Blood and lymph

Blood and lymph

Blood and Lymph are circulatory fluids in animal body having immune and circulatory functions.  Blood flow through blood vessels and lymph through the lymphatic vessels.  Blood contain red blood cells, white blood cells, platelets and plasma while lymph has white blood cells in fluid.   

Blood

Blood helps in the transportation of oxygen, nutrients, and metabolic wastes to different parts of the body.  It is composed of blood cells suspended in plasma. Plasma is more than 90% water and contains proteins, ions, glucose, and hormones. The blood cells are mainly red blood cells or erythrocytes, white blood cells or leukocytes and platelets or thrombocytes.

1.      Erythrocytes (Red Blood Cells)

RBCs have a biconcave disc like shape and they contain hemoglobin, an iron-containing protein, which helps in oxygen transport. The formation of RBCs in the bone marrow is stimulated by a hormone called erythropoietin. RBC have a life span of 120 days.

2.      Leukocytes (White Blood Cells)

There are different types of White Blood Cells with different functions. WBCs protect the body from invasion by pathogens. There are two main types of WBCs: granulocytes and agranulocytes.

A.    Granulocytes -  These are also called polymorphonucleocytes and have small granules within the cytoplasm and a multilobed nuclei. There are three types of granulocytes.

·         Neutrophils are phagocytic cells.

·         Eosinophils function in defending the body against allergens and parasites.

·         Basophils defend parasites and release histamine and heparin.

B.     Agranulocytes or mononuclear leucocytes lack granules. There are two types of agranulocytes

·         Monocytes have a single large nucleus.  They transform into macrophages in tissue.  They are phagocytic cells.

·         Lymphocytes such as T lymphocyte, B lymphocytes and natural killer cells are key cells in immune response

3.   Thrombocytes (Platelets)

Platelets have a round or oval shape and are so named because they look like small plates. Platelets aid in the process of coagulation. When blood cells escape vessels, platelets release factor X which in the presence of calcium reacts with the blood protein, prothrombin, to form thrombin. Thrombin converts a blood protein, fibrinogen, to fibrin, which forms a mesh like fibrin clot which control blood flow and stop bleeding

4.      Plasma

Serum is plasma minus the clotting proteins. Plasma contains the following

1        Water

2        Inorganic substances such as calcium, potassium, sodium, etc

3        Organic substances such as glucose, amino acids, fats, cholesterol, hormones, etc

4        Waste products such as urea, uric acid, ammonia, creatinine, etc

5        Plasma proteins such as serum albumin, serum globulin, fibrinogen and prothrombin

Functions of blood

·         Supply Oxygen and nutrients like glucose, amino acids, and fatty acids to various tissues and organs.

·         Removal of metabolic wastes like CO2, urea, and lactic acid.

·         Immunological functions such as the circulation of white blood cells and the detection of foreign particles using antibodies or immunoglobulins.

·         Coagulation of blood where blood vessel is broken to prevent blood loss.

·         Transport of hormones and signaling molecules

·         Maintenance of homeostasis.

Lymph

Lymph flows through the lymphatic system, which consists of lymph nodes and lymphatic vessels.

It is mainly composed of interstitial fluid which is the fluid that lies in the interstitial spaces of cells and tissues.  As blood circulates under pressure, its fluid component (plasma) seeps through the thin wall of the capillaries into the surrounding tissue.  This fluid is called interstitial fluid and a major portion of this returns to the blood through the capillary membranes. The remainder of this interstitial fluid flows into a network of tiny lymphatic capillaries.  This fluid is now called lymph.  From tiny lymphatic capillaries it flows into a series of progressively larger collecting vessels called lymphatic vessels and reaches lymph node.   As lymph leaves the nodes, it is carried through larger efferent lymphatic vessels, which eventually drain into the circulatory system at the thoracic duct or right lymphatic duct. The largest lymphatic vessel is the thoracic duct.  It empties into the left subclavian vein near the heart.

Lymph leaving the lymph node is richer in lymphocytes. lymph formed in the digestive system is called chyle and it looks milky white because of its high lipid content.

The primary functions of the lymphatic system are

·         It drains and return interstitial fluid to the blood

·         It absorbs and return lipids from the digestive system to the blood

·         It filters fluid of pathogens, damaged cells, cellular debris, and cancerous cells.

·         It transports white blood cells to and from lymph nodes into bone marrow

·         It transports antigen-presenting cells to lymph nodes where immune response occurs.