AP1 Tissues CH 5

Stratified Cuboidal Epithelium Structure

Tow or more layers of cells; cells at the apical surface are about as tall as they are wide

Endocrine glands

- lack ducts - secrete hormones directly into interstitial fluid/blood - long distance messages

What are the six characteristics of epithelial tissue?

-Cellularity -Polarity -Attachment to a basement membrane -Avascularity -Extensive innervation -High regeneration capacity

Simple Cuboidal Epithelium Funtion

Absorption and secretion

Nonciliated Simple Columnar Epithelium Function

Absorption and secretion; secretion of mucin

High regeneration capacity

Because epithelial cells have an apical surface that is exposed to the environment, they are frequently damaged or lost by abrasion. Howeverm both damaged and lost epithelial cells generally are replaced quickly because epithelia have a high regeneration capacity. In other words, the cells undergo mitosis frequently. The continual replacement occurs through the mitotic divisions of the deepest epithelial cells (called stem cells), which are adjacent to the basement membrane.

Transitional Epithelium Relaxed and Distended Function

Distension (stretching and relaxation to accommodate urine volume changes in the urinary bladder, ureters, and part of urethra

Stratified Cuboidal Epithelium Location

Ducts of most exocrine glands and some regions of the male urethra

Keratinized Stratified Squamous Epithelium Location

Epidermis of skin

Cellularity

Epithelial tissue is composed almost entirely of tighly packed cells. A minimal amount of extracellular matrix separates the cells in an epithelium.

Sensations

Epithelial tissues contain nerve endings to detect changes in the external environment at their surface. These sensory nerve endings--and those in the underlying connective tissue--continuously supply information to the nervous system concerning touch, pressure, temperature, and pain. Additionally, several organs contain a specialized epithelium, called a neuroepithelium, that houses specific cells responsible for the senses of sight, taste, smell, hearing, and equilibrium.

Transitional Epithelium Relaxed Structure

Epithelium appearance varies, depending upon whether tissue is stretched or relaxed; relaxed epithelium has polyhedral, rounded cells at the apical surface

Exocrine

Glandular secretions delivered to an apical or luminal surface through a duct.

What is extracellular matrix made of?

Ground substance + Protein fibers = extracellular matrix

Why do you think epithelial tissue doesn not contain any blood vessels? Can you think of any epithelial function that could be compromised if blood vessels were running through the tissue?

If epithelium contained blood vessels, the "gatekkeeper" functions of selective permeability would be compromised. Materials would be able to enter the body by entering the blood without passing through the epithelial cells.

Simple Cuboidal Epithelium Location

Kidney tubules; ducts and secretory regions of most glands; surface of ovary; thyroid gland follicles

Stratified Columnar Epithelium Location

Large ducts of salivary glands and in membranous part of male urethra

Ciliated Simple Columnar Epithelium Location

Larger bronchioles of respiratory tract and lining of uterine tubes

Nonciliated Simple Columnar Epithelium Location

Lining of most digestive tract

Nonkeratinized Stratified Squamous Epithelium Location

Lining of oral cavity, part of pharynx, esophagus, lining of vagina, and anus

Transitional Epithelium Relaxed and Distended Location

Lining of urinary bladder, ureters, and part of urethra

Transitional

Many layers; cells fluffly when relaxed, flat when distended; may be multinucleated

Stratified squamous, keratinized

Many layers; cells in surface are dead, flat, and filled with keratin

Stratified squamous; nonkeratinized

Many layers; no keratin; surface cells are flat and alive

Keratinized Stratified Squamous Epithelium Structure

Multiple cell layers; basal cells are cuboidal or polyhedral, whereas apical cells are squamous; apical cells are dead and filled with the protein keratin

Nonkeratinized Stratified Squamous Epithelium Structure

Multiple cell layers; basal cells are cuboidal or polyhedral, while apical (superficial) cells are squamous; superficial cells are alive and kept moist

Nonciliated Pseudostratified Columnar Epithelium Location

Nonciliated form is rare--lines part of the male urethra and epididymis

Gland

Organ or individual cells that secrete a substance

Stratified Columnar Epithelium Function

Protection and secretion

Stratified Cuboidal Epithelium Function

Protection and secretion

Keratinized Stratified Squamous Epithelium Function

Protection of underlying tissue

Nonkeratinized Stratified Squamous Epithelium Function

Protection of underlying tissue

Ciliated Pseudostratified Columnar Epithelium Function

Protection; ciliated form also involved in movement of mucus across surface by ciliary action

