Biology
11 SC&T/CS&T
The human circulatory system consists of several circuits:

The pulmonary circuit provides blood flow between the heart and lungs.

The systemic circuit allows blood to flow to and from the rest of the body.

The coronary circuit strictly provides blood to the heart (not pictured in the figure below).
Blood and blood vessels
Blood from the heart is pumped throughout the body using blood vessels. Arteries carry blood
away from the heart and into capillaries, providing oxygen (and other nutrients) to tissue and
cells. Once oxygen is removed, the blood travels back to the lungs, where it is re-oxygenated
and returned by veins to the heart.
Arteries
Carry blood away from the heart (always oxygenated apart from the pulmonary artery which
goes from the heart to the lungs). Therefore, blood is under high pressure.
Features:

Have thick muscular walls.

Have small passageways for blood (narrow lumen).

Smooth endothelium and no valves present
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Veins
Carry blood to the heart (always deoxygenated apart from the pulmonary vein which goes
from the lungs to the heart). Blood is therefore travelling under low pressure with the
tendency to back flow.

Have thin walls.

Have larger passageways for blood (wide lumen).

Have valves to prevent blood flowing backwards.
Capillaries

Where gas exchange takes place - oxygen passes through the capillary wall and into
the tissues, while carbon dioxide passes from the tissues into the blood. Therefore,
very low blood pressure exists in the capillaries.

Hair-like

Microscopic – one cell thick.

Permeable because cells making up their walls are not fused; gaps exist between cells.
Class Assignment (10% November grade)
1. Distinguish between Atherosclerosis and Arteriosclerosis. (Write you answer in your note
book)
[10 marks]
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Organ
This table
veins that
the lungs,
1.
Towards organ
Away from organ
Lung
Pulmonary artery
Pulmonary vein
Liver
Hepatic artery
Hepatic vein
Kidney
Renal artery
Renal vein
lists the arteries and
are associated with
liver and kidneys.
Blood Cells
This table explains the functions of various blood components.
Component
Function(s)
Plasma
Transporting carbon dioxide, digested food, urea, hormones and heat
Red blood cells
Transporting oxygen
White blood cells
Ingesting pathogens and producing antibodies
Platelets
Involved in blood clotting
Red blood cells
Red blood cells transport oxygen for aerobic respiration. They must be able to absorb oxygen in
the lungs, pass through narrow blood vessels, and release oxygen to respiring cells.
Red blood cells have adaptations that make them suitable for this:

they contain haemoglobin - a red protein that combines with oxygen

they have no nucleus so they can contain more haemoglobin

they are small and flexible so that they can fit through narrow blood vessels

they have a biconcave shape (flattened disc shape) to maximize their surface area for oxygen
absorption

They have very thin walls for easy diffusion
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Lymphocytes
About 25 per cent of the white blood cells are lymphocytes. They are part of the body’s immune
system and produce soluble proteins called antibodies
Antibodies
Antibodies attach to antigens. Antigens are substances found on the surface of cells,
including bacteria and other pathogens. Different antibodies attach to different antigens. In this
way, the body’s immune system can recognise foreign antigens – antigens that are not
normally produced by the body, but by pathogens instead.
Antibodies can neutralise toxins produced by pathogens. They can also cause the destruction of
pathogens by:

causing bacteria to burst open and die

labelling the pathogen so that it is recognised more easily by phagocytes

sticking pathogens together in clumps so that they can be engulfed by phagocytes more
easily
Phagocytes
About 70 per cent of the white blood cells are phagocytes. They are part of the body’s immune
system, but they do not produce antibodies. Instead, they ingest and destroy pathogens such
as bacteria.
This is what happens:
1. the phagocyte surrounds the bacterial cell, enclosing it in a vacuole
2. enzymes are secreted into the vacuole to destroy the bacterial cell
Blood clotting
If the skin is cut, the wound must be closed to prevent blood loss and the entry
of pathogens. The formation of a scab does just that.
Blood contains tiny fragments of cells called platelets. These platelets are involved in blood
clotting and scab forming.
Class Assignment ( 10 % of Monthly grade - November)
1. Describe how blood moves through the heart.
2. Describe the steps involved in the clotting of blood. Include in your answer blood
proteins, enzymes and clotting factors. (write your answer in your note book)
3. State five functions of blood plasma
[10 marks]
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