Endocrine System Overview – Lecture Vocabulary

Exam Strategy & Logistics

• Comprehensive final covers 10 chapters – 10 questions each (≈100 Qs)
  • ≈80 % = straight definitions or single-function questions
  • ≈20 % = integrated, multi-chapter scenarios
• Balance study time
  • Do NOT only chase weaknesses; polish strengths for confidence & easy points
  • Practice “skip & return” for tough items; prevents 1-pt questions from burning time
• No math on this exam
  • E.g. no stroke-volume / cardiac-output calculations; only conceptual definitions
• Build personal tables/cheat-sheets of each system
  1. Organs involved
  2. Main hormones/structures
  3. Functions & feedback loops
• High-yield review prompts
  • Cardiovascular → What moves what? (pressure, valves, volumes)
  • Respiratory → $\text{O}<em>2$ loading, $\text{CO}</em>2$ unloading
  • Endocrine → Which tier (hypothalamus → pituitary → gland) & stimulus (hormonal, humoral, neural)?

Anterior Pituitary (Adenohypophysis) – “FLAT PG”

Notes

• All six are protein/peptide hormones → surface receptors except GH IGF co-effects can be genomic.
• Hypothalamic releasing/inhibiting hormones (e.g. CRH, TRH, GHRH, PIH) form Tier 1.

Growth Hormone (GH)

• AKA Somatotropin; inhibited by Somatostatin
• Highest secretion: deep sleep, fasting, post-exercise
• Short-term (insulin-antagonist):
  • $\uparrow$ Lipolysis ⇒ fatty acids in blood
  • Hepatic gluconeogenesis ⇒ $\uparrow$ Blood glucose
  • ↓ Glucose uptake in muscle/adipose
• Long-term (via IGF-1 from liver):
  • Protein synthesis, bone lengthening (open epiphyseal plates), muscle hypertrophy
  • Stimulates glucose uptake for growth stage

Pathologies

• Hyposecretion (child) → Pituitary dwarfism
• Hypersecretion (child) → Gigantism; (adult) → Acromegaly (bone width)
• Myostatin vs Somatostatin
  • Myostatin limits skeletal-muscle growth; its deficiency (double-muscled cattle, rare infants) ⇒ extreme hypertrophy & cardiomegaly risk.

Thyroid & Parathyroid Anatomy

• Butterfly gland anterior to trachea; lobes joined by isthmus
• Follicles (cuboidal epithelium): store colloid (thyroglobulin + I⁻) → $T<em>3/T</em>4$
• Parafollicular (C-) cells: secrete Calcitonin
• 4 Parathyroid glands (posterior): chief cells → PTH
• Enlarged thyroid = Goiter
  • Typically iodine deficiency → colloid accumulation
  • Iodised table salt policy solved endemic goiters

Thyroid Hormone – $T<em>3 (Tri-iodothyronine)$ & $T</em>4 (Thyroxine)$

• Biogenic amine but lipid-soluble (iodine shields polarity) ⇒ intracellular receptors, transported by binding proteins
• Systemic targets (virtually all nucleated cells)
• Key actions
  • $\uparrow$ Basal metabolic rate (BMR), ATP turnover, Na⁺/K⁺-ATPase activity
  • Hepatic gluconeogenesis & glycogenolysis
  • Catabolic on adipose (lipolysis)
  • Calorigenic (heat) → Hypothalamus releases TRH when body T↓
  • Synergist with GH for growth, CNS development

Dysfunction Snapshot

• Hypothyroid: weight gain, cold intolerance, bradycardia, lethargy, possible goiter
• Hyperthyroid (e.g. Graves’): weight loss, heat intolerance, tachycardia, anxious, exophthalmos

Calcium Homeostasis Antagonists

Normal Ca²⁺ range $\approx 8.5\text{–}10.5\,\text{mg·dL}^{-1}$

Adrenal Glands

Cortex – “Salt / Sugar / Sex”

Fast Mnemonic: G F R → Salt – Sugar – Sex

Aldosterone Extra Notes

• Also stimulated by $\uparrow$ K⁺ or RAAS (low BP)
• Helps correct acidosis via $\downarrow$ H⁺ reabsorption (alkalinises plasma)

Cortisol & Chronic Stress

• HPA axis: CRH → ACTH → Cortisol
• Diurnal high at dawn; spikes in stress/fasting
• Pharmacology
  • Synthetic analogues (Prednisone, Hydrocortisone) treat autoimmune, transplant rejection, anaphylaxis
• Chronic excess (Cushing’s syndrome) → Moon face, muscle wasting, hyperglycaemia, hypertension

Adrenal Medulla – Catecholamines

• Modified sympathetic ganglion; chromaffin cells
• 80 % Epinephrine, 20 % Norepinephrine
• Short-lived (enzyme MAO/COMT degrade quickly)
• Classic sympathetic effects
  • ↑ HR & contractility, bronchodilation, vasodilation to skeletal muscle, vasoconstriction skin/GI, pupil dilation, glycogenolysis

Pancreatic Islets & Blood Glucose

Mnemonic GA BI / BI GA

Feedback curves

• Post-meal ↑BG ⇒ β-cells secrete insulin ⇒ cells uptake ⇒ BG to baseline
• Fasting ↓BG ⇒ α-cells secrete glucagon ⇒ liver releases glucose ⇒ BG restored

Other Peripheral Hormones

• Leptin – adipose tissue
  • Released when adipocytes swell with triglyceride
  • Target: hypothalamus; induces satiety ↓ appetite
  • Works with insulin & GLP-1; drug analogues exploited for weight control
• Skin (Epidermis) – produces Cholecalciferol (Vit D precursor) under UV; finished in liver/kidney → Calcitriol
• Thymus – thymosins for T-cell maturation (childhood prominence)

Quick Comparative Cheat-Sheet

Study/Memory Aids & Mnemonics

• FLAT PG – Anterior pituitary list
• G F R → Salt, Sugar, Sex – Adrenal cortex layers
• GA BI – Glucagon α / Beta Insulin
• High $[Ca^{2+}]$ = Calcitonin, Low $[Ca^{2+}]$ = PTH (alphabetical ↑↓)
• Somatotropin (grow) vs Somatostatin (stop growth)

Ethical / Practical Connections

• Hormone misuse (HGH, myostatin blockers, corticosteroids) carries systemic risks (cardiomyopathy, immunosuppression, endocrine axis shutdown)
• Public-health success: iodised salt preventing goiter & cretinism
• Insurance & lifelong steroid-immunosuppression for transplant patients – policy change now covers beyond 3 yrs

High-Yield Values to Memorize

• Normal Blood Ca²⁺: $8.5\text{–}10.5\,\text{mg·dL}^{-1}$
• Fasting Glucose: $70\text{–}100\,\text{mg·dL}^{-1}$; Diabetes Dx ≥$126$
• Cortisol diurnal peak: ~08:00

Final Prep Checklist

• Re-create hormone tables from memory (source, stimulus, receptor type, action, antagonist)
• Sleep hygiene → maximizes GH & memory consolidation
• Practice case questions mixing multiple systems (e.g. “Patient on prednisone develops hyperglycaemia & osteoporosis – explain.”)
• Enter exam with skip-return strategy and confidence from strengthened strong areas.