Myofibrils and Myofilaments

The structural and functional subunit of the muscle fiber is the myofibril Skeletal muscles are composed of fascicles, which in turn are composed of individual muscle fibers. The muscle fiber is filled with longitudinally arrayed subunits called myofibrils (Fig. 10.3). Myofibrils are visible in favorable histologic preparations and are best seen in cross sections of muscle fibers. In these sections they give the fiber a stippled appearance. Myofibrils extend the entire length of the muscle...

Supporting Tissues of the Teeth

Supporting tissues of the teeth include the alveolar bone of the alveolar processes of the maxilla and mandible, periodontal ligaments, and gingiva. The alveolar processes of the maxilla and mandible contain the sockets or alveoli for the roots of the teeth The alveolar bone proper, a thin layer of compact bone, forms the wall of the alveolus (see Fig. 15.7) and is the bone to which the periodontal ligament is attached. The rest of the alveolar process consists of supporting bone. The surface...

Connective Tissue Components of a Peripheral Nerve

The bulk of a peripheral nerve consists of nerve fibers and their supporting Schwann cells. The individual nerve fibers and their associated Schwann cells are held together by connective tissue organized into three distinctive components, each with specific morphologic and functional characteristics (Fig. 11.24 also, see Fig. 11.3). These components are Endoneurium, which includes loose connective tissue surrounding each individual nerve fiber Perineurium, which includes specialized connective...

Anchoring Junctions

Anchoring junctions provide lateral adhesions between epithelial cells, using proteins that link into the cytoskeleton of the adjacent cells. Two types of anchoring cell-to-cell junctions can be identified on the lateral cell surface Zonula adherens (pi., zonulae adherentes), which interacts with the network of actin filaments inside the cell Macula adherens (pi., maculae adherentes) or desmo-some, which interacts with intermediate filaments In addition, two other types of anchoring junctions...

Plate 99 Mammary Gland Late Proliferative And Lactating

Mammary glands exhibit a number of changes during pregnancy in preparation for lactation. Lymphocytes and plasma cells infiltrate the loose connective tissue as the glandular tissue develops. As the cells of the glandular portion proliferate by mitotic division, the ducts branch and alveoli begin to develop at their growing ends. Alveolar development becomes most prominent in the later stages of pregnancy, and accumulation of secretory product takes place in the alveoli. At the same time,...

Plate 11 Bone Ground Section

Bone is a specialized connective tissue characterized by a mineralized extracellular matrix. Calcium phosphate, in the form of hydroxyapatite crystals (CaU)(P04)ft0H2), is deposited along the collagen fibrils and in the proteoglycan ground substance. Bone serves as a storage site for calcium and phosphate, which can be released to the blood to maintain homeostatic levels. Osteocytes reside in lacunae in the bone matrix and extend fine cellular processes into canaliculi that connect the lacunae,...

Info

Largest organelle within the cell with distinct boundary often visible nucleoli and chromatin pattern regions Roughly circular, basophilic region within the nucleus visible in living cells throughout interphase with Interference microscopy Often observed as a basophilic region of cytoplasm referred as ergastoplasm Not visible cytoplasm in region of sER may exhibit distinct eosinophilia Sometimes observed as negative-staining region appears as network in heavy-metal-stained preparations visible...

Figure 2131

Photomicrograph of corpus spongiosum, a. This photomicrograph of a H& E-stained section shows the corpus spongiosum and urethra. x20. b. This higher magnification of the corpus spongiosum shows the numerous irregularly shaped vascular spaces. Note the surrounding layer of smooth muscle (SM) forming the subendothelial cushions. X135. Erection of the penis is a vascular event initiated by the CNS and maintained by complex interactions between vascular and neurologic events. The CNS responds to...

