Chpt. 4 EPITHELIAL TISSUE + FACTS OF OTHERS The Tissue level of Organization

ALL ABOUT THE EPITHELIAL TISSUE + FACTS OF OTHERS

Tissues

Collections of specialized cells and cell products that perform specific functions

– Tissues in combination form organs, like the heart or liver

Histology

the study of tissues

4 types of tissue

1. Epithelial

2. Connective

3. Muscle

4. Nervous

Epithelial tissue short def

– Covers exposed surfaces/body surfaces

– Lines internal passageways

– Forms glands

Connective tissue short def

– Fills internal spaces

– Supports other tissues

– Transports materials

– Stores energy

Muscle tissue short def

– Specialized for contraction

– Skeletal muscle, heart muscle, and muscular walls of hollow organs

Nervous tissue short def

– Carries electrical signals from one part of the body to another

Epithelial tissue

Includes epithelia and glands; this is the tissue type itself

Epithelia

(singular, epithelium); Layers of cells covering or lining internal or external surfaces; covers exposed surface of body/delicate types line cavities and passageways

-single strand is simple (epithelium; single noun for tissue/one tissue)

Glands

Structures that produce fluid secretions

Functions of the Epithelial tissue

1. Provide physical protection (protect exposed & internal surfaces)

2. Control permeability (substances that enter or leave epithelium)

3. Provide sensation (info abt ex and internal environments due to large sensory nerve supply)

4. Produce specialized secretions (gland cells)

Characteristics of epithelia

– Polarity (apical and basal surfaces; opposite poles)

– Cellularity (cell junctions; communication)

– Attachment (basement membrane)

– Avascularity (avascular; no blood flow)

– Regeneration

Specializations of epithelial cells

1. Move fluids over the epithelium (protection)

2. Move fluids through the epithelium (permeability; how easily something can pass through a barrier.)

3. Produce secretions (protection and messaging)

Polarity

structural & functional differences between exposed & attached surfaces; Apical surface & Basal/ Basolateral surface; fluids run through on apical side

Apical surface

exposed in a single layer of epithelium cells; has microvilli and cilia

Basolateral surface

Basolateral membrane on lateral sides; basal surface is attached in a single layer of epithelium cells; basal surface is the bottom edge attached to a thin, supportive basement membrane that anchors cell to underlying connective tissue

How is integrity of Epithelia maintained? How is it held tgt?

1. Intercellular connections (intercellular is from the outside; introducing 2 foreign groups)

2. Attachment to the basement membrane (anchoring)

3. Epithelial maintenance and repair

Intercellular connections

support and communication; done by Cell adhesion molecules (CAMs) & cell junctions and Proteoglycans

Cell adhesion molecules (CAMs)

little zippers/velcro, transmembrane proteins that help cell stick tgt of to surrounding materials; like bricks

Proteoglycans

Found between cells; Help provide support and cushioning and help hold the material between cells together; “intercellular cement”; the material filling the spaces around the bricks

Cell junctions

type of intercellular connection; specialized attachment sites; attach one cell to another or to extracellular materials

1. Gap junctions

2. Tight junctions

3. Desmosomes

Gap junctions

– Allow rapid communication; open communication

– Cells held together by interlocking transmembrane proteins (connexons; little tunnels)

– Allow small molecules and ions to pass cell to cell

– Coordinate contractions in the heart muscle

IN THE HEART

Tight junctions

– Between 2 plasma membranes (to prevent leakage)

– Adhesion belt attaches to terminal web (below tight junction, to bind adjacent cells)

– Prevent passage of water & solutes (from leaking)

– Keep enzymes, acids, and wastes in lumen of digestive tract

-nope not getting through

Desmosomes

allowing for stretching/ bending/ twisting/ compression; CAMs and proteoglycans link opposing plasma membranes; Spot desmosomes & Hemidesmosomes (like nailgun)

Spot desmosomes

• Tie cells together; attach on sides

• Allow bending and twisting

• small disc attachment points; attach to intermediate filaments

Hemidesmosomes

• Attach cells to the basement membrane

• half a desmosome

• anchor cell to tissue underneath

• hemigun on the base

Terminal web

tangle made to not be unmade, hold structure; microfilaments that tie to sides of adhesion belt

Attachment to the basement membrane

Basal lamina and the reticular lamina; attached to epithelial cell by a hemidemosome

Basal lamina

attaches the basement membrane; closest to the epithelium; works like a filter restricting proteins & molecules from connective tissue from entering epithelium

Reticular lamina

• Deeper portion of basement membrane

• Provides strength (locked down in roots)

Epithelial maintenance and repair

Epithelial cells are replaced by continual division of stem cells (stim cells → to repair)

• Located near basement membrane

Classification of epithelia

1. Based on shape of the cell

2. Based on layers; number or layers it has

Classification of epithelia based on shape

• Squamous—thin and flat (squatty)

