Bone Growth & Development

General Features

Long Bone Longer than they are

wideConsists of diaphysis (central shaft) & Epiphysis (two ends)Epiphysial plate – for growing bonesEpiphysial line – when growth stops

Short Bone Approx. as broad as

they are longExamples: wrist & ankle bones

Flat Bones Have a relatively thin,

flattened shapeExamples: certain skull bones, ribs, scapulae, and sternum

Irregular Bones Bones not included in

the previous categoriesVertebrae and facial bones

Histological Structure

Cells Osteocyte – mature bone cell, enclosed in lacuna Osteoblast – bone-forming cell; secretes collagen fibers and calcium salts of bone tissue Osteoclast – bone-destroying cell; breaks down ECM to release calcium into the bloodstream

O S T E O B L A S T

O S T E O C L A S T

BAGOB CRAC

Compact BoneMostly solid matrix cells

Spongy BoneConsists of a lacy network of bone wit many small, marrow filled spaces

Marrow

Yellow marrow – fatRed marrow – blood forming cells

Matrix A bonding of multiple fibers and chemicals of different materials Primarily collagen fibers and crystalline salts

Matrix The crystalline salts deposited in the matrix of bone are composed principally of calcium and phosphate, which are combined to form hydroxyapatite crystals.

Calcium (Ca), phosphate (PO4), and hydroxide (OH)

Ca10[PO4]6[0H]2

Growth & Development

Pre-natal Ossification

1. Intramembranous Bone develops from fibrous membrane Forms bones of skull and clavicle (all flat bones) Begins at 8 weeks of development

2. Endochondral Bone develops from

hyaline cartilage Forms all bones below

base of skull Begins 2nd month of

development

Nutrition

Hormonal secretions

Physical exercise  

Factorsfor bonedevelopment

Nutrition

CalciumMakes up 2% of body weight99% Stored in bonesA narrow range of 9-11 mg Ca/100 ml blood maintained at all times.Bone remodeling - key in maintaining proper blood calcium levels

Calcium1% Constant supply of Ca2+ in the blood stream needed for:◦Transmission of nerve impulses◦Muscle contraction◦Blood coagulation◦Cell division

PhosphorusA major mineral in the body's bone crystal, phosphorus is found in dairy products and meat.

MagnesiumPrimarily found in bone crystals, magnesium improves bone strength.Older adults are more likely to be deficient in magnesium.Calcium supplements that contain magnesium can help.

Vitamin KNecessary for bone formation and mineralization, blood clotting, and may assist in channelling calcium directly to the bone rather than the blood vessels.

Vitamin CCollagen is the main protein in bone, and Vitamin C is necessary for collagen synthesis.Vitamin C is present in citrus fruits and tomatoes and in many vegetables.

Vitamin ANecessary for cells to differentiate normally and for normal skeletal growth, and also is extremely important for eye health.Too little vitamin A is a major cause of blindness worldwide.Too much vitamin A can cause bone loss and increase the risk of hip fracture.

Vitamin DVitamin D is necessary for the proper absorption of calcium in the small intestine.

Physical exercise

Physical exercise◦Pull of gravity & muscles◦Activates osteoblasts◦If not active, activates osteoclasts - atrophy

Exposure to sunlight

Exposure to sunlight

Exposure of skin to the ultraviolet portion of sunlight is favorable to bone development, because the skin can produce vitamin D when it is exposed to such radiation.

Hormones

Hormones

Pituitary GlandThyroid glandParathyroid glandsOvaries and testes

Growth Hormone (Somatotropin) From: Pituitary gland Stimulates activity in the epiphyseal plates Main regulator of height

Other fx stimulates bone and muscle growthmaintains the normal rate of protein synthesis in all body cellsspeeds the release of fats as an energy source for growth

Parathyroid Hormone

From: Parathyroid glands

Parathyroid Hormone Low blood calcium Releases PTH Stimulates osteoclasts to break down bone tissue, and as a result, calcium salts are released into the blood.

Calcitonin

From: Thyroid gland

Calcitonin Blood calcium level is excessively high Releases  calcitonin Inhibits osteoclast activity allowing osteoblasts to form bone tissue. The excessive calcium is stored in matrix.

Sex Hormones ↑ - Hinders osteoclast production ↓ - Increased cytokines, Increast osteoclast

Sex HormonesAgingHypogonadism-Diminished functional activity of the gonads-Hypoandrogenism & Hypoestrogenism