Tissues

Characteristics of epithelial tissue

Cellularity, polarity, attachment, avascularity, innervation, regeneration

Cellularity meaning

Composed almost entirely of cells with little extracellular matrix.

Polarity

Has an apical (top) surface and a basal surface which attaches to underlying cells.

Attachment

Basal surface is attached to a thin basement membrane

Avascularity

Lack blood vessels; cells receive nutrients via diffusion from underlying tissues.

Innervation

Contains nerves to detect changes in the environment of a body or organ region.

Regeneration

Apical surface is constantly exposed to the environment, where cells are frequently damaged or die; they are replaced as quickly as they are lost.

Functions of Epithelial tissue

Physical protection, selective permeability, secretions (exocrine cells), sensations (nerve endings)

ET Intercellular junctions

Epithelial cells are strongly bound to each other on their lateral surfaces by sharing membrane specialisations called intercellular junctions.

Shapes of epithelial cells

Squamous, cuboidal, columnar

Layer classification of Epithelium

Simple, stratified, pseudostratified

Exocrine vs endocrine glands

Exocrine glands have ducts, endocrine glands are ductless.

Structure of connective tissue

Cells, protein fibres, ground substance

What is ground substance?

A mixture of proteins and carbohydrates with variable amounts of salt and H2O

Functions of connective tissue

Physical protection, support and structural framework, binding of structure, storage, transport, immune protection

Types of CT

CT proper, supporting CT, fluid CT

Connective Tissue Proper

Two types: Loose CT and Dense CT. Two groups of cells: resident cells permanently in CT and wandering cells primarily leukocytes.

Loose CT Proper

Has fewer protein fibres and more ground substance. Serves as body’s packing material, found in spaces around organs (e.g. fat)

Dense CT Proper

Has more protein fibres and less ground substance. E,g, tendons and ligaments

Types of protein fibres produced by CT cells

Collagen fibres, elastic fibres, reticular fibres

Collagen fibres

Long, strong, flexible and resistant to stretching

Elastic fibres

Thinner than collagen, stretch easily, branch and rejoin. Allows blood vessels to stretch and relax.

Reticular fibres

Thinner than collagen, form a mesh work-like configuration

Types of supporting connective tissue

Cartilage and Bone

What is fluid connective tissue?

Blood made of plasma, erythrocytes (RBC), leukocytes (WBC) and platelets