- In Mammals blood:
Takes oxygen from lungs to organs + muscles
Takes CO2 from organs + muscles to lungs
Takes nutrients from gut to organs + muscles
Takes urea from liver to kidneys
- Also transports heat and hormones
- Single-celled organisms do not have circulatory systems
- Large animals have low surface area to volume ratio, and therefore cannot get oxygen through their surface
- There are two types of circulatory systems:
Single circulatory systems (fish)
Double circulatory systems (mammals)
- There are two parts of “double circulation”:
Pulmonary circulation – blood circulated through the lungs where it is oxygenated.
Systematic circulation – blood is circulated through rest of body and unloads oxygen
- The human circulatory system is made up of:
Blood vessels (carry blood around body)
- Arteries carry blood away from the heart (Arteries = Away)
- Veins carry blood towards the heart (VeINs = In the heart)
- Capillaries carry blood through organs.
Blood (transport medium)
- Main veins + arteries:
Pulmonary Vein – from lungs to heart
Pulmonary Artery – from heart to lungs
Aorta – from heart to organs
Vena Cava – from organs to heart
Hepatic Artery – from heart to liver
Hepatic Vein – from liver to heart
Hepatic Portal Vein – from digestive system to liver
Renal Artery – from heart to kidneys
Renal Vein – from kidneys to heart
- The walls of the heart are made of cardiac muscle.
- Atrium is above, Ventricle is below.
- The medulla controls heart rate.
- Cardiac cycle:
- Blood enters atria and is held there by bicuspid and tricuspid valves.
- Atria contract, raising blood pressure and forcing bicuspid and tricuspid to open.
- Blood enters ventricles, and when they are full they contract, shutting the bicuspid and tricuspid valves.
- Pressure in ventricles rises until semi-lunar valves at base of aorta and pulmonary artery open.
- As ventricles empty, pressure difference closes semi-lunar valves.
- Process is repeated.
· When a chamber of heart contracts it is in systole, when it relaxes it is in diastole.
· Heart rate is controlled by the medulla which reacts to changes in carbon dioxide in blood.
- Arteries are under a lot of pressure, and therefore need to be able to stretch.
- Veins are under small pressure and need to let the blood pass through easily.
Veins contain valves in them which only allow blood to flow in one direction.
· Capillaries need to be small to fit in between cells and allow materials to pass through their walls easily.
· Blood contains 4 main types of cells:
Component of blood
Description of component
Function of component
Liquid part of blood: mainly water
Carries blood cells around body and contains dissolved substances as well as heat
Red blood cells
Biconcave, disk-like, no nucleus
Transport oxygen through haemoglobin
(white blood cell)
(white blood cell)
Same size as red cells and have nucleus
Larger cells with large nucleus
Release chemicals to make blood clot
· Red blood cells are made in bone marrow and have haemoglobin.
· White blood cells protect body against microorganisms.