Saladin 5e Extended Outline

Chapter 5 

Histology

I. The Study of Tissues (pp. 152–154)
A. Histology is the study of tissues and how they are arranged into organs. (p. 152)
B. A tissue is a group of similar cells and cell products that arise from the same region of the embryo and work together to perform a specific role. (p. 152)
1. The four primary tissues are epithelial, connective, nervous, and muscular tissue. (Table 5.1)
2. These tissues differ in the types and functions of their cells, the characteristics of the matrix around the cells, and the relative amount of space cells and matrix occupy.
3. The matrix is composed of fibrous proteins and a clear gel known as ground substance, tissue fluid, extracellular fluid, interstitial fluid, or tissue gel.
C. Human development begins with a single cell, the fertilized egg, which divides to produce scores of identical, smaller cells. (p. 153)
1. The first tissues are organized into three strata called the primary germ layers: ectoderm, mesoderm, and endoderm.
2. The ectoderm is an outer layer that gives rise to the epidermis and nervous system.
3. The endoderm is an inner layer that gives rise to the mucous membranes of the digestive and respiratory tracts and to digestive glands.
4. The mesoderm is between the other two layers and eventually turns into a tissue called mesenchyme; this gives rise to muscle, bone, blood, and some other tissues.
D. Tissue specimens are preserved in a fixative and cut into very thin slices called histological sections only one or two cells thick, and then stained to bring out detail. (pp. 153–154)
1. Sectioning reduces a three-dimensional structure to a two-dimensional slice. (Fig. 5.1)
a. An object may look different when cut in different planes of section.
b. A particular section may miss some structures.
2. A tissue cut in the long direction is a longitudinal section (l.s.); a cut perpendicular produces a cross section (c.s. or x.s.)or transverse section (t.s.); a cut at an angle is an oblique section. (Fig. 5.2)
3. Liquid tissues and soft tissues may be prepared as smears in which the tissue is rubbed or spread across the slide.
4. Membranes and webby tissues are sometimes laid out on a slide as a spread. (Fig. 5.14)
II. Epithelial Tissue (pp. 153–160)
A. Epithelial tissue is a flat sheet of closely adhering cells, one or more cells thick, with the upper surface usually exposed to the environment or to an internal space. (p. 154–155)
1. Epithelium covers the body surface, lines body cavities, forms the external and internal linings of many organs, and constitutes most gland tissue.
2. Epithelium almost always lies on a layer of loose connective tissue and is dependent on this tissue’s blood supply for nutrients and waste removal.
3. The basement membrane anchors an epithelium to the underlying connective tissue.
4. Epithelia are classified into two broad categories: simple and stratified.
a. In a simple epithelium, every cell touches the basement membrane.
b. In a stratified epithelium, some cells rest on top of other cells and to not contact the basement membrane. (Fig. 5.3)
B. Generally, a simple epithelium has only one layer of cells. (p. 155) (Table 5.2) (Figs. 5.4, 5.5, 5.6, 5.7)
1. Three types of simple epithelia are named for the shape of their cells: simple squamous (scaly), simple cuboidal, and simple columnar.
2. In the fourth type, pseudostratified columnar epithelium, shorter cells do not reach the free surface, but all cells reach the basement membrane.
3. Simple columnar and pseudostratified columnar epithelia often produce mucus, which is secreted by goblet cells.
C. Stratified epithelium may have from 2 to 20 layers of cells with only the deepest layer resting on the basement membrane. (pp. 155–160) (Table 5.3) (Figs. 5.8, 5.9, 5.10, 5.11)
1. Three types of stratified epithelia are named for the shapes of the surface cells: stratified squamous, stratified cuboidal, and stratified columnar, which is rare.
2. A fourth type, transitional epithelium, was erroneously through to represent a transitional stage between stratified squamous and stratified columnar, but the name has persisted.
3. Stratified squamous epithelium is the most widespread epithelium in the body.
a. The deepest layer of cells are cuboidal to columnar and undergo continual mitosis.
b. Daughter cells push toward the surface and become flatter (more squamous).
c. Eventually the cells migrate to the surface where they die and flake off, a process called exfoliation or desquamation. (Fig. 5.12)
i. Exfoliated cells can be smeared on a slide, stained, and examined; this is the basis of the Pap test for uterine cancer.
d. Keratinized epithelium, such as found on the skin surface, is covered with a layer of compact, dead squamous cells packed with keratin and coated with a glycolipid water repellent.
e. Nonkeratinized epithelium lacks the surface layer of dead cells; it is found on the tongue, esophagus, vagina, and some other internal membranes.