Nonciliated Pseudostratified Columnar Epithelium Function

Protection; ciliated form also involved in movement of mucus across surface by ciliary action

Simple Squamous Epithelium Function

Rapid diffusion, filtration, and some secretion in serous membrane

Ciliated Simple Columnar Epithelium Function

Secretion of mucin and movement of mucus along apical surface of epithelium by cilia; oocyte movement through uterine tube

Simple Cuboidal Epithelium Structure

Single layer of cells about as tall as they are wide; spherical and centrally located nucleus

Nonciliated Simple Columnar Epithelium Structure

Single layer of cells taller than they are wide; oval-shaped nucleus riented lengthwise in basal region of cell; apical regions of cell may have microvilli; may contain goblet cells that secrete mucin

Nonciliated Pseudostratified Columnar Epithelium Structure

Single layer of cells with varying heights; all cells connect to the basement membrane, but not all cells reach the apical surface, nonciliated form LACKS goblet cells and cilia

Ciliated Pseudostratified Columnar Epithelium Structure

Single layer of cells with varying heights; all cells connect to the basement membrane, but not all cells reach the apical surface; ciliated form has goblet cells and cilia

Ciliated Simple Columnar Epithelium Structure

Single layer of ciliated cells taller than they are wide; oval-shaped nucleu oriented lengthwise in basal region of cell; may contain goblet cells

Secretions

Some epithelial cells are specialized to produce secretions. Individual gland cells may be scattered among other cell types in an epithelium, or a large group of gland cells may form either an exocrine gland or an endocrine gland that produces specific secretions.

What are Resident cells?

Stationary; support, maintain, repair extracellular (EC) matrix

Multipotent

Stem cells are derived from pluripotent stem cells. They have the capacity to differentiate into a restricted number of some cell types and not others. For example, stem cells in the bone marrow may be stimulated to mature and differentiate into different types of blood cells, but not into some other types of cells. Some adult stem cells have the potential to be multipotent.

Unipotent

Stem cells have the ability to differentiate into a single type of cell, yet these cells still retain the ability to renew themselves. Epithelial stem cells (discussed previously) are examples of unipotent stem cells. Many adult stem cells are unipotent.

What are the differences between embryonic and adult stem cells?

Stem cells may be categorized as either embryonic stem cells or adult stem cells. Embryonic stem cells include those that havebegun to divide in the zygote and the cells in the blastocyst. Embryonic stem cells exhibit the greatest degree of potency--and thus, the greatest potential to differentiate into multiple cell types. In contrast, adult stem cells are the immature cells found in postnatal (already born) organisms. Adult stem cells typically are multipotent or unipotent, and thus they exhibit less potency than embryonic stem cells.

Transitional

These cells can readily change their shape, depending upon how stretched the epithelium becomes. They occur where the epithelium becomes. They occur where the epithelium cycles between distended and relaxed states, such as the lining of the bladder, which fills with urine and is later emptied. When transitional epithelium is in a relaxed state, the cells are polyhedral in shape, whereas when this epithelium is stretched, the surface cells become more flattened.

Stratified Columnar Epithelium Structure

Two or more layers of cells; cells at the apical surface are taller than they are wide

Self-renewal

ability to divide repeatedly to produce both new cells for maturatioon and neww stem cells (frequent mitosis)

Extracellular fluid

anything that is not a cell/everything in the connective tissue that isn't cellular

Cuboidal cells

are about as tall as they are wide. The cells do not resemble perfect cubes because their edges are somewhat rounded. The cell nucleus is spherical and located within the center of the cell.

Squamous cells

are flat, wide, and somewhat irregular in shape. The cells are arranged like flattened floor tiles, and the nucleus is somewhat flattened.

Stem Cells

are immature, undifferentiated cells. These cells are able to divide into two cells, the first of which is another stem cell, and the other a cell that could differentiate into a specialized, mature cell with a unique function. Stem cells have generated interest in the scientific and medical communities because of their potential for repair or replacement of damaged or dying cells.

Columnar cells

are slender and taller than they are wide. The cell nucleus is oval and usually oriented lengthwise and in the basal region of the cell.

Adult Stem Cells

are the undifferentiated stem cells in the body after birth. They may be multipotent or unipotent.