• Cuboidal—square shaped (icecube → cuboidal)

• Columnar—tall, slender rectangles like columns bru

Classification of epithelia based on layers

• Simple epithelium—single layer of cells; simple & fragile

• Stratified epithelium—several layers of cells

Squamous epithelia

thin, flat, irregular; Simple squamous epithelia & Stratified squamous epithelia

Simple squamous epithelia

absorption & diffusion; most delicate; lines chambers and passageways, specials types of this are Mesothelium & Endothelium

Endothelium

type of simple squamous epithelia; Forms inner lining of heart and blood vessels

Mesothelium

type of simple squamous epithelia; lines body cavities that enclose the lungs/heart/and abdominal organs

Stratified squamous epithelia

• Protect against mechanical stresses (lots of layers like the skin)

• Keratin adds strength and water resistance

-located on surface of skin, lining of mouth, throat,esophagus

Cuboidal epithelia

hexagonal boxes on apical surfaces; nuclei is near center of cell; simple cuboidal epithelia & stratified cuboidal epithelia

Simple cuboidal epithelia

• allows for Secretion and absorption

• makes up Glands and portions of kidney tubules

Stratified cuboidal epithelia

• Relatively rare

• Ducts of sweat glands and mammary glands

Transitional epithelia

– Tolerate repeated cycles of stretching w/o damage; resist against tearing & stretching

– Appearance changes as stretching occurs (between squamous & cuboidal)

– Found in urinary bladder

Columnar epithelia

appear rectangular & taller/thinner; Simple columnar epithelia/ Pseudostratified columnar epithelia/ Stratified columnar epithelia

Simple columnar epithelia

• found where Absorption and secretion occur

• Found in stomach, small intestine, large intestine

Pseudostratified columnar epithelia

• Typically have cilia

• to get mucus & fluid out

• in nasal cavity, trachea, bronchi

same as simple columnar js have cilia

Appears to contain multiple layers, but all cells contact the basement membrane

Stratified columnar epithelia

• Relatively rare

• Provide protection in pharynx, anus, urethra

• only superficial cells are columnar, bottoms are squished down

Glandular epithelia

gland cells that are specialized for secretion; glands;

Glands

collections of epithelial cells that produce secretions; 2 types: Endocrine glands & Exocrine glands

Exocrine glands

• Produce exocrine secretions/release fluids

• Discharge secretions through ducts onto epithelial surfaces

• sweat/tears in eyes/ milk in mammary glands & pancreas juices

Endocrine glands

• Release hormones that enter bloodstream; straight into the blood

• No ducts

*insulin is an endocrine from pancreas

• endocrine glands; separate organs: thyroid/thymus/pituitary gland

Ways that Exocrine glands are classified?

1. Gland structure

2. Methods of secretion

3. Types of secretion

Gland structure for Exocrine glands

way to classify exocrine glands

– Unicellular glands

– Multicellular glands

Unicellular glands

exocrine; independent individual /scattered gland cell; consist of single goblet cells (unicellular exocrine glands) specialized for secretion

Goblet cells

unicellular exocrine glands; specialized for secretion; In epithelia of intestines; Secrete mucin (concentrate), which mixes with water to form mucus

Multicellular exocrine glands

exocrine; secretory sheet that makes up epithelium that releases secretions into an inner compartment; in pockets/ducts where secretions travel trough

How are Multicellular exocrine glands classified?

1. Structure of the duct

• Simple (undivided)

• Compound (divided)

2. Shape of secretory portion of the gland

• Tubular (tube shaped)

• Alveolar or acinar (blind pockets)

3. Duct and secretory portions relationship

Branched = several secretory parts connect to one duct

Methods of secretion

ways exocrine glands are classified;like sweat

1. Merocrine

2. Apocrine

3. Holocrine

Merocrine secretion

method of secretion to classify exocrine glands;

• product released through exocytosis (release outside cell; w/o losing part of cell

• sweat-glands

Apocrine secretion

method of secretion to classify exocrine glands;

• shed cytoplasm; secretion losses both cytoplasm & secretion product

• Mammary glands

(marshmallow burnt on top , cut top off (cytoplasm) & take out gooeyness (secretions) too

Holocrine secretion

method of secretion to classify exocrine glands;

• cells bursting, killing gland cells

• gets full of secretory vesicle & burst & dies

• stem cells may replace gland cells

• sebaceous glands

Types of secretions produced by exocrine glands

method to classify exocrine glands; Serous glands/Mucous glands/Mixed exocrine glands

Serous glands

Types of secretions produced by exocrine glands; Watery secretions

Mucous glands

Types of secretions produced by exocrine glands; Secrete mucins (can hydrate to make mucus)

Mixed exocrine glands

Types of secretions produced by exocrine glands; Both serous and mucous

Microvilli

increase absorption or secretion; smaller brushes, more surface area for absorption

Cilia

on a ciliated epithelium move fluids; carry things along, like fluids and mucus