Cardiovascular Lecture 5

Question 1

What is the main functional difference between the heart and vasculature?

Answer 1

Heart provides driving force for blood movement, while vasuclature plays active role in regulating blood pressure and distribution

Question 2

What does vasuclature branching and specialization try to match?

Answer 2

Blood flow and demand (size affects velocity)

Question 3

Are vessels specific for structure and function

Answer 3

Yes!

Question 4

What are some different parts of the vasuclature?

Answer 4

Arteries: elastic, absorb blood that comes out
Arterioles: variable radius, which is important
Capillaries: material exchange over a thin wall.
Veins: expandable, but not elastic. Also absorb blood.

Question 5

What is the endothelium?

Answer 5

A smooth, single-celled layer that envelopes the entire circulatory system (from heart to capillaries)

Question 6

What are the functions that endothelial cells provide?

Answer 6

1. Serve as a physical lining that blood cells will not adhere to
2. Serve as permeability barier for exchange of nutriebts, metabolic end products, fluid, etc; regulate transport of macromolecules and other substances
3. Secrete paracrine agents that act on adjacent vascular smooth muscle cells (vasodilators and vasoconstrictors)
4. Mediate angiogenesis (new capillary growth)
5. Central role in vascular remodellig by detecting signals and releasing paracrine agents
6. Contribute to formation and maintenance of extracellular matrix
7. Produce growth factors in response to damage
8. Secrete substances that regulate platelet clumping, clotting and anticlotting
9. Other non-cardiac effects

Question 7

Describe the systemic arteries

Answer 7

Have thick walls with large amounts of elastic tissue and three layers: intima, media, adventitia

Question 8

Describe the intima

Answer 8

Inner layer, single layer of endothelial cells, metabolically active barrier between blood and vessel wall

Question 9

Describe the media

Answer 9

Thickest layer
Vascular smooth muscle, elastin, and collagen fibres
Strength, contraction, and elastic properties

Question 10

Describe the adventitia

Answer 10

Connective tissue

Contains nerves, lymphatics and blood supply to vessel wall

Question 11

Describe the two primary functions of the arterial system based upon their structure

Answer 11

1. Large radius: low-resistance tubes conducting blood to various organs; blood moves quickly through them.
2. Elasticity: Pressure resevoir for maintaining blood flow during diastole (compliance)

Question 12

Describe compliance.

Answer 12

The inverse of stiffness. Compliance = change in volume / change in pressure.

Question 13

Describe elasticity in relation to age.

Answer 13

Decreases, creating additional work for the heart via increased afterload.

Question 14

What are the physiological determinants (can be controlled) of arterial blood pressure?

Answer 14

Cardiac output (how much blood came out)
Heart rate x stroke volume
Peripheral resistance (if arterial radium decreases, resistance increases)

Question 15

What are the physical determinants (can’t be controlled) of arterial blood pressure?

Answer 15

Arterial blood volume (more volume, more pressure)

Arterial compliance

Question 16

What three measurements are taken in account for blood pressire?

Answer 16

Mean (Pa)
Systolic (Ps, maximum)
Diastolic (Pd, minimum)

Question 17

What is pulse pressure (PP)?

Answer 17

PP=Ps-Pd

Question 18

What is Pa?

Answer 18

Pa=Pd+(Ps-Pd)/3

Question 19

What does the dicrotic notch in the blood pressure curve represent?

Answer 19

Aortic valve closure

Question 20

What does arterial volume depend on?

Answer 20

The rate of inflow from the heart (Qh) and rate of outflow through the resistance vessels (Qr)

Question 21

What increases mean pressure?

Answer 21

Increased cardiac output or peripheral resistance

Question 22

What increases pulse pressure?

Answer 22

Increased peripheral resistance, arterial volume, or decreased compliance

Question 23

How does a catheter measure bp?

Answer 23

In peripheral arteries using strain gauges

Question 24

How does a sphygmomanometer measure bp?

Answer 24

Palpating radial artery - while cuff pressure exceeds systolic pressure no pulse percieved, a slight pulse percieved when they are equal
The asculatory method is more sensitive and permits measurement of diastolic pressure (Korotkoff’s sounds)

Question 25

Describe artioles in respect to blood flow

Answer 25

Regulate the rate and distribution of flow

Question 26

Describe the composition of arterioles

Answer 26

Smooth muscles arranged in rings around the vessel, allowing changes in vessel diameter (vasoconstriction and vasodilation)

Question 27

Describe the dual control of arterioles

Answer 27

Intrinsic (local conditions surrounding blood vessels) and extrinsic (nervous system input)

Question 28

What are the three sources of intrinsic control of arterioles?

