Epithelium and Glands

Epithelium and Glands

• Epithelial tissues are composed of contiguous cell layers (epithelia) that line the body's internal and external surfaces.
• Epithelial tissues also include cell clusters (glands) originating from invaginated epithelia.

Epithelial Origin

• Epithelia originate from all three germ layers:
  • Ectoderm: oral and nasal mucosa, cornea, epidermis, cutaneous and mammary glands
  • Endoderm: liver, pancreas, respiratory tract lining, digestive tract, kidney uriniferous tubules
  • Mesoderm: male and female reproductive system lining, circulatory system endothelial lining, body cavity mesothelium

Epithelial Functions

• Protection of underlying tissues against abrasion and injury
• Transcellular molecule transport through epithelial layers
• Mucinogen secretion (mucus precursor), hormones, enzymes, and other gland molecules
• Absorption of materials from the lumen (digestive tract or kidney tubules)
• Selective permeability for material movement control between body compartments
• Sensory sensation detection via taste buds, retina, and specialized ear hair cells

Epithelium Defined

• Epithelium refers to layers of tightly joined contiguous cells forming the body's covering or lining.
• Epithelial cell layers connect firmly via junctional complexes, with minimal extracellular space or matrix.
• A basal lamina and reticular lamina compose the basement membrane, which separates epithelium from an underlying connective tissue matrix.
• The adjacent connective tissue supplies nutrients and oxygen to the avascular epithelium through capillary diffusion across the basal membrane.

Epithelial Classification

• Epithelia classification depends on cell layer arrangement and cell morphology.
• Number of cell layers between the basal lamina and free surface and the morphology of the most superficial epithelial cells determines classification.

Simple Epithelium

• A single cell layer defines this epithelium type.

Stratified Epithelium

• Multiple cell layers define this epithelium type.

Squamous (flat)

• Cells are flat when viewed in sections perpendicular to the basal membrane.

Cuboidal

• Cells are cube-shaped when viewed in sections perpendicular to the basal membrane.

Columnar

• Cells are cylindrical when viewed in sections perpendicular to the basal membrane.

Stratified Epithelia

• Stratified epithelia is classified solely according to superficial layer cell morphology, in addition to the above two main classes, there are two more types of epithelia: pseudo stratified and transitional.

Simple Squamous Epithelium

• A single layer of closely packed, flat, or polygonal cells with a flattened profile which when viewed from the surface, appears as a tiled floor with a bulge.
• Seen in sections, only some cells have nuclei due to the plane of section not always including nuclei.
• Lines pulmonary alveoli, forms Henle's loop and Bowman's capsule parietal layer in the kidney, and lines blood and lymphatic vessels, including pleural, pericardial, and peritoneal cavities.

Simple Cuboidal Epithelium

• Consists of a single layer of polygonal cells that appear square-shaped in perpendicular sections with a central round nucleus.
• Forms ducts of many bodily glands, covers the ovary, and lines multiple kidney tubules.

Simple Columnar Epithelium

• Is composed of tall, rectangular cells with oval nuclei situated at the same level in the basal half of the cell when viewed longitudinally.
• May display a striated border made up of digit-like cytoplasmic extensions or microvilli protruding.
• Lines most of the digestive tract, gallbladder, and large glandular ducts and is ciliated in the uterus, oviducts, efferent ducts, and small bronchi providing lumen protruding cilia.

Stratified Squamous Epithelium (Non-keratinized)

• Consists of multiple cell layers with only the deepest layer contacting the basal lamina, basal cells have a cuboidal form, mid-level cells are polymorphic, and superficial cells are flat (squamous).
• Superficial cells are nucleated, it's typically moist, and it lines the mouth, oropharynx, esophagus, vocal folds, and vagina.

Stratified Squamous Epithelium (Keratinized)

• Similar to non-keratinized stratified squamous epithelium, however, surface layers are made of dead cells replaced by keratin.
• Forms the epidermis, a strong layer resistant to friction and waterproof.

Stratified Cuboidal Epithelium

• Consist of two layers of cuboidal cells and lines sweat gland ducts.

Stratified Columnar Epithelium

• Is composed of a deep layer of low polyhedral to cuboidal cells that are in contact with the basal lamina and a surface layer of cylindrical cells.
• Found in a limited number of bodily regions, like the conjunctiva, some big excretory ducts, and regions of the male urethra.

Transitional Epithelium

• Consists of many cell layers, where basal cells are low cylindrical or cuboidal, and polyhedral cells make up multiple layers above the basal cells.
• Exclusively resides in the urinary system, forming the lining from renal calyces to the urethra.
• Superficial cells are big with a rounded apical part like a cupola when the bladder is empty, sometimes binucleated.
• As the bladder stretches with urine, cells with a dome shape flatten, and the epithelium thins.

