Study Notes on Bones and Skeletal Tissues
Bones and Skeletal Tissues: Part B
Diaphysis and Epiphysis
Diaphysis: The long shaft of a bone.
Epiphysis: The end part of a long bone, initially growing separately from the shaft.
Epiphyseal Plate: A plate of cartilage where bone growth occurs in childhood, allowing for the increase in length of the bone.
Metacarpal Bone: One of the long bones in the hand.
Epiphyseal Plates in X-Rays: X-ray images of a child's hand show visible cartilaginous epiphyseal plates at the ends of long bones. By adulthood, these plates will disappear as epiphyses fuse with diaphyses. Long bones of the hand and fingers typically develop only one epiphyseal plate.
Control of Bone Remodeling
Continuous Process: Remodeling of bone occurs continuously and is regulated by:
Genetic Factors.
**Control Loops: **
Negative Feedback Hormonal Loop for Ca²⁺ Homeostasis: This mechanism controls blood levels of calcium but not bone integrity.
Mechanical and Gravitational Forces: Depending on the forces applied to the bone, remodeling responds to these stresses.
Importance of Calcium in the Body
Functions of Calcium:
Nerve impulse transmission.
Muscle contraction.
Blood coagulation.
Secretion by glands and nerve cells.
Cell division.
Calcium Content in the Body:
The body contains 1200-1400 grams of calcium, 99% of which are found in bone minerals.
Blood calcium levels are tightly regulated between 9-11 mg/dl.
Vitamin D metabolites are necessary for intestinal absorption of calcium.
Dietary intake is essential for maintaining adequate calcium levels.
Hormonal Control of Blood Calcium Levels
Parathyroid Hormone (PTH):
Secreted by parathyroid glands.
Functions to increase calcium levels in the blood by promoting calcium release from bone, regardless of the status of bone integrity.
Calcitonin:
Produced by parafollicular cells of the thyroid gland.
Can temporarily lower blood calcium levels in high doses.
Negative Feedback Hormonal Loop for Calcium Homeostasis
Process of Calcium Regulation:
Falling blood calcium levels stimulate release of PTH.
PTH promotes degradation of the bone matrix by osteoclasts, releasing calcium into the bloodstream.
Resulting increase in blood calcium levels leads to cessation of PTH release, maintaining homeostasis.
Calcium Homeostasis and Its Effects
Consequences of Calcium Fluctuations:
Severe neuromuscular problems may arise from even minute changes in blood calcium levels.
Hyperexcitability when levels are low.
Nonresponsiveness when levels are high.
Hypercalcemia:
Characterized by sustained high blood calcium levels.
Can lead to deposits of calcium salts in blood vessels and kidneys, interfering with their functions.
Bone Homeostasis and Mechanical Stress
Bone Response to Stress:
Bones adapt to the stresses they endure, with the thickest parts of long bones located midway along the diaphysis where bending stress is greatest.
When weight bears on bones or muscles exert pull, this typically results in bending, causing compression on one side and stretching on the other.
Wolff's Law
Wolff's Law Explained:
States that bones grow or remodel in response to the demands placed on them.
Illustrates:
Handedness: The dominant hand's bones become thicker and stronger.
Curved Bones: They are thickest in areas where they are most likely to buckle under stress.
Trabecular Architecture: Trabeculae form trusses along stress lines due to mechanical forces.
Bony Projections: Large projections occur where heavy, active muscles attach, evidencing stress adaptation.
Bone Repair Mechanisms
Types of Fractures:
Fractures are categorized based on:**
Position of Bone Ends After Fracture: **
Nondisplaced: Ends retain normal alignment.
Displaced: Ends are out of alignment.
Completeness of Break:**
Complete: The fracture goes all the way through the bone.
Incomplete: The fracture does not extend through the bone.
Skin Penetration:**
Open (Compound): Skin is penetrated by the fracture.
Closed (Simple): No skin penetration.
Specific Fracture Types
Common Types of Fractures:
Greenstick Fracture: One side of the bone is broken while the other is bent; common in children.
Impacted Fracture: Broken ends of the bone are jammed into each other.
Comminuted Fracture: The bone is splintered into multiple pieces; common in the elderly.
Spiral Fracture: Twisting forces cause the break; frequent in skiing accidents.
Transverse Fracture: The break occurs straight across the bone.
Oblique Fracture: The break occurs at an angle across the bone.
First-Aid for Fractures
Initial Response:
Prevent movement of the affected areas.
Utilize simple splinting after evaluating the situation for further precautions.
Fracture Treatment and Healing
Treatment Strategies:
Reduction: Realignment of broken bone ends.
Closed Reduction: Physician manipulates to correct bone position.
Open Reduction: Surgical pins or wires secure the ends.
Immobilization: Aimed at ensuring healing, implemented through casting or traction depending on fracture severity, the bone involved, and patient age.
Stages of Bone Repair
1. Formation of Hematoma:
Torn blood vessels lead to hemorrhage and hematoma clot formation.
The area becomes swollen, painful, and inflamed.
2. Fibrocartilaginous Callus Formation:
Capillaries grow into the hematoma.
Phagocytic cells clear debris.
Fibroblasts secrete collagen fibers that connect broken ends, beginning reconstruction of bone, thereby forming a fibrocartilaginous callus made of cartilage matrix and spongy bone.
3. Bony Callus Formation:
Within one week, new trabeculae appear, converting the fibrocartilaginous callus to a bony (hard) callus of spongy bone, leading to firm union approximately two months later.
4. Bone Remodeling:
Begins during the callus formation phase and continues for several months.
Excess material is removed from the diaphysis exterior and within the medullary cavity, reconstructing shaft walls to resemble the original structure in response to stressors.
Homeostatic Imbalances
Osteomalacia:
Characterized by poorly mineralized bones due to inadequate calcium salts.
Leads to soft, weak bones causing discomfort when bearing weight.
Rickets:
A pediatric form of osteomalacia, leading to bowed legs and other deformities with enlarged and abnormally long ends; primarily caused by Vitamin D deficiency.
Osteoporosis**
General Overview:
A group of conditions where bone resorption outpaces deposition, leading to significant bone density loss, particularly affecting spongy bone in the spine and neck of the femur.
Risk Factors:
Most commonly seen in aging, postmenopausal women; with 30% of women aged 60–70 years experiencing fractures, and 70% of those aged 80.
Males have a lesser degree of risk.
Sex hormones play a crucial role in maintaining bone health and density; as hormone levels decrease with age, the risk of osteoporosis increases.
Additional Osteoporosis Risk Factors
Physical Attributes: Petite body form, insufficient exercise leading to weak bones.
Dietary Considerations: Deficit of calcium and vitamin D, poor dietary protein intake, smoking.
Hormonal and Health-Related Conditions:
Conditions like hyperthyroidism, diabetes, and medication impacts also contribute to osteoporosis risks.
Preventive Measures for Osteoporosis
Ensure a calcium-rich diet, particularly in early adulthood.
Limit consumption of carbonated beverages and alcohol, which can leach minerals from bones.
Engage in regular weight-bearing exercises to increase bone mass and combat age-related bone loss.
Treatment Options for Osteoporosis
Traditional Treatments:
Supplements: Calcium and Vitamin D; Improvement strategies: Weight-bearing exercises and hormone replacement therapy.
Although effective in slowing bone loss, HRT is controversial due to potential risks of heart disease, stroke, and breast cancer.
New Pharmacological Treatments:
Bisphosphonates, selective estrogen receptor modulators (SERMs), and statins all serve to enhance bone mineral density in different ways. Denosumab, a monoclonal antibody, specifically reduces fractures in men undergoing prostate cancer treatments while improving elderly bone density.
Paget's Disease
Disease Description:
Involves excessive and chaotic bone deposits and resorption, creating poorly constructed bone structure termed as pagetic bone.
This condition typically shows a high ratio of spongy to compact bone and diminished mineralization, commonly affecting the spine, pelvis, femur, and skull, rarely manifesting before age 40.
Treatment includes calcitonin and bisphosphonates for management.
Age-related Changes in Bone
Developmental Stages: During childhood and adolescence, bone formation occurs at a rate exceeding resorption. Young adults typically experience a balance between contributions, with males presenting greater mass.
Genetic Influences: Genetic factors largely determine bone density changes throughout an individual's life cycle. The gene affecting Vitamin D's cellular operation plays a critical role in early-life bone mass establishment; older adulthood sees a decline in bone mass, mineralization, and healing capacities beginning around the fourth decade, especially notable in women and white populations.
Emphasis on Healing: Strategies such as electrical stimulation and daily ultrasound treatments can enhance the repair processes of bone.
