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The Tissue Level of Arrangement

Epithelial Tissue

Learning Objectives

By the end of this section, you will exist able to:

  • Explain the structure and function of epithelial tissue
  • Distinguish betwixt tight junctions, anchoring junctions, and gap junctions
  • Distinguish betwixt simple epithelia and stratified epithelia, besides as between squamous, cuboidal, and columnar epithelia
  • Describe the structure and function of endocrine and exocrine glands and their corresponding secretions

Most epithelial tissues are essentially large sheets of cells roofing all the surfaces of the body exposed to the outside earth and lining the outside of organs. Epithelium besides forms much of the glandular tissue of the body. Skin is not the merely area of the trunk exposed to the outside. Other areas include the airways, the digestive tract, also as the urinary and reproductive systems, all of which are lined by an epithelium. Hollow organs and body cavities that practice not connect to the exterior of the body, which includes, claret vessels and serous membranes, are lined by endothelium (plural = endothelia), which is a blazon of epithelium.

Epithelial cells derive from all three major embryonic layers. The epithelia lining the pare, parts of the mouth and nose, and the anus develop from the ectoderm. Cells lining the airways and most of the digestive system originate in the endoderm. The epithelium that lines vessels in the lymphatic and cardiovascular system derives from the mesoderm and is called an endothelium.

All epithelia share some important structural and functional features. This tissue is highly cellular, with footling or no extracellular material present between cells. Adjoining cells grade a specialized intercellular connection between their prison cell membranes called a cell junction. The epithelial cells showroom polarity with differences in construction and function between the exposed or apical facing surface of the cell and the basal surface close to the underlying body structures. The basal lamina, a mixture of glycoproteins and collagen, provides an attachment site for the epithelium, separating it from underlying connective tissue. The basal lamina attaches to a reticular lamina, which is secreted by the underlying connective tissue, forming a basement membrane that helps hold it all together.

Epithelial tissues are most completely avascular. For instance, no claret vessels cantankerous the basement membrane to enter the tissue, and nutrients must come by diffusion or assimilation from underlying tissues or the surface. Many epithelial tissues are capable of quickly replacing damaged and dead cells. Sloughing off of damaged or dead cells is a characteristic of surface epithelium and allows our airways and digestive tracts to rapidly replace damaged cells with new cells.

Generalized Functions of Epithelial Tissue

Epithelial tissues provide the body's first line of protection from concrete, chemical, and biological clothing and tear. The cells of an epithelium act as gatekeepers of the body controlling permeability and allowing selective transfer of materials beyond a physical bulwark. All substances that enter the body must cross an epithelium. Some epithelia oftentimes include structural features that permit the selective transport of molecules and ions beyond their jail cell membranes.

Many epithelial cells are capable of secretion and release mucous and specific chemic compounds onto their upmost surfaces. The epithelium of the small intestine releases digestive enzymes, for example. Cells lining the respiratory tract secrete mucous that traps incoming microorganisms and particles. A glandular epithelium contains many secretory cells.

The Epithelial Cell

Epithelial cells are typically characterized by the polarized distribution of organelles and membrane-bound proteins between their basal and apical surfaces. Particular structures establish in some epithelial cells are an adaptation to specific functions. Certain organelles are segregated to the basal sides, whereas other organelles and extensions, such as cilia, when nowadays, are on the apical surface.

Cilia are microscopic extensions of the apical cell membrane that are supported by microtubules. They beat in unison and movement fluids besides as trapped particles. Ciliated epithelium lines the ventricles of the brain where it helps circulate the cerebrospinal fluid. The ciliated epithelium of your airway forms a mucociliary escalator that sweeps particles of dust and pathogens trapped in the secreted mucous toward the throat. Information technology is called an escalator because information technology continuously pushes mucous with trapped particles upward. In contrast, nasal cilia sweep the mucous blanket downwardly towards your throat. In both cases, the transported materials are unremarkably swallowed, and end up in the acidic environment of your stomach.

