RECAP **Circulatory system : Blood vessels - structure & function Flashcards
What is the function of the cardiac system?
- A transport system
What is the role of an artery blood vessel?
- distribute blood under high pressure away from the heart
What are the 2 types of arteries called?
- elastic arteries - contain a large amount of elastic tissue
- muscular arteries
what is the role of elastic tissue in arteries?
- it allows them to expand to accept the stroke volume delivered by the heart
- it also allows them to re-coil which helps to drive the blood on through the vessel
- ‘wind- kessel effect’ - expand during systole an recoil during dystole
what is the stroke volume?
- stroke volume (SV) is the volume of blood pumped from the left ventricle per beat.
What are the smallest arteries called?
- arterioles - arteries with an internal diameter of less than 100 micro metres
what is the role of arterioles ?
- regulate blood flow locally
- regulate arterial blood pressure
what are the smallest vessels in the body? what is its function
Capillaries
- function : the main site of exchange of substances between the blood and the tissues
What are examples of ‘resistance’ vessels? Why are they called this?
- small arteries and arterioles are known as ‘resistance vessels’
- they offer a frictional force that opposes blood flow
what happens to blood after passing through the capillaries?
- Blood enters the venous system on its way back to the heart
what are veins and venules often referred to as and why?
- capacitance vessels
- they can store large volumes of blood
What are the three layers in a blood vessel called?
- Lumen
- Media ( middle )
- Intima (inner)
- Adventitia
Compare and contrast the difference in structure between the 3 layers in an artery & vein.
- Arteries - smaller lumen, thicker media ( for contraction )
- Veins larger lumen
Which layer is the broadest layer?
- the outermost layer, the adventitia
Describe the structure of the Tunica Intima layer of the vessel
- thin layer of squamous epithelial cells that line the inside of the blood vessel (lumen)
- the endothelial cells are located on a thin membrane called the basal lamina/ basement membrane
what is located underneath the basal lamina in the intima layer of the blood vessel?
- a subendothelial layer that contains connective tissue and fibroblast cells that lay down the CT
What are the endothelial functions?
- it provides a selective barrier between the blood and tissues
- also provides surface for leucocytes to migrate to a site of inflammation
- haemostasis - blood clotting
Describe the structure of the media layer
- contains vascular smooth muscle
- cells are arranged in layers
- also contains elastin arranged in porous sheets (laminae) (allows molecular movement )
- also contains collagen ( for mechanical strength)
Describe what causes the tunica media vascular smooth muscle to contract and dilate ie vasoconstriction & vasodilation
vasoconstriction : sympathetic NS, noradrenaline, adrenaline, angiotensin II
vasodilation : parasympathetic NS, adrenaline etc
what is the lumen?
- hollow opening / space inside the blood vessel
Describe the structure of the adventitia
- contains collagen and elastin fibres for mechanical support & anchoring vessel
- autonomic nerve fibres also located here that influence the tone of the smooth muscle in the media layer
- contains the vasa vasorum
What is the vaso vasorum?
‘vessel in a vessel’ - small blood vessels that run through the adventitia and provide nourishing blood flow to the tissues within the blood vessel wall
note : blood in lumen of large vessels are too far away from outer vessel layers, so vascular walls need own blood supply
Describe the windkessel function of large elastic arteries
- ‘windkessel ’ - applied to anything that acts to smooth out pressure fluctuations
- elastic arteries expand to accommodate stroke volume during systole
- during diastole, no blood is ejected into the aorta but there is an elastic re-coil of the arterial walls which maintains pressure on blood & keeps it moving
what does the term ‘ elastic re-coil’ mean?
- Elastic Recoil in any tissue (including arteries) refers to the inherent resistance of a tissue to changes in shape, and the tendency of the tissue to revert to its original shape once deformed
What is the highest & lowest pressure in the heart called?
- systole pressure (highest)
- diastole (lowest)
Describe the elastic tissue in arteries.
- made up of elastin protein
- laid down in distinct layers called laminae ( between which are layers of smooth muscle )
- elastin content becomes less and less as muscular content becomes greater
what is the internal elastic lamina? IEL
- distinct elastic layer that separates the smooth muscle ( media layer ) from the intima layer
- located at the intima - media border
- fenestrated
what is the external elastic layer? EEL
- distinct elastic layer that separates the smooth muscle from the adventitia layer ( ie between the media and adventitia)
Is there any elastic tissue in veins?
- There is no elastic tissue arranged in layers
- there are some scattered throughout media and adventitia
Describe the 3 layers in vein
- adventitia layer - collagen fibres & some elastin fibres
- Venous wall is thin in comparison to the lumen diameter
- media has a few smooth muscle layers and in between them we found layers of collagenous tissue
What are the functions of the thin walls and wide lumens in veins?
- they can expand and collapse quickly which means that their volume can change quickly which encouages their function as capacitance vessels
What do veins have that arteries do not?
- VALVES
- they prevent backflow of blood
