PRELIM: EPITHELIAL TISSUE Flashcards
● Avascular (few or no blood vessels) tissue, lacking a direct blood supply
● Nutrients are delivered by diffusion from blood vessels in the neighboring connective tissue
Epithelial tissue
Greek work
epi =
thele =
upon, nipple
distinctive shape, varying from spherical to elongated or elliptic
Epithelial cell nuclei
Facing the surface
apical side
Ability to transport macromolecules from one side of the cell to another
Transcytosis
Type of endocytosis; pino = to drink; cell takes in fluids along with the dissolved small molecules
Transcytosis
Type of endocytosis; pino = to drink; cell takes in fluids along with the dissolved small molecules
Pinocytosis
Facing the basal membrane
Basal side
Moving larger molecules out of the cell
Exocytosis
What are the basic functions of epithelial tissue?
- Protection of the body from abrasion and injury
- e.g. skin and esophagus - Absorption of material from lumen
- e.g. tubules in kidney, small and large intestine - Transportation of material along surface
- e.g. cilia-mediated transport in the trachea - Secretion of mucus, hormones, and proteins
- e.g. glands - Gas exchange
- e.g. alveoli in the lung - Lubrication between two surfaces
- e.g. mesothelium of pleuray cavity
Intertwining elongated processes
Nervous tissue
Aggregated polyhedral cells
Epithelial tissue
Elongated contractile cells
Muscle tissue
Several types of fixed and
wandering cells
Connective tissue
Classification of Epithelial Tissues
Based on the number of layers of cells:
Simple and stratified
Based on the shapes of cells in the superficial layer:
● Squamous epithelium: Thin and flat; flat nuclei
● Cuboidal epithelium: Pyramidal in shape (box); spherical nuclei
● Columnar epithelium: Rectangular in shapel; elliptic or oval nuclei
● Transitional epithelium (urothelium)
Thin and flat; flat nuclei
Squamous epithelium
Pyramidal in shape (box); spherical nuclei
Cuboidal epithelium:
Rectangular in shapel; elliptic or oval nuclei
Columnar epithelium
urothelium
Transitional epithelium
● Also acts as filters which provides structural support for the epithelial cells
● Attach epithelia to underlying connective tissue
● Thin extracellular layer of specialized proteins, usually having two parts (viewed in TEM)
Basement membrane
What are the 6 functional epithelium?
- Mesothelium
- Endothelium
- Myoepithelium
- Endometrium
- Germinal Epithelium
- Glandular Epithelium
Serous lining of cavities such as pericardium, pleura, and peritoneum for lubrication
Mesothelium
Endothelium
Made up of flat cells that line the blood vessels
Basket cells, to remodel the scars in the skin
Myoepithelium
Lining of the uterus
Endometrium
Layer of the ovaries and seminiferous tubules
Germinal Epithelium
For secretions
Glandular Epithelium
Specializations of the Apical Surface (Apical Domain)
Cilia
Microvilli
Stereocilia
- Elongated, motile structures that have a greater diameter and length than microvilli
- Arise from basal bodies
- Has a well-organized core of microtubules in which restricted, dynein-based sliding of
microtubules cause ciliary movement that propels material along an epithelial surface - Kinesin: positive side
- Abundant in simple cuboidal cells where they exhibit rapid beating patterns that move a current
of fluid and suspended matters in one direction along the epithelia
Cilia
9 pairs of triplet microtubules with center pair of microtubules
Axoneme
- Smaller than cilia
- Composed of actin microfilaments that generally function to increase epithelial cells’ apical surface area for absorption
- Brush or striated border that is projecting to the lumen
- Anchored to a network structure–terminal web–which contains actin filaments to stabilize themicrovillus
Microvilli
About 1 micrometer long an 0.1 micrometer wide
Microvillus
- Long microvilli with specialized mechanosensory function (light, touch, hearing, proprioception,
and pain) - Can sense movement, action, and location
