Endocrine System: Parathyroid Gland Flashcards
Parathyroid Hormone:
- Regulates the concentration of = ?
- Secreted when = ?
- Acts on = ?
Parathyroid
Parathyroid Hormone:
- Regulate the concentration of Ca+ in extra-cellular fluid (ECF).
- Secreted when Ca+ (ionized, free Ca+) levels fall.
- Acts on bone, kidney and intestine that are coordinated to increase the plasma Ca+ concentration back to normal.
Calcium Metabolism:
- Total Ca2+ = ?
- Protein-bound Ca2+ = ?
- Ultrafilterable Ca2+ = ?
- Ionized Ca2+ = ?
Parathyroid
Calcium Metabolism - Forms of Ca+:
(a) Total Ca2+:
- This refers to the total amount of calcium present in the blood, including both protein-bound and ionized calcium.
(b) Protein-bound Ca2+:
- This form of calcium is bound to proteins in the blood plasma, mainly albumin.
- It accounts for about 40% of the total calcium in the blood. While it cannot pass through cell membranes, it acts as a reservoir for ionized calcium.
(c) Ultrafilterable Ca2+:
- This form of calcium can pass through the glomerular filtration membrane in the kidneys.
- It accounts for about 60% of the total calcium in the blood and includes both ionized calcium and calcium complexed to small anions.
(d) Ionized Ca2+:
- This is the free, or unbound, form of calcium in the blood plasma.
- Accounts for about 50% of the ultrafilterable calcium and only about 10% of the total calcium.
- Ionized calcium is the most important form of calcium for cellular function, as it is the only form that can readily cross cell membranes.
(d) Calcium complexed to anions:
- This form of calcium is bound to small anions in the blood plasma, such as citrate, phosphate, and bicarbonate. It accounts for about 10% of the ultrafilterable calcium.
Calcium and Albumin:
- Describe their relationship = ?
- Acidemia = ?
- Alkalemia = ?
Read the notes
Parathyroid
Calcium and Albumin:
(a) Acid base abnormalities: Albumin possesses negative charge sites capable of binding with either Ca+ or H+ ions.
(b) Acidemia
- This condition occurs when the blood pH falls below 7.35 = more acidic.
- Results from either a decrease in bicarbonate concentration OR an increase in hydrogen ion concentration.
(c) Alkalemia:
- Alkalemia arises when the blood pH exceeds 7.45 = more alkaline.
- This may stem from an elevation in bicarbonate concentration OR a reduction in hydrogen ion concentration.
(d) Notes:
- The parathyroid gland’s regulation of calcium levels, influenced by parathyroid hormone secretion, is intricately linked with the body’s mechanisms for maintaining acid-base balance.
Based on this picture, we should know:
- Total calcium = ?
- Ultrafilterable calcium = ?
- Ionized calcium = ?
- Protein-bound calcium = ?
Parathyroid
(a) Total calcium:
- This is the sum of all forms of calcium in the blood, including protein-bound and ionized calcium.
- It is typically measured in mg/dL and the normal range is 8.8 to 10.4 mg/dL.
(b) Ultrafilterable calcium:
- This is the form of calcium that can pass through the glomerular filtration membrane in the kidneys.
- It includes both ionized calcium and calcium complexed to small anions.
(c) Ionized calcium:
- This is the free, or unbound, form of calcium in the blood. It is the most important form of calcium for cellular function, as it is the only form that can readily cross cell membranes.
- It is responsible for muscle contraction, nerve transmission, and hormone secretion. The normal range for ionized calcium is 4.6 to 5.3 mg/dL.
(d) Protein-bound calcium:
- This form of calcium is attached to proteins in the blood, mainly albumin.
- It cannot pass through cell membranes and does not directly affect cellular function. However, it acts as a reservoir for ionized calcium.
Hypercalcemia vs. Hypocalcemia
- What’s the difference = ?
- Symptoms of both = ?
Parathyroid
(a.1) Hypercalcemia:
- Increase in plasma Ca+ concentration.
(a.2) Symptoms:
- Constipation
- Polyuria
- Polydipsia
- Hyporeflexia.
(b.1) Hypocalcemia:
- Decrease in plasma calcium concentration.
(b.2) Symptoms:
- Muscle cramps
- Twitching
- Tingling
- Numbness
- Hyperreflexia
Calcium Hemostasis - Key Regulatory Factors:
- 1,25-Dihydroxycholecalciferol (vitamin D3) = ?
- PTH = ?
- Calcitonin = ?
Parathyroid
Overall Calcium Hemostasis:
(a) PTH acts on bone, kidney and intestine to produce an increase in plasma calcium concentration.
(b) Involves coordinated action of three systems:
- Bone
- Kidney
- Intestine
(c) Three hormones:
- PTH
- Calcitonin
- Vitamin D
Key regulatory factors:
(1) 1,25-Dihydroxycholecalciferol (Vitamin D3):
- Increases calcium absorption and reabsorption.
(2) Parathyroid hormone (PTH):
- Increases calcium reabsorption and bone resorption.
(3) Calcitonin:
- Decreases calcium reabsorption and bone resorption.
Actions of Parathyroid Hormone = ?
Parathyroid
Action of PTH:
(a) Bone remodeling:
- Bone formation (osteoblasts)
- Bone resorption (osteoclasts)
(b) Bone resorption:
- Release of Ca+ and phosphate to ECF.
- Phosphate released will bind with Ca+ in the ECF limiting rise in free ionized Ca+ concentration.
- Additional mechanism are required
- Alone, effects of PTH on bone cannot account for its overall action to increase the plasma ionized Ca+ concentration.
(c) Kidney:
- Inhibits phosphate reabsorption in proximal tubule.
