Compendium 10
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Questions and Answers

What role do axon terminals play in the release of neurohormones?

Axon terminals store neurohormones and release them into the circulatory system when action potentials occur.

Describe the function of antidiuretic hormone (ADH) in the body.

ADH stimulates the reabsorption of sodium and water from nephrons, resulting in less and more concentrated urine, thus preserving water.

How does oxytocin function during childbirth?

Oxytocin stimulates uterine contractions during labor.

What is the primary mechanism by which hormone secretion is controlled in the endocrine system?

<p>Hormone secretion is predominantly controlled through negative feedback mechanisms.</p> Signup and view all the answers

What physiological changes does the release of epinephrine and norepinephrine induce in the body during physical activity?

<p>They increase the release of glucose and fatty acids into the blood, raise heart rate, and redirect blood flow to the heart and skeletal muscles.</p> Signup and view all the answers

Differentiate between tropic and non-tropic hormones.

<p>Tropic hormones target other endocrine glands to stimulate hormone secretion, while non-tropic hormones directly affect target tissues.</p> Signup and view all the answers

Explain the role of the anterior pituitary in hormone regulation.

<p>The anterior pituitary secretes tropic hormones that regulate other endocrine glands and are subject to feedback loops.</p> Signup and view all the answers

Explain the role of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the reproductive system.

<p>LH and FSH regulate gamete production and reproductive hormones, promoting the function and growth of the gonads.</p> Signup and view all the answers

What distinguishes tropic hormones from non-tropic hormones, and provide an example of each?

<p>Tropic hormones stimulate other glands to release their hormones, while non-tropic hormones act directly on target cells; examples include LH (tropic) and prolactin (non-tropic).</p> Signup and view all the answers

What is positive feedback in the context of hormone secretion?

<p>Positive feedback enhances the secretion of hormones, leading to an increase in the activity of the hypothalamus and anterior pituitary.</p> Signup and view all the answers

How does the hypothalamus influence the secretion of hormones from the anterior pituitary gland?

<p>The hypothalamus secretes releasing hormones that stimulate or inhibit the secretion of hormones from the anterior pituitary.</p> Signup and view all the answers

How do posterior pituitary hormones reach their target tissues?

<p>Posterior pituitary hormones travel through the blood to their target tissues after being released.</p> Signup and view all the answers

Describe the function of oxytocin and its mechanism of action during breastfeeding.

<p>Oxytocin facilitates the release of breast milk in response to suckling through a positive feedback mechanism.</p> Signup and view all the answers

What is the role of corticotropin-releasing hormone (CRH) in the anterior pituitary?

<p>CRH stimulates the secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary.</p> Signup and view all the answers

How does cortisol exhibit a negative feedback effect?

<p>Cortisol inhibits the release of CRH from the hypothalamus and ACTH from the anterior pituitary.</p> Signup and view all the answers

What stimulates the release of ACTH from the anterior pituitary?

<p>ACTH is released in response to CRH binding to receptors in the anterior pituitary cells.</p> Signup and view all the answers

What physiological effects does cortisol have on target tissues?

<p>Cortisol increases fat and protein breakdown and elevates glucose levels.</p> Signup and view all the answers

Describe the function of oxytocin released from the posterior pituitary.

<p>Oxytocin increases uterine contractions and promotes milk ejection during lactation.</p> Signup and view all the answers

What triggers the hypothalamus to release oxytocin?

<p>Stretch of the uterus or stimulation of the nipples triggers oxytocin release.</p> Signup and view all the answers

What types of hormones does the anterior pituitary secrete?

<p>The anterior pituitary secretes tropic hormones, such as ACTH, that stimulate other glands.</p> Signup and view all the answers

Explain the difference between tropic and non-tropic hormones.

<p>Tropic hormones regulate the secretion of other hormones, while non-tropic hormones directly affect target tissues.</p> Signup and view all the answers

How do action potentials affect the release of oxytocin from the posterior pituitary?

<p>Action potentials stimulate the posterior pituitary to release oxytocin into the bloodstream.</p> Signup and view all the answers

Discuss the role of the hypothalamus in endocrine function.

<p>The hypothalamus produces releasing and inhibiting hormones that control the anterior pituitary.</p> Signup and view all the answers

What role does oxytocin play during childbirth?

<p>Oxytocin stimulates uterine contractions to facilitate childbirth.</p> Signup and view all the answers

How does growth hormone affect muscle and fat metabolism?

<p>Growth hormone stimulates protein synthesis for muscle growth and the breakdown of fats for energy.</p> Signup and view all the answers

Describe the main functions of thyroid hormones T3 and T4.

