the cardio-respiratory system - Coggle Diagram
the cardio-respiratory system
Capillaries are a tiny network of blood vessels that link the arteries and veins.
They make diffusion easier (shorter distance for oxygen or carbon dioxide to travel).
They are very small and can only let 1 red blood cell through at a time.
They are only 1 cell thick.
Veins carry blood towards the heart (mostly deoxygenated blood).
Veins have a large internal diameter (lumen) but thin walls as the pressure inside them is low.
Veins have valves to prevent the backflow of blood, which is a possibility due to the lower pressures. This means that they do not have a pulse.
Blood Vessels in the Heart
Listed below are the main blood vessels found in the heart.
A vein that returns deoxygenated (contains no oxygen) blood back to the right atrium.
Carries deoxygenated blood from the right ventricle to the lungs.
Carries oxygenated (contains oxygen) blood from the lungs back to the left atrium.
The largest artery that carries oxygenated blood from the left ventricle to the rest of the body.
Arteries are elasticated and thick. This lets them cope with the high pressures at which blood is pumped away from the thick, muscular ventricles of the heart. This is why you can feel a pulse in them.
Think of the walls of arteries like elastic bands. They can stretch to cope with the high pressures from the heart but then return to their original shape and size. This prevents them from bursting.
Can vasoconstrict and vasodilate
During exercise, the body can vasoconstrict (make the lumen smaller) or vasodilate (make the lumen larger) to distribute blood efficiently.
E.g. the arteries leading to the stomach will vasoconstrict to reduce blood flow to ‘non-essential’ organs. At the same time, the arteries leading to the working muscles will vasodilate to increase blood flow to where the blood is needed most at that time.
Arteries are the largest in external (outer) diameter and have the thickest walls of all blood vessels.
Because they have such thick walls, they have a slightly smaller lumen (internal diameter).
The atria are the top 2 chambers of the heart. They fill up with blood received from the veins.
The right atrium receives deoxygenated blood from the rest of the body through the superior vena cava.
It then pumps blood through to the right ventricle.
The left atrium receives oxygenated blood from the lungs through the pulmonary vein.
It then pumps the blood into the left ventricle.
The atria are small because the body only needs them to pump blood into the next chamber of the heart (ventricle).
These are the bottom 2 chambers of the heart. They pump blood out through the arteries.
Ventricle structure and function
The right ventricle has thinner walls and is less muscular.
This is because less pressure is needed to pump the deoxygenated blood into the lungs via the pulmonary artery.
The left ventricle has a thick, strong wall.
This is because it needs to pump oxygenated blood to the entire body at a high pressure to make sure it gets there.
Right-side of the heart pumps deoxygenated blood.
Left-side of the heart pumps oxygenated blood.
Not all of the chambers contract at once. The atria contract together first, quickly followed by the ventricle. This is why we hear a ‘lub-dub’ sound.
The Structure of the Heart
The atria are the top 2 chambers of the heart. They fill up with blood received from the veins. The ventricles are the bottom 2 chambers of the heart. They pump blood out through the arteries.
Cardiac Cycle (Deoxygenated Blood)
Blood will travel through a specific pathway during the cardiac cycle:
Deoxygenated blood travels from the body to the right atrium, via the vena cava.
The atrium contracts and blood is pushed through a valve (to prevent backflow) into the right ventricle.
The right ventricle then contracts and pumps blood through the pulmonary artery.
The pulmonary artery carries the deoxygenated blood to the lungs where gaseous exchange takes place.
Cardiac Cycle (Oxygenated Blood)
Having been oxygenated in the lungs, blood then travels along the pulmonary vein back to the heart.
The atrium then contracts and pushes the oxygenated blood through another valve (to prevent backflow) and into the left ventricle.
The left ventricle then contracts to pump blood into the aorta (out to the rest of the body) at a high pressure.
Gaseous exchange in the lungs causes the blood to become oxygenated.
Oxygenated blood enters the left atrium from the pulmonary vein.
Systole and Diastole
Systole is the process of contracting and pumping out blood. Diastole is the process of relaxing and filling up with blood. The heart beats in 2 phases, both of which involve systole and diastole:
Stage 1: atrial systole and ventricular diastole
Firstly, the atria contract together and pump out blood (atrial systole) into the ventricles.
While this happens, the ventricles relax and fill with blood (ventricular diastole).
Stage 2: ventricular systole and atrial diastole
Secondly, the ventricles contract to pump blood out of the heart (ventricular systole).
While this happens, the atria relax and fill with blood (atrial diastole).
Vasoconstriction is the narrowing (constriction) of blood vessels by small muscles in their walls. When blood vessels constrict, blood flow is slowed or blocked.