Figure 131

Overview of the structures constituting the lymphatic system. Because lymphatic tissue is the main component of some organs, they are regarded as organs of the lymphatic system (spleen, thymus, lymph nodes). Lymphatic tissue is present as part of other organs, such as red bone marrow, lymphatic nodules of the alimentary canal (tonsils, vermiform appendix, gut-associated lymphatic tissue GALT ) and of the respiratory system (bronchus-associated lymphatic tissue IBALT ), and, not shown in the...

Plate 48 Parotid Gland

The parotid glands are the largest of the major salivary glands. They are composed of alveoli containing only serous secretory cells. Adipose tissue often occurs in the parotid gland and may be one of its distinguishing features. The facial nerve (cranial nerve VII) passes through the parotid gland large cross sections of this nerve, often found in routine H& E sections of the gland, may also be of help in identifying the parotid. Mumps, a viral infection of the parotid gland, can damage the...

Plate 34 Lymph Node Ii

Immunocompetent B cells that have been exposed to an antigen that they can recognize and bind migrate to a lymph node, where they undergo blastic transformation and begin a series of mitotic divisions that produce large numbers of immature im-munoblasts. The immunoblasts proliferate further and then differentiate into a clone of lymphocytes that differentiate into an-tibody-secreting plasma cells and memory cells. Immunocompetent T lymphocytes behave in a similar manner but differentiate into...

Schwann Cells and the Myelin Sheath

Axons in the peripheral nervous system are described as myelinated or unmyelinated Myelinated axons are surrounded by a lipid-rich layer called the myelin sheath. External to, and contiguous with, the myelin sheath is a thin layer of Schwann cell cytoplasm called the sheath of Schwann, or the neurilemma (Fig. 11.10). This layer contains the nucleus and most of the organelles of the Schwann cell. Surrounding the Schwann cell is a basal or external lamina. Functionally, the myelin sheath with its...

Figure 161

Diagram of general organization of the alimentary canal. This composite diagram shows the wall structure of the alimentary canal in four representative organs esophagus, stomach, small intestine, and large intestine. Note that villi, a characteristic feature of the small intestine, are not present in other parts of the alimentary canal. Mucosal glands are present throughout the length of the alimentary canal but sparingly in the esophagus and oral cavity. Submucosal glands are present in the...

Figure 2317

Schematic diagram of the eye and lacrimal apparatus. This drawing shows the location of the lacrimal gland and components of the lacrimal apparatus, which drains the lacrimal fluid into the nasal cavity. cells. Myoepithelial cells, located below the epithelial cells within the basal lamina, aid in the release of tears. Approximately 12 ducts drain from the lacrimal gland into the reflection of conjunctiva just beneath the upper eyelid, known as the fornix of the lacrimal sac. Tears drain from...

Plate 69 Wall Of Terminal Bronchiole Respiratory Bronchiole And Alveolus

Respiratory bronchioles continue to divide to form alveolar ducts, passages lined solely with rows of alveoli that have rings of smooth muscle in knob-like interalveolar septa. The alveolar ducts terminate in alveolar sacs, enlarged spaces surrounded by clusters of alveoli that open into the spaces. The alveoli are lined with type I alveolar cells, extremely thin squamous cells that cover about 95 of the alveolar surface, and with type II alveolar cells, cuboidal cells that secrete surfactant,...

Structure of the Testis

The testes have an unusually thick connective tissue capsule, the tunica albug nea An unusually thick, dense connective tissue capsule, the tunica albug nea, covers each testis (Fig. 21.4). The inner part of this capsule, the tunica vasculosa, is a loose connective tissue layer that contains blood vessels. Each testis is divided into approximately 250 lobules by incomplete connective tissue septa that project from the capsule. Along the posterior surface of the testis, the tunica albug nea...

Plate 44 Lip A Mucocutaneous Junction

The lips are the entry point of the alimentary canal. Here, the thin keratinized epidermis of face skin changes to the thick parakeratinized epithelium of the oral mucosa. The transition zone, the red portion of the lips, is characterized by deep penetration of connective tissue papillae into the base of the stratified squamous keratinized epithelium. The blood vessels and nerve endings in these papillae are responsible for both the color and the exquisite touch sensitivity of the lips. A H&...

