Unit 3: Ch 7 (Bone Tissue) Flashcards
- genic
to create
- poietic
generation of
5 major types of bones & examples of each
-
Flat bones
- Bone appears flat
- Example: sternum
-
Long bones
- Primarily in the appendicular skeleton
- Example: femur
-
Short bones
- Square, cube shape
- Example: carpal region
-
Irregular bones
- Example: calcaneus, vertebrae
-
Sesamoid bones
- Develop in a tendon; purpose is to relieve stress on a muscle
- Example: patellar
Components of osseous tissue & bones
-
Osseous tissue
- Cells & matrix
-
Bones
- Compact bone
- Spongy bone and bone marrow
- Cartilage
- Adipose tissue
- Nervous tissue
- Dense connective tissue
- Blood vessels
Bone cell lineage
- Osteogenic, osteoblasts, and osteocytes belong to one cell lineage
- Osteoclasts have an independent origin
4 principal bone cells
- Osteogenic cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Bone development
- Development can occur through ossification or osteogenesis
- 2 methods in fetus and children
- Intramembranous ossification
- Endochondral ossification


Bone growth
- Bones grow in two directions
-
Length (interstitial)
- Result of cartilage growth
- Multiplication of chondrocytes
- Deposition of new matrix in the interior
-
Width (appositional)
- Done at endosteum
- Deposition of new bone at the surface
- Primarily a response to environmental factors (ie working out)
-
Length (interstitial)
Bone marrow
- Description
- Types & Description
- Description
- Soft tissue that occupies the marrow cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger central canals
- Types
-
Red bone marrow
- Hematopoietic tissue (produces RBC, WBC & platellets)
- Myeloid tissue
- In adults, most of the red marrow is replaced by fatty yellow bone marrow
- Always found in the axial skeleton
-
Yellow bone marrow
- Post-puberty
- Adipose tissue
- No longer produces blood
- In the event of severe or chronic anemia, it can transform back into red marrow and resume its hematopoietic function
- Found in the appendicular skeleton (if present)
-
Red bone marrow
Bone remodeling
- Bones remodel throughout life by absorbing old bone and depositing new bone
- Process replaces ~ 10% of the skeletal tissue per year due to environmental needs
- Repairs microfractures
- Releases minerals into the blood
- Reshapes bones in response to use and disuse
- Notes
- If a bone is little used, osteoclasts remove matrix and unnecessary mass
- If a bone is heavily used or stress is consistently applied to a particular region of bone, osteoblasts deposit new osseous tissue and thicken it
- The orderly remodeling of bone depends on a precise balance between deposition and resorption, between osteoblasts and osteoclasts
- If one outplaces the other, or both processes occur too rapidly, various bone deformities, developmental abnormalities, and other disorders occur
Calcitonin
- What does it do
- How is it accomplished
- Promotes mineralization and lowers blood Ca2+ concentration in children, but has little effect in adults
- Secreted when the blood calcium concentration rises too high, and it lowers the concentration by:
- Osteoclast inhibition
- Osteoblast stimulation
Calcitriol
- What is it
- What does it do
- How is it accomplished
- Ligand receptor protein
- Negative feedback loop
- 3 organ systems make calcitriol
- Integumentary
- Digestive
- Urinary
- Released when we have low Ca levels
- Promotes intestinal absorption of Ca2+ and phosphate
- Stimulates osteoclast activity
- Promotes resorption & mineralization
- Reduces urinary excretion
- Raises blood Ca2+ concentration in 3 ways
- Absorption by the small intestine
- Resorption from the skeleton
- Resorption by the kidneys
- A symport that originates in the kidney
- Notes
- Behaves as a hormone. It is called a vitamin only because it is added to the diet
- Important for bone resorption and necessary for bone deposition
- Without it, calcium and phosphate levels in the blood are too low for normal deposition
- The result is a softness of the bones called rickets in children and osteomalacia in adults
Calcium functions
- Neuron communication
- Muscle contraction
- Blood clotting
- Exocytosis
Calcium homeostasis
- What is it dependent upon
- How is it regulated
- Depends on a balance between
- dietary intake
- urinary and fecal losses
- exchanges with the osseous tissue
- A negative feedback loop that is regulated by 3 hormones
- Calcitriol
- Calcitonin
- Parathyroid (PTH)
- Linked to phosphate homeostasis
- Notes
- Skeleton exchanges about 18% of its calcium with the blood each year
Calcium overview
- Cation with 2+ charge
- Transportation in the body
- 45% in ion form
- 55% bound to plasma proteins
Calculus
- Abnormal calcification
- Ectopic ossification: bone growing in soft tissues
Compact (Dense) Bone
(aka Cortical Bone)
- Outer shell of dense white osseous tissue
- Shell encloses the marrow cavity, aka medullary cavity, which contains bone marrow
- ~75% of skeleton
Composite
- A combination of two basic structural materials
- Bone is a ceramic and a polymer
- Ceramic is hydroxyapatite and other minerals.