Pseudostratified Columnar Epithelium

• Although appearing stratified, is a single-layered epithelium.
• Basal lamina contact is made by all cells, however, only some cells reach the epithelial surface.
• The cells that do not reach the surface typically have a broad base and narrow at their apical end, while taller cells have a narrow base in contact with the basal lamina and a broader apical surface.
• Nuclei appear at varying levels because of the varying cell heights, giving the appearance of a stratified epithelium; found in the male urethra, epididymis, and larger excretory ducts.
• The most prevalent type of pseudo stratified cylindrical epithelium is ciliated, with apical cell surface protruding cilia which lines most of the trachea, primary bronchi, auditory tube, portion of the tympanic cavity, nasal cavity, and lacrimal sac.

Epithelial Cell Polarity

• Epithelial cells showcase distinct morphological, biochemical, and functional domains, leading to particular regional polarity.
• Epithelial cells display an apical domain that is in contact with the lumen, and a basolateral domain contacting the basal lamina.
• Surface modifications and domain-specific specializations are accounted for by the functional diversity of these regions which may be microvilli or cilia in apical surfaces and cell-to-cell junctions and interdigitations in basolateral regions.
• Tight junctions separate the apical and basolateral domains by encircling the cell’s apical side.

Apical Domain

• The apical domain represents the free surface of the epithelial cells.
• The apical domain possesses several components, including ion channels, transporter proteins, adenosine triphosphatases (ATPases, transmembrane ATPases), glycoproteins, hydrolytic enzymes, and aquaporins, with the apex having water channel forming proteins.
• Regulated secretion products exit through apical domains modify the apical surface, including microvilli (with related glycocalyx), stereocilia, cilia, and flagella to aid cell functions.

Microvilli

• Microvilli are digit-like cytoplasmic projections which protrude from a cell's free surface toward the lumen.
• Microvilli form the brush border on kidney proximal tubule cells and the striated border of intestinal absorption cells, observed through light microscopy.
• Closely packed microvilli identified via electron microscopy, are membrane-bound cylindric projections that are 1–2 µm long which increases surface area.
• Sparse, shorter microvilli are seen in less active cells.
• Each microvillus contains a bundle of 25-30 actin filaments cross-linked by actin-binding proteins such as espin, fascin, villin, and fimbrin.
• Positive actin filament endings are within a noncrystalline area mainly composed of villin, at the microvillus tip.
• Adverse endings are within (bound to) the terminal web, a complex of actin and spectrin molecules along with intermediate filaments situated cortically in epithelial cells.
• Myosin I and calmodulin offer structural support connecting bundle filaments to the microvillus plasma membrane.
• Tropomyosin and the myosin II work on actin filaments to contract the apical cell surface, hence breaking apart microvilli raising access to molecular transport atop the cell.
• Epithelium not involved in absorption or transport may have microvilli without actin filaments.

Glycocalyx

• An amorphous and coating at the periphery of the microvilli is made of carbohydrate residues bound to the plasma membrane transmembrane proteins which participate in cellular protection and recognition.

Stereocilia

• Unlike true cilia, stereocilia are stiff, non-motile microvilli on both the epididymis and sensory hair cells of the inner ear's cochlea.
• Actin filaments are held together by fimbrin in stereocilia.
• Ezrin and Villin 2 join both peripherally placed actin filament beams to the stereocilia membrane.
• Villin is not present on the tip of the stereocilium, where affirmative poles of actin filaments are located.
• Negatively charged poles of actin filaments end in the terminal web.
• In the epididymis, Stereocilia most likely works by increasing surface area.
• In ciliated ear cells, they help create signals.

Cilia

• Cilia form two types: mobile hair-like structures projecting from an apical cell surface (with a core of axoneme structure composed of microtubules) and non-motile primary cilia which are similar, but do not provide mobility.
• Mobile cilia, called simply cilia, are extensions that seem like hairs developing on the surface of certain epithelial cells with a width of 0.2 µm and a length variating up to7-10μm.
• Cilia found in the respiratory tract moves mucus and material to the oral cavity through series of rapid, continuous waves in which it can be swallowed or spat out.
• Cilia found in the ovary move cells that have been fertilized into the uterus.
• Internal structure seen via electron microscopy, shows a core consisting of organized and evenly dispersed microtubules which is called an axoneme and is composed consistently of longitudinal microtubules ordered specifically in 9+2 (see figs 5.11 and 5.12.
• Two central microtubules (singlets) surrounded by 9 microtubule doublets exists as singlets that are discrete, and show a circular layout along cross areas that consist of 13 protofilaments each.
• Each of the 9 doublets consists internally of two pieces.
• Subunit A is on cross regions, and will have 13 protofilaments, showing a circular area. Subunit B possess 10 protofilaments, a cross area showing an interrupted circle, and shares 3 protofilaments coming from subunit A.

