Locomotion - Bird Loco & Metabolic Bone Disease Flashcards
What are the adaptations of the bird’s musculoskeletal system that enable it to fly?
Feathers
Wings
Pneumatic bones
Extended sternum for attachment of wing muscles (pectoralis muscles for adduction of wings)
Numerous bones fused
Ventral musculature
Triosseal canal
What is the purpose of the triosseal canal?
The coracoid, the scapula and the furcula (fused clavicles “wishbone) form the triosseal canal, which houses a strong tendon that connects the supracoracoideus muscles to the humerus. This system is responsible for lifting the wings during the recovery stroke.
What is the role of calcitonin in calcium homeostasis?
What is different in birds compared with mammals with regard to the production of calcitonin, the hormone that reduces serum calcium levels?
Calcitonin reduces the level of calcium absorbed from bones by first inhibiting the absorption of bone calcium by osteoclasts and then reducing the formation of osteoclasts.
In mammals, calcitonin is secreted by the parafollicular C-cells of the thyroid gland. The cells are stimulated by hypercalcaemia: too much calcium in blood causes the parafolliculr cells to secrete more calcitonin.
In birds, calcitonin is secreted by the C-cell-like cells of the ultimobranchial glands.
Are serum-calcium levels increased quicker or slower in response to parathyroid hormone secretion by the parathyroid’s chief cells?
Much quicker
Do birds need Vitamin D supplements if they are free-range and spend all day in the sun?
No.
Does calcitonin play a major or minor role in calcium metabolism in birds relative to its role in domestic animals?
Minor.
Reproductive hormones play a role in avian metabolism of calcium. What are these hormones?
Oestrogen
Androgens
Prostaglandins
Which is the active form of calcium in the body?
A. Ionized calcium
B. Calcium bound to proteins such as albumin
C. Calcium bound to anions
D. None of the above
A. Ionized calcium
The ionized calcium is the physiologically active form, with important roles in bone homeostasis, muscle and nerve conduction, blood coagulation, eggshell calcification, and control of hormone secretions such as vitamin D3 and parathyroid hormone (PTH).
Mammals have about 50% of the extracellular calcium in ionized form, whereas in birds, the ionized form ranges from 20% to 60% of the extracellular calcium.
What percentage of calcium in the body is extracellular?
Less than 0.1%
Which calcium in the body is tightly regulated by PTH, calcitonin and Vitamin D3 metabolites in serum?
A. Intracellular calcium
B. Hydroxyapatite (bone calcium)
C. Extracellular calcium
D. None of the above
C. Extracellular calcium
Approximately 40% of the extracellular calcium is protein bound, mainly to albumin and vitellogenin in birds, and considered to be physiologically in-active (unable to diffuse across capillary membranes). Protein-bound calcium serves as a storage pool or buffering system for ionized calcium. Any change in the serum albumin levels will directly affect the total calcium levels.
The remaining extracellular calcium is bound to interstitial ions (lactate, citrate, bicarbonate), able to diffuse across capillary membranes as ionized calcium.
What percentage of a bird’s calcium stores are in its eggs?
On average, 10%. More for smaller birds that lay proportionally bigger eggs.
What are the two main sources of calcium mobilisation used by birds?
- Intestinal absorption of calcium (70% - much higher in birds than in mammals), largely in response to Vit. D3
- Resorption from medullary bone in hens, in response to gonadal steroids
What is special about the way birds respond to the different forms of active Vitamind D - Vit. D3 (cholecalciferol) and Vit. D2 (ergocalciferol)?
Vita- min D2, which occurs naturally in plants, has only one tenth the efficacy of vitamin D3 in birds.
How does oestrogen affect calcium metabolism in hens?
It increases the availability of calcium in the medullary bones:
At the onset of sexual maturity, with the rise of estrogen concentration in circulation, the function of osteoblasts changes from forming lamellar cor- tcal bone to producing spicules of nonstructural medullary bone in the end-osteal surface than can fill the entire bone cavity.
Medullary bone formation may be initiated by the sex hormones without the presence of vitamin D3 but complete mineralization can only occur if vitamin D3 levels are adequate.
Medullary bone is most prominent in the pelvic limb long bones (femur and tibiotarsus) but can also occur in the thoracic limb long bones (humerus, radius, and ulna) and in other areas of the skeleton.
Medullary bone formation starts around 2 weeks before initiation of egg laying and can be responsible for a 25% increase in the dry fat-free skeletal weight
