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The Blood

Table of Contents
The Lungs
The Trachea
The Testes
The Submaxillary Gland
The Liver
The Stomach and Duodenum
The Blood
The Arteries and Veins
The Adipose Tissue
The Skin
The Pituitary Gland
The Pancreas
The Thyroid
The Kidney
The Spinal Cord
The Cerebellum
The Elastic Cartilage
The Bone
The Smooth Muscle
The Striated Muscle


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Blood is the liquid tissue of the body that functions as the main carrier of nutrients to all parts of the body. It is made up of solid and liquid parts, and contains distinct cells that aid in the body’s protection.


The plasma is what makes up the liquid part of the blood, and is composed mainly of water. However, there are many essential solutes in the plasma, such as electrolytes, which help maintain pH and osmotic balance and controls cell membrane permeability, albumin, which acts as a pH buffer and also maintains osmotic balance, fibrinogen, which aids in blood clotting, and globulins, which transport lipids and white blood cells for defense. The plasma also acts as a distributor of body heat, and transports nutrients, like vitamins, amino acids, oxygen and glucose to cells, as well as receiving their wastes.


The solid part of the blood is composed of erythrocytes, which transport oxygen around the body, and leukocytes, which act as the body’s line of defense against disease.


Erythrocytes are small, bi-concave disk shaped cells whose main function is oxygen transportation. Erythrocytes contain no nuclei, and few organelles, in order to allow optimal room for hemoglobin, an iron-containing molecule which binds to and carries oxygen. Because they lack mitochondria, erythrocytes harvest energy through anaerobic processes. Anemia is the inability of erythrocytes to carry oxygen, and can be caused by changes in shape (sickle-cell anemia).


The second solid part of the blood are the leukocytes, which are less numerous, and unlike erythrocytes, contain a nuclei and functioning organelles. Leukocytes protect the body against the threat of bacteria, viruses, parasites, and tumor cells, and while they are transported in the blood vessels, they can slip in and out of them into surrounding tissues.


Platelets, another solid part of the blood, are essential to clotting. Platelets are tiny cell fragments, which surround and break apart on contact with wounds, forming a netting that clings to the site if the break and prevents blood loss.

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