- Increases the cells’ surface area and facilitates absorption
- Lining of male reproductive system and cells in the inner ear
- Show branching distally
- Consist of actin microfilaments
- FUNCTION: Help with absorption
stereocillia
Specialization of the Lateral Surface (Lateral Domain)
Zonula Occludens
Zonula adherens
Desmosomes
Gap junctions
- Completely surround the apical cells’ borders to seal the underlying intercellular cleft from the
outside environment - Linear arrangements of linked proteins surround the apical ends of the cells and prevent paracellular passage of substances
Zonula occludens (tight junctions)
Interacting transmembrane protein
Claudin and Occludin
- Found just beneath the tight junction, also forming bandlike junctions that surround the entire cell and serve to attract adjacent cells
Zonula adherens (adhering junctions)
Protein associated in adherens
Cadherin family
- Located beneath the adhering junctions, also assist in cell-to-cell attachment
- Resembles a single “spot-weld” and does not form a belt around the cell
Desmosomes
- Communicating junctions
- Provide a low-resistance channel to permit passage of ions and small molecules between
adjacent
Gap junctions
Composed of 6 connexins; forms a channel, allowing the passage of small molecules from one cell to the other
Connexons
Specialization of the Basal Surface (Basal Domain)
Basal lamina
Reticular Lamina
Sheet of ECM on all epithelial cells in contact with subjacent connective tissue as their basal surfaces
Basal Lamina
Large glycoprotein molecules that self-assemble to form a lace-like sheet immediately below the cells’ basal poles where they are held in place by the transmembrane integrins
Laminin
Monomers of type IV collagen contain three polypeptide chains and
self-assemble further to form a felt-like sheet associated with the laminin layer
Type IV collagen
These glycosylated proteins and others serve to link together the laminin and type IV collagen sheets
Entactin (nidogen–a glycoprotein) and Perlecan (proteoglycan with heparin sulfate side chains)
- Layer below basal lamina
- Reticular fibers made of type III collagen in the underlying connective tissues by anchoring fibrils of type VII collagen
Reticular lamina
● Composed of one layer of uniform flat cells which rest on the
basement membrane
● SIMPLEST OF THE EPITHELIA
● Apical surfaces are smooth and the width of cells is greater than height
Simple Squamous Epithelial Cells
● Allows passage of materials by diffusion and filtration in sites
where protection is not important
● Secretes lubricating substances in serosae
● Facilitates the movement of the viscera (mesothelium)
● Active transport by pinocytosis (mesothelium and endothelium)
● Secretion of biologically active molecules (mesothelium)
Simple Squamous EPITHELIAL TISSUE functions
● Lining the posterior surface of the cornea
● Lining blood vessels and lymphatic vessels (endothelium)
● Lining the surface of the body cavities (pericardial–within the heart, pleural–within chest cavity/lungs,
peritoneal–within the visceral or abdominal cavities: mesothelium)
● Lining the alveoli of the lungs
Locations of Simple Squamous Epithelial Tissue
Flattened and elongated, oriented parallel to the direction of blood flow, and rest on a basement membrane
Endothelial Cells
- Junctions that link cells and basement membrane
➢ Composed of transmembrane integrins which attach cells to proteins of the
Hemidesmosomes
Wavy structure
Internal elastic lamina
Comprised of the endothelium, subendothelial connective tissue, and internal elastic lamina
Tunica intima
- Neoplasm that arises from surfaces of the pleural and peritoneal cavities
- Only occasionally found in the pericardial mesothelium
- Commonly seen in individuals who either were exposed to asbestos or who smoke
Mesothelioma (cancer of the mesothelium)
- Formation of deposits of yellowish plaques that contain cholesterol, lipid material, and lipophages (macrophage with engulfed lipids)