III. Connective Tissue (pp. 160–170)
A. Connective tissue consists mostly of fibers and ground substance, with widely separated cells; it often serves to connect, support, bind, and protect organs. (pp. 161)
1. Binding. Tendons bind muscle to bone; ligaments bind bones together.
2. Support. Bones support the body; cartilage supports other structures.
3. Physical protection. Bones such as those of the cranium protect delicate organs, in this case the brain.
4. Immune protection. Connective tissue cells attack foreign invaders.
5. Movement. Bones provide a lever system for movement; cartilage on bone surfaces eases joint movement.
6. Storage. Fat is a connective tissue the forms the body’s major energy reserve.
7. Heat production. Brown fat generates heat in infants and children.
8. Transport. Blood is a connective tissue that transports gases, nutrients, wastes. and other materials.
B. Fibrous connective tissue is the most diverse type. (pp. 161–166)
1. Fibrous connective tissue consists of cellular and fibrous components in a ground substance.
a. Cellular components include six types, depending on the tissue.
i. Fibroblasts are large flat cells that produce the fibers and ground substance of the tissue.
ii. Macrophages are large phagocytic cells that engulf and destroy bacteria, foreign particles, and dead or dying cells; they also respond to antigens.
iii. Leukocytes, or white blood cells (WBCs), enter connective tissues from the blood stream and wander in search of bacteria .
iv. Plasma cells synthesize antibodies.
v. Mast cells near blood vessels secrete heparin and histamine.
vi. Adipocytes, or fat cells, may group together into adipose tissues; they are very large cells that contain a globule of triglycerides.
b. Fibrous components include three types of protein fibers.
i. Collagenous fibers are made of collagen and are tough, flexible, and resist stretching; they are often called white fibers due to their appearance in fresh preparations.
ii. Reticular fibers are thin collagen fibers coated with glucoprotein, forming a spongelike framework in some organs.
iii. Elastic fibers are made of elastin, which can recoil from stretching like a rubber band; these are often called yellow fibers due to their appearance in fresh preparations.
c. Ground substance occupies the space between cells and fibers and usually has a gelatinous consistency because of three classes of molecules.
i. Glycosaminoglycan (GAG) is a long polysaccharide made of amino sugars and uronic acid that is able to absorb and hold water; examples include chondroitin sulfate, heparin, and hyaluronic acid.
ii. Proteoglycans are also gigantic molecules with a central core of protein and bristlelike outgrowths of GAGs. They form thick colloids and structural bonds.
iii. Adhesive glycoproteins are protein–carbohydrate complexes that bind plasma membrane proteins to collagen and proteoglycans outside the cell, holding tissues together.
2. Fibrous connective tissue is divided into two broad categories: loose connective tissue and dense connective tissue. (Table 4.2)
c. In loose connective tissue, much of the space is occupied by ground substance; examples include areolar and reticular tissues. (Table 5.4) (Figs. 5.14, 5.15)
d. In dense connective tissue, fiber occupies more space than cells and ground substance; examples include dense regular connective tissue and dense irregular connective tissue. (Table 5.5) (Figs. 5.17, 5.18)
e. Areolar tissue exhibits loosely organized fibers, abundant blood vessels, and a lot of empty space. (Fig. 5.14)
i. Fibers are randomly organized and mostly collagenous, although elastic and reticular fibers are present.
ii. It is found underlying nearly all epithelia, including the skin and membranes of the body and surrounding blood vessels and nerves.
f. Reticular tissue is a mesh of reticular fibers and fibroblasts forming the structural framework (stroma) of many organs. (Fig. 5.15)
g. Dense regular connective tissue is named for two properties: Closely packed collagen fibers with little open space; and the parallel arrangement of fibers. (Fig. 5.17)
i. The parallel arrangement is an adaptation to directional pull, such as on tendons and ligaments.
ii. In general the only cells are fibroblasts.
iii. Yellow elastic tissue is a dense regular connective tissue found in the vocal cords, suspensory ligament of the penis, and some ligaments of the vertebral column.
iv. Elastic tissue also takes the form of wavy sheets in the walls of the large and medium arteries, allowing expansion and recoil of these arteries.
