Cardiovascular Physiology

Vascular System

Components of Circulatory System

Cardiovascular System (CVS): Heart Blood vessels

Lymphatic System:

Cardiovascular System (CVS)

Cardiac (heart)

Vascular- Arteries- Arterioles- Capillaries- Venules- Veins

Right sided: (volume pump)

Left sided: (Pressure pump)

Major function of Systemic Circulation

1. Transportation: O2 & CO2. digestion products. wastes. distribution of body fluids. 2. Regulation: Hormonal. Immune. Protection. Temperature.

♥ To direct the flow of blood from the heart to capillaries, & back to the heart.

Blood Vessels

■ Walls composed of 3 “tunicas:” Tunica externa:

Outer layer of connective tissue.

Tunica media: Middle layer of smooth

muscle.

Tunica interna: Innermost simple

squamous endothelium. Layer of elastin.

Classification of the vascular system:1. Aorta … (elastic recoil)

■ Numerous layers of elastin fibers b/w smooth ms. Expand when the pressure of the bl rises.

Act as recoil system when ventricles relax.

2. Arteries … (muscular, low resistance vessels) Less elastic & have a thicker layer of smooth ms. Diameter changes slightly as BP raises & falls.

3. Arterioles … (high resistance vessels) Contain highest % smooth muscle.

Expand less under pressure (less compliance). Called resistance vessels (greatest resistance to flow).

Classification of the vascular system (continued)

4. Capillaries … (exchange vessels) Smallest blood vessels.

1 endothelial cell thick. Provide direct access to cells.

Permits exchange of nutrients & wastes.

5. Venules Formed when capillaries unite.

Very porous.

Classification of the vascular system (continued)

6. Veins … (capacitance vessels)

■ Contain little smooth muscle or elastin. Capacitance vessels (blood reservoirs).

Contain 1-way valves that ensure blood flow to the heart.

■ 2/3 of total blood volume is located in veins ( 70%).

Distribution of blood within the circulatory system at rest:

Mean Arterial and Venous pressure (continued)

■ Mean arterial pressure: = 90 – 100 mmHg.

■ Mean venous pressure: Is only 2 mmHg (low).

Due to:

1. Pressure drop b/w arteries & capillaries.

2. High venous compliance.

N.B. Venous pressure is highest in venules (10 mmHg), & lowest at junction of venae cavae w Rt atrium (0 mmHg).

Arteries:

Structure of an arteriole:

Exchange of Fluid between Capillaries and Tissues

Capillaries:

Fluid Movement (continued)

Exchange of Fluid between Capillaries and Tissues

■ Distribution of ECF between plasma and interstitial compartments is in state of dynamic equilibrium. Balance between tissue fluid and blood plasma.

■ Hydrostatic pressure: Exerted against the inner capillary wall. Promotes formation of tissue fluid. Net filtration pressure.

■ Colloid osmotic pressure: Exerted by plasma proteins. Promotes fluid reabsorption into circulatory system.

Net Filtration Pressure

■ Hydrostatic pressure of blood capillaries minus the hydrostatic pressure in the interstitial fluid. Blood hydrostatic pressure (arteriolar pressure) =

37 mm Hg. Blood hydrostatic pressure (venular end) = 17 mm

Hg. Interstitial hydrostatic pressure = 1 mm Hg.

Colloid Osmotic Pressure

■ Pressure exerted by plasma proteins or interstitial proteins.

■ Difference between plasma osmotic pressure and interstitial osmotic pressure is called oncotic pressure. Plasma osmotic pressure = 25 mm Hg. Interstitial osmotic pressure = 0 mm Hg.

Arterioles, Capillaries, & Venules:

Capillary

Lymphatic System

■ Lymphatic vessels present b/w capillaries.

■ 3 basic functions: Drain excess interstitial (tissue) fluid back to the

bl, in order to maintain original bl volume. Transports absorbed fat from small intestine to

the bl. Helps provide immunological defenses against

pathogens.

Lymphatic System (continued)

■ Lymphatic capillaries: Closed-end tubules that

form vast networks in intercellular spaces.

■ Lymph: Fluid that enters the

lymphatic capillaries. Lymph carried from

lymph capillaries, to lymph ducts, and then to lymph nodes.

Lymph nodes filter the lymph before returning it to the veins.