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VETERINARY CLINICAL CARDIOLOGY
CARDIOLOGY CONCEPTS
Cardiovascular Physiology
Structure and Function
1. Anatomy of the cardiovascular system

a. The heart: 4 chambers and 4 sets of valves

  • 2 Atria
  • 2 Ventricles
  • 2 AV valves
  • 2 Semilunar valves

b. The systemic circulatory system

  • Arteries
  • Arterioles

c. The pulmonary circulatory system

  • Veins
  • Venules
2. What is the role of the cardiovascular system?
Via a series of conduits, arteries and capillary beds, to provide nutrients to all organs and via a series of capillary beds and veins to provide a means to remove the effluents of metabolism from these same organs.
3. What is the role of the heart?
As a muscular pump the heart is required to eject into the circulatory system a volume of blood appropriate for the metabolic activity of the organs.
4. What is the role of the systemic arterial system?
a. Of the large arteries

Particularly the aorta, these vessels have two functions:
  • They serve as conducting vessels - transfer blood to the periphery
  • The elastic properties of the vessel wall promote flow through the periphery during diastole as well as systole

b. Of the small arteries

These are the resistance vessels:
  • Relative to the size of the lumen of these vessels, they possess an abundant amount of smooth muscle
  • They control the steady delivery of blood to the capillary beds
  • They control blood pressure via the degree of contraction of their smooth muscle in the vessel wall
5. What is the role of the systemic venous system?
The veins are responsible for the return of blood to the heart. The veins hold 70% of the blood volume. Contraction of the smooth muscle in the venous circulation increases blood return to the heart. Venodilation reduces the return of blood to the heart.
6. What is the role of the pulmonary arterial system?
The pulmonary arterial system receives the output from the right heart, deoxygenated blood, and delivers it to the lungs for carbon dioxide removal and oxygen loading of blood.
7. What is the role of the pulmonary venous system?
The pulmonary venous tree returns the oxygenated blood to the left heart for propulsion to the rest of the body.
8. How is the function of the pulmonary arterial tree different from the systemic arterial tree?
The pulmonary arteries, unlike the other arteries of the body, carry deoxygenated blood. The pulmonary veins, unlike the other veins of the body, carry oxygenated blood. The pulmonary arteries respond to hypoxia with contraction. The systemic arteries respond to hypoxia with vasodilation.
9. How does the anatomy of the pulmonary arterial tree differ from the systemic arterial tree such that it supports the difference in function between the two systems?
The right ventricle ejects the same volume of blood that the left ventricle ejects. The pulmonary arterial system is a low-pressure system, unlike the high pressures encountered in the systemic arterial system. The pulmonary arterial walls contain less smooth muscle than the systemic arteries. The reduced amount of tone that can be generated in the pulmonary arterial system is responsible for the lower pressures in the pulmonary arterial system. This arterial tone is also known as arterial resistance. Hence the pulmonary arterial resistance is much less than the systemic arterial resistance.
10. What is the role of the capillary beds?
The capillary beds are the site of diffusion of gases, nutrients, and waste products within each organ.
11. What is the role of Starling forces?
Starling forces are the "forces" that are involved with the movement of fluid across the permeable membranes of the capillary beds. Within the capillary, the capillary hydrostatic pressure "forces" fluid out of the capillary and into the interstitium; the interstitial hydrostatic pressure "forces" fluid to leave the interstitium and enter the capillary; the capillary plasma colloid osmotic pressure (also called plasma oncotic pressure) "draws" fluid into the capillary; and the interstitial fluid colloid osmotic pressure (also called oncotic pressure) "draws" fluid into the interstitium. The net movement of fluid across the capillary membrane is affected by both the magnitude of the imbalance between the hydrostatic and osmotic forces and the permeability of the capillary membrane to water. Kf is known as the permeability coefficient.

Thus the net movement of water across the capillary membrane can be expressed via the equation: Kf[(HPc-HPif)-(COPc-COPif)].

  • HPc = Hydrostatic pressure in the capillary
  • HPif = Hydrostatic pressure of the interstitial fluid
  • COPc = Colloidal osmotic pressure of the capillary plasma
  • COPif = Colloidal osmotic pressure of the interstitial fluid
  • 12. What are the functions of the components of the heart?

    a. Pericardium: Limits cardiac distention with cardiac filling. This effect is greatest on the thin walled chambers such as the atria and the right ventricle.

    b. Right Atrium: It serves as a storage reservoir for blood returning to the heart via the cranial and caudal vena cavas.

    c. Right Ventricle: It must receive all the blood presented to it via the right atrium and expel this blood to the lungs for gas exchange. Since the pulmonary arterial tree is a rather low-pressure system (as compared to the systemic arteries), the right ventricle develops into a rather thin walled chamber (as compared to the left ventricle).

    d. Left Atrium: It serves as a storage reservoir for blood returning from the pulmonary veins.

    e. Left Ventricle: It must receive all the blood presented to it via the left atrium and expel this blood through the systemic arterial tree to the organs of the body. Since the systemic arterial tree is a rather high-pressure system (as compared to the pulmonary arteries), the left ventricle develops into a rather thick walled chamber (as compared to the right ventricle).

    f. The A-V valves: They function to promote the flow of blood (unidirectional flow only) from the atria to the ventricles during diastole. Flow occurs across these valves when the pressure in the ventricles falls below that of the atria. Flow across the A-V valves is characterized by three phases: rapid filling phase at the onset of diastole (responsible for most of the filling of the ventricle), diastasis (minimal flow occurs at this time), and atrial contraction at the end of diastole.

    g. Semilunar valves: They function to promote the flow of blood from the ventricles into the arterial trees during systole. Flow occurs across these valves when the pressure in the ventricles exceeds that present in the arterial tree. Flow across these valves is uni-modal (unlike the bimodal nature of flow across the AV valves).

    13. What components of the cardiovascular system could be responsible for cardiovascular disease - or - where within the cardiovascular system could malfunction occur?
    Disease/malfunction can occur due to abnormalities within the heart:
  • Obstruction at any valve
  • Insufficiency of any valve
  • Failure of the atria to receive blood
  • Failure of the atria to push blood (contract)
  • Failure of the ventricles to receive blood
  • Failure of the ventricles to expel blood
  • Failure of the arterial tree to maintain pressure
  • Failure of the arterial tree to lower pressure
  • Failure of the pericardium to expand with ventricular filling
  • production