Chapter 21 Flashcards
What are the five main types of blood vessels?
- Arteries
- Arterioles
- Blood capillaries
- Venules
- Veins
Arteries
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. Medium-sized arteries then divide into small arteries, which in turn divide into still smaller arteries called ______. As the ______ enter a tissue, they branch into numerous tiny vessels called ______ or simply ______. The thin walls of ______ allow the exchange of substances between the blood and body tissues. Groups of ______ within a tissue reunite to form small veins called ______. These in turn merge to form progressively larger blood vessels called ______.
Arterioles; arterioles; blood capillaries; capillaries; capillaries; capillaries; venules; veins
Veins
Blood vessels that convey blood from the tissues back to the heart.
What are the three structural layers of a generalized blood vessel?
- Tunica interna (intima)
- Tunica media
- Tunica externa (adventitia)
Tunica interna (intima)
Forms the inner lining of a blood vessel and is in direct contact with the blood as it flows through the lumen.
Lumen
Interior opening of the vessel.
What are the three components of the tunica interna (intima)?
- Endothelium
- Basement membrane
- Internal elastic lamina
Endothelium (of the tunica interna (intima))
Innermost layer. Is continuous with the endocardial lining of the heart. Is a thin layer of flattened cells that lines the inner surface of the entire cardiovascular system (heart and blood vessels). Cells within the endothelial play a role in a variety of vessel-related activities.
Basement membrane (of the tunica interna (intima))
Middle layer. Provides a physical support base for the epithelial layer. Is a framework of collagen fibers, which provide it significant tensile strength. Contains other properties that make it resistant to stretching and recoil. Anchors the endothelium to the underlying connective tissue while also regulating molecular movement. Appears to play an important role in guiding cell movements during tissue repair of blood vessel walls.
Internal elastic lamina (of the tunica interna (intima))
Outermost layer. Forms boundary between the tunica interna (intima) and tunica media. Is a thin sheet of elastic fibers with a variable number of windowlike openings that give it the look of Swiss cheese. These openings facilitate diffusion of materials through the tunica interna (intima) to the tunica media.
Tunica media
Is a muscular and connective tissue layer that displays the greatest variation among the different vessel types. In most vessels, it is a relatively thick layer comprising mainly smooth muscle cells and substantial amounts of elastic fibers. The primary role of the smooth muscle cells is to regulate the diameter of the lumen.
Vasoconstriction
Decrease in the diameter of the lumen of a blood vessel.
Vasodilation
Increase in the diameter of the lumen of a blood vessel.
Vascular spasm
Contraction of smooth muscle when a small artery or arteriole is damaged to help limit loss of blood through the injured vessel.
What are the two components of the tunica media?
- Smooth muscle
- External elastic lamina
External elastic lamina (of the tunica media)
A network of elastic fibers that separates the tunica media from the tunica externa (adventitia).
Tunica externa (adventitia)
The outer covering of a blood vessel. Consists of elastic and collagen fibers. Contains numerous nerves and, especially in larger vessels, vasa vasorum. Help anchor the vessels to surrounding tissues.
Vasa vasorum
Blood vessels that nourish the tunica externa (adventitia).
Arteries
Their walls have the same three layers of a typical blood vessel, but have a thicker muscular-to-elastic tunica media. Due to their plentiful elastic fibers, they normally have high compliance, which means that their walls stretch easily or expand without tearing in response to a small increase in pressure.
Describe the size, tunica interna, tunica media, tunica externa, and function of elastic arteries (conducting arteries)
Function to propel blood onward while the ventricles are relaxing.
Elastic lamellae
Elastic fibers.
Pressure reservoir
What the elastic arteries function as since as they stretch, they momentarily store mechanical energy.
Describe the size, tunica interna, tunica media, tunica externa, and function of muscular arteries (distributing arteries)
Vascular tone
The ability of the muscle to contract and maintain a state of partial contraction. Stiffens the vessel wall and is important in maintaining vessel pressure and efficient blood flow.
Anastomosis
The union of the branches of two or more arteries supplying the same body region. Provide alternative routes for blood to reach a tissue or organ.
Collateral circulation
The alternative route of blood flow to a body part through an anastomosis.
End arteries
Arteries that do not anastomose.
Describe the size, tunica interna, tunica media, tunica externa, and function of arterioles (resistance vessels)
Play a role in regulating resistance.
Resistance
The opposition to blood flow due to friction between blood and the walls of blood vessels.
Metarteriole
The terminal end of the arteriole.
Precapillary sphincter
Monitors the blood flow into the capillary.
