Chapter 4 - The Tissue Level

The nature of the extracellular material that surrounds the tissue cells and the connections between the cells that compose the tissue.

A tissue is a group of cells that work together to perform specific functions in the body.

secrete mucus that traps foreign particles and to use cilia to sweep away mucus for elimination from the body.

• Appears to have several layers because cell nuclei are at various levels.

• All cells are attached to the basement membrane in a single layer, but some cells do not extend to the apical surface, giving a false impression of a multilayered tissue.

Epithelial tissue has many cells tightly packed together with little to no extracellular matrix, while connective tissue has a few scattered cells surrounded by large amounts of extracellular matrix.

Stomach, intestines, and urinary bladder.

1. sites of filtration (such as blood filtration in kidneys)

2. or diffusion (such as diffusion of oxygen into blood vessels of lungs)

3. sites of secretion in serous membranes.

4. It is not found in body areas subject to mechanical stress (wear and tear).

Tight junctions consist of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells.

Transitional epithelium allows urinary organs to stretch and maintain a protective lining while holding variable amounts of fluid without rupturing.

Cilia beat in unison, moving mucus and foreign particles toward the throat, where they can be coughed up and swallowed or spit out. Cilia also help move oocytes expelled from ovaries through uterine tubes into the uterus.

Histology is the science that deals with the study of tissues.

It lines the airways of most of the upper respiratory tract.

Tight junctions.

The relationship where epithelial tissue relies on the connective tissue for support and nutrient exchange.

It lines part of the urethra, large excretory ducts of some glands (such as esophageal glands), small areas in the anal mucous membrane, and part of the conjunctiva of the eye.

Adherens junctions contain plaque and cadherins that join cells. They help epithelial surfaces resist separation during contractile activities.

Hemidesmosomes anchor cells to the basement membrane using integrins.

Basal layers usually consist of shortened, irregularly shaped cells; only the apical layer has columnar cells.

The four basic types of tissues are epithelial, connective, muscular, and nervous tissues.

Stratified squamous epithelium has two or more layers of cells; cells in the apical layer and several layers deep to it are squamous, while cells in deeper layers vary from cuboidal to columnar. As basal cells divide, daughter cells push upward toward the apical layer, becoming dehydrated and less metabolically active as they move away from the blood supply.

It is found in the ducts of adult sweat glands and esophageal glands, and part of the male urethra.

Endocrine gland secretions enter the interstitial fluid and then diffuse into the bloodstream without flowing through a duct.

Multicellular exocrine glands are categorized according to whether their ducts are branched or unbranched and the shape of the secretory portions of the gland.

Simple squamous epithelium is a single layer of flat cells that resembles a tiled floor when viewed from the apical surface; it has a centrally located nucleus that is flattened and oval or spherical in shape.

Keratinized stratified squamous epithelium forms the superficial layer of the skin.

Secretion and absorption.

The two main types of epithelial tissue are covering and lining epithelium (surface epithelium) and glandular epithelium.

Females aged 30 to 65 should have Pap testing and HPV testing (cotesting) every five years or a Pap test alone every three years.

Tissues may be hard (bone), semisolid (fat), or liquid (blood).

Keratinized stratified squamous epithelium develops a tough layer of keratin in the apical layer of cells and several layers deep to it, while nonkeratinized stratified squamous epithelium does not contain large amounts of keratin and is constantly moistened by mucus.

Protection; limited secretion and absorption.

Connective tissue protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity to disease-causing organisms.

Epithelial tissue functions to protect, secrete (mucus, hormones, and enzymes), absorb (nutrients in the gastrointestinal tract), and excrete (various substances in the urinary tract).

Exocrine glands secrete their products into ducts that empty onto the surface of a covering and lining epithelium such as the skin surface or the lumen of a hollow organ.

Hemidesmosomes in the basal surfaces of the deepest layer of epithelial cells anchor the epithelium to the basement membrane.

A gland where the tubular secretory part is branched and attaches to a single unbranched duct. Example: gastric glands.

Gap junctions allow ions and small molecules to diffuse between neighboring cells, facilitating communication and the spread of nerve or muscle impulses.

Nonkeratinized stratified squamous epithelium lines wet surfaces such as the lining of the mouth, esophagus, part of the epiglottis, part of the pharynx, and vagina, and covers the tongue.

All glands of the body are classified as either endocrine or exocrine.

Pseudostratified epithelium appears to have multiple layers of cells because the cell nuclei lie at different levels, but it is actually a simple epithelium because all its cells rest on the basement membrane.