Cell to Cell Junctions

Cells of epithelia are closely connected and are not separated by intracellular material. Three basic types of connections let varying degrees of interaction between the cells: tight junctions, anchoring junctions, and gap junctions ((Figure)).

Types of Cell Junctions

The three basic types of jail cell-to-cell junctions are tight junctions, gap junctions, and anchoring junctions.

These three illustrations each show the edges of two vertical cell membranes. The cell membranes are viewed partially from the side so that the inside edge of the right cell membrane is visible. The upper left image shows a tight junction. The two cell membranes are bound by transmembrane protein strands. The proteins travel the inside edge of the right cell membrane and cross over to the left cell membrane, cinching the two membranes together. The cell membranes are still somewhat separated in between neighboring strands, creating intercellular spaces. The upper right diagram shows a gap junction. The gap junctions are composed of two interlocking connexins, which are round, hollow tubes that extend through the cell membranes. Two connexins, one from the left cell membrane and the other from the right cell membrane, meet between the two cells, forming a connexon. Even at the site of the connexon, there is a small gap between the cell membranes. On the inside edge of the right cell membrane, the gap junction appears as a depression. Three connexins are embedded into the membranes like buttons on a shirt. The bottom images show the three types of anchoring junctions. The left image shows a desmosome. Here, the inside edge of both the right and left cell membranes have brown, round plaques. Each plaque has tentacle-like intermediate filaments (keratin) that extend into each cell's cytoplasm. The two plaques are connected across the intercellular space by several interlocking transmembrane glycoproteins (cadherin). The connected glycoproteins look similar to a zipped-up zipper between the right and left cell membranes. The right image shows an adheren. These are similar to desmosomes, with two plaques on the inside edge of each cell membrane connected across the intercellular space by glycoproteins. However, the plaques do not contain the tentacle-like intermediate filaments branching into the cytoplasm. Instead, the plaques are ribbed with green actin filaments. The filaments are neatly arranged in parallel, horizontal strands on the surface of the plaque facing the cytoplasm. The bottom image shows a hemidesmosome. Rather than located between two neighboring cells, the hemidesmosome is located between the bottom of a cell and the basement membrane. A hemidesmosome contains a single plaque on the inside edge of the cell membrane. Like the desmosome, intermediate filaments project from the plaque into the cytoplasm. The opposite side of the plaque has purple, knob-shaped integrins extending out to the basal lamina of the basement membrane.

At ane end of the spectrum is the tight junction, which separates the cells into upmost and basal compartments. When 2 next epithelial cells form a tight junction, there is no extracellular space between them and the motion of substances through the extracellular space betwixt the cells is blocked. This enables the epithelia to deed as selective barriers. An anchoring junction includes several types of prison cell junctions that assist stabilize epithelial tissues. Anchoring junctions are common on the lateral and basal surfaces of cells where they provide potent and flexible connections. In that location are 3 types of anchoring junctions: desmosomes, hemidesmosomes, and adherens. Desmosomes occur in patches on the membranes of cells. The patches are structural proteins on the inner surface of the cell'due south membrane. The adhesion molecule, cadherin, is embedded in these patches and projects through the cell membrane to link with the cadherin molecules of adjacent cells. These connections are especially important in belongings cells together. Hemidesmosomes, which wait like half a desmosome, link cells to the extracellular matrix, for example, the basal lamina. While similar in appearance to desmosomes, they include the adhesion proteins chosen integrins rather than cadherins. Adherens junctions utilise either cadherins or integrins depending on whether they are linking to other cells or matrix. The junctions are characterized by the presence of the contractile protein actin located on the cytoplasmic surface of the cell membrane. The actin can connect isolated patches or grade a chugalug-similar structure inside the cell. These junctions influence the shape and folding of the epithelial tissue.

In contrast with the tight and anchoring junctions, a gap junction forms an intercellular passageway between the membranes of next cells to facilitate the movement of minor molecules and ions between the cytoplasm of next cells. These junctions let electric and metabolic coupling of adjacent cells, which coordinates function in large groups of cells.

