Chapter 4 - Tissue (Histology)

White blood cells

(WBCs or leukocytes, including neutrophils, eosinophils, and lymphocytes) and other cell types that are concerned with tissue response to injury.

mammography

(X-ray examination of breast tissue)

connective tissue proper subclasses:

- loose connective tissues (areolar, adipose, and reticular) - dense connective tissues (dense regular, dense irregular, and elastic)

Categorization of Compound Glands

- tubular: if the secretory cells form tubes - alveolar: if the secretory cells form small, flasklike sacs (alveolus = "small hollow cavity") - tubuloalveolar: if they have both types of secretory units. *Note that many anatomists use the term acinar (as´ĭ-nar; "berrylike") interchangeably with alveolar.

Reticular connective tissue (connective tissue - proper - loose - reticular)

Description: loose network of reticular fibers in a gel-like ground substance; reticular cells lie on the fibers. Function: fibers form a soft internal skeleton (stroma) that supports other cells types including white blood cells, mast cells, and macrophages. location: lymphoid organs (lymph nodes, bone marrow, and spleen) Resembles areolar connective tissue but the only fibers in its matrix are reticular fibers

Adipose (Fat) Tissue (connective tissue - proper - loose - adipose)

Description: matrix as in aerolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplets. Function: provides reserve food fuel; insulates against heat loss, supports and protects organs. location: under the skin in subcutaneous tissue; around the kidney and eyeballs; within abdomen; in breasts.

In connective tissue, the role of elastic fibers is to __________.

Elastic fibers contain elastin, a rubberlike protein that allows them to stretch and recoil like rubber bands.

How do endocrine and exocrine glands differ?

Endocrine glands secrete substances (hormones) into blood without the use of ducts, whereas exocrine glands use ducts to secrete substances into the external environment.

Which of the following is a property of epithelial tissue?

Epithelial tissue is an innervated, avascular tissue that exhibits polarity. Epithelial tissue is also highly regenerative.

Epithelial tissue is the only tissue type that has polarity, that is, an apical and a basal surface. Why is this important?

Epithelial tissue lines body cavities and covers the body's external surface; thus polarity with one free (apical) surface is a requirement.

Connective tissues share two characteristics that together set them apart from other primary tissues:

Extracellular matrix: Nonliving material in connective tissue consisting of ground substance and fibers; separates the living cells. Common origin. All connective tissues arise from mesenchyme (an embryonic tissue).

What is the purpose of fixing tissue for microscopic viewing?

Fixing tissue preserves it and prevents it from deteriorating.

areolar connective tissue

Function: wraps and cushions organs Location: widely distributed under epithelia of body

endocrine glands

Often called ductless glands, hey produce hormones, chemical messengers that they secrete by exocytosis directly into the extracellular space. From there the hormones enter the blood or lymphatic fluid and travel to specific target organs. Each hormone prompts its target organ(s) to respond in some characteristic way.

osteoblasts and osteocytes

Osteoblasts produce the organic portion of the matrix, and then bone salts are deposited on and between the fibers. Mature bone cells, or osteocytes, reside in the lacunae within the matrix they have made (Figure 4.11j). A cross section of bone tissue reveals closely packed structural units called osteons that look like tree rings. Osteons are concentric rings of bony matrix (lamellae) surrounding central canals containing the blood vessels and nerves serving the bone.

Osteoblasts (Bone-forming cells.) in bone become

Osteocyte - Mature bone cell.

It has been observed that aging cartilage tends to calcify or ossify and its cells die. What survival needs are not being met in these cells and why is this so?

Oxygen and nutrient needs are not being met because the calcified cartilage matrix is too hard to allow them to reach the cells by diffusion. Remember, cartilage is avascular.

Some epithelia are pseudostratified. What does this mean?

Pseudostratified epithelia appear to be stratified because their cells' nuclei lie at different distances from the basement membrane. However, all cells rest on the basement membrane.

Fibroblast cells

Responsible for the formation of fibers and aid in the production of collagen and elastin. Plays a critical role in wound healing.

Mucin

a complex glycoprotein that dissolves in water when secreted. Once dissolved, mucin forms mucus, a slimy coating that protects and lubricates surfaces.

