Blood vessels 8.2 Flashcards
What are the different components utilised in blood vessels
Elastic fibres
Smooth muscle
Collagen
What are the features of elastic fibres found in blood vessels
these are composed of elastin and can stretch and recoil, providing vessel walls with flexibility
what are the features of smooth muscle found in blood vessels
contracts or relaxes, which changes the size of the lumen
what are the features of collagen
provides structural support to maintain the shape and volume of the vessel
what is the function of arteries
The arteries cary blood away from the heart to the tissues of the body. They carry oxygenated blood expect in the pulmonary artery, which carries deoxygenated blood from the heart to the lungs and (during pregnancy)the umbilical artery, which carries deoxygenated blood from the foetus to the placenta.
What is the pressure of the blood in arteries
The blood in the arteries is under higher pressure than the blood in the veins
What layers make up an artery from the inside to the outside
Describe the structure of an artery
The elastic fibres enable them to withstand the force of the blood pumped out of the heart and stretch (within limits maintained by collagen) to take larger blood volume.l
In between contractions of the heart, the elastic fibres recoiled return to their original length. This helps to even out the surges of blood pumped from the heart to give a continuous flow. However you can still feel a pulse (surge of blood) when the heart contracts, which the elastic fibres cannot completely eliminate. The lining of an artery (endothelium) is smooth so the blood flows easily over it
what is the role of arterioles
Arterioles line the arteries and the capillaries
Describe the structure of arterioles
They have more smooth muscle and less elastin in their walls than arteries ( as they have little pulse surge)
They can constrict and dilate to control the flow of blood into individual organs
Explain how vaso-constriction and dilation are connected to arterioles
when the smooth muscle in the arteriole contracts it constricts the vessel and prevent blood flowing into a capillary bed (vasoconstriction).
When the smooth muscle in a wall of an arteriole relaxes, blood flows through into the capillary bed (vasodilation)
what is an aneurysm
A bulge or weakness in a blood vessel
what are capillaries
The capillaries are microscopic blood vessels that link the arterioles with the venules
Describe the structure & function of a capillary
they form an extensive network through all the tissues of the body
The lumen of a capillary is so small that red blood cells have to travel through in single file.
Substances are exchanged through the capillary walls between the tissue cells and the blood.
The gaps between the endothelial cells that make up the capillary walls in most areas of the body are relatively large. This is where many substances pass out of the capillaries into the fluid surrounding the cells.
The exception is the capillaries in the central nervous system, which have very tight junctions between the cells
describe the oxygenation of the blood going into and out of the capillaries
In most organs of the body the blood entering the capillaries from the arterioles is oxygenated.
By the time it leaves the capillaries for the venules it deoxygenated.
the lungs and the placenta are exceptions with deoxygenated blood entering the capillaries and oxygenated blood leaving in the venules
what are some key ways the capillaries are adapted for their role
They provide a very large surface area for the diffusion of substances into and out of the blood
The total cross-sectional area of the capillaries is always greater than the arteriole supplying them so the rate of blood flow falls. The relatively slow movement of blood through capillaries gives more time from the exchange of materials by diffusion between the blood and the cells
The walls are a single endothelial cell thick, giving a very thin layer for diffusion
what is the function of the veins
Veins carry blood away from the cells of the body towards the heart, they carry deoxygenated blood.
With 2 exceptions, the pulmonary vein carries oxygenated blood from the lungs to the heart and during pregnancy the umbilical vein carries oxygenated blood from the placenta to the fetus
what are the layers of a vein in order from inside to out
Explain how the blood gets from the capillaries to the veins
Deoxygenated blood flows from the capillaries into very small veins called venules and then into larger veins
what are the 2 main vessels that bring deoxygenated blood back to the heart
The inferiors vena cava brings blood from the lower parts of the body
The superiors vena cava brings blood from the head and upper body
Why do veins not have a pulse
the surges from the heart pumping are lost as the blood passes through the narrow capillaries and blood pressure decreases
Where can most of the blood in your body be found at any one time
Veins do hold larger reservoir of blood - up to 60% of your blood volume is in your veins at any one time
what are the 3 main adaptations that enable veins to overcome low blood pressure
- have one-way valves at intervals.
^prevent backflow of blood - bigger veins run between big, active muscles in the body
^muscles contract, squeeze veins, force blood towards heart - breathing movements of the chest act as a pump.
^pressure changes and squeezing actions move blood in veins in chest and abdomen towards heart
Describe the composition of the walls of veins
The walls contain lots of collagen and relatively little elastic fibre and the vessels have a wide lumen and a smooth, thin lining (known as the endothelium) so the blood flows easily
what links capillaries and veins
venules
Describe the structure of venules
They have very thin walls with just a little smooth muscle
several venules join to from a vein