- When hardened, may occlude blood flow to distant tissues, and blood clots may form on exposed collagen in subendothelial connective tissue
- Clot formation or dislodged pieces of plaque may result in vascular occlusion and stroke
Atherosclerosis
Clinical Significance
Simple Squamous Epithelial Tissue
Endothelial cells
Mesothelioma
Atherosclerosis
● Composed of one layer of uniform cuboidal cells, which rest on the
basement membrane
● Cell’s height, width, and depth are roughly equal
● Nuclei: Centrally placed and spherical in shape
Simple Cuboidal Epithelium
Characterized by the overproduction of thyroid hormone
- Seen most often in women 20-40 years old
- ↑T3 and T4, ↓TSH: the immune system produces an anti-TSH that counters it
- Undergoes radioactive iodine therapy along with Grave’s disease
Hyperthyroidism
SYMPTOMS:
- Nervousness, irritability, tachycardia, increased perspiration, difficulty sleeping, muscle
weakness, warm moist skin, trembling hands, and hair loss
Hyperthyroidism
- Most common form of hyperthyroidism
- Autoimmune disease (antibodies to the TSH receptor)
- SIGNS: Exophthalmos
- DIAGNOSTIC TEST: Antibody Test
Grave’s Disease
- Most common cause of hypothyroidism
- Associated with enlargement of the thyroid gland (goiter)
- Mostly manifests goiter
- Chacterized by high TSH and positive TPO (thyroperoxidase) antibody
Hashimoto’s thyroiditis
● Composed of one layer of columnar cells resting on the basement
membrane
● Cell’s height is greater than width
Simple Columnar Epithelium
● Absorption
● Secretion of mucus, enzymes, and other substances
● Ciliated type propels mucus (or reproductive cells) by ciliary action
Simple Columnar Epithelium
LOCATION:
● Found in the digestive tract
● Oviducts in the female reproductive system
● Ductuli efferentes testis of the male reproductive system
Simple Columnar Epithelium
- Disorder of the small intestine
- If left untreated, can lead to malabsorption, anemia, bone disease, and rarely, some forms of
cancer
HISTOLOGIC FEATURES: - Blunting of villi
- Presence of lymphocytes among epithelial cells (intraepithelial lymphocytes)
- Increased lymphocytes within the lamina propia (connective tissue)
Celiac (coeliac) Disease
FUNCTION:
● Secretion, particularly of mucus
● Population of mucus by ciliary action
LOCATION:
● Nonciliated type in male’s sperm-carrying ducts and ducts of large glands
● Ciliated variety lines the trachea, most of the upper respiratory tract
Pseudostratified Ciliated Columnar Epithelium
Clinical Significance
Simple Columnar Epithelium
Celiac (coeliac) disease
● Composed of one layer of nonuniform cells that varyin shape and height
● Often referred to as RESPIRATORY EPITHELIUM
● Cells appear similar to stratified cells, but all cells are in contacts with the basement membrane
Pseudostratified Columnar Epithelium
- Disease marked by acute or chronic inflammation of the bronchial tubes
- Inflammation may be caused by infection (virus, bacteria) or by exposure to irritants
Bronchitis
Surface epithelium may undergo hyperplasia (enlargement of
tissue/organ) and loss of cilia; the pseudostratified epithelium is often replaced by squamous epithelium
chronic bronchitis
Clinical Significance
Pseudostratified columnar epithelium
Bronchitis
● Contains several layers of cells in the superficial layer being flattened
● Thick membrane composed of several layers
● Basal cells: Cuboidal or columnar and metabolically active; active in
mitosis and produce the cells of the more superficial layers
● Surface cells: Flattened
FUNCTION:
● Protects the body against injury, abrasion, dehydration, and infection
Stratified Squamous epithelium
2 Types of Stratified Squamous Epithelium
Keratinized and non keratinized
LOCATION: Skin
- Flattened, nonnucleated dead cells–filled with tonofilaments
keratinized
LOCATION: Linings of the oral cavity, esophagus, vagina, and true
vocal cords
- Flattened, nucleated dead cells
Non keratinized
- Common chronic inflammatory skin disease typically characterized by pinl-salmon colored
