Anatomy of Blood

Source : http://www.ivy-rose.co.uk/HumanBody/Blood/Blood_StructureandFunctions.php


1.

The Functions of Blood
(generally - as opposed to the functions of particular components of blood).
2.

The Composition of Blood
(incl. the different types of blood cells and their properties and functions).
3.

Process of Oxygenation of Tissues due to Circulation of Blood
4.

Types of Leucocytes (White Blood Cells)


1. Functions of Blood


Transports:

Dissolved gases (e.g. oxygen, carbon dioxide);

Waste products of metabolism (e.g. water, urea);

Hormones;

Enzymes;

Nutrients (such as glucose, amino acids, micro-nutrients (vitamins & minerals), fatty acids, glycerol);

Plasma proteins (associated with defence, such as blood-clotting and anti-bodies);

Blood cells (incl. white blood cells 'leucocytes', and red blood cells
'erythrocytes').
2. Maintains Body Temperature

3. Controls pH. The pH of blood must remain in the range 6.8 to 7.4, otherwise it begins to damage cells.

4.Removes toxins from the body

The kidneys filter all of the blood in the body (approx. 8 pints), 36 times every 24 hours. Toxins removed from the blood by the kidneys leave the body in the urine.
(Toxins also leave the body in the form of sweat.)
5.

Regulation of Body Fluid Electrolytes

Excess salt is removed from the body in urine, which may contain around 10g salt per day
(such as in the cases of people on western diets containing more salt than the body requires).

2. Composition of Blood

Blood consists of many components (constituents).
These include:
55% Plasma

45% Components, i.e. 'Blood Cells'.

Of these, 99% are erythrocytes (red blood cells) and 1% are leucocytes (white blood cells) and thrombocytes (blood platelets).


The summary chart above includes: erythrocytes (red blood cells), thrombocytes (blood platelets) and leucocytes (white blood cells). It also includes categories of leucocytes: agranulocytes and granulocytes (also known as polymorphonucleocytes), which may also be sub-divided into lymphocytes, monocytes, basophils, neutrophils and eosinophils.


The following table includes further general information about the constituents of blood.

Structure

Functions

Plasma

Normal blood plasma is 90-92 % water.
This is the straw-coloured fluid in which the blood cells are suspended, and consists of:

The medium in which the blood cells are transported around the body (by the blood vessels) and are able to operate effectively.

Helps to maintain optimum body temperature throughout the organism.

Helps to control the pH of the blood and the body tissues, maintaining this within a range at which the cells can thrive.

Helps to maintain an ideal balance of electrolytes in the blood and tissues of the body.


Dissolved substances including electrolytes such as sodium, chlorine, potassiun, manganese, and calcium ions;

Blood plasma proteins (albumin, globulin, fibrinogen);

Hormones.
Erythrocytes
(Red blood
cells)

Immature erythrocytes have a nucleus but mature erythrocytes have no nucleus.

Carry oxygen (process described in more detail - below).

Haem

Erythrocytes have a "prosthetic group" (meaning "in addition to" - in this case, in addition to the cell). The active component of this prosthetic group is Haem.

Haem relies on the presence of iron (Fe).

Haem combines with oxygen to form oxyhaemoglobin:

... continued in section below.


Erythrocytes are eventually broken down by the spleen into the blood pigments bilinubin and bilviridin, and iron. These components are then transported by the blood to the liver where the iron is re-cycled for use by new erythrocytes, and the blood pigments form bile salts. (Bile breaks down fats.)


Have a longevity of approx. 120 days.


There are approx. 4.5 - 5.8 million erythrocytes per micro-litre of healthy blood (though there are variations between racial groups and men/women).



Leucocytes
(White blood
cells)


There are different types of leucocytes (described in more detail - below), classified as:

Granular: e.g. Neutrophils, Eosinophils, Basophils.

Agranular (do not contain granules): e.g. Monocytes, Lymphocytes.


Major part of the immune system.


Have a longevity of a few hours to a few days (but some can remain for many years).


There are approx. 5,000 - 10,000 leucocytes per micro-litre of blood.

