Pressures & Flows in Systemic Circulation

Question 1

Systolic blood pressure =

Answer 1

The pressure being exerted against the arterial wall during ventricular systole (contraction)

Question 2

Diastolic blood pressure =

Answer 2

The pressure being exerted against the arterial wall during ventricular diastole

Question 3

Mean arterial pressure =

Answer 3

The average arterial pressure during one cardiac cycle

Question 4

What’s the function of baroreceptors?

Answer 4

Pressure sensors detecting stretch throughout vascular tree - high pressure baroreceptors are located in arteries and low pressure in veins/R side of the heart

Compensate for sudden changes in BP

Question 5

What’s the function of chemoreceptors? How do they respond to O2/CO2?

Answer 5

Stimulated by change in environment eg hypoxia, hypercapnia, pH change

O2 receptors in carotid body, low O2 = hyperventilation and vasodilation
Low CO2 in medulla = hypoventilation and vasoconstriction

Question 6

How does pressure change across the vascular tree?

Answer 6

Systemic circulation has higher pressure than pulmonary.

So L side of heart has greater pressure than the R (aorta has much higher pressure than pulmonary arteries)

Question 7

Outline the arterial pressure curve

Answer 7

Aortic valve opens: systolic upstroke
Systolic peak pressure then declines (dichrotic notch where aortic valve shuts) then diastolic runoff to end diastolic pressure

Question 8

Explain the function of veins

Answer 8

Capacitance vessels (storage)
One way flow back to heart
Venous return regulates cardiac output
Resistance provided by fixed obstructions (eg 1st rib, neck)

Question 9

What’s the function of lymphatics

Answer 9

Return interstitial fluid from tissues to circulation
Nutrient transport from bowel
Enters circulation by one-way valves between endothelial cells

Question 10

What are local acute responses to blood pressure?

Answer 10

Vasodilation in response to tissue hypoxia or vasodilators (ADP/NO)
Endothelin is vasoconstrictor (released from damaged endothelium)

Question 11

What are local chronic response to blood pressure?

Answer 11

Angiogenic growth factor increases tissue vascularity (sprouting of new vessels)

Question 12

What are systemic responses to blood pressure?

Answer 12

Neural control to innervate vessels by release of Adrenaline/NA and alter tone of cholinergic sympathic fibres
Cardiac innervation, hormonal control, local mediators

Question 13

Where are the most important arterial baroreceptors located?

Answer 13

Aortic arch and carotid sinus (at the bifurcation of the external and internal carotids)

Question 14

Why does pulse pressure increase as you move more peripherally?

Answer 14

Vessel wall rigidity increases - concept of pulse pressure augmentation

Question 15

Why can arterioles influence blood flow with relatively minor vessel radius change?

Answer 15

Because of the Poiseuille equation whereby radius is to the 4th power

Each vessel running in parallel controls its own flow but vasoconstriction in one will increase the combined resistance

Question 16

What are the outcomes of controlling local perfusion?

Answer 16

Delivery of oxygen to tissues
Delivery of nutrients (glucose, amino acids, fatty acids)
Removal of CO2
Removal of H+ ions
Maintenance of ion concentrations in tissues
Transport of hormones and other regulatory substances to tissues

Question 17

Which part of the brain controls blood pressure etc?

Answer 17

Vasomotor centre in medulla

Question 18

What are cardiovascular changes in sepsis?

Answer 18

Hyperdynamic circulation
Local factor vasodilation
Relative hypovolaemia
Increased tissue O2 demand
Decreased cardiovascular supply

Question 19

Outline the 3 ways of neural BP control

Answer 19

Afferents to vasomotor centre in medulla (directly stimulated by co2/hypoxia and send excitatory or inhibitory inputs)

Vessel innervation: vasoconstrictor nerve fibres have constant tone, NA endings on all vessels

Cardiac innervation: sympathetic stimulation causes + ionotropy and chronotropy - constant opposition of vagal tone

Question 20

Which hormones have a VASOCONSTRICTIVE effect so increase blood pressure when active?

Answer 20

NA
RAAS: Angiotensin II production
Aldosterone
ADH
Ca2+ (local mediator on smooth muscles)

Question 21

Which hormones cause VASODILATION in bp control?

Answer 21

Histamine (released from mast cells in inflammation)
Bradykinin (Kallikrein -> Kallidin) in inflammation
ANP (by increased stretch in atrial cells, causes increased Na+ and H20 excretion from kidney)

Question 22

What are the actions of Angiotensin II?

Answer 22

Acts on hypothalamus to stimulate ADH release from posterior pituitary, and Aldosterone release from adrenal cortex
Directly vasoconstrictor arteries and increases thirst

ADH inserts aquaporins to collecting duct
Aldosterone increases Na+ reabsorption = h20 follows osmotically

Question 23

How can Histamine cause oedema?

Answer 23

Produced in mast cells and released in response to allergic tissue inflammation
Vasodilator and increases tissue permeability = oedema

Question 24

What effect do ions such as: H+, Mg2+, Ca2+ and CO2 have on arterioles?

Answer 24

Ca2+ vasoconstriction of smooth muscle

Mg2+, H+ and CO2 causes vasodilation

Question 25

How does Atrial Natriuretic hormone work?

Answer 25

Stretch receptors in atrial cells stimulate release
Causes increased Na+ and H20 excretion
Increases GFR by dilating afferent and constricting efferent renal arterioles = increases filtration pressure
Inhibits Renin and Aldosterone release