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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
- 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
- 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.
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)
- Located on either end of a long bone
- these are the knoby ends of bone and form joint surfaces
The shaft of a long bone
the transistion between the epiphysis and the diaphysis
- 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.
The growth of lang bones at the epiphyseal plate, and the growth of bones in many other places, occurs through ________ ____ ________.
endochondral bone formation
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
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).
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
- 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
- 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
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
True or False: A balance between osteoblasts and osteoclasts is critical, and is under hormonal control.
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.
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.
What are the three hormones involved in hormonal control of the blood?
- 1. Calcitonin
- 2. Parathytroif hormone (PTH)
- 3. Calcitriol
- inhibirs osteoclasts
- stimulates osteoblasts
- decreases blood calcium
- increases bone formation
Parathyroid hormone (PTH)
- stimulates osteoclasts
- inhibits osteoblasts
- increase blood calcium
- decrease bone formation
- not directly invoved with bone
- however, PTH stimulates kidneys to release calcitriol, which increases absorption of calciumfrom food
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
True or false: Vitamin D is importand in the intestinal absoption of calcium.
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
- 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.