iGCSE Biology - Blood and Circulation

 

• 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:

                Heart (pump)

                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:

Sorry, diagrams don;t work in text, so refer to image.

1. Blood enters atria and is held there by bicuspid and tricuspid valves.
2. Atria contract, raising blood pressure and forcing bicuspid and tricuspid to open.
3. Blood enters ventricles, and when they are full they contract, shutting the bicuspid and tricuspid valves.
4. Pressure in ventricles rises until semi-lunar valves at base of aorta and pulmonary artery open.
5. As ventricles empty, pressure difference closes semi-lunar valves.
6. 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
Plasma	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
Lymphocytes (white blood cell) Phagocytes (white blood cell)	Same size as red cells and have nucleus Larger cells with large nucleus	Produce antibodies     Engulf bacteria
Platelets	Smallest cells	Release chemicals to make blood clot

·        Red blood cells are made in bone marrow and have haemoglobin.

·        White blood cells protect body against microorganisms.