<p>T3 and T4 increase metabolism, regulate body temperature, and promote growth and development.</p> Signup and view all the answers

What triggers the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary?

<p>ACTH is released in response to corticotropin-releasing hormone from the hypothalamus.</p> Signup and view all the answers

What is the difference between tropic and non-tropic hormones?

<p>Tropic hormones target other endocrine glands, while non-tropic hormones directly affect tissues.</p> Signup and view all the answers

What is the significance of the hypothalamohypophysial portal system?

<p>This system allows the hypothalamus to control the anterior pituitary by delivering hormones directly.</p> Signup and view all the answers

What is the primary stimulus for the adrenal medulla to secrete epinephrine?

<p>Increased sympathetic nervous system activity triggers the adrenal medulla to release epinephrine.</p> Signup and view all the answers

What are the key components necessary for the production of thyroid hormones?

<p>Iodine and tyrosine are necessary for the production of T3 and T4.</p> Signup and view all the answers

How does growth hormone influence nutrient levels after meals?

<p>Growth hormone regulates blood levels of nutrients after meals by promoting nutrient uptake and metabolism.</p> Signup and view all the answers

What effect does the inner medulla of the adrenal glands have during stress?

<p>The adrenal medulla secretes epinephrine and norepinephrine to enhance the body's stress response.</p> Signup and view all the answers

What is the primary function of the hypothalamus in relation to the pituitary gland?

<p>The hypothalamus regulates the secretions of the anterior pituitary by releasing hormones into the blood.</p> Signup and view all the answers

Describe the structural difference between the anterior and posterior parts of the pituitary gland.

<p>The anterior pituitary is derived from glandular tissue, while the posterior pituitary is an extension of nervous tissue from the hypothalamus.</p> Signup and view all the answers

Give an example of a tropic hormone produced by the anterior pituitary and its function.

<p>Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to secrete thyroid hormones T3 and T4.</p> Signup and view all the answers

What hormones are classified as non-tropic, and what is their primary role?

<p>Non-tropic hormones like growth hormone (GH) initiate effects directly on body tissues rather than stimulating other glands.</p> Signup and view all the answers

How do hypothalamic releasing hormones influence the anterior pituitary?

<p>Releasing hormones travel through the bloodstream to the anterior pituitary, stimulating it to release hormones.</p> Signup and view all the answers

What role does the adrenal cortex play in the endocrine system?

<p>The adrenal cortex secretes hormones like cortisol and aldosterone, which are involved in stress response and metabolism.</p> Signup and view all the answers

Name the hormones produced in the posterior pituitary and their function.

<p>The posterior pituitary stores and releases oxytocin and antidiuretic hormone (ADH), which regulate uterine contractions and water balance, respectively.</p> Signup and view all the answers

Discuss the connection between the hypothalamus and adrenal medulla.

<p>The adrenal medulla is innervated by the nervous system and responds to stress by releasing epinephrine and norepinephrine.</p> Signup and view all the answers

What is the significance of the thymus gland in the endocrine system?

<p>The thymus gland plays a crucial role in the immune system, particularly during puberty when its function changes significantly.</p> Signup and view all the answers

How does the mode of transport differ between the nervous system and the endocrine system?

<p>The nervous system uses axons for rapid signaling, while the endocrine system transports hormones through the bloodstream over longer periods.</p> Signup and view all the answers

What is the role of growth hormone in muscle mass and energy metabolism?

<p>Growth hormone stimulates protein synthesis to build muscle mass and promotes the breakdown of fats for energy.</p> Signup and view all the answers

How does the thyroid gland regulate body metabolism?

<p>The thyroid gland releases hormones T3 and T4, which increase metabolism and body temperature.</p> Signup and view all the answers

What hormones are secreted by the adrenal cortex, and what are their main functions?

<p>The adrenal cortex secretes cortisol and aldosterone, which regulate stress response and sodium/water balance, respectively.</p> Signup and view all the answers

Describe the process by which TSH affects the thyroid gland.

<p>Thyroid-stimulating hormone (TSH) from the anterior pituitary stimulates the thyroid gland to produce T3 and T4.</p> Signup and view all the answers

What is the significance of iodine in thyroid hormone synthesis?

<p>Iodine is crucial for the production of thyroid hormones T3 and T4, as it is a key component in their structure.</p> Signup and view all the answers

What triggers the release of epinephrine from the adrenal medulla?

