circulatory system(3.5) Flashcards
how do humans have a closed double circulatory system
blood passes through the heart twice, the right side of the heart pumps deoxygenated blood to the lungs blood then returns to the left side of the heart so oxygenated blood can be pumped around the body at high pressure.
describe the main vessels to the heart
pulmonary artery-carries deoxygenated blood from the right ventricle to the lungs
vena cava-carries deoxygenated blood into the right atrium
pulmonary vein-carries oxygenated blood from the lungs to the heart
aorta-carries oxygenated blood out of the heart to the rest of the body.
what are arterioles
arteries branch into narrower blood vessels called arterioles which transport blood into the capillaries
describe the structure of the arteries
-thick elastic layer
-narrow lumen
-thick muscular layer
describe the structure of the veins
-wider lumen
-thin elastic layer
-thin muscle layer
-has valves
describe arterioles compared to arteries
-thinner layer of elastic fibres
-thicker layer of muscle to control and stop blood flow
describe the structure of capillaries
-one cell thick
-narrow diameter lumen
-form capillary beds
what is tissue fluid
liquid that surrounds cells containing oxygen ,amino acids ,glucose ,ions and fatty acids
how is tissue fluid formed
-at the arteriole end of the capillaries there is a high hydrostatic pressure this forces liquid and small molecules through the gaps in the capillaries
what molecules remain in the capillary
-large proteins
-platelets
-red blood cells
how is tissue fluid returned to the capillaries
-the large proteins that remain in the capillaries create a lowered water potential
-at the venule end of the capillary the hydrostatic pressure is lowered due to the loss of liquid
-the water potential gradient between the tissue fluid and capillary causes water to flow back into the capillaries
how is excess tissue fluid returned to the circulatory system
-absorbed by the lymphatic system
-eventually drains back into bloodstream
describe diastole in the cardiac cycle
-the ventricles and atria are relaxed
-blood enters the atria via the vena cava and pulmonary vein
-this blood flow into the atria increases pressure within the atria
describe atrial systole in the cardiac cycle
-the atria muscular walls contract futher increasing the pressure
-the pressure in the atria exceeds the pressure in the ventricles causing the AV valves to open and blood to flow into the ventricles
-the ventricles are in diastole at this point
Describe ventricular systole in the cardiac cycle
-the ventricle walls contract increasing the pressure beyond that of the atria so the AV valves close and the semilunar valves open
-blood is forced out the ventricles into the pulmonary artery and aorta.
