Cytology · MU Pleven

Topic 25 General histology – introduction. Tissues – definition, general features, classification

Introduces histology as the microscopic study of tissues and how they form organs, then defines tissues and lists the four basic types with their general features. Covers general tissue responses such as hypertrophy, hyperplasia, atrophy, metaplasia and neoplasia, and breaks epithelia, connective tissue and muscle into their subtypes with examples of where each is found.

Inside: 3 sections · 3 labelled pictures · 14 flashcards · 4 min

Topic 25 of 59 in the MU Pleven syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 3 sections, about 606 words (4 min of reading), with 14 flashcards.

In this note

  1. TOPIC 25 General histology – introduction. Tissues – definition, general features, classification
  2. Histology
  3. Tissues

Histology

It is the microscopic study of the tissues of the body and their organisation to form organs

Two main components of tissues are studied – cells and extracellular matrix

Importance of histology: – Aids in understanding of pathology of tissues in the case of defective development or congenital absence of an organ or tissue.

Tissues

In complex organisms, cells with similar structure and function group together to form tissues. Tissues give the organs their specific functions for essential biological processes.

There are 4 types of tissues:

  • Epithelial – composed of closely grouped polyhedral cells with strong adhesion to one another and attached to a thin layer of ECM (extracellular matrix). Lines the cavities of organs and covers the body and organ surfaces.
  • Connective – protect, support and connect other structures like organs/tissues. Abundant ECM produced by its cells. Most abundant type of basic tissue.
  • Nervous – composed of cells with long, fine processes specialised to receive, generate and transmit nerve impulses.
  • Muscular – composed of elongated cells specialised for contraction and movement.

All of the tissue types contain cells and molecules of the extracellular matrix (ECM) exist in association with one another in variable proportions and morphologies, forming the organs of the body

Main characteristics of the 4 basic tissue types:

General properties of all the tissues:

  • Regeneration
  • Degeneration/deterioration
  • Hypertrophy – increase in cell size
  • Hyperplasia – increase in cell number from cell proliferation
  • Atrophy – Reduction of the cell volume and/or number of cell in a given tissue
  • Aplasia – defective development or congenital absence of an organ or a tissue.
  • Metaplasia – change in cell form/type
  • Neoplasia – abnormal growth of tissue, forming a mass called a tumor

Epithelia can be further divided into: (with examples of distribution)

1. Covering epithelia

  • Simple squamous – lining of vessels, serous lining of cavities pericardium, peritoneum
  • Simple cuboidal – covering the ovary, thyroid
  • Simple columnar – lining of intestine, gall bladder, covers ducts of exocrine glands
  • Pseudostratified – lining of trachea, bronchi, nasal cavity, epididymis
  • Stratified squamous keratinised – epidermis
  • Stratified squamous non keratinised – mouth, oesophagus, larynx, vagina, anal canal
  • Stratified cuboidal – sweat glands, developing ovarian follicles
  • Stratified columnar – large ducts of salivary glands, part of urethra
  • Transitional – lines urinary tract – ureters and bladder

2. Secretory (glandular) epithelia

  • Endocrine – ductless, secrete hormones directly into tissues and blood. E.g. adrenal glands

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