1. List the functions of the lymphatic vessels. 2. Describe the structure and di

ID: 71755 • Letter: 1

Question

1. List the functions of the lymphatic vessels. 2. Describe the structure and distribution of lymphatic vessels. 3. Describe the source of lymph and mechanism(s) of lymph transport. 4. Describe the general location, histological structure, and functions of lymph nodes. 5. Compare and contrast the structure and function of the spleen and lymph nodes. 6. Define MALT and list its major components. 7. Describe the structure and function of the thymus.

Possible Essay Questions 1. Explain why and how lymphedema occurs after a modified radical mastectomy or other such surgery. 2. Indicate the reason a physician checks for swollen lymph nodes in the neck when examining a patient who shows respiratory symptoms. 3. Describe, briefly, the role of the thymus gland in the body’s immune response. 4. Discuss the importance of mucosa-associated lymphoid tissue (MALT) and gut-associated lymphoid tissue (GALT) in immune system learning.

Explanation / Answer

Lymphatic vessels send back the fluid that has leaked from blood vessels into extracellular spaces. The vessels return the fluid back to cardiac circulation, and thus maintain the volume and viscosity of blood

Lymphatic vessels are studded with lymph nodes wherever there is a junction of the vessels. Lymph nodes filter the lymph from particulate material and potential pathogens.

Lymph transports fats from digestive system to the blood stream.

The lymphatic vessels are thin walled and valved structures. The walls are lined by endothelial cells, and are covered by smooth muscles. Lymph vessels drain into thoracic duct which empties into subclavian veins. Lymph vessels are contractile in nature, and thus, can propel the fluid in them. There is other pumping system or driving force for lymph.

Lymphatic vessels are distributed throughout the body except the brain and cornea. They are more abundant at axillae.

The source of lymph is blood. The cell free blood that leaks from capillaries into surrounding tissue spaces is collected as lymph. Lymphatic capillaries that originate from the tissue spaces carry the lymph back to circulation. The lymphatic vessels are contractile due to the smooth muscle that surrounds the vessels, and thus act as low pressure conduits.

Lymph nodes occur wherever two lymphatic vessels fuse to form a larger vessel. They at as filtering stations of lymph, and prevent any pathogen in tissue spaces from entering the blood circulation. A lymph node has three regions, outer densely populated cortex, a sparsely populated medulla, and a corticomedullary junction that is present in between these two. The organ is covered with a fibrous capsule, the projections of these capsule into the organ divides it into lobes. The projections are called trabeculae. Several afferent lymphatic vessels bring lymph. The lymph percolated through cortex which contain a large proportion of T cells, then to corticomedullary junction, and then into medulla. A single efferent lymphatic vessel leaves the node that carries filtered lymph. The medulla contains germinal centers. The cortex contains both primary and secondary lymphoid follicles along with free lymphoid cells.

Spleen

Lymph node

It is filtering station of blood

It filters lymph

Immune response against carbohydrate antigens is elicited in spleen

Only peptide antigens are dealt

The organ is divided into several lobes, which contain free cells, primary, and secondary lymphoid organs.

Marginal zones and vascular sinuses are present

Sinuses are absent

A thick sheath of macrophages is present surrounding the sinuses. The microenvironment of macrophages and dendritic cells along with less abundant lymphocytes creates a milieu for carbohydrate antigen processing

Macrophages are less abundant than lymphocytes

MALT: Mucosa associated lymphoid tissue is a diffuse lymphoid tissue that occurs at various sites in the body, associated with mucous. The tissue contains lymphocytes, dendritic cells, macrophages, and a special type of cells called M cells. The tissue plays important role in transport of Ig-A antigbodies across the mucous.