B12

Circulatory system

A system of blood vessels with a pump (heart) and valves to ensure one

Double circulation

Blood passes through the heart twice in one complete circuit (heart → lungs → heart → body → heart).

Pulmonary circulation

Movement of blood between the heart and lungs.

Systemic circulation

Movement of blood between the heart and the rest of the body.

Heart

A muscular organ that pumps blood around the body.

Muscular wall (myocardium)

Thick muscle layer that contracts to pump blood.

Septum

Wall separating the left and right sides of the heart.

Atrium (atria)

Upper chambers that receive blood.

Ventricle

Lower chambers that pump blood out of the heart.

Valves

Structures that prevent backflow of blood.

Coronary arteries

Blood vessels supplying oxygenated blood to the heart muscle.

Heartbeat / cardiac cycle

Sequence of atrial contraction → ventricular contraction → relaxation.

Atrial contraction

Atria contract to push blood into ventricles.

Ventricular contraction

Ventricles contract to pump blood out of the heart

ECG (electrocardiogram)

Measures electrical activity of the heart.

Pulse rate

Number of heartbeats per minute.

Arteries

Blood vessels carrying blood away from the heart (high pressure).

Veins

Blood vessels carrying blood back to the heart (have valves).

Capillaries

Tiny blood vessels where exchange of substances occurs.

Blood

Fluid that transports substances around the body.

Plasma

Liquid part transporting cells, nutrients, hormones, CO₂, and ions.

Red blood cells (erythrocytes)

Cells that carry oxygen using haemoglobin.

Haemoglobin

Protein in red blood cells that binds oxygen.

White blood cells (leukocytes)

Cells that defend against disease.

Phagocytosis

Process where white blood cells engulf pathogens.

Antibodies

Proteins produced to destroy specific pathogens.

Platelets

Cell fragments that help blood clot.

Gas exchange

Process of oxygen entering blood and carbon dioxide leaving.

Alveoli

Tiny air sacs where gas exchange occurs.

Diffusion

Movement of particles from high to low concentration.

Larynx

Voice box.

Trachea

Windpipe carrying air to bronchi.

Bronchi

Two tubes leading into lungs.

Bronchioles

Smaller branches of bronchi.

Capillaries (lungs)

Surround alveoli for gas exchange.

Inspired air

More oxygen, less carbon dioxide, less water vapour.

Expired air

Less oxygen, more carbon dioxide, more water vapour.

Coronary heart disease (CHD)

Blockage of coronary arteries reducing blood flow to the heart.

Atherosclerosis

Buildup of fatty deposits in arteries.

Emphysema

Damage to alveoli → reduced surface area.

COPD (Chronic Obstructive Pulmonary Disease)

Longterm breathing disease (includes emphysema + chronic bronchitis).

Causes of lung diseases

Smoking, pollution, infections.

Independent variable

The factor you change (e.g. exercise intensity).

Dependent variable

The factor you measure (e.g. heart rate).

Control variables

Factors kept constant for a fair test.

Heart rate investigation

Measure pulse before and after exercise.

Breathing rate investigation

Measure breaths per minute at different activity levels.

Validity

Whether the experiment measures what it is supposed to.

Reliability

Consistency of results (repeat trials).