Endocrine Module Flashcards
Osteoporosis
Systemic skeletal disorder characterized by decreased bone mass density leading to diminished stature, bone fragility, increased risk of bone fracture
After what age in women do bone strength and density begin to decline?
35
What fraction of men/women have osteoporosis?
1/4 women
1/8 men
Where is the body’s calcium located?
99% in teeth and bones
1% in extracellular fluid and soft tissue
Metabolic processes calcium is involved in
Cell membrane function and permeability
Neuronal excitability and transmission of electrical impulses
Contraction of muscle
Conduction of electrical impulses in the heart
Blood coagulation
Platelet adhesion
Hormone secretion
Enzymatic activity
Catecholamine release from adrenal medulla
Release of chemical mediators
Bone
Mineralized connective tissue that provides structural support and acts as reservoir for calcium, phosphorus, magnesium, sodium, carbonate
Two main forms of calcium in bone tissue
Calcium phosphate
Calcium carbonate
A small amount exists in an unbound, unionized form that moves from bone to bloodstream when serum calcium is low
What % of consumed calcium is absorbed in the intestine?
30-50% - the rest is lost in feces
Absorption of calcium is increased by
Presence of vitamin D, lactose, moderate amounts of fat, high protein intake, physiologic need
Absorption of calcium is impaired with
Vitamin D deficiency, high fat diet, diarrhea
How much calcium should adults consume?
1000 mg/day
How much calcium should growing children, pregnant/lactating women and postmenopausal women (no HRT) consume?
1200 mg/day
What is the best source of calcium?
Milk and milk products (also contain vitamin D and lactose which increase calcium absorption)
What are good sources of calcium besides milk?
Broccoli, spinach, kale, shellfish such as clams and oysters
Which 3 hormones regulate calcium and bone metabolism?
Parathyroid hormone
Calcitonin
Calcitriol
Parathyroid hormone
Secreted from parathyroid gland when serum calcium falls
Stimulates activity of osteoclasts to increase bone resorption
Increases reabsorption of calcium in tubules of kidneys
Activates calcitriol (active form of vitamin D) in the intestines
Calcitonin
Secreted from thyroid gland when serum calcium rises
Inhibits activity of osteoclasts to stimulate rate of deposition
Inhibits reabsorption of calcium in tubules of kidneys to increase amount excreted in urine
2 forms of vitamin D
Ergo-calciferol obtained from diet
Cholecalciferol - synthesized from cholesterol in skin when exposed to UV light
Calcifediol
Intermediate metabolite of vitamin D (formed in liver)
Calcitriol
Active form of vitamin D (formed in kidneys)
Enhances intestinal absorption of calcium
2 types of receptors calcitriol works on
- Membrane level - activates L-type calcium channels to modulate calcium influx across cell borders
- Intracellular protein - calcitriol protein complex enters nucleus and causes nuclear DNA to generate an mRNA specific for production of a calcium binding protein that intermediates in the system effects of calcitriol
Action of calcitriol at the tissue/system level
Stimulates intestinal calcium and phosphate transport
Increases serum calcium and phosphate from bone resorption through inducing differentiation of osteoclasts
Decreases renal excretion of calcium and phosphate
What is indicative of undetected osteoporosis?
Shortened stature
Back pain
Spinal deformity
Causes of osteoporosis
Inadequate dietary calcium
Inadequate calcium absorption
Vitamin D deficiency
Disruption of calcium and bone metabolism (hypersecretion of PTH, hyposecretion of calcitonin)
Which body areas are particularly vulnerable to osteoporosis related fracture?
Vertebrae of lower dorsal and lumbar spines
Wrists
Hips
When to osteoporotic fractures often occur?
After bending or lifting movements, slips, trips, falls
Alterable/minor risk factors
- Smoking - increases calcium excretion via kidneys
- Calcium and vitamin D deficiency - increases bone resorption
- Increased sodium or protein intake - increases calcium excretion via kidneys and increases bone resorption
- Caffeine and alcohol - cause diuresis leading to increased calcium excretion
- Lack of exercise - exercise helps retain calcium and increases bone mass density
Major risk factors
Female gender (esp. with advanced age, prolonged amenorrhea, menopause because estradiol limits activity of osteoclasts and progesterone stimulates osteoblasts to build new bone)
Fragility fractures (less than 40 y/o)
Ancestry - Asian or Caucasian
Small frame - smaller bones, less mass
Family history - especially maternal
Glucocorticoid therapy for more than 3 months - inhibits bone deposition and increases resorption
Who should be assessed for presence of risk factors for osteoporosis?
All adults over 50
Anyone over 50 should undergo bone mass density testing if…
They are over 65 Fragility fractures after age 40 Family history of osteoporotic fracture Use of high dose systemic glucocorticoid therapy for 3 months Current smoking or alcohol Low body weight Rheumatoid arthritis