Insight 5.1 Marfan Syndrome—A Connective Tissue Disease
h. Dense irregular connective tissue also has closely packed collagen fibers, but the collagen bundles run in random directions. (Fig. 5.18)
i. Random orientation allows resistance to unpredictable stresses.
ii. This tissue constitutes most of the dermis and forms protective capsules around organs such as kidneys, tests, and spleen; it also forms a sheath around bones, nerves, and cartilage.
C. Adipose tissue, or fat, is tissue in which adipocytes are the dominant cell type. (p. 166) (Table 5.6) (Fig. 5.18)
1. Adipocytes range from 70 to 120 µm in diameter, but may be five times as large in obese people.
2. Stored triglycerides in adipocytes are constantly being turned over, with an equilibrium between synthesis and hydrolysis, energy storage and energy use.
3. Adipose tissue also provides thermal insulation, anchoring, and cushioning.
4. Women have more fat relative to body weight than men do.
5. Most adipose tissue is white fat, but fetuses, infants, and children have a heat-generating tissue called brown fat, which accounts of up to 6% of an infant’s weight.
a. Brown fat gets its color from an abundance of blood vessels and certain enzymes in its mitochondria.
b. The oxidation pathway is not linked to ATP synthesis, so when fat is oxidized, all of the energy is released as heat.
c. Hibernating animals accumulate brown fat in preparation for winter.
D. Cartilage is a supportive connective tissue with a flexible rubbery matrix. (pp. 166–168) (Table 5.7) (Figs. 5.19, 5.20, 5.21)
1. Cells called chondroblasts secrete and surround themselves with matrix until they are trapped in cavities called lacunae, at which type they are called chondrocytes.
2. Cartilage is usually free of blood vessels, so diffusion of nutrients and wastes is slow and chondrocytes have low rates of metabolism and cell division; cartilage heals slowly.
3. Cartilage is classified based on the predominant type of fiber.
a. Hyaline cartilage is clear and glassy in microscopic appearance; the collagen fibers are very fine and invisible.
b. Elastic cartilage has conspicuous elastic fibers.
c. Fibrocartilage has coarse, readily visible bundles of cartilage.
d. Elastic cartilage and most hyaline cartilage are surrounded by a sheath of dense irregular connective tissue called the perichondrium.
e. Hyaline cartilage is found in the Adam’s apple in front of the larynx; elastic cartilage gives shape to the ear.
E. The term bone refers either to an organ such as the femur and mandible, composed of multiple tissue types, or to bone tissue (osseous tissue), which makes up most of the mass of the bones. (pp. 168–169)
1. Spongy bone fills the heads of long bones and forms the middle layer of flat bones such as the sternum.
2. Compact (dense) bone is a calcified tissue with no spaces visible to the naked eye; spongy bone, when present, is always covered by compact bone. (Table 5.8) (Fig. 5.22)
a. Compact bone is arranged in cylinders of tissue that surround central (haversian or osteonic) canals that run longitudinally through long bones; blood vessels and nerves travel through the canals.
b. Bone matrix is deposited in concentric lamellae around each central canal.
c. A central canal and its surrounding lamellae are called an osteon.
d. Lacunae between the lamellae are occupied by mature bone cells called osteocytes.
i. Tiny canals called canaliculi radiate between lacunae allowing osteocytes to contact each other.
e. The bone as a whole is covered with a fibrous periosteum.
f. Two-thirds of the weight of bone is calcium salts deposited around the collagen fibers.
F. Blood is a fluid connective tissue that travels through tubular vessels. (p. 169) (Table 5.9) (Fig. 5.23)
1. The primary function of blood is to transport cells and dissolved matter through the body.
2. Blood consists of plasma as the ground substance, and cells and cell fragments called formed elements.
a. Erythrocytes (red blood cells) are the most abundant formed elements; they have no nuclei and transport oxygen and carbon dioxide.
b. Leukocytes (white blood cells) have roles in immune defenses; they have conspicuous nuclei.
c. Platelets are small cell fragments; they are involved in clotting and other mechanisms for minimizing blood loss and for secreting growth factors to promote blood vessel growth.
