Endocrine system
65 flashcards covering Endocrine system for the MCAT Biology & Biochemistry section.
The endocrine system is a network of glands that produce and release hormones into the bloodstream, acting as chemical messengers to regulate various bodily functions. These hormones control processes like growth, metabolism, reproduction, and stress response, helping maintain homeostasis. For instance, the thyroid gland releases hormones that influence energy levels, while the adrenal glands handle fight-or-flight reactions. This system works alongside the nervous system but operates more slowly, with effects lasting from minutes to days, making it essential for long-term body regulation.
On the MCAT, the endocrine system frequently appears in Biology & Biochemistry questions that test hormone identification, feedback mechanisms, and related disorders. Expect multiple-choice items asking about hormone functions, such as how insulin affects blood sugar, or scenarios involving disruptions like hypothyroidism. Common traps include mixing up similar hormones, like estrogen and progesterone, or overlooking negative feedback loops that regulate hormone levels. Focus on key glands, major hormones, and their interactions with other systems to avoid pitfalls and answer effectively.
Practice drawing feedback loops to solidify your understanding.
Terms (65)
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Endocrine system
The endocrine system is a network of glands that produce and secrete hormones directly into the bloodstream to regulate various bodily functions such as metabolism, growth, and reproduction.
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Hormone
A hormone is a chemical messenger produced by endocrine glands and released into the blood to affect target cells or organs, influencing processes like growth and metabolism.
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Steroid hormone
Steroid hormones, derived from cholesterol, are lipid-soluble molecules that pass through cell membranes and bind to intracellular receptors to alter gene expression.
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Peptide hormone
Peptide hormones are chains of amino acids that are water-soluble and bind to cell surface receptors, often triggering second messenger systems inside the cell.
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Amine hormone
Amine hormones are derived from amino acids like tyrosine and include molecules such as epinephrine, which act quickly to regulate functions like stress response.
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Hypothalamus
The hypothalamus is a brain region that links the nervous system to the endocrine system by producing releasing and inhibiting hormones that control the pituitary gland.
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Pituitary gland
The pituitary gland, often called the master gland, is a small structure at the base of the brain that secretes hormones regulating other endocrine glands and bodily functions.
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Anterior pituitary
The anterior pituitary produces and releases tropic hormones like ACTH and TSH, which stimulate other endocrine glands to secrete their own hormones.
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Posterior pituitary
The posterior pituitary stores and releases hormones produced by the hypothalamus, such as oxytocin and vasopressin, which are involved in childbirth and water balance.
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Thyroid gland
The thyroid gland in the neck produces hormones like thyroxine that regulate metabolism, growth, and development by controlling the body's energy use.
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Thyroxine (T4)
Thyroxine, or T4, is a thyroid hormone that increases metabolic rate and is converted to T3 in target tissues to exert its effects on cellular activity.
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Triiodothyronine (T3)
Triiodothyronine, or T3, is the active form of thyroid hormone that binds to nuclear receptors to influence gene expression and boost metabolic processes.
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Calcitonin
Calcitonin is a hormone secreted by the thyroid that lowers blood calcium levels by inhibiting bone resorption and promoting calcium excretion in the kidneys.
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Parathyroid gland
The parathyroid glands, located near the thyroid, secrete parathyroid hormone to maintain blood calcium levels by stimulating bone breakdown and calcium reabsorption.
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Parathyroid hormone (PTH)
Parathyroid hormone increases blood calcium by promoting bone resorption, renal calcium reabsorption, and vitamin D activation.
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Adrenal gland
The adrenal glands, situated above the kidneys, produce hormones that regulate stress response, blood pressure, and metabolism through their cortex and medulla.
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Adrenal cortex
The adrenal cortex secretes steroid hormones like cortisol and aldosterone, which manage stress, inflammation, and electrolyte balance.
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Adrenal medulla
The adrenal medulla produces catecholamines such as epinephrine and norepinephrine, which trigger the fight-or-flight response during stress.
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Cortisol
Cortisol is a glucocorticoid hormone from the adrenal cortex that increases blood glucose by promoting gluconeogenesis and suppresses immune responses.
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Aldosterone
Aldosterone is a mineralocorticoid hormone that regulates sodium and potassium balance by promoting sodium reabsorption in the kidneys.
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Epinephrine
Epinephrine, released by the adrenal medulla, is a catecholamine that rapidly increases heart rate, blood pressure, and energy availability during stress.
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Norepinephrine
Norepinephrine is a catecholamine that acts as both a hormone and neurotransmitter, helping to constrict blood vessels and maintain blood pressure.
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Pancreas
The pancreas functions as both an endocrine and exocrine gland, secreting hormones like insulin and glucagon to regulate blood glucose levels.
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Insulin
Insulin is a hormone from the beta cells of the pancreas that lowers blood glucose by promoting its uptake into cells and storage as glycogen.
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Glucagon
Glucagon is a hormone from the alpha cells of the pancreas that raises blood glucose by stimulating glycogen breakdown and gluconeogenesis in the liver.
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Ovaries
The ovaries in females produce estrogen and progesterone, which regulate the menstrual cycle, pregnancy, and secondary sexual characteristics.
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Estrogen
Estrogen is a sex hormone that promotes the development of female secondary sexual characteristics and regulates the reproductive cycle.
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Progesterone
Progesterone prepares the uterus for pregnancy by maintaining the endometrial lining and supporting gestation if fertilization occurs.