Classification of Epithelial Tissues

Epithelial tissues are classified according to the shape of the cells and number of the prison cell layers formed ((Effigy)). Cell shapes can be squamous (flattened and thin), cuboidal (boxy, as wide as it is tall), or columnar (rectangular, taller than it is wide). Similarly, the number of cell layers in the tissue can be one—where every cell rests on the basal lamina—which is a uncomplicated epithelium, or more than one, which is a stratified epithelium and but the basal layer of cells rests on the basal lamina. Pseudostratified (pseudo- = "false") describes tissue with a single layer of irregularly shaped cells that give the appearance of more than one layer. Transitional describes a form of specialized stratified epithelium in which the shape of the cells can vary.

Cells of Epithelial Tissue

Simple epithelial tissue is organized as a single layer of cells and stratified epithelial tissue is formed by several layers of cells.

This figure is a table showing the appearance of squamous, cuboidal and columnar epithelial tissues. Simple and compound forms are shown for each tissue type. In a simple squamous epithelium, the cells are flattened and single layered. In a simple cuboidal epithelium, the cells are cube shaped and single layered. In a simple columnar epithelium, the cells are rectangular and are attached to the basement membrane on one of their narrow sides, so that each cell is standing up like a column. There is only one layer of cells. In a pseudostratified columnar epithelium, the cells are column-like in appearance, but they vary in height. The taller cells bend over the tops of the shorter cells so that the top of the epithelial tissue is continuous. There is only one layer of cells. A stratified squamous epithelium contains many layers of flattened cells. Stratified cuboidal epithelium contains many layers of cube-shaped cells. Stratified columnar epithelium contains many layers of rectangular, column-shaped cells.

Uncomplicated Epithelium

The shape of the cells in the single prison cell layer of simple epithelium reflects the functioning of those cells. The cells in simple squamous epithelium take the advent of sparse scales. Squamous cell nuclei tend to exist apartment, horizontal, and elliptical, mirroring the form of the cell. The endothelium is the epithelial tissue that lines vessels of the lymphatic and cardiovascular system, and it is made upwards of a single layer of squamous cells. Simple squamous epithelium, considering of the thinness of the cell, is present where rapid passage of chemical compounds is observed. The alveoli of lungs where gases lengthened, segments of kidney tubules, and the lining of capillaries are also fabricated of simple squamous epithelial tissue. The mesothelium is a simple squamous epithelium that forms the surface layer of the serous membrane that lines body cavities and internal organs. Its primary function is to provide a smooth and protective surface. Mesothelial cells are squamous epithelial cells that secrete a fluid that lubricates the mesothelium.

In simple cuboidal epithelium, the nucleus of the box-similar cells appears circular and is mostly located near the center of the cell. These epithelia are active in the secretion and absorptions of molecules. Uncomplicated cuboidal epithelia are observed in the lining of the kidney tubules and in the ducts of glands.

In simple columnar epithelium, the nucleus of the tall column-like cells tends to be elongated and located in the basal stop of the cells. Like the cuboidal epithelia, this epithelium is active in the assimilation and secretion of molecules. Simple columnar epithelium forms the lining of some sections of the digestive system and parts of the female reproductive tract. Ciliated columnar epithelium is composed of simple columnar epithelial cells with cilia on their upmost surfaces. These epithelial cells are found in the lining of the fallopian tubes and parts of the respiratory system, where the beating of the cilia helps remove particulate matter.

Pseudostratified columnar epithelium is a type of epithelium that appears to exist stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. In pseudostratified epithelium, nuclei of neighboring cells appear at different levels rather than amassed in the basal end. The organisation gives the appearance of stratification; but in fact all the cells are in contact with the basal lamina, although some practise not achieve the upmost surface. Pseudostratified columnar epithelium is found in the respiratory tract, where some of these cells have cilia.