<p>The release of epinephrine is triggered by stress, physical activity, and low blood glucose levels.</p> Signup and view all the answers

What are the effects of growth hormone on nutrient levels after meals?

<p>Growth hormone helps to regulate blood levels of nutrients post-meal by promoting uptake and utilization of amino acids and fats.</p> Signup and view all the answers

Explain the function of adrenal androgens released from the adrenal cortex.

<p>Adrenal androgens are weak sex hormones that contribute to the development of secondary sexual characteristics.</p> Signup and view all the answers

How does the release of corticotropin-releasing hormone (CRH) affect the anterior pituitary?

<p>CRH binds to specific receptors in the anterior pituitary, stimulating the secretion of adrenocorticotropic hormone (ACTH).</p> Signup and view all the answers

What triggers the secretion of oxytocin from the posterior pituitary?

<p>The stretch of the uterus and stimulation of the breasts' nipples trigger the hypothalamus to release oxytocin.</p> Signup and view all the answers

Describe the feedback mechanism involving cortisol and its impact on CRH and ACTH release.

<p>Cortisol inhibits the release of CRH from the hypothalamus and ACTH from the anterior pituitary, demonstrating a negative feedback loop.</p> Signup and view all the answers

What is the role of adrenocorticotropic hormone (ACTH) in the adrenal glands?

<p>ACTH binds to receptors in the adrenal cortex, stimulating the secretion of glucocorticoids, primarily cortisol.</p> Signup and view all the answers

Explain the action of glucocorticoids like cortisol on target tissues.

<p>Glucocorticoids increase fat and protein breakdown, leading to elevated glucose levels in the bloodstream.</p> Signup and view all the answers

What is the primary function of autocrine signaling in chemical communication?

<p>Autocrine signaling primarily allows a cell to release signals that affect the same cell type, influencing its own functions.</p> Signup and view all the answers

What distinguishes paracrine signaling from endocrine signaling?

<p>Paracrine signaling affects nearby cells locally without entering the bloodstream, while endocrine signaling involves hormones traveling through the circulatory system to reach distant target cells.</p> Signup and view all the answers

In what way do neurotransmitters differ from hormones in terms of their action distance?

<p>Neurotransmitters act over short distances, influencing adjacent postsynaptic cells, while hormones can travel long distances in the bloodstream to reach target tissues.</p> Signup and view all the answers

Describe the hormone secretion category defined as 'acute'.

<p>Acute hormone secretion refers to a sudden and rapid release of hormones in response to immediate stimuli, such as the release of adrenaline during stress.</p> Signup and view all the answers

What are two primary functions of the endocrine system related to metabolism?

<p>The endocrine system regulates metabolism and controls blood glucose levels through hormones like insulin and glucagon.</p> Signup and view all the answers

How do target cells respond to hormones released by the endocrine system?

<p>Target cells respond to hormones because they possess specific receptors that bind to those hormones, triggering a physiological response.</p> Signup and view all the answers

What role do glands play in the endocrine system?

<p>Glands in the endocrine system secrete hormones into the circulatory system to regulate various bodily functions and maintain homeostasis.</p> Signup and view all the answers

Can you name two examples of chronic hormone secretion and their related hormones?

<p>Chronic hormone secretion includes sustained release of thyroid hormones and growth hormones, which help maintain metabolic balance and growth.</p> Signup and view all the answers

What impact does the endocrine system have on heart rate and blood pressure regulation?

<p>The endocrine system influences heart rate and blood pressure through hormones like epinephrine, which increase heart rate during stress responses.</p> Signup and view all the answers

Explain how hormone action can be related to tissue maturation.

<p>Hormones such as growth hormone and sex hormones regulate processes crucial for tissue maturation, including development during puberty and wound healing.</p> Signup and view all the answers

What is the overall effect of epinephrine and norepinephrine on the body's glucose levels during physical activity?

<p>They lead to increased release of glucose from the liver into the blood.</p> Signup and view all the answers

How does melanocyte stimulating hormone (MSH) impact skin cells?

<p>MSH stimulates melanocytes to produce melanin, the pigment responsible for skin color.</p> Signup and view all the answers

What key functions do luteinizing hormone (LH) and follicle-stimulating hormone (FSH) have in the reproductive system?

<p>They regulate the production of gametes and reproductive hormones in both males and females.</p> Signup and view all the answers

What regulates the secretion of prolactin, and how does it relate to breastfeeding?

<p>Prolactin secretion is governed by the prolactin inhibiting factor and it increases with demand during breastfeeding.</p> Signup and view all the answers

What is the primary role of anti-diuretic hormone (ADH) in the body?