IV. Nervous and Muscular Tissue—Excitable Tissues (pp. 170–172)
A. The basis for nerve and muscle excitation is an electrical charge difference called the membrane potential. (p. 170)
B. Nervous tissue consists of neurons and neuroglia (glial cells), which protect and assist the neurons. (pp. 170–171) (Table 5.10) (Fig. 5.24)
1. Neurons detect stimuli, respond, and transmit information rapidly.
a. Each neuron has a coma, or cell body, that contains the nucleus and organelles and is the center of genetic control and protein synthesis.
b. Dendrites are multiple short, branched processes extending from the soma that receive signals from other cells.
c. An axon, or nerve fiber, conducts outgoing signals from the soma to other cells; some are more than a meter long.
2. Glial cells outnumber neurons and make up most of the volume of nervous tissue; they provide support, protection, and housekeeping functions.
C. Muscular tissue consists of elongated cells that contract in response to stimulation; their primary function is to exert physical force on other tissues and organs. (p. 171–172)
1. Muscular tissue is responsible for movements of the body and limbs, the motions of digestion and waste elimination, and contraction of some organs, as well as breathing, speech, and blood circulation.
2. The three types of muscle are skeletal, cardiac, and smooth, which differ in appearance, physiology, and function. (Table 5.11) (Figures 5.25, 5.26, 5.27)
a. Skeletal muscle consists of long cells called muscle fibers.
i. Most skeletal muscle is attached to bones, but there are some exceptions such as in the tongue and some sphincters.
ii. Each fiber contains multiple nuclei adjacent to the plasma membrane.
iii. Skeletal muscle appeared striated, that is, it contains alternating light and dark bands (striations).
iv. Skeletal muscle is also voluntary in that it is under conscious control.
b. Cardiac muscle is limited to the heart.
i. Cardiac muscle cells are called myocytes or cardiocytes.
ii. Myocytes contain only one nucleus.
iii. Cardiac muscle also appears striated.
iv. Myocytes are joined end to end by intercalated discs that allow electrical excitation to travel rapidly from cell to cell; in this way, all myocytes contract almost simultaneously.
v. Cardiac muscle is considered involuntary because it usually is not under conscious control.
c. Smooth muscle lacks striations and is involuntary.
d. Most of the smooth muscle, called visceral muscle, forms layers in the walls of the digestive, respiratory, and urinary tracts as well as in blood vessels, the uterus, and other viscera.
i. In the esophagus and small intestine, smooth muscle forms two layers: one that encircles the tubelike organ and one that runs longitudinally; contractions move contents through the organ.
ii. Smooth muscle controls the diameter of blood vessels and thus has an impact on blood flow and blood pressure.
V. Intercellular Junctions, Glands, and Membranes (pp. 173–178)
A. The connections between one cell and another are called intercellular junctions. (pp. 173–174) (Fig. 5.28)
1. These junctions enable cells to resist mechanical stress and communicate with each other.
2. A tight junction is a region in which adjacent cells are bound together by fusion of the outer layer of their plasma membranes
a. In epithelia, tight junctions form a zone that encircles each cell, sealing off the intercellular space and preventing substances from passing between cells.
3. A desmosome is a patch that holds cells together more like a snap than a zipper.
a. Desmosomes keep cells from pulling apart, but they do not prevent substances from passing between cells.
b. Desmosomes are common in the epidermis, other epithelia, and cardiac muscle.
c. Each cell contributes half of each desmosome structure.
i. J-shaped proteins hook the cytoskeleton to a protein plaque on the inner surface of the plasma membrane.
ii. Proteins of the plaque are linked to transmembrane protein that interdigitate with transmembrane proteins of the adjacent cell, forming a zone of adhesion.
iii. Basal cells of an epithelium are linked to the basement membrane by hemidesmosomes (half-desmosomes).
4. A gap junction (communicating junction) is formed by a ringlike connexon.
a. Each connexon consists of a ring of six proteins with a central pore.
b. Ions, glucose, and other solutes can pass through this pore from one cell to another.
c. Gap junctions are found in intercalated discs of cardiac muscle and between the cells of most smooth muscle, where they allow the flow of ions during excitation; they are absent from skeletal muscle.
