A&P Ch. 6 Bones part 2

What is the calcium blood level?

9-11 mg/dL tightly regulated

How much is bone being remodeled? Renewed?

At any given time about 5% of the total bone mass is being remodeled Renewal rate Compact bone 4% per year Spongy bone 20% per year

What happens after the fibrocartilage callus formation?

Bony callus formation Osteoblasts lay down spongy (trabecular) bone Fibrocartilage converts into spongy bone Bony callus lasts 3-4 months Hard callus

What happens if serum levels of calcium decreased?

Detection by parathyroid gland Increase in cyclic AMP which causes increase in parathyroid hormone (PTH) synthesis and release

What factors affect bone growth?

Minerals, vitamins, and hormones

How is bone related to calcium?

Bone is the major storage site for calcium (99%) Role of the bone is the "buffer" of blood calcium levels Releases calcium from bone when blood plasma levels too low Deposit calcium into bone if blood plasma levels too high These processes regulated by hormones

What happens after bony callus formation?

Bone remodeling Bone resorbed by osteoclasts Compact bone replaces spongy bone Healed bone may actually be stronger than it was prior to the break Sometime fracture line undetectable but can see thickened area on surface of bone

After fracture hematoma, what formation occurs?

Fibrocartilage callus formation Procallus- active connective tissue (this is procallus) Fibroblasts synthesize collagen Chondroblasts synthesize fibrocartilage This mass (fibrous tissue and cartilage) bridges the broken ends of the bone Takes about 3 weeks to form Soft callus

What are the steps in fracture repair?

Formation of fracture hematoma Fibrocartilage callus formation Bony callus formation Bone remodeling

What does calcitonin do?

Inhibit osteoclasts in bone so no further breakdown and increases calcium deposition into bone

Hormones in bone

Insulinlike growth factors (IGFs) (important for bone growth) produced by liver and bone tissue (Human growth hormone pathway) Thyroid hormones Insulin Sex hormones Puberty Estrogen and testosterone (estrogen slows bone resorptionn by triggering apoptosis of osteoclasts)

Minerals in bone

Large amounts of calcium and phosphorus are needed for bone Smaller amounts of magnesium, fluoride, and manganese are also needed

What are the parathyroid hormones made from? What is the feedback system?

Made by the 4 parathyroid glands that are located on the posterior surface of the thyroid gland Negative feedback system

During remodeling, after osteoclasts degrade bone, where do old bone components diffuse into? What happens afterward?

Nearby capillaries Afterwards, osteoclasts depart and osteoblasts arrive to lay down new bone

What does calcium do in the body?

Nerve conduction Muscle contraction Many enzymes require calcium for proper functioning Required for normal blood clotting Stored as bone

Is the rate of remodeling the same everywhere?

No Remodeling takes place at different rates in different regions of the body Distal portion of femur replaced every 4 months In contrast, bone in certain areas of shaft of femur will not be replaced completely during a person's life

After a fracture, describe formation of fracture hematoma

Occurs due to blood vessels being ruptured from fracture. A mass of blood forms around fracture. Forms 6-8 hours after injury Clean up by neutrophils and macrophages Angiogenesis This stage can last several weeks

Which cells are involved in bone resorption? Deposition?

Osteoclasts Osteoblasts

Besides bone, where does the PTH act on? What does it stimulate?

PTH also acts on kidney to reabsorb more calcium in the tubular system. Stimulates the production of calcitriol (the active form of Vitamin D) which causes increased absorption of calcium in the upper GI tract.

What happens when PTH is released?

PTH travels to its target tissue-bone Osteoclasts are activated to resorb bone which enters the bloodstream Serum calcium levels return to normal Parathyroid gland ceases increased production of PTH

What happens if there are increased serum calcium levels?

Parafollicular cells (located in the thyroid but totally separate from thyroid hormone producing cells) Synthesize and secrete calcitonin

What does remodeling do for the bone? Triggered when?

Removes injured bone Can be triggered by Exercise Sedentary lifestyle Changes in diet New bone is more resistant to fracture than old bone Shape of bone can also be altered due to stress as well as growth

What happens after osteoclasts degrade tissue?

The degraded tissue enters the osteoclast via endocytosis, is transported across in vesicles, and is released via exocytosis on the side opposite the ruffled border (process of transcytosis) Working together several osteoclasts can carve a small tunnel in old bone

what is the remodeling of bone?

The ongoing replacement of old bone tissue by new bone tissue

Vitamins in bone and function

Vitamin A stimulates osteoblasts Vitamin C needed for synthesis of collagen Vitamins K and B12 needed for synthesis of bone proteins Vitamin D needed for calcium absorption in gut

What do osteoclasts do during remodling?

osteclasts attaches tightly to bone surface at its ruffled border and creates a leakproof seal Releases lysosomal enzymes that digest protein into the sealed pocket