Cuboidal

as tall as they are wide; rounded edges; spherical nucleus in center of cell

Exocrine glands - Structural classification Compound

branched ducts

Apocrine

budding of membrane containing secretion, portion of cytoplasm, and portion of cell membrane - repair damage quickly - Mammary glands - Axillary, public sweat glands

Mast cells

close to blood vessels; secrete heparin to inhibit blood clotting; secrete histamine to dilate blood vessels, increase blood flow

epithelium

composed of one or more layers of closely packed cells, and it contains little to no extracellular matrix between these cells (also, no blood vessels penetrate the epithelium

What are Wandering cells?

concinuously move; components of immune system (commonly leukocytes); repair

Epithelial Tissue

covers the body surfaces, lines the body cavities, and forms the majority of glands

After the embryoblast cells differentiate what three primary germ layers are formed?

ectoderm mesoderm endoderm

When the three primary germ layers have formed what is the growing structure now called?

embryo

Physical protection

epithelial tissues protect both external and internal surfaces from dehydration, abrasion, and destruction by physical, chemical, or biological agents.

Adipocytes

fat cells; store triglycerides

Squamous

flat, wide, irregular shape; flat nucleus

What is the Ectoderm responsible for?

forming many externally placed tissues, such as the epidermis of the skin, hair, nails, and the exocrine glands of the skin. Only some epithelial tissue is derived from the ectoderm. Tooth enamel, the lens of the ye, and the adrenal medula are derived from ectoderm, as is all nervous tissue such as the brain, spinal cord, and nerves.

Where is the best place to locate Simple Epithelium?

found in areas where stress is minimal and where filtration, absorption, or secretion is the primary function. Examples of locations include the lining of the air sacs of the lung, and the intestines, and blood vessels.

Tissues

groups of similae cells and extracellular material that perform a common function (ex. providing protection or facilitating body movement)

Glands

individual or multicellular organs composed predominantly of epithelial tissue. They secrete substances either for use elsewhere in the body or for elimination from the body. Glandular secretions may include mucin, electrolytes, hormones, enzymes, enzymes, and urea (a nitrogenous waste produced by the body.)

Extracellular matrix

is a collection of extracellular molecules secreted by cells that provides structural and biochemical support to the surrounding cells.

Endocrine glands

lack ducts and secrete their products, called hormones, directly into the interstitial fluid and blood. Hormones act as chemical messengers to influence cell activities elsewhere in the body.

Fixed Macrophages

large; irregularly shapes; phagocytose damaged cells and pathogens; stimulate immune system

Endocrine

long distance messages (hormones)

Pseudostratified Epithelium

looks layers because the cells' nuclei are distributed at different levels between the apical and basal surfaces. Although all of these epithelial cells are attached to the basement membrane, some of them do not reach its apical surface. For our purposes, we have classified this as a type of simple epithelium, because all of the cells are attached to the basement membrane.

Where is the Mesoderm located in the embryo?

middle primary germ layer

Free macrophages

mobile, phagocytic cells

Other leukocytes

neutrophils (phagocytic), lymphocytes (kill antibody-tagged cells)

Avascular

no blood vessels; nutrients obtained via diffusion

Cilia

numerous, short, membrane-attaches projections that move fluid, mucus, and materials over the cell surface

Simple Epithelium

one cell layer thick, and all of the epithelial cells are in direct contact with the basement membrane.

Simple cuboidal

one layer of cells about as tall as they are wide

Simple columnar

one layer of cells that are taller than hey are wide; may contain microvilli or cilia

Pseudostratified columnar

one layer of cells with varying height, may contain cilia and goblet cells

Simple Squamous

one layer of flattened cells

Simple Epithelium

one layer thick; all cells bound together and attached directly to basement membrane

Embryonic stem cells

originate from the dividing cells of the zygote or embryoblast protion of the blastocyst. They may be totipotent or pluripotent.

Merocrine

package secretion into vesicles and release via exocytosis - no damage to gland - Lacrimal glands (tears) - Salivary glands - Eccrine glands (sweat) - Pancreas - Gastric (stomach)

Plasma cells

produce antibodies to pathogens

Transitional

readily change shape; dome-shape = flat

Where is the best place to locate Stratified Epithelium?

resembles a brick wall, where the bricks in contact with the ground represent the apical (superficial) layer. It is found in areas likely to be subjected to abrasive activities or mechanical stresses, as multiple layers of cells are better able to resist the wear and tear (e.g., the skin, internal lining f the esophagus, and the internal lining of parts of the pharynx). Cells in the basal layer continuously regenerate as the cells in the apical layer are lost due to abrasion or stress.

