LYMPHATIC SYSTEM

ORGANIZATION OF LYMPHATIC SYSTEM

• Lymphatic system arises from tissue spaces as a meshwork of delicate vessels called lymph capillaries.
• Lymph capillaries start from tissue spaces as enlarged, blind-ended terminals called capillary bulbs.
• Capillary bulbs contain valves which allow flow of lymph in one direction only.
• Some muscle fibers are present around the capillary bulbs.
• Contraction of these muscle fibers pushes lymph through the vessels.
• Lymph capillaries are lined by endothelial cells.
• Capillaries unite to form large lymphatic vessels.
• Lymphatic vessels become larger and larger because of joining of many tributaries along their course.

DIFFERENCE BETWEEN LYMPH CAPILLARIES AND BLOOD CAPILLARIES

• Lymph capillaries are more porous.
• The cells lie overlapping on one another.

DRAINAGE OF LYMPHATIC SYSTEM

Larger lymph vessels ultimately form:

1. Right lymphatic duct
2. Thoracic duct

• Thoracic duct drains lymph from more than two-thirds of tissue spaces in the body.

SITUATION OF LYMPH VESSELS

REGIONS OR STRUCTURES HAVING LYMPH VESSELS

1. Deeper layers of skin and subcutaneous tissues.
2. Diaphragm, wall of abdominal cavity and omentum.
3. Linings of:
   • Respiratory tract (except alveoli)
   • Digestive tract
   • Urinary tract
   • Genital tract
4. Liver and heart.

REGIONS OR STRUCTURES WITHOUT LYMPH VESSELS

1. Superficial layers of skin.
2. Central nervous system.
3. Cornea.
4. Bones.
5. Alveoli of lungs.

LYMPH NODES

DISTRIBUTION OF LYMPH NODES

Lymph nodes are present along the course of lymphatic vessels in:

• Elbow
• Axilla
• Knee
• Groin

Lymph nodes are also present at certain points in:

• Abdomen
• Thorax
• Neck

These are areas where many lymph vessels join.

FUNCTIONAL STRUCTURE OF LYMPH NODES

• Each lymph node consists of masses of lymphatic tissue covered by a dense connective tissue capsule.
• Structures are arranged in 3 layers:

1. Cortex
2. Paracortex
3. Medulla

1. CORTEX

• Cortex of lymph node consists of:
• Primary lymphoid follicles
• Secondary lymphoid follicles
• Primary follicle develops first.
• When some antigens enter the body and reach lymph nodes:
• Cells of primary follicle proliferate.
• Active proliferation occurs in a particular area of follicle called the germinal center.
• After proliferation of cells → primary follicles become secondary follicles.
• Cortex also contains some B lymphocytes, usually aggregated into primary follicles.
• Macrophages are also present in the cortex.

2. PARACORTEX

• Paracortex lies between:
• Cortex
• Medulla
• Paracortex contains T lymphocytes.

3. MEDULLA

Medulla contains:

• B lymphocytes
• T lymphocytes
• Macrophages
• Blood vessels of lymph node pass through the medulla.

LYMPHATIC VESSELS TO LYMPH NODE

• Lymph node receives lymph through one or two lymphatic vessels called afferent vessels.
• Afferent vessels divide into small channels.
• Lymph passes through:
1. Afferent vessels
2. Small channels
• It reaches the cortex.
• Lymph circulates through:
• Cortex
• Paracortex
• Medulla
• From medulla, lymph leaves the node through one or two efferent vessels.

FUNCTIONS OF LYMPH NODES

• Lymph nodes serve as filters which filter:
• Bacteria
• Toxic substances
• These are filtered from lymph.

FUNCTIONS

1. When lymph passes through lymph nodes, it is filtered:
   • Water and electrolytes are removed.
   • Proteins and lipids are retained in lymph.
2. Bacteria and other toxic substances are destroyed by macrophages of lymph nodes.
   
   Because of this, lymph nodes are called defense barriers.

