Chapter 6 Flashcards
What is bone made out of
Osseous tissue, cartilage, dense connective tissue, epithelium, adipose tissue, and nervous tissue
Main functions of bone
Support, protection, movement, store and release minerals, blood cell production, triglyceride storage
Structure of a long bone: epiphysis
The ends of a long bone, made of spongy bone holding red bone marrow. Contains articulate cartilage
Articulatr cartilage is made of _______. What is the function?
Hyaline cartilage
- forms joints and reduces friction
Structure of a long bone: metaphysis
Between the epiphysis and diaphysis, contains the epiphyseal growth plate/line
The epiphyseal growth plate/line is made of ________. What is the function?
Hyaline cartilage (turns to bone by calcification when it not longer grows)
Allows for growth in length.
Structure of the long bone: diaphysis
Made of compact bone, the shaft of the long bone
Contains the periosteum, endometrium and medullary cavity
The periosteum of the diaphysis is made up of an outer fibrous layer of _________ tissue and inner _________ layer of _____.
Dense irregular connective tissue
Osetogenic
Cells
Function of the periosteum
Connective sheath with blood supply that surrounds the outer bone surface. Helps with bone growth, protection, repair, nourishment, and attachments
The endosteum of the diaphysis is a single layer of ________ cells and ______ tissue that lines the medullary cavity
Bone forming
Connective
The medullary cavity contains ___________ and ______.
Fatty yellow bone marrow
Blood vessels
Function of the medullary cavity
Supply nutrients and provide strength
Why is bone considered a connective tissue ?
Has a large extracellular matrix that separates cells
What is bone extracellular matrix made of
Water, collagen fibres and crystallized mineral salts (like calcium phosphate and calcium hydroxide that combine to form crystals)
Calcification is initiated by bone building cells called
Osteoblasts
4 types of cells in bone tissues
Osteoprogenitor
Osteoblasts
Osteocytes
Osteoclasts
Features of osteoprogenitor
-Develop into osteoblasts
-only bone cell that cell division occurs
-Derive from mesenchyme where connective tissues form
- found within bone blood vessel canals
Features of osteoblasts
- form extracellular matrix
- synthesize and secrete collagen fibres and organic molecules
- initiate calcification and surround themselves with extracellular matrix
Features of osteocytes
- osteoblasts get trapped by extracellular matrix secretions and become osteocytes
- maintains bone tissue
- matured bone cell
- metabolize in bone tissue, exchange nutrients and wastes with blood
Features of osteoclasts
- resorption and breakdown of the extracellular matrix
- large cells derived from many monocytes (type of WBC)
- release lysosomal enzymes and acids that digest proteins and minerals
- part of development, maintenance and repair of bone tissue
Osteons are found in what type of bone tissue
Compact bone tissue
Trabeculae are found in what type of bone tissue
Spongy bone tissue
Lamellae in compact bone tissue is a plate of ________, which surround ____________ of the central canal
Mineral extracellular matrix
Blood vessels and nerves
Lamellae of spongy bone tissue is structured in
Irregular patterns of thin columns
Lacunae is between the ______ and contains
Lamellae
Osteocytes
Canalculi radiate from lacunae and are filled with __________ and ________ processes that _________ with eachother via gap junctions
Extracellular fluid
Osteocyte
Communicate
The trabeculae of spongy bone tissue contains
Red bone marrow and yellow bone marrow
Function of compact bone tissue
Protection and support, resist stress of weight and movement
Osteons within compact bone tissue exchange nutrients and oxygen and remove wastes
Function of spongy bone tissue
Allow for easy movement, support and protect red bone marrow
Blood vessels are abundant in bone containing red bone marrow that pass into the _________ veins and arteries, and exit through _______ and ______
Metaphyseal
Epiphysis and metaphysis
_______ veins and arteries exit through the periosteum
Periosteal
Nerves accompany blood vessels that supply bone. They are rich in the ______. _______ nerves carry pain sensation
Periosteum
Sensory
4 situations for ossification and osteogenesis
- FORMATION as an embryo
- GROWTH till adulthood
- REMODELLING by replacing old with new
- REPAIR when fractured
What is the difference between intramembranous and endochondrial ossification
Intramembraneous - bone forms directly within the mesenchyme
Endochondrial - bone forms within hyaline cartilage developed from mesenchyme
4 steps of intramembranous ossification
1: develop the ossification centre
2: calcification
3: trabeculae formation
4: periosteum development
