Histology of Integumentary & Musculoskeletal Systems PDF

Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ● Sodium influx will generate an action potential in the sarcolemma ● Action potential travels down T tubule ● Sarcoplasmic reticulum releases calcium ● Calcium binds with troponin to move the troponin, tropomyosin complex ● Binding site...

Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ● Sodium influx will generate an action potential in the sarcolemma ● Action potential travels down T tubule ● Sarcoplasmic reticulum releases calcium ● Calcium binds with troponin to move the troponin, tropomyosin complex ● Binding sites in the actin filament are exposed ● Myosin head attach to binding sites and create a power stroke ● ATP detaches myosin heads and energizes them for another contraction ● When action potentials cease, the muscle stop contracting CREATINE PHOSPHATE ● Molecule with stored ATP energy ○ Creatine phosphate + ADP >> Creatine + ATP MUSCLE FATIGUE ● Lack of oxygen causes ATP deficit ● Lactic acid builds up from anaerobic respiration MUSCLE ATROPHY ● Weakening and shrinking of a muscle ● May be caused by: ○ Immobilization ○ Loss of neural stimulation Figure 69. Pathway of Smooth Muscle Contraction MOTOR UNIT ● All muscles are controlled by one nerve cell MUSCLE HYPERTROPHY Enlargement of a muscle More capillaries More mitochondria Caused by: ○ Strenuous exercise ○ Steroid hormones ● Steroid hormones ○ Stimulate muscle growth and hypertrophy ● Muscle tonus ○ Tightness of a muscle; some fibers are always contracted ● Tetany ○ Sustained contraction of a muscle. Result of a rapid succession of nerve impulses ● ● ● ● TETANUS Figure 70. Motor Unit MOTOR UNIT RATIOS ● Back muscles: 1 100 ● Finger muscle: 1 10 ● Eye muscle: 1 1 Figure 72. Muscle Tension-Stimuli Graph for Tetanus REFRACTORY PERIOD CREATINE ● Molecule capable of storing ATP energy ○ Creatine + ATP >> Creatine Phosphate + ADP ● Brief period of time in which muscle cells will not respond to a stimulus Figure 73. Refractory Period, a Figure 71. ATP Structure Figure 74. Refractory Period, b AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 19 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ISOMETRIC CONTRACTION ● Produces no movement ● Used in: ○ Standing ○ Sitting ○ Posture ISOTONIC CONTRACTION ● Produces movement ● Used in: ○ Walking ○ Moving any part of the body V. BONES ● Like other connective tissues, these consist of cells, fibers, and ground substance, but unlike the others, its extracellular components are calcified ● High tensile and compressive strength ● Dynamic living material ○ Constantly being renewed and reconstructed throughout the lifetime of the individual ● Functions: ○ Mechanical → Provides for the internal support of the body → Attachment of the muscles and tendons essential for locomotion → Protects vital organs of the cranial and abdominal cavities → Encloses the blood-forming elements of the bone marrow ○ Metabolic → Mobilizable storage of calcium A. MACROSCOPIC STRUCTURES OF BONES ● Macroscopic structures of bones: ○ Compact bone Substantia compacta) ○ Spongy or Cancellous bone Substantia spongiosa) ● Long bones (e.g. femur and humerus) ○ The shaft (diaphysis) consists of a thick-walled hollow cylinder with voluminous central marrow cavity (medullary cavity) occupied by the bone marrow ○ The ends consist mainly of spongy bone covered by a thin cortex of compact bone COMPACT OR CORTICAL BONE ● Appears as a solid continuous mass ● Spaces can be seen only with microscope ● Covered by specialized connective tissue called periosteum with osteogenic potency ○ It has the ability to form bone ● Cellular elements and bone matrix ● Osteons are the functional unit ● Osteocytes are inside the lacunae ● Osteoblasts ○ Produces Vitamin K-dependent osteocalcin and sialoprotein osteopontin → Their synthesis is stimulated by 1,25-dihydroxycholecalciferol (the active