Ch. 21: Cardiovascular System Flashcards
What is the tunica interna, and what are its layers?
Epithelial inner lining of blood vessel. Endothelium (inner) –> basement membrane –> internal elastic lamina (outer).
Describe the endothelium of the tunica interna.
Innermost layer, continuous with endocardial lining of the heart, reduces surface friction, secretes locally acting chemical mediators, assist in capillary permeability.
Describe the basement membrane of the tunica interna.
Resilient for stretching and recoil, anchors endothelium to connective tissue, regulates molecular movement, guides cell movements during tissue repair, is supported by collagen fibres.
Describe the internal elastic lamina of the tunica interna.
Outermost layer, forms boundary between tunica interna and tunica media, thin sheet of elastic fibres, facilitate diffusion of materials through the tunica interna to the tunica media.
What is the tunica media?
Middle layer of blood vessel, smooth muscle, elastic connective tissue, the most variable of the tunics.
What is the tunica externa?
Outer layer of blood vessel, connective tissue, elastic and collagen fibres, nerves, tiny blood vessels (vasa vasorum), anchors the vessel to surrounding tissues.
What is vasoconstriction?
An increase in sympathetic stimulation causes the smooth muscle of the tunica media to contract and narrow the lumen.
What is vasodilation?
A decrease in sympathetic stimulation, or in the presence of certain chemicals, or in response to blood pressure, the smooth muscle of the tunica media relaxes and widens the lumen.
What is vascular spasm?
When the smooth muscle of the tunica media contracts in response to damage.
What are elastic arteries?
Also called conducting arteries, largest arteries in the body, largest diameter, propel blood onward while ventricles are relaxed.
How do elastic arteries function as pressure reservoirs?
As blood is ejected from the heart to elastic arteries, the walls stretch and the elastic fibres momentarily store mechanical energy. Then, elastic fibres recoil and convert potential energy in the vessel to kinetic energy in blood.
What are muscular arteries?
Also called distributing arteries, medium-sized arteries, capable of greater vasoconstriction and vasodilation, branch and deliver blood to each organ, cannot recoil or propel blood.
Examples of elastic arteries.
Aorta, pulmonary trunk, aorta’s major initial branches (brachiocephalic, subclavian, common carotid, common iliac).
What are muscular arteries responsible for?
Vascular tone; stiffens the vessel wall, important in maintaining vessel pressure and efficient blood flow.
What is an anastomose?
The union of the branches of 2+ arteries supplying the same body region.
Anastomoses between arteries provide…
Alternative routes for blood to reach a tissue. This is called collateral circulation. Anastomoses can also occur between veins and between arterioles and venules.
What are end arteries, and what happens when one is obstructed?
Arteries without anastomoses. Blood supply to a whole organ segment will be interrupted.
What is the metarteriole?
The terminal end of an arteriole which tapers toward the capillary junction.
What alters the diameter of arterioles and varies the rate of blood flow and resistance through these arterioles?
Unmyelinated sympathetic nerves and local chemical mediators.
Arterioles are also known as…
Resistance vessels because they regulate resistance and blood flow from arteries into capillaries.
What is a microcirculation?
The flow of blood from a metarteriole through capillaries and into a postcapillary venule.
Capillaries are also called…
Exchange vessels because their primary function is the exchange of substances.
What forms the U-turns that connect the arterial outflow to the venous return?
Capillaries.
Which body tissues have extensive capillary networks?
High metabolic requirements (muscles, brain).
Which tissues do not have capillaries?
Epithelia, cornea, lens, cartilage.
Capillaries are composed of…
A single layer of endothelial cells and a basement membrane (no tunica media or tunica externa).
What is a capillary bed?
Network of capillaries that arise from a single metarteriole.
Continuous capillaries.
Most common capillaries, plasma membrane of endothelial cells form a continuous tube that is interrupted by intercellular clefts, CNS, lungs, muscle tissue, skin.
Fenestrated capillaries.
Plasma membrane of endothelial cells have many fenestrations, kidneys, villi of small intestine, choroid plexuses of ventricles, ciliary processes of eyes, endocrine glands.
Sinusoids.
Endothelial cells have very large fenestrations, no basement membrane, large intercellular clefts that allow proteins and blood cells to pass from a tissue into the bloodstream, contain specialized lining cells that are adapted to the function of the tissue, liver, spleen, anterior pituitary, parathyroid, adrenal gland.
Portal system.
