Week 2 3 Histology The study of the

Week 2 -3 Histology The study of the tissues of the body

What is a tissue? • Two or more cells that share a common – Structure – Function • Secretion • Protection – Embryological origin

Tissues in perspective:

There are four tissue categories: Epithelial Tissue Muscle Tissue Connective Tissue Nerve Tissue Histology is the study of tissues.

Objective 1: Epithelial Tissues • Location – Covers body surfaces – Lines internal cavities • Functions – Diffusion, secretion, absorption, filtration, protection Note: the singular form is epithelium; plural form epithelia

Classification of epithelium By cell shape By number of layers One layer = Simple More then one layer = Stratified

Putting it all together: To classify an epithelium state the number of layers then cell shape.

Some specializations: Cilia Microvilli

Simple Epithelia Simple squamous Simple cuboidal Look for a flattened nucleus Look for a rounded nucleus Simple columnar Look for an oval nucleus

Stratified Epithelia Named according to the shape of the apical layer of cells Stratified cuboidal Stratified squamous Stratified columnar

More Epithelia Pseudostratified Transitional

Identify the Epithelial Tissue

Identify the Epithelial Tissue

Identify the Epithelial Tissue

Objective 2: Tissue • Locations – Most abundant tissue, found everywhere – Except for body surfaces What type of tissue is found on body surfaces? • Functions – Binding and support, protection, insulation, transportation Connective

Connective tissue has cells, fibers, and ground substance. Cell types • Fibroblasts (cytes)*- secrete /maintain ground substance • Chondroblasts (cytes)*- secrete /maintain ground substance • Mast cells – secrete histamine, heparin • Macrophages – phagocytes • Adipocytes – fat storage * Blasts secrete ground substance; cytes maintain ground substance

Cells Note: Unlike epithelial tissue, connective tissue is relatively cell poor Fibroblast Adipocytes Mast cells Macrophage

Ground substance • Interstitial fluid • Proteoglycans Fibers • Collagen fibers • Elastic fibers • Reticular fibers

Areolar Connective Tissue (AKA Loose connective tissue) The prototype of connective tissues. Other connective tissues contain variations in the amount or type of cells, ground substance or fibers found in areolar connective tissue

Classes of Connective Tissue

Mesenchyme: tisssue embryologic connective ground substance cells fibers

Connective Tissues Proper Areolar connective tissue cells collagen fibers reticular fibers ground substance

Connective Tissue Proper Adipose tissue adipocytes adipocyte nucleus

Wouldn’t you know it. . .

Connective Tissue Proper Dense regular fibrocyte collagen fibers

Connective Tissue Proper Dense Irregular collagen fibers

Connective Tissue Proper Reticular tissue mast cell reticular fibers

Hyaline Cartilage matrix lacuna chondrocytes

Elastic Cartilage elastic fibers chondrocyte in a lacuna

Fibrocartilage collagen fibers chondrocytes in lacuna

Objective 3: Membranes are simple organs composed of two tissues: • epithelium • connective tissue Serous Membrane simple squamous epithelium areolar connective tissue (lamina propria) Mucous Membrane stratified squamous or simple columnar epithelium areolar connective tissue (lamina propria)

Serous Membrane Identify the epithelium Lamina propria

Mucous Membrane Esophagus Trachea ? a pri ro ? La m p ina Lamina propria

Questions to ask while identifying tissues Tissue Closely packed cells little or no intercellular material Cells separated by intercellular material Epithelial tissue Connective tissue

Epithelial tissue Cells flat scale like? Simple squamous One layer of cells? Many layers of cells? Simple epithelium Stratified epithelium Cells cubical? Apical layer retangular flat and Round Oval nuclei? scale like? nucleus? Stratified Simple squamous cuboidal columnar Apical cells cuboidal? Stratified cuboidal Apical cells rectangular? Stratified columnar Apical cells rounded, scalloped? Transitional

Use similar reasoning to classify connective tissues! Try it yourself What questions do you need to ask and in what order?