Set 10 Flashcards
What kind of tissue is bone?
Supporting connective tissue
What are the characteristics of the extracellular components of bone?
- Components are hard and calcified
- ECM contains lots of collagen
What allows bone to serve protective and supportive functions?
Rigidity and strength
What are the five functions of bone?
- Support
- Protection
- Movement
- Mineral storage reservoir
- Hematopoiesis
What minerals do bones store?
Calcium and phosphorus
What are the four types of bones?
- Long bones
- Short bones
- Irregular bones
- Flat bones
What is compact bone used for? What is its structure?
- For support
- Dense
What is spongy bone also called? What does it form?
- Trabecular bone
- Calcified lattice
- Characterized by open space partially filled with needle-like structures
Why does bone regenerate well?
Because it is highly vascularized
What is epiphysis and diaphysis?
- Epiphysis: end of a long bone
- Diaphysis: shaft of a long bone
What is the epiphysis made up mostly of?
Spongy bone
What is the epiphyseal plate?
Site of bone growth
How do bones vary?
In their proportions of compact and cancellous (spongy) bone
What is the main shaft of a long bone?
Diaphysis
What is the primary function of the diaphysis?
Provide strong support without cumbersome weight
What is the structure of the diaphysis?
- Hollow
- Cylindrical shape
- Thick, compact bone
What forms both ends of a long bone?
Epiphysis
What is the structure of the epiphysis?
- Cancellous bone filled with marrow
- Bulbous shape
What is the primary function of the epiphysis?
Provide attachments for muscles and give stability to joints
Where is articular cartilage found in long bones? What is it?
- Layer of hyaline cartilage
- Covers the articular surface of epiphyses
What is the function of hyaline cartilage?
- Elastic cartilage
- Cushions jolts and blows (absorbs shocks)
Which layer of bone contains cells that form and destroy bone?
Periosteum
What is the structure and function of the periosteum?
- Dense, white, fibrous membrane that covers bones
- Attaches tendons firmly to bones
- Essential for bone survival and bone formaiton
Which layer of bone contains blood vessels that send branches into bone and are important in growth and repair?
Periosteum
What is the endosteum?
Thin epithelial membrane that lines medullary cavity
What is the medullary (or marrow) cavity?
Tube-like, hollow space in the diaphysis
What is the medullary (marrow) cavity filled with in adults?
Yellow marrow
What is the inner portion of short, flat, and irregular bones?
Cancellous bone, covered on the outside with compact bone
Where are large amounts of red bone marrow found?
- Flat bones
- Ex: ribs, pelvis, skull
Spaces inside cancellous bone of a few irregular and flat bones are filled with ___________.
red bone marrow
The composition of bone matrix can be divided into two fractions. What are they?
- Inorganic salts
- Organic matrix
The hardness of bone results from the deposition of what?
- Hydroxyapetite
- Highly specialized chemical crystals of calcium and phosphate
Where is hydroxyapetite found? What is its function?
- Spaces between collagen
- Effectively resist stress and mechanical deformation
What inorganic salts are found in bone?
- Largely calcium and phosphate (hydroxyapetite)
- Calcium carbonate (10%)
- Magnesium
- Sodium
What is the organic matrix of bone secreted by? What are they drived from?
Osteoblasts, derived from mesenchymal stem cells
What is the organic matrix of bone composed of?
- Collagenous fibers
- Mixture of protein and polysaccharides, which forms the ground substance
What are the functions of the ground substance in bone?
- Bone growth, repair and remodeling
- Acts as a medium for the diffusion of nutrients, wastes, and oxygen
What does the organic matrix combine with to give bone its rigidity?
Large amounts of crystallized minerals (mostly calcium)
What are the four types of structures that make up an osteon?
- Lamellae
- Lacuanae
- Canaliculi
- Havarsian canal
What are lamellae?
Concentric rings that are islands of calcified matrix
Which structure of an osteon is altered by growth?
Lamellae
What are lacunae?