- Enables a bone to support the weight of the body without sagging
- Polymer is collagen
- Protects a bone from fracture by dissipating shock. The bonds re-form when collagen is relieved of stress
- Ceramic is hydroxyapatite and other minerals.
Cortisol
- What is it
- What does it do
- What happens if it is in excess?
- Steroid hormone that inhibits osteoclast activity
- If secreted in excess can cause osteoporosis/Cushing disease by:
- stimulating osteoclasts to resorb bone
- inhibiting growth hormone secretion
- reducing bone deposition (inhibiting cell division and protein synthesis)
Epiphyseal plate & line
- The epiphyseal plate serves as a growth area, allowing the diaphysis to increase in length until early adulthood
- When growth stops, the epiphyseal plate is replaced with bone, then becoming the epiphyseal line
- Both occur within the metaphysis
Endochondral ossification process
- Description
- Steps
- Bone formation that begins in cartilage
- Develops from a preexisting model composed of hyaline cartilage (fetal & adolescence)
- Steps
- Formation of primary ossification center, bony collar, & periosteum
- Vascular invasion and formation of primary marrow cavity & secondary ossification center
- At birth, enlarged primary marrow cavity & secondary marrow cavity in one epiphysis
- Epiphyses fills with spongy bone
- Remaining cartilage in the plate is generally consumed and the gap closes
- Notes
- Bone development that begins in the fetus and continues into a person’s 20s
Epiphysial plate
- A region of transition from hyaline cartilage to bone
- Functions as a growth zone where the bones elongate
Epiphysial line
- Ossified epiphysial plate
- Point of fusion between the epiphysis and the diaphysis
- Slightly denser spongy bone between the epiphysis and the diaphysis
Factors affecting bone homeostasis
- Vitamins
- A
- B12
- C
- D
- K
- Anabolic steroids
- Accelerate the transition of hyaline cartilage into compact bone
- Rate of bone growth during puberty & adolescence
- Estrogen: Higher in females, results in quicker conversion of the epiphyseal plate into epiphyseal line
- Testosterone
Examples of flat bone
- Most of the cranial bones
- Sternum
- Scapula
- Ribs
- Hip
Growth hormone
- Stimulates bone elongation and cartilage proliferation at the epiphysial plate
- Increases urinary excretion of Ca2+
- Increases intestinal Ca2+ absorption
hemo -
blood
Insulin
- Stimulates bone formation
- Significant bone loss occurs in untreated diabetes mellitus
Intramembranous ossification process
- Description
- Stages
- Bone formation that begins in a membrane
- Produces the flat bones of the skull, most of the clavicle, and part of the mandible
- Stages
- Deposition of osteoid tissue into embryonic mesenchyme
- Calcification of osteoid tissue and entrapment of osteocytes
- Honeycomb of spongy bone with developing periosteum
- Filling of space to form compact bone at surfaces, leaving spongy bone in the middle
Examples of irregular bones
- Vertebrae
- Some skull bones
List the zones of metaphysis
- Zone of reserve cartilage
- Zone of cell proliferation
- Zone of cell hypertrophy
- Zone of calcification
- Zone of bone deposition
Long bones
- Primary long bones
- Principal features
- Most important bones in movement
- Include
- Humerus
- Ulna/radius
- Femur
- Tibia/fibula
- Metacarpals/metatarsals
- Phalanges
- Principal features
- Diaphysis (shaft): provides leverage
- Epiphysis (expanded head at each end): provides added surface area for the attachment of tendons and ligaments
Metaphysis
- The neck portion of a long bone between the epiphysis and the diaphysis
- Contains the growth plate, the part of the bone that grows during childhood, and as it grows it ossifies near the diaphysis and the epiphyses
Mineral deposition (mineralization)
- Hardening process of osseous tissue
- A crystallization process in which calcium, phosphate, and other ions are taken from the blood plasma and deposited in bone tissue, mainly as crystals of hydroxyapatite
Mineral resorption
- Process of dissolving bone
- Releases minerals into the blood
- Resorption is carried out by osteoclasts
Organ systems important for calcium
- Integumentary
- Digestive
- Urinary
Osseous tissue