Trombocytes
(Platelets)


Blood platelets are cell fragments;




To facilitate blood clotting - the purpose of which is to prevent loss of body fluids.


Disk-shaped;





Diameter 2-4 um
(1 micro-metre = 1 um = 0.000001m);





Have many granules but no nucleus;





Have a longevity of approx. 5-9 days.





There are approx. 150,000 - 400,000 platelets per micro-litre of blood.







3. The Oxygenation of Blood

The oxygenation of blood is the function of the erythrocytes (red blood cells) and takes place in the lungs.
The sequence of events of the blood becoming oxygenated (in the lungs) then oxygenating the tissues (in the body) is as follows:



The Right Ventricle (of the heart) sends de-oxygenated blood to the lungs.



While in the lungs:
1. Carbon Dioxide diffuses out of the blood into the lungs, and
2. Oxygen (breathed into the lungs) combines with haemoglobin in the blood as it passes through the lung capillaries.



Oxyhaemoglobin returns to the heart via the pulmonary vein and then enters the systemic circulation via the aorta.



There is a low concentration of oxygen in the body tissues. They also contain waste products of the metabolism (such as carbon dioxide).



Due to the high concentration of oxygen in the blood and the low concentration of oxygen in the tissues,




... the high concentration of carbon dioxide in the tissues diffuses into the blood. (95% of this carbon dioxide dissolves in the blood plasma.)



Blood returns from the tissues back to the heart via the superior vena cava (from the upper-body) and the inferior vena cava (from the lower-body)


4. Types of Leucocytes (White Blood Cells)


Lymphocytes:


Monocytes:




*Basophils:


*Neutrophils:


*Eosinophils:

Approx. 24% of leucocytes are lymphocytes. These produce anti-bodies and include:
*T-Cells
*B-Cells
*Natural Killer Cells


Approx. 4% of leucocytes are monoocytes. These are also known as phagocytes.
They combat microbes by the process of phagocytosis.




60-70% of leucocytes are basophils.
Diameter 10-12 micro-metres.

Phagocytosis. Destruction of bacteria with lysozyme and strong oxidants.


2-4% of leucocytes are neutrophils.
Diameter 10-12 micro-metres.

Combat the effects of histamine in allergic reactions;
Phagocytize antigen-antibody complexes;
Destroy some parasitic worms.


0.5-1% of leucocytes are eosinophils.
Diameter 8-10 micro-metres.

Liberate heparin, histamine, and seratonin in allergic reactions, intensifying inflammatory response.





* It is only possible to observe the differences between these by staining them.

Further notes about the types of leucocytes identified above:
Lymphocytes:


The term "antigen" refers to something that is not naturally present and 'should not be in the body'.



T Cells (lymphocytes) are activated by the thymus gland.



B Cells (lymphocytes) are activated by other lymphoid tissue. The 'B' indicates 'bone marrow' cells.



Both T-cells and B-cells:
(1) destroy antigens, and
(2) produce 'memory cells' and anti-bodies.

Basophils:


An increased (higher than usual) percentage of basophils in the blood may indicate an inflammatory condition somewhere in the body.

Neutrophils & Monocytes:



Neutrophils are the first leucocytes to respond to bacterial invasion of the body. They act by carrying out the process of phagocytosis (see opposite), and also be releasing enzymes - such as lysozyme, that destroy certain bacteria.
Monocytes take longer to reach the site of infection than neutrophils - but they eventually arrive in much larger numbers.Monocytes that migrate into infected tissues develop into cells called wandering macrophages that can phagocytize many more microbes than neutrophils are able to.
Monocytes also clear up cellular debris after an infection.

Eosinophils:


An increased (higher than usual) percentage of eosinophils in the blood may indicate parasitic infection somewhere in the body.



Phagocytosis:


A phagocyte is a cell able to engulf and digest bacteria, protozoa, cells, cell debris, and other small particles. Phagocytes include many leucocytes (white blood cells) and macrophages - which play a major role in the body's defence system.


Phagocytosis is the engulfment and digestion of bacteria and other anigens by phagocytes.

This is illustrated below.