Unit 2

Histology

the study of tissues, especially with a

microscope

Tissues

Aggregation of similar cells, their products, and materials surrounding. Have specific structure & function

Tissue Components

Cells and Extracellular Matrix

Extracellular Matrix (ECM) Components

ECM Components that vary by tissue type, Extracellular Fluid- mostly water, and Proteins: glycoproteins attacked to plasma membrane, Fibrous proteins, and Proteoglycans

Fibrous Proteins

long, thin proteins like collagen

Proteoglycans

enormous carbohydrates with multiple protein-carbohydrate attachments

ECM Functions

• Protection of cells

• Holds cells together

• Facilitates cellular communication

Other names for ECM

• Interstitial fluid

• Tissue fluid

Four Principal tissues:

1. Epithelial

2. Connective

3. Nervous

4. Muscular

Epithelial Tissue Types:

A. Simple

I. Simple Squamous

II. Simple Cuboidal

III. Simple Columnar

IV. Pseudostratified

Columnar

B. Stratified

I. Stratified Squamous

II. Stratified Columnar

III. Stratified Cuboidal

IV. Transitional

Connective Tissue Types

Fibrous Connective Tissue:

• Loose Fibrous Connective Tissue (Areolar, Reticular, Adipose);

• Dense Fibrous Connective Tissue (Dense Regular, Dense Irregular, Elastic);

Cartilage:

• Hyaline, Elastic, Fibrocartilage

Bone

• Spongey, Compact

Blood

Types of Muscular tissue

skeletal, smooth, cardiac

Junctions

• what joins tissues, especially epithelial, together

• Binds Cells together

• allows near-instant cell-to-cell communication

• Located in lateral and basal surface

Lateral surface

a junction location on the side of cells, holds tight junctions, gap junctions and desmosomes

Basal surface

cell junction location on the bottom of the cell, holds Hemidesmosomes

Tight Junctions

• Tightly joins epithelial cells near apical surface

• Seals space between cells

Prevents fluids squeezing between cells

Prevents bacterial invasion

• Weak- can be broken easily

Desmosomes

• Holds cells together

• Strong- Resists mechanical stress

• Loose, not continuous like tight junctions

Hemidesmosomes

• Bind basal cells of epithelial tissue to underlying fibers (basement membrane)

• Prevents cells from peeling away

Gap Junctions

• AKA Communicating Junction

• 6 proteins forming a large channel

• Solutes and water pass through cell-to-cell

• Allows near-instant communication

• Common in smooth muscle & cardiac muscle

How do Tissues Grow?

• Hyperplasia- growth due to increase in cell number

• Hypertrophy- growth due to increase in cell size

Stem Cells

Differentiate to give rise to cell/ tissue types including: Embryonic stem cells (totipotent and pluripotent) and adult stem cells (multipotent and unipotent)

Embryonic stem cells

give rise to ALL cell types: Totipotent and pluripotent

Totipotent cells

an embryonic stem cell that can become all adult cell types and placenta cells

Pluripotent

an embryonic stem cell that can become all adult cell types

Adult stem cells

give rise to 1 or a small number of cell types (multipotent and unipotent)

multipotent

adult stem cells that can make a few types of cells

unipotent

adult stem cells that can become on type of cell

Atrophy

loss of cell size caused by disuse and/or aging

apoptosis

planned loss of cell number

• Programmed cell death

• Non-inflammatory

• Functions:

• Organ development- removing excess cells

• Normal maintenance- cycling out older/damaged cells

necrosis

death of cells

• Due to lack of blood supply or damage

• Inflammatory

• Not always reversible

regeneration

• Replacing dead cells with cells of same type

• Restores organ function

Fibrosis

• Replacing dead cells with scar tissue- Mostly fibrous proteins like collagen

• Does not fully restore organ function

• Faster, requires fewer resources

Epithelial tissue (Epithelium) Structure

• Closely adhering cells, one or more layers thick

• Almost no extracellular matrix

• Cells closely packed- Many tight junctions and desmosomes

• Supported by connective tissue- just superficial to connective tissue usually

Epithelial tissue functions

• Line organs, form glands

• Protection, Secretion, Absorption, Filtration and/or Sensation

Cell Polarity

cells are not perfectly symmetrical

• Apical surface- upper

• Basal surface- lower

• Lateral surface- side

Avascular

no blood vessels, describes epithelial tissue

Innervated

nerves are present, describes epithelial tissue

How are epithelial tissues classified?

based on number of cell layers and cell shape

How many layers are in simple, stratified, and pseudostratified epithelial tissue?

1, 2, looks like multiple but is 1

What is the cell shape of squamous, cuboidal, and columnar?

Flat/scaly, cube, rectangular

Simple squamous epithelial

• Single layer of flat cells

• Used for rapid diffusion between areas

• Location: air sacs (alveoli) of lungs, capillaries

Simple Cuboidal epithelial

• Single layer of square cells

• Form ducts (tubes) and glands

• Location: tubules of kidney, salivary glands

Simple columnar epithelial

• Single layer of tall cells

• Lines lumen (hollow center) of many organs

• Useful for absorption (esp in digestive tract)

pseudostratified columnar epithelial

• Type of simple epithelial tissue

• Single layer of tall cells that looks multi-layered

• Lines respiratory tract

Stratified squamous epithelial

• Many layers of flat cells

• Provides great protection against abrasive forces

• Can be keratinized or non-keratinized

Keratinized

stratified epithelium, Contains large amounts of protein Keratin, Outer layer of skin

non-keratinized

Stratified epithelium. Lacks much keratin. Mucous membranes of mouth, esophagus, and reproductive tract

Stratified columnar epithelial

• Many layers of tall cells

• Almost never seen

Stratified cuboidal epithelium

• Many layers of square cells

• Found in ducts of some sweat glands

• Not very common: small part of esophagus

Transitional epithelium

• Type of stratified epithelium

• Multiple layers of rounded columnar or cuboidal cells

• Location: urinary tract, urinary bladder

• When urinary bladder/tract is distended, transitional epithelium transitions

• Stretches

• Cells become more flat/squamous

• More basal cells can slide past one another, forming fewer layers

Connective tissue structure

• Tissues in which cells occupy less space than the extracellular matrix

• Cells usually do not directly contact one another

• Most abundant, distributed, variable tissue type

• Varying vascularity

Connective tissue functions

• Binding/ Connecting

• Support

• Protection- Physical and Immunity

• Movement

• Storage

• Heat Production

• Transport

Connective tissue cell name siffuxes

• -Blasts= create the extracellular matrix

• Ex: Fibroblast- makes collagen fibers

• -Clasts= break down extracellular matrix for remodeling

• Ex: Osteoclast- breaks down bone matrix

• -Cytes= maintain extracellular matrix

• Ex: Chondrocyte- maintains cartilage