Unit 6

How does calcitonin help lower the calcium ion concentration of blood?

2 major functions i) Inhibiting osteoclast activity ii) Increasing the rate of excretion of calcium ions by the kidneys

What effect would increased PTH secretion have on blood calcium levels?

3 major effects i) Stimulating osteoclast activity and enhancing the recycling of minerals by osteocytes. [PTH also stimulates osteoblast activity, but to a lesser degree] ii) Increasing the rate of intestinal absorption of calcium ions by enhancing the action of calcitriol. Under normal circumstances, calcitriol is always present, and parathyroid hormone controls its effect on the intestinal epithelium. iii) Decreasing the rate of excretion of calcium ions by the kidneys.

How could x-rays of the femur be used to determine whether a person has reached full height?

At puberty, the combination of rising levels of sex hormones, growth hormone, and thyroid hormones stimulates bone growth dramatically. Osteoblasts now begin producing bone faster than chondrocytes are producing new epiphyseal cartilage. As a result, the osteoblasts "catch up" and the epiphyseal cartilage gets narrower and narrower until it ultimately disappears. The timing of this even can be monitored by comparing the width of the epiphyseal cartilages in successive x-rays.

Explain how heavy-metal ions could be incorporated into bone matrix.

Because of their biochemical similarity to calcium, heavy metal ions such as lead, strontium, cobalt, or radioactive uranium or plutonium can be incorporated into the matrix of bone. (Example - Chernobyl nuclear reactor incident).

During intramembranous ossification, which type of tissue is replaced by bone?

Fibrous connective tissue is replaced when osteoblasts differentiate within a mesenchymal (fibrous connective tissue).

How would the compressive strength of a bone be affective if the ratio of collagen to hydroxyapatite increased?

Hydroxyapatite make the bone hard, by adding more collagen the bone would become flexible allowing for twisting and bending of the bone. However the more collagen the less compression the bone can handle.

List the steps involved in fracture repair, beginning at the onset of the bone break.

In even a small fracture, many blood vessels are broken and extensive bleeding occurs. i) Fracture hematoma, a large blood clot soon closes off the injured vessels and leaves a fibrous meshwork in the damaged area. ii) An internal callus forms as a network of spongy bones unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges. iii) As repair continues, osteoblasts replace the central cartilage of the external callus with spongy bone. When this conversion is complete, the external and internal calluses from an extensive and continuous brace at the fracture site. Struts of spongy bone now unite the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced. iv) Osteoclast And osteoblast continue to remodel the region of the fracture for a period ranging from four months to well over a year. When the remodeling is complete, the bone of the calluses is gone and only living compact bone remains. (The bone may be slightly thicker and stronger than normal at the fracture site).

Define osteopenia?

Inadequate ossification. The bones of the skeleton become thinner and weaker as a normal part of the aging process.

A 7-year old child has a pituitary gland tumor involving the cells that secrete growth hormone (GH), resulting in increased levels of GH. How will this condition affect the child's growth?

Increased levels of GH would result in excessive bone growth causing abnormal bone development much like that of gigantism.

Identify the hormones involved in stimulating and inhibiting the release of calcium ions from bone matrix?

Parathyroid hormone and calcitonin, coordinate the storage , absorption, and excretion of calcium ions. 3 target sites and functions are involved: i) The bones (storage) ii) The digestive tract (absorption) iii) The kidney (excretion)

Why is osteoporosis more common in older women than in older men?

Sex hormones are important in maintaining normal rates of bone deposition. After menopause, the condition accelerates due to a decline in circulating estrogens. Men continue to produce androgens until late in life.

A child who enters puberty several years later than the average age is generally taller than average as an adult. Why?

Since bone remodeling is an ongoing process and the child that enters puberty later will have continued to grow therefore the epiphyseal closure will happen later. (allowing the bone structure to continue to grow before being stopped by the epiphyseal closure)

At which point in fracture repair would you find an external callus?

Step number 2, an external callus, or enlarged collar of cartilage and bone forms and encircles the bone at the level of the fracture.

If the activity of osteoclast exceeds the activity of osteoblast in a bone, how will the mass of the bone be affected?

The bone would become less dense, bones would weaken.

What effect would increased PTH secretion have on blood calcium levels?

The bones of children with rickets are so poorly mineralized that they become very flexible. Because the walls of each femur can no longer resist the tension and compression forces applied by the body weight, the bones bend laterally and affect individuals develop a bowlegged appearance. (Lack of vitamin D).

In endochondral ossification, what is the original source of osteoblasts?

The cells of the inner layer of the perichondrium in this region then differentiate into osteoblasts and begin producing a thin layer of bone around the shaft of the cartilage.

Describe bone remodeling.

The organic and mineral components of the bone matrix are continuously being recycled and renewed through the process of remodeling.

A sample of bone has lamellae, which are not arranged in osteons. Is the sample most likely taken from the epiphysis or diaphysis?

The sample would be found in the epiphysis because in the spongy bone, lamellae are not arranged in osteons.

Why would you expect the arm bones of a weight lifter to be thicker and heavier than those of a jogger?

The turnover and recycling of minerals give each bone the ability to adapt to new stresses. Whenever a bone is stressed, the mineral crystals generate minute electrical fields. Osteoblasts are apparently attracted to these electrical fields and, once in the area, begin to produce bone. (this finding has led to the successful use of small electric fields in stimulating bone healing).

Define bone markings.

a) Elevation and projections i) Process ii) Ramus b) Processes of formed where tendons or ligaments attach i) Trochanter ii) Tuberosity iii) Tubercle iv) Crest v) Line vi) Spine c) Process formed for articulation with adjacent bones i) Head ii) Neck iii) Condoyle iv) Trochlea v) Facet d) Depressions i) Fossa ii) Sulcus e) Openings i) Foramen ii) Canal iii) Meatus iv) Fissure v) Sinus

Name the five primary functions of the skeletal system

a) Support b) Storage of Minerals and Lipids c) Blood Cell Production d) Protection e) Leverage

Identify the six broad categories for classifying a bone according to shape.

a) Sutural bones (wormian bones) b) Irregular bones c) Short bones d) Flat bones e) Long bones f) Sesamoid bones

Compare the structures and functions of compact bone and spongy bone.

a) The basic functional unit of mature compact bone is the osteon, or Haversian system. In an osteon, the osteocytes are arranged in concentric layers around a central canal, or Haversian canal which contains a capillary & a venule. Unlike spongy bone compact bones thrive at stress points. compact is solid, strong, and resistant to bending b) Spongy bone, lamellae are not arranged in osteons. The matrix in spongy bone forms a meshwork of supporting bundles of fibers called trabeculae which have NO capillaries or venules in the matrix of the spongy bone. Spongy bone receives its nutrients by diffusion along canaliculated that open onto the surface of trabeculae, red bone marrow is found between the trabeculae of spongy bone and blood vessels within this tissue deliver nutrients to the trabeculae and remove wastes generated by the osteocytes. Spongy bone provides strength and its bony plates are most highly developed in the regions of the epiphyses that are subjected to forces of compression. Both compact and spongy tissues are usually present in every bone. Compact bone in the diaphysis of a long bone forms a rigid tube with a hollow chamber called the "medullary cavity." The cavity is continuous with the spaces of the spongy bones.

Mature bones cells are known as _______, bone-building cells are called _______ and _____ are bone-resorbing cells.

osteocytes osteoblasts osteoclast