Step 1 of intramembranous ossification: developing the ossification centre
Chemical messages cause the mesenchyme cells to cluster (this site is the ossification centre)
Mesenchyme cells then differentiate (osteoprogenitor form into osteoblasts)
Step 2 of intramembranous ossification: calcification
- secretion if extracellular matrix stops
- osteocytes in lacunae extend into the canalculi
- calcium mineral salts deposit and the extra cellular matrix hardens causing “calcification”
Step 3 of intramembranous ossification: trabeculae formation
- bone forms and develop trabeculae which fuse with another and form “spongy bone” around blood vessels
- connective tissue with blood vessels in the trabeculae differentiate into red bone marrow
Step 4 of intramembranous ossification: periosteum development
- mesenchyme condense at the edge of the bone to form the periosteum
- compact none replace the surface layer of spongy bone which remains in the center
6 steps of endochondrial ossification
- Develop cartilage model
- Cartilage model growth
- Primary ossification centre development
- Medullary cavity development
- Secondary ossification centre development
- Articulation cartilage and epiphyseal growth plate formation
Step 1 of endochondrial ossification: cartilage model development
Chemical messages cause mesenchyme cells to CROWD together and form the bones shape
- develop chondroblasts: which secrete cartilage extracellular matrix, produce a cartilage model of hyaline cartilage and perichondrium develops around the model
Step 2 of endochondrial ossification: growth of cartilage model
Chondroblasts bury in the extracellular matrix and become chondrocytes
Chondrocytes hypertrophy and surround the cartilage extracellular matrix causing it to calcify
The lacunae form, and chondrocytes begin to die as they can no longer diffuse through the harder matrix, when they die they leave spaces/small cavities
How does growth in length occur when the cartilage model grows
Interstitial endogenous growth: Cell division if the chondrocytes and secretion of cartilage extracellular matrix
How does growth in width occur when the cartilage model grows
Appositional exogenous growth: the deposit of extracellular matrix material on the surface of the model by new chondroblasts of the perichondrium
Step 3 of endochondrial ossification: developing the primary ossification centre
- Nutrient artery penetrate the perichondrium and calcify the cartilage model via nutrient foramen
- This stimulates osteoprogenitor cells to differentiate into osteoblasts
- PERICHONDRIUM becomes PERIOSTEUM when bone is formed
- periosteal capillaries grow into disintegrated calcified cartilage (promotes GROWTH of the primary ossification centre)
- primary ossification center is the SITE where BONE REPLACES CARTILAGE
- osteoblasts deposit bond extracellulsr matrix from calcified cartilage and form spongy bone trabeculae
Step 4 of endochondrial ossification: medullary cavity development
Osteoclasts breakdown the newly formed trabeculae replacing it with compact bone on the diaphysis wall
Step 5 of endochondrial ossification: secondary ossification center development
Branches of the epiphyseal artery ENTER the epiphysis
- difference from primary is that secondary proceeds outwards (from center to surface)
- spongy bone remain in the interior and there is no medullary cavity
Step 6 of endochondrial ossification: formation of articulation cartilage and epiphyseal growth plate
Hyaline cartilage covering the epiphysis becomes articulate cartilage
Hyaline remains at the epiphyseal growth plate and is responsible for lengthwise growth
Interstitial growth vs appositional growth
Interstitial: responsible for length, grows the cartilage of the epiphyseal side of the epiphyseal plate
Appositional: responsible for width which occurs in the diaphysis (in the periosteum and endosteum)
Length of the bone in the diaphysis side occurs by
Replacing cartilage by endochondrial ossification
Process of Appositional growth
Occurs at the surface
1. Periosteal cells differentiate into osteoblasts which secrete collagen fibers and form extracellular matrix
2. The osteoblasts then form into osteocytes and cream a ridge on both sides of the Periosteal blood vessels
3. The ridge enlarges and creates a groove when it folds over and fuses (tunnel) and enclosed around the blood vessel
4. Periosteum becomes endosteum
5. Osteoblasts of the endosteum form the Lamellae
6. tunnel fills and forms Osteons
7. Cycle repeats increasing the thickness of the bone
4 zones of bone growth for length
Resting cartilage
Proliferating cartilage
Hypertrophic cartilage
Calcified cartilage
Resting cartilage
Scattered chondrocytes
Anchor to epiphyseal plate
Proliferating cartilage
Larger chondrocytes arranged in stacks
Divide and replace dead chondrocytes in the diaphysis side and secrete extracellular matrix