form of Vitamin D Figure 76. Compact Bone (a thick ground section of the tibia, the cortical compact bone and the lattice of trabeculae of cancellous bone) GROUND SUBSTANCE ● Osteocalcin ○ Vitamin-K dependent protein ○ 5.8 kD protein, constituting 2% of the total matrix proteins ○ Found in the extracellular matrix, bound to hydroxyapatite ○ Has 3 γ-carboxyglutamic acid residues per molecule ● Osteopontin ○ 63 kD sialoprotein ○ Binds tightly to hydroxyapatite ○ Contains a cell-binding sequence similar to that of fibronectin ○ Speculated to be involved in binding of osteoblast or osteoclast to bone ● Bone Sialoprotein BSP ○ 78 kD protein ○ Also has a cell-binding sequence ○ Its synthesis is stimulated by 1,2 OH2D3 ○ Function is unclear ● Glycosaminoglycans ○ Chondroitin sulfate ○ Keratan sulfate ○ Hyaluronic acid Figure 75. Compact Bone vs. Spongy Bone Sagittal section of the proximal end of the humerus) AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 20 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS SPONGY OR CANCELLOUS BONE B. MICROSCOPIC STRUCTURES OF BONES ● Lighter and less dense than compact bone ● Consists of a three-dimensional lattice of branching bony spicules, or trabeculae, delimiting a labyrinthine system of interspaces that are occupied by bone marrow ● The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply ● May appear that the trabeculae are arranged in a haphazard manner, but they are organized to provide maximum strength similar to braces that are used to support a building ● The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes CELLS OF BONE Figure 77. Spongy Bone: A Closer Look Figure 78. Spongy Bone Histology, a ● 4 Kinds: ○ Osteoprogenitor cells → Stem cells in the bone; derived from embryonic mesenchymal cells → Progenitors of osteoblasts → Persist throughout postnatal life and are found on or near all of the free surfaces of bones ■ Endosteum ■ Inner layer of the periosteum ■ Trabeculae of calcifying cartilage at the metaphysis of growing bones → Nuclei are pale-staining and oval or elongated → Scant cytoplasm is acidophilic or faintly basophilic → Most active during the growth of bones but are reactivated in adult life in the repair of bone fractures and other forms of injury ○ Osteoblasts → Bone-forming cells of developing and mature bones → During active deposition of new matrix, they are arranged as an epithelioid layer of cuboidal or columnar cells on the bone surface → Nucleus is usually located at the end of the cell farthest away from the bone surface → Cytoplasm is intensely basophilic → Prominent Golgi complex appears as a paler staining area between the nucleus and the cell base ○ Osteocytes → Principal cells of mature bones, which reside in lacunae within the calcified matrix → Cell body is flattened, conforming to the shape of the lenticular cavity that it occupies, but there are numerous slender cell processes that extend for some distance into the canaliculi that radiate from the lacuna into the surrounding matrix → Nuclear and cytoplasmic characteristics (as observed with the light microscope) are similar to those of osteoblasts, except that: ■ The Golgi area is less conspicuous ■ The surrounding cytoplasm exhibits less affinity for basic dyes ○ Osteoclasts → Originate from precursors of bone marrow → Responsible for bone resorption → Huge cells up to 150 μm in diameter and containing as many as 50 nuclei ■ Howshipʼs lacunae ⎻ Shallow concavities produced by the erosive action of osteoclasts in underlying bone ● Cell modulation ○ Progressive irreversible specialization in the structure and function of cells ● Osteoid ○ Unmineralized matrix Figure 79. Spongy Bone Histology, b AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 21 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS BONE MINERALS Figure 80. Cells of Bones C. BONE MATRIX ● The interstitial substance of bone is composed of two major