When do the embryoblast cells differentiate?

second and third weeks of development

Exocrine glands - Structural classification Tubular

secretory portion and duct are niform diameter

Exocrine glands - Structural classification Acinar

secretory portion forms expanded sac

Stem cells exhibit which two characteristics?

self-renewal and potency

Simple Squamous Epithelium Structure

single layer of thin, flat cells resembling irregular floor tiles; the single nucleus of each cell bulges at its center "fried egg"

Exocrine glands - Structural classification Simple

single, unbranched duct

Totipotent

stem cells have a "total potential," meaning that they exhibit the ability to differentiate into any cell type within an organism. A totipotent cell is produced when a secondary oocyte is fertilized by a sperm, giving rise to a zygote. The first few cell divisions of the zygote result in equall totipotent cells. Thus, only embryonic (and not adult) stem cells have the potential to be totipotent.

Histology

study of tissues

Potency

the potential for differentiation; Different stem cells have varying ability to differentiate into almost any type of cell. Stem cells exhibit four levels of potency: totipotency, pluripotency, multipotency, and unipotency

Primary germ layers and their derivatives

the primary germ layers (ectoderm, mesoderm, endoderm) are formed during the third week of development and will give rise to all of the tissues in the body.

microvilli

tiny projections on the apical surface of the cell that increase the surface area for secretion and absorption

Exocrine glands

typically originate from an invagination of epithelium that burrows into the deeper connective tissue. These glands usually maintain their connection with the epithelial surface by means of a duct , an epithelium-lined tube through which the gland sections are discharged onto the epithelial surface. Examples of exocrine glands include sweat glands, mammary glands, and salivary glands.

Goblet cells

unicellular glands --secrete mucin (mixed with water = mucus)

Zygote

when an occyte (egg) is fertilized by a sperm, it forms a diploid cell

Blastocyst

zygote undergoes multiple cell divisions eventually forming this multicellular structure

How are epithelial tissues characterized?

by layers and shape

Innervated

detect changes in environment

Mesenchymal cells

embryonic stem cell; upon damage, divides into another mesenchumal cell and a cell that is needed to repair damage

Stem cells Characteristics Self renewal

frequent mitosis

Where is the ectoderm located in the embryo?

located on the dorsal and external surfaces

Columnar

slender, taller than they are wide; oval nucleus near basal surface

Microvilli

small projections of membrane, increases surface area

Embryoblast

the cells that form the embryo are collectively known as this

Reticular Connective tissue: protein fibers

- Thinner than collagen fibers, but similar - Coated with glycoprotein - Tough, but flexible branching network - Lymph nodes, spleen, liver

Selective permeability

All substances that enter or leave the body must pass through an epithelium, and thus epithelial cells act as "gatekeepers." An epithelium typically exhibits a range of permeability; it may be relatively impermeable to some substances, while promoting and assisting the passage of other molecules.

Ciliated Pseudostratified Columnar Epithelium Location

Ciliated form lines larger airways of respiratory tract, including nasal cavity, part of pharynx, larynx, trachea, and bronchi

Totipotent

Embryonic; can become any cell/tissue in the body (created by sperm + egg = zygote)

Pluripotent

Embryonic; can become many tissue, but not complete organism (zygote = blastocyst)

Extensive innervation

Epithelia are richly innervated to detect changes in the environment at the body or organ region.

Transitional Epithelium Distended Structure

Epithelial appearance varies, depending upon whether tissue is stretched or relaxed. Distended Epithelium has flattened cells at the apical surface; some cells are binucleated

Endocrine

Hormonal secretions that are transported by the blood.

What are the two types of cells found in the connective tissue?

Resident and Wandering cells - Each class contains specific cells; not in direct contact with each other

Attachment to a basement membrane

The epithelial layer is bound to a thin basement membrane at its basal surface. This is a complex structue produced by the collective efforts of the epithelium and underlying connective tissue. The basement membrane may be observed as a single layer internal to the epithelium using the light microscope--however, in reality it consists of three layers when viewed using an electron microscope; the lamina lucida, the lamina densa, an the reticular lamina. The two lamina closest to the epithelium contain collagen fibers as well as specific proteins and carbohydrates. Together, these basement membrane components strengthen the attachment and fom a selective molecular barrier between the epithelium and the underlying connective tissue.