Which of the following does NOT describe a multicellular exocrine gland?

a gland that secretes hormones - endocrine glands

Proto-oncogenes

benign forms of oncogenes in normal cells, were discovered later. Proto-oncogenes code for proteins that are essential for cell division, growth, and cellular adhesion, among other things. Many proto-oncogenes have fragile sites that break when exposed to carcinogens, converting them to oncogenes

Major Functions of Connective Tissue

binding and support, protecting, insulating, storing reserve fuel, and transporting substances (blood)

chondroblasts and chondrocytes

cells of cartilagehe predominant cell type in growing cartilage, produce new matrix until the skeleton stops growing at the end of adolescence. Chondrocytes (mature cartilage cells) are typically found in small groups within cavities called lacunae

Mutations

changes in DNA that alter the expression of certain genes.

The fibers of connective tissue are proteins that provide support. Three types of fibers are found in connective tissue matrix:

collagen, elastic, and reticular fibers

Adipocytes

commonly called adipose or fat cells, which store energy as fat.

Stratified epithelia

composed of two or more cell layers stacked on top of each other, are common in high-abrasion areas where protection is important, such as the skin surface and the lining of the mouth.

four main classes of connective tissue and several subclasses

connective tissue proper, cartilage, bone, and blood.

simple epithelial tissue

consist of a single cell layer. They are typically found where absorption, secretion, and filtration occur and a thin epithelial barrier is desirable.

gland

consists of one or more cells that make and secrete a particular product.

Collagen fibers

constructed primarily of the fibrous protein collagen. Collagen molecules are secreted into the extracellular space, where they assemble spontaneously into cross-linked fibrils, which in turn are bundled together into the thick collagen fibers seen with a microscope. Because their fibrils cross-link, collagen fibers are extremely tough and provide high tensile strength (the ability to resist being pulled apart) to the matrix.

muscle tissue

contracts to produce movement; muscles attached to bones (skeletal), muscles of the heart (cardiac), muscle of walls of hollow organs (smooth)

Three types of covering and lining membranes

cutaneous, mucous, and serous

Reticular Lamina (epithelial)

deep to the basal lamina. It consists of a layer of extracellular material containing a fine network of collagen protein fibers that "belongs to" the underlying connective tissue.

granulation tissue

delicate pink tissue that contains capillaries that grow in from nearby areas and lay down a new capillary bed. Granulation tissue is actually named for these capillaries, which protrude nublike from its surface, giving it a granular appearance. These capillaries are fragile and bleed freely, as we see when someone picks at a scab.

The three varieties of dense connective tissue:

dense regular, dense irregular, and elastic. Since all three have fibers as their prominent element, dense connective tissues are often called fibrous connective tissues.

Dense regular connective tissue (connective tissue - proper - dense - regular)

descrip: primarily parallel collagen fibers; a few elastic fibers, major cell type is the fibroblast. function: attaches muscle to bone or to muscles; attaches bones to bones; withstands a great tensile stress when pulling force is applied in one direction . location: tendon, most ligaments, aponeroses --------------- Tendons. Tendons are cords that attach muscles to bones. Aponeuroses. Aponeuroses (ap˝o-nu-ro´sēz) are flat, sheetlike tendons that attach muscles to other muscles or to bones. Ligaments. Ligaments bind bones together at joints. They contain more elastic fibers than tendons and are slightly more stretchy.

Three primary germ layers

ectoderm, mesoderm, endoderm These primary germ layers then specialize to form the four primary tissues—epithelium, nervous tissue, muscle, and connective tissues—that make up all body organs.

Myofilaments

elaborate networks of the actin and myosin filaments that bring about movement or contraction in all cell types.

peritoneum serous membrane

encloses the abdominopelvic viscera

pericardium (pericardial sac)

encloses the heart and holds it in place; consists of 2 layers: outer fibrous pericardium and inner serous pericardium (epicardium)

Fibroblasts (Young, actively mitotic cell that forms the fibers of connective tissue.) in connective tissue proper become:

fibrocytes (Mature fibroblast; maintains the matrix of fibrous types of connective tissue.)

simple epithelia

are most concerned with absorption, secretion, and filtration. Because they consist of a single cell layer and are usually very thin, protection is not one of their specialties. - located in kidney glomeruli, air sac of the lungs, lining of the heart, blood vessels, and lymphatic vessels

apocrine secretion

are present in other animals, there is some controversy over whether humans have this gland type. Like holocrine glands, apocrine glands accumulate their products, but in this case only just beneath the free surface. Eventually, the apex of the cell pinches off (apo = from, off), releasing the secretory granules and a small amount of cytoplasm. The cell repairs its damage and the process repeats again and again. The closest to an example of this process in humans is the release of lipid droplets by lactating mammary glands. However, most histologists classify mammary glands as merocrine glands because this is the means by which milk proteins are secreted.