components: ○ 35% organic materials (proteoglycans and collagen fibers) ○ 65% inorganic matter (calcium phosphate) ● Bone minerals contain citrate ion and carbonate ion ● Sulfated glycosaminoglycans are present ○ Despite their presence, bone matrix is acidophilic in histological sections, owing to its content of abundant closely packed collagen ● In contrast to the very large proteoglycans of cartilage matrix, the proteoglycans of bone consist of short core proteins with relatively few glycosaminoglycan side-chains Figure 81. Bone Matrix COLLAGEN Constitutes 90% of the organic portion of the bone matrix Predominantly Type I Fibers are 50 70 nm in diameter and 67 nm cross-banding Slightly differs from soft-tissue collagen ○ Bone collagen has a greater number of intermolecular cross-links, which accounts for its failure to swell in dilute acids and its insolubility in some solvents ● In mature lamellar bone, the collagen fibers have a highly ordered arrangement ● ● ● ● ● The inorganic matter of bone consists of submicroscopic deposits of a form of calcium phosphate very similar, but not identical, to the mineral hydroxyapatite ● In mature bone, the mineral is in the form of slender rod-like crystals about 40 nm in length and 1.5 3 nm in thickness ○ The crystals are not randomly distributed but recur at regular intervals of 60 70 nm along the length of the collagen fibers ○ In Type I collagen, the molecules are parallel, with nearest neighbors staggered by 67 nm. This arrangement results in an ordered array of gaps roughly 40 nm long and 2.5 nm wide within the substance of the fiber. ● Bone mineral contains significant amounts of the citrate ion and carbonate ion ○ Citrate is considered to be a separate phase, located on the surfaces of the crystals ○ Site of carbonate is unknown ● Magnesium and sodium are also present in bone mineral, ○ Serves as a storage depot for these elements ● The isotopes 45Ca and 32P can substitute for the stable 40Ca and 31P in the hydroxyapatite crystal ● Foreign cations such as Pb , Sr++, and Ra++ 226 Ra), if ingested, may also substitute for Ca++ ● During growth, the amount of organic material per unit volume of bone remains relatively constant, but the amount of water decreases and the proportion of bone mineral increases ○ Inorganic minerals in adults make up 65% of fat free dry weight, but in Rickets and Osteomalacia, it becomes 35% VI. SUMMARY ● Skin consists mainly of a superficial stratified squamous epithelium, the epidermis, and a thicker layer of connective tissue, the dermis, which overlies a subcutaneous hypodermis. ● The epidermis-dermis interface is enlarged and strengthened by interdigitating epidermal ridges or pegs and dermal papillae in which microvasculature also supplies nutrients and O2 for the epidermis. ● Melanocytes in the basal epidermis synthesize dark melanin pigment in melanosomes and transport these to adjacent keratinocytes, which accumulate them to protect nuclear DNA from UV damage. ● The dermis has two major layers: a superficial papillary layer or loose connective tissue with a microvascular plexus, and a thicker dense irregular reticular layer containing larger blood vessels. ● Sensory receptors in the epidermis include free nerve endings, which detect pain and temperature extremes, and basal Merkel cells, light-touch (tactile) receptors associated with sensory fibers. ● Hairs form in hair follicles, in which keratinocytes comprising the matrix of the deep hair bulb proliferate rapidly and undergo keratinization to form the medulla, cortex, and cuticle of a hair root. ● Nails are formed in a manner similar to hairs: keratinocytes proliferate in the matrix of the nail root and differentiate with the formation of hard keratin as a growing nail plate with edges covered by skin folds. ● Sebaceous glands produce sebum by terminal differentiation of sebocytes, the classic example of holocrine secretion, secreting