انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة

the bone4

الكلية كلية طب الاسنان     القسم  العلوم الاساسية     المرحلة 2
أستاذ المادة ندى مهدي عبد الرضا الخفاجي       16/01/2020 05:06:00
Bone Development : Human bones grow until about age 25
1- Osteogenesis: bone formation
2- Ossification: the process of replacing other tissues with bone
Osteogenesis and ossification lead to:
The formation of the bony skeleton in embryos, bone growth until early adulthood ,bone thickness, remodeling, and repair through life.
Bones development being in the embryo by two distinct processes
1- Intramembranous ossification : is the process by which mesenchymal tissue is directly replaced by bone without an intermediate cartilage step. It occurs most notably in the bones of the skull.
2- Endochondral Ossification: occurs in the embryo when mesoderm initially forms a hyaline cartilage model, which then develops a primary ossification center at the diaphysis .Later, secondary ossification center form at the epiphysis at each end of the bone . Bones that form via endochondral ossification include the humerus ,femur ,tibia and other long bones.

Growth in length of long bones
Occurs at the epiphyseal plate, which includes a number of zones as indicated below
a-the zone of reserve contains resting chondrocytes.
b-the zone of proliferation contains chondrocytes undergoing mitosis and forming isogenous groups.
c- the zone of hypertrophy contains hypertrophied chondrocytes, which secrete alkaline phosphatase to increase calcium and phosphate levels.
d- the zone of calcification contain dead chondrocytes and calcified cartilage matrix called spicules .
e- the zone of ossification contain Osteoprogenitor cells that congregate on spicules and differentiate into osteoblasts. Osteoblasts deposit bone on the surface of spicule to form a mixed spicule , which consists of calcified cartilage matrix and bone .



Growth in diameter of long bones
Occurs at the diaphysis by deposition of bone at the periphery (oppositional growth) as Osteoprogenitor cells within the periosteum differentiate into osteoblasts.

Bone Remodeling
Remodeling is the mechanism by which older bone is replaced by the coordinated action of bone (resorbing the osteoclasts and bone forming osteoblasts. This follows a specific sequence of events, and takes about three months in total to complete:
1- Activation - Osteoblasts induce osteoclasts to break down bone matrix. This process lasts for approximately 3 days.
2- Resorption - In resorption, the ruffled border of the osteoclast forms a sealing zone which isolates the area of bone erosion. Organic acids and lysosomal enzymes dissolve the mineral component and break down the organic matrix. This process occurs at approximately 14 days.
3- Reversal - Osteoblasts begin to replace osteoclasts at the site of bone turnover.
4- Formation - Osteoblasts begin to lay down new lamellar bone on top of old bone. In doing so, cement lines are created to mark the borders between old and new bone matrix. This can take up to 70 days to complete.

Hormonal mechanism
-rising blood ca +2 levels trigger the thyroid to release calcitonin
- calcitonin stimulates calcium salt deposit in bone
* parathyroid hormone binds to receptor in osteoblast this is a signal to produce a osteoclast stimulating factor which increase the number of osteoclast and release ca+ in to blood
Red bone marrow supplies nutrients to osteocytes in trabeculae forms red and white blood cells. Yellow bone marrow yellow because it stores fat, located in the skull,sternum,pelvis & the ends of long bones.


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .