Neuroendocrinology: Hormones and Sex

Comprehensive vocabulary flashcards covering neuroendocrine signaling, hypothalamic-pituitary axes, hormone classes, feedback regulation, and the biology of sexual differentiation and orientation.

Neuroendocrinology

The study of how the nervous system and endocrine system interact to control bodily functions and behavior.

Endocrine System

A network of ductless glands that produce and release chemical messengers known as hormones into the bloodstream to regulate bodily functions.

Hormones

Chemical messengers secreted by endocrine cells into the bloodstream that travel to act on specific target tissues to modulate neural activity, muscle movement, and stimulus salience.

Neural Communication

Signaling wherein neurotransmitters are released into the synaptic cleft to target nearby postsynaptic neurons over short distances (millimeters) with rapid on/off action (milliseconds), precise localized targeting, and all-or-none effects.

Endocrine Communication

Signaling wherein hormones are released into the bloodstream to selectively affect distant target organs over long distances (up to meters) with slow on/off action (minutes, hours, or days), diffuse targeting, graded effects, and often pulsatile secretion.

Pheromone Communication

Chemical communication in which chemical signals are released outside the body for detection by other individuals of the same species.

Allomone Communication

Chemical signaling in which chemical signals are released outside the body by members of one species to alter the behavior of individuals of another species.

Peptide Hormones

A chemical class of hormones made of short chains of amino acids, such as adrenocorticotropic hormone (ACTH), growth hormone (GH), insulin, glucagon, oxytocin, and vasopressin.

Amine Hormones

A chemical class of hormones derived from single modified amino acids, including epinephrine (adrenaline), norepinephrine, thyroid hormones (thyroxine), and melatonin.

Steroid Hormones

A chemical class of lipid-derived hormones synthesized from cholesterol, encompassing estrogens (such as estradiol), progestins (such as progesterone), androgens (testosterone and dihydrotestosterone), glucocorticoids (cortisol), and mineralocorticoids (aldosterone).

Dual-Action Chemical Messengers

Molecules whose function depends on site of release, such as norepinephrine, which serves locally as a neurotransmitter regulating attention and arousal in the nervous system, but acts as a stress hormone when secreted into the bloodstream by the adrenal glands.

Cell-Surface Receptors (Peptides and Amines)

Receptors located on the plasma membrane (mostly G protein-coupled receptors) that bind water-soluble peptide and amine hormones, triggering intracellular second messenger cascades on a timescale of seconds to minutes.

Intracellular Receptors (Steroid Hormones)

Receptors located inside the cytoplasm or nucleus that bind lipid-soluble steroids that freely diffuse across the cell membrane; the resulting steroid-receptor complex acts as a transcription factor regulating gene expression over hours, days, or years.

Hypothalamus

A structure located at the base of the brain beneath the thalamus that serves as the neuroendocrine bridge, integrating neural and hormonal signals to govern pituitary secretions, body temperature, hunger, thirst, sleep, and emotional states.

Pituitary Gland

A pea-sized endocrine structure at the base of the brain attached to the hypothalamus via the infundibulum (stalk); regarded as the 'master gland' because it coordinates and regulates peripheral endocrine glands.

Anterior Pituitary

The front lobe of the pituitary gland that synthesizes and secretes six major hormones: growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin.

Posterior Pituitary

The rear lobe of the pituitary gland that does not synthesize hormones of its own, but stores and releases oxytocin and vasopressin produced by hypothalamic neuroendocrine cells.

Tropic Hormones

Pituitary hormones released into the systemic circulation that specifically stimulate other peripheral endocrine glands to release their own hormones.

Hypothalamic-Pituitary Portal System

A local vascular network into which hypothalamic neurons secrete releasing and inhibiting hormones, directly carrying them to the anterior pituitary gland.

HPT Axis (Hypothalamic-Pituitary-Thyroid)

The endocrine loop controlling basal metabolic rate and heat generation, where hypothalamic TRH triggers anterior pituitary TSH release, prompting the thyroid gland to secrete T3 and T4.

HPS Axis (Hypothalamic-Pituitary-Somatotropic)

The endocrine loop regulating growth and cellular metabolism, in which hypothalamic GHRH triggers GH release from the anterior pituitary (inhibited by somatostatin), stimulating the liver to produce IGF-1.

HPA Axis (Hypothalamic-Pituitary-Adrenal)

The neuroendocrine pathway mediating the stress response, in which hypothalamic CRH stimulates anterior pituitary ACTH release, triggering cortisol secretion from the adrenal cortex.

HPG Axis (Hypothalamic-Pituitary-Gonadal)

The endocrine loop driving reproductive development and function, wherein hypothalamic GnRH prompts the anterior pituitary to secrete LH and FSH, stimulating sex steroid production and gametogenesis in the gonads.

Vasopressin (Antidiuretic Hormone / ADH)

A hypothalamic peptide released from the posterior pituitary in response to increased blood osmolality or decreased blood pressure, which functions to elevate blood pressure and reduce urine formation.

Oxytocin

A hypothalamic peptide released by the posterior pituitary during labor in response to cervical stretch or during lactation in response to suckling, driving uterine smooth muscle contractions and milk ejection.

Negative Feedback Regulation

A homeostatic mechanism where rising concentrations of a circulating target hormone bind receptors at the pituitary and hypothalamus to inhibit further synthesis and secretion of releasing and tropic hormones.

