Introduction to Histology & Connective Tissue – 1

1. Introduction to Histology&Connective Tissue – 1 Human Structure & Development ANHB 2212 Semester 1, 2008 Avinash Bharadwaj

2. Histology – What and Why • Histology – “Study of Tissues” • By extension, microscopic structure of the body • Basic Histology – study of tissues • “Systemic Histology” – Organs and Systems • Also called microanatomy. • Histology - the basis of function • Stepping stone to cellular basis of disease (Histopathology, a medical discipline)

3. A Different World…! • Microscopes – many varieties • Special preparation of material • Largely two-dimensional • Interpretation, analysis and application • Makes functional anatomy meaningful

4. Theory and Lab Work • Go hand-in-hand! • Read preliminary material – manual, website (Week 1) • Some lab work is aimed at understanding and interpretation of slides • Concepts and functional interpretation matter most!

5. Primary (Basic) Tissues • Recap from ANHB 1101. • Four tissue and subtypes. • Tissue – a group of cells serving a common function. • (In histological technique the term is used in a slightly different sense).

6. Epithelium • Covering of external surfaces • Lining of cavities • Limiting structure • Control passage substances across • Variety of other functions • Compact sheets of cells • Very little intercellular substance • Basement membranes • Avascularity … supporting tissue required.

7. Muscle Tissue • Movement • Sliding protein filaments in cytoplasm • Classification details later! • Three structural types. • Intimately associated with connective tissue in most places.

8. Nervous Tissue • Generation and conduction of nerve impulses • “Excitable” cells • Neurons and their processes • Few neuron bodies in peripheral nervous system – largely nerve fibres. • Neuroglia

9. Connective Tissue • Ubiquitous • Wide variety of structural features • Wide variety of functions • Connects other structures and tissues • Binds together • Nutritional support • Site of defense reactions • Transmits and resists forces • Skeletal support • Yet, all varieties have a common plan!

10. Integration… as seen in the intestine Muscle – movement Lining epithelium Barrier, secretion, absorption Supporting CT Thin muscle layer Entire unit : Mucosa Submucosa – CT in between Neurons/nerve plexuses

11. Connective Tissue – General Features • Large amount of intercellular (extracellular) substance called matrix • Fibres (also called “formed” elements) • Mostly protein, but in some cases combined with other substances • Ground substance (“Amorphous”) • Complex chemical composition • Cells • One principal type of cells produces matrix • Other cell types may be present

13. Connective Tissue Matrix – Fibres • Collagen • Thicker bundles, generally wavy • Resist stretching or transmit forces • Types of collagen – biochemistry and electron microscopy • Elastic material (“Elastica”) • Fibres or sheets (laminae) • Fibres thin, straight, branched • Biochemical composition • Reticular fibres • Variety of collagen – not seen in routine preparation • Very thin, form network • Abundant as supporting tissue in highly cellular structures

14. Matrix – Ground Substance • Variety of biochemical compounds • Protein-carbohydrate complexes • Some have special features like sulfate ions • Ground substance generally difficult to distinguish in routine sections • Variable amount in different connective tissues.

15. Connective Tissue – Main Types • “General” – fibrous – connective tissue “proper” • Special varieties • Adipose tissue • Skeletal tissues – cartilage and bone • Lymphoid tissues • Even blood! • All connective tissue is mesodermal!

16. Connective Tissue Proper • Principal cells – “fibroblasts” • Fibroblasts are active cells • When resting, usually called fibrocytes. • Classified into types (somewhat overlapping!) • Classification mainly based on fibre arrangement and density. • Loose connective tissue (“Areolar” Tissue) • Dense, irregular tissue • Dense, regular tissue

17. Loose Connective Tissue • Fewer fibres • Abundant ground substance • Functions • Supports epithelia • Mechanical support • Blood vessels and nerves • Separates and covers individual muscle cells and their small bundles • Also carries blood vessels and nerves • Loose collagen bundles allow movement to a certain extent (give examples!) but limit it as well • Elastic fibres allow restoration after movement (think of elastic fibre damage!) • Site of formation of tissue fluid • Often site of initial defense reactions

19. Loose Connective Tissue – 2 • Other cells • Fixed cells • Wandering cells • White blood cells • Others (may be derived from WBCs) • Most cells other than fibroblasts involved in defense reactions and associated vascular changes • (More details next time!)

20. Ep

21. Dense Irregular Tissue • Denser, more abundant fibre bundles • Often like sheets of cloth • Binds and separates structures (like muscles) • Deep fascia is a good example • Also, thick capsules of organs • Forms the dermis of the skin • Also carries major blood vessels and nerves of skin

22. Ep

23. Dense Regular Tissue • Orderly or parallel bundles • Arranged in the direction of forces to be resisted • Thick bundles • Tendons, ligaments (also cornea) • Most principal cells seen as resting cells • Fibrocytes • Flattened between fibre bundles

24. Ep

25. Next Week… • More on fibres and cells • Cartilage as a connective tissue • More illustrations!... Last Slide