Question

histological structure of different vertibrate tissue

Answer 1

The development of a fertilized egg into a newborn child requires an average of 41 rounds of mitosis (241 = 2.2 x 1012). During this period, the cells produced by mitosis enter different pathways of differentiation; some becoming blood cells, some muscle cells, and so on.

There are more than 100 visibly-distinguishable kinds of differentiated cells in the vertebrate animal. These are organized into tissues; the tissues into organs. Groups of organs make up the various systems — digestive, excretory, etc. — of the body.

The actual number of differentiated cell types is surely much larger than 100.

All lymphocytes, for example, look alike but actually represent a variety of different functional types, e.g., B cells, T cells of various subsets.

The neurons of the central nervous system consist of hundreds of different functional types, each representing the result of a particular pathway of differentiation.

This page will give a brief introduction to the major types of animal tissues. The links along the left side of the figure will take you directly to the individual paragraphs indicated.

Epithelial

Muscle

Connective

Nerve

Blood

1. Epithelial

Epithelial tissue is made of closely-packed cells arranged in flat sheets. Epithelia form the surface of the skin, line the various cavities and tubes of the body, and cover the internal organs.

Subsets of Epithelia

Epithelia that form the interface between the internal and external environments.

Skin as well as the lining of the mouth and nasal cavity. These are derived from ectoderm.

Inner lining of the GI tract, lungs, urinary bladder, exocrine glands, vagina and more. These are derived from endoderm.

The apical surface of these epithelial cells is exposed to the "external environment", the lumen of the organ or the air. [View example]

Mesothelia. These are derived from mesoderm.

pleura — the outer covering of the lungs and the inner lining of the thoracic (chest) cavity.

peritoneum — the outer covering of all the abdominal organs and the inner lining of the abdominal cavity.

pericardium — the outer lining of the heart.

Endothelia. The inner lining of the heart, all blood and lymphatic vessels — derived from mesoderm.