Blood circulatory system

What are the 4 main transport functions of blood?

Oxygen: lungs → body

Carbon dioxide: body → lungs

Nutrients: intestine → body

Urea: liver → kidneysAlso transports: hormones, antibodies, heat.

Why don't single-celled organisms have circulatory systems?

Very high surface area:volume ratio

Diffusion is fast enough

Oxygen diffuses directly through membrane

Whole cell is close to external surface

Why do large animals require circulatory and gas exchange systems?

Low SA:volume ratio → diffusion too slow

Need organs: lungs/gills

Need circulatory system to deliver oxygen + nutrients to all cells

Difference between single and double circulatory system

Single (fish): Heart → gills → body → heart (one circuit)

Double (mammals): Heart → lungs → heart → body → heart

Double allows higher pressure and faster oxygen delivery.

Name the 4 chambers of the heart.

Right atrium

Right ventricle

Left atrium

Left ventricle

Name and locate the 4 heart valves.

Tricuspid → right atrium → right ventricle

Pulmonary (semilunar) → right ventricle → pulmonary artery

Bicuspid/Mitral → left atrium → left ventricle

Aortic (semilunar) → left ventricle → aorta

List the pathway of deoxygenated → oxygenated blood through pulmonary circulation.

Vena cava → R atrium → tricuspid → R ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary veins → L atrium

List the pathway of oxygenated → deoxygenated blood in systemic circulation.

L atrium → bicuspid → L ventricle → aortic valve → aorta → body → veins → vena cava → R atrium

What happens during atrial systole?

Atria fill → pressure rises

AV valves open

Blood → ventricles

Semilunar valves closed

Systole

Definition: The phase of the cardiac cycle when the heart muscles contract to pump blood out of the chambers.

Types:

Atrial systole: Atria contract → push blood into ventricles.

Ventricular systole: Ventricles contract → push blood into arteries (pulmonary artery & aorta).

Key Point: Blood pressure is high in the chambers during systole.

Diastole

Definition: The phase of the cardiac cycle when the heart muscles relax after contraction.

What happens:

Atria and ventricles relax.

Blood flows into the atria from veins (vena cava or pulmonary veins).

Semilunar valves (aortic & pulmonary) close to prevent backflow.

Key Point: Blood pressure is low in the chambers during diastole.

What happens during ventricular systole?

Ventricles contract

AV valves close ("lub")

Pressure increases

Semilunar valves open

Blood ejected into pulmonary artery + aorta

What happens during diastole?

Heart relaxes

Semilunar valves close ("dub")

Blood flows into atria

Cycle restarts

Why is the left ventricle wall thicker than the right?

Pumps at high pressure

Must deliver blood to entire body

Right ventricle pumps only to lungs → low pressure

What is the coronary circulation and why is it essential?

Coronary arteries branch from aorta

Supply oxygen + glucose to heart muscle

Blockage → heart attack (myocardial infarction)

How does the heart rate increase during exercise?

More CO₂ produced

Chemoreceptors detect CO₂

Send signals to medulla

Accelerator nerve stimulated

Heart rate + contraction strength increase

What do the accelerator nerve and vagus (decelerator) nerve do?

Accelerator nerve: increases heart rate & force

Vagus nerve: decreases heart rate & forceBoth controlled by medulla.

Adaptations of arteries for high-pressure blood?

Thick muscular wall

Elastic tissue to stretch/recoil

Small lumen

No valves

Adaptations of veins for low-pressure blood?

Thin walls

Large lumen

Valves to prevent backflow

Blood moved by skeletal muscle contractions

How are capillaries adapted for exchange?

One cell thick → short diffusion distance

Narrow → slow blood flow

Large network → high surface area

List the 4 components of blood.

Plasma

Red blood cells

White blood cells

Platelets

What does plasma transport?

CO₂, urea, nutrients, hormones, heat

Blood cells in suspension

How are red blood cells adapted for oxygen transport?

Biconcave

No nucleus

Packed with haemoglobin

Short diffusion distance

What do phagocytes do?

Engulf pathogens

Form vacuole

Release enzymes

Digest bacteria(Process = phagocytosis)

What do lymphocytes do?

Produce antibodies

Bind to antigens

Cause agglutination / neutralization / lysis

Memory cells → immunity

Why do memory cells provide immunity?

Rapid secondary response

More antibodies produced quickly

Pathogen destroyed before symptoms occur

How do vaccines create immunity?

Inject weakened/dead pathogen or antigens

Lymphocytes respond → form memory cells

Secondary immune response on real infection

How do platelets help blood clot?

Release chemicals → fibrinogen → fibrin

Fibrin forms mesh

Traps RBCs

Forms clot → scab