- Connective tissue in which the matrix is hardened by the deposition of calcium phosphate and other minerals
Osteoblasts
- Bone-forming cell that arises from an osteogenic cell, deposits bone matrix, and eventually becomes an osteocyte
Osteoclasts
- Description
- Components
- Macrophage of the bone surface that dissolves the matrix and returns minerals to the ECF
- Comes from a blood stem cell lineage different than the osteoblast
- Components
- Multinucleated
- Several lysosomes
- Ruffled border
Describe osteocyte & osteoclast development

Osteocytes
- Mature bone cell that is formed when an osteoblast becomes surrounded by its own matrix and trapped in lacuna
Osteogenesis
Bone-building activity
Osteogenic Cells
- Stem cells that develop from embryonic mesenchyme
- Give rise to most other bone cell types
- Occur in the endosteum and inner layer of the peristeum
Osteon (aka Haversian system)
- The basic structural unit of compact bone
- Consists of a central canal and its lamellae
Parathyroid hormone (PTH)
- Indirectly activates osteoclasts, which resorb bone and raise blood Ca2+ concentration
- Inhibits urinary Ca2+ excretion
- Promotes calcitriol synthesis
- PTH raises Ca level by 4 mechanisms:
- Binds to receptors on the osteoblasts
- Promotes calcium reabsorption by the kidneys
- Promotes the final step of calcitriol synthesis
- Inhibits collagen synthesis by osteoblasts, thus inhibiting bone deposition
Perforating canals
Join central canals of an osteon
Periosteum
- Sheath that covers a bone
- Tough, outer fibrous layer of collagen and an inner osteogenic layer of bone-forming cells
Phosphate homeostasis
- Description
- Regulated by
- Required for bone strength, DNA, RNA, ATP & phospholipids
- Able to act as a buffer
- Anion
- __Regulated by
- Calcitriol: Calcitriol raises the phosphate level by promoting its absorption from the diet by the small intestine
- PTH: Parathyroid hormone lowers the blood phosphate level by promoting its urinary excretion
Examples of short bones
- Wrist
- Ankle
Skeleton functions/roles
- Support
- Protection: Protect critical organs
- Movement: Interrelationships between skeleton & muscles
- Electrolyte balance
- Acid-base balance
- Blood formation: how bone marrow gives rise to RBC, WBC, & platelets
Spongy Bone
- Always enclosed by a shell of compact bone
- Loosely organized form of osseous tissue
- Few osteons and no central canals
- Spongelike appearance composed of
- Spicules
- Trabecule
- Red bone marrow
- Interstitial lamellae
- Osteocytes
- Lacunae
- Canaliculi
- Skeleton is ~ 25% spongy bone
Testosterone
- Stimulates osteoblasts and promotes protein synthesis, thus promoting adolescent growth and epiphysial closure
Thyroid hormone
- Essential to bone growth
- Enhances synthesis and effects of growth hormone
- Excesses can cause
- hypercalcemia
- increased Ca2+ excretion in urine
- osteoporosis
What does vitamin A do?
- Promotes glycosaminoglycan (chondroitin sulfate) synthesis
What is vitamin C (ascorbic acid) required for?
- Collagen synthesis
- Bone growth
- Fracture repair
What is the study of bones called?
Osteology
Wolff’s Law of Bone
- The architecture of a bone is determined by the mechanical stresses placed upon it, and the bone thereby adapts to withstand them
- Balance of osteoblast and osteoclast activity
- An example of the complementarity of form and function, showing that the form of a bone is shaped by its functional experience
- Example: Tennis players and “racket arm”
Zone of bone deposition
- Zone 5
- Breakdown of lacuna walls, leaving open channels
- Death of chondrocytes
- Bone deposition by osteoblasts, forming trabeculae of spongy bone
Zone of calcification
- Zone 4
- Temporary calcification of cartilage matrix between columns of lacunae
Zone of cell proliferation
- Zone 2
- Chondrocytes multiply and line up in rows of small flattened lacunae
Zone of hypertrophy
- Zone 3
- Cessation of mitosis
- Enlargement of chondrocytes and thinning of lacuna walls
Zone of reserve cartilage
- Zone 1
- Typical histology of resting hyaline cartilage
3 main areas of a long bone
- Epiphyses
- Metaphyses
- Diaphysis
What is the physiological significance of the epiphysial line?
Because its presence indicates that the bone has completed in growth