Insight 5.2 Pemphigus Vulgaris—A Result of Defective Desmosomes
B. A gland is a cell or organ that secretes substances for use elsewhere or for elimination. (pp. 174–176)
1. A gland is composed of epithelial tissue but usually has a supportive connective tissue framework and capsule.
2. Exocrine glands usually maintain contact with the surface by way of a duct; examples are sweat, mammary, and tear glands, and also salivary glands, the liver, and the pancreas.
3. Endocrine glands have no ducts; they secrete their products into the blood via the capillaries.
a. The secretions, called hormones, function as chemical messengers that act on cells elsewhere in the body.
b. Examples of endocrine glands include the pituitary, thyroid, and adrenal glands.
4. Some glands have both exocrine and endocrine function, such as the liver.
5. Unicellular glands are secretory cells found in an epithelium that is nonsecretory; and example is the goblet cells of the respiratory tract, which secrete mucus.
6. Exocrine glands are enclosed in a fibrous capsule with extensions called septa or trabeculae that divide the gland into lobes. (Fig. 5.29)
a. Finer septa may divide each lobe into microscopic lobules.
b. The connective tissue framework is called the gland’s stroma; it provides support and organization.
c. The cells that carry out synthesis and secretion are called the parenchyma; it is typically simple cuboidal or simple columnar epithelium.
d. Exocrine glands with a single unbranched duct are called simple; those with branched ducts are called compound.
e. Tubular glands have a duct and secretory portion of uniform diameter; acinar glands have secretory cells that form a dilated sac; tubuloacinar glands have secretory cells in both the tubular and acinar portions. (fig. 5.30)
7. Glands may also be classified by the nature of their secretions.
a. Serous glands produce thin, watery fluids, such as tears.
b. Mucous glands secrete a glycoprotein called mucin, which absorbs water once it is secreted to form the sticky product mucus; examples are the goblet cells.
c. Mixed glands contain both serous and mucous cells, such as the salivary glands in the chin.
d. Cytogenic glands release whole cells; only the testes and ovaries are cytogenic glands.
8. Glands may be classified as merocrine or holocrine depending on how secretions are produced. (Fig. 5.31)
a. Merocrine glands (eccrine glands) have vesicles that release secretions by exocytosis, such as tear glands.
b. Holocrine glands accumulate the product in their cells, and then these cells disintegrate to release the product; and example is oil-producing glands of the scalp.
c. Sweat glands and mammary glands are named apocrine glands from an earlier belief that the secretion consisted of apical cytoplasm; these glands have been found to be primarily merocrine in their mode of secretion.
C. Membranes line body cavities as well as covering the outside of the body (pp. 176–178)
1. The largest membrane of the body is the cutaneous membrane, or skin, consisting of stratified epithelium (epidermis) resting on a layer of connective tissue (dermis); it is relatively dry and resists dehydration of the body.
2. The two principle kinds of internal membranes are mucous membranes and serous membranes. (Fig. 5.32)
a. A mucous membrane (mucosa) lines passageways that open to the exterior environment, such as digestive, respiratory, urinary, and reproductive tracts.
i. Mucous membranes consist of an epithelium, an areolar connective tissue called the lamina propria, and a smooth muscle layer called the muscularis mucosae.
ii. These membranes are often covered with mucus that traps bacteria and foreign particles, preventing them from invading the body.
b. A serous membrane (serosa) lines the insides of some body cavities, such as the pleura, pericardium, and peritoneum, and forms a smooth outer surface on some of the viscera.
i. A serous membrane consists of a simple squamous epithelium resting on a thin layer of connective tissue.
ii. These membranes produce watery serous fluid, which is similar to blood serum in composition.
3. The circulatory system is lined with a simple squamous epithelium called endothelium, derived from mesoderm.
a. The endothelium and supporting connective tissues make up a membrane called the tunica interna of the blood vessels and the endocardium of the heart.
4. The simple squamous epithelium that lines the pleural, pericardial, and peritoneal cavities is called mesothelium.
5. Some joints are lines by fibrous synovial membranes made only of connective tissue; these secrete slippery synovial fluid into the joint.
VI. Tissue Growth, Development, Repair, and Death (pp. 178–183)
A. Tissue growth occurs either because cells increase in number or because the existing cells grow larger. (pp. 178–179)
1. Hyperplasia is growth through cell multiplication, and it occurs during embryonic development and childhood.
2. Hypertrophy is the enlargement of preexisting cells, such as muscle fibers upon exercise and enlargement of adipocytes upon storage of triglycerides.