Columnar cells

are tall and column shaped

basal surface of epithelial tissue

attached to the underlying connective tissue

Cartilage is :

avascular (lack of blood cells)

Unicellular Exocrine Glands

mucous cells and goblet cells Unicellular glands are sprinkled in the epithelial linings of the intestinal and respiratory tracts amid columnar cells with other functions

exocrine glands

secrete their products onto body surfaces (skin) or into body cavities. The unicellular glands do so directly (by exocytosis), whereas the multicellular glands do so via an epithelium-walled duct that transports the secretion to the epithelial surface. Exocrine glands are diverse. They include the liver (which secretes bile); the pancreas (which synthesizes digestive enzymes); mucous, sweat, oil, and salivary glands; and many others.

Reticular Fibers

short, fine fibers are made of a different type of collagen than the more common, thicker collagen fibers. They connect to the coarser collagen fibers, but they branch extensively, forming delicate networks (reticul 5 network) that surround small blood vessels and support the soft tissue of organs. They are particularly abundant where connective tissue is next to other tissue types, for example, in the basement membrane of epithelial tissues, and around capillaries, where they form fuzzy "nets" that allow more stretch than the larger collagen fibers.

You observe a tissue under a microscope. There appears to be a lumen on one side of the tissue. Lining this lumen is a single layer of epithelial cells that seem to have long, fingerlike projections. Beneath the projections, the cells seem to have the shape of shoeboxes and are packed tightly together. What type of tissue are you looking at?

simple columnar epithelium

Simple glands (exocrine)

single unbranched duct

Three kinds of muscle tissue:

skeletal, cardiac, smooth

biopsy

surgically removing a tissue sample and examining it microscopically for malignant cells. Increasingly, diagnosis includes chemical or genetic analysis of the sample—typing cancer cells by which genes are switched on or off.

basement membrane

that reinforces the epithelial sheet, helps it resist stretching and tearing, and defines the epithelial boundary. The basement membrane consists of two layers: a basal lamina (described above) and a reticular lamina

Neoplasm (tumor) Stands for "new growth"

the abnormal, excessive and uncontrolled multiplication of cells with the formation of a mass or new growth of tissue. Neoplasms are classified as benign ("kindly") or malignant ("bad"). Cancers are malignant neoplasms, nonencapsulated masses that grow relentlessly. Benign neoplasm is strictly a local affair. Its cells remain compacted, are often encapsulated, tend to grow slowly, and seldom kill their hosts if removed before they compress vital organs.

pericardium (pericardial sac)

the double-walled membranous sac that encloses the heart

Mesothelium (simple squamous)

the epithelium found in serous membranes, the membranes lining the ventral body cavity and covering its organs.

Nervous tissue

the main component of the nervous system—the brain, spinal cord, and nerves—which regulates and controls body functions. It contains two major cell types: neurons and supporting cells Neurons are highly specialized nerve cells that generate and conduct nerve impulses (Figure 4.13). Typically, they are branching cells with cytoplasmic extensions or processes that enable them to: Respond to stimuli (via processes called dendrites) Transmit electrical impulses over substantial distances within the body (via processes called axons)

Serosa membranes, or serosae

the moist membranes found in closed ventral body cavities - line body cavities that are close to the exterior.

Stratified squamous epithelium

the most widespread of the stratified epithelia. Composed of several layers, it is thick and well suited for its protective role in the body. Its free surface cells are squamous, and cells of the deeper layers are cuboidal or columnar. This epithelium is found in areas subjected to wear and tear, and its surface cells are constantly being rubbed away and replaced by division of its basal cells. Because epithelium depends on nutrients diffusing from deeper connective tissue, the epithelial cells farther from the basement membrane are less viable and those at the apical surface are often flattened and may even be dead. The outer layer, or epidermis, of the skin is keratinized (ker´ah-tin″īzd), meaning its surface cells contain keratin, a tough protective protein. The other stratified squamous epithelia of the body are nonkeratinized.

Chondroblasts (Actively mitotic cell of cartilage.) in cartilage become:

Chondrocyte (kon′dro-sīt) Mature cell of cartilage.

Which tissues have little to no functional regenerative capacity?

Cardiac muscle and the nervous tissue in the brain and spinal cord have virtually no functional regenerative capacity, and they are routinely replaced by scar tissue.

Bone (osseous tissue)

A connective tissue that forms the bony skeleton. has an exceptional ability to support and protect body structures. Bones of the skeleton also provide cavities for storing fat and synthesizing blood cells. Bone matrix is similar to that of cartilage but is harder and more rigid because, in addition to its more abundant collagen fibers, bone has an added matrix element—inorganic calcium salts (bone salts).

