4.lymphatic system

Compiled by: Prof. Anwar Baig- AIKTC-SOP

4. Lymphatic system

Presented by: Prof.Mirza Anwar BaigAsisstant Professor,AIKTC-School of Pharmacy,New

Panvel,Mumbai


Contents:1.Introduction2.Organization of lymph vessels3.Formation and flow of lymph4.Lymphatic organs and tissues


1. Introduction:Important terms:

lymphatic system: lymph, lymphatic vessels, lymphatic tissues, and red bone marrow.

lymph: Clear fluid, is interstitial fluid but located within lymphatic vessels and lymphatic tissue.

Lymphatic tissue: Specialized form of reticular connective tissue that contains large numbers of lymphocytes. Two typesof lymphocytes participate in adaptive immune responses: B cells and T cells.


Functions of Lymphatic system:Three primary functions:

1. Drains excess interstitial fluid.

Lymphatic vessels drain excess interstitial fluid from tissue spaces and return it to the blood.

2. Transports dietary lipids.

Lymphatic vessels transport lipids and lipid-soluble vitamins (A, D, E, and K) absorbed by the gas-

trointestinal tract.

3. Carries out immune responses.

Lymphatic tissue initiates highly specific responses directed against particular microbes or abnormal cells.


2. Organization of lymph vessels• lymphatic capillaries. tiny

vessels,located in the spaces between cells, are closed at one end , lymphatic capillaries unite to form larger lymphatic vessels , resemble veins in structure but have thinner walls and more valves.

• At intervals along the lymphatic vessels, lymph flows through lymph nodes, encapsulated bean-shaped organs consisting of masses of B cells and T cells.

• lie in the subcutaneous tissue of skin.

• Tissues that lack lymphatic capillaries include avascular tissues (such as cartilage, the epidermis, and the cornea of the eye), the central nervous system, portions of the spleen, and red bone marrow.



EDEMA• Edema is the excess

accumulation of fluids in tissue spaces. as a result of decreased plasma protein, increased capillary permeability or lymphatic blockage, can result in swelling and congestion of the extravascular compartment.


Lymphatic trunk and ducts:• The principal trunks are the lumbar,

intestinal, bronchomediastinal, subclavian, and jugular trunks.

1. The lumbar trunks: lower limbs, the wall and viscera of the

pelvis, the kidneys, the adrenal glands, and the abdominal wall.

2. The intestinal trunk drains lymph from the stomach, intestines,

pancreas, spleen, and part of the liver.

3. The bronchomediastinal trunks: drain lymph from the thoracic wall, lung, and heart.

4. The subclavian trunks drain the upper limbs. The jugular trunks

drain the head and neck.

5. The jugular trunks drain the head and neck.



Formation and Flow of Lymph

1. Most components of blood plasma filter freely through the capillary walls to form interstitial fluid, but more fluid filters out of blood capillaries than returns to them by reabsorption.

2. The excess filtered fluid—about 3 liters per day—drains into lymphatic vessels and becomes lymph.

3. interstitial fluid contains only a small amount of protein.

Proteins that do leave blood plasma cannot return to the blood by diffusion because the concentration gradient.

4. The proteins can, however, move readily through the more permeable lymphatic capillaries into lymph.

5. Thus, an important function of lymphatic vessels is to return the lost plasma proteins to the bloodstream.


Schematic diagram showing the relationship of the lymphatic system to the cardiovascular

system.


Two “pumps• Aid the return of venous blood to the heart maintain

the flow of lymph.1. Skeletal muscle pump:

The “milking action” of skeletal muscle contractions compresses lymphatic vessels (as well as veins) and forces lymph toward the junction of the internal jugular and subclavian veins.

2. Respiratory pump. Lymph flow is also maintained by pressure changes that occur during inhalation (breathing in).

• Lymph flows from the abdominal region, where the pressure is higher, toward the thoracic region, where it is lower.

• When the pressures reverse during exhalation (breathing out), the valves prevent backflow of lymph. In addition, when a lymphatic vessel.


2. Lymphatic organs and tissues

Classified into two groups based on their functions.

1. Primary lymphatic organs: Sites where stem cells divide and become immunocompetent, that is, capable of mounting an immune response. Examples red bone marrow (in flat bones and the epiphyses of long bones of adults) and the thymus.

