Visual Anatomy & PhysiologyFirst Edition

Martini & Ober

Chapter 4

Epithelial Tissues

Lecture 9

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Lecture Overview

• Introduction to Tissues

• Epithelial Tissues– Location– General characteristics– Functions– Classification

• Glandular Epithelium

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Where are Tissues in Our Organizational Scheme?

Figure from: Hole’s Human A&P, 12th edition, 2010

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Introduction to Tissues

Four primary types of tissues found in the adult :

1. Epithelial (covering/lining, protection, glands) [ pl. epithelia]2. Connective (binding together, support, transport, energy)3. Muscle (movement, heat production)4. Nervous (information and short-term control)

Tissue - a group of cells working together to perform one or more specific functions

Histology – the microscopic study of tissues

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Major Types of Epithelial Tissues

• Covering and Lining Epithelium– External Surfaces, e.g., skin– Internal surfaces

• Communicate with outside, e.g., digestive, respiratory, reproductive and urinary tracts

• Don’t communicate with outside, e.g., chest cavity, abdominal cavity, endothelium of blood vessels and heart

• Glandular Epithelium– Often lie in clusters deep to covering and lining

epithelium– Specialized for secretion into ducts, on to a

surface, or into the blood

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Functions of Epithelial Tissue• Physical protection

– Protect from abrasion, dehydration, and destruction by chemical or biological agents

• Control of permeability – Secretion– Absorption– Filtration

• Provide sensation– Extensively innervated by sensory nerves– May function in senses (smell, taste, etc.)

• Provide specialized secretions (glands)

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Characteristics of Epithelial Tissue

• Specialized contacts with other cells

• Polarity (different ends of cell do different things)

• Avascularity (no blood supply)

• Regeneration (can divide to make new cells)

• Cellularity (lots of cells in close contact)

Remember: Epithelial tissues always have a free surface and a basement membrane

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Characteristics of Epithelial TissueSpecialized Contacts

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Characteristics of Epithelial TissuePolarity

Outside surface – note modifications

Inner surface – attached to underlying tissue by a basement membrane

Notice the polarity and differential distribution of the cellular organelles

Figures from: Martini Visual A&P, 1st edition, 2011

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Characteristics of Epithelial TissueAvascularity and Regeneration

• Does not contain blood vessels (avascular)– Nutrients must be obtained by

• Diffusion from underlying tissue (125 µm limit)

• Absorption from free surface

• High rate of cell division and replacement– Lost cells are continually replaced by dividing

epithelial stem cells– Rate of cell division (mitotic rate) is much

higher than other tissues

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Characteristics of Epithelial TissueCellularity

- Cells are bound closely together

- Little intercellular material

- May form sheets; cells usually slough off in sheets

Figure from: Hole’s Human A&P, 12th edition, 2010

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Modifications of Epithelial Cells

Cilia – movement of substances

Microvilli – greatly increase absorptive (surface) area

Figures from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Basal Lamina

Two components:

Lamina Lucida - glycoproteins and fine protein filaments - Barrier for passage of substances from underlying tissue into epithelium

Lamina Densa - bundles of coarse protein fibers - gives basal lamina its strength

Formerly called: Basement membrane

Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004

Lamina = thin layer

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Classification of Epithelial Tissues

• Shape– Squamous (Thin, flat, irregular in shape)– Cuboidal (Square or cuboidal)– Columnar (Rectangular, tall)

• Type of layering (stratification)– Simple (one layer)– Stratified (two or more layers)– Note that classification of stratified

epithelium is based on the shape of the superficial, not deep, layers

Epithelial tissues are classified according to both their:

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Epithelial Tissues

Simple squamous –• single layer of flat cells• substances pass easily through• line air sacs of lung, blood vessels, lymphatic vessels• reduce friction, absorption/secretion

Mesothelium – lines ventral body cavities

Endothelium – lines blood vessels

Figure from: Hole’s Human A&P, 12th edition, 2010

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Epithelial Tissues

Simple cuboidal –• single layer of cube-shaped cells

• line kidney tubules

• cover ovaries

• line ducts of some glands

• limited protection, secretion/absorption

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Epithelial Tissues

Simple columnar –• single layer of elongated cells• sometimes possess cilia or microvilli• often have goblet cells• line uterus, stomach, intestines• protection, secretion, absorption

Figure from: Hole’s Human A&P, 12th edition, 2010

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Epithelial Tissues

Pseudostratified columnar –• single layer of elongated cells• appear stratified, but they ARE NOT• all cells attach to basement membrane; some do not reach surface• often have cilia and goblet cells• line respiratory passageways• protection, secretion

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Epithelial Tissues

Stratified squamous –

• many cell layers

• top cells are flat

• can accumulate keratin

• outer layer of skin

• line oral cavity, throat, vagina, and anal canal

Main function is protection (abrasions, pathogens, chemicals)

