Changes

==Overview==

==Overview==

[[Image:Horse Skeleton.jpg|thumb|right|250px|Horse Skeleton - Copyright Nottingham]]

[[Image:Horse Skeleton.jpg|thumb|right|250px|Horse Skeleton - Copyright Nottingham]]

Bone comprises the structure of the skeletal system and provides lever arms for locomotion. Bone also plays important roles in maintaining mineral homeostasis, as well as providing the environment for [[Haematopoiesis - Overview|hematopoesis]] in [[Bone Marrow|marrow]].

Bone comprises the structure of the skeletal system and provides lever arms for locomotion. Bone also plays important roles in maintaining mineral homeostasis, as well as providing the environment for [[Haematopoiesis - Overview|hematopoesis]] in [[Bone Marrow|marrow]].

==Bone Growth==

==Bone Growth==

 

===Length===

===Length===

The '''epiphyseal growth plate (EGP)''' is a transverse disc of cartilage between the two ossification centers and allows the bone to continue to grow in length after birth. It then closes. The EGP is a region of continuous chondroblast differentiation and maturation and can be divided into five zones:

The '''epiphyseal growth plate (EGP, physis)''' is a transverse disc of cartilage between the two ossification centers and allows the bone to continue to grow in length after birth. It then closes. The EGP is a region of continuous chondroblast differentiation and maturation and can be divided into five zones:

# '''Germinal Zone''' - chondroblast division at a low rate, and self renewal.

# '''Germinal Zone''' - chondroblast division at a low rate, and self renewal.

Found in the skull, pelvic girdle, and scapula. It expands in two directions, with a broad surface for attachment of large muscle masses and protection of underlying structures.

Found in the skull, pelvic girdle, and scapula. It expands in two directions, with a broad surface for attachment of large muscle masses and protection of underlying structures.

4. '''Sesamoid Bones'''

4. '''Irregular Bone'''

 

 

5. '''Sesamoid Bone'''

Eg. Patella and navicular bone. Found within tendons, where they change direction over prominences that would otherwise cause damage. They form '''synovial joints''' with major bones with which they are in contact. They also serve to displace tendon from the axis of the joint, increasing the leverage exerted by the muscle.

Eg. Patella and navicular bone. Found within tendons, where they change direction over prominences that would otherwise cause damage. They form '''synovial joints''' with major bones with which they are in contact. They also serve to displace tendon from the axis of the joint, increasing the leverage exerted by the muscle.

5. '''Splanchnic Bones'''

6. '''Splanchnic Bone'''

Develop in soft organs remote from skeletal connection, eg. '''os penis'''.  

Develop in soft organs remote from skeletal connection, eg. '''os penis'''.  

6. '''Pneumatic Bones'''

7. '''Pneumatic Bone'''

Excavated to contain air spaces, such as the skull in the instance of paranasal sinuses, and the post-cranial skeleton of birds.

Excavated to contain air spaces, such as the skull in the instance of paranasal sinuses, and the post-cranial skeleton of birds.

'''Osteoclasts'''

'''Osteoclasts'''

Osteoclasts are giant (multinucleate [[Monocytes|monocytes]]) cells. Histologically, they are large, often multinucleated cells. They have an acidophilic cytoplasm. They sit in the bone surface depression known as, '''howship's lacuna'''. Osteoclasts respond to [[Calcium#Calcitriol (Activated Vitamin D3)|vitamin D by increasing their numbers and activity (parathyroid independent). Osteoclasts act to resorb the bone extracellular matrix (ECM). They firstly dissolve mineral followed by collagen, using the brush border. They do <u>not</u> have receptors for PTH, but do have receptors for [[Calcium#Calcitonin|calcitonin]].  

Osteoclasts are giant (multinucleate [[Monocytes|monocytes]]) cells. Histologically, they are large, often multinucleated cells. They have an acidophilic cytoplasm. They sit in the bone surface depression known as, '''howship's lacuna'''. Osteoclasts respond to [[Calcium#Calcitriol (Activated Vitamin D3)|vitamin D]] by increasing their numbers and activity (parathyroid independent). Osteoclasts act to resorb the bone extracellular matrix (ECM). They firstly dissolve mineral followed by collagen, using the brush border. They do <u>not</u> have receptors for PTH, but do have receptors for [[Calcium#Calcitonin|calcitonin]].  

Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from the stromal fibroblastic system ('''osteoprogenitor cells'''). Osteoclasts are derived from the haematopoietic system.

Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from the stromal fibroblastic system ('''osteoprogenitor cells'''). Osteoclasts are derived from the haematopoietic system.

==Organization of Bone==

==Organisation of Bone==

The normal progression of bone is from woven bone to lamellar bone, even in pathology, except for [[Bones Hyperplastic and Neoplastic - Pathology#Craniomandibular osteopathy|canine craniomandibular osteopathy]] and [[Bones Metabolic - Pathology#Hypervitaminosis D|hypervitaminosis D]], where lamellar bone is replaced by woven bone.

The normal progression of bone is from woven bone to lamellar bone, even in pathology, except for [[Craniomandibular Osteopathy|canine craniomandibular osteopathy]] and [[Hypervitaminosis D|hypervitaminosis D]], where lamellar bone is replaced by woven bone.

===Woven bone===

===Woven bone===

[[Category:Musculoskeletal System - Anatomy & Physiology]]

[[Category:Bone and Cartilage - Anatomy & Physiology]]

[[Category:A&P Done]]

[[Category:A&P Done]]