Chapter 6 left off
Attendance Roll Call
Instructor calls names for attendance
All students respond "Here" or similar affirmative.
Course Overview
Focus on osseous tissue in class
Exam only covers material through Chapter 6
Chapter 7 introduction will not appear on the Thursday exam
Osseous Tissue
Types of osseous tissue discussed:
Compact tissue
Spongy tissue
Functional Units
Osteons: Functional unit of compact tissue
Trabeculae: Functional unit of spongy tissue
Ossification Processes
Endochondral ossification: A detailed discussion previously held.
Intramembranous ossification: Mentioned, but less detail provided.
Role of Blood Vessels
Blood vessels in bones are vital for understanding fracture repair processes.
Hormonal Effects on Bone
Thyroid hormone:
Increases blood calcium by removing calcium from bones.
Calcitonin hormone:
Decreases blood calcium levels, storing calcium in bones.
Fractures
Defined as cracks or breaks in bones due to physical stress.
Types of fractures discussed but specifics not required for exam.
Important focus on the general process of fracture repair:
Fracture Hematoma:
Initial bleeding leads to formation of a clot (hematoma) to stop bleeding.
Callus Formation:
External callus: Made of cartilage and bone, surrounds the break.
Internal callus: Helps in aligning the medullary cavity with a network of spongy bone.
Spongy Bone Formation:
Trabeculae are formed and replace cartilage.
Formation of compact bone, leading to remodeling over time.
Osteoblasts actively involved in rebuilding.
Bone Remodeling:
A year-long process where the initial bump from the fracture heals and potentially results in slightly thicker, stronger bone.
Importance of Osteoblasts
Osteoblasts:
Build new bone.
Activities to stimulate healing after fractures include:
Weight-bearing exercises.
Electrical stimulation with electrodes in severe cases.
Aging and Bone Health
Bone density decreases with age, leading to conditions:
Osteopenia: Normal aging process, reduction of bone mass.
Osteoporosis: Severe bone loss, more common in women post-menopause.
Clinical Relevance
Concerns with bone fragility in elderly leading to fractures, particularly of:
Hip (trochanters).
Vertibra and jaw injuries increase loose teeth.
Bone Health Management
Hormone replacements and weight-bearing exercises help maintain stronger bones.
Focus on lifestyle and hormonal shifts contributing to osteoporosis, particularly after menopause for women.
Specific Bone Conditions
Osteomalacia: Softening of bones due to vitamin D deficiency; known as Rickets in children.
Osteogenesis Imperfecta: Genetic disorder leading to brittle bones due to collagen mutation.
Variants include severity from minor fragility to fatal complications.
Terminology for Bone-related Conditions
Osteo-: Referring to bone.
Genesis: Formation of new tissue.
Lysis: Dissolving of tissue.
Osteopenia: Reduced bone mass.
Osteoporosis: Increased porosity of bone leading to fracture risk.
Osteomalacia: Soft bones, distinct from osteoporosis.
Exam Preparation
Review definitions of the following terms:
Osteoblast, osteoclast, osteopenia, osteoporosis, osteomalacia.
Study axial skeleton (not for exam but important future knowledge).
Axial vs Appendicular Skeleton
Axial skeleton includes:
Skull, vertebral column, rib cage.
Appendicular skeleton includes:
Limbs and their attachment bones.
Structure of the Skull
Comprised of 22 bones, categorized into cranial and facial bones.
Cranial bones: Protect the brain, primarily visible from outside.
Facial bones: Protect entrances to digestive and respiratory tracts.
Major Sutures of the Skull
Lamboid Suture: Connects occipital bone to parietals.
Sagittal Suture: Connects two parietal bones.
Coronal Suture: Connects frontal bone to parietals.
Squamous Suture: Connects temporal bone to parietals.
Functions of the Axial Skeleton
Support and protect body cavities and organs.
Serves as attachment points for muscles.
Important Bone Markings & Functions
Cranium protects brain.
Mandibular fossa of temporal bone articulates with mandible (jawbone).
Foramen magnum: Key opening for spinal cord entry into skull.
Sinuses
Air-filled spaces that lighten skull and prevent particle entrance into lungs.
Become inflamed leading to sinus headaches, specifically in frontal/maxillary regions.
Cartilage and Bone Development
Differentiator between bones that fuse versus dissolve in size.
Babies have ~270 bones, adults have 206 due to fusion.
Interesting Facts about Bones
Most human cervical vertebrae match with size in giraffes.
Varied shapes and sizes in skull bones relate to functions and lifestyle of different species.
Final Notes on the Hyoid Bone
Isolated bone in the neck that can indicate strangulation if broken, serves as a base for tongue attachment.
Summary
Extensive review of bone formation, types of fractures, repair processes, and implications on aging and health.
Understanding of the axial skeleton structure leading to future study on the appendicular region and joint functions.
Preparation for Upcoming Exam
Emphasis on definitions and understanding functions and structures of skeletal system.
Continued focus on Chapter 6 material with significant review of osseous tissue, fractures, and relevant conditions.
Attendance Roll Call
Instructor conducts attendance via name-calling.
Students provide an affirmative response such as "Here."
Course Overview and Exam Scope
The current focus is strictly on osseous tissue (bone anatomy and physiology).
Exam Constraint: Material for the upcoming Thursday exam is capped at the end of Chapter 6.
Chapter 7 (Introduction): Preliminary material discussed regarding Chapter will not be included on the exam; focus exclusively on the mechanics and cellular structure of bone.
Osseous Tissue: Structural Composition
Bone is a dynamic living tissue that consists of a mineralized matrix and various specialized cells.
