MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 3a Nervous Endocrine Integration

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This deck focuses on 3a Nervous Endocrine Integration, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Identify the feedback type: rising $T_3/T_4$ reduces TRH and TSH secretion.

Answer: Negative feedback. This regulatory loop suppresses TRH and TSH to prevent excessive thyroid hormone levels and maintain metabolic equilibrium.

Flashcard 2: What type of signaling is used when a neuron releases a hormone into the bloodstream?

Answer: Neuroendocrine signaling. This mechanism allows neurons to influence distant targets by secreting hormones into the blood, bridging neural and endocrine systems.

Flashcard 3: What is the term for a hormone acting on the same cell that secreted it?

Answer: Autocrine signaling. This self-regulatory mechanism enables cells to modulate their own activity through receptors binding their secreted signaling molecules.

Flashcard 4: What is the immediate second messenger produced by adenylyl cyclase in GPCR signaling?

Answer: cAMP. Adenylyl cyclase catalyzes ATP conversion to cAMP, which activates protein kinase A to propagate GPCR-mediated signals.

Flashcard 5: What type of feedback does cortisol exert on CRH and ACTH secretion under normal physiology?

Answer: Negative feedback on hypothalamus and anterior pituitary. This mechanism inhibits CRH and ACTH production to maintain glucocorticoid homeostasis and prevent overactivation of the stress response.

Flashcard 6: What is the main anatomical link that integrates the nervous and endocrine systems?

Answer: Hypothalamus (via control of the pituitary gland). The hypothalamus receives neural inputs and modulates endocrine activity by regulating pituitary hormone secretion through releasing and inhibiting factors.

Flashcard 7: What is the key difference in how the anterior versus posterior pituitary releases hormones?

Answer: Anterior: secretes; posterior: releases hypothalamic-made hormones. The anterior pituitary synthesizes its own hormones in response to hypothalamic signals, while the posterior stores and secretes pre-made hypothalamic hormones.

Flashcard 8: What is the hypothalamic-pituitary-thyroid (HPT) axis hormone sequence for thyroid hormone release?

Answer: TRH $$ TSH $$ $T_3/T_4$. TRH prompts pituitary TSH secretion, which stimulates thyroid production of $T_3$ and $T_4$ for metabolic regulation.

Flashcard 9: Which adrenal region secretes steroid hormones such as cortisol and aldosterone?

Answer: Adrenal cortex. Derived from mesoderm, it produces glucocorticoids, mineralocorticoids, and androgens to regulate metabolism, electrolytes, and reproduction.

Flashcard 10: What is the term for a hormone acting on nearby cells without entering systemic circulation?

Answer: Paracrine signaling. Local diffusion of signaling molecules affects neighboring cells, facilitating tissue-specific communication without broad systemic effects.

Flashcard 11: Which class of hormones typically binds intracellular receptors and alters gene transcription?

Answer: Steroid hormones (and thyroid hormone). These lipophilic molecules cross membranes to bind nuclear receptors, directly influencing DNA transcription for prolonged effects.

Flashcard 12: Which adrenal region secretes catecholamines and is functionally analogous to a sympathetic ganglion?

Answer: Adrenal medulla. As a modified sympathetic ganglion, it releases catecholamines in response to neural input, amplifying fight-or-flight effects.

Flashcard 13: What is the hypothalamic-pituitary-adrenal (HPA) axis hormone sequence for cortisol release?

Answer: CRH $$ ACTH $$ cortisol. CRH from the hypothalamus stimulates pituitary ACTH release, which induces adrenal cortisol production for stress adaptation.

Flashcard 14: What is the term for a hormone traveling through blood to act on distant target tissues?

Answer: Endocrine signaling. Hormones secreted into the bloodstream reach distant organs, enabling coordinated physiological responses across the body.

Flashcard 15: Which class of hormones typically binds cell-surface receptors and uses second messengers?

Answer: Peptide/protein hormones and catecholamines. Hydrophilic nature prevents membrane crossing, so they activate surface receptors, triggering intracellular cascades via molecules like cAMP.

Flashcard 16: What is the physiologic role of the sympathetic-adrenal medullary axis in acute stress?

Answer: Rapid release of epinephrine and norepinephrine for fight-or-flight. Sympathetic stimulation of the adrenal medulla triggers catecholamine release, preparing the body for immediate stress response via metabolic and cardiovascular changes.

Flashcard 17: What is the portal blood system that carries hypothalamic hormones to the anterior pituitary?

Answer: Hypothalamic-hypophyseal portal system. This vascular connection enables direct delivery of hypothalamic regulatory hormones to anterior pituitary cells, bypassing systemic circulation for efficient control.

Flashcard 18: What is the hypothalamic-pituitary-gonadal (HPG) axis pituitary hormone released in response to GnRH?

Answer: LH and FSH. GnRH stimulates release of these gonadotropins, which regulate gametogenesis and sex hormone production in the gonads.

Flashcard 19: What is the defining feature of a target cell for a given hormone?

Answer: It expresses the specific receptor for that hormone. Hormone specificity arises from receptor expression, allowing only responsive cells to transduce the signal into cellular changes.

Flashcard 20: Which anterior pituitary hormone is primarily inhibited (not stimulated) by hypothalamic dopamine?

Answer: Prolactin. Dopamine from the hypothalamus tonically inhibits prolactin to control lactation, reproduction, and immune functions.

Flashcard 21: Which option best describes epinephrine action: intracellular receptor or cell-surface receptor?

Answer: Cell-surface receptor (adrenergic GPCR). As a hydrophilic catecholamine, it activates membrane-bound GPCRs to initiate rapid intracellular signaling via second messengers.

Flashcard 22: Which hormone mediates uterine contractions and milk ejection and is classically regulated by positive feedback?

Answer: Oxytocin. Positive feedback amplifies its release during labor and nursing, enhancing contractions and milk let-down for parturition and breastfeeding.

Flashcard 23: Identify the endocrine hormone released in response to increased plasma osmolarity to conserve water.

Answer: ADH (vasopressin). Detected by hypothalamic osmoreceptors, it triggers ADH release to enhance renal water reabsorption and maintain osmotic balance.