Human Health And Systems

Question 1

Plasma

Answer 1

Liquid part of the blood
Pale yellow
Chemicals (Useful): Food, Hormones
– Chemicals (Waste): CO2, Salts, Urea
– Heat: Generated from chemical reactions, transported around to maintain 37°C
• Also carries the red blood cells, white blood cells, and platelets.

Question 2

Red Blood Cells

Answer 2

Round, flattened discs, curve inward near centre
• Small, no nucleus, formed in bone marrow
• Very numerous – approx 5million per drop blood
• Function : transport oxygen to cells
• Red colour comes from haemoglobin
they contain.
• Haemoglobin picks up oxygen in the lungs
• It later releases it in other parts - e.g. muscle

Question 3

White Blood Cells

Answer 3

• Larger than Red Blood Cells but fewer in number
• No definite shape – shape can change
• They are also made in the bone marrow
• Function : to fight infection
• Some can surround micro-organisms and destroy them
• Others produce proteins called antibodies
• Antibodies help to destroy micro-organisms such as bacteria

Question 4

Platelets

Answer 4

Smaller than red or white blood cells
• They are formed in the bone marrow
• They are formed from larger cells breaking down into pieces
• Function: help to form blood clots
• When a blood vessel is injured, platelets help to form a clot
• Clotting prevents loss of blood, and prevents micro- organisms getting in
• Clots are temporary barriers while repair and healing is taking place

Question 5

Arteries

Answer 5

Carry blood AWAY from the heart
• Flow of blood is strong and at high pressure
• Artery walls are thick and strong to withstand this pressure
• Blood is under pressure – forced to move in one direction
• There is no need for valves in arteries to prevent backwards flow
• All arteries (except pulmonary artery) carry oxygenated blood

Question 6

Veins

Answer 6

Carry blood BACK to the heart
• Flow of blood is weaker and pressure is low
• Vein walls are thinner and weaker than artery walls
• Pressure is low, so there is a danger of backward flow of blood, especially when flow direction is against gravity
• Valves in veins at regular intervals, allow blood to flow forwards, but prevent reverse flow
• All veins (except pulmonary vein) carry deoxygenated blood

Question 7

Capillaries

Answer 7

These are tiny blood vessels
• There are a huge number of them in the body
• Capillaries are found between arteries and veins
• Capillaries have very thin walls which allow materials to pass in and out with the surrounding cells and tissue.

Question 8

The Heart

Answer 8

Is an organ about the size of a clenched fist
• Function: pumps blood around the body
• It pumps blood by contracting periodically
• Cardiac muscle provides the contraction
• Unlike regular muscle, cardiac muscle doesn’t tire easily
• Resting heart rate in adults is about 72 bpm(beats per minute)
• In exercise, the heart beats faster, so that the blood can carry chemicals faster around the body e.g. Oxygen

Question 9

Pulse Rates

Answer 9

When the heart contracts, it squeezes blood into the arteries under pressure.
• As blood flows down the arteries, surges of pressure can be felt where the arteries are close to the surface
• Areas where it can be felt are:
– Atthewrist
– Innerarmnearelbowjoint – Atthesidesoftheneck
• A surge of blood felt at these locations is called a pulse
• The pulse rate is at the same pace as the heart rate

Question 10

Two Blood Circuits

Answer 10

• The human circulatory system has what is known as Double Circulation
• Blood passes through the heart twice on its journey around the body
• It consists of two circuits:
• 1: Pulmonary Circulation
– Bloodleavestheheart
– goestothelungstobecomeoxygenated – returnstotheheart
• 2: Systemic Circulation
– Bloodleavestheheart
– travelstootherpartsofthebody – returnstotheheart