Which hormone is most abundant?
T4
Parathyroid glands are:
Pea sized glands located on the posterior thyroid
Parathyroid glands can be:
Ectopic in about 10-20% of the population
Blood supply to the parathyroid
Inferior thyroid arteries, drain into thyroid veins & lymphatics
Parathyroid is adjacent to
Right and left recurrent laryngeal nerves
If parathyroid tumor develops
This can push on laryngeal nerve
Pressure on laryngeal nerve can cause
voice changes and difficulty swallowing
PTH is synthesized in
Chief cells
Parathyroid glands produce
PTH
PTH regulates
Ca++ in extracellular fluids
Most calcium is found
bound to albumin
When we measure calcium, we measure
Calcium bound to albumin
If albumin lab value is low this can also alter:
Calcium levels
In addition to calcium, PTH also regulates
Phosphoprous and vitamin D
Calcium thermostat is another name for
Parathyroid gland
CaSR is
calcium-sensing receptors
Where are CaSR found?
Outside of parathyroid cells
Bone response to PTH
Osteoclasts accelerate the erosion of bone matrix.
Kidney response to PTH
Increases production of calcitrol
Calcitrol
Acts to increase renal absorption of calcium
Where do kidneys reabsorb calcium?
distal convoluted tubule
Gut response to PTH
Calcitrol stimulates calcium absorption in the intestines
Cholesterol in our skin cells react to
UV light to start the process of Vitamin D production
1,25 hydroxy vitamin D means
Carbons at 1 and 25, hydroxylated
PTH summary of functions
Activates & increases osteoclasts to free calcium
Increases
renal tubular reabsorption of ca++
Increases renal excretion of
phosphate
Increases conversion of vitamin D to active
form
Increases intestinal calcium absorption indirectly by
increasing active form of vitamin D
1,25 hydroxy vitamin D
Normal storage form of Vit D
Active Vit D
2,25 hydroxylated vitamin D
25 hydroxy vitamin D becomes hydroxylated (OH) again to become
2,25 hydroxylated vitamin D, the active form
Calcitonin
is polypeptide hormone secreted by parafollicular C-cells within the medulla of the thyroid gland
calcitonin opposes the actions of
PTH
calcitonin is the anti
PTH
Calcitonin is secreted in respnse to
increased calcium levels
calcitonin acts by
inhibiting bone resorption by inhibiting osteoclasts
BMP
Basic metabolic panel
CMP
comprehensive metabolic panel
Ca++ in the blood levels:
~8.5-10.5mg/dL
Vitamin D is a
Prohormone
Vitamin D is needed for
Calcium homeostasis
Vitamin D absorption
Bone resorption
Kidney excretion
Gut absorption
Which osteocyte is involved in the proliferation of new bone?
Osteoblasts
Calcitonin is produced in
Medulla of thyroid
What type of cells produce PTH
Chief cells
Parathyroid conditions
Hypo
Hyper
Hypercalcemia
Osteoporosis
HypoPTHism causes
-Most common in people with thyroid surgically removed
-Genetic
abnormal gland development (DiGeorge
syndrome)
-Autoimmune
-Metabolic
-PTH
resistance
-Drug induced
Glucagon, heparin, and lasix can all cause
Hypoparathyroidism
HypoPTHism
Inadequate PTH, low calcium
Low calcium -> High phosphate and
low VIT D
Low VIT D -> reduced CA++ absorption in gut ->
Break down of ca++ from bones
Low magnesium can also lower
calcium
Low magnesium can cause
hypoparathyroidism
Primary hyperparathyroidism
due to excessive PTH production and secretion at the PTH gland
Primary hyperparathyroidsim can also be caused by
Reduced PTH supression by elevated ca++
Primary hyperPTHism
shifts the threshold on the thermostat
What hormones oppose PTH
Calcitonin
Most common cause of primary hyperPTHism
genetics
Hypercalcemia
too much calcium
Hypercalcemia symptoms
Increase in bones, stones, grones and psychiatric overtones
Abnormal bone remodeling caused bhy
hypercalcemia
increase in kidney stones caused by
hypercaclemia
Too much calcium in digestive tract causes
abdominal cramping, nausea, constipation
Lethargy, depressed mood, psychosis, cognitive dysfunction are all caused by
hypercalcemia
hypercalcemia effect on brain
psychiatric overtones
hypercalcemia effect on abdomen
groans
hypercalcemia effect on bones
abnormal, bizarre bone growth/remodeling and fracture risk
kidney stones
hypercalcemia
hypercalcemia defined as:
>10.5 with normal albumin
Primary hyperparathyroidism presentation
Elevated PTH, low phos, shortened QT
Most common 2 HyperPTHism
kidney disease
kidney disease causes
hypocalcemia, hyperphosphatemia due to decreased calcitrol
increased PTH in 2 hyperPTHism is a
positive feedback loop
excessive PTH, secondary, due to chronic kidney disease
cannot absorb calcium in kidneys, cannot absorb calcium in GI, which causes increase in PTH
Elevated PTH but low calcium
most common diagnostic for secondary hyperPTH
Primary vs secondary hyperPTHism
Primary, high ca++
Secondary, low ca++
Osteoporosis
State of low bone mass with microarchitectural deterioration of bone structure, strength, fragility
Max peak bone mass depends on
nutrition, physical activity, general health, hormones
Peak bone mass in your
thirties
Msost important factor is gonadal steroid deficiency
estrogen
testosterone
Osteomalacia
Soft/weak bones
Most common cause of osteomalacia
vitamin D deficiency