The Lymphatic SystemAnatomy & physiology

Dr.Ryan G.AlGhanemi

Overview of the lymphoid immune system

Lymphocytes evolve from pluripotent stem cells located in the bone marrow, and differentiate into two major functional cell types:

1. B lymphocytes, comprising the humoral immune system, whose ultimate function is the production of antibodies2. T lymphocytes, comprising the cellular immune system, whose functions include

a. Direct killing of foreign or intracellularly infected cells, cytotoxic T cells,

b. Fine control of the immune response through the secretion of cytokines, helper and suppressor T cells.

Overview of the lymphoid immune system

The anatomical organization of the lymphoid immune system can also be divided into two major functional groups:

1. The primary immune organs, which are the sites of initial maturation from immature precursors into immune competent cells:

a. B cells- bone marrow

b. T cells- thymus

Overview of the lymphoid immune system

2. The secondary immune organs, which are the sites of antigen driven replication and differentiation into committed effector cells

a. Lymph nodes

b. Spleen

c. Mucosal Associated Immune System (MALT)-lymphoid cells lining the respiratory and gastrointestinal tracts

d. Everywhere else

LYMPHATIC SYSTEM consists of:

complex capillary networks which collect the lymph in the various organs and tissues.

collecting vessels which conduct the lymph from the capillaries to the large veins of the neck at the junction of the internal jugular and subclavian veins, where the lymph is poured into the blood stream.

lymph glands or nodes which mainly filtering the lymph as it passes through them and contributing lymphocytes to it.

Lymphatic System is developmentally an offshoot of the venous system

In the human embryo the lymph sacs from which the lymphatic vessels are derived are six in number; two paired, the jugular and the posterior lymph-sacs; and two unpaired, the retroperitoneal and the cisterna chyli. “ at the junction of certain of the embryonic veins”

These lymph-sacs are developed by the confluence of numerous venous capillaries.

Initially lose their connections with venous system, but subsequently, on the formation of the sacs regain them.

The lining walls of its vessels are always endothelial.

Lymphatic System is Developmentally an Offshoot Of The Venous System

From the lymph-sacs the lymphatic vessels bud out along fixed lines corresponding more or less closely to the course of the embryonic blood vessels.

Lymphatic vessels have been found in nearly every texture and organ of the body which contains blood vessels.

Such non-vascular structures as cartilage, the nails, cuticle, and hair have none, but with exceptions

Lymphatic System is Developmentally an Offshoot Of The Venous System

Both in the body-wall and in the wall of the intestine, the deeper plexuses are the first to be developed; by continued growth of these the vessels in the superficial layers are gradually formed.

All the lymph-sacs except the cisterna chyli are, at a later stage, divided up by slender connective tissue bridges and transformed into groups of lymph glands.

Lymphatic Capillaries

The complex capillary plexuses which consist of a single layer of thin flat endothelial cells lie in the connective-tissue spaces in the various regions of the body to which they are distributed and are bathed by the intercellular tissue fluids.

That mode of covering help the physical process of filtration, diffusion and osmosis, as well as active secretory function.

lymph fluid is colorless plasma like fluid with more lymphocytes & frequently red blood corpuscles.

Lymphatic Capillaries

 The lymphatic capillary plexuses vary greatly in form:

Anastomoses are usually numerous

blind ends or cul-de-sacs are especially common in the intestinal villi, the dermal papillae and the filiform papillae of the tongue.

The plexuses are often in two layers: a superficial and a deep, the superficial being of smaller caliber than the deep and thery varies between micromillimeters to one millimeter

The capillaries are without valves.

Distribution

The Skin:- Lymphatic capillaries are abundant in the dermis where they form superficial and deep plexuses, the former sending blind ends into the dermal papillae.The plexuses are especially rich over the palmar surface and plantar surface.The epidermis and subcutaneous tissue without capillaries.

The Muscle:- The tendons of striated muscle and muscle sheaths are richly supplied. In muscle, however, their existence is still disputed.

The bone:- The periosteum of bone is richly supplied and they have been described in the Haversian canals. They are absent in cartilage and probably in bone marrow.

Lymphatic Vessels

The internal coat: is thin, transparent, slightly elastic, and consists of a layer of elongated endothelial cells with wavy margins by which the contiguous cells are dovetailed into one another; the cells are supported on an elastic membrane.

The middle coat: is composed of smooth muscular and fine elastic fibers, disposed in a transverse direction.

The larger lymphatic vessels are each composed of three coats:

Lymphatic Vessels

The external coat: consists of connective tissue, intermixed with smooth muscular fibers longitudinally or obliquely disposed; it forms a protective covering to the other coats, and serves to connect the vessel with the neighboring structures.

The thoracic duct has a more complex structure than the other lymphatic vessels

Lymphatic Valves

The lymphatic vessels are formed of thin layers of fibrous tissue covered on both surfaces by endothelium which presents the same arrangement as on the valves of veins.

In form the valves are semilunar; they are attached by their convex edges to the wall of the vessel, the concave edges being free and directed along the course of the contained current.

Usually two such valves, of equal size, are found opposite one another; but occasionally exceptions occur, especially at or near the anastomoses of lymphatic vessels. Thus, one valve may be of small size and the other increased in proportion.

Lymphatic Valves

In the lymphatic vessels the valves are placed at much shorter intervals than in the veins.

They are most numerous near the lymph glands, and are found more frequently in the lymphatic vessels of the neck and upper extremity than in those of the lower extremity.

Lymphatic Valves

The wall of the lymphatic vessel immediately above the point of attachment of each segment of a valve is expanded into a pouch or sinus which gives to these vessels, when distended, the knotted or beaded appearance.

They are interrupted at intervals by constrictions, which give them a knotted or beaded appearance; these constrictions correspond to the situations of valves in their interior.

Lymph Glands (lymphoglandulae)

The lymph glands are small oval or bean-shaped bodies

Situated in the course of lymphatic and lacteal vessels so that the lymph and chyle pass through them on their way to the blood.

Each generally presents on one side a slight depression—the hilus—through which the blood vessels enter and leave the interior.

The efferent lymphatic vessel also emerges from the gland at this spot, while the afferent vessels enter the organ at different parts of the periphery.