
Blood will not flow through the vasculature unless it is forced to do so by application of pressure, which is required to overcome the resistance to flow.

Question 2

afterload

Answer 2

the pressure the heart must work against to eject blood during systole (ventricular contraction). afterload is proportional to average arterial pressure.

Question 3

equation for flow

Answer 3

flow= (Pi-Po)/R

Q= ((Pi-Po) x (Pi x r^4)) / 8 x0 L x (viscosity)

Question 4

vessel radius- directly related to flow

Answer 4

• vessel radius is the primary determiant of vascular resistance and hence flow. radius is variable because of the vascular smooth muscle cells VSMCs.

Question 5

blood viscosity

Answer 5

blood viscosity varies with flow. a fluids viscosity is measured relative to water. electrolytes and organic molecules raise the viscosity. RBCs have the greatest impact.

Question 6

haematocrit

Answer 6

Hct measures the % of whole blood volume that is occupied by RBCs. separates the cells from the plasma. Normal ranges:

• 41-53% for males
• 36-46% for females

Question 7

equation for systemic vascular resistance

Answer 7

SVR = (MAP - CVP) / CO

MAP = (CO x SVR) + CVP

MAP is a time-averaged value that recognises that arterial pressure rises and falls in step with the cardiac cycle

Question 8

large arteries

Answer 8

• must carry blood at high pressure so their walls are thick and their lumens proportionally narrow. the walls of the larger arteries contain smooth muscle layers and are rich in elastin fibres

Question 9

muscular artery

Answer 9

well developed media, lots of smooth muscle. prominent IEL and EEL

Question 10

small arteries and arterioles

Answer 10

• the walls of the smallest arteries and arterioles are dominated by their smooth muscle layers. collectively known as resistance vessels, they control blood flow to the capillaries.
• when a tissues demand for O2 and nutrients is high, the VSMCs relax, and flow to the tissues increases

Question 11

capillaries

Answer 11

• bring blood with 30 micrometers of virtually every cell in the body
• designed to keep the blood within the vasculature while maximising the opportunity for exchange of materials between blood, interstitium, tissues.
• walls are the thickness of a single endothelial cell plus the basal lamina.
• capillaries permit direct communication between blood cells via junctional clefts between adjacent cells, fenestrations

Question 12

venules and veins

Answer 12

• they are low-pressure conduits that direct blood back to the heart.
• venules widen and fuse with eachother as they progress towards the heart
• the paucity of muscles means that vein walls are thin, making them highly distensible and able to accomodate large volumes of blood
• under resting conditions ~65% of total blood volume resides in the venous compartment, can boost ventricular preload and cardiac output CO when the need arises

Question 13

preload

Answer 13

a load that is applied to a myocyte and establishes muscle length before contraction begins. in the LV, preload equates with the volume of blood entering the chamber during diastole (EDV)

Question 14

venoconstriction

Answer 14

vein walls contain layers of vascular smooth muscle cells (VSMCs) that are innervated by and contract during sympathetic activation.

1) mobilized the blood reservoir. valves ensure that blood is forced forward towards the heart
2) reduces the overall capacity
3) decreases transit time

Question 15

venomotor tone

Answer 15

The constant excitatory influence by sympathetic nerves on the smooth muscle of veins is called venomotor tone. Because of this, the walls of the veins remain in a partially contracted state even under resting condition. When the venomotor tone is increased, the capacity of veins decreases.