Describe the size, tunica interna, tunica media, tunica externa, and function of capillaries (exchange vessels)
Microcirculation
The flow of blood from a metarteriole through capillaries and into a postcapillary venule.
Capillary bed
A network of 10-100 capillaries that arise from a signel metarteriole.
What are the two ways in which blood can flow through a capillary network from an arteriole into a venule?
- Capillaries
- Thoroughfare channel
Vasomotion
Intermittent contraction and relaxation of the smooth muscle of metarterioles and the precapillary sphincters.
Thoroughfare channel
A channel that provides a direct route for blood from an arteriole to a venule. Bypasses capillaries.
What are the three different types of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Sinusoids
Continuous capillaries
What most capillaries are. The plasma membranes of endothelial cells form a continuous tube that is interrupted only by intercellular clefts (gaps between neighboring endothelial cells). Found in the central nervous system, lungs, muscle tissue, and the skin.
Fenestrated capillaries
The plasma membranes of the endothelial cells in these capillaries have many fenestrations (small pores (holes)). Found in the kidneys, villi of the small intestine, choroid plexuses of the ventricles in the brain, ciliary processes of the eyes, and most endocrine glands.
Sinusoids
Are wider and more winding than other capillaries. Their endothelial cells may have unusually large fenestrations. Have an incomplete or absent basement membrane and very large intercellular clefts that allow proteins and in some cases even blood cells to pass from a tissue into the bloodstream. Contain specialized lining cells that are adapted to the function of the tissue. Found in the liver, spleen, anterior pituitary, and parathyroid and adrenal glands.
Portal vein
A vein that allows blood to pass from one capillary network into another.
Portal system
A circulation in which blood passes from one capillary network into another.
Venules
Have thin walls that do not readily maintain their shape. Drain the capillary blood and begin the return flow of blood back toward the heart.
Describe the size, tunica interna, tunica media, tunica externa, and function of postcapillary venules
Describe the size, tunica interna, tunica media, tunica externa, and function of muscular venules
Describe the size, tunica interna, tunica media, tunica externa, and function of veins
Composed of the same three layers as arteries.
Valves
Thin folds of tunica interna (intima) that form flaplike cusps. Aid in venous return by preventing the backflow of blood, so that blood flows in one direction only - towards the heart.
Vascular (venous) sinus
A vein with a thin endothelial wall that has no smooth muscle to alter its diameter. Has surrounding dense connective tissue that replaces the tunica media and tunica externa in providing support. An example of vascular (venous) sinuses would be dural venous sinuses and the coronary sinus.
Anastomotic veins
Paired veins that escort muscular arteries and connect with one another via venous channels.
Superfical veins
Veins found in the subcutaneous layer, that are unaccompanied by parallel arteries. Form anastomoses with deep veins, allowing for communication between the deep and superficial flow of blood.
Deep veins
Veins that travel between the skeletal muscles. Form anastomoses with superficial veins, allowing for communication between the deep and superficial flow of blood.
How can blood be distributed in the cardiovascular system at rest?
- Systemic veins and venules (blood reservoirs) (64%)
- Systemic arteries and arterioles (13%)
- Pulmonary vessels (9%)
- Heart (7%)
- Systemic capillaries (7%)
Blood reservoirs
What systemic veins and venules function as since they contain a large percentage of the blood volume. Blood can be diverted quickly from these areas if the need arises.
Venoconstriction
Constriction of veins.
Capillary exchange
The movement of substances between blood and interstitial fluid. The 7% of the blood in systemic capillaries at any given time is continually exchanging materials with interstitial fluid.
What three basic mechanisms do substances enter and leave capillaries by?
- Diffusion
- Transocytosis
- Bulk flow
Diffusion (of substances entering and leaving capillaries)
Water soluble substances such as glucose and amino acids pass across capillary walls through intercellular clefts or fenestrations. Lipid-soluble materials, such as O2, CO2, and steroid hormones, may pass across capillary walls directly through the lipid bilayer of endothelial cell plasma membranes. The capillaries of the brain allow only a few substances to move across their walls, due to the blood-brain barrier (BBB).
Transocytosis
A process in which substances in blood plasma become enclosed within tiny pinocytic vesicles that first enter endothelial cells by endocytosis, then move across the cell and exit on the other side by exocytosis. This method of transport is important mainly for large, lipid-insoluble molecules that cannot cross capillary walls in any other way.
Bulk flow
Is a passive process in which large numbers of ions, molecules, or particles in a fluid move together in the same direction. The substances move at rates far greater than can be accounted for by diffusion alone. Occurs from an area of higher pressure to an area of lower pressure, and it continues as long as a pressure difference exists.
Filtration
Pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid.