Human Anatomy & Physiology I PDF

BIOL243 – HUMAN ANATOMY & PHYSIOLOGY I Charles Smith, PhD CSCS HUMAN ANATOMY & PHYSIOLOGY Ch. 6 – Bone & Skeletal Tissues CHEMICAL MAKEUP OF BONE Organic: Osteoprogenitors, osteoblasts, osteocytes, osteoclasts, osteoids Inorganic: Mineral Salts (mainly calcium phosphate...

BIOL243 – HUMAN ANATOMY & PHYSIOLOGY I Charles Smith, PhD CSCS HUMAN ANATOMY & PHYSIOLOGY Ch. 6 – Bone & Skeletal Tissues CHEMICAL MAKEUP OF BONE Organic: Osteoprogenitors, osteoblasts, osteocytes, osteoclasts, osteoids Inorganic: Mineral Salts (mainly calcium phosphate) 65% of bone mass Provide hardness & resistance to compression Bone ½ as strong as steel against compression; as strong as steel resisting tension FUNCTION OF BONES 1. Support for body & soft organs 2. Protection for CNS & vital organs 3. Movement via joint articulations & muscle origin/insertions 4. Mineral Storage for calcium and phosphorous 5. Blood Cell Formation, both red & white in bone marrow 6. Triglyceride Storage for energy BONE CLASSIFICATIONS Human Body: 206 total named bones in skeleton 2 Groups (based on location) Axial Skeleton “Long axis” of body Skull, vertebral column, rib cage Appendicular Skeleton Bones of upper & lower limbs Girdles attach limbs to axial skeleton BONE CLASSIFICATIONS Each bone classified based on shape 1. Long Bones Longer than they are wide (c) Flat bone (sternum) i.e., limb bones (femur & humerus) 2. Short Bones (a) Long bone (humerus) Cube-shaped i.e., bones of wrist and ankle Sesamoid bones form within tendons i.e., patella 3. Flat Bones Thin, flat, slightly curved (b) Irregular bone (vertebra), i.e., sternum, scapulae, ribs, cranial bones (d) Short bone (talus) 4. Irregular Bones Complicated or “weird” shapes i.e., vertebrae BONE STRUCTURE Compact Bone: Dense, outer layer on every bone Appears smooth & solid Consist of: Osteons: Elongated cylinders running parallel to bone axis “weight-bearing pillars” made of collagenous lamellae rings Canals & Canaliculi: contain vessels & nerves Central (Haversian) canal: core of osteon Perforating (Volkmann’s) canals: perpendicular to central canal Spongy Bone: “honeycomb” of flat pieces of bone (trabeculae) Spaces between trabeculae filled with marrow Act like cables on suspension bridge to resist stress BONE STRUCTURE Short, Irregular & Flat Bones: Thin plates of spongy bone covered by compact bone Spongy bone Compact bone sandwiched between: (diploë) Compact Periosteum: outer membrane covering bone Endosteum: inner membrane covering No defined marrow cavity Trabeculae of spongy bone  Articular cartilage BONE STRUCTURE Proximal epiphysis Spongy bone Long Bones: Diaphysis: shaft along axis of bone Periosteum Compact bone Compact bone surrounding medullary cavity filled with marrow Medullary Yellow Marrow found here cavity (lined Can convert to red bone marrow by endosteum) Diaphysis Will have Red Marrow for infants Epiphyses: ends of long bones Separated from diaphysis by epiphyseal line Ossified epiphyseal plate (growth plate) where bone growth occurs Compact bone exterior, spongy bone interior Red Marrow found in trabecular cavities in all infant bones Distal epiphysis In head of femur & humerus for adults Articular cartilage at ends covering joint surfaces BONE STRUCTURE Long Bones have 2 Membranes: Periosteum: double layered membrane covering external surface Anchor point for tendons & ligaments Do not cover joint surfaces Endosteum: delicate, internal membrane Covers trabeculae of spongy bone BONE MARKINGS Sites of muscle, ligament, and tendon attachment on external surfaces Areas involved in joint formation or conduits for blood vessels & nerves 3 Types: Projections: outward bulges May be due to increase stress from muscle or a joint modification Depressions: bowl-like cut-outs Passage for vessels & nerves May play a role in joint formation Openings: holes/canals Passage for vessels & nerves BONE CELLS Osteogenic (osteoprogenitor) cells Mitotically active stem cells Differentiate into osteoblasts or bone-lining cells In periosteum & endosteum Osteoblasts Bone-forming cells Secrete unmineralized bone matrix (osteoid) Made of collagen (90%) & calcium-binding proteins Contribute to bone’s tensile strength Actively mitotic Osteocytes Mature bone cells (no longer divide) Maintain bony matrix Respond to mechanical stimuli (force/weight) Communicate information to osteoblasts & osteoclasts Osteoclasts Bone resorption (breakdown) BONE DEVELOPMENT Skeleton starts out as just cartilage Ossification: process of bone