Parathyroid and Adrenal — Revision Notes

⚡ 30-Second Revision

Parathyroid Glands: — Secrete PTH. \( \uparrow \) blood $Ca^{2+}$, \( \downarrow \) blood $PO_4^{3-}$. Stimulated by \( \downarrow \) $Ca^{2+}$. Targets: bone (resorption), kidney (reabsorption $Ca^{2+}$, excretion $PO_4^{3-}$, activate Vit D). \n- Adrenal Glands: \n - Cortex (Steroids): \n - Zona Glomerulosa: Aldosterone (Mineralocorticoid). \( \uparrow Na^+ \) reabsorption, \( \uparrow K^+ \) excretion. Regulated by RAAS, \( \uparrow K^+ \). \n - Zona Fasciculata: Cortisol (Glucocorticoid). \( \uparrow \) blood glucose, anti-inflammatory, stress response. Regulated by HPA axis (ACTH). \n - Zona Reticularis: Androgens (Gonadocorticoids). Minor sex hormone contribution. \n - Medulla (Catecholamines): Epinephrine, Norepinephrine. 'Fight or Flight' response. \( \uparrow \) HR, BP, blood glucose. Stimulated by sympathetic nerves.

2-Minute Revision

The parathyroid glands, typically four small structures behind the thyroid, are crucial for calcium homeostasis. They release Parathyroid Hormone (PTH) in response to low blood calcium. PTH raises calcium by stimulating bone resorption, increasing renal calcium reabsorption, and activating Vitamin D for intestinal calcium uptake.

It also causes renal phosphate excretion. \n\nThe adrenal glands, situated atop the kidneys, have two main parts. The outer adrenal cortex produces steroid hormones. The zona glomerulosa secretes aldosterone (a mineralocorticoid) to regulate sodium and potassium balance, impacting blood pressure via the RAAS.

The zona fasciculata produces cortisol (a glucocorticoid) for glucose metabolism, stress response, and anti-inflammatory effects, regulated by the HPA axis. The zona reticularis produces weak androgens.

The inner adrenal medulla secretes catecholamines, epinephrine and norepinephrine, which mediate the rapid 'fight or flight' response by increasing heart rate, blood pressure, and blood glucose, preparing the body for immediate action.

Disorders like Addison's (hypocortisolism/hypoaldosteronism) and Cushing's (hypercortisolism) diseases highlight their critical roles.

5-Minute Revision

Let's consolidate our understanding of the parathyroid and adrenal glands, focusing on their hormones, regulation, and key disorders. \n\nParathyroid Glands: These small glands are the primary regulators of calcium and phosphate.

Their sole hormone, Parathyroid Hormone (PTH), is released when blood calcium levels drop. PTH acts on: \n1. Bones: Stimulates osteoclasts to break down bone, releasing calcium and phosphate. \n2.

Kidneys: Increases calcium reabsorption and decreases phosphate reabsorption. Crucially, it also activates Vitamin D. \n3. Intestines: Activated Vitamin D then enhances dietary calcium absorption.

\n*Disorders:* Hyperparathyroidism (excess PTH) leads to hypercalcemia, causing bone issues, kidney stones, and neurological symptoms. Hypoparathyroidism (deficient PTH) results in hypocalcemia, leading to neuromuscular excitability (tetany).

\n\nAdrenal Glands: These glands sit atop the kidneys and have two distinct parts: \n\nA. Adrenal Cortex (Steroid Hormones): \n1. Zona Glomerulosa: Produces mineralocorticoids, mainly aldosterone.

\n * *Function:* Regulates $Na^+$ and $K^+$ balance in kidneys, increasing $Na^+$ reabsorption and $K^+$ excretion. This helps maintain blood volume and pressure. \n * *Regulation:* Primarily by the Renin-Angiotensin-Aldosterone System (RAAS) and high plasma $K^+$.

\n2. Zona Fasciculata: Produces glucocorticoids, mainly cortisol. \n * *Function:* Raises blood glucose (gluconeogenesis), breaks down proteins and fats, suppresses inflammation, and helps cope with stress.

\n * *Regulation:* Hypothalamic-Pituitary-Adrenal (HPA) axis (CRH $\rightarrow$ ACTH $\rightarrow$ Cortisol). \n3. Zona Reticularis: Produces weak gonadocorticoids (androgens). \n * *Function:* Contribute to secondary sex characteristics.

\n*Disorders:* Addison's Disease (adrenal insufficiency) involves low cortisol and aldosterone, causing fatigue, hypotension, and electrolyte imbalance. Cushing's Syndrome (excess cortisol) leads to 'moon face', 'buffalo hump', central obesity, and hyperglycemia.

