Tissue refers to a group of similar cells that carries out a function.

Histology is the science of tissues.

Blood Tissue

examples of tissues

• Muscular tissue – designed to contract

• Nervous tissue – conduct, sense, store information

• Epithelial tissue – forms coverings (skin) & linings (blood

• Muscular tissue – designed to contract

• Nervous tissue – conduct, sense, store information

• Epithelial tissue – forms coverings (skin) & linings (blood

Four categories of tissues

• Epithelial tissue – forms coverings (skin) & linings (blood vessels)

• Connective tissues – support, transport, protect

• Epithelial tissue – forms coverings (skin) & linings (blood vessels)

• Connective tissues – support, transport, protect

Cellular junctions

1. Tight Junction• Cell membranes of adjacent cells are fused together

- no space between cells

• Tight junctions prevent the passage of unwanted & harmful substances

• Examples: Blood Brain Barrier & Digestive Tract

Cells may be separated by a matrix or connected together by cellular junctions.

• Examples: Blood Brain Barrier & Digestive Tract

Interlocking membranes form tight junction between two cells

Cell 1

Cell 2

2.Desmosome• Desmosomes form “spot welds” between cells• Provides structural support• Examples in the epidermis of the skin

Cellular Junctions

Cells connected by desmosomes

3.Gap Junction• Cells connected by protein ion channels• Ion channels allow for cell-to-cell diffusion of ions• Example: intercalated discs of cardiac muscle

Cellular Junctions

Intercalated discs of cardiac muscle are one type of gap junction.

Types of Tissues: Epithelial Tissue

• Lines cavities, such as the digestive & respiratory tracts

• Forms coverings, such as the skin

• Functions: protection, secretion, absorption, excretion

Epithelial Tissue:

Epithelium: structure

• Epithelium is anchored to a layer of connective tissue, called the basement membrane.

• A Basal surface faces the basement membrane

• The free (apical) surface is exposed to the open space (lumen)

Open space = lumen

Basement membrane

Open space = lumen

Characteristics of Epithelial Tissue

• Tightly packed cells

• No blood supply, instead they receive nutrients by diffusion

• Readily divide, so they are continually replaced = rapid healing

1. Simple = Single layer of epithelial cells

Classifications of Epithelial Tissues

2. Stratified = two or more layers of cells

Layers

Shape of cells1. Squamous = scale-like

Nucleus

2. Cuboidal = cube-like shape

Nucleus3. Columnar = tall cells

Types of Epithelial Tissues

Simple Squamous Epithelium

• single layer of flattened cells

• Common at sites of diffusion and filtration• lines air sacs of lungs (alveoli)• lines walls of capillaries

Surface View Alveoli of lung

Squamous cells

Types of Epithelial Tissues

Simple Cuboidal Epithelium

• Single layer of cube-shaped cells• Lines ducts of certain glands & tubules within kidneys• Secretes chemicals in glands•Functions in reabsorption & secretion in kidneys

lumen

Cross-section of tubules in kidneys

Types of Epithelial Tissues

Simple Columnar Epithelium

• Single layer of elongated cells

• Nuclei appear as a single row

• Functions in absorption, secretion, or transport

• Often contain goblet cells • Goblet cells secrete mucus onto apical surface

• Some are ciliated, and others have microvilli

Cilia beat constantly in a rhythmic motion to propel substances across the cell surface.

Simple Columnar Epithelium

Some simple columnar epithelium are covered with cilia on their free surface.

• Cilia propels the egg through uterine tube

Microvilli are extensions of the cell membrane that increases the surface area of a cell.Microvilli are extensions of the cell membrane that increases the surface area of a cell.

Simple Columnar Epithelium

Some simple columnar epithelium are covered with microvili on their free surface.

• example: microvili on intestinal epithelium increases the amount of contact each cell makes with food.

•Microvilli greatly enhance absorption of nutrients

• example: microvili on intestinal epithelium increases the amount of contact each cell makes with food.

•Microvilli greatly enhance absorption of nutrients

Pseudostratified Columnar Epithelium

• Appear striated, but are actually simple columnar

• Each cell touches basement membrane

Psuedostratified columnar epithelium:

• Cells appear to have two or more rows of nuclei

• Usually ciliated

• Contain goblet cells that secrete mucus

Pseudostratified Columnar Epithelium

• Lines respiratory tract•Mucus from goblet cells traps debris &• Cilia moves the mucus (and trapped debris) away from the lungs

• Lines respiratory tract•Mucus from goblet cells traps debris &• Cilia moves the mucus (and trapped debris) away from the lungs

Stratified Squamous Epithelium

• Several layers of cells = thick tissue

• Superficial cells are squamous

• Deeper cells are cuboidal or columnar

•May be keratinized or nonkeratinized•May be keratinized or nonkeratinized

• found in the epidermis (outer layer) of skin• Older, outer epidermal cells of skin are keratinized • Keratin = insoluble protein• Outer layer layer hardens & dies • Forms protective coating

Keratinized Stratified Squamous Epithelium

Stratified squamous epithelium of epidermis

Non-keratinized (moist) stratified squamous epithelium lines esophagus, oral cavity, vagina, and anal canal.

Non-keratinized (moist) stratified squamous epithelium lines esophagus, oral cavity, vagina, and anal canal.

Non-keratinized Stratified Squamous Epithelium

Apical surface

Stratified squamous epithelium of vagina

Transitional Epithelium

• Transitional epithelium is specialized to form an expandable lining

• Found in the inner layer of urinary bladder & ureters

• The Lining is several layers thick when bladder is contracted (empty).

• Only few cell layers thick when urinary bladder is distended (full), and the

cells appear squamous.

Contracted bladder Distended bladderContracted bladder

Glandular Epithelium

• Glandular epithelium is specialized to produce & secrete substances

• Glandular epithelium form glands

Exocrine Glands

• Secretes substances through ducts onto open surface

• Includes goblet cells, sweat glands, mammary glands

Duct of a sweat gland

Endocrine Glands

• Secretes substances (hormones) directly into blood or tissue fluid• Includes thyroid gland, pituitary gland, adrenal glands, ect.

Glandular Epithelium

Follicles of thyroid gland are composed of simple cuboidal epithelium

End of Section 1, Chapter 5