Obj 5 Skeletal Ch 6 - 2022.pptx

PN 1109 ANATOMY & PHYSIOLOGY Objective 5: Chapters 6, 7, & 8 SKELETAL SYSTEM  Made up of bones, cartilage, ligaments, & tendons  Counts for 20% of body weight  Contains 206 bones  Rigid structure that forms the framework of the body; strong but lightweight  All bones have surface markings &...

PN 1109 ANATOMY & PHYSIOLOGY Objective 5: Chapters 6, 7, & 8 SKELETAL SYSTEM  Made up of bones, cartilage, ligaments, & tendons  Counts for 20% of body weight  Contains 206 bones  Rigid structure that forms the framework of the body; strong but lightweight  All bones have surface markings & unique characteristics that makes bones unique: holes, depressions, projections and lines  Contain active tissues that participate in our body’s functioning  Microscopic unit of compact bone is the osteon CARTILAGE  Gristle-like material allows cartilage to sustain great weight or serve as a shock absorber  Mostly made up of water (accounts for resiliency)  Avascular and no nerve supply  Surrounded by perichondrium; acts like a girdle and provides nutrients via blood vessels  Three types: hyaline, elastic, and fibrocartilage (fig. 6.1 p. 174)  All three contain chondrocytes, are encased in small cavities with an extracellular matrix SKELETAL CARTILAGE: HYALINE  Provides support, flexibility and resilience  Most abundant  Collagen fibers only  articular cartilages  costal cartilage  respiratory cartilage  nasal cartilages SKELETAL CARTILAGE: ELASTIC  Resembles hyaline cartilage but contains elastic fibers  Can bend more easily  Only found in the external ear and epiglottis SKELETAL CARTILAGE: FIBROCARTILAGE  Highly compressible and has great tensile strength  Found in areas subjected to pressure and stretch  Knee and vertebral discs GROWTH OF CARTILAGE  Appositional growth  To outer surface only  During late adolescence and throughout adulthood  Interstitial growth  Chondrocytes divide and secrete new matrix, expanding cartilage from within  During childhood and early adolescence FUNCTIONS OF BONES  Gives form and shape to the body  Play an important role in homeostasis  Functions include:        Support, Protection Anchorage Mineral and Growth Factor Storage Blood Cell Formation Triglyceride (Fat) Storage Hormone Production FUNCTIONS OF BONES Support  rigid framework that supports soft organs  Support against the pull of gravity  Lower limb bones support our upper body when standing Protection  Protects soft body parts  Rib cage: heart/lungs, cranium or skull: brain, Vertebrae: spinal cord FUNCTIONS OF BONES Anchorage  Sites for muscle attachment  Levers for muscle action  Design of joints determines the types of movement Mineral and Growth Factor Storage  Reservoir for minerals such as calcium and phosphate  Also contains other compounds needed in the body; sodium (Na), magnesium (Mg), potassium (K) and carbonate (CO3) important growth factors FUNCTIONS OF BONES Blood Cell Formation  Aka: hematopoiesis takes place in the red marrow of bone  Infants: red marrow is found in most bones  Adults: replace some red marrow with yellow for fat storage; red marrow is limited to spongy bone such as that found in the skull, ribs, sternum, clavicles, vertebrae and pelvis  Red marrow: RBCs, WBCs, blood platelets  Iliac crests – site for bone marrow extraction FUNCTIONS OF BONES Triglyceride (fat) Storage  Stored in bone cavities or yellow marrow; used for an energy source Hormone Production (will discuss further in Endocrine)  Osteocalcin produced by bones helps regulate insulin secretion, maintain homeostasis and energy expenditure CLASSIFICATION OF BONES  Classified based on:  Region  Shape CLASSIFICATION OF BONES BY REGION  Divided into two groups based on location:  Axial skeleton  Long axis of body  Skull, vertebral column, rib cage  Appendicular skeleton  Bones of upper and lower limbs  Girdles attaching limbs to axial skeleton CLASSIFICATION OF BONES BY SHAPE  Long Bones:  Longer than they are wide  Long shaft (diaphysis) with two bulky ends (epiphysis)  Named for the elongated shape not their actual size  Eg: thigh, leg, arm & forearm  Short Bones:  cube shaped (wrist & ankle)  Sesamoid bones special type of short bone that forms in a tendon (patella)  Vary in size and number in different