Endocrine L3: PTH Flashcards
What are 8 functions of calcium that are important for physiological processes?
- Structural component of bones and teeth
- Contributes to restin g p membrane potential
- Maintains normal excitability of nerve & muscle cells
- Involved in neurotransmitter & hormone release
- Muscle contraction (skeletal)
- Activation of many enzymes
- Coagulation of blood
- Milk production
What is the distribution of calcium in the body?
99% of calcium is found in the _____ and ____, This means that they are fairly stable.
bones; teeth
What are 3 regulators of calcium?
Depends on hormonal control – balance maintained between ECF and three body maintained between ECF and three body compartments
What are the 2 types of control for the regulation of calcium?
- Acute control
- Chronic control
What are 2 characteristics of acute control in the regulation of calcium?
- Must maintain constant free Ca++ concentration in plasma concentration in plasma
- Mostly by rapid exchange between bone and ECF and ECF
Used all the time
What are 2 characteristics of acute control in the regulation of calcium?
- Maintain total Ca++ level in body long-term Adjust gastrointestinal absorption and urinary excretion
- Only when need to change total Ca++ level
When is acute control in the regulation of calcium use vs chronic control?
Acute: All the time
Chronic: Only when need to change total Ca++ level
What are the 3 hormones that regulate Ca++ metabolism?
- Parathyroid Hormone (PTH)
- Vitamin D3
- Calcitonin
Other involved include steroids, thyroid hormones, GH and other local fac tors
Is parathyroid hormone related to thryoid hormone?
Not thyroid hormone (not related at all) = Comes from the parathyroid gland which happens to be next to the thyroid glands
What hormone is the most important for releasing Ca++?
Parathyroid hormone (PTH)
What are 3 types of cells that are important for bone formation and resorption?
- Osteoblasts
- Osteoclasts
- Osteocytes
What are osteoblasts?
synthesise and secrete collagen synthesise and secrete collagen & promote deposition of CaPO4 crystals
What are osteoclasts?
promote resorption of bone
What are osteocytes?
essential role in exchange of Calcium between ECF & bone
What does the structure of bone look like?
What does fast and slow exchange of Ca+ from mineralised bone to plasma look like?
What are 6 characteristics of the parathyroid hormone?
- Parathyroid glands are 4 small glands located on the posterior glands located on the posterior surface of the thyroid gland
- PTH secreted from chief cells in direct response to changing plasma Ca++ concentrations
- Overall Ca Overall Ca++ PO in plasma
- PTH is a peptide, 84 amino acid chain
- Half -life in plasma of <20 minutes life in plasma of <20 minutes
- Actions on bone, kidneys & GIT
Parathyroid glands are ____ small glands located on the______ glands located on the posterior surface of the thyroid gland
4; posterior
PTH secreted from _____ cells in direct response to changing plasma _____ concentrations
chief; Ca++
Overall, there is a _____ (increase/decrease) Ca++ and ____ (increase/decrease) PO in plasma
increase; decrease
PTH is a ____ with 84_____ chain
peptide; amino acids
PTH has a half-life in plasma of <20 minutes. What does that mean?
Very short/fast acting
What is the short term function of parathyroid hormone on bone?
Stimulates Ca++ membrane pump in membrane pump in osteocytes, so Ca++ moves from bone fluid to plasma in central canal
- Stimulates Ca++ transporters
What is the long term function of parathyroid hormone on bone?
stimulates osteoclasts (Bone starts to get broken down) inhibits stimulates osteoclasts, inhibits osteoblasts, so Ca++ and PO 4 increase in plasma (Bone starts to get broken down)
What is function of parathyroid hormone on the kidneys?
Retain more Ca++ from reabsoption
Decreases Ca++ loss - increased tubular reabsorption of Ca++ and decreased tubular reabsorption of PO4
- Getting phosphate from bone and this level needs to be decreased
What is function of parathyroid hormone on the GIT?
Indirectly increases Ca++ and PO4 – increases absorption by small intestine by stimulating activation of Vitamin D 3
Vitamin D3 can be eaten in diet or can be produced naturally by the body
Most ingested Ca++ ____ (is/is not) absorbed by GIT, but lost in faeces lost in faece
is not
How can Vit D be available?
Can eat it or produce it naturally… that is why we need sunlight on skin (make Vit.D in response to sunlight
Why do we need sunlight on our skin?
make Vit.D in response to sunlight
Vitamin D is produced either in the ___ or ____, and is activated by the ____ and ___ to 1,25 dihyroxycholecalciferol (Vitamin D3)
skin; ingested; liver; kidney
What are 4 functions of Vitamin D?