Compact Tissue (Cortical Bone):
Dense, hard outer layer that provides strength and resistance to compression.
Makes up approximately of total bone mass in the human body.
Spongy Tissue (Cancellous/Trabecular Bone):
Located at the ends of long bones (epiphyses) and the interior of other bones.
Contains a honeycomb-like network that reduces the weight of the skeleton and houses red bone marrow for hematopoiesis (blood cell formation).
Functional Units of Bone
Osteons (Haversian Systems): The fundamental unit of compact bone.
Central Canal (Haversian Canal): Contains blood vessels and nerves.
Concentric Lamellae: Layers of calcified matrix.
Lacunae: Small "lakes" housing osteocytes.
Canaliculi: Microscopic channels connecting lacunae for nutrient and waste exchange.
Trabeculae: The lattice-like struts of spongy bone.
Unlike osteons, trabeculae lack central canals; nutrients are absorbed directly from the surrounding marrow space.
Ossification: Bone Development
Endochondral Ossification:
Process where a hyaline cartilage model is gradually replaced by bone.
Occurs in most bones below the skull (e.g., femur, humerus).
Includes primary ossification centers in the diaphysis and secondary centers in the epiphyses.
Intramembranous Ossification:
Process where bone develops directly from mesenchymal (embryonic) connective tissue.
Responsible for the formation of flat bones such as the skull, mandible, and clavicles.
Vascularization and Metabolic Exchange
Bones are highly vascularized, contrary to common perception.
Blood vessels enter bones through nutrient foramina.
This blood supply is essential for the delivery of and phosphate required for mineralization, and for responding to cellular signals during repair.
Hormonal Regulation of Calcium ()
Parathyroid Hormone (PTH) & Thyroid Interactions:
Often associated with thyroid/parathyroid signaling.
Increases blood calcium levels by stimulating osteoclasts to dissolve bone matrix (resorption).
Calcitonin (Produced by the thyroid C-cells):
Decreases blood calcium levels by inhibiting osteoclasts and stimulating excretion by the kidneys.
Promotes calcium deposition into the bone matrix, increasing bone density.
Fractures and the Physiological Repair Process
Fracture: A break or crack resulting from high impact, stress, or medical conditions that weaken bone.
The Four Stages of Fracture Repair:
Fracture Hematoma Formation:
Damaged blood vessels bleed, forming a large clot (hematoma) within several hours.
Inflammatory response triggers the arrival of phagocytes to clean debris.
Callus Formation:
External Callus: Chondrocytes and osteoblasts create a collar of hyaline cartilage and bone to stabilize the outer edges.
Internal Callus: Formed within the medullary cavity to close the gap between broken ends.
Spongy Bone Formation:
Osteoblasts replace the cartilage of the calli with spongy bone trabeculae through a process similar to endochondral ossification.
Bone Remodeling:
Over a period of months to a year, osteoclasts and osteoblasts reshape the bone.
The "bulge" of the callus is reduced, and compact bone replaces spongy bone where needed. The resulting bone may be thicker and stronger than the original at the site of the break.
Cellular Roles in Bone Health
Osteoblasts: Immature bone cells that secrete the organic components of the matrix (osteoid); they are "bone builders."
Osteoclasts: Large, multinucleated cells that use acid and enzymes to break down bone (resorption).
Clinical Stimulation:
Weight-Bearing Exercise: Mechanical stress stimulates osteoblast activity, increasing bone density.
Electrical Stimulation: Used clinically to treat "non-union" fractures by mimicking natural bioelectrical signals that trigger bone growth.
Aging, Pathology, and Bone Density
Osteopenia: A condition of reduced bone mineral density that is less severe than osteoporosis; often considered a natural part of aging where bone resorption exceeds formation.
Osteoporosis: A metabolic bone disease characterized by significant loss of mass and deterioration of microarchitecture.
Post-menopausal women are at higher risk due to the decline in estrogen, which normally inhibits osteoclast activity.
Osteomalacia/Rickets: Softening of bones due to inadequate mineralization, usually caused by Vitamin D or calcium deficiency. Called Rickets in children, often leading to bowed legs.
Osteogenesis Imperfecta (OI): A genetic "brittle bone" disorder caused by mutations in the genes responsible for producing Type I Collagen, the protein framework of bone.
Axial Skeleton: Structure and Function
The axial skeleton consists of approximately bones forming the central axis of the body.
Skull: Comprised of bones ( cranial, facial).
Sutures: Syndesmoses (fibrous joints) that lock skull bones together:
Lambdoid: Occipital to Parietal.
Sagittal: Between the two Parietal bones.
Coronal: Frontal to Parietal.
Squamous: Temporal to Parietal.
Foramen Magnum: The large opening in the occipital bone that allows the brainstem to connect to the spinal cord.
Sinuses (Paranasal Sinuses): Mucous-membrane-lined, air-filled cavities (frontal, ethmoid, sphenoid, maxillary).
Functions: Lighten the skull and resonate sound (voice).
Comparative Anatomy and Development
Bone Fusion: Newborns have roughly bones, whereas adults have due to the fusion of elements like the sacrum, coccyx, and parts of the skull (fontanelles).
Cervical Vertebrae: Mammalian consistency; humans and giraffes both typically have cervical vertebrae, despite the extreme difference in neck length.
Hyoid Bone: A U-shaped bone in the mid-neck. It is unique because it does not articulate with any other bone; it is suspended by ligaments and serves as an attachment for tongue and neck muscles. Forensic significance: Fracture often indicates manual strangulation.