Histology of Integumentary & Musculoskeletal Systems PDF

Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ● Medulla ○ Large, vacuolated, and moderately keratinized cells at the center of the hair root ○ Covered by the cortex ● Capillaries ○ Blood vessels that supply the hair shaft ● Hairs vary in length and diameter in the different regions...

Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ● Medulla ○ Large, vacuolated, and moderately keratinized cells at the center of the hair root ○ Covered by the cortex ● Capillaries ○ Blood vessels that supply the hair shaft ● Hairs vary in length and diameter in the different regions of the body ● Compared to the animalʼs fur coat, vestigial hairs of humans provide little or no thermal insulation but they are significant for tactile sensation ● They act as minute levers and when deformed they exert pressure that is detected by sensory nerves around the hair follicles ● Absent in: ○ Palms, soles, lateral surface of the feet, glans penis, clitoris, inner surface of the prepuce, and labia minora and majora ○ On the eyelids, hairs do not project beyond their follicles, whereas on the scalp, they may grow to well over 1 m in length ● Bulb ○ Found at the base of each hair follicle enclosing a loop of capillaries called the hair papilla ○ In its underside is a hair papilla and provides nourishment to the hair ○ One of the few living parts of the hair, and is responsible for hair growth ○ Epithelial cells covering the papilla are comparable to those of the stratum basale elsewhere in the epidermis. Together they form the hair matrix and their proliferation is responsible for the growth of the hair and its base. PARTS OF THE HAIR ● Cuticle ○ Transparent ○ Covers the hair shaft like shingles on a roof, protecting it from the elements and chemicals, and from losing moisture ● Cortex ○ Provides most of the hairʼs weight ○ Contains melanin which provides color to the hair, stores oils, provides flexibility and elasticity, and adds shape to the hair ○ When the cuticle is damaged and exposes the cortex, hair looks dull and dry Figure 23. Hair Follicle, a Figure 24. Hair Follicle, b Figure 21. Parts of the Hair ● Medulla ○ Inner hollow core that runs the length of the shaft ○ In some types of hair, medulla is formed when those situated above the apex of the papilla produce large vacuolated cells Figure 25. Hair Follicle, c B. NAILS ● Fingernails and toenails are hard keratin structures that protect the ends of the fingers and toes. ● Nail root, or germinal matrix or nail bed Figure 22. Bulb AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 7 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ○ Begins several millimeters into the finger and extends to the edge of the white, crescent-shaped lunula. This is where the growth occurs 1 mm per week). Figure 26. Nail Anatomy ● The under-surface of the nail plate or body of the nail has grooves that help anchor it ● Nails are formed by proliferation and keratinization of epithelial cells in a nail matrix that is comparable to the hair matrix but simpler in organization ● The nail root and its matrix are located under a fold of skin called the proximal nail fold ● Cuticle or Eponychium ○ Fuses the nail plate and the skin of the finger together to form a waterproof barrier ● Hyponychium ○ Under the free edge of the nail. It also creates a waterproof barrier, fusing the skin of the finger to the underside of the nail plate ● A lost finger or toenail will regenerate C. SEBACEOUS GLANDS ● Oil glands ○ They have tiny ducts that open into each hair follicle ● Secretes sebum ○ Complex mixture of lipids that includes wax esters, squalene, cholesterol, and triglycerides that are hydrolyzed by bacterial enzymes after secretion ○ Lubricates the hair and skin. The amount of secretion varies with age, puberty, and pregnancy. ○ Helps maintain the stratum corneum and hair shafts and exerts weak antibacterial and antifungal properties ● Found in the dermis of the entire integument (except: palms, soles, and sides of the feet, where hairs are lacking) ○ Also occur on the lips, areola of the nipples, labia minora, and on the inner aspect of the prepuce ● Appendages of the hair follicle ○ 0.2 - 2 mm in diameter located above the insertions of the arrector pili muscle ● Have a lobular structure consisting of elongated acini that open into a short duct ● Have a peripheral row of small basal cells having a peripheral nucleus, the usual cytoplasmic organelles, and a few vacuoles ● Have no lumen but are filled with large pale staining cells with pyknotic nuclei ● Production of sebum by holocrine secretion ● The ducts are lined by stratified squamous epithelium ○ Continuous with that of the external root sheath at their opening into the follicular canal ● Sebaceous glands are relatively inactive until puberty ○ When they are stimulated by the rising levels of sex hormones ● Teenagers suffer from acne ○ An inflammation of isolated sebaceous glands, usually on the face, chest, and upper back Figure 27. Nails ● Ingrown nails ○ Those that have curled down or around and are growing into the skin ○ They may become swollen and inflamed ● Note: Trim toenails straight across to avoid this growth pattern and relieve inflammation. Figure 29. Sebaceous Gland Figure 28. Ingrown Toenail Figure 30. Disintegrating and Intact Sebum-containing Secretory Cell AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 8 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS D. SWEAT GLANDS ● Sudoriferous glands are the sweat glands ○ About 2 million are distributed over the surface of the body ● Round to oval ducts (under microscope) ● Outlined by cuboidal cells ● More numerous on the palms of hands, soles of the feet, forehead, and axillae or underarms ● Produce sweat or perspiration ○ As sweat collects on the skin surface, it evaporates and creates a cooling effect ○ Sweat also gets rid of the body of waste through the pores of the skin Figure 35. Glands of the Skin Figure 31. Epithelial Cells of Sweat Glands ● As it accumulates, sweat may become odorous by the action of bacteria ● The average person loses approximately ½ liter of fluid through sweating each day Table 1. Eccrine VS Apocrine Gland Bloom and Fawcett) Eccrine Glands Apocrine Glands No connection with hair follicles Appendages of hair follicles Functions throughout life Begin to function at puberty Watery secretion Slightly viscous secretion Innervated by cholinergic nerves Innervated by adrenergic nerves Both have a merocrine mode of secretion E. BLOOD AND LYMPH VESSELS Figure 32. Sweat Glands, a Figure 33. Sweat Glands, b Figure 34. Sweat Glands, c ● Rete cutaneum ○ Plexus parallel to the skin surface at the boundary between the dermis and the hypodermis ● Rete subpapillary ○ Second plexus formed from the ramification of small ascending arteries; located at the boundary between the reticular and papillary layers of the dermis ● Each hair follicle receives blood from two sources ● The venous limbs of the capillaries in the dermal papillae drain into a venous plexus beneath the rete subpapillary and veins from this drain into a venous plexus associated with the rete cutaneum - veins descend to large veins in the subcutaneous tissue ● Arteriovenous anastomoses ○ Open: shunting blood directly from arteries to veins without an intervening capillary bed ○ Play an important role in the thermoregulation by controlling blood flow to the superficial layers of the skin, where the heat may be lost to a cold environment ● The skin has a rich lymphatic drainage, beginning in blind-ended lymphatic capillaries in the dermal papillae that join an extensive network underlying the dermoepidermal junction ○ Branches descend through the reticular layer of the dermis to its boundary with the hypodermis, where they join a deeper network of lymphatics associated with the rete cutaneum ● Larger lymph vessels with valves AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 9 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS F. NERVES ● Two broad categories of sensory nerve-endings: ○ Free nerve endings ○ Encapsulated nerve ending FREE NERVE ENDINGS ● Lack morphologically recognizable receptor specializations at their ends ● Most common are in the epidermis ● Myelinated nerves approaching the epidermis from below lose their myelin sheath and continue on a vertical course through interstices among the keratinocytes to terminate in blind endings in the stratum granulosum ● Function: pain receptors or thermoreceptors ● Other myelinated afferent nerves have disc-like expansions called Merkel endings, in contact with the plasmalemma of Merkel cells near the base of epidermis ENCAPSULATED NERVE ENDING ● Cellular and extracellular components that are organized to convey a mechanical stimulus to an axon in their interior ● Several kinds: ○ Pacinian corpuscles ○ Meissnerʼs corpuscles → Mechanoreceptors responding to slight deformation of the skin ○ Krausʼ end bulbs ○ Ruffini corpuscles → Mechanoreceptor responding to tensional forces ● Classification: ○ Function → Voluntary → Involuntary ○ Structure → Striated vs. Non-striated Figure 36. Types of Muscle and Location of Nucleus, a ● Histologic characteristics of different muscle types: ○ Focus on the presence of striations and the position of the nucleus. Table 2. Classification of Muscles Skeletal Very long bundles, Structure cylindrical Striations IV. MUSCLES ● Differentiated cells containing contractile proteins, generating forces for cellular contraction which results to movement ● Mesodermal or mesenchymal in origin ● Makes up much of the mass of the body ● Present in close association in many organs of