Both uncomplicated and pseudostratified columnar epithelia are heterogeneous epithelia because they include additional types of cells interspersed among the epithelial cells. For case, a goblet prison cell is a mucous-secreting unicellular "gland" interspersed betwixt the columnar epithelial cells of mucous membranes ((Figure)).

Goblet Prison cell

(a) In the lining of the pocket-sized intestine, columnar epithelium cells are interspersed with goblet cells. (b) The arrows in this micrograph point to the mucous-secreting goblet cells. LM × 1600. (Micrograph provided by the Regents of Academy of Michigan Medical Schoolhouse © 2012)

This illustration shows a diagram of a goblet cell. The goblet cell is shaped roughly like an upside down vase. The enlarged end at the top contains six finger like projections labeled microvilli. Between the microvilli, secretary vesicles containing mucin are moving from the upper half of the cell toward the microvilli. Below the secretory vesicles are several rough endoplasmic reticula and an irregularly shaped Golgi apparatus with secretory vesicles budding off of it. The narrow, lower half of the cell contains the oval-shaped nucleus as well as a few mitochondria and segments of the endoplasmic reticulum.

The second image is a micrograph of the innermost lining of the small intestine. This innermost lining is a simple columnar epithelium, with a single layer of rectangular cells oriented in a line. Occasionally, the line of epithelial cells is interrupted by a goblet cell. Goblet cells are thinner than the epithelial cells and appear roughly pill shaped. In this micrograph, the cells did not stain as darkly as the epithelial cells.

Stratified Epithelium

A stratified epithelium consists of several stacked layers of cells. This epithelium protects against physical and chemical vesture and tear. The stratified epithelium is named past the shape of the most apical layer of cells, closest to the free space. Stratified squamous epithelium is the most mutual type of stratified epithelium in the human body. The apical cells are squamous, whereas the basal layer contains either columnar or cuboidal cells. The acme layer may be covered with expressionless cells filled with keratin. Mammalian skin is an example of this dry, keratinized, stratified squamous epithelium. The lining of the oral cavity cavity is an example of an unkeratinized, stratified squamous epithelium. Stratified cuboidal epithelium and stratified columnar epithelium can also exist found in certain glands and ducts, but are uncommon in the human body.

Some other kind of stratified epithelium is transitional epithelium, so-called because of the gradual changes in the shapes of the apical cells as the float fills with urine. Information technology is found only in the urinary organization, specifically the ureters and urinary bladder. When the bladder is empty, this epithelium is convoluted and has cuboidal apical cells with convex, umbrella shaped, apical surfaces. As the bladder fills with urine, this epithelium loses its convolutions and the apical cells transition from cuboidal to squamous. It appears thicker and more multi-layered when the bladder is empty, and more stretched out and less stratified when the float is full and distended. (Figure) summarizes the different categories of epithelial jail cell tissue cells.

