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Structure and Function of the Cardiovascular System

Dr Robin Johns, 10 Oct 2011
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Two main functions of the cardiovascular system
#1 - transport (main)
#2 - help regulate temperature
What does the CV system transport?
#1 - O2 and nutrients into tissues
#2 - Waste products (CO2, etc) from cellular metabolism to the kidneys and other excretory organs
#3 - Circulates electrolytes and hormones
#4 - Transports various immune substances (IL-2, IL-6) that contribute to the body's defense mechanisms.
Pulmonary vs Systemic Circulation
Pulmonary - moves blood through the lungs; creates a link with the gas exchange function of the respiratory system.
Systemis - moves blood to the rest of the body
What are 3 functions of capillaries?
They serve as an exchange system for the transfer of:
1) gases
2) nutrients
3) wastes
Components of Pulmonary and Systemic systems
Pulmonic - right half of the heart, pulmonary artery (only artery that carries deoxygenated blood!), pulmonary capillaries, pulmonary veins
Systemic - left half of the heart, aorta and its branches, capillaries supplying brain and peripheral tissues, systemic venous system and vena cava
Compare arterial and venous blood pressures
Arterial - MUCH stronger (90-100 mmHg)
Venous - much weaker (0-12 mmHg)
Define hemodynamics
The physical principles governing pressure, flow, and resistance as they relate to the CV system.

(hemo = blood; dynamic = relationship between motion and forces)
What is laminar blood flow?
Laminar blood flow is how most blood flows. It is nice and smooth because of the layering of the blood components in the center of the bloodstream, which reduces friction and prevents clotting factors from coming in contact with the vessel wall.
What is turbulent blood flow, and how can you identify it during a physical assessment?
It is disordered flow; blood moves both crosswise and lengthwise through the vessel.

It can be heard during a physical assessment as a bruit or murmur, and palpated as a thrill (feels like a kitten purring).
What it Laplace's law?
This law states that wall tension becomes greater as the radius of a vessel increases. (Think of inflating a balloon.) As the wall becomes thinner, the tension increases, and vice versa.
Transmural pressure
pressure across the wall of a vessel or cardiac chamber
Define compliance, and relate compliance to volume and pressure changes.
Compliance - total quantity of blood that can be stored in a given portion of the circulation for each mmHg rise in pressure. (basically, how a vessel responds in terms of transmural pressure changes to a change in volume)

The more compliant a vessel is, the easier it is to increase volume without increasing transmural pressure.
Compare the compliance of an vein to that of its corresponding artery.
A vein is 24 times more compliant than its corresponding artery!

(3x more volume and 8x more distensible. Veins hold 64% of your body's blood!)
List and describe the three layers surrounding the heart from the outside inward.
Pericardium - forms a fibrous covering around the heart, holding it in a fixed position, providing physical protection and acting as a barrier to infection.

Myocardium - muscular portion that forms the wall of the atria and ventricles; thickest layer, responsible for pumping action; generally what is affected when someone has an MI

Endocardium - thin, three-layered membrane surrounding the heart itself
What ensures one way flow into and out of the heart?
AV (bicuspid/mitral on left and tricuspid on right) and semilunar (aortic on left and pulmonic on right) valves
What is unique about the pulmonary arteries and veins?
Only arteries in the body to carry deoxygenated blood; only veins in the body to carry oxygenated blood
Blood flow is based on which of the following properties: pressure, vessel compliance, volume, contraction of the heart, distensibility of the heart
all of them!
Compare systole and diastole
Systole - the working phase of the myocardium; ventricles are contracting to propel blood forward