Exocrine glands - Structural classification Tubuloacinar

both tubules and acinar

Holocrine

cells accumulaate a product and then disintegrate - secretion is mixture of cell fragments and product - dead cells replaced by mitotic epithelial cells - Sebaceous glands (oil)

Stratified Epithelium

contains two or more layers of epithelial cells. Only the cells in the deepest (basal) layer are in direct contact with the basement membrane.

Exocrine

direct secretions - Unicellular - goblet cells - Multicellular --- Structure: simple, compound, tubular, acinar, tubiloacinar --- Function: merocrine, apocrine, holocrine

Fibroblasts

flat with tapered ends; produce fibers anf ground substance

Where is the Endoderm located?

innermost germ layer when the embryo undergoes shape changes

Stem Cells Characteristics Potency

potential to become any other cell

Pluripotent

stem cells are derived from totipotent stem cells. These stem cells are formed from the embryoblast portion (inner cell mass) of the blastocyst. The blastocyst is a ball of cells that develops during the first week of development of development from the zygote. The embryoblast is the portion of the blastocyst that will eventually become an embryo and then a fetus. Pluripotent stem cells can form cells in any of the tissue layers of the embryo, but they cannot form structures such as the placenta. Again, only embryonic stem cells have the potential to be pluripotent

Stratified Epithelium

- 2+ layers - Only deepest layers are in contact with basement membrane - Found in areas prone to abrasion, damage - Cells in basal layer undergo frequent mitosis as apical cells are lost due to abrasion

Connective tissues - functions Storage

- Adipose - energy reserve - Bone - calcium and phosphorus

Selective permeability

- All substances tha enter/leave body must pass through epithelium - Impermeable to many substances, permeable to others

Polar

- Apical surface --- free/superficial surface exposed to space (lumen) --- may have cilia, microvilli - Basal surface - fixed; attached to basement membrane

Connective tissues - functions Transport

- Blood carries nutrients, gases,wastes

Physical protection

- Both internal and external surfaces - Dehydration, abrasion, destruction (physical, chemical, or biological agents)

Stem cells Immature, undifferentiated cells

- Can become more stem cells - Can become specialized, mature cells

What are the 3 basic components of connective tissues?

- Cells - Protein fibers - Ground substance

What are the three types of protein fibers in Connective tissue?

- Collagen - Elastic - Reticular -- THese strengthen and support tissue

Elastic Connective tissue: protein fibers

- Conatin elastin - Branch, rejoin, appear wavy - Stretch, recoil: allow skin, lungs, arteries to return to normal shape after stretching - Yellow in fresh tissue; "yellow fibers" - Black in tissue sections with special stain (silver)

Sensations

- Contain nerve endings - Detect changes in external environment - Supply information about touch, pressure, temperature, pain - Neuroepithelium - senses sight, tast, smell, hearing, equilibrium

What are the protein fibers that help make up the extracellular matrix?

- Elastic fiber - Collagen fiber - Reticular fiber

What are the four types of Resident cells that are found in Connective tissue?

- Fibroblasts - Adipocytes - Mesenchymal cells - Fixed Macrophages

Highly regenerative

- Frequently damaged and replaced - Mitosis of cells closest to basement membrane

Secretions

- Glands; sweat, oil, hormones

Connective tissues - functions Binding of structures

- Ligaments: bone to bone; tendons: muscle to bone - Dense irregular: anchors skin to muscle, bone

Pseudostratified Epithelium

- Looks layered due to varying location of nuclei - All cells attached to basement membrane , not all reach apical surface

What are the four types of Wandering cells that are found in the Connective tissue?

- Mast cells - Plasma cells - Free macrophages - Other leukocytes

Connective tissues - characteristics

- Most diverse, abundant tissue - Supports, protects, and binds organs - Three basic components ---- Cells ---- Protein fibers ---- Ground substance

Connective tissues - functions Support, structural framework

- Muscle attachment - Keeps lungs, airways open - Capsules around kidney, spleen

Multicellular exocrine gland

- Numerous cells work together to produce secretion - Alcini - clusters of cells that produce secretion - Duct - small channels that merge to form larger duct that transports secretion to epithelial surface - Typically surrounded by fibrous capsule divided into lobes

Simple Epithelium

- One layer - Great for filtration, absorption, secretion

What are the four Epithelial tissue functions?