Small spaces containing tissue fluid in which bone cells (osteocytes) are located between hard layers of the lamellae
What are canaliculi?
Small canals radiating from the osteocytes and connecting them to each other and to the Havarsian canal
What is the Havarsian canal?
- Extends lengthwise through the center of each osteon
- Contains blood vessels and lymphatic vessels
- Allows excretion and absorption of nutrients
There are no ________ in cancellous bone. Instead, it has ___________.
- osteons
- trabeculae-needle like bony spicules
How are nutrients delivered and waste products removed in cancellous bone?
By diffusion through tiny canaliculi
How do bony spicules enhance the bone’s strength in cancellous bone?
Arranged along lines of stress
What do osteogenic cells differentiate into?
Osteoblasts
How do osteoblasts become osteocytes?
Become trapped into the matrix when it calcifies
What do osteoclasts stem from?
Macrophages (NOT osteogenic cells)
What is the primary function of osteoblasts?
- Deposit calcium as they create new bone matrix
- Bring about the formation of new bone
What is the primary function of osteoclasts?
Break down bone matrix during bone resorption
All bone surfaces are covered with a layer of cells mostly made of _________, and less _________.
- osteoblasts
- osteoclasts
Are osteoblasts or osteoclasts larger?
Osteoclasts are considerably larger
How are osteoclasts formed? Where do they develop? How do they attach to bone surface?
- Formed by the fusion of several precursor cells (multiple nuclei, mitochondria, and lysosomes)
- Develop from stem cells in the bone marrow
- Attach to bone surface by integrins
How do osteoclasts bring about the resorption of bone?
- Secretion of collagenase, matrix metalloproteinases (MMPs), and lactic/citric acids
- MMPs destroy ECM, such as collagen
What is the final differentiation state for an osteoblast?
Osteocyte
Where is RANKL found? What is the RANK receptor found?
- RANKL: surface of osteoblast
- RANK receptor: surface of osteoclast precursor
What does the interaction between RANKL and RANK receptor lead to?
- Differentiation of osteoclast precursor cells
- Activation of osteoclasts to resorb bone
What are stimulators of the RANKL process?
- Parathyroid hormone
- Release from thyroid to trigger release of calcium
How does estrogen inhibit RANKL? What occurs when estrogen levels reduce in menopause?
- Normally, OGP binds to RANK to inhibit RANKL binding (and osteoclast differentiation)
- Menopausal women: decreased levels of OGP leads to more RANKL and RANK receptor binding, and more osteoclasts
What is OGP produced by? What does it do?
- Osteoblasts
- Binds to RANKL, which inhibits RANK receptor binding
- Acts as a regulatory
Why is vitamin D important in the maintenance of blood calcium?
Precursor for calcitriol, which is involved with reabsorption of calcium in the gut
What is the calcium balance in growing children? In post-menopausal women? In adults?
- Growing children: positive balance
- Post-menopausal women: negative balance
- Adults: should be balanced
When is parathyroid hormone released? By what?
- When plasma calcium is low
- Parathyroid gland
When does parathryoid hormone stimulate and enhance?
- Enhances renal reabsorption of calcium
- Stimulates release of calcitriol
What is the function of calcitriol? What is the precursor?
- Increases intestinal calcium reabsorption
- Vitamin D
What percentage of calcium is contained in the extracellular pool, intracellular pool, and bone matrix?
- Extracellular: 0.1%
- Intracellular: 0.9%
- Bone matrix: 99%
When is calcitonin release? By what?
- In response to high blood calcium
- Thyroid gland
What are the effects of calcitonin?
- Decreases bone resorption
- Increases renal calcium excretion
How is vitamin D acquired?
- Absorbed from the diet
- Synthesized from exposure to skin to UV lights converting a cholesterol precursor to vitamin D
Where is vitamin D produced?
Liver and kidneys
What are the actions of vitamin D on calcium regulation? (3)
- Increased calcium reabsorption in the proximal and distal convoluted tubules of the kidney
- Stimulates osteoblast activity
- Increases the synthesis of calcium binding proteins in the intestine
What do disorders of vitamin D lead to?
