Psychological processes are regulated by two interacting communication networks: the electrochemical nervous system and the humoral endocrine system. Simultaneously, behavioral individual differences emerge from the interplay between an individual's genetic architecture and environmental exposures, formalised by behavioral genetics and epigenetics.
For CUET PG Psychology (HUQP20), Unit 4 questions in this domain focus on:
- Endocrine versus Nervous System Communication: Peptide versus steroid hormones, second messengers, and systemic blood circulation.
- The Master Glands & Target Organs: Hypothalamic-Pituitary axis (Anterior portal system vs. Posterior axonal neurosecretion), Pineal, Thyroid, Parathyroid, Adrenal (Cortex vs. Medulla), Pancreas, and Gonads.
- The Neurobiology of Stress: The Hypothalamic-Pituitary-Adrenal (HPA) Axis cascade (), negative feedback loops, and chronic glucocorticoid neurotoxicity.
- Foundations of Behavioral Genetics: Chromosomes, alleles, monogenic versus polygenic traits, and the mathematical definition of Heritability ().
- Chromosomal & Genetic Syndromes: Down (), Turner (), Klinefelter (), Fragile X, Phenylketonuria (PKU), and Huntington's chorea.
- Quantitative Methods & Epigenetics: Twin designs (MZ vs DZ concordance, Bouchard's MZA study), DNA methylation, histone modification, and Meaney's maternal care paradigm.
1. Endocrine vs. Nervous System Communication
| Feature | Nervous System | Endocrine System |
|---|---|---|
| Chemical Messenger | Neurotransmitters | Hormones |
| Transmission Medium | Microscopic synaptic cleft (~20–40 nm) | Systemic bloodstream (humoral circulation) |
| Speed of Onset | Milliseconds (Rapid, immediate) | Seconds, minutes, or hours (Gradual) |
| Duration of Action | Milliseconds (Brief, transient) | Prolonged (Minutes, hours, or days) |
| Target Selectivity | Discrete, highly localized postsynaptic receptors | Widespread across all body tissues expressing specific receptors |
Chemical Classification of Hormones:
- Peptide & Protein Hormones: Water-soluble chains of amino acids (e.g., Insulin, ACTH, Oxytocin, Vasopressin). Cannot freely cross lipid bilayers; bind to cell-surface GPCRs, activating intracellular second messengers (cAMP, ).
- Steroid Hormones: Lipid-soluble molecules synthesized from cholesterol (e.g., Cortisol, Aldosterone, Estrogen, Progesterone, Testosterone). Freely diffuse across the plasma membrane, binding to intracellular cytoplasmic/nuclear receptors to act as transcription factors altering DNA expression.
- Amine Hormones: Modified single amino acids (e.g., Epinephrine and Norepinephrine derived from tyrosine; Melatonin derived from tryptophan).
2. Master Endocrine Glands & Functional Hormone Matrix
| Feature | Anterior Pituitary (Adenohypophysis) | Posterior Pituitary (Neurohypophysis) |
|---|---|---|
| Embryological Origin | Glandular epithelial tissue (outgrowth of oral ectoderm / Rathke's pouch). | Neural tissue extension originating directly from the ventral hypothalamus. |
| Vascular / Neural Link | Connected via the Hypophyseal Portal System (blood vessel network conveying releasing hormones). | Connected via the Hypothalamo-hypophyseal tract (unmyelinated neurosecretory axons). |
| Hormone Synthesis | Actively synthesizes and secretes 6 major tropic hormones: GH, ACTH, TSH, Prolactin, FSH, LH. | DOES NOT SYNTHESIZE HORMONES! Only stores and releases hypothalamic peptides: Oxytocin & Vasopressin (ADH). |
Master Endocrine Glands & Pathology Matrix:
| Gland | Hormones Produced | Primary Physiological Function | Clinical Pathology / Disorder |
|---|---|---|---|
| Hypothalamus | CRH, GnRH, TRH, GHRH, Somatostatin, Dopamine | Regulates anterior pituitary secretion; master visceral controller. | Hypothalamic amenorrhea; central endocrine dysregulation. |
| Anterior Pituitary | ACTH (Adrenocorticotropic); TSH (Thyroid-stimulating); GH (Growth Hormone); FSH / LH (Gonadotropins); Prolactin | Drives adrenal cortex, thyroid, and gonads; somatic cellular growth, milk synthesis. | Excess GH: Gigantism (childhood), Acromegaly (adulthood). Deficit GH: Pituitary Dwarfism. |
| Posterior Pituitary | Oxytocin; Vasopressin (ADH) (Both synthesized in hypothalamus) | Oxytocin: uterine contractions, milk letdown, pair bonding. ADH: renal water retention, vasoconstriction. | Deficit ADH Diabetes Insipidus (extreme polyuria and thirst; unlinked to blood sugar!). |
| Pineal Gland | Melatonin | Synthesized from serotonin; regulates circadian sleep-wake cycles; suppressed by blue light via SCN. | Jet lag, Shift-work sleep disorder, Seasonal Affective Disorder (SAD). |
| Thyroid Gland | Thyroxine (); Triiodothyronine () | Sets Basal Metabolic Rate (BMR), neural development, cellular respiration. | Hyperthyroidism (Grave's): Tachycardia, weight loss, anxiety. Hypothyroidism: Lethargy, weight gain, depression, Cretinism (congenital intellectual disability). |
| Parathyroid | Parathyroid Hormone (PTH) | Elevates blood calcium () via bone resorption and renal reabsorption. | Tetany, muscle spasms (hypoparathyroidism); kidney stones (hyperparathyroidism). |
| Adrenal Cortex | Cortisol (Glucocorticoid); Aldosterone (Mineralocort.); Androgens | Fuel mobilization, immunosuppression, sodium retention, long-term stress response. | Cushing's Syndrome: Hypercortisolemia (moon face, buffalo hump, depression). Addison's Disease: Hypocortisolemia (fatigue, hypotension, hyperpigmentation). |
| Adrenal Medulla | Epinephrine (80%); Norepinephrine (20%) | Secreted directly in response to sympathetic preganglionic ACh; acute fight-or-flight shock. | Pheochromocytoma (catecholamine-secreting tumor causing severe paroxysmal hypertension). |
| Pancreas (Islets) | Insulin (Beta cells); Glucagon (Alpha cells) | Insulin: drives cellular glucose uptake (lowers blood sugar). Glucagon: stimulates glycogenolysis in liver. | Diabetes Mellitus (hyperglycemia); reactive Hypoglycemia (irritability, anxiety, shakiness). |
| Gonads (Testes/Ovaries) | Testosterone (Leydig cells); Estrogen & Progesterone | Primary/secondary sex characteristics; reproductive behavior, neural sexual dimorphism. | Organizational vs Activational effects (Phoenix et al., 1959). |
[!IMPORTANT] Organizational vs. Activational Effects of Sex Hormones:
- Organizational Effects: Permanent, irreversible structural differentiation of neural circuitry and anatomy occurring during early critical perinatal developmental windows (e.g., prenatal testosterone organizing male genitalia and masculinizing the hypothalamic preoptic area).
- Activational Effects: Transient, reversible physiological and behavioral modulations induced by circulating hormones in mature adult organisms (e.g., testosterone facilitating adult sexual motivation or aggressive displays; estrogen modulating menstrual mood).