\n\nB. Adrenal Medulla (Catecholamines): \n* Produces epinephrine (adrenaline) and norepinephrine (noradrenaline). \n* *Function:* Mediates the rapid 'fight or flight' response: increases heart rate, blood pressure, blood glucose, dilates airways, and redirects blood flow.

\n* *Regulation:* Direct sympathetic nervous stimulation. \n*Disorders:* Pheochromocytoma (tumor) causes excessive catecholamine release, leading to episodic hypertension, palpitations, and anxiety.

\n\nRemember the interconnectedness: PTH and calcitonin balance calcium; aldosterone and ADH balance water/salt; cortisol and glucagon balance glucose. These glands are vital for maintaining the body's delicate internal equilibrium.

Prelims Revision Notes

Parathyroid Glands: — \n - Location: 4 small glands, posterior to thyroid. \n - Hormone: Parathyroid Hormone (PTH). \n - Function: \( \uparrow \) Blood Calcium ($Ca^{2+}$), \( \downarrow \) Blood Phosphate ($PO_4^{3-}$). \n - Mechanism: \n - Bone: Stimulates osteoclasts (resorption). \n - Kidney: \( \uparrow Ca^{2+} \) reabsorption, \( \downarrow PO_4^{3-} \) reabsorption (excretion), activates Vitamin D. \n - Intestine: Indirectly \( \uparrow Ca^{2+} \) absorption via activated Vitamin D. \n - Regulation: Stimulated by \( \downarrow Ca^{2+} \) (hypocalcemia), inhibited by \( \uparrow Ca^{2+} \). \n - Disorders: \n - Hyperparathyroidism: Excess PTH $\rightarrow$ Hypercalcemia. Symptoms: 'bones, stones, abdominal groans, psychic moans'. \n - Hypoparathyroidism: Deficient PTH $\rightarrow$ Hypocalcemia. Symptoms: Tetany, muscle cramps, tingling. \n\n- Adrenal Glands: \n - Location: Superior to kidneys. \n - Parts: Cortex (outer, 80-90%), Medulla (inner, 10-20%). \n\n- Adrenal Cortex (Steroid Hormones from Cholesterol): \n - Zona Glomerulosa (Outer): \n - Hormones: Mineralocorticoids (e.g., Aldosterone). \n - Function: Regulates $Na^+$, $K^+$ balance. \( \uparrow Na^+ \) reabsorption, \( \uparrow K^+ \) excretion in renal tubules. \( \uparrow \) blood volume/pressure. \n - Regulation: Renin-Angiotensin-Aldosterone System (RAAS), \( \uparrow K^+ \). \n - Zona Fasciculata (Middle, thickest): \n - Hormones: Glucocorticoids (e.g., Cortisol). \n - Function: \( \uparrow \) blood glucose (gluconeogenesis), protein catabolism, fat mobilization, anti-inflammatory, immunosuppressive, stress adaptation. \n - Regulation: Hypothalamic-Pituitary-Adrenal (HPA) axis (CRH $\rightarrow$ ACTH $\rightarrow$ Cortisol). \n - Zona Reticularis (Inner): \n - Hormones: Gonadocorticoids (e.g., Androgens like DHEA). \n - Function: Minor contribution to secondary sex characteristics. \n - Regulation: Primarily ACTH. \n - Disorders: \n - Addison's Disease: Hyposecretion of cortisol & aldosterone. Symptoms: Fatigue, weight loss, hypotension, hyperpigmentation, hyponatremia, hyperkalemia. \n - Cushing's Syndrome: Hypersecretion of cortisol. Symptoms: 'Moon face', 'buffalo hump', central obesity, hyperglycemia, hypertension, muscle weakness. \n - Conn's Syndrome: Hypersecretion of aldosterone. Symptoms: Hypertension, hypokalemia. \n\n- Adrenal Medulla (Catecholamines): \n - Hormones: Epinephrine (Adrenaline, ~80%), Norepinephrine (Noradrenaline, ~20%). \n - Function: 'Fight or Flight' response. \( \uparrow \) HR, BP, blood glucose, bronchodilation, blood flow redistribution. \n - Regulation: Direct sympathetic nervous stimulation. \n - Disorders: \n - Pheochromocytoma: Tumor causing excess catecholamines. Symptoms: Episodic hypertension, palpitations, sweating, headache, anxiety.

Vyyuha Quick Recall

Adrenal Cortex Layers (GFR): Get Fresh Really. \n* Glomerulosa $\rightarrow$ Mineralocorticoids (Aldosterone) \n* Fasciculata $\rightarrow$ Glucocorticoids (Cortisol) \n* Reticularis $\rightarrow$ Gonadocorticoids (Androgens) \n\nParathyroid Hormone (PTH) Actions (B.K.I.): \n* Bone (resorption) \n* Kidney (calcium reabsorption, phosphate excretion, Vit D activation) \n* Intestine (calcium absorption via Vit D)