tissue formation Cartilage replaced by bone everywhere except where flexibility required Endochondral Ossification: Bone replaces hyaline cartilage Begins at primary ossification center (center of shaft) Bone grows “out” Forms all bones inferior to skull (except clavicle) LONG BONE GROWTH Long bones grow lengthwise via interstitial (longitudinal) growth of epiphyseal plate Bones increase thickness via appositional growth Bones stop growing during adolescence (F/AFAB: ~18 yrs; M/AMAB: ~21 yrs) Chondroblasts divide less often Epiphyseal plate thins & is replaced by bone Epiphyseal plate closure: epiphysis & diaphysis fuse Some facial bones continue to grow throughout life EPIPHYSEAL ZONES 1. Resting (Quiescent) Zone: inactive cells 2. Proliferation (Growth) Zone: rapidly dividing cells 3. Hypertrophic Zone: cells enlarge 4. Calcification Zone: cells die & calcify 5. Ossification (Osteogenic) Zone: osteoblasts lay new bone BONE REMODELING Back & forth of: Resorption: breakdown Osteoclasts will Secrete enzymes & protons (H+) to breakdown matrix Converts calcium salts to soluble forms Phagocytize demineralized matrix & dead osteocytes Products transferred to blood stream Deposition: laying down new bone Osteoblasts WOLFF’S LAW Trigger for remodeling unknown but may be related to Wolff’s Law “Bone grows or remodels in response to the demands placed upon it” Bone anatomy reflects the stress the bone endures Importance of weight-bearing exercises Explains differences due to Handedness: dominant side has thicker, stronger bone Larger projections found where heavy, active muscles attach Compare humerus to femur Weightlifter v non-weightlifter Fetal bones have no features due to lack of stress on bone FRACTURES Breaks in bone due to trauma or weakening in bone Classified based upon: 1. Position of bone ends after fracture Nondisplaced: ends in normal positions Displaced: ends out of normal alignment 2. Completeness of break Complete: broken all the way through Incomplete: not broken all the way through 3. Skin Penetration Yes = Open (compound) No = Closed (simple) FRACTURE REPAIR 4 Stages: 1. Hematoma (first few days) Torn blood vessels hemorrhage forming massive blood clot (hematoma) Site swollen, painful, inflamed 2. Fibrocartilaginous (Soft) Callus (2 – 3 wks) Fibroblasts secrete collagen Span break, connecting broken ends Bone reconstruction begins Cartilage matrix forms to repair tissue Osteoblasts form spongy bone within matrix 3. Bony (Hard) Callus (4 – 16 wks) Soft callus converted to hard callus of spongy bone Continues for ~2 mos until firm union forms 4. Bone Remodeling (6 – 12 mos) Excess material in diaphysis exterior & medullary cavity removed Compact bone laid down reconstructing shaft walls OSTEOMALACIA & OSTEOPOROSIS Osteomalacia: bone softening (in adults) Rickets in children Caused by vitamin D and/or calcium deficiency Causes pain on weight bearing Will also lead to bowed legs and other deformities in children Osteoporosis: bone resorption exceeds bone deposition Bone matrix is norm, but bone mass declines Most common in vertebrae & femur Postmenopausal women at greatest risk Men largely protected by effects of testosterone SKELETAL TISSUE SUMMARY Bones are just hardened cartilage As we grow, osteogenic cells become osteoblasts which lay down a matrix which either interstitially or appositionally grow and ossify Bones are classified based upon their structure Long, Short, Flat, Irregular Compact bone exteriors with spongy bone middles filled with trabeculae Bones grow and harden based upon how they are stressed (Wolff’s Law) Osteoclasts resorb the damaged bone and stimulate osteoblasts to begin the bone remodeling process Bones which are not stressed or where resorption exceeds deposition fall victim to osteoporosis Bones which get overly stressed and fail (break) are fractured Fractures classified based upon how the bone has been damaged Ends still in-line? Bone broken clean through? Bone breaking the skin? Fracture repair is a multi-stage process which can take months or up to a year to complete SAMPLE QUESTIONS 1. Define Wolff’s Law. 2. Which type of bone contains trabeculae? 3. In which zone of the epiphysis do cells enlarge or get bigger? 4. Which type of incomplete fracture is characterized by the bone flexing causing only one side of the shaft to fracture? 5. During which stage of fracture repair do fibroblasts secrete collagen to span the break while osteoblasts lay down a soft bony matrix?  COPYRIGHT © Pearson Edited by Charles Smith, PhD CSCS 2024