Classification of Tissues Classification of Tissues

• Relationship of Cell Specialization to Tissue Function

• Characteristics Distinguishing Tissue Types

• Functions of Major Tissue Types

• Epithelial Tissues: Introduction

Relationship of Cells to TissuesRelationship of Cells to Tissues

• Cells are specialized to perform specific functions (secretion, support, contraction, neurotransmission, energy storage, etc.)• Groups of cells form tissues with specific functions.• Question: how many types of tissues are there?• Answer: four

-epithelial tissue-connective tissue-muscle tissue-nervous tissue

(epithelial and connective tissues are the most diverse)• Groups of tissues form organs with specific functions

Features which differ between tissue types Features which differ between tissue types

• The proportion of cells in the tissue

• The types of cells that make up the tissue

• The proportion of extracellular matrix in the tissue

• The amount of cell to cell contact

• The rate of cell division (mitosis)

Rate of cell divisionRate of cell division

In general, the mitotic rate is inversely

related to the life span of the cell.

epithelial tissue: high mitotic rate

connective tissue: intermediate

muscle tissue: lower

nervous tissue: lowest mitotic rate

Life Span

Mit

oti

c R

ate

MINUTE QUIZMINUTE QUIZ

Which tissue has the lowest mitotic Which tissue has the lowest mitotic rate?rate?A. Muscle A. Muscle

B. EpithelialB. Epithelial

C. NervousC. Nervous

D. ConnectiveD. Connective

Functions of Major Tissue TypesFunctions of Major Tissue Types

• Epithelial: permeability (absorption, filtration), secretion, protection

Functions of Major Tissue TypesFunctions of Major Tissue Types

• Connective: structural support, energy storage, blood cell formation

Functions of Major Tissue TypesFunctions of Major Tissue Types

• Muscle: movement, support of body, protection, heat generation

Functions of Major Tissue TypesFunctions of Major Tissue Types

• Nervous: sensation and response to environment, regulation of body systems (cardiac, respiratory, endocrine, etc.)

The function of an organ is determined by the types of tissues which form it.The function of an organ is determined by the types of tissues which form it.

Epithelial TissuesEpithelial Tissues

• Recall that epithelial tissues play important functional roles in:

• protection (skin, lining of organs))• selective permeability (absorption,

filtration)• secretion (glands)

Characteristics of Epithelial TissueCharacteristics of Epithelial Tissue

• Consists almost entirely of cells• Covers body and organ surfaces, and forms glands• Has one free surface (luminal) and basement membrane• Has specialized cell contacts• Is avascular (no direct blood supply)• Cells retain the ability to undergo mitosis

Classification of Epithelial CellsSimple vs stratifiedClassification of Epithelial CellsSimple vs stratified

stratified

Lateral and basilar surfaces of epithelia cells have connections which do three things:

Types of Epithelial Cell ConnectionsTypes of Epithelial Cell Connections

1) bind the cells together,2) form a permeability barrier, and 3) provide a mechanism of cell-to-cell

communication

Types of Epithelial Cell ConnectionsTypes of Epithelial Cell Connections

Desmosomes: Disk-shaped structure containing glycoproteins and intermediate filaments that bind cells together strongly.

Tight junctions: Form a permeability barrier through fusion of cell membranes (zonula occludens)and adhesive glycoprotein (zonula adherens). Permeability barrier to water.

Gap Junctions: Composed of protein channels connecting the lateral surfaces of two neighboring cells. Allow cell-to-cell communication.

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Water, Solutions, and Membranes