Bones and Skeletal Tissues: Part B
Diaphysis and Epiphysis
Diaphysis: The long shaft of a bone.
Epiphysis: The end part of a long bone, initially growing separately from the shaft.
Epiphyseal Plate: A plate of cartilage where bone growth occurs in childhood, allowing for the increase in length of the bone.
Metacarpal Bone: One of the long bones in the hand.
Epiphyseal Plates in X-Rays: X-ray images of a child's hand show visible cartilaginous epiphyseal plates at the ends of long bones. By adulthood, these plates will disappear as epiphyses fuse with diaphyses. Long bones of the hand and fingers typically develop only one epiphyseal plate.
Control of Bone Remodeling
Continuous Process: Remodeling of bone occurs continuously and is regulated by:
Genetic Factors.
Control Loops:
Negative Feedback Hormonal Loop for Ca²⁺ Homeostasis: This mechanism controls blood levels of calcium but not bone integrity.
Mechanical and Gravitational Forces: Depending on the forces applied to the bone, remodeling responds to these stresses.
Importance of Calcium in the Body
Functions of Calcium:
Nerve impulse transmission.
Muscle contraction.
Blood coagulation.
Secretion by glands and nerve cells.
Cell division.
Calcium Content in the Body:
The body contains 1200-1400 grams of calcium, 99\% of which are found in bone minerals.
Blood calcium levels are tightly regulated between 9-11 mg/dl.
Vitamin D metabolites are necessary for intestinal absorption of calcium.
Dietary intake is essential for maintaining adequate calcium levels.
Hormonal Control of Blood Calcium Levels
Parathyroid Hormone (PTH):
Secreted by parathyroid glands.
Functions to increase calcium levels in the blood by promoting calcium release from bone, regardless of the status of bone integrity.
Calcitonin:
Produced by parafollicular cells of the thyroid gland.
Can temporarily lower blood calcium levels in high doses.
Negative Feedback Hormonal Loop for Calcium Homeostasis
Process of Calcium Regulation:
Falling blood calcium levels stimulate release of PTH.
PTH promotes degradation of the bone matrix by osteoclasts, releasing calcium into the bloodstream.
Resulting increase in blood calcium levels leads to cessation of PTH release, maintaining homeostasis.
Calcium Homeostasis and Its Effects
Consequences of Calcium Fluctuations:
Severe neuromuscular problems may arise from even minute changes in blood calcium levels.
Hyperexcitability when levels are low.
Nonresponsiveness when levels are high.
Hypercalcemia:
Characterized by sustained high blood calcium levels.
Can lead to deposits of calcium salts in blood vessels and kidneys, interfering with their functions.
Bone Homeostasis and Mechanical Stress
Bone Response to Stress:
Bones adapt to the stresses they endure, with the thickest parts of long bones located midway along the diaphysis where bending stress is greatest.
When weight bears on bones or muscles exert pull, this typically results in bending, causing compression on one side and stretching on the other.
Wolff's Law
Wolff's Law Explained:
States that bones grow or remodel in response to the demands placed on them.
Illustrates:
Handedness: The dominant hand's bones become thicker and stronger.
Curved Bones: They are thickest in areas where they are most likely to buckle under stress.
Trabecular Architecture: Trabeculae form trusses along stress lines due to mechanical forces.
Bony Projections: Large projections occur where heavy, active muscles attach, evidencing stress adaptation.
Bone Repair Mechanisms
Types of Fractures:
Fractures are categorized based on:
Position of Bone Ends After Fracture:
Nondisplaced: Ends retain normal alignment.
Displaced: Ends are out of alignment.
Completeness of Break:
Complete: The fracture goes all the way through the bone.
Incomplete: The fracture does not extend through the bone.
Skin Penetration:
Open (Compound): Skin is penetrated by the fracture.
Closed (Simple): No skin penetration.
Specific Fracture Types
Common Types of Fractures:
Greenstick Fracture: One side of the bone is broken while the other is bent; common in children.
Impacted Fracture: Broken ends of the bone are jammed into each other.
Comminuted Fracture: The bone is splintered into multiple pieces; common in the elderly.
Spiral Fracture: Twisting forces cause the break; frequent in skiing accidents.
Transverse Fracture: The break occurs straight across the bone.
Oblique Fracture: The break occurs at an angle across the bone.
