Lecture 3: Tissue Structure and Histology

Polarization

A cell that has a distinct, asymmetrical internal organization and arrangement of its components

Differentiation

Unspecialized cell changes into a specialized cell type with a distinct structure and function

Tissue

A group of similar cells working together to perform specific functions

Organ

2+ types of tissues working together to perform specific functions

4 Types of Tissue

Epithelial, muscle, nervous, connective

Epithelial Tissue (what does it cover?)

Covers surfaces in the body (external surfaces internal cavities & passageways, and secreting surfaces)

Functions of Epithelial Tissue

Provides physical protection

Control permeability

Provide sensation

Produce specialized secretions

Epithelium/Epithelia

A sheet of connected epithelial cells attached to a basement membrane

What does epithelial tissue encompass?

Epithelia, exocrine glands, endocrine glands

Basement Membrane

A thin extracellular material that supports and anchors epithelial tissue to the connective tissue underneath it

Apical Surface of Epithelial Cells

Top layer of an epithelial cell that faces the body’s exterior or the internal cavity (lumen) of an organ

Basolateral Surface of Epithelial Cells

Layer in contact with interstitial fluid

Ways that cells within an epithelium are bound to each other

Tight junctions, adhesion belt, gap junctions, desmosomes

Paracellular Transprot

Movement of particles across an epithelium by passing through the intracellular space between adjacent cells

Transcellular Transport

Movement of particles across an epithelium through the interior of a cell

Leaky Tight Junctions vs Tight Tight Junctions

Allows paracellular transport of water and solutes

Do not allow paracellular transport

Simple epithelia vs stratified epithelia

Single layer

Multiple layers

Squamous vs cuboidal vs columnar

Scale-like, cube-like, rectangular-like

Pseudo-stratified

A single layer of irregularly shaped cells that look like multiple layers because its nuclei sit at different heights

How does the apical surface compare to the lateral surface in squamous vs. cuboidal vs. columnar cells

Squamous: Apical surface is wider than it is tall; cells are flat

Cuboidal: Apical surface width is approximately equal to cell height

Columnar: Apical surface is narrower than cell height; cells are tall

Connective Tissue (what makes something connective tissue?)

The presence of extracellular protein fibres and cells suspended within a ground substance (matrix), but can fulfill many functions

Functions of Connective Tissue

Establish a structural framework for the body

Transport fluids and dissolved materials

Protect delicate organs

Support, surround, and interconnect other types of tissue

Store energy, especially in the form of triglycerides

Defend the body from invading microorganisms

Types of connective tissue

Connective tissue proper, fluid connective tissue, supporting connective tissue

Types of connective tissue proper

Loose and dense

Types of loose connective tissue

Areolar, adipose, reticular

Types of dense connective tissue

Regular, irregular, elastic

Types of fluid connective tissue

Blood and lymph

Types of supporting connective tissues

Cartilage and bone

Characteristics of loose connective tissue

Low density of extracellular fibres

High diversity of cell types

Characteristics of dense connective tissue

High density of extracellular fibres

Low diversity of cell types

Fixed cells and examples found in loose connective tissue

Remain permanently in the tissue

Fibroblasts, fibrocytes, melanocytes

Wandering cells and examples found in loose connective tissue

Can move into or through tissue depending on physiological demands

Mesenchymal cells

Fibroblasts

Secrete the proteins of the extracellular matrix (builds)

Fibrocytes

Maintain the proteins of the extracellular matrix (maintains)

Mesenchymal cells

Stem cells that can divide to replace damaged cells (fibroblasts)

Extracellular fibres in connective tissue proper

Elastin and collagen fibres

Elastin fibres

Stretch and recoil

Not in all connective tissues

Collagen fibres

High tensile strength (strong but not stretchy)

At least some in all other connective tissue

Tissue membrane

Cover body surfaces (inside and out)

A layer of epithelial tissue + underlying layer(s) of connective tissue

Fasciae

Layer of connective tissue that surround organs, providing physical support

Only connective tissue that are not directly connected to epithelium

Epithelium strategy for repair

Rapid proliferation

Connective strategy for repair

Increased rates of secretion of fibres

Defense mechanisms when connective tissue is injured

Clot and scar

Clot

Forms out of blood tissue

Scar

Forms when a dense web of collagen fibres is secreted at the injury site