Cartilage

A connective tissue that is more flexible than bone and that protects the ends of bones and keeps them from rubbing together. it is avascular (lack of blood vessels) and lacks nerve fibers.

Elastic Connective Tissue (connective tissue - proper - dense - elastic)

A few ligaments, such as those connecting adjacent vertebrae, are very elastic. The dense regular connective tissue in those structures is called elastic connective tissue . Additionally, many of the larger arteries have stretchy sheets of elastic connective tissue in their walls. Location: walls of large arteries, within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes

tumor suppressor genes (TP53)

A gene whose protein product inhibits cell division, thereby preventing the uncontrolled cell growth that contributes to cancer. Over half of cancer involve malfunction of loss of TP53

What type of membrane consists of epithelium and connective tissue, and lines body cavities open to the exterior?

A mucous membrane consists of both connective tissue and epithelium. It lines body cavities open to the exterior.

involuntary muscle

A muscle that is not under conscious control. (smooth and cardiac)

voluntary muscle

A muscle that is under conscious control - skeletal muscle

Why are adipose tissue, blood, and bone all considered to be connective tissues?

Adipose tissue, bone, and blood (like all connective tissues) are derived from mesenchyme, an embryonic tissue. Also common to all connective tissues is the presence of cells surrounded by extracellular matrix that consists of fibers and ground substance.

pseudostratified columnar epithelium

All of its cells rest on the basement membrane, but only the tallest reach the free surface of the epithelium. Because the cell nuclei lie at different levels above the basement membrane, the tissue gives the false (pseudo) impression that several cell layers are present; hence "pseudostratified." The short cells are relatively unspecialized and give rise to the taller cells. This epithelium, like the simple columnar variety, secretes or absorbs substances. A ciliated version containing mucus-secreting goblet cells lines most of the respiratory tract. Here the motile cilia propel sheets of dust-trapping mucus away from the lungs.

Which connective tissue has a soft weblike matrix capable of serving as a fluid reservoir?

Answer: Areolar connective tissue, because of its loose weblike nature, is capable of serving as a fluid reservoir.

You are looking at muscle tissue through the microscope and you see striped branching cells that connect with one another. What type of muscle are you viewing?

Answer: Cardiac muscle cells have striations and are branching cells.

What are four functions of connective tissue?

Answer: Connective tissue functions to bind, support, protect, and insulate body organs. In addition, blood acts to transport substances throughout the body.

What type of connective tissue is damaged when you cut your index finger tendon?

Answer: Dense regular connective tissue is damaged when you lacerate a tendon.

What are the three types of fibers found in connective tissues?

Answer: Reticular, collagen, and elastic fibers are found in the various connective tissues.

Stratified epithelia are named according to the shape of the cells in the _________ layer.

Apical

Avascular but innervated (epithelial tissue)

Avascular (containing no blood vessels), it is innervated (supplied by nerve fibers) -Epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue.

Hyaline cartilage (connective tissue - cartilage - hyaline)

Gristle, is the most abundant cartilage in the body. Although it contains large numbers of collagen fibers, they are not apparent and the matrix appears glassy (hyal 5 glass, transparent) blue-white when viewed by the unaided eye. Chondrocytes account for only 1-10% of the cartilage volume It covers the ends of long bones as articular cartilage, providing springy pads that absorb compression at joints. It supports the tip of the nose. It connects the ribs to the sternum. It supports most of the respiratory system passages (for example, the trachea). It makes up most of the embryonic skeleton before bone forms. Skeletal hyaline cartilage persists during childhood as the epiphyseal plates (e˝pĭ-fis´e-ul; growth plates), actively growing regions near the ends of long bones.

Tissues

Groups of cells that are similar in structure and perform a common or related function. Four primary tissue types interweave to form the "fabric" of the body. These basic tissues are epithelial, connective, muscle, and nervous tissue.

What types of stains are used to stain tissues to be viewed with a transmission electron microscope?

Heavy metal salts are used to stain tissues viewed by electron microscopes.

goblet cells

Individual cells (unicellular glands) that produce mucus. accumulating mucin distends the top of the cell, making the cells look like a glass with a stem

Fibrocartilage (connective tissue - cartilage - fibrocartilage)

Its rows of chondrocytes (a cartilage feature) alternate with rows of thick collagen fibers (characteristic of dense regular connective tissue) (Figure 4.11i). Because it resists both compression and tension well, fibrocartilage is found where strong support and the ability to withstand heavy pressure are required: for example, the intervertebral discs (resilient cushions between the bony vertebrae) and the spongy cartilages of the knee. Homeostatic Imbalance 4.