Answer 28

1. autoregulation/myogenic regulation
   -blood flow adjusted to metabolic activity of tissue
   -when metabolism steady, increased arterial blood pressure regults in changes in vascular resistance to maintain stable flow
   -vessels contrict when blood pressure elevated and dilated when reduced
   -due to changes in pressure across vessel wall (transmural pressure)
   -related to stretch-induced Ca2+ release
   -inactive under normal conditions, as baroreceptor reflex maintains constant blood pressure
2. Endothelium-mediated regulation
   -endothelium lining produces substances that relax (ie nitric oxide) or contract (ie angiotensin II and endothelin) vascular smooth muscle
3. metabolic regulation
   -Inadequate Inadequate O2 supply to tissue (increased metabolic rate or decreased O2
   delivery) results in release of vasodilator metabolites that act locally to dilate
   resistance vessels
   • Candidate Vasodilator Substances:
   - Lactic acid, CO2, H+, PO2, K+, inorganic phosphates, interstitial osmolarity, Adenosine, Prostaglandins
   • Basal tone: (i) myogenic response to stretch;
   (ii) high PO2 of arterial blood; (iii) presence of Ca2+
   • Responsible for reactive hyperemia

Question 29

What are the three sources of extrinsic control for arterioles?

Answer 29

1. Sympathetic regulation
   • Several regions in cerebral medulla influence vessel tone
   • Stimulation of dorsal lateral medulla (pressor region) causes
   vasoconstriction
   • Stimulation of cerebral centres caudal and ventromedial
   to this region (depressor region) causes
   inhibition, resulting in vasodilation
   • Both undergo rhythmic changes in tonic activity,
   causing blood pressure oscillations: (i) with
   respiration (Traube-Hering waves); (ii) at a lower
   frequency (Mayer waves)
2. Humoral regulation
   Epinephrine and norepinephrine influence peripheral blood vessels
   • Low concentrations of epinephrine dilate resistance vessels (-adrenergic
   effect), while high concentrations result in constriction (-adrenergic effect)
   • Norepinephrine causes vasoconstriction
   • Adrenal medulla can release both, but under normal conditions less
   important than norepinephrine release from sympathetic nerve endings
3. Reflex regulaton
   • Cerebral medulla under influence of neural impulses from:
   - Baroreceptors
   - Chemoreceptors
   - Hypothalamus
   - Cerebral cortex
   - Skin
   • Also affected by blood concentrations of CO2 and O2
   • Arterial Baroreceptors:
   - Stretch receptors in the carotid sinuses and the aortic arch
   - Inhibit sympathetic outflow to peripheral blood vessels (depressor effect)
   - Respond more to pulsatile pressure than constant pressure
   -Carotid sinus baroreceptors more sensitive than aortic barorecpetors
   - Sensitivity enhanced by sympathetic stimulation
   - Key to short term adjustment of blood pressure
   • Cardiopulmonary Baroreceptors:
   - Stretch receptors in the atria, ventricles, and pulmonary vessels
   - Innervated by vagal and sympathetic afferent nerves
   - Tonically active and alter peripheral resistance in response to changes in
   intracardiac, venous, or pulmonary vascular pressure
   - Similarly inhibit sympathetic outflow to peripheral blood vessels, but also
   inhibit release of factors important for water retention by kidney
   (angiotensin, aldosterone, vasopressin)
   • Peripheral Chemoreceptors:
   - Small bodies in the region of the aortic arch and carotid sinuses
   - Stimulated by decreased blood PO2 and pH, and increased PCO2
   - Primarily influence respiration, but also stimulate vasoconstrictor regions
   - Also located in the heart, causing pain with reduced O2
   (angina pectoris)
   • Central Chemoreceptors:
   - Increased PCO2 and decreased pH stimulate chemosensitive regions of
   medulla, causing vasoconstriction and increased peripheral resistance
   - PO2 has little direct effect on medullary vasomotor region
   • Hypothalamus:
   - Stimulation of anterior hypothalamus decreases blood pressure
   - Stimulation of posterolateral hypothalamus increases blood pressure
   - Also contains temperature sensation that affects blood flow to the skin
   • Cerebral Cortex:
   - Stimulation of motor and premotor areas results in pressor response, yet
   emotional stimulus may cause depressor response (blushing / fainting)
   • Skin:
   - Stimuli elicit either pressor or depressor response; distension generally
   causes depressor response, while pain typically causes pressor response