Chapter 19- Blood vessels Flashcards
“Vaso-“
Vessels
“Vasa-“
Vessels
3 layers of the vessel wall
- Tunica intima
- Tunica media
- Tunica externa
Tunica intima
Innermost layer of the vessel wall. Contains endothelium of simple squamous cells, continuous with the lining of the inside of the heart. It provides slick surface to reduce friction as the blood moves, and helps to increase flow of blood
Tunica media
Middle layer. Contains smooth muscle, and is thicker in arteries than in veins. Function- maintaining blood pressure and circulation
Vasodilation
Dilates blood vessels (lumen becomes larger), which decreases pressure in the blood vessel. Carried out by the tunica media in the blood vessel wall.
Vasoconstriction
Constricts blood vessels (lumen becomes smaller). Less blood can move through, increases blood pressure. Carried out by the tunica media in the blood vessel wall.
Tunica externa
Outermost layer of the blood vessel wall. Contains collagen fibers- protects the blood vessel, anchors blood vessels to surrounding structures. This prevents the blood vessel from twisting.
Vasa vasorum
Found in large blood vessels like the pulmonary artery, pulmonary vein, and aorta. It consists of small blood vessels on the outside of the large blood vessels so the tissue doesn’t die- too much distance for nutrients from the blood to diffuse through.
Arteries
Blood vessels that carry blood away from the heart. They branch several times to form smaller blood vessels (ex- arterioles). Systemic arteries carry oxygenated blood, pulmonary arteries carry oxygen poor blood.
Types of arteries (3)
- Elastic arteries
- Muscular arteries
- Arterioles
Elastic arteries
Conducting arteries, including the aorta and its largest branches. Three walls contain large amounts of elastin, and expand and recoil as heart pumps blood- blood flows continuously (rather than start-stop start-stop). Importance- maintains blood flow during diastole
How does a large lumen in the blood vessels affect resistance?
A large lumen decreases resistance
Muscular arteries
Distributing arteries that are derived from elastic arteries and have a thicker tunica media. They don’t have much elastic quality, but are very good for vasoconstriction- influences blood pressure
Arterioles
Resistance arteries- these are the smallest arteries. The body can constrict/dilate the arterioles to affect resistance to blood flow into the capillaries. Arterioles flow directly into capillary beds.
Capillaries definition
Exchange vessels. No tunica media or externa, need a thin wall to diffuse materials through. They have an extremely small diameter- RBCs have to pass through single file.
Capillaries function
Contact tissue cells, allow for gas exchange, waste removal, etc. Capillaries are structurally suited for exchange across a thin wall. Cells joined by tight junctions, but have intercellular clefts- allows passage of fluids and small solutes
Types of capillaries (3)
- Continuous capillaries
- Fenestrated capillaries
- Sinusoid capillaries
Continuous capillaries
Most common, but least permeable. Found in the skin and skeletal muscle tissue
Fenestrated capillaries
Large pores, more permeable. Found mostly in places of the body where absorption and filtration is frequent, ex- small intestine and kidneys
Sinusoid capillaries
Least common, but most permeable. They have large intercellular clefts between cells with an incomplete basement membrane and a larger lumen than other capillary types. Found in the liver, spleen, red bone marrow- want blood cells to be able to get out of the red bone marrow through the capillaries
Microcirculation definition
The flow of blood from an arteriole to a venule through a capillary bed.
How does arteriole diameter affect flow into the capillary bed?
Dilation- blood enters capillary bed
Constricted- blood is diverted past the capillary bed. Decreases the amount of blood, but it’s never completely reduced.
How does microcirculation occur?
The terminal arteriole branches several times to form a network of capillaries. Pressure from arterioles controls how much blood flows through the capillary bed, and the capillary bed empties into a postcapillary venule. If blood is provided to capillary beds via arterioles- gas exchange, metabolic waste removal, etc. will occur here
Venules
The smallest veins that lead from capillary bed to larger veins. Tend to be very porous, allow easy passage from bloodstream.