What should you keep in mind when attempting to identify epithelial types?

Keep the nuclear shape in mind.

Elastic Fibers

Long, thin, elastic fibers form branching networks in the extracellular matrix. These fibers contain a rubberlike protein, elastin, that allows them to stretch and recoil like rubber bands. Elastic fibers are found where greater elasticity is needed, for example, in the skin, lungs, and blood vessel walls.

Mature connective tissue types:

Mature connective tissue that isn't "connective tissue proper" - Bone, cartilage, blood

Three defenses at the body's external boundaries:

Mechanical barriers such as the skin and mucosae, the cilia of epithelial cells lining the respiratory tract, and the strong acid (chemical barrier) produced by stomach glands

mesenchyme

Mesenchyme has a fluid ground substance containing fine sparse fibers and star-shaped mesenchymal cells. It arises during the early weeks of embryonic development and eventually differentiates (specializes) into all other connective tissue cells. However, some mesenchymal cells remain and provide a source of new cells in mature connective tissues.

Why does a deep injury to the skin result in abundant scar tissue?

More severe injuries damage and destroy more tissue, requiring greater replacement with scar tissue.

Anticancer drugs also have unpleasant side effects:

Nausea, vomiting, hair loss—because they kill all rapidly dividing cells, including normal tissue cells. The anticancer drugs also can affect the brain, producing mental fuzziness and memory loss

Which of the following describes a holocrine gland?

Secretory cells of holocrine glands accumulate their products within them until they rupture. They are replaced by the division of underlying cells. Sebaceous (oil) glands of the skin are the only true example of holocrine glands in the human body.

Stratified epithelia are "built" for protection or to resist abrasion. What are the simple epithelia better at?

Simple epithelia are "built" to provide for efficient absorption and filtration across their thin epithelial barriers.

Which muscle type(s) is voluntary? Which is injured when you pull a muscle while exercising?

Skeletal muscle tissue is voluntary and is the muscle tissue injured when you "pull a muscle" while exercising.

Stratified columnar epithelium

Small amounts are found in the pharynx, the male urethra, and lining some glandular ducts. This epithelium also occurs at transition areas or junctions between two other types of epithelia. Only its apical layer of cells is columnar.

Stage from 1 to 4

Stage 1 has the best probability of cure, stage 4 the worst

connective tissue

Supports, protects and holds the body together -bones -tendons -fat and other soft padding tissue

Connective Tissue Cells Each major class of connective tissue has a resident cell type that exists in immature (-blast) and mature (-cyte) forms.

The immature blast cells are actively mitotic. Each type of blast cell secretes the ground substance and the fibers characteristic of their particular matrix. Once they synthesize the matrix, the blast cells assume their mature, less active -cyte form. The mature cells maintain the health of the matrix.

How does the extended length of a neuron's processes aid its function in the body?

With extended processes, a neuron can conduct electrical signals a great distance within the body.

Three patients are in intensive care because of damage and widespread cell death in three different organs. One patient has brain damage from a stroke, another has had a heart attack, and a third has a damaged liver (a gland) due to a car accident. All of these patients will survive, but only one will regain full function through tissue regeneration in the damaged organ. Which one? Why?

The liver is a gland that is derived from epithelial tissue. Epithelial tissue regenerates well. Nervous tissue in the brain and cardiac muscle exhibit virtually no functional regeneration.

What type of membrane lines the thoracic walls and covers the lungs, and what is it called?

The serous membranes called pleurae line the thorax walls and cover the lungs.

metastasis

The spread of cancer cells beyond their original site

What are the three main steps of tissue repair?

The three main steps of tissue repair are inflammation, organization, and permanent repair via regeneration and fibrosis.

Chemotherapy

The use of drugs to treat diseases such as cancer. Some cancer cells can eject the drugs in tiny bubbles or flattened vesicles dubbed exosomes. These resistant cells multiply, forming new tumors that are also resistant to chemotherapy.

Your classmate, Jennifer, is confused by all the different types of membranes. To help her understand, explain the key differences between the serous and mucous membranes, the plasma membrane (see Chapter 3), and the basement membrane (see p. 118 ).

These membranes differ from each other in their size, composition, and location. Plasma membranes surround cells and are tiny, made of two layers of phospholipid molecules with embedded proteins. The basement membrane is larger than the plasma membrane and is a layer of extracellular material that lies just outside the basal surface of epithelial cells. Serous and mucous membranes are much larger still. They consist of many cells and, because they consist of two types of tissues, they are considered organs.