The pre-T cells in turn migrate to the thymus, where they become immunocompetent T cells.

2. Secondary lymphatic organs: Most immune responses occur.They include lymph nodes, the spleen, and lymphatic nodules (follicles).


Thymus gland:


Thymus• Capsule: separates the two lobes

• Trabeculae: Extensions of the capsule, penetrate inward and divide each lobe into lobules

• Cortex: Immature T cells (pre-T cells) migrate from red bone marrow to the cortex of the thymus, where they proliferate and begin to mature.

• Composed of

1. Dendritic cells: derived from monocytes, assist the maturation process.

2. Epithelial cells help “educate” the pre-T cells in a process known as positive selection. Additionally, they produce thymic hormones that are thought to aid in the maturation of T cells. Only about 2% of developing T cells survive in the cortex. The remaining cells die via apoptosis (programmed cell death).

3. Thymic macrophages: clear out the debris of dead and dying cells. The surviving T cells enter the medulla.


The medulla:Consists of 1. Mature T cells2. Epithelial cells3. Dendritic cells3. Macrophages 4. Thymic (Hassall’s) corpuscles.

Some of the epithelial cells become arranged into concentric layers of flat cells that degenerate and become filled with keratohyalin granules and keratin. may serve as sites of T cell death in the medulla.

T cells that leave the thymus via the blood migrate to lymph nodes, the spleen, and other lymphatic tissues where they colonize parts of these organs and tissues.


Lymph node:


Lymph node:



Lymph Nodes• Located along lymphatic vessels are about 600 bean-shaped

lymph nodes. scattered throughout the body, both superficially and deep, and usually occur in groups.

• Large groups of lymph nodes are present near the mammary glands and in the axillae and groin.

• Lymph nodes are 1–25 mm (0.04–1 in.) long.

Fuction: 1. Lymph nodes function as a type of filter. 2. As lymph enters one end of a lymph node, foreign substances

are trapped by the reticular fibers within the sinuses of the lymph node.

3. Macrophages destroy some foreign substances by phagocytosis4. Lymphocytes destroy others by immune responses. 5. The filtered lymph then leaves the other end of the lymph node.


Spleen• The oval spleen, largest lymphatic

tissue, about 12 cm (5 in.) in length.

• Located in the left hypochondriac region between the stomach and diaphragm.

• The superior surface of the spleen is smooth and convex and conforms to the concave surface of the diaphragm.

• Impresions —the gastric impression (stomach),the renal impression (left kidney), and the colic impression (left colic flexure of large intestine).

• Hilum: Through it pass the splenic artery, splenic vein, and efferent lymphatic vessels.


Spleen1. A capsule of dense connective tissue surrounds the spleen.

2. Trabeculae extend inward from the capsule.

3. The capsule plus trabeculae, reticular fibers, and fibroblasts constitute the stroma of the spleen.

4. Parenchyma of the spleen consists of two different kinds of tissue called white pulp and red pulp.

5. White pulp is lymphatic tissue,consisting mostly of lymphocytes and macrophages.

6. The red pulp consists of blood-filled

venous sinuses and splenic cords.

i. Splenic cords consist of red

blood cells, macrophages, lymphocytes,

plasma cells, and granulocytes.

7. Veins are closely associated with

the red pulp.


White pulp consist of

i) B cells and T cells carry out immune functions

ii) Spleen macrophages destroy blood-borne pathogens by

phagocytosis.

Functions of Spleen

(1) Removal by macrophages of ruptured, worn out, or

defective blood cells and platelets;

(2) Storage of platelets, up to one-third of the body’s

supply.

(3) Production of blood cells (hemopoiesis) during fetal

life.


Lymphatic Nodules

• Egg-shaped masses of lymphatic tissue that are not surrounded by a capsule.

• Scattered throughout the lining of the gastrointestinal, urinary,and reproductive tracts and the respiratory airways, also referred to as mucosa-associatedlymphatic tissue (MALT).

• Among these are the tonsils in the pharyngeal region.

• Usually there are five tonsils, which form a ring at the junction of the oral cavity and oropharynx and at the junction of the nasal cavity and nasopharynx.

• The tonsils are strategically positioned to participate in immune responses against inhaled or ingested foreign substances.

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4.lymphatic system