TRANSPORT SYSTEM IN HUMANS

1. Superior vena cava

 Carries deoxygenated blood from the upper body (head, arms)

to the right atrium.

2. Pulmonary vein

 Carries oxygenated blood from the lungs to the left atrium (the
only veins carrying oxygen-rich blood).

3. Right atrium

 Receives deoxygenated blood from the body (via vena cava) and
pumps it into the right ventricle.

4. Pulmonary valve

 A one-way valve that stops blood from flowing back into the right
ventricle after it’s pumped to the lungs.

5. Tricuspid valve

 Prevents backflow of blood from the right ventricle back into

the right atrium.

6. Inferior vena cava

 Carries deoxygenated blood from the lower body (legs,

abdomen) to the right atrium.
7. Right ventricle

 Pumps deoxygenated blood to the lungs via the pulmonary

artery (thinner wall than left ventricle).

8. Aorta

 The largest artery; carries oxygenated blood from the left

ventricle to the entire body.

9. Pulmonary artery

 Carries deoxygenated blood from the right ventricle to

the lungs (the only artery carrying oxygen-poor blood).

10. Left atrium

 Receives oxygenated blood from the pulmonary veins and pumps

it into the left ventricle.

11. Mitral valve (bicuspid valve)

 Stops blood from flowing back from the left ventricle into the left
atrium.

12. Aortic valve

 Prevents oxygenated blood in the aorta from flowing back into

the left ventricle.

13. Left ventricle

 Pumps oxygenated blood to the whole body via the aorta (has
the thickest muscle wall for high pressure).

FUNCTION OF THE CIRCULATORY SYSTEM

• To move nutrients, gases and wastes to and from cells throughout the
body, and to stabilize body temperature, pH such that cells can carry out
their functions. In other word the circulatory system provides a rapid mass
flow of materials around the body over distances where diffusion could be
slow.

• It regulates the body’s temperature and increases blood flow to meet

demands during exercise.

• This system also sends parts of the immune system (white blood cells
and antibodies) to fight off foreign substances upon their invasion. Should
injury or bleeding occur, it sends clotting cells and proteins to help stop
bleeding and promote healing.
  An efficient circulatory system must have the pump (heart) which
brings about momentum.

 It must have the fluid which is pumped or circulated around the

body.

 There must be vessels/tubes through which the fluid/blood flows

as it is pumped.  The human circulatory system is made up of the
heart and blood vessels (capillaries, veins and arteries)

THE BLOOD VESSELS

The main blood vessels are;

Aorta – main artery carrying oxygenated blood from the heart to the rest
of the body

Vena cava - carries deoxygenated from the rest of the body back to heart.

Pulmonary vein – carrying oxygenated blood from the lungs to the heart
Pulmonary artery – conveys deoxygenated from the heart blood to the
lungs

Hepatic artery – carries blood to the liver

Hepatic portal vein – conveys blood rich with absorbed food nutrients from
the alimentary canal

Hepatic vein – carries blood from the liver towards the heart

Renal artery – conveys blood to the kidneys

Renal vein – carries blood from the kidneys

IMPORTANCE OF DOUBLE CIRCULATION

1. Complete Separation of Oxygenated and Deoxygenated

Blood:

o In a double circulatory system, blood is pumped twice by the

heart in one complete circuit. This creates two distinct loops:
the pulmonary circulation (heart to lungs and back) and the
systemic circulation (heart to body and back).

o This complete separation ensures that oxygenated blood

(coming from the lungs) never mixes with deoxygenated
blood (returning from the body tissues).

o Justification: Mixing would reduce the oxygen concentration

of the blood delivered to the body tissues, making oxygen
delivery less efficient. Humans have high metabolic rates and
oxygen demands, so delivering blood with the highest possible
oxygen concentration is crucial.

2. Maintenance of High Systemic Blood Pressure:

After blood has travelled through the very fine capillaries of the lungs
(the pulmonary circulation) to pick up oxygen and release carbon
dioxide, its pressure drops significantly. This is because the capillaries
are very narrow and offer a lot of resistance to blood flow, which is
necessary for efficient gas exchange.

 The Need for Re-pumping: If this now oxygenated blood were to

continue directly from the lungs to the rest of the body without
being re-pressurized, its flow would be too slow and inefficient. It
wouldn't have enough force to reach all the distant tissues of the
body (like your brain, muscles, or toes) quickly and effectively.

 The Role of the Left Side of the Heart: This is where the crucial
re-pumping action of the heart comes in.

o The oxygenated blood returns from the lungs to the left

atrium.
 o From the left atrium, it moves into the powerful left
ventricle.

o The left ventricle then contracts strongly to re-pump this

oxygenated blood into the aorta (the body's main artery),
sending it out to the entire systemic circulation at a
consistently high pressure.

 Justification (Why High Pressure is Necessary):

o Overcoming Resistance: It provides the necessary force to

overcome the resistance offered by the vast network of
arteries, arterioles, and capillaries throughout the body.

3. Efficient Oxygen Delivery to Meet High Metabolic Demands:

o Humans are endothermic, meaning we maintain a constant,

high body temperature, which requires a continuous and large
supply of energy. This energy is produced through aerobic
respiration, which requires a constant and efficient supply of
oxygen.