- Stimulates Ca+ reabsorption in in distal convoluted tubule.
(d) Small intestine:
- Activates vitamin D, which stimulates Ca+ absorption.
- Inhibits osteoclastic bone resorption
- Decreases the plasma calcium concentration
- Released by thyroid gland
What am I = ?
Parathyroid
Calcitonin:
- Inhibits osteoclastic bone resorption.
- Decreases the plasma calcium concentration.
- Released by thyroid gland.
- Help reabsorb calcium from GI tract.
- Promotes mineralization of new bone.
What am I = ?
Parathyroid
Vitamin D:
(a) Vitamin D, in conjunction with PTH is the major regulatory hormone for Ca+ and phosphate metabolism.
- Help reabsorb calcium from GI tract.
- Promotes mineralization of new bone.
- Its action are coordinated to increase both Ca+ and phosphate concentration in plasma so that these elements can be deposited in new bone mineral.
Describe how Vitamin D is synthesized = ?
Parathyroid
Synthesis of Vitamin D - Synthesis steps:
(a) UVB absorption:
- UVB radiation is absorbed by 7-dehydrocholesterol, causing a molecular rearrangement.
(b) Previtamin D3 formation:
- 7-dehydrocholesterol is converted to previtamin D3.
(c) Isomerization (thermal process):
- Previtamin D3 spontaneously converts to the active form, vitamin D3 (cholecalciferol).
- This process is temperature-dependent and slower than the initial conversion.
(d) Diffusion:
- Vitamin D3 diffuses to the bloodstream and binds to carrier proteins for transport to the liver.
Vitamin D:
- Major action of vitamin D = ?
- Major action of 1,25- dihydroxycholecalciferol = ?
Parathyroid
Vitamin D:
(a) Major role of vitamin D:
- To increase plasma concentration of phosphate and Ca+
- To promote mineralization of new bone
(b) Major action of 1,25- dihydroxycholecalciferol are on:
- Intestine = Stimulates both Ca+ and phosphate absorption.
- Bone = Stimulate bone resorption of old bone and so that new bone can be mineralized (bone remodeling).
When kidney is unable to produce active form of vitamin D…
- What happens = ?
Parathyroid
Active Vitamin D:
(a) When kidney is unable to produce active form of vitamin D, no matter how much vitamin D is supplemented in the diet, it will be inactive.
- Congenital absence of 1α-hydroxylase.
- Chronic renal failure.
Parathyroid
Hyperparathyroidism:
- What it is = ?
- Results in = ?
- Most common cause = ?
- Gender most affected = ?
Parathyroid
(a) Hyperparathyroidism: Over activity parathyroid glands that disrupts calcium, phosphate, and bone metabolism.
- Excessive secretion of PTH = increased release of calcium from the bones into the bloodstream.
- PTH acts on the bones to stimulate the breakdown of bone tissue, resulting in the release of calcium ions.
(b) Most common cause: tumor
- Women are more affected than men.
Disorders of Parathyroid gland
Hyperparathyroidism:
- Clinical Manifestations = ?
Parathyroid
Hyperparathyroidism - Clinical Manifestations:
(a) Bone damage
- Bone resorption
- Bone demineralization = reduced bone strength and density
- Bone pain = fragile
- Fractures (compression)
- Deformities (kyphosis)
(b) Diminished DTRs
(c) Hypercalcemia
- Hypertension
- Atherosclerosis = calcium deposits in blood vessels
- Hypercalciuria = excessive calcium in the urine
- Hypergastrinemia = excess gastrin (hormone that stimulates secretion of gastric acid and pepsin).
- Abdominal pain
- Peptic ulcers
- Nausea
- Vomiting
- Constipation
(c) May see cases of ruptured tendons
(d) Kidney damage
- Deposit of calcium phosphate within renal tubules = nephrocalcinosis.
- Calcium salts are insoluble in urine = kidney stones composed of calcium phosphate develop.
(d) Other manifestations:
- Lethargy
- Paresthesia
- Poor memory
- Depression
- Occasionally glove stocking distribution sensory loss
- Arthralgia
- Myalgia
- Proximal muscle weakness
- Loss of appetite
- Weight loss
Note:
- Symptoms in early stages are attributable to ageing, depression
- As serum calcium level rises- symptoms intensify.
“Stones, bones, groans and psychiatric overtones”
Hypoparathyroidism:
- Clinical Manifestations = ?
Parathyroid
Hypoparathyroidism - Clinical Manifestations:
(a) Mild:
- Asymptomatic
(b) Hypocalcemia:
- Neuromuscular irritability (hypocalcemia increases permeability of neural membranes to sodium).
- Tetany (involuntary muscle spasm/ contraction) = Spasm of intercostal muscles and diaphragm compromising breathing).
- Paresthesia
- Cardiac arrhythmias
(c) Acute tetany
- Tingling in fingertips, around mouth.
- Spreads and becomes more severe producing spasm, grimacing, laryngospasm and arrhythmias
(d) Positive Chvostek’s sign:
- Hyperirritability of facial nerve when tapped.
(e) Trousseau sign (carpal spasm)
- Induction of carpopedal spam when sphygmomanometer is inflated above SBP for 3 minutes
- Carpopedal spam = adduction of thumb, flexion of wrist and MCP, extension of IP.
(f) CNS:
- Irritability
- Anxiety
- Agitation
- Depression
- Seizures
(g) CVS:
- Cardiac arrhythmias / eventual heart failure
(h) Integumentary:
- Dry, scaly, coarse, pigmented skin
- Thin hair
- Nails become brittle and form ridges.
- Tendency to have skin infections
(i) GI
- Nausea
- Vomiting
- Abdominal pain
(j) Hypocalcemia:
- Increased DTRs