- Physical protection - Selective permeability - Secretions - Sensations

What is ground substance made of?

- Produced by CT cells - Largee molecules + water ---- Large molecules attract & absorb water ---- Glycoaminoglycans (GAG) ---- Proteoglycan - protein attached to GAG - Viscous (blood), semisolid (cartilage), or solid (bone) depending on components

What are the six functions of Connective tissue?

- Protection - Support, structural framework - Binding of structures - Storage - Transport - Immune protection

Connective tissues - functions Protection

- Skeleton protects delicate organs - Adipose protects organs (kidneys, eyes)

Neuroepithelium

- Specialized epithelium that houses specific cells responsible for the senses of sight, taste, smell, hearing, and equilibrium

Attached to basement membrane

- Three layers of connective tissue - Collagen fibers, proteins, and carbohydrates - barrier between epithelial tissue and underlying connective tissue

Collagen Connective tissue: protein fibers

- Unbranched - Strong, flexible, resistant to stretch - White in fresh tissue; "white fibers" - Pink in H&E-stained sections - Common in tendons, ligaments

Cellular

- composed almost entirely of tighly packed cells - minimal extracellular matrix, if any

Basal surface

- fixed or deep surface - where the epithelium is attached to the underlying connective tissue

Unicelluar exocrine gland

- no duct; close to epithelium - goblet cells

Exocrine glands

- pocket in underlying connective tissue - connected to epithelial surface by duct

Mesoderm

-Dermis of skin -Epithelial lining of blood vessels, lymph vessels, serous membranes -Muscle tissue -Connective tissue -Adrenal cortex -Heart -Kidneys and ureters -Internal reproductive organs -Spleen

Ectoderm

-Epidermis of skin and epidermal derivatives (hair, nails, sweat glands, mammary glands) -Nervous tissue and sense organs -Pituitary gland -Adrenal medulla -Enamel of teeth -lens of eye

Endoderm

-Epithelial lining of respiratory tract, GI tract, tympanic cavity, auditory tube, urinary tract, reproductive tract -Liver (most of) -Gallbladder -Pancreas -Palatine tonsils (portion of) -Thyroid gland -Parathyroid glands -Thymus

What does the Mesoderm form?

-It forms all muscle tissue and the epithelial lining of vessels and serous membranes that line the body cavities. -This becomes mesenchyme, which then goes on to form all connective tissues in the body. -The dermis of the skin, adrenal cortex, heart, spleen, kidneys and ureters, and internal reproductive structures are also derived from this

What are the three layers of the basement membrane?

-Lamina Lucida -Lamina Densa -Reticular Lamina

Connective tissues - functions Immune protection

-Leuocytes - protect body from disease - Repair of tissues - Viscous EC matrix inhibits spread of pathogens

What does the Endoderm form?

-forms the epithelial linings of the tympanic cavity (middle ear) and auditory tube, as well as the digestive, respiratory, reproductive, and urinary tracts. -also forms organs such as the thyroid gland, parathyroid glands, the thymus and portions of the palatine tonsils, as well as most of the liver, gallbladder, and pancreas.

Apical surface

-free, superficial, surface -exposed either to the external environment or to some internal body space -may have microvilli or cilia

Stratified columnar

2+ layers of cells; apical layer is columnar-shaped

Stratified cuboidal

2+ layers of cells; apical layer is cuboidal-shaped

Stratified Epithelium

2+ layers thick; only deepest layer attached to basement membrane

Multipotent

Adult; derived from pluripotent; limited potency (bone marrow = many blood cells)

Unipotent

Adult; only become one type of cell, but are capable of self-renewal (epidermis = epithelial cells)

Simple Squamous Epithelium Location

Air sacs in lungs (alveoli); lining of lumen of lymph vessels and blood vessels (endothelium); serous membranes of body cavities (mesothelium) Oxygen = Nutrients Carbon Dioxide = Waste

Avascularity

All epithelial tissues lack blood vessels. Nutrients for epithelial cells are obtained either directly across the apical surface or by diffusion across the basal surface from the underlying connective tissue

Polarity

Apical surface - free or superfficial surface exposed to space (lumen) --- may have cilia, microvilli Basal surface - fixed; attached to basement membrane