this oily substance onto hair in the follicles or pilosebaceous units. AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 22 of 26 Y1B4M1L2 HISTOLOGY OF INTEGUMENTARY & MUSCULOSKELETAL SYSTEMS ● Eccrine sweat glands in the dermis produce sweat that is mostly water onto the skin surface, where its evaporation provides an important mechanism for cooling the body. ● Apocrine sweat glands are restricted to skin of the axillae and perineum, have much wider lumens than eccrine glands, develop after puberty, and secrete protein-rich sweat onto the hair of hair follicles. ● There are three major types of muscle: 1 skeletal or striated muscle, 2 cardiac muscle, and 3 smooth or visceral muscle. ● Skeletal muscle cells are very long, multinucleated fibers, cylindrically shaped and with diameters up to 100 μm. ● The sarcolemma of each fiber is surrounded by an external lamina and thin connective tissue endomysium, containing capillaries. ● Groups of fibers called fascicles are surrounded by perimysium; all fascicles are enclosed within a dense connective tissue epimysium. ● Cardiac muscle fibers are also striated, but they consist of individual cylindrical cells, each containing one (or two) central nuclei and linked by adherent and gap junctions at prominent intercalated discs. ● Smooth muscle fibers are individual small, fusiform (tapering) cells, linked by numerous gap junctions. ● Bones, which are dynamic living materials with high tensile and compressive strength, consist of cells, fibers, ground substance and calcified extracellular components, and perform mechanical and metabolic functions. ● Bone structures can either be compact (dense and made up of osteons) or spongy (lighter and less dense, made up of trabeculae). ● The four types of cells in bones are: 1 osteoprogenitor cells, which are stem cells in the bone that give rise to osteoblasts; 2 osteoblasts, the bone-forming cells; 3 osteocytes, the principal cells of mature bones; and 4 osteoclasts, which are responsible for bone resorption. D. Stratum Basale 7. More slender and having more fibrils than nodal myocytes. It is relatively slow thus contributing to the atrioventricular delay which is essential for optimal filling of the ventricles A. Transitional myocytes B. Nodal myocytes C. Cardiac myocytes D. Purkinje myocytes 8. All muscles are controlled by one nerve cell A. True B. False 9. Most common free nerve ending are found in the dermis A. True B. False 10. Each hair follicle receives blood from two sources A. True B. False Answer: 1B, 2C, 3A, 4B, 5B, 6C, 7A, 8A, 9B, 10A References: 1. Aureum Trans 2. Dagitab Trans 3. Fawcett, D. W. 1994 . Bloom and Fawcett: A textbook of histology, 260 304; 525 556. 4. Junqueira, L. C., & Mescher, A. L. 2013 . Junqueira's basic histology: text & atlas/Anthony L. Mescher. New York: McGraw-Hill Medical. 5. Salazar, 2021 . Integumentary System 6. Structure of bone tissue | SEER training. (n.d.). https://training.seer.cancer.gov/anatomy/skeletal/tiss ue.html#:~:text=Spongy%20(cancellous)%20bone%2 0is%20lighter,to%20receive%20their%20blood%20su pply. 7. Vergara 2021 . Muscle Tissue VIII. REVIEW QUESTIONS 1. The following choices are true for dermis, EXCEPT A. Makes for the thickness of skin B. Avascular C. Contains Connective Tissues and Nerves D. Also called Corium 2. Term used for enlargement of the Muscle A. Muscle Atrophy B. Muscle Dystrophy C. Muscle Hypertrophy D. Muscle Hyperplasia 3. Slow twitch fibers A. Red B. White C. Yellow D. Intermediate 4. The cuticle is also called hyponychium A. True B. False 5. About 4 million of sweat glands are distributed over the surface of the body A. True B. False 6. Also known as Stratum Malphigii. With less intensely basophilic cytoplasm than the stratum basale A. Stratum Granulosum B. Stratum Corneum C. Stratum Spinosum AGULAN, ARENGA, BOLAÑO, DUARTE, FRANCISCO, NACIONALES, PIONELO, SEÑALISTA, TRESPECES, VIAJE | MG 9 23 of 26