Human body consists of countless cells as an essential component of different tissues. The entire lot of cells originates from typical cell, the ovum or the egg cell. Ovum or the egg cell is composed of protoplasm and contains a nucleus. After fertilization this cell multiplies to form a ball shaped structure called embryo, which by the way of differentiation develops into various tissues required to form organs and various parts of the body. The embryo or the ball of cells developed from the fertilized ovum could be divided into three layers at the very early stage:
- Outer Layer or Ectoderm: The outer part of the skin, nails, hair follicle and sweat glands mucus membrane lining of the mouth and nasal cavities develop from the ectoderm. The nervous system also develops from the ectoderm.
- Middle Layer or Mesoderm: Muscles, bones, fat and some parts of the cardiovascular system develop from the mesoderm.
- Inner Layer or Endoderm: The lining of the alimentary canal and respiratory tract develop from the endoderm.
Tissue: A tissue is an aggregation of cells of a unique shape and size destined to perform a particular task. The special function of a tissue may be governed by biological substances and/or nervous system. Elementary tissues of our body are of four types:
- Epithelial Tissue
- Connective Tissue
- Muscular Tissue
- Nervous Tissue
Subtypes of Epithelial Tissue:
A). Covering and Lining Epithelial Tissue: [1. Simple Epithelial Tissue (Pavement Epithelium: Figure-1, Cuboidal Epithelium: Figure-2, Columnar Epithelium: Figure-3); 2. Stratified Epithelial Tissue; 3. Transitional Epithelial Tissue]
Fig-1: Pavement Epithelium
Fig-2: Columnar Epithelium
Fig-3: Ciliated Columnar Epithelium
B). Glands: [Exocrine Glands (Simple Exocrine Glands, Compound Exocrine Glands); Endocrine Glands]
Subtypes of Connective Tissue:
A). Loose Connective Tissue or Areolar Tissue
B). Fatty Connective Tissue or Adipose Tissue
C). Dense Connective Tissue or Fibrous Tissue. Ultrastructural view of collagenous fibres has been depicted in figure-4.
Fig-4: Ultrastructural view of Collagenous Fibres, 27000x
F: Blood (Blood is also a form of connective tissue suspended in liquid matrix called plasma).
Subtypes of Muscular Tissue:
A). Voluntary Muscle (Striated or striped muscle). Ultrastructural view of striated muscle has been depicted in figure-5.
Fig-4: Ultrastructural view of Striated Muscle, 6000x
B). Involuntary Muscle (Smooth or plain muscle)
C). Cardiac Muscle (Striated involuntary muscle)