Bone Tissue and Skeleton Functions

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Questions and Answers

What is the initial step in intramembranous ossification?

Condensation of mesenchyme into trabeculae (correct)

Osteoblasts forming compact bone at the surface

Calcium phosphate being deposited in the matrix

Osteoclasts creating the marrow cavity

Which of the following best describes the role of osteoblasts during endochondral ossification?

They form bony collars around dying chondrocytes (correct)

They create the initial cartilage model

They break down bone tissue to create marrow cavities

They lay down uncalcified bone or osteoid

Where are secondary ossification centers typically found during endochondral ossification?

In the ends of the bone (correct)

Throughout the shaft of the bone

At the surface of the periosteum

Within the marrow cavity

What happens to the epiphyseal (growth) plates by early twenties?

They completely disappear Signup and view all the answers

Which zone is responsible for the multiplication of chondrocytes in the epiphyseal growth plate?

Zone of proliferation Signup and view all the answers

Which type of bone fracture involves one bone staying in place?

Nondisplaced fracture Signup and view all the answers

What is the main component of phosphorus in the human body?

Bone Signup and view all the answers

Which hormone is primarily responsible for stimulating growth during puberty?

Estrogen Signup and view all the answers

At what age does osteoporosis typically begin to affect bone density?

40 years Signup and view all the answers

How does the use of anabolic steroids in teenagers affect bone growth?

Causes premature closure of the growth plate Signup and view all the answers

What process results in the increase of the length of bones during growth?

Interstitial growth of the epiphyseal plate Signup and view all the answers

What is the role of osteoblasts in the process of mineralization?

They produce collagen fibers. Signup and view all the answers

How does calcitriol affect calcium levels in the body?

Promotes calcium reabsorption by kidneys Signup and view all the answers

What does Wolff's law of bone state?

The architecture of bone is determined by mechanical stresses. Signup and view all the answers

Which effect does calcitonin have on bone health?

It inhibits osteoclast activity. Signup and view all the answers

During which scenario are osteoclasts stimulated to remove bone?

When there is reduced pressure on the tooth Signup and view all the answers

What primarily influences the density and mass of bone in athletes?

Mechanical stresses experienced by the bone Signup and view all the answers

What is the effect of parathyroid hormone (PTH) on calcium levels?

Stimulates osteoclasts and promotes bone resorption Signup and view all the answers

What is the primary function of osteocytes in bone tissue?

They maintain the bone matrix and communicate with other bone cells. Signup and view all the answers

Which of the following correctly describes the composition of osseous tissue?

1/3 organic matter and 2/3 inorganic matter. Signup and view all the answers

What structure is responsible for connecting osteocytes within compact bone?

Canaliculi. Signup and view all the answers

What characterizes the function of osteoclasts in osseous tissue?

They degrade bone tissue and assist in bone remodeling. Signup and view all the answers

What type of bone provides strength while remaining lightweight due to its structure?

Spongy bone. Signup and view all the answers

Which of the following is NOT a recognized function of the skeleton?

Digestion. Signup and view all the answers

What is the role of periosteum in bone structure?

It provides a covering for bone and serves as an attachment point for muscles. Signup and view all the answers

Where does intramembranous ossification primarily occur?

In flat bones of the skull and clavicle. Signup and view all the answers

Which type of bone is characterized as a lever acted upon by muscles?

Long bones. Signup and view all the answers

Which component of bone matrix resists tensile forces?

Collagen. Signup and view all the answers

Study Notes

Bone Tissue

Bone tissue is a connective tissue hardened by minerals like calcium phosphate.
Bone is continuously remodeling itself.
It's not the hardest substance; tooth enamel is harder.

Functions of the Skeleton

Support: Supports limbs and other structures
Protection: Protects internal organs (brain, spinal cord, heart, lungs, etc.)
Movement: Enables limb movements and breathing
Electrolyte balance: Stores and releases calcium and phosphate
Acid-base balance: Buffers blood pH, regulating alkaline phosphate and carbonate salts.
Blood formation: Red bone marrow produces blood cells (including white blood cells).
Hormone secretion: Secretes hormones influencing insulin secretion and action, moderating the stress response.

Bone (Osseous) Tissue

Connective tissue with a mineralized matrix (calcium phosphate, etc.).
Calcification is the hardening process.
Constantly remodels itself.
Other components of Bone Tissue: collagen, glycosaminoglycans, proteoglycans, glycoproteins.

Shapes of Bones

Long bones: Act as levers for muscle action.
Short bones: Allow gliding across each other.
Flat bones: Protect soft organs.
Irregular bones: Have various shapes.

General Features of Bones

Shaft (diaphysis): Cylindrical structure of compact bone with a marrow cavity lined with endosteum.
Enlarged ends (epiphyses): Strengthen joints and attach ligaments.
Joint surface covered with articular cartilage.
Shaft covered with periosteum (outer fibrous layer of collagen).
Epiphyseal plate/line (growth plate in young, line in adults) allows bone growth.

Structure of a Flat Bone

External and internal surfaces composed of compact bone.
Middle layer: Spongy bone and bone marrow.
Skull fracture may leave inner compact bone unharmed.

Cells of Osseous Tissue

Osteogenic cells: Arise from embryonic fibroblasts, give rise to osteoblasts, found in the endosteum, periosteum, or central canals.
Osteoblasts: Mineralize organic matter of the matrix.
Osteocytes: Mature cells, trapped in the matrix, connected by gap junctions.
Osteoclasts: Develop from fusion of 3-50 blood stem cells, reside in resorption pits to break down bone.