3. Neoplasia is the development of a tumor composed of abnormal, nonfunctional tissue.
B. Tissues are capable of changing from one type to another, within limits, a process known as differentiation. (p. 179)
1. Metaplasia is a change from one type of mature epithelium into another, such as occurs in the human vagina at puberty when the vaginal lining of simple cuboidal epithelium changes to stratified squamous epithelium.
C. Stem cells are undifferentiated cells that have the potential to change into one or more types of mature functional cells. (p. 179)
1. Embryonic stem cells compose the early human embryo; these are totipotent cells, meaning they can develop into any type of human cell.
2. About 4 days after fertilization, at the embryonic blastocyst stage, the inner mass of cells are pluripotent: they can become any cell type in the embryo, but not cells of the placenta or amniotic sac. (Fig. 29.4)
3. Adult stem cells occur in small numbers in mature organs and tissues.
a. Some adult stem cells are multipotent and can develop into two or more different cell lines (but not just any type of cell).
b. Unipotent adult stem cells can produce only one mature cell type.
D. Tissues are repaired through regeneration or fibrosis (p. 179–181)
1. Regeneration is the replacement of dead or damaged cells with the same type of cells as before; an organ’s function is restored in this way.
2. Fibrosis is the replacement of damaged tissue with scar tissue, composed mainly of collagen produced by fibroblasts; fibrosis does not restore normal function.
3. Healing of an injury such as a cut in the skin occurs in four stages. (Fig. 5.33)
a. Bleeding occurs, and mast cells and damaged cells release histamine increasing blood flow and capillary permeability.
b. A blood clot forms in the tissue, knitting the edges of the cut together and helping to prevent entry of pathogens; the surface of the clot forms a scab while macrophages underneath begin to clean up tissue debris.
c. New blood capillaries grow into the wound, and the mass of capillaries and fibroblasts is called granulation tissue; macrophages remove the blood clot and fibroblasts deposit new collagen in its place.
d. Surface epithelial cells around the wound multiply and migrate into the wounded area, beneath the scab; the scab loosens and falls off, and the epithelium grown thicker; epithelium undergoes regeneration while underlying connective tissue undergoes fibrosis (scarring); remodeling of the injured area may take up to two years.
E. Atrophy is the shrinkage of a tissue through a loss in cell size or number (p. 181)
1. Senile atrophy is a result of normal aging.
2. Disuse atrophy results from lack of use, as in muscles that are not exercised.
F. Necrosis is the premature, pathological death of tissue due to trauma, toxins, or infection. (p. 181)
1. Infarction is the sudden death of tissue such as may occur in cardiac muscle or brain tissue when the blood supply is cut off.
2. Gangrene is tissue necrosis resulting from an insufficient blood supply, usually involving infection.
a. Dry gangrene often occurs in diabetics, especially in the feet, due to arterial and nerve damage; a decubitus ulcer (bed sore) is a form of dry gangrene caused by continual pressure on the skin.
b. Gas gangrene is necrosis of a wound resulting from infection with Clostridium species; this is a deadly condition that may require amputation.
G. Apoptosis (programmed cell death) is the normal death of cells that have completed their function. (p. 181)
1. Cell undergoing apoptosis are quickly phagocytized and their cell contents never escape.
2. Every cell has a built-in “suicide program” that enables the body to dispose of it when necessary.
a. Some cells respond to an extracellular suicide signal that binds to the Fas protein in the plasma membrane.
b. Other cells undergo apoptosis if they stop receiving growth factors from other cells.
3. Apoptosis dissolves the webbing between fingers and toes during embryonic development and causes the shrinkage of the uterus after pregnancy, among other things.
Insight 5.3 Tissue Engineering (Fig. 5.34)
Insight 5.4 The Stem Cell Controversy

Cross References
Additional information on topics mentioned in Chapter 5 can be found in the chapters listed below.

Chapter 3: Exocytosis
Chapter 6: The skin
Chapter 7: Compact and spongy bone
Chapters 12–16: Structures of nervous tissue
Chapter 13: Types of glial cells
Chapter 17: Endocrine glands
Chapter 18: Types of leukocytes
Chapter 19: Arteriosclerosis