The Cardiovascular System: Blood Vessels and Hemodynamics

The five main types of blood vessels

• Arteries

• Arterioles

• Capilliaries

• Venules

• Veins

It carry blood away from the heart to other organs. Large, elastic arteries leave the heart and divide into medium-sized, muscular arteries that branch out into the various regions of the body.

Arteries

Medium-sized arteries then divide into small arteries, which in turn divide into still smaller arteries, small vessels that branch into capillaries upon entering tissues?

Arterioles

The thin walls of capillaries allow the exchange of substances between the blood and body tissues

Capillaries

Groups of capillaries within a tissue reunite to form small veins

Venules

The blood vessels that convey blood from the tissues back to the heart.

Veins

The innermost layer, Is a thin layer of flattened cells that lines the inner surface of the entire cardiovascular system (heart and blood vessels)

Endothelium

Deep to the endothelium. It provides a physical support base for the epithelial layer. Its framework of collagen fibers affords the basement membrane significant tensile strength, yet its properties also provide resilience to stretching and recoil.

Basement membrane

The outermost part of the tunica interna, which forms the boundary between the tunica interna and tunica media, a thin sheet of elastic fibers with a variable number of windowlike openings that give it the look of Swiss cheese that allows openings facilitate diffusion of materials through the tunica interna to the thicker tunica media.

Internal elastic lamina

The innermost layer of a blood vessel, in direct contact with blood flowing through the lumen (interior opening). Contributes minimally to vessel wall thickness.

Tunica Interna/Intima

Interior opening, the inside space or cavity of a tubular structure, such as a blood vessel, intestine, or organ.

Lumen

The middle layer of a blood vessel; the most variable of the three tunics. Composed mainly of smooth muscle cells and elastic fibers.

Tunica media

An increase in sympathetic stimulation typically stimulates the smooth muscle to contract, squeezing the vessel wall and narrowing the lumen.

Vasoconstriction

When sympathetic stimulation decreases, or in the presence of certain chemicals (such as nitric oxide, H+, and lactic acid), or in response to changes in blood pressure, smooth muscle fibers relax. The resulting increase in lumen diameter

Vasodilation

Extent of contraction controls flow rate through different body regions

Blood flow regulation

Smooth muscle contraction in specific vessels is crucial to maintaining pressure

Blood pressure regulation

Regulating blood flow and blood pressure, smooth muscle contracts when a small artery or arteriole is damaged to help limit loss of blood through the injured vessel

Vascular spasm

Smooth muscle helps produce elastic fibers → allows vessels to stretch and recoil

Elasticity

The outer covering of a blood vessel, consists of elastic and collagen fibers

Tunica Externa

Contains numerous nerves that supply the vessel wall in Tunica Externa

Nerves

Small vessels that supply blood to the tissues of the vessel or vessels to the vessels; they are easily seen on large vessels such as the aorta.

Vasa Vasorum

3 components of Tunica Interna/intima

• Endothelium

• Basement membrane

• Internal Elastic Lamina

The largest arteries in the body, ranging from the garden hose–sized aorta and pulmonary trunk to the finger-sized branches of the aorta. Also called as conducting arteries

Elastic arteries

A thick tunica media that is dominated by elastic fibers

Elastic lamellae

Medium-sized arteries, because their tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries. Also called distributing arteries because they branch out to deliver blood to various organs

Muscular arteries

Most tissues of the body receive blood from more than one artery. The union of the branches of two or more arteries supplying the same body region

Anastomosis/Anastomoses

The alternative route of blood flow to a body part through an anastomosis

Collateral circulation

Literally meaning small arteries, abundant microscopic vessels that regulate the flow of blood into the capillary networks of the body’s tissues. Also called as resistance vessels

Arterioles

Key structural features of arterioles

• Metarteriole

• Precapillary sphincter

The terminal end of the arteriole, tapers toward the capillary junction

Metarteriole

At the metarteriole–capillary junction, the distal-most muscle cell which monitors the blood flow into the capillary; the other muscle cells in the arteriole regulate the resistance (opposition) to blood flow

Precapillary sphincter

The smallest of blood vessels have diameters of 5 10 μm, and form the U-turns that connect the arterial outflow to the venous return. Also called exchange vessels — primary function is exchange of substances between blood and interstitial fluid.

Capillaries

Three Types of Capillaries:

• Continous capillaries

• Fenestrated capillaries

• Sinusoids capillaries

Continuous endothelial tube; gaps called intercellular clefts. Allows exchange of water, gases, and small molecules

Continuous capillaries

Small pores in endothelial cells. Allow greater exchange of fluid and larger molecules

Fenestrated capillaries

Wider and more winding than other capillaries. Their endothelial cells may have unusually large fenestrations. In addition, to having an incomplete or absent basement membrane. Have very large intercellular clefts that allow proteins and, in some cases, even blood cells to pass from a tissue into the bloodstream

Sinusoids capillaries

Regulate blood flow into capillary beds using precapillary sphincters located at the openings of capillary beds.

Metarterioles

Contracts to limit blood flow through capillaries; blood moves through fair channels, bypassing bed. When relax, it allows perfusion of capillary beds.

Precapillary sphincters

Pass blood into muscular venules; permit exchange of nutrients and wastes between blood and interstitial fluid and function in white blood cell emigration.

Postcapillary venules

Pass blood into vein; act as reservoirs for accumulating large volumes of blood

Muscular venules

Return blood to heart, facilitated by valves in limb veins

Veins

A vein with a thin endothelial wall that has no smooth muscle to alter its diameter. In a vascular sinus, the surrounding dense connective tissue replaces the tunica media and tunica externa in providing support

Vascular sinus

Some veins are paired and accompany medium- to small-sized muscular arteries. These double sets of veins escort the arteries and connect with one another via venous channels

Anastomotic veins

The subcutaneous layer deep to the skin is another source of veins. Run through the subcutaneous layer unaccompanied by parallel arteries and connect to deep veins via anastomoses.

Superficial veins

Travel between the skeletal muscles. These connections allow communication between the deep and superficial flow of blood. The amount of blood flow through superficial veins varies from location to location within the body.

Deep veins