Figure 2216

Photomicrograph of a sagittal section of a human uterus. This section shows the three layers of the uterine wall the endometrium, the innermost layer that lines the uterine cavity the myometrium, the middle layer of smooth muscle and the perimetrium, the very thin layer of peritoneum that covers the exterior surface of the uterus. The deep portion of the myometrium contains the larger blood vessels (BV) that supply the uterus. x8. the development of new fibers through the division of existing...

Thyroid gland

The thyroid gland is located in the anterior neck region adjacent to the larynx and trachea The thyroid gland is a bilobate endocrine gland located in the anterior neck region and consists of two large lateral lobes connected by an isthmus, a thin band of thyroid tissue. The two lobes, each 5 cm in length, 2.5 cm in width, and 20 to 30 g in weight, lie on either side of the larynx and upper trachea. The isthmus crosses anterior to the upper part of the trachea. A pyramidal lobe often extends...

O Histochemistry And Cytochemistry

Specific chemical procedures can provide detailed information about the function of the cells and extracellular components of the tissues Histochemical and cytochemical procedures may be based on specific binding of a dye, use of a fluorescent dye-labeled antibody to a particular cell component, or the inherent enzymatic activity of a cell component. In addition, many large molecules found in cells can be localized by autoradiography, in which radioactively tagged precursors of the molecule are...

Serosa and Adventitia

Serosa or adventitia constitutes the outermost layer of the alimentary canal The serosa is a serous membrane consisting of a layer of simple squamous epithelium, called the mesothelium, and a small amount of underlying connective tissue. It is equivalent to the visceral peritoneum described in gross anatomy. The serosa is the most superficial layer of those parts of the digestive tract that are suspended in the peritoneal cavity. As such, the serosa is continuous with both the mesentery and the...

Plate 22 Smooth Muscle

Smooth muscle is the simplest appearing muscle tissue and is the intrinsic muscle of the alimentary canal, blood vessels, genitourinary tract, respiratory tract, and other hollow and tubular organs. Smooth muscle generally occurs as bundles or sheets of elongated fusiform cells, also called fibers. Smooth muscle is specialized for slow, prolonged contraction. There are no direct neural endings on smooth muscle cells nerve terminals in smooth muscle are in the immediately adjacent connective...

Muscularis Externa

In most parts of the digestive tract, the muscularis externa consists of two concentric and relatively thick layers of smooth muscle. The cells in the inner layer form a tight spiral, described as a circularly oriented layer those in the outer layer form a loose spiral, described as a longitudinally oriented layer. Located between the two muscle layers is a thin connective tissue layer. Within this connective tissue lies the myenteric plexus (Auerbach's plexus) containing nerve cell bodies...

Diffuse Lymphatic Tissue and Lymphatic Nodules

Diffuse lymphatic tissue and lymphatic nodules guard the body against pathogenic substances and are the site of the initial immune response The alimentary canal, respiratory passages, and genitourinary tract are guarded by accumulations of lymphatic tissue that are not enclosed by a capsule. Lymphocytes and other free cells of this tissue are found in the lamina propria (subepithelial tissue) of these tracts. This form of lymphatic tissue is called diffuse lymphatic tissue or mucus-associated...

Figure 1119

Protoplasmic astrocyte in the gray matter of the brain. This schematic drawing shows the foot processes of the protoplasmic astrocyte terminating on a blood vessel and the axonal process of a nerve cell. The foot processes terminating on the blood vessel contribute to the blood-brain barrier. The bare regions of the vessel as shown in the drawing would be covered by processes of neighboring astrocytes, thus forming the overall barrier. limitans, a relatively impermeable barrier surrounding the...

Figure 89

Electron micrograph showing active bone formation. This electron micrograph is similar to the growing surface of the bone spicule in the preceding light micrograph (Fig. 8.8). The marrow cavity (M) with its developing blood cells is seen in the lower right corner. Osteoprogen-itor cells (Opc) are evident between the marrow and the osteoblasts (Ob). They exhibit elongate or ovoid nuclei. The osteoblasts are aligned along the growing portion of the bone, which is covered by a layer of osteoid...

Plate 17 Granulocytes

Granulocytes are characterized by a lobed nucleus and by the specific staining characteristics of granules in the cytoplasm. Three kinds of granulocytes are present in a peripheral blood smear neutrophils (polymorphonuclear leukocytes), 55 to 60 eosinophils, 2 to 5 and basophils, 1 or less. All of the granulocytes leave the bloodstream and enter the connective tissue to perform their specific functions. Neutrophils are actively phagocytic cells that have both specific granules and azurophilic...

Kidney Lobes and Lobules

The number of lobes in a kidney equals the number of medullary pyramids Each medullary pyramid and the associated cortical tissue at its base and sides (one half of each adjacent renal column) constitutes a lobe of the kidney. The lobar organ ization of the kidney is conspicuous in the developing fetal kidney (Fig. 19.5). Each lobe is reflected as a convexity on the outer surface of the organ, but they usually disappear after birth. The surface convexities typical of the fetal kidney may...

Figure 105

Sarcomeres in different functional stages. In the resting state (middle), interdigitation of thin (actin) and thick (myosin) filaments is not complete the H and I bands are relatively wide. In the contracted state (bottom), the interdigitation of the thin and thick filaments is increased according to the degree of contraction. In the stretched state (top), the thin and thick filaments do not interact the H and I bands are very wide. The length of the A band always remains the same and...

Absorptive Cells

That drives Na+ and water across the basal lamina into the connective tissue. , In epithelia with more permeable tight junctions, such as those in the duodenum and jejunum, a sodium pump also creates low intracellular Na+ concentration. When the contents that pass into the duodenum and jejunum are hypotonic, however, considerable absorption of water, along with additional Na+ and other small solutes, takes place directly across the tight junctions of the enterocytes into the intercellular...

Mature Bone

The matrix of immature bone has more ground substance than does the matrix of mature bone. The matrix in immature bone stains more intensely with hematoxylin, whereas the matrix of mature bone stains more intensely with eosin. Although not evident in typical histologic sections (Fig. 8.6), immature bone is not heavily mineralized when it is initially formed, whereas mature bone undergoes prolonged secondary mineralization. The secondary mineralization of mature bone is evident in...

Acidic And Basic Dyes

Hematoxylin and eosin are the most commonly used dyes in histology An acidic dye, such as eosin, carries a net negative charge on its colored portion and is described by the general formula Na+dye . A basic dye carries a net positive charge on its colored portion and is described by the general formula dye+CI J. Hematoxylin does not meet the definition of a strict basic dye but has properties that closely resemble those of a basic dye. The color of a dye is not related to whether it is basic or...

Plate 75 Urinary Bladder

The urinary bladder receives the urine from the two ureters and stores it until neural stimulation causes it to contract and expel the urine via the urethra. It, too, is lined with transitional epithelium. Beneath the epithelium and its underlying connective tissue, the wall of the urinary bladder contains smooth muscle that is usually described as being arranged as an inner longitudinal layer, a middle circular layer, and an outer longitudinal layer. As in most distensible hollow viscera that...

The Contraction Cycle

Shortening of a muscle involves rapid contraction cycles that move the thin filaments along the thick filament. Each contraction cycle consists of five stages attachment, release, bending, force generation, and reattachment. Attachment is the initial stage of the contraction cycle, in which the myosin head is tightly bound to the actin molecule of the thin filament At the beginning of the contraction cycle, the myosin head is tightly bound to the actin molecule of the thin filament, and ATP is...