individuals CLASSIFICATION OF BONES BY SHAPE  Flat Bones:  Thin, flattened & often curved  Eg: bones of the skull, sternum, scapula, ribs  Irregular Bones:  Bones that fall outside other categories  Complicated shapes  Eg: vertebrae, some skull bones, and hip bones, facial GROSS ANATOMY Bone textures:  Compact and spongy bone  Differ in density Compact  Dense outer layer; smooth and solid Spongy (cancellous or trabecular)  Honeycomb of flat pieces of bone deep to compact called trabeculae; inner  Ligher; less dense STRUCTURE OF SHORT, IRREGULAR, AND FLAT BONES  Thin plates of spongy bone covered by compact bone  Bone plates sandwiched between connective tissue membranes  Periosteum (outer layer)  Endosteum  No shaft or epiphyses  Bone marrow throughout spongy bone; no marrow cavity  Hyaline cartilage covers articular surfaces STRUCTURE OF A LONG BONE  Diaphysis:  long shaft of the bone;  compact bone which attributes to the strength of the bone  Compact bone covers medullary cavity       Epiphysis: enlarged ends of the long bone; meet with a second bone at a joint; made up of compact bone overlying spongy bone; articular cartilage covers articular surfaces (hyaline) Epiphyseal line: remnant of childhood bone growth at epiphyseal plate LONG BONE STRUCTURE BONE MEMBRANES: PERIOSTEUM  White double-layered membrane  Outer fibrous layer of dense irregular connective tissue  Inner osteogenic layer  Contains primitive stem cells called osteogenic cells that form and destroy bone  Essential for bone cell survival & bone formation  Covers external surfaces except joint surfaces  Many nerve fibers and blood vessels  Anchoring points for tendons, ligaments, & muscles BONE MEMBRANES: ENDOSTEUM  Delicate membrane covering internal bone surface  Covers trabeculae of spongy bone  Lines canals that pass through compact bone  Contains osteogenic cells that can differentiate into other bone cells HEMATOPOIESIS Hematopoietic tissue in bones  Red marrow  found within trabecular cavities of spongy bone and diploë of flat bones, such as sternum  In newborns, medullary cavities and all spongy bone contain red marrow  In adults, red marrow is located in heads of femur and humerus, but most active areas of hematopoiesis are flat bone diploë and some irregular bones (such as the hip bone)  Yellow Marrow     storage of fats cells called adipocytes fat can be used as an energy source as needed. Yellow marrow can convert to red, if person becomes anemic BONE MARKINGS  External surfaces of bone display projections, depressions and openings.  Sites of muscle, ligament, and tendon attachment on external surfaces  Areas involved in joint formation or conduits for blood vessels and nerves © 2016 Pearson Education, Inc. BONE MARKINGS  Projection: outward bulge of bone  May be due to increased stress from muscle pull or is a modification for joints  Ex: tuberosity, crest, trochanter, spine, process, condyle, head, facet  Depression & openings:  passageways for vessels and nerves  Ex: fissures, fossa, foramen, meatus © 2016 Pearson Education, Inc. CELLS OF BONE TISSUE  Each comes from osteogenic stem cells  osteoblasts  osteocytes  osteoclasts CELLS OF BONE TISSUE Osteoblasts  Bone forming cells which secrete bone matrix or osteoid  Includes collagen and calcium-binding proteins  Collagen = 90% of bone protein  Actively mitotic CELLS OF BONE TISSUE Osteocytes  Mature bone cells in lacunae  Monitor and maintain the bone matrix  Act as stress or strain sensors  Respond to mechanical stimuli such as increased force on bone or weightlessness  Communicates this info between osteoblasts and osteoclasts re: bone modeling CELLS OF BONE TISSUE Osteoclasts  Responsible for active erosion of bone minerals/bone breakdown  Function in bone resorption  Continuous osteoblast activity balanced with osteoclast activity to maintain homeostasis of bone tissue BONE CELLS BONE DEVELOPMENT  Osteogenesis (ossification)  process of bone formation  Begins as early as the first few weeks after conception and continues on into early adulthood  Begins in 2nd month of fetal development  Bone will continue to repair/remodel itself if damaged and remodel to meet changing lifestyles (lifelong) TWO TYPES OF OSSIFICATION  Endochondral ossification  Bone forms by