<p>ADH reduces urine formation and increases water retention in the body.</p> Signup and view all the answers

How do the pancreatic alpha and beta cells differ in hormone secretion?

<p>Alpha cells secrete glucagon, while beta cells secrete insulin.</p> Signup and view all the answers

In what way does the release of oxytocin differ from that of tropic hormones?

<p>Oxytocin is a non-tropic hormone that primarily functions in milk ejection and uterine contractions without acting on other endocrine glands.</p> Signup and view all the answers

What physiological changes occur in the body due to increased heart rate in response to hormones like epinephrine?

<p>Increased heart rate enhances blood flow to key muscles and organs, preparing the body for physical activity.</p> Signup and view all the answers

What is the impact of decreased blood flow through the vessels of internal organs during hormone release?

<p>It prioritizes blood flow to the heart and skeletal muscles, enhancing their performance during stress or activity.</p> Signup and view all the answers

How does norepinephrine contribute to physiological responses in stressful situations?

<p>Norepinephrine increases alertness, heart rate, and blood flow to essential muscles.</p> Signup and view all the answers

What effect does decreased blood pressure have on the secretion of ADH?

<p>It stimulates increased secretion of ADH to promote water reabsorption and raise blood pressure.</p> Signup and view all the answers

How does oxytocin contribute to the process of lactation?

<p>Oxytocin facilitates the ejection of milk from lactating breasts during nursing.</p> Signup and view all the answers

Describe how negative feedback regulates hormone secretion in the endocrine system.

<p>Negative feedback involves hormones from target endocrine cells inhibiting the secretion of tropic hormones from the hypothalamus and anterior pituitary.</p> Signup and view all the answers

What is the role of positive feedback in the secretion of anterior pituitary hormones?

<p>Positive feedback amplifies hormone secretion, wherein hormones from target cells enhance the release of tropic hormones from the hypothalamus and anterior pituitary.</p> Signup and view all the answers

How do neurohormones released by the posterior pituitary reach their target tissues?

<p>They travel through the circulatory system to their specific target tissues.</p> Signup and view all the answers

In what way does the secretion of reproductive hormones involve the anterior pituitary?

<p>The anterior pituitary secretes tropic hormones like LH and FSH, which stimulate the gonads to produce sex hormones.</p> Signup and view all the answers

Which hormone is responsible for stimulating uterine contractions during childbirth?

<p>Oxytocin is responsible for stimulating uterine contractions during labor.</p> Signup and view all the answers

What physiological role does vasopressin (another name for ADH) play apart from water retention?

<p>Vasopressin also causes vasoconstriction, which helps increase blood pressure.</p> Signup and view all the answers

Explain the role of the hypothalamus in the release of anterior pituitary hormones.

<p>The hypothalamus secretes releasing hormones that stimulate the anterior pituitary to release its tropic hormones.</p> Signup and view all the answers

What triggers the secretion of oxytocin during breastfeeding?

<p>The act of the baby suckling at the breast triggers the release of oxytocin.</p> Signup and view all the answers

Study Notes

Neurohormones

  • Axon terminals of neurons store neurohormones.
  • Action potentials cause the release of neurohormones into the circulatory system.
  • Posterior pituitary hormones travel in the blood to target tissues.

Posterior Pituitary Hormones

  • Antidiuretic hormone (ADH) stimulates increased sodium and water reabsorption from nephrons, resulting in less concentrated urine.
  • ADH is also known as vasopressin, which constricts blood vessels and increases blood pressure.
  • Oxytocin stimulates uterine contraction during birth and milk ejection from the lactating breast (let-down reflex).

Control of Hormone Secretion

  • Negative Feedback
    • The anterior pituitary secretes a tropic hormone that travels in the blood to the target endocrine cell.
    • The hormone from the target endocrine cell travels to its target tissue.
    • The hormone from the target endocrine cell has a negative feedback effect on the hypothalamus and anterior pituitary, decreasing secretion of the tropic hormone.
  • Positive Feedback
    • The anterior pituitary secretes a tropic hormone that travels in the blood to the target endocrine cell.
    • The hormone from the target endocrine cell travels to its target tissue.
    • The hormone from the target endocrine cell has a positive feedback effect on the hypothalamus and anterior pituitary, increasing secretion of the tropic hormone.
    • Example: Immune system regulation

