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Questions and Answers
What is the primary function of the skeletal system?
What is the primary function of the skeletal system?
- Providing support, movement, and protection (correct)
- Producing hormones
- Regulating body temperature
- Facilitating digestion
Which osseous cells are involved in the regulation of calcium and phosphate levels in the bone?
Which osseous cells are involved in the regulation of calcium and phosphate levels in the bone?
- Chondrocytes
- Osteoblasts
- Osteoclasts
- Osteocytes (correct)
What is the role of osteocalcin in bone physiology?
What is the role of osteocalcin in bone physiology?
- Stimulates fat storage
- Promotes bone decay
- Regulates blood glucose levels (correct)
- Increases bone density
How do ligaments differ from tendons?
How do ligaments differ from tendons?
What type of marrow is responsible for blood cell production?
What type of marrow is responsible for blood cell production?
Which minerals are primarily stored in bone tissue?
Which minerals are primarily stored in bone tissue?
What is the medullary cavity filled with in an adult long bone?
What is the medullary cavity filled with in an adult long bone?
How does aging affect bone health?
How does aging affect bone health?
What is a consequence of mechanical stress on bone structure?
What is a consequence of mechanical stress on bone structure?
How much bone mass can astronauts potentially lose per month during long-term missions?
How much bone mass can astronauts potentially lose per month during long-term missions?
What role does Vitamin D play in bone health?
What role does Vitamin D play in bone health?
Which nutrient is primarily responsible for bone mineralization?
Which nutrient is primarily responsible for bone mineralization?
What might happen to a bone in a cast during immobilization?
What might happen to a bone in a cast during immobilization?
What is one of the primary functions of magnesium in bone health?
What is one of the primary functions of magnesium in bone health?
Which of the following factors can affect calcium metabolism?
Which of the following factors can affect calcium metabolism?
What is one of the roles of Omega-3 fatty acids related to bone health?
What is one of the roles of Omega-3 fatty acids related to bone health?
What type of bone growth increases the length of bones?
What type of bone growth increases the length of bones?
Which type of ossification involves the replacement of hyaline cartilage?
Which type of ossification involves the replacement of hyaline cartilage?
During which phase of bone remodeling do osteoclasts create a resorption pit?
During which phase of bone remodeling do osteoclasts create a resorption pit?
What is the main function of osteoblasts in bone remodeling?
What is the main function of osteoblasts in bone remodeling?
What initiates the activation phase of bone remodeling?
What initiates the activation phase of bone remodeling?
Which of the following statements is true regarding bone metabolism?
Which of the following statements is true regarding bone metabolism?
What is one consequence of constant bone remodeling?
What is one consequence of constant bone remodeling?
What occurs during the reversal phase of bone remodeling?
What occurs during the reversal phase of bone remodeling?
What type of bone tissue fills the epiphysis?
What type of bone tissue fills the epiphysis?
What is the main purpose of the trabeculae in spongy bone?
What is the main purpose of the trabeculae in spongy bone?
Which of the following components mainly forms the bone matrix?
Which of the following components mainly forms the bone matrix?
Which structure serves as the outer lining of a bone?
Which structure serves as the outer lining of a bone?
What is the primary role of hydroxyapatite in bone structure?
What is the primary role of hydroxyapatite in bone structure?
The space within spongy bone that protects red bone marrow is created by which of the following?
The space within spongy bone that protects red bone marrow is created by which of the following?
How does compact bone primarily gain its strength?
How does compact bone primarily gain its strength?
During growth, what does the metaphysis contain?
During growth, what does the metaphysis contain?
What role does calcitriol play in bone health?
What role does calcitriol play in bone health?
Which hormone is stimulated by low blood calcium levels?
Which hormone is stimulated by low blood calcium levels?
How does elevated phosphate levels affect calcitriol production?
How does elevated phosphate levels affect calcitriol production?
What is the primary consequence of osteoporosis?
What is the primary consequence of osteoporosis?
Which process is directly promoted by calcitriol in the kidneys?
Which process is directly promoted by calcitriol in the kidneys?
