Tissues Introduction

Epithelial Tissue Classification

Glands

Cell Specialization Multicellularity requires a division

of labor Cells look and function differently

(specialize) in different parts of the body (ex. bone cell vs. nerve cell)

Cells specialize into types of tissues, then form organs.

Histology

Study of tissues (groups of cells that are similar in structure and function)

4 Tissue Types

1. Connective Tissue Support Connect layers of tissue to each

other Bone, ligaments, fat(we will study these in great detail in class later…)

2. Nervous Tissue Control Brain, nerves,

spinal cord Highly

specialized cells that generate and conduct nerve impulses

3. Muscular Tissue Movement Highly vascular Contracts with cytoskeletal

microfilament (actin) that works with motor protein called myosin

2 categories: Striated muscle tissue (voluntary or

indirect voluntary control) Smooth muscle tissue (involuntary)

3. Muscular Tissue Striated Muscle

Ex. Skeletal Attached to skeletal bones Long, cylindrical multi-nucleited cells (as

in background) Visible striations Voluntary control

Ex. Cardiac Also striated, but uni-nucleated Branching cells fit tightly with special

junctions called intercalated discs

3. Muscular Tissue Smooth muscle No striations Spindle shaped One central nucleus Involuntary muscle

Ex. digestive system

4. Epithelial TissueInterface tissue that forms boundaries

between environments and lines surfaces

“epithe-” means “laid on”

Coverings and Protection (ex. skin, serous membranes)

Excretion & Secretion (ex. glands) Filtration (ex. kidneys) Absorption (ex. digestive system)

Identifying Characteristics of Epithelial Tisues

1. Tight fitting sheets

Regardless of cell shape or number of layers

Identifying Characteristics2. Apical-Basal Polarity Apical Surface = top

surface that borders an “open” space called LUMEN

Basal Surface = bottom surface that borders underlying supportive connective tissue

LUMEN

Connective Tissue

Identifying CharacteristicsApical Surface Often w/ microvilli

(brush border) Increases SA in

areas that need to absorb or secrete

Some with cilia (longer) to move substances along lumen

LUMEN

Connective Tissue

Identifying CharacteristicsBasal Surface Has adhesive sheet of

glyco-proteins secreted by epithelial cells called the basal lamina

Connective Tissue beneath secretes collagen, creating the Reticular Lamina.

Basal Lamina + Reticular Lamina = Basement Membrane (defines the epithelial boundary)

LUMEN

Connective Tissue

LUMEN

Identifying Characteristics3. Avascular (a =

without) Lacks blood vessels Nourished by

connective tissueBut Innervated

w/ nerve fibers

4. Regeneration and repair quickly

Classification of Epithelial Tissue:

Cell ShapeCross-section

Squamous – flat, like a fried egg, or scale-like

Cuboidal – cubes, large spherical central nuclei

Columnar – columns, long oval nuclei, usually near basal surface

Classification of Epithelial Tissue Cell Layers

Simple (one layer) Thin: limited, no

protection Sparse cytoplasm Found where rapid

diffusion is a priority (ex. kidneys, lungs)

Stratified (many layers)

Thick Protective role,

subject to wear and tear

Regenerate from basal surface to replace apical surface cells that rub off or die

Cells differ in shape at apical and basal surface. (named for apical surface)

Pseudo-stratified

Shapes vary in height Nuclei at different levels – appear

stratified, but aren’t. All cells reach basement membrane;

only a few reach the surface

false

Simple Squamous Epithelium

Function and Location Areas of high diffusion rates:

gasses (ex lungs)nutrients and waste exchange (blood

vessels and surrounding cells)filtrates (kidneys)

Makes lubricating fluid in lining of body cavities (ex. serous membranes)

One layer Flat

Simple Squamous Epithelium(Top View) – cells fit like tiled

floor

Figure 4.2

LUMEN

Simple Squamous Epithelium(side view/cross section) – cells look like fried egg

LUMEN

Nucleus of squamous cell

Kidney

Simple Cuboidal Epithelium

Function and Location Secretion and Absorption Covers walls of SMALL ducts, glands,

kidney tubules, ovaries

One layer Cubed

LUMEN

Spherical, large nuclei

Basement membrane

Cuboidal Cell

Apical surface

LUMENSpherical, large nuclei Apical surface

Basal surface

Simple Columnar Epithelium

Function and Location Absorption & Secretion (ex. digestive tract) When in open to body cavities – called

mucous membranes Special Features

Often w/ microvilli on apical surface (brush border)

Goblet cells, single cell glands, produce protective mucus.

One layer columns

LUMEN

Apical surface

Basal surface

Pseudostratified Epithelium

Function Absorption Secretion of mucus by goblet cells Cilia (larger than microvilli) sweep

mucus Location

Respiratory Linings & Reproductive tract

LUMEN

CiliaBasement Membrane

Multilevel nuclei

LUMEN

Stratified Squamous Epithelium

Structure Cells often cuboidal or columnar below

apical squamous layer Function and Location

Protection Keratin (protein) is accumulated in older

cells near the surface – waterproofs and toughens skin

Location Skin (keratinized), mouth & throat

Multi-layer (thick!)

Flat (only cells on apical surface)

keratin

Dense-Irregular Connective Tissue

Basement Membrane

Squamous

Cuboidal

Columnar

Transitional Epithelium

Structure Multi-layer Basal surface cells are cuboidal or

columnar Apical surface cells vary: changes shape

to accommodate for change in volume due to stretching

Function Allows stretching

Location Urinary bladder, ureters & urethra

Figure 4.10

Glands Cells that secrete or export a product. Secretion = protein, lipids, hormones,

steroids, acids Endocrine glands (internally secreting)

No duct, release secretion into blood vessels Often hormones Thyroid, adrenal and pituitary glands

Exocrine glands (externally secreting) Contain ducts, empty onto epithelial surface Sweat, Oil glands, Salivary glands, Mammary

glands.

Shapes of Exocrine glandsBranching of ducts Simple – single, unbranched duct Compound – branched duct.

Shape of glands: Tubular – tube - like Alveolar – flasks or sacs Tubuloalveolar – has both tubes and sacs in gland

Modes of Secretion

Merocrine Released by exocytosis Gland is not altered (Ex: Sweat glands and salivary

glands)

Holocrine Gland ruptures and releases secretion

and dead cells as well. Sebaceous (ex. oil glands on the face)

Merocrine

Holocrine