Examples of multicellular exocrine glands include sudoriferous (sweat), sebaceous (oil), and salivary glands.

It is based on how their secretions are released.

The five most important types of cell junctions are tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.

Transitional epithelium lines the urinary bladder and portions of the ureters and urethra.

Desmosomes attach to intermediate filaments of the cytoskeleton, while adherens junctions attach to microfilaments.

Ciliated simple columnar epithelium is a single layer of ciliated columnlike cells with oval nuclei near the base of cells. Goblet cells are usually interspersed.

Nonciliated pseudostratified columnar epithelium appears to have several layers because the nuclei of the cells are at various levels. Even though all the cells are attached to the basement membrane in a single layer, some cells do not extend to the apical surface. It contains cells without cilia and lacks goblet cells.

Epithelial tissue lacks blood vessels and forms surfaces, so it is always found adjacent to blood vessel-rich connective tissue to enable exchanges with blood necessary for oxygen and nutrient delivery and waste removal.

The basement membrane attaches epithelial cells to underlying connective tissue, providing structural support and regulating exchanges between the epithelium and connective tissue.

Squamous cells are thin and flat, which allows for the rapid passage of substances through them.

A gland where the secretory portion is rounded and attaches to a single unbranched duct. Example: glands of penile urethra.

Holocrine glands.

Cell junctions are contact points between the plasma membranes of tissue cells.

It contains cells that extend to the surface and secrete mucus (goblet cells) or bear cilia.

Its multiple layers and elasticity make it ideal for lining hollow structures subject to expansion from within.

Exocrine glands release their secretory products into ducts that empty onto the surface of a covering and lining epithelium, such as the skin surface or the lumen of a hollow organ.

It lines some bronchioles of the respiratory tract, uterine tubes, uterus, some paranasal sinuses, central canal of the spinal cord, and ventricles of the brain.

Protection and secretion.

Epithelial tissue covers body surfaces and lines hollow organs, body cavities, and ducts; it also forms glands.

It lines the gastrointestinal tract (from stomach to anus), ducts of many glands, and the gallbladder.

Endocrine secretions have far-reaching effects because they are distributed throughout the body by the bloodstream.

The basal lamina contains proteins such as laminin and collagen, as well as glycoproteins and proteoglycans.

Transitional cells change shape from squamous to cuboidal and back, as organs such as the urinary bladder stretch to a larger size and then collapse to a smaller size.

The secretory product accumulates at the apical surface of the secreting cell, and that portion of the cell pinches off by exocytosis to release the secretion. Example: milk fats in the mammary glands.

Gap junctions function in communication between adjacent cells.

In a relaxed state, transitional epithelium looks like stratified cuboidal epithelium, with apical layer cells that are large and rounded.

Exocrine glands produce substances such as sweat to help lower body temperature, oil, earwax, saliva, or digestive enzymes.

A pathologist is a physician who examines cells and tissues to help other physicians make accurate diagnoses.

Stratified epithelium consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear.

Covering and lining epithelial tissue are classified according to the arrangement of cells into layers and the shapes of the cells.

When stretched, transitional epithelium cells become flatter, giving the appearance of stratified squamous epithelium.

Exocrine glands can be found in the sweat, oil, and earwax glands of the skin, as well as in digestive glands such as salivary glands (secreting into the mouth cavity) and the pancreas (secreting into the small intestine).

Simple multicellular exocrine glands have a single unbranched duct, while compound multicellular exocrine glands have a branched duct.

Its functions are absorption and secretion.

Goblet cells are modified columnar epithelial cells that secrete mucus, a slightly sticky fluid, at their apical surfaces. The mucus accumulates in the upper portion of the cell, causing it to bulge and making the whole cell resemble a goblet or wine glass.

Epithelial tissue consists of cells arranged in continuous sheets, in either single or multiple layers, with little intercellular space between adjacent plasma membranes.

Simple epithelium functions in diffusion, osmosis, filtration, secretion, or absorption.

The function of glandular epithelium is secretion, which is accomplished by glandular cells that often lie in clusters deep to the covering and lining epithelium.

A gland where the duct branches.

A gland where the tubular secretory part is straight and attaches to a single unbranched duct. Example: glands in the large intestine.

A gland where the secretory portion is tubular and attaches to a branched duct. Example: bulbourethral (Cowper’s) glands.

Stratified cuboidal epithelium has two or more layers of cells; cells in the apical layer are cube-shaped.

Multicellular exocrine glands are structurally classified based on the branching pattern of the duct and the shape of the secreting portion.

It lines the epididymis, larger ducts of many glands, and parts of the male urethra.

