3.4.1.3: Blood vessels Flashcards
name the 3 types of blood vessels
arteries, capillaries, veins
Describe and explain the difference between the wall thickness and lumen diameter between an artery and a vein
an artery has a smaller lumen diameter and a much thicker wall than a vein because the arteries are under much higher blood pressure than veins. In a vein, blood pressure is much lower and the blood moves more slowly, hence, it has a larger lumen diameter and a thinner wall
How does the total cross sectional area change as blood vessels become smaller and increase in number
total cross sectional area increases as blood vessels become smaller and increase in number
Describe the rate of flow in smaller and larger blood vessels
rate of flow is smaller in smaller blood vessels, higher in larger blood vessels
describe the blood pressure starting from the aorta and as blood flows further away from the heart
highest in the aorta, and decreasing in fluctuation as blood flows further away from the heart
describe the structure of arteries
collagen fibres, thick layer of smooth muscle and elastic tissue, endothelium, lumen
describe the structure of capillaries
basement membrane (collagen), endothelium cell, lumen
describe the structure of veins
collagen and connective tissue, thin layer of smooth muscle and elastic tissue, endothelium, semilunar valve, lumen
do arteries have valves?
no
do capillaries have valves?
no
do veins have valves?
yes, semilunar valves to prevent backflow of blood caused by low blood pressure
what is the importance of the thick elastic tissue layer in the walls of arteries
allows walls to expand with each pulse of blood and then return to original shape - elastic recoil, this evens out blood flow and maintains a high blood pressure
what is the importance of the thick smooth muscle layer in the walls of arteries
can contract/relax under nervous stimulation, therefore altering blood pressure
what is the importance of the lumen in arteries having a narrow diameter
high resistance to blood flow which maintains pressure
describe the structure of the walls in capillaries
wall has fenestrations (small pores) making it permeable so small molecules can filter out, wall is made from single, squamous layer of endothelial cells which reduces the diffusion pathway
what is the importance of the lumen in capillaries being narrow
and why is low blood pressure significant?
causes increase in total cross sectional area, so more surface is in contact with blood, causing greater friction between blood and capillary wall, resulting in loss of blood pressure
low blood pressure means a reduced flow allowing more time for diffusion of substances into/out of capillary
describe the thin elastic tissue layer in the walls of veins
thin elastic tissue layer as there is no need to expand with each pulse of blood therefore no need for elastic recoil
describe the thin smooth muscle layer in the walls of veins
less muscle to contract so will not narrow lumen to resist blood flow
what is the importance of the lumen in veins being wide
less resistance to blood flow, which helps blood return to heart
How is high blood pressure maintained in arteries
during systole, elastic fibres can expand to withstand high pressure and during diastole elastic fibres recoil to maintain the pressure
What is venous return
blood being returned to the heart via Vena Cava
describe the process of venous return
- skeletal muscles contract, squeezing the vein, volume decreases, increases blood pressure, valve in front opens and valve behind closes and so blood is forced through the front valve
- suction effect pulling blood back to heart due to atrial diastole, and so due to lower pressure in thoracic cavity during inhalation
How are capillaries adapted to provide a large surface area for exchange
dense network of capillaries
How are capillaries adapted to provide a short diffusion pathway
single squamous layer of endothelial cells, narrow lumen causes RBCs to pass in single file and RBCs are in contact with the capillary wall
what feature of capillaries allow oxygen and carbon dioxide to easily diffuse
their walls are permeable to gas
what feature of capillaries allow molecules and plasma to pass out of blood for tissue fluid formation
fenestrations between endothelial cells
explain why there is a greater proportion of smooth muscle in an arteriole and how this helps to redistribute blood around the body
the muscle can contract and partially shut of blood flow to particular organs, e.g. during exercise, blood flow to the stomach and intestines is reduces, allowing greater blood flow to the muscles being exercised
