Human Transport System
The human transport system consists of two significant systems, the blood circulatory system as well as the lymphatic system. Both systems are associated and interconnected with each other. In this article, we shall discuss the human blood circulatory system.
As far as the human blood circulatory system concerns, it is a closed circulatory system, in which blood remains in blood vessels during circulation and doesn’t leave the network of the blood vessels. On contrary, the blood circulatory system of invertebrates (spider, butterfly, house fly, etc.) is an open circulatory system. The open circulatory system pumps blood into the hemocoel with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood. The human blood circulatory system consists of the heart, blood, and blood vessels (arteries, veins, and capillaries).
BLOOD: It is a particular type of fluid consisting of connective tissues, a liquid called blood plasma, and blood cells. The average adult body contains approximately 5 liters of blood and the weight of the blood in the body is about 1/12th of the body. In a normal person, plasma constitutes 55% by volume of blood, and cells or cell-like bodies are about 45% by volume of the blood.
BLOOD PLASMA: It is generally, water in which salts, metabolites, proteins, and wastes are present in dissolved form. Sodium chloride and salts of bicarbonate are present in considerable quantities in blood plasma. Plasma contains about 90-92% water and 8-10% dissolved substances. PH of the blood is 7.4 to 7.5 in normal conditions. Changes in the concentration of any salt can change the PH of blood. Zn, Cu, Ca, K, and Mg are found in trace amounts. Plasma has proteins 7-9% by weight. Respiratory gases (CO2 and O2) are also present in plasma. Albumin, fibrinogen (blood-clotting protein), and antibodies are important proteins present in blood plasma. Blood also contains nitrogenous wastes absorbed digested food and hormones. Cells pour their wastes into the plasma. The plasma then removes waste products from the body. Proteins and antibodies in the plasma are used in therapies for chronic autoimmune disorders and hemophilia. Plasma in people with blood group AB is universal because it can be used by anyone.
BLOOD CELLS and CELLS-LIKE BODIES
These include white blood cells (leukocytes) red blood cells (erythrocytes) and platelets (thrombocytes).
- White blood cells (leukocytes): These blood lack pigments, so they are colorless. They are not restricted to blood vessels. Their life span ranges from months to years, demanding on body’s need. One cubic millimeter of blood consists of 7000 to 8000 WBCs. These are cells of the immune system that are involved in protecting the body against both infectious diseases and germs. All white blood cells are produced in multipotent cells present in the bone marrow called hematopoietic stem cells.
There are two main types of WBCs. Granulocytes and A-granulocytes.
Granulocytes: They have granular cytoplasm. These include (a) neutrophils (b) eosinophils (c) basophils. The functions of each type of cell of Granulocytes are described below.
- Neutrophils: These cells destroy small particles by phagocytosis. These represent the majority of the white blood cells.
- Eosinophils: They kill small particles and break inflammatory substances. They also play a significant role in the general immune response.
- Basophils: These cells prevent blood clotting. These represent less than 1% white blood cells.
A-granulocytes: They have clear cytoplasm and include monocytes, B and T lymphocytes Natural killer cells
- Monocytes: Produce macrophages that kill micro-organism.
- B and T lymphocytes: Produce antibodies that kill germs.
- Natural killer cells: These cells are responsible for killing viral cells and cancer cells.
Red blood cells: (Erythrocytes)
These are the most abundant of blood cells. In mammals, when the red blood cells become mature, their nucleus is lost and after the loss of the nucleus, RBCs enter the blood. Approximately 95% of the cytoplasm of RBCs is filled with hemoglobin, which transports oxygen and carbon dioxide. The remaining 5% Of RBCs contain salts, enzymes, and proteins. One cubic millimeter of blood contains 5 to 5.5 million RBCs in males and 4 to 4.5 million RBCs in females. RBCs are biconcave and have an elastic cell membrane. They are produced in the bone marrow of short and flat bones e.g. sternum, ribs, and vertebrae in adults. While in embryo they are produced in the spleen and liver. Their average life span is four months.
RBCs are flexible and consider bell shape. They are covered with a membrane consisting of lipids and proteins, lacks a nucleus, and hemoglobin a protein that binds oxygen.
The red blood cells develop in several stages in bone marrow, from a hemocytoblast, then it becomes erythroblasts, from two to five days during the period of development.
The erythroblast slowly fills with hemoglobin and its nucleus and mitochondria disappear. In a late-stage, the cell is a so-called reticulocyte, which eventually converted into a mature red blood cell.
Function: As far as the function of RBCs concerns, RBCs and hemoglobin carry oxygen from lungs and gills to all body tissues. They carry carbon dioxide and wastes (metabolites) to the lungs where these products are excreted.
Size: RBCs are approximately 7.8 micrometers in diameter.
Shape: They have a biconcave shape.
- Platelets (Thrombocytes)
These are not considered cells but are fragments of cells of bone marrow, called megakaryocytes. Platelets only found in mammals. They are colorless. Their life span is very short just from 7 to 8 days. They do not have a nucleus. One cubic millimeter of blood consists of 250,000 platelets.
Function: These tiny particles assist the body to form clots and help to stop bleeding, the clot serves as a temporary seal at the damaged area.
Number: One micro-meter blood contains 150,000 to 450,000 platelets in normal conditions. Risks for bleeding created if their numbers fall below 10,000 to 20,000.
Low platelet concentration is called thrombocytopenia while elevated platelet concentration is called thrombocytosis.
Thrombocytopenia is either due to decreased production or increased destruction, whereas is either congenital or due to unregulated production.
Increased blood platelets: Following food items help the blood to increase the number of platelets,
- Vitamin K rich food