Figure

Photomicrograph of brown adipose tissue from a newborn in a H& E-stained paraffin preparation. The ceils contain fat droplets of varying size. Note the large blood vessels within the tissue. xl50. b. This photomicrograph obtained at a higher magnification shows the brown adipose cells with round and often cen trally located nuclei. Most of the cells are polygonal and are closely packed, with numerous lipid droplets. In some cells, large lipid droplets displace nuclei...

Plate 65 Olfactory Mucosa

Olfactory mucosa is located in the roof and part of the walls of the nasal cavity. Its pseudostratified epithelium is thicker than that of nonsensory epithelium, and it serves as the receptor for smell. Olfactory epithelium consists of olfactory cells, supporting (sustentacular) cells, basal cells, and brush cells (see Fig. 18.3, page 582). Olfactory cells are bipolar neurons. The apex of the cell is expanded into the olfactory vesicle from which nonmotile cilia, the actual receptors, extend...

Plate 35 Spleen I

The spleen is the largest lymphatic organ it is surrounded by a capsule and located in the path of the bloodstream (splenic artery and vein). The spleen filters the blood and reacts immunologically to blood-borne antigens. It has both morphologic and immunologic filtering functions. The substance of the spleen, the splenic pulp, consists of red pulp and white pulp, so named because of their appearance in fresh tissue. The white pulp is rich in lymphocytes that form a periarterial lymphatic...

Maternal Circulation

Exchange of gases and metabolic products occurs. The maternal blood finally leaves the intervillous space (black arrows) through endometrial veins. The fetal blood enters the placenta through the umbilical arteries that divide into a series of radially disposed arteries within the chorionic plate. Branches from the vessels pass into the main stem villi and there form extensive capillary networks. The veins within the villi then cany the blood back through a system of veins that parallels the...

Seminiferous tubules Cycle of the Seminiferous Epithelium

Differentiating spermatogenic cells are not arranged at random in the seminiferous epithelium specific cell types are grouped together. These groupings or associations occur because intercellular bridges are present between the progeny of each pair of type Ap spermatogonia and because the synchronized cells spend specific times in each stage of maturation. All phases of differentiation occur sequentially at any given site in a seminiferous tubule as the progeny of stem cells remain connected by...

Plate 80 Adrenal Gland I

There are two adrenal glands, one at the upper pole of each kidney. The gland is a composite of two distinct structural and functional components a cortex and a medulla. The cortex develops from mesoderm and secretes steroid hormones the medulla develops from neuroectoderm of the neural crest and secretes catecholamines. The cortex is divided into three zones according to the type and arrangement of its parenchymal cells. These are designated zona glomerulosa, zona fasciculata, and zona...

Accessory Structures of the

The conjunctiva lines the space between the inner surface of the eyelids and the anterior surface of the eye lateral to the cornea The conjunctiva is a thin, transparent mucous membrane that extends from the corneoscleral limbus located on the lateral margin of the cornea across the sclera (bulbar conjunctiva) and covers the internal surface of the eyelids (palpebral conjunctiva). It consists of a stratified columnar epithelium containing numerous goblet cells and rests on a lamina propria...

Structure of Cardiac Muscle

The cardiac muscle nucleus lies in the center of the cell The central location of the nucleus in cardiac muscle cells is one feature that helps distinguish them from multinucleated skeletal muscle fibers, whose nuclei lie immediately under the plasma membrane. The transmission electron microscope (TEM) reveals that the myofibrils of cardiac muscle separate to pass around the nucleus, thus outlining a biconical juxtanuclear region in which the cell organelles are concentrated. This region is...

Visceral Surface

Central And Hepatic Vein

Prothrombin and fibrinogen, important components of the blood-clotting cascade. Nonimmune a- and -globulins, which also help maintain plasma colloid osmotic pressure and serve as carrier proteins for various substances (see Chapter 9, page 216). The liver stores and converts several vitamins and iron Several vitamins are taken up from the bloodstream and are then stored and or biochemically modified by the liver. They include Vitamin A (retinol), an important vitamin in vision. Vitamin A is...