Blood passes from one capillary network into another through a portal vein.
Blood can flow through a capillary network from an arteriole into a venule through…
Capillaries and thoroughfare channels.
1) Capillaries: Arteriole –> capillaries –> postcapillary venues.
1) Thoroughfare channels: The distal end of a metarteriole where there is no smooth muscle, and this provides a direct route for blood from an arteriole to a venule.
What is vasomotion?
When blood flows intermittently through capillaries due to alternating contraction and relaxation of the smooth muscles of metarterioles and precapillary sphincters. Due to chemicals release by the endothelial cells.
At any given time, blood flows through only ___ of capillaries?
25%
Postcapillary venules are the…
Smallest venues and have loosely organized intercellular junctions. They function as sites of exchange of nutrients and wastes and WBC emigration.
As the postcapillary venules move away from capillaries…
They acquire 1-2 layers of circularly arranged smooth muscle cells.
Describe valves in veins.
Thin folds of tunica interna that form flaplike cusps that project into the lumen and point towards the heart.
Vascular sinus.
A vein with a thin endothelial wall that has no smooth muscle to alter its diameter.
Anastomotic veins.
Cross accompanying artery to form ladder-like rungs between paired veins.
Superficial veins.
Course through the subcutaneous layer unaccompanied by parallel arteries, and form small anastomoses with deep veins that travel between the skeletal muscles.
Describe superficial veins in upper limbs.
They are larger than the deep veins, and serve as major pathways from capillaries of the upper limbs back to the heart.
What colours do superficial and deep veins appear?
Superficial: blue. Deep: red.
What percentage of blood volume do your systemic veins and venules hold during rest?
64%
What percentage of blood volume do your systemic arteries and arterioles hold during rest?
13%
Systemic capillaries, pulmonary blood vessels and the heart hold what percentage of blood volume during rest?
7%, 9%, 7%
In which ways do substances enter or leave capillaries?
Diffusion, transcytosis, bulk flow.
What is the most important method of capillary exchange?
Diffusion.
Which substances move in and out of capillaries via diffusion?
O2, CO2, glucose, amino acids, hormones.
How do water soluble substances diffuse through capillaries?
Through intercellular clefts or fenestrations.
How do lipid soluble substances diffuse through capillaries?
Through the lipid bilayer of endothelial cell plasma membranes.
Which brain structures lack a BBB?
Hypothalamus, pineal gland and pituitary gland.
Describe how substances move through capillaries via transcytosis.
Substances in blood plasma become enclosed within pinocytic vesicles that enter endothelial cells by endocytosis, and then move across the cell and exit by exocytosis.
Which substances rely on transcytosis to move through capillaries?
Large lipid-insoluble molecules.
What is bulk flow?
Passive process of filtration and reabsorption where large numbers of ions, molecules and particles in a fluid move together in the same direction. Occurs from an area of high pressure to low pressure, and continues as long as a pressure difference exists.
Describe filtration of bulk flow.
Pressure driven movement of fluid and solutes from blood capillaries into interstitial fluid.
Describe reabsorption of bulk flow.
Pressure driven movement of fluid and solutes from interstitial fluid into blood capillaries.
Blood hydrostatic pressure.
Generated by the pumping heart. Promotes filtration. 35 mmHg at arterial end. 16 mmHg at venous end.
Interstitial fluid osmotic pressure.
Promotes filtration. Opposes blood colloid osmotic pressure. 1 mmHg.
Blood colloid osmotic pressure.
Promotes reabsorption. Caused by the colloidal suspension of plasma proteins. 26 mmHg.
Starling’s Law of Capillaries.
The volume of fluid and solutes reabsorbed is as large as the volume filtered.
Within vessels, the hydrostatic pressure is due to the…
Pressure that water in blood plasma exerts against blood vessel walls.
Interstitial fluid hydrostatic pressure.
Opposes blood hydrostatic pressure. Promotes reabsorption. 0 mmHg.
What is the net filtration pressure?
NFP = (BHP + IFOP) - (BCOP + IFHP)
What is the net filtration pressure at the arterial end of a capillary?
NFP = (35 + 1) - (26 + 0) = 10 mmHg
What is the net filtration pressure at the venous end of a capillary?
NFP = (16 + 1) - (26 + 0) = -9 mmHg
What percentage of fluid filtered out of capillaries is reabsorbed?
85%
What generates blood pressure?
Contraction of ventricles.