Justification: The combination of separate oxygenated blood and high

systemic pressure ensures that oxygen is delivered to all cells quickly and
in sufficient quantities to support high metabolic rates, locomotion, and
maintaining body temperature.

In contrast to single circulation (e.g., in fish): In a single circulation,

blood flows from the heart, to the respiratory organs (gills), and then
directly to the rest of the body before returning to the heart. This system
suffers from a significant drop in blood pressure after the gills, meaning
blood flows to the body tissues at a much lower pressure and slower
speed, which is less efficient for animals with high metabolic rates.

FUNCTION OF BLOOD COMPONENTS IN THE DEFENCE MECHANISM

1 Platelets & Fibrin. (Blood Clotting)

Function: Prevents excessive blood loss and blocks pathogens from

entering wounds.

 Platelets (thrombocytes) stick to damaged blood vessels and form

a temporary plug.

 Fibrin (a protein) forms a mesh that traps blood cells, creating

a scab.

 Importance: Stops bleeding and prevents infections.

2. White Blood Cells – Lymphocytes (Antibody Production)

Function: Recognizes and neutralizes pathogens (e.g., bacteria, viruses).

A) Natural Immunity (Inborn Defence)

 Lymphocytes produce antibodies when infected.

 Memory cells remain in the body, providing long-term

immunity against the same pathogen.

B) Artificial Immunity (Vaccination)

 Vaccines contain weakened/dead pathogens.

 Lymphocytes produce antibodies and memory cells without

causing disease.

 Example: Measles vaccine trains the body to fight future infections.

3. White Blood Cells – Phagocytes (Phagocytosis)

Function: Engulfs and digests pathogens.

 Phagocytes detect foreign cells (e.g., bacteria) and engulf them.

 Enzymes inside the phagocyte break down the pathogen.

 Example: Macrophages patrol the bloodstream, destroying harmful

microbes.

EXCHANGE OF SUBSTANCES BETWEEN CELLS AND BLOOD.

The exchange happens mainly in the capillaries, which are tiny blood
vessels that connect arteries to veins.

Substances Moving from Blood to Cells:

 Oxygen (O₂): for respiration.

 Glucose: for energy production.

 Amino acids: for building proteins.

 Hormones: to regulate cell activities.

 Water: to maintain balance.

Substances Moving from Cells to Blood:

 Carbon dioxide (CO₂): waste from respiration.

 Urea: waste from protein metabolism.

 Other waste products: to be removed by kidneys or lungs.

How it works:

 Blood arrives in capillaries carrying oxygen, glucose, amino acids,

and other nutrients.

 The walls of capillaries are thin (one cell thick) to allow easy
diffusion.

 Substances move from the blood into the tissue fluid, and from the
tissue fluid into cells.

Process involved:

 Diffusion: movement of substances from high to low concentration.

 Osmosis: movement of water across a semi-permeable membrane.

 Active Transport: for substances that move against the

concentration gradient (requires energy).

Role of Tissue Fluid:

 Tissue fluid (interstitial fluid) surrounds cells

 Acts as a medium through which substances pass between

capillaries and cells. (Why? it allows for the direct transport of
nutrients and waste products between the two.)

Blood Vessel Structure & Blood Diseases

STROKE

Causes:

Blood vessel problem:

 Usually caused by:

o Blocked artery (ischaemic stroke): A clot blocks blood
flow in brain arteries.
o Burst artery (haemorrhagic stroke): Weak blood vessel
wall (aneurysm) bursts, causing bleeding in the brain.

Structure link:

 Arteries supplying the brain become narrowed by

atherosclerosis (fatty plaques).
 The walls may become weak or stiff, making them prone to
bursting.
 Blocked or burst arteries stop oxygen from reaching brain cells
→ brain damage.

Cardiac Arrest

Blood vessel problem:

 Sudden stop in heart’s function — not always due to blood

vessels, but can be caused by:
o Severe blockage in coronary arteries.
o Damage to heart muscle from previous heart disease.

Structure link:

 Blocked coronary arteries (due to plaque) reduce blood flow to

heart muscle.
 This affects the heart's electrical system, possibly leading to
cardiac arrest.

3️.Coronary Heart Disease (CHD)

Blood vessel problem:

 Coronary arteries (supply heart muscle) become narrowed or

blocked by fatty deposits (plaque).

Structure link:

 Healthy coronary arteries are wide and elastic, allowing good

blood flow.
 In CHD:
o Plaque builds up inside the artery walls (atherosclerosis).
o Artery walls become narrow, stiff, less elastic.
o Less oxygen reaches heart muscle → chest pain (angina),
or heart attack if fully blocked.
4️⃣ Hypertension (High Blood Pressure)

Blood vessel problem:

 Long-term high pressure in arteries.

Structure link:

 Arteries are normally elastic to absorb pressure.

 In hypertension:
o Artery walls become thickened and less elastic.
o Narrowed lumen (inside space) increases resistance.
o The heart works harder to push blood → raises blood
pressure further.
 Can lead to damage in kidneys, eyes, brain, and heart.