Summary of Epithelial Tissue Cells

This figure is a table with three columns and eight rows. The leftmost column is titled cells, and contains a drawing in each row showing how epithelial cells are arranged above a basement membrane. The middle column is titled location, while the rightmost column is titled function. In a simple squamous epithelium, the cells are flattened and single-layered. Simple squamous cells are found in the air sacs of the lungs, in the lining of the heart, blood vessels and lymphatic vessels. Their function is to allow materials to pass through by diffusion and filtration, as well as to secrete lubricating substances. In a simple cuboidal epithelium, the cells are cube shaped and single layered and located in ducts and secretory portions of small glands as well as in the kidney tubules. The function of simple cuboidal epithelium is to secrete and absorb. In a simple columnar epithelium, the cells are rectangular and are attached to the basement membrane on one of their narrow sides, so that each cell is standing up like a column. There is only one layer of cells. Simple columnar epithelium is found in ciliated tissues including the bronchi, uterine tubes, and uterus, as well as in smooth, nonciliated tissues such as the digestive tract bladder. The function of simple columnar epithelium is to absorb substances but also to secrete mucous and enzymes. In a pseudostratified columnar epithelium, the cells are column-like in appearance, but they vary in height. The taller cells bend over the tops of the shorter cells so that the top of the epithelial tissue is continuous. There is only one layer of cells. Pseudostratified columnar epithelium lines the trachea and much of the upper respiratory tract. The function of pseudostratified columnar epithelium is to secrete mucous and also move that mucus using the hair like cilia projecting from the top of each cell. A stratified squamous epithelium contains many layers of flattened cells. Stratified squamous epithelium lines the esophagus, mouth, and vagina. The function of stratified squamous epithelium is to protect against abrasion. Stratified cuboidal epithelium contains many layers of cube-shaped cells. Stratified cuboidal epithelium is found in the sweat glands, salivary glands, and mammary glands. The function of stratified cuboidal epithelium is to protect other tissues of the body. Stratified columnar epithelium contains many layers of rectangular, column-shaped cells. Stratified columnar epithelium is located in the male urethra and the ducts of some glands. The function of stratified columnar epithelium is to secrete and protect. Transitional epithelium consists of many layers of irregularly shaped cells with diverse sizes. Transitional epithelium is found lining the bladder, urethra and ureters. The function of transitional epithelium is to allow the urinary organs to expand and stretch.

Watch this video to find out more nearly the beefcake of epithelial tissues. Where in the trunk would one find non-keratinizing stratified squamous epithelium?

Glandular Epithelium

A gland is a structure fabricated upward of one or more cells modified to synthesize and secrete chemical substances. Most glands consist of groups of epithelial cells. A gland can be classified as an endocrine gland, a ductless gland that releases secretions direct into surrounding tissues and fluids (endo- = "inside"), or an exocrine gland whose secretions leave through a duct that opens directly, or indirectly, to the external environment (exo- = "outside").

Endocrine Glands

The secretions of endocrine glands are called hormones. Hormones are released into the interstitial fluid, diffused into the bloodstream, and delivered to targets, in other words, cells that have receptors to bind the hormones. The endocrine arrangement is part of a major regulatory system analogous the regulation and integration of body responses. A few examples of endocrine glands include the anterior pituitary, thymus, adrenal cortex, and gonads.

Exocrine Glands

Exocrine glands release their contents through a duct that leads to the epithelial surface. Mucous, sweat, saliva, and breast milk are all examples of secretions from exocrine glands. They are all discharged through tubular ducts. Secretions into the lumen of the gastrointestinal tract, technically outside of the body, are of the exocrine category.

Glandular Structure

Exocrine glands are classified as either unicellular or multicellular. The unicellular glands are scattered single cells, such as goblet cells, constitute in the mucous membranes of the modest and big intestine.

The multicellular exocrine glands known as serous glands develop from elementary epithelium to course a secretory surface that secretes direct into an inner cavity. These glands line the internal cavities of the abdomen and chest and release their secretions direct into the cavities. Other multicellular exocrine glands release their contents through a tubular duct. The duct is single in a uncomplicated gland but in compound glands is divided into 1 or more branches ((Figure)). In tubular glands, the ducts tin be straight or coiled, whereas tubes that grade pockets are alveolar (acinar), such as the exocrine portion of the pancreas. Combinations of tubes and pockets are known as tubuloalveolar (tubuloacinar) compound glands. In a branched gland, a duct is connected to more than than one secretory grouping of cells.

Types of Exocrine Glands

Exocrine glands are classified by their structure.

