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 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).

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 epitheliumBarrier, 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!)

Ep

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

Ep

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

Ep

Next Week…

More on fibres and cells Cartilage as a connective tissue More illustrations!...

Last Slide