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jnikrap
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Dense regular connective tissue is represented in the skeletal system by ________, band-like structures that strap one _____ to _____.
ligaments, bone, another
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Ligaments
- Ligaments join bones together (Tendons join muscles to bone)
- the strong parallel orientation fo collagen fibers at the microscopic level gives ligaments a striated appearance
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Periosteum
- a very important dense irregular tissue in the skelatal system
- a thin membrane that surrounds all bones.
- paperl-like membrane theat you encounter on the suface of ribs at a barbecue
- it has a rich blood supplay
- has plenty of nerve endings, so its the source of both blood (swelling) and pain when you break a bone
- it connects tendons and ligaments to bones
- its also important in bone repair and remodeling.
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What are the freatures of a long bone?
- they are longer than they are wide
- cylindrical bones like the femur, tibia and fibula of the lowere extremity, and the phalanges(finger and toe bones of the upper and lower extremities)
- Three natural parts ( or regions) of long bones
- 1. epiphysis (nearest articular surfaces)
- -proximal epiphysis
- - distal epiphysis
- - these are where new bone develope in children
- - in adults epiphyseal line is a rmnant of this location
- 2. metahpysis
- 3diaphysis ("shaft" of bone)
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epiphysis
- Located on either end of a long bone
- these are the knoby ends of bone and form joint surfaces
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diaphyisis
The shaft of a long bone
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Mataphysis
the transistion between the epiphysis and the diaphysis
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epiphyseal plate
- the site if bone growth in an immature skeleton
- this increases the length of long bones until the pituitary stops providing human growth hormone( hGH)
- when epiphyseal plate continues growth -the plates are "open"
- when hGH levels drop- the plates "close" or become mineralized.
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The growth of lang bones at the epiphyseal plate, and the growth of bones in many other places, occurs through ________ ____ ________.
endochondral bone formation
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Endochondral bone formation
- bone formation using a cartilage "model" to shape the bone
- cartilage is evetually replaced with compact or spongy bone
- In fetuses and young children, many of the future bones are conpletely cartiliginous.
- Primary Ossification center appears in the center of a forming bone where the diaphysis will be
- Later secondary ossification center will develope near the joint surface.
- Both of these will expand, the leftover region of cartilage between these is where the epiphyseal plate lies
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epiphyseal line
the remnant of the epiphyseal plate, found in adults, who are done growing in height (this is seen as a landmark in x-rays of bone).
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Intramembranous bone formation
- again the future bone begins as a cartilage model
- they are multiple ossification centers that start as islands and then spreat outward. As these spread, they form spongy bone.
- Along the out side of the bone, spongy bone eveentually remodels to a thin shell of compact bone with the spongy bone remaining in the center
- Occurs in bones of he skull and other flat bones
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Osteoblasts
- they make bone
- they lay down the organic and inorganic extyracellular matrix of bone
- they follow behaind osteoclasts rebuilding bone
- in this way bone is constanly remodeled
- If osteoblastic activity > osteoclastic activity
- -calcium is deposited into inoganic matrix
- -bone becomes thicker and stronger
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Osteoclasts
- brake bone into pieces
- they constantly travel throu bone, using acid to dissolve mineralized matix and enzymes to dissolve organic matrix
- If osteoclasts activity > osteoblasts activity
- -calcium is released from inorganic matrix into bloodstreem
- -bone becomes thinner and weaker
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If blood _________ is low, the body breaks down ________ _______ to release calcium into the bloodstream. If blood calcium is high, the body stores ______ in ______for future needs.
calcium, mineralized bone, calcium, bone
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True or False: A balance between osteoblasts and osteoclasts is critical, and is under hormonal control.
True.
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If you have low blood calcium...
- the body withraws calcium from its calcium "bank": bone tissue
- Parathyroid hormone is released from a set of small pea-shaped glands next to the thyroid
- this increased osteoclasts activity
- Osteoclasts break down the mineral portion of bone and calcium is released into the bloodstream.
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If blood calcium is too high...
- Calcitonin is made by parafolicular cells (C cells) in the thyroid gland
- -it is released when calcium is high and stimulates osteoblasts
- Theses absorb calcium form the bloodstream and dposit it as hydroxyapatite in bone.
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What are the three hormones involved in hormonal control of the blood?
- 1. Calcitonin
- 2. Parathytroif hormone (PTH)
- 3. Calcitriol
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Calcitonin
- inhibirs osteoclasts
- stimulates osteoblasts
- decreases blood calcium
- increases bone formation
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Parathyroid hormone (PTH)
- stimulates osteoclasts
- inhibits osteoblasts
- increase blood calcium
- decrease bone formation
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Calcitriol
- not directly invoved with bone
- however, PTH stimulates kidneys to release calcitriol, which increases absorption of calciumfrom food
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There are two D vitamins. Vitamin D2 (___________) and vitamin D3 (___________) are made in the skin with the help of UV-B light (i.e. ______ _______).
ergocalciferol, cholecalciferol, natural sunlight
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True or false: Vitamin D is importand in the intestinal absoption of calcium.
true.
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In the absences vitamin D...
- blood calcium levels drop and bones become soft and flexible (bones are nostly colagen because mineral portion is lacking)
- In children this results in rickets
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Osteomalacia
- In adults, inability to form mineralized bone
- May result from metabolic disturbances, cancer, or cancer chemotherapy
- Scan shows radioactiv 99Tc concentrating in areas that are making organic bone matrix but not the inorganic materialized porttionof bone.
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