Cancer immunotherapy

These therapies range from antibodies that block specific receptors on cancer cells, to various methods to activate the immune system to attack and kill cancer cells, to vaccines that block the development of cancer in the first place. This is an area of active research and drug development, with many clinical trials under way.

multicellular exocrine glands

They have two basic parts: an epithelium-derived duct and a secretory unit (acinus) consisting of secretory cells.

Interrupting the signaling pathways that fuel cancer growth:

This approach proved its worth in a few specific types of cancer in which all of the cases share mutations in the same signaling pathway. Pioneer drugs such as imatinib dramatically improved outcomes for patients with a specific kind of leukemia. Unfortunately, most types of cancer are more diverse in the pathways that are mutated. Now that we can sequence the DNA of a patient's tumor, we can determine exactly which signaling pathways are disrupted. We can then select appropriate drugs to target those pathways in an individual's particular cancer. Such "personalized medicine" approaches are less likely to damage noncancerous tissues while being more effective at targeting cancerous cells.

While examining a multicellular exocrine gland under the microscope, you notice that there are many cells in metaphase. Is this gland a merocrine or holocrine gland? Explain.

This gland is a holocrine gland. Holocrine glands have the highest rate of cell division. The secretory cells rupture when they secrete, and so they must be continuously replaced.

basal lamina

This noncellular, adhesive sheet consists largely of glycoproteins secreted by the epithelial cells plus some fine collagen fibers. The basal lamina acts as a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter the epithelium. The basal lamina also acts as scaffolding along which epithelial cells can migrate to repair a wound.

motile cilia

Typically associated with epithelial cells that line the passageways respiratory and reproductive tracts

The two layers of serous membranes are held together by serous fluid, which is largely water. Which of the properties of water (Chapter 2) makes these layers "stick" together?

Water's high surface tension (due to its hydrogen bonds) makes the layers of serous membrane stick together.

Secondary cancer masses

Whereas normal cells die when they lose contact with the surrounding matrix, malignant cells tend to break away from the parent mass—the primary tumor—and travel via blood or lymph to other body organs, where they form secondary cancer masses. - This process of traveling to other parts of the body is called metastasis.

Squamous cells

are flattened and scale-like (squam = scale).

Epithelial tissue (epithelium)

a sheet of cells that covers a body surface or lines a body cavity (epithe = laid on, covering). There are two forms of epithelial tissue: - Covering and lining epithelium, which forms the outer layer of the skin; dips into and lines the open cavities of the urogenital, digestive, and respiratory systems; and covers the walls and organs of the closed ventral body cavity - Glandular epithelium, which fashions the glands of the body

Simple cuboidal epithelium

a single layer of cells as tall as they are wide. The generally spherical nuclei stain darkly. Important functions of simple cuboidal epithelium are secretion and absorption. This epithelium forms the walls of the smallest ducts of glands and of many kidney tubules.

Simple columnar epithelium

a single layer of tall, closely packed cells, aligned like soldiers in a row. It lines the digestive tract from the stomach through the rectum. Columnar cells are mostly associated with absorption and secretion, and the digestive tract lining has two distinct modifications that make it ideal for that dual function: -Dense microvilli on the apical surface of absorptive cells -Tubular glands made primarily of cells that secrete mucus-containing intestinal juice

holocrine secretion

accumulate their products within them until they rupture. (They are replaced by the division of underlying cells.). Sebaceous (oil) glands of the skin are the only true example of holocrine glands

secretion

an aqueous (water-based) fluid that usually contains proteins. However, some glands release a lipid- or steroid-rich secretion.

cutaneous membrane (skin)

an organ system consisting of a keratinized stratified squamous epithelium (epidermis) firmly attached to a thick layer of connective tissue (dermis). Unlike other epithelial membranes, the cutaneous membrane is exposed to the air and is a dry membrane.

Cuboidal cells

are boxlike, approximately as tall as they are wide.

Blood

fluid within blood vessels, is the most atypical connective tissue. It does not connect things or give mechanical support. It is classified as a connective tissue because it develops from mesenchyme and consists of blood cells, surrounded by a nonliving fluid matrix called blood plasma The vast majority of blood cells are red blood cells, or erythrocytes, but scattered white blood cells and platelets (needed for blood clotting) are also seen. The "fibers" of blood are soluble protein molecules that precipitate, forming visible fiberlike structures during blood clotting. Blood functions as the transport vehicle for the cardiovascular system, carrying nutrients, wastes, respiratory gases, and many other substances throughout the body.

epithelial tissue

forms boundaries between different environments, protects, secretes, absorbs, filters -lining of digestive tract organs and other hollow organs -glands (pancreas) skin surface(epidermis)

Transitional epithelium

forms the lining of hollow urinary organs, which stretch as they fill with urine. Cells of its basal layer are cuboidal or columnar. The apical cells vary in appearance, depending on the degree of distension (stretching) of the organ. When the organ is distended with urine, the transitional epithelium appears to thin from about six cell layers to as few as three, and its domelike apical cells flatten and become squamouslike. The ability of transitional cells to change their shape (undergo "transitions") allows a greater volume of urine to flow through a tubelike organ. In the bladder, it allows more urine to be stored.

