Chapter 4

What are tissues?

Group of cells of similar structure that perform a common function

What is histology?

the microscopic study of tissues and organs through sectioning, staining, and examining those sections under a microscope

can observe and evaluate

What are intracellular attachments or cell junctions?

Specialized structures that connect neighboring cells, facilitating communication and strength among tissues

3 types

What are the three types of cell junctions?

1. tight

2. gap

3. desmosomes

What are cell adhesion molecules?

CAMs: transmembrane proteins responsible for cell junctions

Tight junctions

closed; prevent movement between cells

• impermeable junctions

• form continuous seals around the cell

• prevent molecules from passing between cells

Where are tight junctions (epithelial)?

stomach: enterocyte cells

brain (areas that need to be sealed)

Desmosomes

small openings/spaces; anchor cells to each other

• anchoring junctions

• bind adjacent cells together like molecular Velcro

• help keep cells from tearing apart

Where are desmosomes?

used as anchors; found in basal and lateral side

Gap junctions

form passageways

• communicating junctions

• allow ions and small molecules to pass from cell to cell

• particularly important in heart cells and embryonic cells

Where are gap junctions (epithelial)?

heart (allow electrical signals to pass)

What is the behavior of desmosomes as cell juncitons?

resist damage for stretching and twisting (blister)

connection between epidermis and dermis

What is the importance of hemidesmosomes?

attached to another tissue; maintain cell structure together

Where are desmosomes found?

connection between epidermis and dermis

How is the connection between epidermis and dermis created?

hemidesmosomes and basal lamina

What are hemidesmosomes?

tie epidermal cells to fibers of the basal lamina

What is the basal lamina?

basement membrane; acellular layer between epidermis and dermis

What is an autoimmune disease associated with cell junctions?

Pemphigus

blisters in mouth, esophagus, eyes, nose, vagina, anus

How are cell junctions important in resistance to damage?

pressure from skin rubbing on a new shoe, for example, anchoring junctions like hemidesmosomes and desmosomes provide strength and stability to epithelial tissues; deal with the friction

blister forms (ECF fills from movement)

What are the four primary tissue types?

epithelial

connective

muscle

nervous

What is the specialized function of epithelial tissue?

• covers exposed surfaces

• lines internal pasageways and chambers

• produces glandular secretions

forms GLANDS

What is the specialized function of connective tissue?

• fills internal spaces

• provides structural support (soft organs)

• stores energy

ALMOST EVERYWHERE

What is the specialized function of muscle tissue?

• contracts to produce movement (and force!)

• includes skeletal muscle, cardiac muscle, and smooth muscle

3 types: skeletal, cardiac, smooth

What is the specialized function of nervous tissue?

• conducts electrical impulses

• carries information

sends electrical signals

What makes up epithelial tissue?

sheets of cells that cover: exposed surfaces, line internal cavities and passageways

Where can epithelial tissue be found?

integumentary system

pleural cavity (resp. sys)

digestive system (intestine)

urinary and reproductive systems

Characteristics of epithelial tissue:

• cellularity

• specialized cell junctions

• supported by connective tissue

• polarity

• avascularity

• high regeneration (sheets or layers)

What is cellularity?

cells bound tightly together by specialized junctions

property of epithelial tissue: no space in between tissue, just the cells themselves

Ie Lumen of intestine of kidney: cellularity and specialized junctions → apical membrane

faces the lumen

Ie Lumen of intestine of kidney: cellularity and specialized junctions → tight junction

prevents movement of substances between the cells

Ie Lumen of intestine of kidney: cellularity and specialized junctions → basolateral membrane

faces the ECF

Epithelial cells are usually _____ and interconnected by ____.

Epithelial cells are usually packed together and interconnected by intercellular attachments.

At their basal surfaces, epithelia are attached to what?

a basement membrane that forms the boundary between the epithelial cells and the underlying connective tissue

What are epithelial cells supported by?

connective tissue

How does epithelial tissue demonstrate cellularity?

hemidesmosomes and desmosomes create high density of cells (layering) of fibers → basement membrane

What does the basement membrane look like, in relation to supporting epithelial cells?

What is polarity?

tight junctions polarized the cell membrane in two regions

distribution of the organelles is different (cell function)

What are the two sides in a cell (in relation to polarity)?

1. apical (lumen: space in tubular structures; ie: intestine)

2. basolateral (ECF)

Where are tight junctions found (which side)?

apical side of the cell

Where are organelles found (which side)?

towards the ECF

The nucleus is ___ to the tight junctions.

inferior

The nucleus is ___ to the ECF.

proximal

What membrane faces the lumen?

apical

What membrane faces the ECF?

basolateral

What is avascularity in relation to epithelial tissue?

Epithelial tissue does not contain blood vessels

thus → can’t bleed if damaged

How are epithelial cells important: composed of layers and high regeneration?

replacement of cells

Why is regeneration important to epithelial cells?

composed of layers → stem cells are the most inferior, so they grow upward to replace dead or damaged cells, ensuring tissue integrity and function.