This table shows the different types of exocrine glands: alveolar (acinar) versus tubular and those with simple ducts versus compound ducts. Each diagram shows a single layer of columnar epithelial cells with a line of cells travelling along the surface of a tissue (surface epithelium) and then dipping into a hole in the tissue. The cells travel down the right side of the hole until they reach the bottom, then curve around the bottom of the hole and then travel up the left side. Finally, the cells emerge back onto the surface of the tissue. The surface epithelial cells are those that are on the surface of the tissue; the duct cells are those that line both walls of the hole. The gland cells are those that line the bottom of the hole. The shape of the hole differs in each gland. In the simple alvelolar (acinar) gland, the duct and gland cells are bulb shaped with the gland cells being the larger end of the bulb. Simple alveolar glands are not found in adults, as these represent an early developmental stage of simple, branched glands. In simple tubular glands, the duct and gland cells are U shaped. Simple tubular glands are found in the intestinal glands. In simple branched alveolar glands, the gland cells form three bulbs at the end of the duct, similar in appearance to a clover leaf. The sebaceous (oil) glands are examples of simple branched alveolar glands. In simple coiled tubular glands, the duct and gland cells form a U, however, the bottom of the U, which is all gland cells, is curved up to the right. Merocrine sweat glands are examples of simple coiled tubular glands. In simple branched tubular glands, the duct is very short and the gland cells divide into three lobes, similar in appearance to a bird's foot. The gastric glands of the stomach and mucous glands of the esophagus, tongue and duodenum are examples of simple branched tubular glands. Among the glands with compound ducts, compound alveolar (acinar) glands have three sets of clover leaf bulbs, for a total of six bulbs. Two of the clover leaf shaped structures extend parallel to the surface epithelium in opposite directions to each other. The third clover leaf extends down into the tissue, perpendicular to the surface. The duct is cross-shaped. The mammary glands are an example of compound alveolar glands. Compound tubular glands have a similar structure to compound alveolar glands. However, instead of three cloverleaf shaped bulbs, the compound tubular gland has three bird's foot shaped bulbs. The duct is also cross-shaped in the compound tubular gland. The mucous glands of the mouth and the bulbourethral glands of the male reproductive system are examples of compound tubular glands, which are also found in the seminiferous tubules of the testis. Compound tubuloalveolar glands are a hybrid between the compound alveolar gland and the compound tubular gland. The two sets of bulbs that run parallel to the surface are bird-foot shaped; however, the set of bulbs that runs perpendicularly below the surface is cloverleaf shaped. The salivary glands, glands of the respiratory passages and glands of the pancreas are all compound tubuloalveolar glands.

Methods and Types of Secretion

Exocrine glands can be classified by their manner of secretion and the nature of the substances released, likewise as by the construction of the glands and shape of ducts ((Figure)). Merocrine secretion is the nearly common type of exocrine secretion. The secretions are enclosed in vesicles that move to the apical surface of the jail cell where the contents are released by exocytosis. For example, watery mucous containing the glycoprotein mucin, a lubricant that offers some pathogen protection is a merocrine secretion. The eccrine glands that produce and secrete sweat are some other example.

Modes of Glandular Secretion

(a) In merocrine secretion, the cell remains intact. (b) In apocrine secretion, the apical portion of the jail cell is released, every bit well. (c) In holocrine secretion, the cell is destroyed as information technology releases its product and the cell itself becomes part of the secretion.

These three diagrams show the three modes of secretion. All three diagrams show three orange cells in a line with attached to a basement membrane. Each cell has a large nucleus in its lower half. The upper half of each cell contains a Golgi apparatus, which appears like an upside down jellyfish. Yellow secretory vesicles are budding from the top end of the Golgi apparatus. Each vesicle contains several orange circles, which are the secreted substance. In merocrine secretion, the secretory vesicles travel to the top edge of the cells and release the secretion from the cell by melding with the cell membrane. In apocrine secretion, the top third of the cell, which contains the secretory vesicles, pinches in at the sides and then completely disconnects above the Golgi complex. The pinched off portion of the cell is the secretion, as it contains the majority of the secretory vesicles. In holocrine secretion, the upper third of the cell, just above the Golgi complex, forms many finger like projections. Each projection contains several vesicles. The tips of the projections that contain secretory vesicles bud off from the cell. In this method of secretion, the mature cell eventually dies and becomes the secretory product.