It covers the surface of the ovary, lines the anterior surface of the capsule of the lens of the eye, forms the pigmented epithelium at the posterior surface of the retina of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the secreting portion of some glands such as the thyroid gland and ducts of some glands such as the pancreas.

Muscular tissue is composed of cells specialized for contraction and generation of force, and it generates heat that warms the body.

Epithelial tissue has many tightly packed cells with little or no extracellular matrix, while connective tissue has a large amount of extracellular material separating widely scattered cells.

Epithelial tissue is arranged in two general patterns: covering and lining various surfaces, and forming the secreting portions of glands.

The apical (free) surface of an epithelial cell faces the body surface, a body cavity, the lumen of an internal organ, or a tubular duct that receives cell secretions.

Columnar cells are much taller than they are wide, like columns, and protect underlying tissues. Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption.

Glands with tubular secretory parts.

Secretions are synthesized on ribosomes attached to rough ER, processed, sorted, and packaged by the Golgi complex, and released from the cell in secretory vesicles via exocytosis. Example: salivary glands and pancreas.

Both types protect against abrasion, water loss, ultraviolet radiation, and foreign invasion, forming the first line of defense against microbes.

Secretion and absorption. Larger columnar cells contain more organelles and thus are capable of a higher level of secretion and absorption than cuboidal cells. Secreted mucus lubricates the linings of the digestive, respiratory, and reproductive tracts, and most of the urinary tract; it also helps prevent the destruction of the stomach lining by acidic gastric juice secreted by the stomach.

The secretions of endocrine glands are called hormones.

The apical surfaces of epithelial cells may contain cilia or microvilli.

A gland where the tubular secretory part is coiled and attaches to a single unbranched duct. Example: sweat glands.

As cells move toward the surface and away from the blood supply in the underlying connective tissue, they become dehydrated, less metabolically active, and eventually die. Tough proteins predominate as the cytoplasm is reduced, and the cells become tough, hard structures.

Microvilli are fingerlike cytoplasmic projections that increase the surface area of the plasma membrane, thus increasing the cell’s rate of absorption.

A biopsy is the removal of a sample of living tissue for microscopic examination to help diagnose disorders, especially cancer, and to discover the cause of unexplained infections and inflammations.

The basement membrane anchors the epithelium to underlying connective tissue, forms a surface for epithelial cell migration during growth or wound healing, restricts passage of larger molecules between epithelium and connective tissue, and participates in blood filtration in the kidneys.

A high rate of cell division allows epithelial tissue to constantly renew and repair itself by sloughing off dead or injured cells and replacing them with new ones.

A Papanicolaou test (Pap test) is used to detect early changes in the cells of the female reproductive system that may indicate a precancerous condition or cancer.

Glands with rounded secretory portions, also called alveolar glands.

Simple cuboidal epithelium is a single layer of cube-shaped cells with a round, centrally located nucleus.

Nonciliated simple columnar epithelium is a single layer of nonciliated columnlike cells with oval nuclei near the base of the cells. It contains columnar epithelial cells with microvilli at the apical surface and goblet cells.

Nervous tissue detects changes inside and outside the body and responds by generating electrical signals called nerve action potentials that activate muscular contractions and glandular secretions.

Epithelial tissue is avascular and relies on the blood vessels of adjacent connective tissue to bring nutrients and remove wastes through diffusion.

A gland that does not branch.

Glands that have both tubular and rounded secretory parts.

A gland where the rounded secretory part is branched and attaches to a single unbranched duct. Example: sebaceous glands.

The basement membrane commonly consists of two layers: the basal lamina and the reticular lamina.

Cuboidal cells are as tall as they are wide and are shaped like cubes or hexagons. They may have microvilli at their apical surface and function in either secretion or absorption.

A gland where the secretory portion is both tubular and rounded and attaches to a branched duct. Example: acinar glands of the pancreas.

In untreated diabetes mellitus, the basement membrane of small blood vessels thickens, which can lead to improper blood vessel function, potentially resulting in blindness and kidney failure.

A gland where the secretory portion is rounded and attaches to a branched duct. Example: mammary glands.

Merocrine glands.

The secretory product accumulates in the cytosol, and as the secretory cell matures, it ruptures and becomes the secretory product. Example: sebaceous glands.

1. cardiovascular and lymphatic systems (heart, blood vessels, lymphatic vessels) as endothelium,

2. forms the epithelial layer of serous membranes (peritoneum, pleura, pericardium) as mesothelium.

3. air sacs of lungs, glomerular (Bowman’s) capsule of kidneys,

4. inner surface of the tympanic membrane (eardrum).