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. Maintains High Blood Pressure for Efficient Oxygen Delivery

 Systemic circuit (body): The left ventricle pumps oxygenated

blood at high pressure to all body tissues, ensuring rapid delivery
of oxygen and nutrients.

 Pulmonary circuit (lungs): The right ventricle

pumps deoxygenated blood at lower pressure to the lungs to
avoid damaging delicate capillaries.

 Single circulation (e.g., fish) cannot maintain high pressure in

both circuits, making it inefficient for large, active animals.

2. Prevents Mixing of Oxygenated & Deoxygenated Blood

 The septum (heart wall) and four chambers keep oxygen-rich and
oxygen-poor blood separate, maximizing oxygen supply to tissues.

 In fish, blood mixes in the heart, reducing oxygen efficiency.

3. Supports Endothermy (Warm-Bloodedness)

 Mammals need constant body temperature, requiring more

oxygen for cellular respiration and heat production.

 Double circulation ensures fast, high-volume oxygen delivery,

unlike single circulation in ectothermic (cold-blooded) animals like
fish.

4. Meets High Metabolic Demands

 Active mammals (e.g., humans, dogs) need continuous energy for

movement, digestion, and brain function.

 Double circulation supplies oxygen and glucose faster than single

circulation.

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:

 Structure of Capillaries Facilitating Exchange:

 Thin Walls: Capillary walls are only one cell thick (endothelial
cells), providing a very short diffusion distance for substances to
move between the blood and tissue fluid (interstitial fluid).

 Narrow Lumen: The lumen (internal diameter) of capillaries is very

narrow, often only wide enough for red blood cells to pass through in
single file. This slows down blood flow, increasing the time available
for exchange.

 Extensive Network: Capillaries form vast, branching networks

(capillary beds) within tissues, providing a huge total surface area
for efficient exchange.

 2. The Role of Tissue Fluid (Interstitial Fluid):

 Substances don't directly move from blood into cells. Instead, they
first move from the blood into the tissue fluid (also known as
interstitial fluid), which bathes the cells. Exchange then occurs
between the tissue fluid and the cells.

 3. Mechanisms of Exchange:

 The exchange is driven by differences in hydrostatic pressure

(blood pressure) and osmotic pressure (due to protein
concentration), as well as concentration gradients.

 At the Arterial End of the Capillary (Fluid Outflow):

 High Blood Hydrostatic Pressure (BHP): At the arterial end, the

blood pressure inside the capillary is relatively high (around 35
mmHg). This pressure is greater than the opposing forces (tissue
fluid hydrostatic pressure and blood osmotic pressure).
 Fluid Filtration: This high BHP forces water, small solutes (like
glucose, amino acids, ions, oxygen), and small waste products out of
the capillary and into the surrounding tissue fluid. Larger molecules
like plasma proteins and blood cells are generally too large to pass
through the capillary walls, so they remain in the blood.

 Mid-Capillary:

 As fluid leaves the capillary, the BHP gradually drops.

 The blood osmotic pressure (BOP), largely due to the plasma

proteins that remain in the blood, becomes relatively more
significant as fluid has left the capillary, increasing the
concentration of solutes in the blood.

 At the Venous End of the Capillary (Fluid Reabsorption):

 Lower Blood Hydrostatic Pressure: At the venous end, the blood

pressure inside the capillary has dropped significantly (around 15
mmHg).

 Higher Blood Osmotic Pressure: The concentration of solutes

(especially plasma proteins) in the blood is now relatively higher
than in the tissue fluid.

 Fluid Reabsorption: Due to the higher blood osmotic pressure

(which draws water in) compared to the lower blood hydrostatic
pressure, most of the fluid (about 85-90%) from the tissue fluid is
drawn back into the capillary by osmosis.

 4. Exchange of Specific Substances:

 Oxygen (O2): Diffuses from the blood (high O2 concentration) in

the capillaries, through the tissue fluid, and into the cells (low O2
concentration, as it's used in respiration).

 Carbon Dioxide (CO2): Diffuses from the cells (high CO2

concentration, as it's a waste product of respiration), through the
tissue fluid, and into the blood (low CO2 concentration).

 Glucose & Amino Acids: Diffuse from the blood (high

concentration, after absorption from digestion) into the tissue fluid
and then into the cells (low concentration, as they are used for
energy or building blocks).

 Waste Products (e.g., Urea): Diffuse from cells (high

concentration, as waste products) into the tissue fluid and then into
the blood (low concentration) to be transported to excretory organs
(like the kidneys).
  Hormones: Released into the blood and diffuse into the tissue fluid
to reach target cells.

 Ions: Move based on concentration gradients and electrochemical

gradients, often involving pumps or channels in cell membranes.