Plate 81 Adrenal Gland Ii

The cells of the adrenal medulla develop from the same source as the postganglionic cells of the sympathetic nervous system. They are directly innervated by preganglionic cells of the sympathetic system and may be regarded as modified postganglionic cells that are specialized to secrete. These cells produce the catecholamines epinephrine and norepinephrine. The adrenal medulla receives its blood supply via two routes by arterioles that pass through the cortex and by capillaries that continue...

The Lateral Domain And Its Specializations In Celltocell Adhesion

The lateral domain of epithelial cells is in close contact with the opposed lateral domains of neighboring cells. Like the other domains, the lateral domain is characterized by the presence of unique proteins, in this case the adhesion molecules that are part of junctional specializations. The molecular composition of the lipids and proteins that form the lateral cell membrane differ significantly from the composition of those that form the apical cell membrane. In addition, the lateral cell...

Plate 21 Cardiac Muscle Purkinje Fibers

All cardiac muscle cells exhibit a spontaneous rhythmic contraction or beat. This beat is evident in embryonic cardiac muscle cells as well as in isolated cardiac muscle cells in tissue culture. In the heart, this beat is initiated, locally regulated, and coordinated by specialized, modified cardiac muscle cells that are organized into nodes and bundles to transmit the contractile impulse to various parts of the myocardium in a precise sequence. The beat of the heart is initiated at the...

Testis

The adult testes are paired ovoid organs that lie within the scrotum, located outside the body cavity. Testes are sus Intermediate mesoderm that forms the urogenital ridges on the posterior abdominal wall Mesodermal epithelium (coelomic mesothelium) that lines the urogenital ridges

Bulbourethral Glands

Muscle Cells

The bulbourethral glands secrete preseminal fluid The paired bulbourethral glands Cowper's glands are pea-sized structures located in the urogenital diaphragm see Fig. 21.1 . The duct of each gland passes through the inferior fascia of the urogenital diaphragm and joins the initial portion of the penile urethra. The glands are compound tubuloalveolar glands that structurally resemble mucus secretory glands Fig. 21.29 . The simple columnar epithelium, which varies considerably in height...

Plate 61 Liver I

The liver is the largest mass of glandular tissue in the body and the largest internal organ. It is unique because it receives its major blood supply from the hepatic portal vein, which carries venous blood from the small intestine, pancreas, and spleen. Thus the liver is directly in the pathway that conveys materials absorbed in the intestine. This gives the liver the first exposure to metabolic substrates and nutrients it also makes the liver the first organ exposed to noxious and toxic...

Plate 60 Anorectal Junction

At the anorectal junction, there is a transition from the simple columnar epithelium of the intestinal mucosa to the keratinized stratified squamous epithelium of the skin. Between these two distinctly different epithelia there is a narrow region where the epithelium is first stratified columnar or stratified cuboidal and then nonkeratinized stratified squamous. At the level of the anorectal junction, the muscularis mucosae disappears. At the same level, the circular layer of the mus-cularis...

Dendrites and Axons

Axon Hillock

Dendrites are receptor processes that receive stimuli from other neurons or from the external environment The main function of dendrites is to receive information from other neurons or from the external environment and carry that information to the cell body. Generally, dendrites are located in the vicinity of the cell body. They have a greater diameter than axons, are unmyelinated, are usually tapered, and form extensive arborizations called den-dritic trees. Dendritic trees significantly...

Plate 15 Intramembranous Bone Formation

Figure 1, fetal head, human, Mallory trichrome x45. A cross section of the developing lower jaw bone, as seen at this relatively early stage of development, consists of bone spicules BS of various sizes and shapes. The bone spicules interconnect and, in three dimensions, have the general shape of the mandible. Other structures present that will assist in orientation include developing teeth DT , the tip of Meckel's cartilage MC , also referred to as the mandibular process, seen on the left...