Cardiac muscle

found only in the walls of the heart. Its contractions help propel blood through the blood vessels to all parts of the body. Like skeletal muscle cells, cardiac muscle cells are striated. However, cardiac cells differ structurally in that they are: Generally uninucleate (one nucleus) with the nucleus situated centrally Branching cells that fit together tightly at unique junctions called intercalated discs.

Oncogenes

genes that cause cancer by blocking the normal controls on cell reproduction. Oncogenes may also "switch on" dormant genes that allow cells to become invasive and metastasize. Known oncogenes now number over 100.

Connective tissues have three main components:

ground substance, fibers, and cells - Ground substance and fibers make up the extracellular matrix Some people use the term matrix to indicate the ground substance only.

compound glands (exocrine)

have a branched duct. (A. is a simple gland, the other examples are of compound glands)

What type of healing does the body do for infections?

healing is solely by regeneration

Immature blood cell-forming type (once called a hemocytoblast) is called

hematopoietic stem cell (hem˝ah-to-poy-et´ik)

There are three varieties of cartilage:

hyaline cartilage, elastic cartilage, and fibrocartilage

Side-Effects of X rays:

in passing through the body, they destroy healthy tissue as well as cancer cells.

Endoderm

innermost germ layer; develops into the linings of the digestive tract and much of the respiratory system

nervous tissue

internal communication; brain, spinal cord, nerves

HOW ARE ANIMAL TISSUES PREPARED FOR MICROSCOPIC VIEWING?

it must be fixed (preserved) and then cut into sections (slices) thin enough to transmit light (in light microscopy) or electrons (in electron microscopy). Finally, the specimen must be stained to enhance contrast between structures.

Macrophages

large, irregularly shaped cells that avidly devour a broad variety of foreign materials, ranging from foreign molecules to entire bacteria to dust particles. These "big eaters" also dispose of dead tissue cells, and they are central actors in the immune system. Macrophages are peppered throughout loose connective tissue, bone marrow, and lymphoid tissue. They may be attached to connective tissue fibers (fixed) or may migrate freely through the matrix. Some macrophages have selective appetites. For example, those of the spleen primarily dispose of aging red blood cells

lamina propria of mucosa

layer of areolar connective tissue

Mucous membranes, or mucosae

line all body cavities that open to the outside of the body, such as the hollow organs of the digestive, respiratory, and urogenital tracts (Figure 4.14b). In all cases, they are "wet," or moist, membranes bathed by secretions or, in the case of the urinary mucosa, urine. Notice that the term mucosa refers to the location of the membrane, not its cell composition, which varies. However, most mucosae contain either stratified squamous or simple columnar epithelia. The epithelial sheet lies directly over a layer of areolar connective tissue called the lamina propria (lam′ĭ-nah pro´pre-ah; "one's own layer"). In some mucosae, the lamina propria rests on a third (deeper) layer of smooth muscle cells.

Pleurae

line the thoracic wall and cover the lungs

cell type initiates inflammatory responses to infection or tissue damage?

mast cell, which produces and secretes inflammation-triggering chemicals, such as histamine. Note the secretory granules within the pictured cell.

3 modes of secretion of exocrine glands

merocrine, apocrine, holocrine

Mesoderm

middle germ layer; develops into muscles, and much of the circulatory, reproductive, and excretory systems

Smooth muscle and dense regular connective tissue regenerative properties:

moderate capacity for regeneration

Areolar connective tissue (connective tissue - proper - loose - areolar)

most widely distributed connective tissue in the body, and it serves as a universal packing material between other tissues. It binds body parts together while allowing them to move freely over one another. It is the connective tissue that most epithelia rest on and is present in all mucous membranes as the lamina propria The functions of areolar connective tissue include: Supporting and binding other tissues (the job of the fibers) Holding body fluids (the ground substance's role) Defending against infection (via the activity of white blood cells and macrophages) Storing nutrients as fat in adipocytes (fat cells)

Smooth muscle

named because its cells have no visible striations. Individual smooth muscle cells are spindle shaped (tapered at both ends) and contain one centrally located nucleus . Smooth muscle is found mainly in the walls of hollow organs other than the heart (digestive and urinary tract organs, uterus, and blood vessels). It squeezes substances through these organs by alternately contracting and relaxing.