- promotes absorption of Ca ++
- promotes absorption of Ca++ from the intestine by from the intestine by increasing its transport across intestinal epithelium
- promotes absorption of PO4 in intestine increases bone resorption
- stimulates Ca++ & PO4 reabsorption in kidneys
What happens when you don’t get enough sunlight?
Decreased vitamin D and that means decreased Ca++
How does Vit. D help Ca++ and PO43-?
____ has the opposite role to vit. D and PTH
Calcitonin
Calcitonin is produced in the ____ cells of the ____gland in response to high plasma Ca++ levels
C; thyroid
What is something special about calcitonin?
Doesn’t usually exists and is only produced when body needs it Increased Ca++ levels are quite rare
What are the 2 functions of calcitonin?
- decreases bone resorption (effects osteoclasts)
- decreases Ca++ reabsorption in kidneys, promotes increased excretion
What is the overall action of action?
Increase Ca++ and decrease PO in plasma
Calcitonin protects against _____.
hypercalcemia If Ca++ levels become ahigh (while its quite rare)
How can calcitonin be used clinically?
Can give a synthetic amount to decrease Ca++ levels
What are 3 mechanism to help improve Ca++ levels?
What are the 2 main abnormalities of calcium metabolism?
- PTH hypersecretion (hyperparathyroidism)
- PTH hyposecretion (hypoparathyroidism)
What are 6 features of PTH hypersecretion (hyperparathyroidism)?
- Most frequently caused by PTH Most frequently caused by PTH -secreting adenomas leads to hypercalcemia
- Increased Ca++ mobilisation from bones causes mobilisation from bones causes softening & fractures
- Increased Ca++ excretion through kidneys cause polyuria (Urinate a lot), polydipsia (Very thirsty = drink a lot) and nephrocalcinosis (Formation of kidney stones made of Ca++)
- Decreased excitability of nerves & muscles leads to weakness, depression & coma
- Hypercalcemia leads to nausea, constipation &increased
- incidence of peptic ulcers
What is PTH hypersecretion abnormality (hyperparathyroidism) usually called? Why?
“Bones, stones and groans”
- Weakening of bones, kidney stones and upset tummy (GIT)
What do the bones for a person with hypothyroidism look like?
Developing holes in their bones = completely lost CaPO4 crystals
What are 5 features of PTH hyposecretion (hypoparathyroidism)?
- Most frequently caused by gland destruction, leads to severe hypocalcemia
- Parathyroid glands are essential for life
- Hypocalcemia causes increased nerve & muscle excit bilit it ability
- Severe hypocalcemia leads to death by asphyxiation caused by laryngospasm caused by laryngospasm
- Mild hypocalcemia causes cramps, twitches & tingles ( tingles ( pins ‘ and needles and needles’ sensation)
What is PTH hyposecretion (hypoparathyroidism) frequently caused by?
gland destruction, leads to severe hypocalcemia
What is PTH hypersecretion (hyperparathyroidism) frequently caused by?
by PTH -secreting adenomas secreting adenomas, leads to hypercalcemia
What are 4 other causes for hypocalcemia apart from PTH hyposecretion?
- High demand for Ca++ in pregnancy/lactation – causes tetany or paralysis
- Lack of Vitamin D/sunlight- causes rickets in children, osteomalacia in adults
- Change in blood pH- alkalosis (less free Ca++)
- Pancreatitis
Condition of low bone mass & structural disruption that results in fractures after minimal trauma that results in fractures after minimal trauma are especially prevalent in______ ______ (men/women) but can occur in all aged population
post-menopausal women;
What are 4 common fracture sites in osteoporosis?
- vertebral bodies
- distal radius
- neck of femur
- ribs
Why do post menopausal women have a decline in bone mass and density?
Loss of estrogen = protective of bone mass
- Loss bone mass
- Increased risk of fracture
Drinking ____ (eg. ____) can inhibit Ca++ uptake and laying down of bone mass. What does that impact?
PO43- (coke/coca cola) = never reach peak
What is 4 features that influence bone mass gain?
- genetic factors
- physical activity
- Ca++ intake
- hormones – esp oestradiol
What are 5 risk factors which reduce the maintenance of bone mass in ageing?
- toxic exposure
- smoking
- alcohol excess
- immobility
- glucocorticoids
In ageing, bone ____ declines prior to accompanying measurable loss in density
strength
What are 5 treatments for the prevention of osteoporosis?
- Regular exercise (especially weight bearing)
- Nutrition in growing phase (Ca++ & Vitamin D)
- Post-menopause – HRT (but side-effects & increased risk CV disease and cancer)
- Androgens & SERMs (selective-oestrogen receptor modulators)
- Calcitonin