- Weak bones
- Rickets in children
- Osteomalacia in adults
What is the skeleton made of in the fetus? What is it eventually replaced by?
- Cartilage
- Replaced with calcified bone matrix
How does exercise make bones stronger?
Stimulates osteoblasts to secrete more collagen
What are the two mechanisms for bone formations?
- Intramembranous
- Endochondral
What types of bones undergo intramembranous osteogenesis?
- Occurs when fibrous membranes are replaced by bone tissue (less common)
- Flat bones (skull, sternum, clavicle)
What are the characteristics of intramembranous osteogenesis?
- Does NOT begin with the cartilage model
- Dense areas of mesenchymal cells differentiate, forming early spincules
What are the two major steps of intramembranous osteogenesis?
1) Spongy bone tissue begins to develop at sites within the membranes (centers of ossification, where osteoblasts are clustered together)
2) Red bone marrow forms within the spongy bone tissue, followed by the formation of compact bone on the outside
What types of bones undergo endochondral osteogenesis?
- Most bones begin as a cartilage model, with bone formation spreading essentially from the center to the ends
- Vascular, long and flat bones
What are the major steps of endochondral osteogenesis?
- Mesenchymal cells are induced to become chondrocytes
- Cartilage forms the shape of the bone, and is surrounded by the periosteum (envelope of connective tissue)
- Osteoblasts differentiate from the inner surface
- Endochondral ossification forms from the diaphysis toward each epiphysis
In what direction does endochondral ossification occur?
From the diaphysis toward each epiphysis
How do bones elongate during endochondral ossification?
As chondrocytes in the cartilage of the epiphyseal plate divide
What are the four layers of the epiphyseal plate?
- Zone of proliferation
- Zone of hypertrophy
- Zone of calcification
- Ossification zone
What occurs at the zone of proliferation?
Chondrocytes undergo active mitosis, causing the layer to thicken and the plate to increase in length
What occurs at the zone of hypertrophy?
Older, enlarged cells undergo degenerative changes associated with calcium deposition
What occurs at the zone of calcification?
Dead or dying cartilage cells undergo rapid calcification
_____________ is the site of bone growth.
Epiphyseal plate
What occurs to epiphyseal plates during puberty?
Until bone growth in length is complete (puberty)
Which bones exhibit closing of epiphyseal plates early? Late?
- Early: digits
- Late: arm, leg, pelvis
Does ossification increase or decrease as we age (until puberty)?
Increase
How do osteoclasts affect bone growth?
Enlarge the diameter of the medullary cavity
How do osteoblasts affect bone growth?
From the periosteum, build new bone around the outside of the bone
What is appositional bone growth?
Enlargement in the diameter of bones occurs as it is growing in length
What are symptoms of osteoporosis?
- Frequent fractures
- Loss of height over time
- Stooped posture
What treatments are used for osteoporosis?
- Drugs: raloxifene and calcitonin
- Estrogen replacement therapy
- Exercise
What is the relation between estrogen and OGP?
- Estrogen acts on osteoblasts to stimulate the production of TGF-beta
- TGF-beta causes osteoblast cells to make osteoprotegerin (OPG)
___________ continuously remove and replace surrounding calcium salts in adult bones.
Osteocytes in lacunae
Remodeling is so rapid that about _____ of the skeletal mass is replaced each year.
1/5
What does the epiphysis of the epiphyseal plate contain?
Continuously dividing columns of chondrocytes
Why don’t adults with growth hormone hypersecretion grow taller?
Because their epiphyseal plates have closed
What does hypercalcemia do to neuronal membrane potential, and why does that effect depress neuromuscular excitability?
Hypercalcemia hyperpolarizes the membrane potential, which makes it harder for the neuron to fire an action potential
Why does prolactin stimulate calcitriol synthesis?
To ensure maximal absorption of calcium from the diet at a time when metabolic demands for calcium are high
