Biology - Human Circulation

All mammals, including humans are multicellular organs and have a small surface area to volume ratio. They cannot rely on diffusion alone for gas exchange and thus need a transport system to deliver oxygen and remove carbon dioxide from their bodies. That's why all mammals have a circulatory system.

Blood

• Complex, reddish fluid that is used to transport gases and nutrients

• Removes waste products from cells

Blood components

• Plasma

• RBCs

• WBCs and Platelets

Red blood cells

• Specialised cells that carry oxygen around the body and remove carbon dioxide

• Contain a special protein called haemoglobin

• No nucleus to make more space for haemoglobin and so, more oxygen

• Biconcave shape that allows them to easily bend through narrow blood vessels

• Most abundant cell in our body

• Blood appears red due to RBCs

Phagocytes

Specialised cells that attack and destroy pathogens

Lymphocytes

• Identify and remember specific pathogens to help the body fight against then

• After infection , they provide immunity against future infections by producing antibodies which help the body “remember” the pathogen.

Antibodies

• Y shaped proteins that attach to pathogens via antigens

• Pathogens are then destroyed by phagocytosis

Platelets

• Activates when there is a wound to form blood clots

• Blocks the wound and prevents blood loss and pathogens from entering the bloodstream

Blood groups

• Based on antigens

• Important for blood donation

• A, B, AB, O

Arteries

• Carry oxygenated blood from the heart to cells

• Thicker muscular and elastic walls

• Narrow lumen for blood to flow at a high pressure so oxygenated blood arrives to cells as quickly as possible

Veins

• Carry deoxygenated blood from the cells to the heart

• Thinner muscular walls

• Wider lumen which allows the blood to flow under low pressure

• Have valves that prevent backflow of blood

Capilleries

• smallest blood vessels

• made of one layer of cells to exchange nutrients, gases and fluids between blood and cells in tissues by diffusion

Heart

• large, muscular organ

• pumps blood around the body to ensure that the cells and tissues are supplied with oxygen which they use during respiration to produce energy

Heart structure

Four chambers

Upper chambers - atria

Lower chambers - ventricles

Four major blood vessels

Vena cava - largest vein in the body, delivers deoxygenated blood to the heart from the rest of the body

Pulmonary artery - only artery in the body that delivers deoxygenated blood. The blood goes to the lungs from the heart.

Aorta - largest artery in the body, delivers oxygenated blood to the rest of the body from the heart.

Pulmonary vein - only vein in the body which delivers oxygenated blood. The blood goes from the heart to the lungs.

Valves

close the atria to prevent backflow.

Right side - tricuspid valve and pulmonary valve

Left side- mitral/bicuspid valve and aortic valve

The heart is made out of cardiac muscle that work automatically.

The heart is divided into two sides by a thick muscular wall called the septum. This keeps the oxygen-rich blood from mixing with the oxygen-poor blood.

Blood circulation

• blood flows through the heart twice [double circulation]

• heart receives deoxygenated blood from body and oxygenated blood is quickly sent to the cells where they are used to produce energy