8.2- The Blood Vessels Flashcards
What is the role of elastic fibres, smooth muscle and collagen?
Elastic fibres- composed of elastin. Can stretch and recoil, providing vessel walks with flexibility.
Smooth muscle- contacts or relaxes which changes the size of the lumen.
Collagen- provides structural support to maintain shape and volume of vessel.
What are the arteries?
- they carry blood away from the heart to the tissues of the body.
- carry oxygenated blood, except the pulmonary artery.
- blood is under higher pressure than in veins.
Structure of artery:
Tough outer layer(collagen) - muscle layer - elastic layer - endothelium- lumen.
-largest artery = aorta (highest pressure flow)
Explain the role of elastic fibres in artery walls?
- enable them to withstand force of blood pumped out the heart and stretch to an extent (due to collagen) to take larger volumes.
- in between contractions of the heart, elastic fibres recoil and return to original length. This helps even out the surges of blood to give a continuous flow.
- however you can still feel a pulse (surge of blood) as elastic fibres can’t completely eliminate it.
- endothelium (lining if artery) is smooth so blood easily flows over it.
What is the pulmonary artery?
An artery that carries deoxygenated blood from the heart to the lungs.
During pregnancy, carries blood to the umbilical artery, which carries deoxygenated blood from the fetus to placenta.
What are the arterioles?
- link the arteries and capillaries.
- have more smooth muscle.
- less elastin in walls than arteries as they have little pulse surge.
- can constrict/dilate to control the flow of blood into individual organs.
What is vasoconstriction and vasodilation?
Vasoconstriction- smooth muscle in the arteriole contracts, constricting the vessel, prevents blood flowing into a capillary bed.
Vasodilation- smooth muscle in arteriole wall relaxes, blood flows through into the capillary bed.
What are capillaries?
- microscopic blood vessels that link arterioles with the venules.
- form extensive network through all tissues.
- very small lumen. Red blood cells have to travel in single file.
- substances exchanged through capillary walls between tissue cells and blood.
- gaps between endothelial cells (make up capillary walls) relatively large. Substances pass out of capillaries into fluid surrounding cells from here.
- except capillaries in CNS. Have very tight junctions in between.
What blood do the capillaries carry?
-Blood entering the capillaries from the arterioles= oxygenated.
- by the time it leaves for the venules = deoxygenated.
Lungs and placenta= exceptions:
- deoxygenated blood enters capillaries, oxygenated leaves into venules.
How are the capillaries adapted for their role?
- provide a large surface area for the diffusion of substances into/out of blood.
- total cross-sectional area is greater than the arteriole supplying them, so rate of blood flow falls, allowing more time for exchange of materials by diffusion between blood and cells.
- walls = single endothelial cell thick = thin layer for diffusion.
What are the veins?
- carry deoxygenated blood away from body cells towards heart. Except pulmonary/umbilical vein.
- don’t have a pulse. Surges from heart pumping are lost as blood passes through the narrow capillaries.
- hold large reservoir of blood (60% of bloods volume at any one time)
- blood pressure very low compared to arteries.
- walls contain lots of collagen, little elastic fibre. Vessels have large lumen, and smooth thin lining (endothelium) for easy blood flow.
How is deoxygenated blood returned to the heart?
-deoxygenated blood flows from capillaries to venules to larger veins.
Finally it reaches the two main vessels, carrying deoxy blood back to heart:
- Inferior vena cava (from lower body parts)
-superior vena cava (from head+upper body).
The blood is under low pressure and needs to move against gravity so there are adaptations to help this.
What are venules?
- links the capillaries with the veins.
- very thin walls with a little smooth muscle.
- several venules join to form a vein.
What are the 3 adaptations to help deoxy blood flow from veins back to heart?
- most veins have one way valves (infoldings of inner lining)at intervals. If blood starts to flow backwards, valves close.
- many bigger veins run between the big,active body muscles. When they contract, they squeeze veins, forcing blood up towards heart. (Valves prevent back flow when muscles relax)
- breathing movements of chest act as pump. Pressure changes and squeezing actions move blood up.
