exam 4- circulatory 2 Flashcards
arteries are composed of 3 layers of tissue:
1- internal layer called tunica intima (made of single layer of endothelial cells which contact blood)
2- middle layer called tunica media (made of collagen, elastic fibers, and smooth muscle - the proportions depend on the type of artery) - tunica media is very thick & well-developed
3- outer layer called tunica adventitia (made of connective tissue)
name 3 classes of arteries
1- elastic artery
2- muscular artery
3- arteriole
describe properties of elastic arteries
1- the largest arteries- closest to the heart
2- ex: aorta, pulmonary artery, common carotid, subclavian, and common iliac
3- very thick tunica media made primarily of elastic fibers (proportion of smooth muscle is low)
4- very thin tunica adventitia - very flexible, when blood pumped in, can expand like a spring
5- very poorly innervated, not a lot of NS control – contract mainly due to heart –> so called conducting arteries (conduct blood from heart to other arteries
what controls arterial smooth muscle tone?
sympathetic NS
which arteries are called the conducting arteries and why
elastic arteries
contract mainly due to heart (not NS control) - conduct blood from heart to other arteries
describe properties of muscular arteries
1- medium-sized
2- ex: superior mesenteric, radial artery (most of the smaller unnamed arteries)
3- tunica media made primarily of smooth muscle- 25-40 layers (low proportion of elastic fibers)
4- primarily innervated by the sympathetic NS, have abundance of alpha1 receptors on them –> called the distributive arteries (responsible for distributing blood to major organ systems of the body by opening or closing diameter
5- smaller muscular arteries are adapted for vasodilation & vasoconstriction
describe properties of arterioles
1- smallest diameter arteries & have the thinnest walls
2- tunica intima has single layer of endothelial cells
3- tunica media has only 1 or 2 surrounding layers of smooth muscle
4- feed blood to individual capillary beds
5- what sets them apart= circular rings of smooth muscle around each capillary –> creates a pre-capillary sphincter (this opens or closes the capillary bed, controls blood flow to capillary beds within tissues)
6- typically not innervated, they respond to diff signals
list the 4 functions of arteries
1- route of distribution of blood from heart to major organ systems of body
2- pressure reservoir
3- dampen pressure oscillations of the heart
4- regulates distribution of blood to systemic organs
describe the arterial function of pressure reservoir
when LV contracts, it generates large pressure (120 mmHg) –> this gets pushed into elastic arteries which stretch & expand –> when heart relaxes, pressure drops to 0 –> elastic arteries then spring back and apply inward pressure on the blood in them (stores pressure when heart contracts & releases it when heart relaxes)
describe the arterial function of dampening pressure oscillations of the heart
ventricle contracts (systole- 120 mmHg), ventricle relaxes (diastole- 0 mmHg)
huge change/pressure oscillation, the diff b/w systolic & diastolic pressure is called the pulse pressure –> in the ventricle, results in a pulsatile flow (flow in discrete individual pulses) - not good for supplying metabolically active tissue with blood (gets blood, then no blood; gets oxygen, then no oxygen)
–> so what happens is when the heart/ventricle contracts, the systolic pressure in aorta is 120 mmHg, but when heart relaxes, the aorta releases stored pressure, its diastolic pressure only drops to 80 mmHg (so pulse pressure is only 40 mmHg, much less of a fluctuation) – by storing & releasing pressure of the heart, the arteries dampen the pressure oscillation (arteries convert pulsatile flow to laminar flow- continuous flow in smooth lines)
describe the arterial function of regulating distribution of blood to systemic organs
regulates distribution by opening or closing pre-capillary sphincters – not every capillary bed in body is open at one time
what is the major feature of veins structurally
they still have the 3 layers (tunica intima, media & adventitia), but the tunica media is much less developed
–> very little smooth muscle in veins
describe the 2 major functions of veins
1- route of return of blood to the heart
2- volume reservoir: means that at rest, about 60% of total blood volume is in your veins (blood volume not evenly distributed throughout circulatory system)
- reservoir for when you need extra blood, for example, during exercise- drawn into arteries to feed active metabolizing tissue, or, if you are injured and are losing blood, the blood lost from artery will be replaced by draining down reserve in the veins
- veins are considered high volume, low pressure component of the system (but if low pressure, how does blood flow thru the veins…?)
___% of blood volume is in arteries % arterioles at a given time
15
how is blood able to flow through veins since veins have low pressure?
veins run through major skeletal muscle systems of the body (whenever you move and contract skeletal muscle, skeletal muscle squeezes down on veins, putting external pressure on the veins, moving blood thru them)
- one way direction thru pocket valves (when blood moves toward heart, pocket valves relax- when moving backward, pocket valves close & prevent backflow