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Testes
The testes in males produce testosterone, which is essential for sperm production and the development of male secondary sexual characteristics.
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Testosterone
Testosterone is the primary male sex hormone that stimulates spermatogenesis and the growth of muscle and bone mass.
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Pineal gland
The pineal gland produces melatonin, which helps regulate the sleep-wake cycle by responding to light-dark signals from the environment.
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Melatonin
Melatonin is a hormone that induces sleep and regulates circadian rhythms by being released in response to darkness.
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Negative feedback
Negative feedback is a regulatory mechanism in the endocrine system where an increase in hormone levels inhibits further release to maintain homeostasis.
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Positive feedback
Positive feedback amplifies a process, such as the release of oxytocin during childbirth, to push it to completion rather than maintaining balance.
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Hypothalamic-pituitary axis
The hypothalamic-pituitary axis is a key regulatory pathway where the hypothalamus controls the pituitary gland's hormone secretion to influence other endocrine functions.
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Thyrotropin-releasing hormone (TRH)
TRH is a hypothalamic hormone that stimulates the anterior pituitary to release TSH, which in turn prompts the thyroid to produce thyroid hormones.
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Corticotropin-releasing hormone (CRH)
CRH from the hypothalamus triggers the release of ACTH from the pituitary, leading to cortisol production by the adrenal glands.
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Second messenger system
A second messenger system, like cAMP, relays signals from hormone-bound receptors on the cell surface to alter intracellular activities.
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Hormone receptor
A hormone receptor is a protein on or inside target cells that binds specifically to a hormone, initiating a cellular response.
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Down-regulation
Down-regulation occurs when prolonged exposure to a hormone decreases the number of receptors on target cells, reducing sensitivity to that hormone.
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Up-regulation
Up-regulation is the increase in receptor numbers on target cells in response to low hormone levels, enhancing sensitivity to the hormone.
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Diabetes mellitus
Diabetes mellitus is a disorder characterized by high blood glucose due to insufficient insulin production or ineffective insulin action.
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Type 1 diabetes
Type 1 diabetes results from autoimmune destruction of pancreatic beta cells, leading to absolute insulin deficiency and requiring insulin therapy.
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Type 2 diabetes
Type 2 diabetes involves insulin resistance and relative insulin deficiency, often linked to obesity and managed through lifestyle and medications.
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Addison's disease
Addison's disease is a condition caused by insufficient adrenal cortex hormones, leading to symptoms like fatigue and low blood pressure.
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Cushing's syndrome
Cushing's syndrome results from excessive cortisol, causing symptoms such as weight gain and high blood pressure due to adrenal or pituitary issues.
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Goiter
A goiter is an enlargement of the thyroid gland, often due to iodine deficiency or hormonal imbalances, which can disrupt thyroid function.
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Acromegaly
Acromegaly is a disorder from excess growth hormone in adults, leading to enlarged bones and tissues, typically caused by a pituitary tumor.
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Gigantism
Gigantism occurs when excess growth hormone is secreted before puberty, resulting in abnormal body growth and increased height.
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Hormone transport
Hormones are transported in the blood, with lipid-soluble ones often bound to carrier proteins to increase solubility and extend their half-life.
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Hormone half-life
The half-life of a hormone is the time it takes for its concentration in the blood to halve, varying by type and affecting how long its effects last.
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Endocrine vs. exocrine glands
Endocrine glands secrete hormones into the bloodstream, while exocrine glands release substances like enzymes into ducts.
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Tropic hormone
A tropic hormone targets another endocrine gland to stimulate its hormone production, such as TSH stimulating the thyroid.
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Non-tropic hormone
A non-tropic hormone acts directly on non-endocrine tissues, like growth hormone affecting muscle and bone growth.
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Oxytocin
Oxytocin is a posterior pituitary hormone that stimulates uterine contractions during labor and milk ejection during breastfeeding.
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Vasopressin
Vasopressin, or ADH, is released by the posterior pituitary to conserve water by increasing its reabsorption in the kidneys.
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Growth hormone (GH)
Growth hormone, secreted by the anterior pituitary, promotes growth and metabolism by stimulating protein synthesis and fat breakdown.
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Prolactin
Prolactin is an anterior pituitary hormone that stimulates milk production in mammary glands after childbirth.
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Follicle-stimulating hormone (FSH)
FSH, from the anterior pituitary, stimulates ovarian follicle development in females and spermatogenesis in males.
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Luteinizing hormone (LH)
LH, secreted by the anterior pituitary, triggers ovulation in females and testosterone production in males.
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Renin-angiotensin-aldosterone system
The RAAS is a hormone pathway that regulates blood pressure and fluid balance by having renin trigger aldosterone release to retain sodium.
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Insulin resistance
Insulin resistance is a condition where cells fail to respond properly to insulin, leading to elevated blood glucose and often preceding type 2 diabetes.
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Thyroid-stimulating hormone (TSH)
TSH, from the anterior pituitary, stimulates the thyroid gland to produce and release thyroid hormones.
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cAMP pathway
The cAMP pathway is a second messenger system activated by hormones like epinephrine, amplifying signals to alter cellular functions like glycogen breakdown.
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Hormone feedback loop
A hormone feedback loop is a control mechanism, usually negative, that adjusts hormone secretion based on the levels of the hormone or its effects.