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

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)

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

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!

Primary (Basic) Tissues Recap from ANHB 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).

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.

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

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

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!

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

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

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

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.

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!

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

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

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!)

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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

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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

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