Lecture 9: Blood vessels Flashcards
What is the function of elastic arteries (sometimes called conducting arteries
They help to smooth the pulsatile flow of blood leaving the ventricles by stretching to accomodate the bolus of blood. The stretching stores elastic potential energy which is used to push the blood through the arteries as kinetic energy as the ventricle relaxes (diastole).
What is the structure and location of elastic arteries
They are the first arteries to leave the heart, finger size. They have many thin sheets of elastin in the middle tunic
What is the function of muscular artery
Maintains blood flow and blood pressure (using vascular tone) to distribute blood around the body at high pressure (to lungs at medium pressure) channeling it to where its needed. The smooth muscle is used to vary the radius of the vessel which has a large effect on flow. Change in Flow is proportional to the change in radius^4.
What is the structure and location of muscular arteries
Found distributing blood to the organs, pencil to pin size. They have many layers of circular smooth muscle wrapped around the vessel in the middle tunic. Less elastic tissue in the vessel but thicker tunica externa > tunica media with collagen, fibroblasts and elastic fibres all longitudinal to allow changes in diameter but no shortening if the vessel is cut.
What is the function of an Arteriole
It regulates blood flow to capillary beds by changing the resistance to blood flow and therefore causing blood pressure to change. They increase resistance by vasoconstriction. These vessels have the greatest pressure drop and greatest resistance. The degree of constriction determines the total peripheral resistance which in turn affects the mean arterial blood pressure.
What is the structure and location of an Arteriole
These are located in the peripheries before the capillaries, hair size but strong. They have the thickest muscular wall relative to their size than all other vessels. They have 1-3 layers of circular smooth muscle wrapped around the vessel in the tunica media. In the tunica externa they also have unmyelinated sympathetic nerve supply
What is the function of a Capillary
It allows the exchange of gases, nutrients and wastes between the blood and the surrounding tissue fluid (interstitial fluid) which is between the capillary and tissue cells. The amount of blood flow in the capillary network increases with metabolic needs, although blood flow is slow to allow time for exchange to occur. Plasma escapes through these leaky vessels and the hydrostatic pressure means that more fluid is leaving than returning by osmosis.
What is the structure and location of capillaries
They are found near almost every cell in the body, with higher numbers proportional to the metabolic requirements. Some tissues with none such as covering, lining epithelium, cornea, lens of eye and cartilage. Capillaries are 5-10 um diameter (RBC size) and form branching networks to increase SA for exchange. The capillary wall itself is made of a single layer of endothelium (with external basement membrane). It has no tunica media or externa so no connective tissue or smooth muscle. Fixed diameter.
What is the function of a Venule
These are low pressure vessels that drain capillary beds. They function as sites of exchange as well as white blood cell emigration where white blood cells leave the blood circulation to attack bacteria in the tissue alongside.
What is the structure and location of venules
Venules can be as small as capillaries in the post capillary venules but as they get closer to veins they get bigger. Small venules have layer of endothelium + connective tissue. Larger venules have a single layer of circular smooth muscle in tunica media.
What is the function of a Vein
Veins are thin walled low pressure vessels that drain back to the atria (except portal veins). The walls are thin and soft and stretch easily (compliant). Veins aren’t designed to handle high pressures. A small change in venous blood pressure results in a large change in venous blood volume so veins can act as a resovoir which stores excess blood.
What is the structure and location of veins
Veins are found from the peripheries to the heart. They have very thin walls relative to their diameter (much less muscle and connective tissue), and their lumen is bigger than a comparable artery. Larger veins (like in the limbs) have valves made from cusps of tunica interna which prevent backflow. As leg muscles alongside the vein alternately contract and relax during walking, the system acts as a venous pump which returns blood to the right atrium.
Describe the function, structure and location of the coronary arteries
These arteries arise from the aorta just downstream from the aortic valve and supply the muscle of the heart (myocardium). They are muscular arteries matchstick size.
What happens when the coronary artery is narrowed to about 20% of its normal cross section by atheroma and you exercise
There is significant obstruction to blood flow to the area down stream so when you exercise, not enough oxygen can get to the myocardium = ischemia and this causes chest pain (angina). Severe ischemia results in the death of the local myocardium area supplied by that artery branch = infarction.
What are the different ways the heart can have failure- the heart works harder for a long time but eventually is not able to keep up with the demand- and explain how these all lead to failure
-Infarction due to lack of blood supply.
-when the left ventricle isn’t working well
- damage to the heart valves causing leaking which means blood is flowing back.
This causes the ejection fraction to decrease which will mean that the heart rate will increase to compensate but eventually can’t keep up.