replacing hyaline cartilage  Bones formed from a cartilage model (endochondral) bone  Forms most of skeleton  Intramembraneous ossification  Bone develops from fibrous membrane  Bones called membrane bones  Forms flat bones ex: clavicles, skull ENDOCHONDRAL OSSIFICATION  All bones below skull except clavicles  Primary ossification center  5 steps:  - bone collar forms around the diaphysis of the hyaline cartilage model  - cartilage in the center of the diaphysis calcifies and then develops cavities  - The periosteal bud invades the internal cavities and spongy bone forms  - the diaphysis elongates and a medullary cavity forms; secondary ossification centers appear in the epiphyses  - the epiphyses ossify; when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages INTRAMEMBRANOUS OSSIFICATION  Cranial bones and clavicles  Mesenchymal cells  4 steps:  -ossification centers appear in the fibrous connective tissue membrane  -osteoid is secreted within the fibrous membrane and calcifies  -woven bone and periosteum form  -lamellar bone replaces woven bone, just deep to the periosteum; red marrow appears BONE GROWTH  Interstitial (longitudinal) growth  Increase in bone length  Appositional growth  Increase in bone thickness INTERSTITIAL BONE GROWTH: LENGTH OF LONG BONES  Requires presence of epiphyseal cartilage (plate)  Epiphyseal plate maintains constant thickness  Rate of cartilage growth on one side balanced by bone replacement on other  Concurrent remodeling of epiphyseal ends to maintain proportion INTERSTITIAL GROWTH: LENGTH OF LONG BONES  Near end of adolescence chondroblasts divide less often  Epiphyseal plate thins then is replaced by bone  Epiphyseal plate closure     Bone lengthening stops (requires presence of cartilage) Bone of epiphysis and diaphysis fuses Females = 18 yrs Males = ~21 yrs APPOSITIONAL GROWTH: BONE WIDTH  Allows lengthening bone to widen  Occurs throughout life  Osteoblasts beneath the periosteum secrete bone matrix on external bone  Osteoclasts remove bone on endoseal surface  Usually more building up than breaking down  leads to thicker, stronger bone that is not too heavy APPOSITIONAL BONE GROWTH: BONE WIDTH STAGES OF BONE REPAIR  Bone remodeling  Begins during bony callus formation  Continues for several months  Excess material on diaphysis exterior and within medullary cavity is removed  Compact bone is laid down to reconstruct shaft walls  Final structure resembles original structure  Responds to same mechanical stressors HORMONAL CONTROL: CALCIUM Functions of calcium:          nerve transmission muscle contraction blood coagulation gland and nerve secretions cell division 99% of body calcium found in bone Amount in body tightly regulated Intestinal absorption requires vitamin D Dietary intake required REGULATION OF BLOOD CALCIUM LEVELS  Bones store/release calcium & phosphate  Calcium moves into and out of blood during bone remodeling  During bone formation, the osteoblasts remove calcium from blood and lower circulating levels  During breakdown, osteoclasts release calcium into blood and increase circulating levels  Even minute changes in blood calcium can be dangerous HORMONAL CONTROL OF BLOOD CALCIUM LEVELS Parathyroid hormone (PTH)      produced by parathyroid glands in response to low blood calcium levels Main regulator of calcium Stimulates osteoclasts to resorb bone Calcium is released into blood, raising levels PTH secretion stops when homeostatic calcium levels are reached Calcitonin  produced by cells of thyroid gland  lower blood calcium levels by stimulating osteoblasts and inhibiting osteoclasts  Removes calcium from the blood  Stimulates bone mineralization NEGATIVE FEEDBACK: CALCIUM HOMEOSTASIS Controlled by PTH Low Blood Calcium levels PTH release PTH stimulates osteoclasts to breakdown bone matrix, releasing calcium Increased blood calcium levels PTH release ends PTH CONTROL OF BLOOD CALCIUM LEVELS RESULTS OF MECHANICAL STRESSORS  Bones grow or remodel in response to demands placed on it  Explains:      Dominant hand is thicker and stronger bone Curved bones thickest where most likely to buckle Trabeculae form trusses along lines of stress Large, bony projections occur where heavy, active muscles attach Bones of fetus and bedridden featureless