Veins
Carry blood toward the heart, systemic veins carry oxygen poor blood, pulmonary veins carry oxygenated blood. Have thinner tunics and larger lumen than arteries of comparable size. Large lumen allows for large amounts of blood to stored- blood reservoirs
How do the thin vessel walls of veins affect the pressure inside the vessels?
Thin tunics= low pressure within veins. Problem- low pressure in veins (with thin tunica media) dampens ability to return blood to the heart
Adaptations of veins to increase return flow to heart (2)
- Large diameter lumen
2. Venous valves
How does the large diameter of the lumen in veins help to return blood to the heart?
Causes little resistance to blood flow. Benefit- doesn’t take a lot of work to move blood through veins
How do venous valves help to return blood to the heart?
Prevents backward flow of blood through veins. Greater number of valves in appendages, because the appendages are very long and have a greater chance of backflow of blood.
Varicose veins
A homeostatic imbalance where leaky valves cause backflow of blood, causing blood to pool and walls of veins to stretch.
3 important factors of circulation
- Blood flow
- Blood pressure
- Resistance
Blood flow
The volume of blood flowing through a vessel, an organ, or the entire circulation in a given period. Blood flows from high pressure to low pressure- arteries have high pressure due to thicker tunica media, veins have low blood pressure
Hydrostatic pressure difference
Refers to different pressures in arteries vs veins. This must exist or the blood would stop moving.
Blood pressure (circulation factor)
The force exerted on a blood vessel wall by the contained blood. Blood always “pushes against” the vessel it is flowing through, and blood pressure is highest in the aorta since the aorta receives blood directly from the heart. As you travel from arteries- capillaries- veins, blood pressure decreases. We are usually only concerned with arterial blood pressure
Resistance
Opposition of blood flow through a vessel due to the friction between the vessel wall and the flowing blood. Peripheral resistance- resistance is highest in systemic circulation. As resistance decreases, flow increases, and as resistance increases, flow decreases.
Sources of resistance (3)
- Blood viscosity, more viscous= greater the resistance
- Vessel length, longer blood vessels= greater resistance
- Vessel diameter, smaller diameter vessels= greater resistance
Relationship between resistance, blood pressure, and blood flow
ΔP/R= F
As change in blood pressure (ΔP) increases, blood flow (F) increases
As peripheral resistance (R) increases, blood flow decreases
General rule of systemic blood pressure
The pumping action of the heart generates blood flow. Blood pressure results when blood flow is opposed by resistance. Blood pressure is a general indicator of cardiovascular health.
Pulsatile
Rises and falls in a regular fashion. Describes blood pressure in the arteries near the heart.
Arterial blood pressure is affected by (2)
- Distensibility of blood vessel walls- degree of stretch of blood vessels. Less elasticity= higher pressure
- Volume of blood being pumped into arteries. Higher blood volume= higher blood pressure
Systolic blood pressure
Pressure peak generated by contraction of the left ventricle (during heart beat). Ventricle contracts, forcing blood into the aorta and stretching its walls. In healthy adults, it’s about 120 mm Hg
Diastolic blood pressure
Pressure when heart is relaxed (between heart beats). Walls of aorta relax and recoil, but still maintain enough pressure to move blood. In healthy adults, it’s about 70-80 mm Hg
Pulse pressure
The difference between systolic and diastolic blood pressure (subtracting). Represents the force the heart generates with each contraction. Ex- for an individual with a blood pressure of 120/80, the pulse pressure is 40
What is pulse pressure used to diagnose?
Can be used to diagnose cardiovascular system conditions that are asymptomatic. Anything over 60 can indicate risk for certain diseases (heart attack, etc.). However, 180/140 blood pressure gives a pulse pressure of 40 but is still very dangerous
Where can pulse pressure be felt?
Can be felt (palpated) at several points in the body as a pulse. Ex- wrist and neck
Capillary blood pressure
Low blood pressure is typical in capillary beds. Importance- thin walls of capillaries could burst under high pressure, low pressure allows for maximal trade of respiratory gasses at tissues