8.2 - Blood Vessels Flashcards
Why do multicellular organisms require transport systems?
- large size - small SA:V ratio - subsequently high metabolic rates
- demand for oxygen is high - need a specialised system to ensure a strong supply to all respiring tissues
Summarise the different types of circulatory system
• Open = blood can diffuse out of vessels eg. Insects
• closed = blood confined to vessels eg. Fish , mammals
Single = blood passes through pump once per circuit of the body
Double = blood passes through heart twice per circuit of the body
What are the 3 layers of the arteries?
- tunica externa
- tunica media
- tunica intima
Explain the structure of the tunica intima
- made up of an endothelial layer - layer of connective tissue and a layer of elastic fibres
- endothelium is one cell thick and lines the lumen - very smooth and reduces friction for free blood flow
Explain the structure of the tunica media
• made up of smooth muscle cells and a thick layer of elastic tissue
• very thick
• layer of muscle cells strengthen the arteries so they can withstand high pressure- enables them to contract and narrow the lumen for reduced blood flow
• elastic tissue - helps maintain blood pressure- stretches and recoils to even out any fluctuations in pressure
Explain the structure of the tunica externa
• covers the exterior of the artery and it’s mostly made up of collagen
• collagen - strong protein protects blood vessels from damage by overstretching
Why do arteries have narrow lumens?
Helps maintain a high blood pressure
Is a pulse present in arteries?
Yes
What is the structure of the arterioles?
• have a muscular layer that means they can contract and partially cut off blood flow to specific organs
• lower proportion of elastic fibres and a large number of muscle cells
• presence of muscle cells allows them to contract and close their lumen to stop and regulate blood flow
What is the structure of the veins?
• tunica media is much thinner in veins
• no need for a thick muscular layer as veins don’t have to withstand high pressure
• large/ wide lumen - helps ensure that the blood returns to the heart at a adequate speed
• rate of blood flow is slower
• large lumen means the volume of blood delivered per unit of time is equal
• contain valves
Is there a pulse in veins?
No
What is the structure of the venules?
• few or no elastic fibres and a large lumen
• blood is at low pressure after passing through the capillaries there is no need for a muscular layer
• connect capillaries to the veins
What is the structure and function of capillaries?
- thin walls that are leaky - allowing substances to leave the blood to reach the body’s tissues
- Form networks called capillary beds which are important exchange surfaces
- very small diameter ( lumen )
- forces blood to travel slowly - provides more opportunity for diffusion to occur
- large number of capillaries branches between cells
- substances can diffuse between the blood bs cells quickly as there is a short diffusion distance
- wall is made from a single layer of endothelial cells
- only one cell thick - reduces the diffusion distance for oxygen and carbon dioxide between the blood and tissues of the body
- cells of the wall have gaps called pores which allow blood plasma to leak out and form tissue fluid
Describe the single circulatory system in fish
• deoxygenated blood is pumped to the gills from the heart
• gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood
• oxygenated blood flows from the gills to the rest of the body
• travels through the Capillaries in organs - delivering oxygen and nutrients
• blood returns to the heart
• heart only has one atrium and one ventricle
Describe the process of the double circulatory system in mammals
• left side - oxygenated blood
• right side - deoxygenated blood
• blood on the right side of the heat leaves and travels to the lungs
• blood returns on the left side of the heart before being pumped around the rest of the body
