Class XI, BIOLOGY, "Lymphatic System"

Lymphatic System

MAIN FUNCTION OF LYMPHATIC SYSTEM
All body tissues are bathed in a watery fluid derived from the blood stream. This intercellular or tissue fluid is formed when blood passes trough the capillaries. The capillary walls are permeable to all components of blood except the R.B.C’s & blood proteins. The fluid passes from the capillary into the intercellular spaces as the inter-cellular or tissue fluid. About 85% of the tissue fluid returns into the blood at the venous end of capillary. The rest 15 % of tissue fluid drains into lymphatic capillaries as lymph along with W.B.C’s, cell debris & micro organism like Bacteria , are transported back to the heart through lymphatic system.
COMPONENTS OF LYMPHATIC SYSTEM
Lymphatic System Consists of
1. Lymph
2. Lymphatic tissues
3. Lymphatic vessels or Lymphatics
4. Lymph nodes (type of lymphatic tissue)
DETAILS OF COMPONENTS
1. LYMPH
DEFINITION
“Lymph is the name given to the tissue fluid once it has entered a lymphatic vessel. OR It can be defined as “Colour less body fluid that contains lymphocytes (agranular WBC’S), small proteins & fats”.
EXPLANATION
Lymph is a medium of exchange between blood & body cells. It takes the fluid substances from cell of tissues & intercellular spaces, which cannot penetrate the blood capillaries.
2.LYMPHATIC TISSUES
DEFINITION
“Lymphatic tissues are a type of connective tissues that contain large no. of lymphocytes”
ORGANS THAT CONTAIN LYMPHATIC TISSUES
Lymphatic tissue is organized into following structures (organs).

• Lymph nodes
• Thymus
• Spleen
• Tonsils
• Some of the patches of tissues in vermiform appendix & in small intestine.

FUNCTION
Lymphatic tissue is essential for immunologic defenses of the body against viruses & bacteria.
3. LYMPHATICS
DEFINITION
Lymphatic vessels or lymphatics are blind tubes that assist the cardiovascular system in removal of tissue fluid from tissues spaces of the body, the vessels then return the fluid to the blood.
AREAS WHERE LYMPHATIC ARE NOT PRESENT
Lymphatics are present in all tissues & organs of the body except.

• Central Nervous System
• The eye ball
• Internal Ear
• Epidermis of Skin
• Cartilage & bone

TYPES
Two Types of Lymphatics are there:-
SMALL - LYMPH CAPILLARIES
LARGE - LYMPH VESSELS.
1. LYMPH CAPILLARIES
DEFINITION
“Lymph capillaries are a network of thin walled, anastomosing, microscopic vessels which are closed towards the tissue sinuses & drain the Lymph from tissues.”
2. LYMPH VESSELS
DEFINATION
The capillaries are in turn drained by lymph tubes having larger diameters & beaded appearance, called the Lymph vessels.
These vessels contain smooth muscles in them as well as Internal valves to prevent the back flow of Lymph. The Lymph circulates through the Lymph vessels by the contraction of surrounding skeletal muscles in one direction (towards the heart). These vessels converge into collecting ducts i.e right
Lymphatic duct & thoracic duct that drain into large veins at the root of neck.
4. LYMPH NODES
DEFINITION
“Lymph nodes are lymphoid tissue which are present through out the course of Lymphatics, through which the lymph must passes”
INTERNAL STRUCTURE
Each node consists of a thin, fibrous, outer capsule & an inner mass of lymphoid tissue.
AFFERENT VESSELS
Several small Lymphatics which carry the lymph into the lymph node are referred to as “Afferent vessels.”
EFFERENT VESSEL
A single large vessel which carry the lymph away from the node is called “Efferent vessel”
FUNCTION
Lymph nodes act as filters that trap the microorganisms & other foreign bodies in the lymph. The Lymphocytes & macro-phages present here, neutralize & engulf the microorganisms, respectively.
MAJOR FUNCTIONS OF LYMPHATIC SYSTEM.
From Text Book Pg. 379.
EDEMA
DEFINITION
“Whenever the tissue fluid accumulates rather than being drained into the blood by the lymphatic system, tissue & body cavities become swollen. This condition is known as “Edema”.

TYPES OF EDEMA
There are two types of Edema.
1. INTRACELLULAR
2. EXTRACELLULAR
1. INTRACELLULAR EDEMA
“Accumulation of excess of fluid within the cells causing cellular swelling is called “Intra cellular Edema. It usually occurs after severe extracellular Edema.
2. EXTRACELLULAR EDEMA
“Excess fluid accumulation in extra cellular spaces is called Extracellular Edema. ”
It is the most commonly occurring form of Edema.
FACTORS CAUSING EDEMA
Any factor that increases the tissue fluid high enough than normal value can cause excess tissue fluid volume causing edema. Some of these factor are as follows.

• High blood pressure
• Kidney failure
• Hart failure & etc.

CAUSES OF EDEMA
Following are three main causes of Edema.
1. HYPOPROTEINEMIA (SEVERE DIETARY PROTEIN DEFICIENCY)
When body is starving for Amino acids, it consumes its own blood proteins. This reduces the osmotic potential of the blood causing tissue fluid to accumulate in body tissues rather than being drawn back into capillaries, resulting in Edema.
2. LYMPHATIC OBSTRUCITON (COMMONEST CAUSE –FILARIASIS )
Another cause of edema is lymphatic obstruction, which results in more & more protein collection in the local tissue fluid hence, the increased volume. Commonest cause of lymphatic obstruction is FILARIASIS (infection by NEMOTODES) such condition is also called as “Elephantiasis” (because of swollen legs).
3. INCREASED PERMEABILITY OF CAPILLARIES (CAUSES-BURNS & ALLERGIC REACTIONS)
Sometimes the permeability of capillaries increase due to burns or allergic reactions, so blood proteins & plasma come out of capillaries & enter the tissue fluid thus causing Edema.