plaques with silver scales and sharp margins - T-lymphocyte-mediated immunologic reactions are believed to cause the clinical feature
SYMPTOMS: - Itching, joint pain, nail pitting, and nail discoloration
PATHOLOGIC EXAMINATION: - Thickened epidermis
- Extensive overlying parakeratotic scales
- Microabscesses form by neutrophils in the stratum corneum layer
- Micropustules within the stratum granulosum and spinosum layers
Psoriasis
- Complication of gastroesophageal reflux disease marked by metaplasia of the simple squamous
epithelium of the distal esophagus into a simple columnar epithelium as a response to
prolonged reflux-induced injury - Patients have high risk of developing adenocarcinoma
Barrette Syndrome
Clinicak Significance
Stratified Squamous Epithelium
Psoriasi
Barrett Syndrome
● Composed of two or three layers of cells
● Top layer: Columnar in shape
● Basal layer: Usually cuboidal in shape
● Not a common type of epithelium
LOCATION:
● Conjunctiva (thin, clear membrane protecting the eye)
● Some large ducts in the exocrine glands
Stratified Cuboidal Epithelium
Clinical condition that can result from blockage of a duct/s, so that saliva is not able to exit in the mouth
- Causes the saliva to back up inside the duct, resulting in gland swelling
Salivary Gland Swelling
Most common blockage which forms from salts contained in the saliva
➢ Blocked duct and gland filled stagnant saliva may become infected with bacteria
Salivary Stone (calculus/calculi)
Most common blockage which forms from salts contained in the saliva
➢ Blocked duct and gland filled stagnant saliva may become infected with bacteria
Salivary Stone (calculus/calculi)
● Stratified epithelium often referred to as urothelium
● May contain 4-6 layers in the relaxed state
● Histological appearances can be changed when stretched
● Surface cells: Often described as “dome-shaped”–dome cells (may contain 2
nuclei) or umbrella cells (contain extra cell membrane)
LOCATION:
● Lines the excretory channels leading from the kidney (renal calyces, ureters,
bladder, and proximal segment or the urethra
Transional epithelium
Spread of malignant neoplasm from its site of origin to a remote site, usually through blood and
lymphatic vessels
Metastasis
- General term for describing a disorder of lipoprotein metabolism causing amounts of lipids and
lipoproteins in the blood - Certain dyslipidemias constitute a major risk factor in developing atherosclerosis such as
hypercholesterolemia
Dyslipidemia
- Abnormal bone mineralization producing weak, soft bones
- May be caused by vitamin D deficiency or kidney disorders, including renal Fanconi syndrome
Osteomalacia
Reversible process by which one mature cell type changes into another mature cell type, as in
squamous metaplasia of respiratory or glandular
Metaplasia
Collection of neutrophils and neutrophil debris within the parakeratotic scale in the skin disease psoriasis
microabscess
Collection of neutrophils within the epidermis, abutting the parakeratotic scale in the skin disease psoriasis
Micropostule
Persistence of the nuclei of keratinocytes into the stratum corneum of the skin or mucous
membranes
- Parakeratotic scales containing neutrophils are seen in the skin disease psoriasis
Parakeratosis
● Composed of epithelial tissue
Glands
According to how the secretory product leaves the gland:
Endocrine glands
Exocrine glands
Release their products into interstitial fluid or directly into the bloodstream
endocrine glands
Secrete their products either through ducts into the lumen of an organ or directly onto the blood surfaces
Exocrine glands
Produce mucus or goblet cells
Mucous glands
Produce largely enzymes and stain darkly with H&E due to the cells’ content of RER and secretory granules
Serous glands
According by product:
Serous glands
Mucous glands
Mixed glands (seromucous)
Sebaceous glands
According to mechanisms or secretion:
Merocrine
Apocrine
Holocrine
According to morphology:
Unicellular
Multicellular