Apocrine secretion accumulates about the apical portion of the jail cell. That portion of the cell and its secretory contents pinch off from the prison cell and are released. Apocrine sweat glands in the axillary and genital areas release fat secretions that local leaner break downwardly; this causes body odor. Both merocrine and apocrine glands go along to produce and secrete their contents with little damage caused to the cell considering the nucleus and golgi regions remain intact after secretion.

In contrast, the process of holocrine secretion involves the rupture and destruction of the unabridged gland prison cell. The cell accumulates its secretory products and releases them just when it bursts. New gland cells differentiate from cells in the surrounding tissue to replace those lost by secretion. The sebaceous glands that produce the oils on the skin and pilus are holocrine glands/cells ((Figure)).

Sebaceous Glands

These glands secrete oils that lubricate and protect the peel. They are holocrine glands and they are destroyed after releasing their contents. New glandular cells class to supplant the cells that are lost. LM × 400. (Micrograph provided past the Regents of University of Michigan Medical School © 2012)

Image A depicts a cross section of the skin layers. The surface of the skin is at the top of the diagram, with the outer layer occupying about one fifth of the cross section. The outer layer has an irregular border with the inner skin layer, which occupies the remainder of the cross section. A hair follicle is embedded within the inner layer. However, the outer layer actually invaginates into the inner layer around the outside of the follicle, completely sheathing the follicle. The follicle has a bulb at its bottom that is connected to blood vessels. The hair projects from the bulb and travels through the sheath to erupt from the skin surface. The sebaceous gland is an irregular, yellow structure attached at the midpoint of the hair shaft near the border between the inner and outer layers of skin. Its duct actually connects into the side of the hair follicle. Image B shows a micrograph of a sebaceous gland connected to a hair follicle. The bulb of the hair follicle is evident in the micrograph as a bundle of cell surrounding the growing hair at its center. The sebaceous gland is connected to the right of the follicle bulb. The gland appears as an oval shaped mass of pink staining, cube shaped cells with purple nuclei.

Glands are also named afterwards the products they produce. The serous gland produces watery, blood-plasma-similar secretions rich in enzymes such as alpha amylase, whereas the mucous gland releases watery to viscous products rich in the glycoprotein mucin. Both serous and mucous glands are common in the salivary glands of the oral fissure. Mixed exocrine glands contain both serous and mucous glands and release both types of secretions.

Affiliate Review

In epithelial tissue, cells are closely packed with little or no extracellular matrix except for the basal lamina that separates the epithelium from underlying tissue. The primary functions of epithelia are protection from the environment, coverage, secretion and excretion, absorption, and filtration. Cells are bound together by tight junctions that grade an impermeable barrier. They can also be connected by gap junctions, which allow free exchange of soluble molecules betwixt cells, and anchoring junctions, which attach cell to cell or cell to matrix. The different types of epithelial tissues are characterized past their cellular shapes and arrangements: squamous, cuboidal, or columnar epithelia. Single prison cell layers class unproblematic epithelia, whereas stacked cells class stratified epithelia. Very few capillaries penetrate these tissues.

Glands are secretory tissues and organs that are derived from epithelial tissues. Exocrine glands release their products through ducts. Endocrine glands secrete hormones directly into the interstitial fluid and blood stream. Glands are classified both according to the type of secretion and past their structure. Merocrine glands secrete products every bit they are synthesized. Apocrine glands release secretions by pinching off the upmost portion of the jail cell, whereas holocrine gland cells store their secretions until they rupture and release their contents. In this case, the prison cell becomes part of the secretion.

Interactive Link Questions

Watch this video to notice out more about the beefcake of epithelial tissues. Where in the body would one find non-keratinizing stratified squamous epithelium?

The inside of the rima oris, esophagus, vaginal canal, and anus.

Review Questions

In observing epithelial cells under a microscope, the cells are arranged in a single layer and look tall and narrow, and the nucleus is located shut to the basal side of the prison cell. The specimen is what type of epithelial tissue?

  1. columnar
  2. stratified
  3. squamous
  4. transitional

Which of the following is the epithelial tissue that lines the interior of blood vessels?