Diastole - the resting phase of the myocardium; ventricles are relaxed and filling with blood
What is atrial kick / when does it occur?
It is the time in the heart during which atria and ventricles are both in diastole; it causes a passive inflow of blood, leading to increased ventricular injection due to increased preload.
What is the normal amount of blood the heart pumps per minute? What is average?
Normal is 3.5-8.0 L/min, although average is closer to 3.5-4.0 L/min.
How is cardiac output determined, and what three factors can affect it?
CO = HR x SV
Affected by preload, afterload, and contractility
What is preload?
Preload represents the amount of blood that the heart must pump with each beat; greatly determined by the venous return to the heart
What is afterload? What happens if it is increased?
Afterload is the pressure that the heart must generate to move blood into the aorta, and must be greater than the resistance from the vessels in the systemic circulation. If the heart does not have enough pressure to pump the blood out, it can ultimately back up into the lungs and lead to congestive heart failure. The #1 cause of increased afterload is hypertension.
What is contractility?
Contractility is the ability of the heart to change its force of contraction without changing its resting length.
Define ionotrophic. What do +/- ionotrophic drugs do?
Ionotrophic refers to contractility of the myocardium.
+ Ionotrophic drugs increase contractility, and vice versa.
Define chronototrophic. What do +/- chronototrophic drugs do?
chronototrophic refers to heart rate.
+ chronototrophic drugs increase rate; and vice versa.
What is the Frank-Starling Mechanism?
The greater the volume of blood in the heart before contraction, the greater the volume of blood ejected. However, if the heart is stretched too much, contractility will decrease. (think of a rubber band)
What is cardiac reserve, and what is the normal amount for a healthy, young, adult?
The maximum percentage of increase in cardiac output achieved above normal resting level.

A healthy, young, adult can have cardiac reserve of up to 300-400%, or 32L/min.
True or False: Cardiac output is a direct reflection of how well blood is flowing through the arteries and veins.
False: CO is a measure of blood flow out of the heart, but it does not reflect the flow through the circuit. There are many factors affecting the flow once blood leaves the heart (bp, peripheral resistance, etc).
Function of the vascular system
Delivery of oxygen and nutrients and removal of wastes from the tissues
List and describe the three layers of a blood vessel from outside to inside.
Tunica externa: fibrous connective tissues that support the vessel
Tunica media: smooth-muscle layer that constricts to control the diameter of the vessel
Tunica intima: elastic layer that joins the tunica media to the thin layer of endothelial cells that lie adjacent to the blood
Describe arteries
Thick-walled vessels with large amounts of elastic fibers; stretch during systole and relax during diastole.
Describe arterioles
Serve as resistance vessels for the circulatory system; act as valves through which blood is released as it moves into the capillaries.

Problems with hypertension happen here.
How is blood pressure calculated?
BP = CO x peripheral vascular resistance (pvr)
What 3 factors affect hemodynamic function?
pressure, volume, resistance (antihypertensive drugs work on one or more of these factors)
What 4 changes can negatively affect autoregulation of blood flow?
1 - lack of oxygn
2 - accumulation of tissue metabolites
3 - endothelial control
4 - hyperemia (increase in blood flow to ischemic area)
What is collateral circulation?
If there is an obstruction, over time your body will figure out a way to bypass it through anastomotic channels.
Are the following vasoconstrictors, vasodilators, or both: epinephrine, norepinephrine, angiotensin 2, histamine, serotonin, bradykinin, prostaglandins
Vasoconstrictors: epinephrine (major!), norepinephrine, serotonin

Vasodilators: angiotensin 2, histamine, bradykinin

Both/either: prostaglandins
What is hydrostatic pressure?
It is pressure based on the force of blood on the vessel.
Should you feel pulsation in the blood at capillaries?
no
What is diffusion across the capillaries dependent upon?
It is dependent upon osmotic pressure and the presence of toxic substances (they increase it).
Nutrient flow vs non-nutrient flow
Nutrient flow - blood diffuses oxygen/waste products properly

Non-nutrient flow - bed is bypassed by means of a shunt; oftentimes occurs when trying to increase the temperature because diffusion is not necessary
Where are autonomic controls for blood pressure and cardiac function located?
medulla oblongata
medullary cardiovascular neurons are grouped into three distinct pools that lead to sympathetic innervation of the _______________ and parasympathetic innervation of the ______.
1) heart and blood vessels
2) heart only (specifically heart rate)
What does the vasomotor center control, and what mediates it?
It controls sympathetic-mediated acceleration of the heart rate and blood vessel tone. It is mediated by norepinephrine (majorly), epinephrine, and dopamine.
What does the cardioinhibitory center do, and what mediates it?
It controls parasympathetic-mediated inhibition of the heart rate, and is mediated by acetylcholine (ACH).