blood vessels and cardiac cycle Flashcards
Compare the physical features of the atrium and the ventricle (similarities and differences)
Both are elastic
atrium = thin-walled
Ventricle= much thicker muscular wall
Why do ventricles have thick walls?
because it has to strongly contract to pump blood to the lungs or the body
What are the names of the right atrioventricular valve and the left one
right = bicuspid
left = tricuspid
What are the roles of the aorta, vena cava, pulmonary artery and the pulmonary vein?
Aorta: carries oxygenated blood to all parts of the body except the lungs
Vena cava: brings deoxygenated blood back from the tissues of the body (except lungs)
Pulmonary artery: carries deoxygenated blood to the lung
Pulmonary vein: brings oxygenated blood back from the lungs
What are the roles of the coronary artery?
supplies the heart with oxygenated blood
When the arteries stretch and recoil
Stretching = accommodate increase in blood volume
Recoil = when blood pressure decreases
How are the arteries adapted for its function? (muscle layer, elastic layer, outer layer, valves, lumen, endothelium )
- Thick muscle layer = smaller arteries can be constricted when the muscle contract and dilated when the muscle relaxes = control the volume of blood passing through them
- Thick elastic layer = allows to stretch during systole and recoil during diastole. This helps maintain high pressure and smooths pressure surges
- Thick outer layer = resists the vessel from bursting from high pressure
- No valves = due to carrying blood away from the heart it has a high blood pressure, so no backflow
- Small lumen = control blood
- Smooth endothielium lining = less friction and therefore resistance to red blood cells
What are arterioles?
vessels which carry blood under low pressure from the arteries to the capillaries
How are arterioles adapted for their function? (muscle layer, elastic layer)
Thick outer layer = contraction of muscles allows constriction of the lumen, which restricts blood flow, hence controlling blood movement into the capillaries. Muscles also determine the direction of blood flow
Thin elastic layer (compared to arteries) = lower pressure due to the arteries
How are the veins adapted for its function? (muscle layer, elastic layer, outer layer, valves)
- Thinner muscle layer = the veins do not need to constrict as there is no need to control blood flow to tissues due to the blood having a lower pressure. Thin muscle layer allows for a wide lumen.
- thin elastic layer = low pressure of the blood means a thick wall is not needed to withstand pressure
- valves = ensures that there is no backflow of blood (as the pressure low), makes sure the blood flows in only one direction (towards the heart)
- wide lumen = easier blood flow, prevents resistance to red blood cells
- Smooth endothelium lining = less friction and therefore resistance to red blood cells
How are the capillaries adapted for its function? (Endothelial wall, surface area, diameter, lumen, spaces)
- Single layer of endothelial cell as the wall = short diffusion pathway = efficient diffusion
- Highly branched and numerous = Large surface area and ensures that cells are never going to be too far away from a red blood cell (short diffusion pathway)
- Narrow diameter= short diffusion pathway
- Narrow lumen = allows only one red blood cell at a time, which gives time for diffusion. This also means that red blood cells are squeezed flat against the side of a capillary, bringing them closer to the cells which they supply oxygen (short diffusion pathway)
- Narrow lumen also slows down the rate of blood flow by causing greater friction due to the increased contact the surface has with the blood
- Spaces between the endothelial cells= allows white blood cells to escape in order to deal with infections within tissues
What is tissue fluid?
watery liquid that surrounds cells, which contains glucose, amino acids, fatty acids, dissolved ions and oxygen
Unlike blood, tissue fluid doesn’t contain red blood cells or big proteins. Why?
Because they are too large to be pushed out through he capillary walls
How is tissue fluid useful to the body?
it supplies glucose, amino acid, fatty acids, ions in solution and oxygen to tissues and it receives CO2 and other water materials from tissue.
This means tissue fluid is needed for the exchange of materials between blood and cells
Describe the formation of tissue fluid
When blood is at the arteriole end of a capillary, the hydrostatic pressure is great enough to push molecules out of the capillary
Proteins remain in the blood; the increased protein content creates a water potential between the capillary and the tissue fluid
At the venule end of the capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced
The water potential gradient between the capillary and the tissue fluid remains the same as at the arteriole end, so water begins to flow back into the capillary from the tissue fluid
Overall, more fluid leaves the capillary than returns, leaving tissue fluid behind to bathe cells
If blood pressure is high (hypertension) then the pressure at the arteriole end is even greater
Describe what happens during diastole
- blood returns to the atria of the heart through the pulmonary vein and the vena cava.
- As the atria fill, the pressure in them rises
- When the pressure exceeds that of the ventricles, the atrioventricular valves open allowing the blood to pass into the ventricles (passage of blood aided by gravity)
- Muscular walls of the atria and ventricles are relaxed at this stage
- The relaxation of the ventricle walls causes them to recoil and reduced the pressure within the ventricle = pressure lower than that in the aorta and the pulmonary artery
- this causes the semi-lunar valve in the aorta and the pulmonary artery to close.
