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