First-Aid for Fractures
Initial Response:
Prevent movement of the affected areas.
Utilize simple splinting after evaluating the situation for further precautions.
Fracture Treatment and Healing
Treatment Strategies:
Reduction: Realignment of broken bone ends.
Closed Reduction: Physician manipulates to correct bone position.
Open Reduction: Surgical pins or wires secure the ends.
Immobilization: Aimed at ensuring healing, implemented through casting or traction depending on fracture severity, the bone involved, and patient age.
Stages of Bone Repair
1. Formation of Hematoma:
Torn blood vessels lead to hemorrhage and hematoma clot formation.
The area becomes swollen, painful, and inflamed.
2. Fibrocartilaginous Callus Formation:
Capillaries grow into the hematoma.
Phagocytic cells clear debris.
Fibroblasts secrete collagen fibers that connect broken ends, beginning reconstruction of bone, thereby forming a fibrocartilaginous callus made of cartilage matrix and spongy bone.
3. Bony Callus Formation:
Within one week, new trabeculae appear, converting the fibrocartilaginous callus to a bony (hard) callus of spongy bone, leading to firm union approximately two months later.
4. Bone Remodeling:
Begins during the callus formation phase and continues for several months.
Excess material is removed from the diaphysis exterior and within the medullary cavity, reconstructing shaft walls to resemble the original structure in response to stressors.
Homeostatic Imbalances
Osteomalacia:
Characterized by poorly mineralized bones due to inadequate calcium salts.
Leads to soft, weak bones causing discomfort when bearing weight.
Rickets:
A pediatric form of osteomalacia, leading to bowed legs and other deformities with enlarged and abnormally long ends; primarily caused by Vitamin D deficiency.
Osteoporosis
General Overview:
A group of conditions where bone resorption outpaces deposition, leading to significant bone density loss, particularly affecting spongy bone in the spine and neck of the femur.
Risk Factors:
Most commonly seen in aging, postmenopausal women; with 30\% of women aged 60–70 years experiencing fractures, and 70\% of those aged 80.
Males have a lesser degree of risk.
Sex hormones play a crucial role in maintaining bone health and density; as hormone levels decrease with age, the risk of osteoporosis increases.
Additional Osteoporosis Risk Factors
Physical Attributes: Petite body form, insufficient exercise leading to weak bones.
Dietary Considerations: Deficit of calcium and vitamin D, poor dietary protein intake, smoking.
Hormonal and Health-Related Conditions:
Conditions like hyperthyroidism, diabetes, and medication impacts also contribute to osteoporosis risks.
Preventive Measures for Osteoporosis
Ensure a calcium-rich diet, particularly in early adulthood.
Limit consumption of carbonated beverages and alcohol, which can leach minerals from bones.
Engage in regular weight-bearing exercises to increase bone mass and combat age-related bone loss.
Treatment Options for Osteoporosis
Traditional Treatments:
Supplements: Calcium and Vitamin D; Improvement strategies: Weight-bearing exercises and hormone replacement therapy.
Although effective in slowing bone loss, HRT is controversial due to potential risks of heart disease, stroke, and breast cancer.
New Pharmacological Treatments:
Bisphosphonates, selective estrogen receptor modulators (SERMs), and statins all serve to enhance bone mineral density in different ways. Denosumab, a monoclonal antibody, specifically reduces fractures in men undergoing prostate cancer treatments while improving elderly bone density.
Paget's Disease
Disease Description:
Involves excessive and chaotic bone deposits and resorption, creating poorly constructed bone structure termed as pagetic bone.
This condition typically shows a high ratio of spongy to compact bone and diminished mineralization, commonly affecting the spine, pelvis, femur, and skull, rarely manifesting before age 40.
Treatment includes calcitonin and bisphosphonates for management.
Age-related Changes in Bone
Developmental Stages: During childhood and adolescence, bone formation occurs at a rate exceeding resorption. Young adults typically experience a balance between contributions, with males presenting greater mass.
Genetic Influences: Genetic factors largely determine bone density changes throughout an individual's life cycle. The gene affecting Vitamin D's cellular operation plays a critical role in early-life bone mass establishment; older adulthood sees a decline in bone mass, mineralization, and healing capacities beginning around the fourth decade, especially notable in women and white populations.
Emphasis on Healing: Strategies such as electrical stimulation and daily ultrasound treatments can enhance the repair processes of bone.