What are 5 functions of the circulatory system?
1) Carry blood, keeping pulmonary and systemic circulation separate
2) Exchange nutrients, waste products, and gases with tissues
3) Transport substances
4) Regulate blood pressure within a normal range
5) Direct blood flow to tissue
What are 3 types of blood vessels?
Arteries
Venules/veins
Capillaries
What are the three wall layers of arteries and veins? Inner->Outer
Tunica intima
Tunica media
Tunica adventitia
What is the tunica intima? (general)
Innermost wall of arteries and venules.
Endothelium, mainly simple squamous
What layers make up the tunica intima? Inner->Outer
Basement membrane
Laminar propria
Internal elastic membrane
What is the tunica media? What does it allow for?
Smooth muscle cells arranged circularly around the blood vessel
Allows for vasoconstriction and vasodilation
What is the tunica adventitia made up of?
Connective tissue.
Varies from dense (near media) to loose (merges with surrounding connective tissue)
What are the three types of arteries?
Elastic
Muscular
Arterioles
What are elastic arteries (e.g.)? What is the function of elastic arteries?
Is blood pressure high or low in elastic arteries?
Conducting arteries, e.g. the aorta. Elastic arteries expand and recoil to prevent drops in blood pressure
Blood pressure is high.
What are muscular arteries? How thick are their walls? What is their function?
Distributing arteries.
Contain 25-40 layers of smooth muscle.
Vasoconstrict and vasodilate to regulate blood supply
What are arterioles? What is their function?
Small muscular arteries, which decrease in size, diameter and wall thickness to the terminal arterioles.
Carry blood from small arteries to capillaries.
What are venules? What is their function? What are their walls made up of?
Very small veins.
Drain fluid from the capillary network.
Made up of endothelial cells, basement cells, and a few smooth muscle cells.
What are veins? Is blood pressure low or high in them? Why?
Blood vessels with a large lumen, thin walls, and valves to prevent backflow.
Low blood pressure.
Veins can hold a lot of blood at very low pressure.
What are capillaries? What is their average diameter? What is their function?
Very small blood vessels. Average diameter of 10μm.
Allow for rapid exchange of nutrients and metabolites between bloodstream and interstitial fluid.
What are the walls of capillaries made up of? Inner->outer
Basement membrane
Endothelial cells
Thin layer of connective tissue
Which substances are able to diffuse directly through the plasma membrane of the capillary?
Lipid-soluble molecules
Some water soluble-molecules
How do molecules which are unable to diffuse through the capillary’s plasma membrane transport?
Through fenestrae in the basement membrane, or through gaps between endothelial cells
What are 3 types of capillaries?
1) Continuous
2) Fenestrated
3) Sinusoidal
What are the characteristics of continuous capillaries? Where might they be found?
Contain no gaps between endothelial cells
Found in muscle, nervous tissue and skin
What are the characteristics of fenestrated capillaries? Where might they be found?
Highly permeable. Contain numerous fenestrae.
Found in the villi of the small intestine, glomeruli in the kidneys and in endocrine glands.
What are the characterstics of sinusoidal glands? Where might they be found?
Large diameter and large fenestrae. Basement membrane sparse, or often missing.
Found in liver and bone marrow.
What are arteriovenous anastomoses?
Specialised vascular connections allowing blood to bypass capillaries and flow directly from arterioles to venules
What is blood pressure determined by?
Pressure, flow, and resistance.
What is blood pressure directly proportional to?
Pressure differences