APPLIED PHYSIOLOGY: LYMPH NODE SWELLING

• During infection or any other process in a particular region of the body:
• Activities of lymph nodes in that region increase.
• This causes swelling of lymph nodes.
• Sometimes, swollen lymph nodes cause pain.
• Most common cause of swollen lymph nodes is infection.
• Lymph nodes situated near an infected area swell immediately.
• When the body recovers from infection:
• Lymph nodes gradually restore their original size.
• This occurs in 1 or 2 weeks.

LYMPH

FORMATION OF LYMPH

• Lymph is formed from interstitial fluid, due to the permeability of lymph capillaries.
• When blood passes through blood capillaries in tissues:
• 9/10th of fluid passes into the venous end of capillaries from the arterial end.
• The remaining 1/10th of fluid passes into lymph capillaries.
• Lymph capillaries have more permeability than blood capillaries.
• Therefore, when lymph passes through lymph capillaries:
• Composition of lymph is more or less similar to that of interstitial fluid.
• This includes the protein content.
• Proteins present in interstitial fluid cannot enter blood capillaries because of their larger size.
• Therefore, proteins enter lymph vessels, which are permeable to large particles also.

ADDITION OF PROTEINS AND FATS

• Tissue fluid in:
• Liver
• Gastrointestinal tract (GIT)
• Contains more protein and lipid substances.
• Therefore, proteins and lipids enter the lymph vessels of liver and GIT in large quantities.
• Thus, lymph in larger vessels contains more:
• Proteins
• Lipids

CONCENTRATION OF LYMPH

• When lymph passes through lymph nodes, it becomes concentrated because of absorption of:
• Water
• Electrolytes
• Proteins and lipids are not absorbed.

RATE OF LYMPH FLOW

• About 100 mL/h flows through the thoracic duct.
• 20 mL/h flows through the right lymphatic duct.

COMPOSITION OF LYMPH

1. WATER — 96%

Inorganic Substances

In lower concentration than plasma:

1. Sodium
2. Calcium
3. Potassium

In higher concentration than plasma:

1. Chlorides
2. Bicarbonates

2. SOLIDS — 4%

Organic Substances

I. Proteins

1. Albumin
2. Globulin
3. Fibrinogen
4. Prothrombin
5. Other clotting factors
6. Antibodies
7. Enzymes

II. Lipids

1. Chylomicrons
2. Lipoproteins

III. Carbohydrate

• Glucose

IV. Amino Acids

• All amino acids present in plasma

V. Nonprotein Nitrogenous Substances

1. Urea
2. Creatinine

Cellular Contents

1. Lymphocytes
2. Monocytes
3. Macrophages
4. Plasma cells

FUNCTIONS OF LYMPH

1. Important function of lymph → return proteins from tissue spaces into the blood.
2. Lymph flow plays an important role in redistribution of fluid in the body.
3. Through lymph:
   • Bacteria
   • Toxins
   • Other foreign bodies
   are removed from tissues.
4. Lymph flow is responsible for maintenance of structural and functional integrity of tissue.
   • Obstruction of lymph flow affects various types of tissues, particularly:
   • Myocardium
   • Nephrons
   • Hepatic cells
5. Lymph flow serves as an important route for intestinal fat absorption.
   
   This is the reason for the milky appearance of lymph after a fatty meal.
6. Lymph plays an important role in immunity by transport of lymphocytes.

LYMPHATIC SYSTEM AND CARDIOVASCULAR SYSTEM

SIMILARITIES

1. Both cardiovascular system and lymphatic system transport fluids that contain important materials.
2. Both systems remove unwanted materials.
   • Lymph removes waste materials from the body tissues.
   • Blood removes waste materials and carbon dioxide.
3. Both systems can develop cancer.
   • Lymphatic system drains cancer cells from affected tissues or organs into blood.
   • Blood carries the cancer cells to other tissues or organs, resulting in metastasis (spread of disease to other areas of body).

DIFFERENCES BETWEEN CARDIOVASCULAR AND LYMPHATIC SYSTEMS