Changes

**Accelerate epiphyseal closure

**Accelerate epiphyseal closure

*Oestrogen  

*Oestrogen  

**Stimulates [[Bones - normal#Normal structure|osteoblasts]] to produce matrix

**Stimulates [[Bones - Anatomy & Physiology|osteoblasts]] to produce matrix

**Inhibits [[Bones - normal#Normal structure|osteoclasts]]

**Inhibits [[Bones - Anatomy & Physiology|osteoclasts]]

*'''Hypogonadism''' in growing skeleton -> delayed epiphyseal closure and skeletal maturation

*'''Hypogonadism''' in growing skeleton -> delayed epiphyseal closure and skeletal maturation

*Hypovitaminosis from dietary deficiency of dam -> teratogenic in pigs and large cats  

*Hypovitaminosis from dietary deficiency of dam -> teratogenic in pigs and large cats  

*More commonly, deficiency in neonates (puppies, kittens, calves, piglets) on vitamin-deficient diets

*More commonly, deficiency in neonates (puppies, kittens, calves, piglets) on vitamin-deficient diets

*Dietary deficiency -> failure of [[Bones - normal#Normal structure|osteoclastic remodelling]] resulting in bone overgrowth and nerve compression

*Dietary deficiency -> failure of [[Bones - Anatomy & Physiology|osteoclastic remodelling]] resulting in bone overgrowth and nerve compression

*Optic nerves particularly affected

*Optic nerves particularly affected

[[Image:Hypervitaminosis A.jpg|right|thumb|100px|<small><center>Hypervitaminosis A (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]

[[Image:Hypervitaminosis A.jpg|right|thumb|100px|<small><center>Hypervitaminosis A (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]

*Main lesions:

*Main lesions:

**Injury to growth cartilage -> [[Bones - normal#Physis (Growth plate)|premature closure of growth plate]]

**Injury to growth cartilage -> [[Bones - Anatomy & Physiology|premature closure of growth plate]]

**[[Bones Degenerative - Pathology#Osteoporosis (Atrophy)|Osteoporosis]]

**[[Bones Degenerative - Pathology#Osteoporosis (Atrophy)|Osteoporosis]]

**'''Exostoses'''

**'''Exostoses'''

*'''Chronic poisoning'''

*'''Chronic poisoning'''

**Grossly:

**Grossly:

***Intense [[Bones - normal#Normal structure|osteoclastic activity]] -> active resorption of bone, especially [[Bones - normal#Bone organisation|trabecular]]  

***Intense [[Bones - Anatomy & Physiology|osteoclastic activity]] -> active resorption of bone, especially [[Bones - Anatomy & Physiology|trabecular]]  

**Microscopically:

**Microscopically:

***Excessive production of [[Bones - normal#Normal structure|osteoid]] - appears both eosinophilic and basophilic in different places

***Excessive production of [[Bones - Anatomy & Physiology|osteoid]] - appears both eosinophilic and basophilic in different places

***Marrow cavity may be obliterated

***Marrow cavity may be obliterated

***Mineralisation of soft tissues, especially [[Arterial Calcification|blood vessel walls]]

***Mineralisation of soft tissues, especially [[Arterial Calcification|blood vessel walls]]

**Due to inhibition of [[Bones - normal#Bone resorption|PTH]] and increase of [[Bones - normal#Bone resorption|calcitonin]]

**Due to inhibition of [[Calcium|Parathyroid Hormone (PTH)|PTH]] and increase of [[Calcium#Calcitonin|calcitonin]]