B3.2 Transport Flashcards
B3.2.1 Adaptations of capillaries - Function
Function = exchange materials between the cells in tissues and blood travelling at low pressure.
Arteries branch -> arterioles -> capillaries, reducing pressure as vessel volume increases. This slows blood flow, ensuring all cells are near a supply. After exchange, capillaries -> venules -> veins.
B3.2.1 Adaptations of capillaries - specialised structures
Small diameter (~ 5 µm) -> passage of only a single red blood cell at a time (optimal exchange).
Capillary wall = single cell layer, less diffusion distance.
Basement membrane: permeable to necessary materials. May have pores -> aid in material transport.
B3.2.1 How does capillary structure vary depending on where it is located?
The capillary wall may be continuous, with endothelial cells held together by tight junctions to limit permeability of large molecules (e.g. muscles, lungs).
In tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores).
B3.2.2 Structure of Arteries and Veins
Arteries have thick walls + narrow lumens bc they transport blood at high pressure.
Veins have thin walls with wide lumens + valves bc they transport blood at low pressure.
B3.2.3 How are arteries adapted to maintain high blood pressure and efficient blood flow?
Narrow lumen = maintain high blood pressure (~80–120 mmHg). Thick walls w/ collagen fibers prevent rupture under pressure.
Elastic fibers allow stretching and recoiling to sustain pulse flow. Smooth muscle regulates vessel diameter and blood flow.
B3.2.3 What are the main structural layers of an artery (adaptations)?
Tunica externa – Outer layer with collagen for strength and protection.
Tunica media – Middle layer with smooth muscle and elastic fibers for flexibility and contraction.
Tunica intima – Inner layer of smooth endothelial cells that reduce friction and support elasticity.
B3.2.3 Adaptations of muscle fibres for high pressure blood flow in the arteries
Muscle fibres form rigid arterial walls -> withtand pressure + prevent rupture.
Muscle fibres contract to narrow the lumen -> increases pressure between pumps + sustaining it throughout cardiac cycle.
B3.2.3 Adaptations of elastic fibres for high pressure blood flow in the arteries
Elastic fibres allow the arterial wall to stretch and expand upon the flow of a pulse through the lumen.
Elastic recoil ensures pressure exerted on the wall is returned to the blood when artery size returns. This causes the blood to push forward, maintaining arterial pressure between pump cycles.
B3.2.4 Blood flow in veins and mechanisms aiding it
Blood at low pressure= difficult to move against downward force of gravity.
One-way valves prevent backflow and maintain blood circulation.Skeletal muscles contract around veins, squeezing them to push blood forward from the site of compression.
B3.2.6 Occlusion of the coronary arteries
Occlusion = blockage
Coronary arteries branch off from the aorta to supply the heart muscle with nutrients and oxygen.
Occlusion of the coronary arteries leads to coronary heart disease (CHD), a cardiovascular disease.
B3.2.6 Causes of occlusion of the coronary arteries
Buildup of plaque, a fatty substance that is mostly made of cholesterol.
Hardens into deposit: atherosclerotic plaque, narrows diameter of CA -> reduces blood flow to heart.
Atherosclerotic plaque rupture -> expose/damage tissue underneath = forms thrombus, restrict BF more.
a blood clot = thrombus
B3.2.6 Consequences of occlusion of the coronary arteries
Blood flow impeded -> part supplied by that vessel will not receive blood = cardiac muscle cells there don’t obtain oxygen, nutrients. can experience tissue damage/ death, leading to a myocardial infarction.
Also results: shortness of breath, fatigue and pain (angina).
myocardial infarction (heart attack)
