3.1.2c Blood Vessels Flashcards
What are the 5 types of blood vessels
- Arteries
- Arterioles
- Capillaries
- Venules
- Veins
Structural composition of most blood vessels
- Elastic fibres
- Smooth muscle
- Collagen
What do elastic fibres do
Composed of elastin & can stretch and recoil, providing vessel walls with flexibility
What does smooth muscle do
Contracts or relaxes, changing the size of the lumen (channel within blood vessel)
What does collagen do
Provides structural support to maintain the shape and volume of the vessel
Blood flow in ARTERIES
Where: Carry blood away from the heart to body tissues.
What: They carry oxygenated blood (EXCEPT in the pulmonary artery which carries deoxygenated from heart to lungs, & the umbilical artery, which carries deoxygenated from fetus to the placenta)
Pressure? Blood in arteries is under higher pressure than blood in veins
Structure of an ARTERY
- Walls contain elastic fibres, smooth muscle & collagen
Elastic fibres enable them to withstand the force of the blood pumped out of the heart & stretch (within limits maintained by collagen) to take the larger blood volume in between contractions of heart.
Elastic fibres recoil & return to og length - helps to even out the surges of blood pumped from the heart to give a continuous flow. - The lining of artery (endothelium) is folded - allowing artery to expand
What links the arteries and the capillaries
Arterioles
Structure + function of ARTERIOLES
- Have more smooth muscle (to allow them to expand or contract, thus controlling the amount of blood flowing to tissues) & less elastin in their walls than arteries, as they have little pulse surge, but can constrict or dilate to control the flow of blood into organs.
- When the smooth muscle in the arteriole contracts, it constricts the vessel, preventing blood flowing into a capillary bed (this is vasoconstriction). When the smooth muscle relaxes, the vessel dilates & blood flows through into the capillary bed (this is vasodilation)
see ss 14.01, pg80 for dia of artery
see ss 14.01, pg80 for dia of capillary
What are CAPILLARIES
- Microscopic blood vessels that link the arterioles with the venues.
- They form an extensive network through all the tissues of the body
What is significant about the lumen in CAPILLARIES
The lumen of a capillary is so small that red blood cells (dia of only 7.5-8pm) have to travel through in single file
Substance exchange in CAPILLARIES
Substances are exchanged through the capillary walls between the tissue cells and the blood
Structure of CAPILLARIES
- The gaps between the endothelial cells that make up the walls are relatively large.
- This is where many substances pass out of the capillaries into the fluid surrounding the cells. (exception is capillaries in CNS, which have very tight junctions between the cells)
Significance of the size of CAPILLARIES
They are small enough to form the immense networks needed to exchange substances between the blood and the tissues
Blood flow in CAPILLARIES
- Blood entering the capillaries from the arterioles is OXYGENATED. By the time it leaves the capillaries for the venues it has less oxygen & more CO2 (it is deoxygenated)
- Again, the lungs & placenta are exceptions, w deoxygenated blood entering the capillaries & oxygenated leaving in the venules
Ways in which the CAPILLARIES are adapted for their role
- They provide very large SA for diffusion of substances into & 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 for the exchange of materials by diffusion between the blood & the cells
- The walls are a single endothelial cell thick - thin layer for diffusion
What do VEINS do
Carry blood away from the cells of the body towards the heart
Blood flow in VEINS
Carry DEOXYGENATED blood (2 exceptions: pulmonary veins & umbilical vein +)
Order of blood flow in VEINS
- Deoxygenated blood flows from the capillaries into very small veins called venules & then into larger veins
- Finally it reaches the 2 main vessels carrying deox blood back to the heart (the inferior vena cava from lower parts of body & superior vena cava from head/upper body)
Do VEINS have a pulse
- Veins DO NOT have a pulse - the surges from the heart pumping are lost as the blood passes through the narrow capillaries.
- However, they do hold a large reservoir of blood - up to 60% of your blood volume is in veins at any one time
see ss 14.01, pg80 for dia of veins
Structure of VEINS related to function
- Have valves –> prevents backflow of blood
- Inner layer (tunica intima) - endothelium is smooth –> reduces friction, so blood flows more easily
- Middle layer (tunica media) - contains smooth muscle in between elastic fibres –> thin walls can be squared by skeletal muscles to aid venous return
- Outer layer (tunica externa) - made of collagen –> same as above
- Wide lumen –> allows larger volume blood to travel; reduces resistance
Blood pressure in VEINS
Blood pressure in veins is very low compared w the pressure in the arteries
What links the CAPILLARIES with the VEINS
Venules - they have very thin walls with just a little smooth muscle. Several venules join to form a vein
What is the issue with blood flow in VEINS
Deoxygenated blood in the veins must be returned to the heart to be pumped to the lungs & oxygenated again. However, the blood is under low pressure & needs to move against gravity.
There are 3 adaptations that enable body to overcome this
Issue with blood flow in VEINS: 3 adaptations to help body overcome this
- Veins have one-way valves at intervals. These are flaps or infolding of the inner lining of the vein. When blood flows in one direction of the heart, the valves open so the blood can pass through. If the blood starts to flow backwards, the valves close to prevent this
- Many bigger veins run between big, active muscles in body (arms, legs). When the muscles contract they squeeze the vein, forcing blood towards the heart. The valves prevent backflow when the muscle relaxes
- The breathing movements of the chest act as a pump. The pressure changes & the squeezing actions move blood in the veins of the chest & abdomen towards the heart
see ss 14.01 for dia of valves in veins
Arteries
Arteries carry blood from the heart to the rest of the body.
- Their walls are thick & muscular & have elastic tissue to stretch & recoil as the heart beats, helping maintain the high pressure
- Inner lining (endothelium) is folded, allowing the artery to expand - this also helps it maintain high pressure
- All arteries carry oxygenated blood except pulmonary arteries, which carry deoxygenated blood to lungs
Arterioles
Arteries branch into arterioles, which are much smaller than arteries.
- Like arteries, arterioles have a layer of smooth muscle, but they have less elastic tissue
- The smooth muscle allows them to expand or contract, thus controlling amount of blood flowing to tissues
Capillaries
Arterioles branch into capillaries, which are the smallest of the blood vessels.
- Substances like glucose & oxygen are exchanged between cells & capillaries, so theyre adapted for efficient diffusion (eg. walls are only one cell thick)
Venules
Capillaries connect to venules, which have very thin walls that can contain some muscle cells
Veins
Venules joined tg to form veins
- Take blood back to the heart under low pressure.
- Have wider lumen than arteries, with very little elastic or muscle tissue.
- Veins contain valves to stop blood flowing backwards
- Bloodflow through veins is helped by contraction of body muscles surrounding them
- All veins carry deoxygenated blood (bc oxygen has been used up by body cells), except for pulmonary veins, which carry oxygenated blood to heart from lungs