Plate 3 Stratified Epithelia And Epithelioid Tissues

Figure 1, esophagus, monkey, H amp E x250 This part of the wall of the esophagus reveals two different epithelia. On the left is the lining epithelium of the esophagus. It is multilayered with squamous surface cells therefore, it is a stratified squamous epithelium SS . On the right is the duct of an esophageal gland cut in several planes. By examining a region where the plane of section is at a right angle to the surface, the true character of the epithelium becomes apparent. In this case, the...

Plate 4 Loose And Dense Connective Tissue

Connective Tissue Mammary Gland

Figure 1, mammary gland, human, H amp E x160 This micrograph shows, at low magnification, loose connective tissue LCT immediately surrounding the gland epithelium Ep . It is relatively less strained with eosin, compared with the dense connective tissue DCT that occupies much of the field. The dense connective tissue, with its numerous thick fibers, is in contrast to the loose connective tissue that has a relative paucity of fibers. The typical wispy nature of the collagen fibers found in loose...

Epithelial Cell Renewal

Most epithelial cells have a finite life span less than that of the whole organism Surface epithelia and epithelia of many simple glands belong to the category of continuously renewing cell populations. The rate of cell turnover, i.e., the replacement rate, is characteristic of a specific epithelium. For example, the cells lining the small intestine are renewed every 4 to 6 days in humans. The replacement cells are produced by mitotic activity in the lower portion of the intestinal glands...

Cyclic Changes During the Menstrual Cycle

Cyclic changes of the endometrium during the menstrual cycle are represented by the proliferative, secretory, and menstrual phases The menstrual cycle is a continuum of developmental stages in the functional layer of the endometrium. It is ultimately controlled by gonadotropins secreted by the pars dis-talis of the pituitary gland that regulate the steroid secretions of the ovary. The cycle normally repeats every 28 days, during which the endometrium passes through a sequence of morphologic and...

Plate 5 Dense Regular Connective Tissue Tendons And Ligaments

Figure 1, tendon, longitudinal section, human, H amp E x100. This specimen includes the surrounding dense irregular connective tissue of the tendon, the epitendineum Ept . The tendon fascicles TF that make up the tendon are surrounded by a less dense connective tissue than that associated with the epitendineum. In longitudinal sections such as this, the connective tissue that surrounds the individual fascicles, the endotendineum Ent , seems to disappear at certain points, with the result that...

Vascular Coat Uvea

Anterior Pigment Myoepithelium

The iris, the most anterior part of the vascular coat, forms a contractile diaphragm in front of the lens The iris arises from the anterior border of the ciliary body Fig. 23.7 and is attached to the sclera about 2 mm posterior to the corneoscleral junction. The pupil is the central aperture of this thin disc. The iris is pushed slightly forward as it changes in size in response to light intensity. It consists of highly vascularized connective tissue stroma that is covered on its posterior...

Olfactory Segment of the Nasal Cavity

Muscle Cell Under Microscope

The olfactoiy segment is located on part of the dome of each nasal cavity and, to a variable extent, the contiguous lateral and medial nasal walls. It is lined with a specialized olfactoiy mucosa. In living tissue, this mucosa is distinguished by its slight yellowish brown color caused by pigment in the olfactoiy epithelium and the associated olfactory glands. In humans, the total surface area of the olfactory mucosa is only a few square centimeters in animals with an acute sense of smell, the...

Plate 27 Spinal Cord

The spinal cord is organized into two discrete parts. The outer part, called the white matter of the cord because of its appearance in unfixed specimens, contains ascending and descending nerve fibers. Some of the fibers go to and from the brain, whereas others connect different levels of the spinal cord. The inner part of the spinal cord, called the gray matter because of its appearance in unfixed specimens, contains the cell bodies of neurons as well as nerve fibers. The gray matter forms an...