What are the major functions of epithelial tissue?

• protection

• control of permeability

• provide sensation

• produce specialized secretion

Example how epithelial tissue provide sensation:

neuroepithelia: epithelia found in special sense organs

Example of how epithelial tissue produces specialized secretion

unicellular glands

glandular epithelia

What are the specializations of epithelial cells on the apical side?

microvilli, cilia, sterocilia

What are microvilli?

absorption and secretion

extensions of cytoplasm

What are cilia?

movement

extension of cytoplasm

in areas with mucous

What are stereocilia?

sensory organs (inner ear)

one important cilia → kinocilium and smaller steriocilia in the inner ear

What is long cilium?

flagellum

sperm: unique cell with the same function of movement

How are epithelial cells classified?

number of cell layers

simple and stratified

cell shapes

What are the epithelial cell shapes?

squamous (plate or scale)

cuboidal (cube)

columnar (rectangle)

What is the classification of epithelium with one layer?

simple

What is the classification of epithelium with more than one layer?

stratified

simple squamous epithelium

simple cuboidal epithelium

simple columnar epithelium

stratified squamous epithelium

stratified cuboidal epithelium

stratified columnar epithelium

pseudostratified columnar epithelium

What is simple squamous epithelium?

reduces friction; controls vessel permeability; performs absorption and secretion

single layers help to decrease diffusion distance

cells are thin, flat, and irregular

Location of simple squamous epithelium

respiratory exchange surface (CO2 and O2)

circulatory system (blood vessels: endothelium and lymphatic vessels), and lining of body cavities (mesothelium).

What is cuboidal epithelium?

cells have hexagonal box shape

perfectly round nucleus

Location of cuboidal epithelium

regions where secretion or absorption take place

What are regions where secretion or absorption take place?

stomach

intestinal tract

uterine tubes

excretory ducts

Where can you find cuboidal epithelium?

Regions where
secretion or
absorption take place:
Stomach
Intestinal tract
Uterine tubes
Excretory ducts

What is simple columnar epithelium?

protection; secretion; absorption

height of the cell is greater than the width

cells with/wo microvilli

Location of simple columnar epithelium?

areas where absorption and secretion occur

stomach

intestine

uterine tubes

gallbladder

What is stratified squamous epithelium?

provides physical protection against abrasion, pathogens, and chemical attack

keratinized

non-keratinized or mucosal

cells at the surface layer are flat

Found in areas where mechanical or chemical stress are severe

What is keratinized (stratified squamous epithelium)?

where dehydration occurs

palmar skin

keratin prevents water loss and protects from mechanical stress

What is non-keratinized or mucosal (stratified squamous epithelium)?

keep moist

oral cavity, pharynx, esophagus, rectum, anus, vagina

protects from abrasion and chemicals due to layers

Location of stratified squamous epithelium

found in areas where mechanical or chemical stress are severe

What is stratified cuboidal epithelium?

protection and secretion

found with lots of ducts and glands

circular nuclei

Location of stratified cuboidal epithelium

lining the ducts of sweat and mammary glands

What is stratified columnar epithelium?

rare; protection

two or more layers (first is columnar)

Location of stratified columnar epithelium (rare)

small areas of the pharynx, salivary ducts, urethra, and anus

superficial side has columnar shape

What is pseudostratified columnar epithelium?

cell nuclei are located at varying distance from the surface (close to basal area)

usually ciliated cells

Location of pseudostratified columnar epithelium

Nasal cavities
Trachea
Bronchi
portions of the reproductive male tract.

What is transitional epithelium?

dome-shaped cells

stratified epithelium that can stretch without damaging epithelial cells

relaxed: bubble shape

stretched: look squamous

Location of transitional epithelium

Urinary system structures such as:
Urinary bladder, ureters, lining the renal pelvis

What do epithelial cells form?

our glands; produce specialized secretions

What are the types of secretions (epithelial cells which form our glands)?

exocrine

endocrine

What are exocrine glands?

release their secretions onto epithelial surface through epithelial ducts (or surface)

Examples of exocrine glands

serous, mucosal, mixed glands

Serous glands (exocrine)

water and proteins— enzymes

Mucous glands (exocrine)

glycoproteins (mucins)

mucus

Mixed glands (exocrine)

serous and mucus secretions (water, proteins, enzymes)

What are endocrine glands?

release their secretions into the interstitial fluid (ductless glands)

What are examples of endocrine glands?

hormones

associated with the endocrine system

Hormones (endocrine gland)

chemical substances that diffuse into the blood to different tissues, organs

travels through blood

What is the structure of exocrine glands?

1. multicellular

2. unicellular

Multicellular exocrine glands

1. ducts: simple

2. secretory part: tubular and alveolar

Unicellular exocrine glands

goblet cells

secrete mucins

Where simple tubular ducts?

intestinal glands