the body ● Contracting muscle cells – regulate the position and movements of the various parts or the body with respect to one another ● In the hollow viscera, ducts, and blood vascular system the muscles propel ● The body liquids and excretions from place to place ● Muscle cells are always elongated in the directions of the contraction ● Usually grouped into bundles which sometimes reach a considerable length ● Terminologies: ○ Muscle fiber = muscle cell → heart - cardiac myocytes ○ Sarcolemma = plasma membrane/ plasmalemma ○ Sarcoplasm = cytoplasm of the muscle fiber (excluding myofibrils) ○ Sarcoplasmic reticulum = smooth endoplasmic reticulum Nucleus Function Cardiac Elongated, branched, Intercalated disks Striated Striated Multinucleated Striated Peripheral nuclei Striated Central nucleus Voluntary Quick, forceful contraction; Sliding of thin actin & thick myosin filaments Involuntary, vigorous, rhythmic Smooth Fusiform No striations No striations Central nucleus Involuntary Clinical Correlate ● Duchenne Muscular Dystrophy ○ X-linked ○ Lacks dystrophin ○ Structural weakness of the sarcolemma ● Naming of malignancy: ○ Sarcoma = mesenchymal origin ○ Carcinoma = epithelial origin ● Three types: ○ Skeletal ○ Cardiac ○ Smooth AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 10 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS Figure 40. Structure of the skeletal muscle, c Figure 37. Types of Muscle and Location of Nucleus, b A. SKELETAL MUSCLES ● Originated from mesenchymal myoblasts ○ Mesenchymal myoblasts fuse, forming myotubes with many nuclei ○ Myotubes then further differentiate to form striated muscle fibers ○ Myotubes synthesize the proteins to make up myofilaments and gradually begin to show-striations by light microscopy ○ Myotubes continue differentiating to form functional myofilaments, and the nuclei are displaced against the sarcolemma Figure 41. Structure of the skeletal muscle, d Figure 42. Structure of the skeletal muscle, e Figure 38. Structure of the skeletal muscle, a Figure 39. Structure of the skeletal muscle, b Figure 43. Differentiation of Myoblasts AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 11 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ANATOMY AND CELLULAR STRUCTURE ● Composed of 10 - 30 cm long cylindrical bundles of muscle fibers ● A small population of reserve progenitor cells called muscle satellite cells can be found adjacent to most fibers of differentiated skeletal muscle ○ Satellite cells proliferate and produce new muscle fibers following muscle injury ● Muscle fibers = muscle cell ○ Diameter ranges from 10 - 100 μm ○ Multinucleated → Fusion of embryonic mononucleated myoblasts ○ Contains myofibrils → Myofibrils are long cylindrical filamentous bundles, found in sarcoplasm. They are composed of a linear array of sarcomeres ● Unit of organization ○ Fibers are aggregated in bundles called fascicles ● Arrangement of fascicles varies from muscle to muscle ○ Short muscle: oriented parallel to the direction of pull and may continue without interruption throughout its length ○ Long muscle: fibers are shorter than the muscle and are connected to one or more transverse bands of connective tissue spaced at intervals along the length of the muscle ○ Unipinnate: fasciculi are oriented obliquely with respect to a longitudinal band of connective tissue along one side of the muscle ○ Bipinnate: oblique fascicles that radiate from a connective tissue core in the muscle, resulting in a pattern resembling that of the barbs extending obliquely from the axial core of a feather ○ Multipinnate: oblique fascicles radiating from several longitudinal connective tissue strands within the muscle and converge on the tendon ORGANIZATION OF SKELETAL MUSCLE Figure 44. Connective tissue, a Figure 45. Connective tissue, b ● Function of connective tissues: ○ Collagen in these connective tissue layers serve to transmit mechanical forces generated by muscle cells/fibers ○ Blood vessels and lymphatics penetrate muscle within connective tissue ● Skeletal muscle fibers are encased by different types of connective tissues ○ Epimysium → External sheath of dense irregular connective tissue → Surrounds the entire muscle → Septa of this tissue extend inward ■ Larger nerves, blood vessels, ang lymphatics of the muscle ○ Perimysium → Thin connective tissue layer → Immediately surrounds each bundle of muscle fibers or fascicle → Nerves, blood vessels, and lymphatics penetrate the perimysium to supply each fascicle ○ Endomysium → Delicate layer of reticular and scattered fibroblasts → Surrounds the external lamina of individual muscle fibers → In addition to nerve fibers, capillaries for a rich network in the endomysium bringing O2 to the muscle fibers Figure 46. Skeletal Muscle Anatomy, a AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 12 of 26