  1. columnar
  2. pseudostratified
  3. elementary squamous
  4. transitional

Which blazon of epithelial tissue specializes in moving particles across its surface and is institute in airways and lining of the oviduct?

  1. transitional
  2. stratified columnar
  3. pseudostratified ciliated columnar
  4. stratified squamous

The ________ exocrine gland stores its secretion until the glandular cell ruptures, whereas the ________ gland releases its upmost region and reforms.

  1. holocrine; apocrine
  2. eccrine; endocrine
  3. apocrine; holocrine
  4. eccrine; apocrine

Critical Thinking Questions

The structure of a tissue normally is optimized for its function. Describe how the structure of the mucosa and its cells match its office of nutrient absorption.

The mucosa of the intestine is highly folded, increasing the surface area for food assimilation. A greater surface area for absorption allows more than nutrients to be absorbed per unit fourth dimension. In addition, the food-arresting cells of the mucosa have finger-like projections chosen microvilli that further increment the surface area for nutrient assimilation.

Glossary

anchoring junction
mechanically attaches next cells to each other or to the basement membrane
upmost
that role of a cell or tissue which, in general, faces an open infinite
apocrine secretion
release of a substance along with the apical portion of the cell
basal lamina
sparse extracellular layer that lies underneath epithelial cells and separates them from other tissues
basement membrane
in epithelial tissue, a thin layer of fibrous textile that anchors the epithelial tissue to the underlying connective tissue; made upward of the basal lamina and reticular lamina
cell junction
point of cell-to-prison cell contact that connects one jail cell to another in a tissue
endocrine gland
groups of cells that release chemical signals into the intercellular fluid to exist picked upwardly and transported to their target organs past blood
endothelium
tissue that lines vessels of the lymphatic and cardiovascular system, fabricated up of a unproblematic squamous epithelium
exocrine gland
group of epithelial cells that secrete substances through ducts that open to the skin or to internal body surfaces that atomic number 82 to the exterior of the body
gap junction
allows cytoplasmic communications to occur between cells
goblet cell
unicellular gland constitute in columnar epithelium that secretes mucous
holocrine secretion
release of a substance acquired by the rupture of a gland cell, which becomes part of the secretion
merocrine secretion
release of a substance from a gland via exocytosis
mesothelium
unproblematic squamous epithelial tissue which covers the major trunk cavities and is the epithelial portion of serous membranes
mucous gland
group of cells that secrete mucous, a thick, slippery substance that keeps tissues moist and acts as a lubricant
pseudostratified columnar epithelium
tissue that consists of a single layer of irregularly shaped and sized cells that give the advent of multiple layers; found in ducts of certain glands and the upper respiratory tract
reticular lamina
matrix containing collagen and elastin secreted by connective tissue; a component of the basement membrane
serous gland
grouping of cells within the serous membrane that secrete a lubricating substance onto the surface
unproblematic columnar epithelium
tissue that consists of a single layer of cavalcade-like cells; promotes secretion and absorption in tissues and organs
uncomplicated cuboidal epithelium
tissue that consists of a single layer of cube-shaped cells; promotes secretion and absorption in ducts and tubules
uncomplicated squamous epithelium
tissue that consists of a single layer of flat scale-similar cells; promotes diffusion and filtration across surface
stratified columnar epithelium
tissue that consists of two or more layers of column-similar cells, contains glands and is institute in some ducts
stratified cuboidal epithelium
tissue that consists of two or more layers of cube-shaped cells, found in some ducts
stratified squamous epithelium
tissue that consists of multiple layers of cells with the virtually apical existence flat calibration-similar cells; protects surfaces from chafe
tight junction
forms an impermeable bulwark between cells
transitional epithelium
class of stratified epithelium found in the urinary tract, characterized past an apical layer of cells that change shape in response to the presence of urine

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Source: https://opentextbc.ca/anatomyandphysiologyopenstax/chapter/epithelial-tissue/

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