12th Zoology

Peripheral Lymphoid Organs

Peripheral Lymphoid Organs

A. Lymph nodes

The lymph nodes are small, round or ovoid bodies placed along the
course of lymphatic vessels. They are surrounded by a fibrous capsule from
which trabeculae penetrate into the nodes. The node can be differentiated
into an outer cortex and an inner medulla. In the cortex are accumulations
of lymphocytes (primary follicles) within which germinal centers (secondary
follicles) develop during antigenic stimulation.

The follicles contain, besides proliferating lymphocytes, dendritic macrophages which capture and process the antigen. In the medulla, the lymphocytes are arranged as elongated branching bands (medullary cords). The cortical follicles and medullary cords contain B lymphocytes and constitute the bursa or bone marrow dependent areas.

Between the cortical follicles and medullary cords, there is a broad, intermediate zone called paracortical area which contains T lymphocytes and constitutes the thymus dependent area.

Lymph nodes act as a filter for the lymph. Each group of nodes drain
a specific part of the body. They phagocytose foreign materials including
microorganisms. They help the proliferation and circulation of T and B cells.
They enlarge following local antigenic stimulation. In the human body, totally
about 600 lymph nodes are distributed.

B. Spleen :

It is the largest lymphoid organ. It contains red and white pulp regions
that serve as filters. The macrophages within the spleen help to remove
and destroy pathogens.

Functions of Spleen :

1. The spleen serves as the graveyard for effete(aged) red blood cells, 2. It
acts as a reserve tank and setting bed for blood and 3. It acts as a systemic
filter for trapping circulating blood borne foreign particles. (The
immunological function of the spleen is primarily directed against blood borne

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Microbiology Introduction and History of Medical Microbiology

  2. Pasteur, Koch, Lister

  3. Structure of Viruses

  4. Viral genetics

  5. Virus Culture

  6. Viral Diseases

  7. Bacteria Structure Culture

  8. Bacterial Genetics

  9. Bacterial Diseases

  10. Protozoan microbiology

  11. Pathogenecity of Microorganisms

  12. Antimicrobial Resistance

  13. Antibiotics and Chemotherapy

  14. AIDS – HIV

Unit 3 – Immunology Topic List Zoology


  2. Acquired Immunity

  3. Structure and Functions of the Immune System

  4. Peripheral Lymphoid Organs

  5. Secondary Lymphoid Organs

  6. Antigenic determinants and epitopes

  7. Antibodies – Immunoglobulins

  8. Transplantation immunology

  9. Genetic basis of organ transplants

  10. Immune system disorders

Leave a Reply

Your email address will not be published. Required fields are marked *