 In summary, the exchange process in capillaries is a dynamic

interplay of hydrostatic and osmotic pressures that drives fluid
movement, combined with diffusion along concentration gradients
for gases and solutes, ensuring that every cell in the body is
supplied with what it needs and cleared of waste. The remaining
tissue fluid that doesn't return to the capillaries is collected by the
lymphatic system.

 .

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.

4️. 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.

THE LYMPHATIC SYSTEM

The lymphatic system, or lymphoid system, is an organ system in

vertebrates that is part of the immune system and complementary to the
circulatory system.

FUNCTIONS OF THE LYMPHATIC SYSTEM

1. Tissue fluid drainage and fluid balance:

The lymphatic system collects excess tissue fluid (interstitial fluid) that
leaks out of blood capillaries and returns it to the circulatory system via
the subclavian veins. This prevents oedema (swelling) and helps maintain
blood volume and pressure.

2. Absorption of dietary lipids:

In the small intestine, specialised lymphatic vessels called lacteals absorb
dietary lipids and fat-soluble vitamins (A, D, E, K) from the intestinal villi.
The absorbed lipids are transported as chylomicrons via the lymph into
the bloodstream.
3. Immune function and defence:
The lymphatic system transports lymph, which contains lymphocytes (B
cells and T cells), antigen-presenting cells, and antibodies. Lymph nodes
filter the lymph, trapping pathogens, cellular debris, and foreign particles.
Within lymph nodes, lymphocytes can detect antigens and initiate
immune responses, leading to the production of specific antibodies or the
activation of cytotoxic T cells.

4. Transport of large molecules:

The lymphatic system helps transport large molecules (such as proteins)
that cannot easily return to the blood capillaries directly.

In summary, the lymphatic system acts as a drainage system for excess

tissue fluid, a pathway for fat absorption from the digestive tract, and a
key player in the body's defense against disease.
 THE CIRCULATORY SYSTEM

The cardiac cycle describes the complete sequence of events in the heart
from the beginning of one heartbeat to the beginning of the next. It's
fundamentally divided into two main phases: systole and diastole, which
refer to the contraction and relaxation phases of the heart chambers

1. Diastole (Relaxation and Filling)

Diastole is the relaxation phase of the heart, during which the chambers
fill with blood. It's generally longer than systole, especially at slower heart
rates, allowing adequate time for ventricular filling.

 Atrial Diastole:

o Both atria are relaxed.

o Blood from the body (via the superior and inferior vena cava)
flows into the right atrium.

o Blood from the lungs (via the pulmonary veins) flows into the
left atrium.

o The atrioventricular (AV) valves (tricuspid on the right, mitral

on the left) are open, allowing blood to passively flow from the
atria into the ventricles. This accounts for about 70-80% of
ventricular filling.

 Ventricular Diastole:

o Both ventricles are relaxed.

o They are filling with blood passively from the atria.

o The semilunar valves (pulmonary on the right, aortic on the

left) are closed, preventing backflow of blood from the arteries
into the ventricles.

2. Systole (Contraction and Ejection)

Systole is the contraction phase of the heart, during which blood is

pumped out of the chambers.

 Atrial Systole:

o The atria contract (stimulated by the SA node, the heart's

natural pacemaker).

o This contraction pushes the remaining 20-30% of blood into

the ventricles, "topping off" their volume. This is sometimes
called the "atrial kick."
 o At the end of atrial systole, the ventricles are fully loaded with
blood.

 Ventricular Systole:

o Isovolumetric Contraction: The ventricles begin to

contract. For a very brief moment, all four heart valves are
closed. The pressure inside the ventricles rapidly increases,
but no blood is ejected yet (hence "isovolumetric" – volume is
constant).

o Ventricular Ejection: When the pressure inside the

ventricles exceeds the pressure in the great arteries
(pulmonary artery from the right ventricle, aorta from the left
ventricle), the semilunar valves (pulmonary and aortic) are
forced open.

o Blood is then rapidly ejected from the right ventricle into the
pulmonary artery (to the lungs) and from the left ventricle into
the aorta (to the rest of the body).

o During this phase, the AV valves (tricuspid and mitral) are

closed, preventing backflow into the atria.

The Cycle Continues

After ventricular systole, the ventricles relax, the semilunar valves snap
shut (producing the "dub" sound of the heartbeat), and the entire cycle
returns to diastole as the chambers begin to fill again. The closing of the
AV valves at the beginning of ventricular systole produces the "lub" sound.

Essentially, the cardiac cycle is a precisely coordinated series of

contractions (systole) and relaxations (diastole) of the heart's atria and
ventricles, ensuring efficient pumping of blood throughout the body.