Hypertrophic cartilage
Matured chondrocytes arranged in columns
Calcified cartilage
Dead chondrocytes and calcified matrix
Osteoclasts dissolve calcified cartilage
Osteoblasts and capillaries invade and replace cartilage with bone
What is bone remodeling
Replacing old bone tissue with new
What is involved in bone remodeling
Resorption and deposition
Bone resorption is the
Removal of mineral and collagen fibers FROM bone by OSTEOCLASTS (occurs by DESTRUCTION of extracellular matrix)
Bone deposition is the
ADDITION of minerals and collagen fibers TO bone by OSTEOBLASTS (FORM the extracellular matrix)
Process of bone resorption
- Osteoclasts attach to surface (endosteum and periosteum) and form a leak proof seal on the ruffled border
- Osteoclasts then release enzymes to digest collagen fibers and acids that dissolve minerals (from bone)
- Osteoclasts forms a tunnel (like vesicle) in the old bone
- Degraded bone minerals and proteins enter the cell (osteoclast) via Endocytosis, and cross the cell, to then exit via exocytosis on the ruffled border side
- The dissolved substances that exit now enter the interstitial fluid to be resorbed into the blood
- The osteoclasts then leave allowing osteoblasts to move in and rebuild bone
Factors that affect bone growth
minerals, vitamins, hormones, and sex hormones
What minerals help with bone growth
Calcium and phosphate
What minerals help with remodeling
Magnesium, and fluoride
What vitamin stimulates osteoblasts
Vitamin A
What vitamin helps with synthesizing collagen (main bone protein)
Vitamin C
What vitamin helps with building bone and absorbing calcium for bone growth
Vitamin D
What vitamins help with synthesizing bone proteins
Vitamin K and B12
How does insulin-like factors help with bone growth
-IGF stimulates osteoblasts the promote cell division and enhance protein synthesis
How does thyroid hormones help with bone growth
T1 and T2 stimulate osteoblasts
How does sex hormones help with bone growth
Estrogens and androgens
Adrenal glands produce androgens that convert to estrogen
Estrogen increase osteoblast activity and synthesis if the bones extracellular matrix (increase in activity causes growth spurts in adolescents as they have an increase in estrogen during puberty)
In adulthood sex hormones slows resorption of old bone and promotes deposition for remodeling
Estrogen slows resorption by promoting apoptosis of osteoclasts
Why is maintaining calcium levels important
- Nerve and muscle cells depend on stable levels of calcium ion in extra cellular fluid to function for movement
- Important for blood clotting
- Enzymes rely on calcium as a cofactor
- Any change in calcium concentration can be fatal
If calcium concentration is high it can
Stop the heart
If calcium concentration is low it can
Stop breathing
What is the role of bone in calcium concentration
Bone is the body’s biggest calcium reservoir
- maintains the rate of calcium being RESORBED INTO BLOOD and DEPOSITED INTO BONE
- acts as a buffer for blood calcium concentration
Calcium gets released into blood by ______ when levels ______
Osteoclasts
Decrease
Calcium gets absorbed from the blood by _______ when levels _______
Osteoblasts
Increase
How is calcium levels regulated
- The exchange of calcium concentration is mainly regulated by the parathyroid hormone (PTH) secreted by parathyroid glands
- PTH increase blood calcium levels when it is low via negative feedback system
- PTH also act on kidneys (effector) to decrease the loss of calcium in urine by retaining it in the blood
- PTH STIMULATE CALCITROL (a form of Vit D) to promote absorption of calcium into the GI tract from food
- can also be regulated by CALCITONIN which is secreted by parafollicular cells of the thyroid gland (inhibit activity if osteoclasts therefor increase calcium uptake and deposition)
Negative feedback system of low blood calcium levels: stimulus
The blood calcium levels drop
Negative feedback system of low blood calcium levels: receptor
Parathyroid gland cells detect the change
Which increase production of cyclic AMP
Negative feedback system of low blood calcium levels: input
The increase in cyclic AMP is detected intracellularly and sends signals to the control center
Negative feedback system of low blood calcium levels: control center
PTH gene in nucleus of parathyroid gland defects the signal of increase cyclic AMP
Negative feedback system of low blood calcium levels: output
increased PTH synthesis and control center releases more PTH to synthesize
Negative feedback system of low blood calcium levels: effector
The increase level of PTH increase the number and activity of osteoclasts
Osteoclasts act as a catalyst and speed up resorption and release more calcium into the blood from bone to stabilize levels