Figure 1420

Photomicrograph showing a late stage in the epidermal repair of a skin wound. The initial injury was caused by an incision through the full thickness of the skin and partially into the hypodermis, which contains adipose ceils A . The epidermis has re-formed beneath the scab. The asterisk marks an artifact where epithelium separated during specimen preparation. The scab, which contains numerous dead neutrophils in its inferior aspect, is close to the point of release. The dermis at this stage...

Figure 514

Photomicrograph of a connective tissue specimen fixed with glutaraldehyde, embedded in plastic, and stained with H amp E. Thin strands of fibroblast cytoplasm arrow 5 belonging to a few preferentially oriented cells can just barely be recognized between collagen fibers. In routine H amp E-stained, paraffin-embedded preparations, it is usually impossible to distinguish the attenuated and poorly preserved fibroblast cytoplasm from the collagen fibers. Typically,...

Plate 20 Cardiac Muscle

Cardiac muscle consists of fibers that possess the same arrangement of contractile filaments and thus the same cross-banding patterns that are present in striated skeletal and visceral muscle. Although cardiac muscle is, therefore, also striated, it differs in many significant respects from skeletal and striated visceral muscle. Cardiac muscle consists of individual cells that are joined by complex junctions to form a functional unit fiber . The histologically obvious differences between...

Dermis

Attachment of epidermis to dermis is enhanced by an increased interface between the two tissues The junction between the dermis and epidermis is seen in the light microscope as an uneven boundary except in the thinnest skin. Sections of skin cut perpendicular to the surface reveal numerous finger-like connective tissue protrusions, dermal papillae, that project into the undersurface of the epidermis see Figs. 14.1 and 14.2 . The papillae are complemented by what appear to be similar epidermal...

Figure 44

Molecular structure of stereocilia. a. Electron micrograph of stereo-cilia from the epididymis. The cytoplasmic projections are similar to microvilli, but they are extremely long, x 20,000. b. Schematic diagram showing the molecular structure of stereocilia. They arise from the apical cell protrusions, having thick stem portions that are inter connected by cytoplasmic bridges. Note the distribution of actin filaments within the core of the stereocilium and the actin-associated proteins fimbrin...

Functional Aspects of Smooth Muscle

Smooth muscle is specialized for slow, prolonged contraction As noted above, smooth muscle cells may remain contracted for long periods of time without fatiguing. They may contract in a wave-like manner, producing peristaltic movements such as those in the gastrointestinal tract and the male genital tract, or contraction may occur along the entire muscle, producing extrusive movements, e.g., those in the urinary bladder, gallbladder, and uterus. Smooth muscle exhibits a spontaneous contractile...

Plate 6 Elastic Fibers And Elastic Lamellae

Elastic fibers are present in loose and dense connective tissue throughout the body, but in lesser amounts than collagenous fibers. Elastic fibers are not conspicuous in routine H amp E sections but are visualized readily with special staining methods. The following selectively color elastic material Weigert's elastic tissue stain, purple-violet Gomori's aldehyde fuchsin stain, blue-black Verhoeff's hematoxylin elastic tissue stain, black and modified Taenzer-Unna orcein stain, red-brown. By...

Figure 61

Muscle Cells

Diagram of the development of adipose tissue cells. Like all connective tissue cells, adipocytes are derived from mesenchymal cells either mesodermally derived mesenchyme or ectomesenchyme derived from the neural crest . Mesenchymal cells give rise to fibroblasts and fibroblast-like cells that are committed to becoming lipoblasts preadipocytes . Lipoblasts develop an external basal lamina and begin to accumulate numerous lipid droplets in their cytoplasm. In white adipose tissue, these droplets...

Intermediate Filaments

As noted, the molecular structure of intermediate filaments is tissue specific and consists of many different types of proteins. Several diseases are caused by defects in the proper assembly of interme diate filaments. These defects have also been induced experimentally by mutations in intermediate filament genes in laboratory animals. Changes in neurofilaments within brain tissue are characteristic of Alzheimer's disease, which produces neurofibrillary tangles containing neurofilaments and...