Clinical Correlations

• Kartagener syndrome is a genetically inherited defect in the ciliary which in normal conditions, gives energy for bending to cilia, Cilia cells will lose ability due to this, and will not be as mobile.
• Breathing issues may occur, resulting in sensitivity that makes it hard to clear the airways from germs.
• Men may experience infertility when sperm movement becomes limited.
• 9+2 micro tubules go into action in the axoneme inside of most of the cilia until at its base, where it connects to basal body.
• In a basal body, the shape appears near a duplicate of the cetriole as its composed of 9 triplets as not doublets inside of a single unit.
• The basal area along its attached parts allows cilia to stay on cells and has abilities that move all kinds of cilia on its cells without breaks that all work in concert, and flow evenly.
• Basal bodies make the centriole function come to life.
• More structures emerge around the centriole core; once these elongates near B tubules, a tube like C emerges. Protofilaments are added with 13 as well.
• After this body has been developed, it heads for apical cells to then create the cilia. This joining will have nine sets emerge along with a mix from single sets and doublet units.
• Alar sheets come within these crossing areas, joining on to C tubes.
• This semi rigid area creates a cape which reverses from the microtubule C section. This structure is secured at the plasma and splits off what the body will produce from the entire unit, leaving two sections as the basal pole and a line that connects where the apical sections are.
• Cilia need fluids to assist at move. In turn the move of fluids is called axonemic traffic. Anterograde means that it moves from the basis towards tips.
• Transport by anterograde goes in a retrograde pattern.

Flagella

• Flagella are found in human sperm cells. The structure of flagella is covered in chapter 21 within the male's body of reproduction.

Basolateral Domain

• Includes the basal and lateral sides of the plasma membrane.

Basolateral Domain Subdivisions

• Consists of the sideways sections coming from the membrane along with the baseline part on the plasma sections.
• Each domain has special receptors needed hormones along with signal carriers, those that use Na+/K+ atpase with fluid tubes so bodily excretion.

Membrane Specialities

• Structural areas show a part that connects everything tightly together.
• Microscopy can use bars and lines with points that epithelial parts connect to, on the edges and parts inside. Sections show the bars all together as if from what touches each other and the cells close by.
• These bars all together consist intricately, having glue-like features, so a liquid membrane can stay near. They organize tightly to then sort everything into certain types as represented down below
  • Occluding points helps one cell move liquids but keeps things from pouring in-between.
  • Anchoring sites keeps one from coming loose while attached or from a flat floor.
  • Connecting points enable different chemicals or bits to move from 1 place to another so neighboring units have chances to link and touch.

Occluding Connections (Tight Junctions)

• These connections assist with blocking or preventing liquids passing by in-between so the parts will stay together.

Occluding Bands

• Allows any to pour across plasma parts as it cuts between the cells. Belts can make areas that wrap the full measure with all kinds to assist during that action. They might have to be helped during that process so a group is ready when it's needed.

Anchoring Links (Desmosomes -Macula Adherens)

• Similar links act like a sealed seam because they have the function to act tightly so one can withstand forces that split the cell.

Anchoring Points Specifics (Check Table 5.2)

• Anchoring points are another 3 part that have been created in union, so they equally spread like what has been set up as a location to keep things tight.

Adhering Regions

• Take a place behind a barrier, so an area is there to bond; similar to how band's function plus a region comes close and holds together with E Cadherins (a part of epithelia to make it calcified) with transmembrane parts and that uses Ca. They are glue-like in the inside with parts that hold filaments in place so membrane sections meet via calcium. These zones assist at making areas tight by attaching cells but will support through action.

Linear Facias

• Is the same as a band acting as a union aside to circle a section inside. So in a place like that the tape-like figure helps. For example a section for cells used heart traits will link through a tape acting in alignment.

Desmosomes (Anchor like unions)

• A force keeps everything sealed within the cell like welding. The cells may withstand pressure that is about to split a cell open which these points and units prevent.

Desmosome List

• Check Table 5.2; the connections look similar and will evenly separate from across.

Electronic Micro

• Parts on the outerside look like a circle but the tight sections face the plasma part which has links. The cells consist of sugar proteins joined to glue like parts. Plus what connects those assist plasma to stay within the cells. Extra glue parts attach by the presence of calcium to stop something big from causing the cell to break.

Connection Issues Medically

• Cell protein antibodies create issues because the body reacts to desmosomes inside of cells, even around its layer.
• Auto antibody binding which ruins cell functions cause outer skin to develop blisters where fluids escape uncontrollably.
• A disease known a Naxos which may alter cell units from genetic code, so certain changes form inside the cell and the body.

Gap Junctions

• These points, also called connections or inter paths function at connecting the outside spaces.