Figure from: Hole’s Human A&P, 12th edition, 2010

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Epithelial Tissues

Stratified cuboidal – • 2-3 layers• cube-shaped cells• line ducts (rare) of mammary glands, sweat glands, salivary glands, and the pancreas• protection, secretion, absorption

Figure from: Hole’s Human A&P, 12th edition, 2010

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Epithelial Tissues

Stratified columnar –• top layer of elongated cells• cube-shaped cells in deeper layers• line vas deferens, male urethra, and part of pharynx• protection

Figure from: Hole’s Human A&P, 12th edition, 2010

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Epithelial Tissues

Transitional –• many cell layers

• cube-shaped and elongated cells

• line urinary bladder, ureters, and part of urethra

Located in places where acute stretching occurs

Figure from: Hole’s Human A&P, 12th edition, 2010

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Glandular Epithelium

Composed of cells that are specialized to produce and secrete substances

Endocrine glands are ductless – secrete directly into the bloodExocrine glands have ducts – secrete into a duct or on to a surface

Unicellular exocrine gland • composed of one cell • Example: goblet cell

Multicellular exocrine gland • composed of many cells• Examples: sweat glands, sebaceous glands, salivary glands, etc.

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Structural Types of Exocrine Glands

Classified by:

1. Shape of secretory portion of gland

2. Branching pattern of the duct

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Exocrine Glands

Classified by:

1. Shape of secretory portion of gland

2. Branching pattern of the duct

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Types of Glandular SecretionsMerocrine glands

• fluid product• exocytosis• salivary glands• pancreas• sweat glands

Apocrine glands • cellular product• apical portions of cells• mammary glands• ceruminous glands

Holocrine glands• secretory products• whole cells• sebaceous glands in hair follicles

Figure from: Hole’s Human A&P, 12th edition, 2010

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Membranes

Serous• line body cavities that lack openings to outside• reduce friction• inner lining of thorax and abdomen• cover organs of thorax and abdomen• secrete serous fluid

Mucous• line tubes and organs that open to outside world• lining of mouth, nose, throat, digestive tract, etc.• secrete mucus

Cutaneous• covers body• skin

A membrane is a combination of epithelium and connective tissue that covers and protects other structures and tissues. Technically, then, a membrane is an organ.

Synovial• surround joint cavities

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Epithelial Membranes

Figure from: Martini, Anatomy & Physiology, Prentice-Hall, 2001

Notice that each type of membrane is composed of TWO different types of tissues; epithelial and connective

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Review of Epithelial Tissues• Tissue - a group of cells working together to perform

one or more specific functions• Epithelial tissues are covering, lining, and glandular

tissues that function in– Physical protection– Control of permeability– Sensation– Secretion

• Characteristics of epithelial tissue include – Specialized contacts– Polarity– Avascularity– Regeneration– Cellularity

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Review of Epithelial Tissues

• Attached to underlying tissue by a basal lamina (basement membrane)

• Classified according to shape and number of layers

• Epithelial tissue always has a free surface

• Glands are specialized epithelium– Secrete on to a surface– Secrete into a duct (exocrine)– Secrete into the blood (endocrine)

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Review of Epithelial Tissues• Exocrine glands have several different mechanisms of

secretion– Merocrine

• Release of product from vesicles by exocytosis

• Most common mode of secretion

• Example: watery sweat used to cool skin

– Apocrine• Loss of cytoplasm containing secretion

• Apical portion of cytoplasm is shed

• Example: thick, sticky underarm perspiration

– Holocrine• Entire cell is packed with secretion and then bursts

• Destroys cell

• Example: sebaceous glands associated with hair follicles

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Review

NAME OF ET DESCRIPTION STRUCTURE

LOCATION FUNCTION

SIMPLESQUAMOUS

a single layer of flattened cells

linings of air sacs, capillaries, lymph vessels, body cavities; covering ventral organs

diffusion, reduction of friction

SIMPLE CUBOIDAL

a single layer of cube-shaped cells with large centrally located nuclei

linings of kidney tubules, ducts of glands

absorption,secretion

SIMPLE COLUMNAR

a single layer of tall cells with basally located nuclei, goblet cells, & mucrovilli

lining of intestine protection,absorption,secretion

PSEUDO-STRATIFIEDCOLUMNAR

a single layer of tall cells with scattered nuclei, cilia, & goblet cells

lining of trachea,lining of fallopian tube

protection, secretion

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Review

NAME OF ET DESCRIPTION STRUCTURE

LOCATION FUNCTION

STRATIFIEDSQUAMOUS

many layers of flattened cells

keratinized = epidermis;non-keratinized = lining of vagina, anus, throat, mouth

protection

TRANSITIONAL several layers of cells that change shape under pressure

lining of urinary bladder and ureters

Distensibility (able to stretch)

GLANDULAR simple cuboidal lining the ducts of glands

secretion