What is one of the functions of Fibroblast Growth Factor 23 (FGF23)?
What is one of the functions of Fibroblast Growth Factor 23 (FGF23)?
What occurs when high levels of calcitriol are present in the blood?
What occurs when high levels of calcitriol are present in the blood?
Which bones are most commonly affected by osteoporosis?
Which bones are most commonly affected by osteoporosis?
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Study Notes
Skeletal System Overview and Bone Functions
- The skeletal system comprises bones, cartilages, ligaments, and tendons.
- Bones are the primary structural component, providing support, enabling movement, and protecting organs.
- Bones store minerals (calcium, phosphorus), produce osteocalcin (regulates blood glucose and fat), and store fat (yellow bone marrow).
- Red bone marrow produces blood cells (hematopoiesis).
Bone Structure: Macroscopic and Microscopic
- Long bones have a diaphysis (shaft with medullary cavity containing yellow marrow), epiphyses (ends with spongy bone and red marrow), and metaphysis (growth plate region).
- Periosteum covers the outer bone surface; endosteum lines the inner surface.
- Compact bone (80% of bone tissue) is dense and strong, composed of osteons (rings of collagen and calcified matrix).
- Spongy bone (cancellous bone) provides balance, contains osteocytes in trabeculae (matrix spikes), and often houses red marrow.
Bone Composition and Formation
- Bone matrix consists of 1/3 collagen fibers and 2/3 calcium phosphate salts.
- Osteoid is uncalcified collagen secreted by osteoblasts.
- Hydroxyapatite crystals (calcium phosphate, calcium carbonate, other salts) give bone hardness and strength; collagen provides flexibility.
- Bones form through intramembranous (from mesenchymal cells) or endochondral (replacing cartilage) ossification.
Bone Growth and Remodeling
- Longitudinal growth occurs at the epiphyseal plate (cartilage replacement).
- Interstitial growth expands cartilage within bone.
- Bone remodeling involves resorption (osteoclasts) and formation (osteoblasts) to maintain bone strength and calcium homeostasis. Approximately 5-10% of the skeleton is remodeled annually.
- Remodeling is influenced by injury, exercise, and aging. Mechanical stress stimulates bone deposition.
Bone Remodeling Phases
- Activation: Osteoclast precursor activation by RANKL.
- Resorption: Osteoclasts dissolve bone mineral and organic matrix.
- Reversal: Osteoclast apoptosis; mononuclear cells prepare the surface for new bone.
- Formation: Osteoblasts deposit new bone matrix.
- Mineralization: Mineral salts and collagen fibers deposited.
Nutrients and Bone Health
- Calcium: Essential for hydroxyapatite crystal formation.
- Vitamin D: Crucial for calcium absorption and bone mineralization.
- Vitamin K: Supports bone mineralization; may synergize with Vitamin D.
- Magnesium and Fluoride: Structural bone components.
- Omega-3 Fatty Acids: Reduce inflammation affecting osteoblast function.
Calcium Homeostasis
- Calcium is vital for bone, muscle function, nerve impulse transmission, and blood clotting.
- Free ionized calcium, calcium bound to protein, and calcium bound to complex anions are found in the blood.
- Parathyroid hormone (PTH): Stimulates calcium release from bone, increases renal reabsorption, and enhances vitamin D activation (to increase intestinal calcium absorption).
- Calcitriol (active Vitamin D): Increases calcium absorption in the gut, enhances renal reabsorption, and plays a role in bone mineralization.
- Calcitonin: Inhibits bone resorption.
Vitamin D Metabolism
- Vitamin D metabolism is regulated by PTH, calcium and phosphate levels, FGF23, and calcitriol feedback.
- PTH stimulates calcitriol production. Low calcium stimulates PTH. High phosphate inhibits calcitriol synthesis. FGF23 reduces calcitriol production. Calcitriol inhibits its own production via feedback mechanisms.
Aging and Bone Tissue
- Osteoporosis is characterized by decreased bone mass due to resorption exceeding formation.
- It commonly affects the femur, vertebrae, and wrist.
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