Elastic Cartilage (connective tissue - cartilage - elastic)

nearly identical to hyaline cartilage. However, elastic cartilage has many more elastic fibers. Found where strength and exceptional stretchability are needed, elastic cartilage forms the "skeletons" of the external ear and the epiglottis (the flap that covers the opening to the respiratory passageway when we swallow).

apical surface of epithelial tissue

not attached to surrounding tissue and is exposed to either the outside of the body or the cavity of an internal organ.

Ectoderm

outermost germ layer; produces sense organs, nerves, and outer layer of skin

Dense connective tissue is:

poorly vascularized (consisting of vessels that carry blood)

connective tissue

prevalent in the body, its amount in particular organs varies. For example, skin consists primarily of connective tissue, while the brain contains very little.

endothelium (simple squamous epithelium)

provides a slick, friction-reducing lining in lymphatic vessels and in all hollow organs of the cardiovascular system (blood vessels and the heart). Capillaries consist exclusively of endothelium, and its exceptional thinness encourages the efficient exchange of nutrients and wastes between the bloodstream and surrounding tissue cells.

scanning electron microscopy (SEM)

provides three-dimensional pictures of an unsectioned tissue surface

Stratified cuboidal epithelium

quite rare in the body, mostly found in the ducts of some of the larger glands (sweat glands, mammary glands). It typically has two layers of cuboidal cells.

Epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, and blood-forming tissue regenerative properties:

regenerate extremely well

Repair occurs in two major ways:

regeneration and fibrosis. Which of these occurs depends on (1) the type of tissue damaged and (2) the severity of the injury.

inflammatory response

relatively nonspecific reaction that develops quickly wherever tissues are injured

merocrine secretion

release of a substance from a gland via exocytosis

Fibrosis

replaces destroyed tissue with scar tissue, which is dense connective tissue.

Regeneration

replaces destroyed tissue with the same kind of tissue.

Dense irregular connective tissue (connective tissue - proper - dense - irregular )

the same structural elements as the regular variety. However, the bundles of collagen fibers are much thicker and they are arranged irregularly; that is, they run in all directions. This type of tissue forms sheets in body areas where tension is exerted from many different directions. It is found in the skin as the leathery dermis, and it forms fibrous joint capsules and the fibrous coverings that surround some organs (kidneys, bones, cartilages, muscles, and nerves).

Skeletal muscle

tissue is packaged by connective tissue sheets into organs called skeletal muscles that are attached to the bones of the skeleton. These muscles form the flesh of the body, and as they contract they pull on bones or skin, causing body movements. Skeletal muscle cells, also called muscle fibers, are long, cylindrical cells that contain many peripherally located nuclei. Their obvious banded, or striated, appearance reflects the precise alignment of their myofilaments

transmission electron microscopy (TEM)

tissue sections are stained with heavy metal salts. These metals provide contrast by deflecting electrons in the beam to different extents. Electron-microscope images are in shades of gray because color is a property of light, not of electron waves.

Mast cells

typically cluster along blood vessels. These oval cells detect foreign microorganisms (e.g., bacteria, fungi) and initiate local inflammatory responses against them. Mast cell cytoplasm contains secretory granules (mast = stuffed full of granules) with chemicals that mediate inflammation, especially in severe allergies. These chemicals include: Heparin (hep´ah-rin), an anticoagulant chemical that prevents blood clotting when free in the bloodstream (but in human mast cells it appears to regulate the action of other mast cell chemicals) Histamine (his´tah-mēn), a substance that makes capillaries leaky Proteases (protein-degrading enzymes) Other enzymes

ground substance of connective tissue

unstructured material that fills the space between the cells and contains the fibers. It has three components: Interstitial fluid Cell adhesion proteins Proteoglycans

tissues regenerative properties:

vary widely in their ability to regenerate

Cardiac muscle and the nervous tissue in the brain and spinal cord regenerative properties:

virtually no functional regenerative capacity, and they are routinely replaced by scar tissue

Muscle tissues

well-vascularized tissues that are responsible for most types of body movement. As in epithelial tissue, the cells in muscle tissue are all tightly packed together

Leukoplakia

white patches in the mouth caused by the chronic irritation of ill-fitting dentures. Many cancers are preceded by lumps or other structural changes in tissue