Path 1 - Endocrine 5

isabellepjk's version from 2018-03-03 00:38

Endocrinology 6.5: Parathyroid Gland

Question Answer
WHAT DOES PTH DO?It acts to ↑ the concentration of Ca in the blood (usually via bone resorption)
If I say Hypoparathyroidism, what condition are you thinking of?Hypocalcemic tetany/ Milk fever
***If I say Hyperparathyroidism, what 2 conditions are you think?Fibrous Osteodystrophy & Hypercalcemia
What are 2 possible czs of Hypoparathyroidism?(1) Lymphocytic parathyroiditis
(2) Parturient paresis (milk fever)
**Parturient paresis (milk fever) → Due to/prob w/ HYPO or HYPER parathyroidism?HYPO! Cow will be down w/in a few hours!!
Parturient paresis (milk fever) occurs in who? How? What are the resulting derangements?Occurs in cows fed a ↑ Ca diet prepartum. Then there is an inadequate response of parathyroids to sudden Ca loss in milk, especially in face of anorexia & ↑ calcitonin secretion prepartum. Bc of this there are derangements progressive hypocalcemia, hypophosphatemia & paresis w/ the onset of lactation
What happens w/ Ca & P in milk fever? What are the main results of this clinically?HYPOcalcemia, HYPOphosphatemia (bc hypoparathyroidism). This will result in PARESIS when the cow starts to lactate
What risk factor ↑ the risk of parturient paresis (milk fever)? ↓ risk?Risk ↑ w/ ↑ Ca diets & risk ↓ w/ diets ↓ in Ca or diets supplemented w/ therapeutic doses of Vit D
Explain why if a cow is fed lots of Ca, that it will cz HYPOcalcemia & HYPOphosphatemia postpaturenetly?Cows fed ↑ Ca diet are less able to maintain serum Ca near parturition. This is bc w/ ↑ [blood Ca2+], PTH secretion ↓ (pre parturition). Plasma PTH lvls are lower prepartum w/ a further decline at 48 hours postpartum... thus, ↓ mobilization of Ca2+ from bone (bc less PTH was being secreted to begin w/ since it didnt have to bc cow was eating lots of Ca). ALSO!!! Since they are being fed a lot of Ca → hypercalcemia. In response to the hypercalcemia, CT (calcitonin) secretion is ↑ w/ ↓ bone resorption near parturition → hypocalcemia & THEN things are compounded when anorexia associated w/ ↑ blood estrogen lvls at parturition ↓ intestinal Ca absorption


Question Answer
What are the 2 kinds of Hyperparathyroidism?1º & 2º
What is happening in 1º hyperparathyroidism?Fxnal neoplasms of chief cells
parathyroid hyperplasia
parathyroid adenomas
parathyroid carcinomas
What is happening in 2º hyperparathyroidism?Can be due to nutritional imbalances OR renal dz
**What are the 3 neoplasms which are seen in 1º hyperparathyroidism? Which is more common & happens most commonly in who?(1) Parathyroid Hyperplasia
(2) Parathyroid Adenomas = MORE COMMON (occur in older dogs; usually single, encapsulated & fxnal)
(3) Parathyroid Carcinomas (rarely)
**Explain what is happening in 1º hyperparathyroidism which leads to lameness?Tumor produces excess PTH → osteolytic & osteoclastic bone → fibrous osteodystrophy → lameness due to fractures
1º hyperparathyroidism → What would the lab parameters look like? What would the overall temperment of the animal be? How would the GI be affected? How is the renal system affected?Hypercalcemia
Polyuria & Polydipsia
How does hyperparathyroidism affect the musculoskeletal system?Weakening of bones & generalized muscular weakness due to ↓ neuromuscular excitability
**Dietary 2º hyperparathyroidism happens in who? Which species in which dietary circumstances, specifically?This can occur in all species, but especially in:
Dogs & cats on all-meat diets
Horses on ↑ grain/poor quality roughage or all-bran diets (Miller's Dz)

Nonhuman primates
**In general terms, which kind of diets lead to dietary 2º hyperparathyroidismGenerally, ↓ Ca ↑ P diets
Why can a diet ↑ in P lead to 2º nutritional hyperparathyroidism?Interferes w/ the intestinal absorption of Ca
Which type of diet has SWINE at a risk of 2º hyperparathyroidism?Unsupplemented cereal grain rations
*Which type of diet has CATS/DOGS at a risk of 2º hyperparathyroidism?All-meat diets
*Which type of diet has HORSES at a risk of 2º hyperparathyroidism?↑ grain/poor quality roughage or all-bran diets
Renal 2º hyperparathyroidism usually happens in who?Mainly dogs & cats
**Explain how renal failure leads to 2º hyperparathyroidismRenal dz, the kidney is unable to save Ca or excrete P so P starts building up in the system (due to ↓ GFR)
ALSO kidney has impaired activation of Vit D3 (effect on intestine/kidney is ↓ renal degradation of PTH so ↑ PTH means body sucks more Ca out of bones → RUBBER JAW IN DOGS & CATS
What are the lesions formed in both types of 2º hyperparathyroidism?Bilateral enlargement of parathyroids, fibrous osteodystrophy
Explain the pathogenesis of Fibrous osteodystrophyThere is a hypocalcemia, so PTH needs to ↑ in order to keep the Ca balance in the blood. Inc PTH czs bone resorption via ↑ osteoclastic resorption of cancellous & cortical bone w/ proliferation of fibrous tissue
How does fibrous osteodystrophy present in horses?"Big head" dz


Question Answer
What IS Pseudohyperparathyroidism? How does it happen?Paraneoplastic syndrome characterized by hypercalcemia & hypophosphatemia. This is due to the secretion of humoral factors from tumor cells (e.g., PTH-related protein [PTH-rP] which mimics the action of PTH)
How come hypercalcemia occurs in pseudohyperparathyroidism?Stimulation of osteoclastic bone resorption
↑ Ca reabsorption from the kidney
↑ Ca absorption from the intestinal tract
(all this is stimulated by the tumors humoral factors, ie PTH-rP)
What are the 3 mechanisms behind pseudohyperparathyroidism?(1) Humoral hypercalcemia of malignancy (HHM)
(2) Hypercalcemia induced by metastases of solid neoplasms to bone
(3) Hematologic malignancies
Humoral hypercalcemia of malignancy (HHM) → What are some possible humoral factors produced by the tumor which lead to a hyperparathyroid-like state?PTH
Vit D3
Hypercalcemia induced by metastases of solid neoplasms to bone → How common is this? Explain how this worksUncommon in animals. The tumors which have metastasized to the bone secrete cytokines that stimulate local bone resorption. There is ALSO indirect stimulation of bone resorption by tumor-induced cytokine secretion from local immune or bone cells (such as PTH-rP, TGF-α & -β & prostaglandin E2)
Hematologic malignancies leading to pseudohyperparathyroidism → What are 2 tumors that can cz this?Lymphosarcoma, multiple myeloma (B-cell tumor)
(Pseudohyperparathyroidism) adenocarcinoma of apocrine glands of the anal sac → Who does this occur in most often? What are the blood Ca & P levels like? What are the clinical signs?Mainly occurs in female dogs. You will see persistent hypercalcemia & mild hypophosphatemia.
Clinical signs:
Generalized muscular weakness
Polyuria & Polydipsia