Matrix of Osseous Tissue

Dry weight: one-third organic matter, two-thirds inorganic matter.
Organic matter: Collagen, glycosaminoglycans, proteoglycans, and glycoproteins.
Inorganic matter: 85% hydroxyapatite (calcium phosphate), 10% calcium carbonate, and trace minerals.
Combination for strength & resilience: Mineral resists compression; collagen resists tension.

Histology of Compact Bone

Osteon: Basic structural unit, formed by concentric lamellae that surround a central (Haversian) canal.
Perforating (Volkman) canals: Perpendicular canals connecting central canals.
Osteocytes connect with each other and blood supply by processes in canaliculi.

Blood Vessels of Bone

Central canals contain blood vessels and nerves.
Perforating canals carry vessels further into bone.

Spongy Bone

Sponge-like appearance formed by trabeculae, spaces filled with bone marrow.
Trabeculae have few osteons or central canals; close proximity of osteocytes to blood supply.
Provides strength with minimal weight.
Trabeculae develop along bone's lines of stress.

Bone Marrow

Found in the marrow cavity of long bones and between trabeculae.
Red marrow: Produces blood cells; found in vertebrae, ribs, sternum, some pelvic girdle, proximal heads of femur and humerus in adults.
Yellow marrow: Fatty marrow in the medullary cavity of long bones in adults, mainly found in the shafts of long bones.

Intramembranous Ossification

Produces flat bones of the skull and clavicle.
Condensation of mesenchyme into trabeculae, followed by osteoblast laying down osteoid tissue (uncalcified bone), calcification of the osteoid tissue, and formation of compact bone at surface.

Endochondral Ossification

Bone develops from a pre-existing cartilage model.
Most bones form this way by a process involving the development of the primary ossification center, marrow cavity, secondary ossification centers, articular cartilage, and epiphyseal plates.
The development of the bony collar, chondrocytes swelling and dying, stem cells giving rise to osteoblasts and osteoclasts, bone laid down, and marrow cavity created.
Cartilage remains in articular surfaces and epiphyseal plates to enable bone growth during childhood/adolescence. Primary and secondary cavities unite over time.

Fetal Skeleton @ 12 Weeks

Shows different stages of cartilage and calcified endochondral bone within the developing fetal skeleton.

Epiphyseal Growth Plate

Epiphyseal plates (growth plates) have five zones allowing bone to grow in length: Reserve cartilage, proliferation, hypertrophy, calcification, and bone deposition.
Growth plates allow longitudinal bone growth; chondrocytes divide, enlarge, and die, allowing for replacement of cartilage with bone.

Bone Growth

Bones increase in length by interstitial growth at epiphyseal plates, increasing in width by appositional growth through osteoblasts laying down new bone matrix on the outer surface, and osteoclasts removing bone from the inner surface.

Bone Remodeling

Bones remodel throughout life, changing based on mechanical stresses (Wolff's law).
Osteoblasts and osteoclasts work together, resorption, reversal, formation, and mineralization are part of the process.

Mineral Deposition

Crystallization process where osteoblasts produce collagen fibers, minerals deposit along fibers.
Abnormal calcification (ectopic) can occur in tissues other than bone.

Mineral Resorption

Osteoclasts dissolve bone and release minerals into the blood.
Dental braces can stimulate more resorption or remodeling in teeth and jawbones.

Calcium and Phosphate

Phosphate: Component of DNA, RNA, and ATP.
Calcium: Needed for neurons, muscle contraction, blood clotting, and exocytosis.

Calcium Regulation

Calcitriol (vitamin D): Increases calcium absorption from the digestive tract, resorption from skeleton, stimulates osteoblast to differentiate into osteoclasts, and promotes reabsorption by the kidneys.

Calcitonin Regulation

Osteoclast inhibition (reducing activity by about 70% within 15 minutes).
Osteoblast stimulation (increasing activity within 1 hour) to deposit more calcium in the skeleton to decrease blood calcium levels.

Parathyroid (PTH) Regulation

Raises calcium levels by promoting osteoclast activity, promoting calcium reabsorption by the kidneys, promoting the final step of calcitriol synthesis in the kidneys, and inhibiting osteoblast activity to inhibit calcium.

Calcium Homeostasis

Balance of blood calcium levels affected by intakes, absorption from intestines, filtration and reabsorption in kidneys, and deposits/resorption of bone.
Calcitonin and PTH regulate blood calcium levels.

Phosphate Homeostasis

Phosphate homeostasis, like calcium, is important but not as tightly regulated. Phosphate is critical for bone strength and essential components like ATP, DNA, RNA, and other products.

Other Factors Affecting Bone

Hormones, vitamins, and growth factors affect bone growth, such as growth spurts during puberty, estrogen effects on girls' growth, and closing of the epiphyseal plates.
Anabolic steroids can prematurely close growth plates.

Bone Fractures

Types of fractures: Nondisplaced, displaced, comminuted, greenstick.

Healing of Bone Fractures

Four steps: Hematoma formation, soft callus formation, hard callus formation, and bone remodeling.

Osteoporosis

Most common bone disorder, characterized by bone density declines, which leads to becoming brittle.
Occurs more frequently as we age, and affected by sex hormones like estrogen, genetic predisposition and ethnicity.

Bone Disorders

Table details various conditions like Osteitis deformans, Osteomyelitis, Osteogenesis imperfecta, and Osteosarcoma.

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Description

This quiz covers the essential aspects of bone tissue, including its structure, functions of the skeleton, and the processes involved in bone remodeling. Test your knowledge about how bones support the body, protect organs, and contribute to various physiological functions.