Positive Feedback Regulation

A regulatory mechanism where an initial hormonal response stimulates an escalating release of the same hormone to intensify a process until a specific endpoint is achieved (e.g., oxytocin during childbirth).

Thyroid Goiter

An enlargement of the thyroid gland triggered by dietary iodine deficiency, which prevents synthesis of T3 and T4, removes negative feedback inhibition, and causes chronically elevated TSH secretion that overstimulates the gland.

Pituitary Dwarfism

A condition characterized by significantly reduced bodily stature and stunted skeletal development resulting from growth hormone (GH) deficiency in the anterior pituitary during childhood.

Gigantism and Acromegaly

Disorders resulting from GH hypersecretion (commonly from benign pituitary adenomas), producing gigantism when occurring in children prior to epiphyseal fusion, and acromegaly (enlarged hands, feet, and facial features) in adults.

Cushing's Disease

An endocrine disorder caused by a benign pituitary tumor oversecreting ACTH, which induces excessive cortisol release characterized by central body obesity, thin limbs, hip/thigh muscle wasting, hypertension, and diabetes.

Central Diabetes Insipidus

A disorder caused by damage to the hypothalamus or posterior pituitary resulting in deficient vasopressin secretion, leading to excessive urination, extreme thirst, and potential dehydration.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion)

A condition stemming from damage to the hypothalamus or posterior pituitary that causes excessive vasopressin secretion, leading to systemic water retention and dilutional hyponatremia (abnormally low blood sodium).

Sex (Biological Sex)

The biological categorization of an organism as male or female based on chromosomal composition, gonadal anatomy, and sex steroid profiles.

Gender

An individual's psychological sense of self and social or cultural identity (such as man, woman, non-binary, or bi-gender), distinct from biological sex.

Brain Connectivity Sex Differences

Patterns identified by Verma et al. (2013) demonstrating that male brains show greater front-to-back intra-hemispheric connectivity (linking perception to motor execution), whereas female brains display greater left-to-right inter-hemispheric connectivity (facilitating communication between analytical and intuitive processing).

Mental Rotation Task

A spatial ability test (studied by Vandenburg and Kuse, 1978) on which males on average achieve higher visual-spatial performance scores than females, despite substantial overlap in population distributions.

SRY Gene

The Sex-determining Region Y gene located on the short arm of the Y chromosome that initiates testes development in early embryos; in its absence, the indifferent gonads develop into ovaries.

Indifferent Gonads

The early embryonic reproductive tissue present at approximately 5 to 6 weeks of gestation that possesses the capacity to develop into either testes or ovaries, accompanied by both Wolffian and Müllerian duct systems.

Wolffian Ducts

Embryonic precursor structures that differentiate into male internal genitalia (epididymis, vas deferens, and seminal vesicles) under the stimulation of testosterone from fetal testes.

Müllerian Ducts

Embryonic precursor structures that develop into female internal genitalia (fallopian tubes, uterus, and upper vagina) in the absence of anti-müllerian hormone.

Anti-Müllerian Hormone (AMH)

A peptide hormone secreted by the developing testes that actively induces the regression and disappearance of the Müllerian ducts during male fetal differentiation.

Organizing Effects of Hormones

Permanent, irreversible structural modifications to bodily anatomy and neural circuits caused by steroid exposure during prenatal or pubertal critical (sensitive) periods.

Activating Effects of Hormones

Reversible, transient alterations in physiology or behavior that occur across adulthood and fluctuate depending on current circulating levels of sex hormones.

Berthold's Experiment (1849)

A classic experiment involving testicular transplantation in roosters that provided the initial proof of the organizational effects of circulating hormones during a critical developmental window.

Sexually Dimorphic Nucleus of the POA (SDN-POA)

A densely populated subregion of the medial preoptic area in the hypothalamus that is 2 to 3 times larger in males than in females, whose volume is established by perinatal exposure to testosterone.

INAH-3 (Interstitial Nuclei of the Anterior Hypothalamus-3)

The human hypothalamic equivalent of the rat SDN-POA; reported by Simon LeVay (1991) to be significantly smaller in homosexual men compared to heterosexual men.

Biological Hypothesis of Sexual Orientation

The scientific framework indicating that sexual orientation is shaped by prenatal hormonal and genetic factors rather than social influence, supported by early gender nonconformity (ages 4–5), identical twin concordance, and fraternal birth order effects.

Androgen Insensitivity Syndrome (AIS / Morris Syndrome)

A condition in XY individuals caused by mutations in the androgen receptor gene; testes develop and produce testosterone, but lack of receptor responsiveness results in female external anatomy, absent uterus, undescended testes, and female-typical behavior.

Congenital Adrenal Hyperplasia (CAH)

A condition in XX individuals where defective adrenal steroidogenesis leads to prenatal overproduction of androgens, resulting in varying degrees of masculinized (intersex) external genitalia despite the presence of normal ovaries.

Turner's Syndrome

A genetic condition characterized by a single X chromosome (45,X); because no Y chromosome or SRY gene is present, the individual develops as a female without masculinization.

Klinefelter's Syndrome

A genetic condition in males possessing an extra X chromosome (XXY), leading to abnormal testicular development, low circulating testosterone levels, reduced muscle mass, and occasionally enlarged breasts.

Triple X Syndrome

A chromosomal condition in females characterized by three X chromosomes (XXX), typically presenting with normal female anatomical and reproductive development.