Gap Junctions Wide Use

• The points that allow parts to move touch the cells while making a tight hold connecting like an adhesion. As long as the membrane is on, those will allow bits to head across and keep from damage along with fluids to keep working.

Cell Links

• These links are critical because of cell-to-cell contact, as needed, so any can pass via the tight bonds. If those lines are shut with high alkaline levels it can cause unions to shut down, causing certain bits or fluids that go higher break from parts that cause blockage.

Connection Make up

• Transmembrane connections are made up when parts bunch to then make a chanel (hemichanel from its outside so almost 1.5 will float through the parts. They also keep fluid between the cells while preventing bigger damage but keep the entire cell as a strong sealed base.

Surface Specialty

• A surface keeps all from moving around the way it would and anchors and separates what protects.

Area To Assist Cells from Bumps

• Cells may show how the plasma touches base; by doing so the bumps will assist at providing energy as well to the cell. While the cell is segmented a part that produces energy that allows an even flow so water is as secured cell for cells in like those from the tubules.

Desmosome Area

• These desm ensure adhesion parts have strength and may offer types such as: hemis the type, is commonly found. The other works but makes the parts very stable. Both will appear to the structure as if acting as a sealant with the capacity to maintain plasma connections (refer section 5.18).

Surface Changes

• Hemidos work the similar functions for the areas that it anchors so parts act in similar fashion.

Integrin Numbers

• Units show by cell glue protein amounts; proteins appear and work close. Tonofilaments. Plakin sections; they all join to the interior parts of the glue areas, stopping fluid issues. Ebin joins by connecting proteins,

Cellular Issues

• Cell proteins will gather, and cause issues. Certain substances start to lack so more are made by forming something new to work on

Focal Adhesions

• Connections help cell adhere to it by a layer with the basolateral sections made from proteins. It may have to adjust in place.

Cell Renewal

• The regeneration process which assist at finding what can be renewed to a body is steady to where those are needed. So renewal will continue until there is enough with enough time to fix those cells. Then the cells are renewed and its parts are set evenly.

Epidermis

• Cell layers within come and move. It is made in 28 days from the bottom which means that parts may need shorter times. It is repaired in the same pattern and even amount to assist the population to be repaired.

Epithelium

• It must be noted the importance between different cell types to stay aligned with their task. Metaplasdia happens on a change-like cycle inside.

Cilindria Areas

• These need a layer of protection inside; however smoking will damage what will give cells. The process reverses upon someone halting the addiction. Any growths must be looked at to ensure positive or otherwise.

Growth

• Tumours could cause issues so carcinomas, a malignant growth, spreads and damages as a malignant cells may take over. For older generations cancers are like that.

Glands

• Organs are generated with protection that the organ would need, the glands create an outer barrier and provide liquid to create. Then outer part will act as an organ element which enters.

Cells

• Cell parts develop and take place intracellulars such as hormones, serous bodies, then may secret from sudoriparous liquids to the water coming off of the body. Even the vessels help take shape as the gland changes with liquids.

What Can Cause Secretes:

• Glands are graded into the 2 ways it moves products from:
  • outer bodies, the exterior is used but is outside or in where it runs across.
  • Outer organs don't hold paths inside and are cut off where they came so a liquid that runs into tissues nearby it may flow as the part spreads.
• Cells need connections and hormones will come in as molecules for signals which allows interaction.

Cytokins

• Cytokins help spread when connections have been made and those activate other cells when those sensors come alive, it makes a chain process for cells (check the 2nd unit).

Endocrine

• Cells will then begin their tasks so it may touch or have contact with each other. The range and parts could then do one of 3:
  • Work around as an independent, working for what its set for.
  • Paracrino sections for contact and working so pieces aren't too distanced.
  • endocrine/long distance when those come under a lymph or other vessel like liquid.

Constantly Releasing (Secrete)

• There is on and off, but steady creation that constantly lets what is produced. Some produce a solid state, and those will work through certain signaling while areas that have something regulated will contain what needs to be secreted after an aid for signaling happens-section 2; (2.20+2.23).

Liquid Organs

• Glands that excrete and work on a path for release.

Outer Section

• They are graded with production coming from a single cell which has several working units. Those outer sections produce different materials from mucus to serous and mix which are described for digestive sections.

Mucus

• This generates proteins to assist in lubrication and is viscous.

Liquid Production

• Serous gives juice with fluids that enzymes produce. Mixed will have several, serous or lubricant or mucus on units, with liquid sections which can be made with cells that produce a surface.

Cells That Do Excrete Must..

• Those liquid units do 1 or 2 from: mero or aprocino plus holocrinomero helps cell make stuff and then excrete parts with the process of what will make it, which stops it, what produces plasma to assist and the cell part. They will send things. With the 3 types mentioned, there has to be action to keep things moving as a whole so what is to made is delivered correctly. An organ might need aid from certain stimulation for protection to coat a cell section.