Endocrine Glands of the Body

  • Pineal Gland
    • Key endocrine gland.
    • Regulates sleep and wake cycles (circadian rhythm).
  • Hypothalamus
    • Part of the central nervous system.
    • Produces key hormones, such as oxytocin and ADH.
    • Regulates the anterior pituitary.
  • Pituitary Gland
    • Composed of anterior and posterior parts.
    • Major source of tropic hormones.
  • Thyroid Gland
    • Plays a role in stress response and growth.
  • Parathyroid Gland
    • Located on the dorsal aspect of the thyroid gland.
    • Involved in bone metabolism.
  • Thymus Gland
    • Part of the immune system.
    • Experiences significant changes at puberty.
  • Adrenal Gland
    • Has an outer cortex and inner medulla.
    • Cortex: secretes cortisol and aldosterone.
    • Medulla: secretes adrenaline and noradrenaline.
  • Pancreas
    • Regulates sugar metabolism.
  • Ovary
    • Produces oocytes and key hormones.
  • Testes
    • Produces sperm and key hormones.

Nervous vs Endocrine Systems

  • Similarities
    • Both are associated with the brain.
      • Endocrine: hypothalamus.
    • Both use chemical messengers:
      • Nervous system: neurotransmitters.
      • Endocrine: hormones.
    • Both systems cooperate.
      • Example: Adrenal medulla is innervated by the nervous system.
  • Differences
    • Mode of Transport
      • Nervous system: Axon.
      • Endocrine system: Blood.
    • Speed of Response
      • Nervous system: Instant/milliseconds.
      • Endocrine system: Minutes/days.

Structure of the Pituitary Gland

  • The "master gland" connected to the hypothalamus via the infundibulum.
  • Due to their different embryonic origins, the two parts are composed of different tissues:
    • Posterior pituitary (neurohypophysis): Extension of the nervous system via the infundibulum. Secretes neuropeptides.
    • Anterior pituitary (adenohypophysis): Develops from the embryonic oral cavity and secretes traditional hormones.

The Pituitary Gland and the Hypothalamus

  • The interaction point for the nervous and endocrine systems.
  • The hypothalamus regulates secretions of the anterior pituitary.
  • The posterior pituitary is an extension of the hypothalamus.
    • The hypothalamus makes neuropeptides which travel down the stalk and are released by the posterior pituitary.
  • The pituitary gland produces nine major hormones that:
    • Regulate body functions.
    • Regulate the secretions of other endocrine glands.

Hypothalamic Control of the Posterior Pituitary

  • Hormones produced in neurons in the hypothalamus are stored in the posterior pituitary.
    • Axons from the hypothalamohypophysial tract.
  • Action potentials in these neurons cause hormone release.
  • Hypothalamic Control of Anterior Pituitary
    • Blood vessels of the hypothalamohypophysial portal system connect the areas.
    • Hypothalamic releasing and inhibiting factors stimulate or inhibit hormone release from the anterior pituitary.

Hypothalamus, Anterior Pituitary, Target Tissues

  • Stimuli within the nervous system regulate the secretion of releasing hormones from neurons in the hypothalamus.
  • Releasing hormones travel to the anterior pituitary.
  • Releasing hormones stimulate the release of hormones from the anterior pituitary.
  • Anterior pituitary hormones travel in the bloodstream to target tissues, which may be other endocrine glands.

Some Examples of Hypothalamic Hormones

  • Growth hormone-releasing hormone increases secretion of growth hormone.
  • Prolactin-releasing hormone causes increased prolactin secretion.

Anterior Pituitary Hormones

  • Growth Hormone (GH)
    • Acts on most cells of the body to regulate overall metabolism and growth.
  • Thyroid-Stimulating Hormone (TSH)
    • Stimulates the thyroid to secrete T3 and T4.
  • Adrenocorticotropic Hormone (ACTH)
    • Stimulates the adrenal cortex to secrete cortisol and aldosterone.
  • Melanocyte-Stimulating Hormone (MSH)
    • Causes melanocytes to produce more melanin.
  • Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)
    • Both hormones regulate the production of gametes and reproductive hormones.
      • Testes: testosterone production and spermatogenesis.
      • Ovaries: estrogen and progesterone production, and oogenesis.
  • Prolactin
    • Plays a role in milk production (lactation).

Tropic vs Non-Tropic Hormones

  • Tropic Hormones
    • Stimulate the secretion of other hormones from other target cells.
    • Many anterior pituitary hormones are tropic.
  • Non-Tropic Hormones
    • Initiate an effect directly.

Hypothalamus, Posterior Pituitary, Target Tissues

  • Stimuli within the nervous system cause neurons in the hypothalamus to increase or decrease their action potential frequency.
  • Action potentials are conducted along neurons from the hypothalamus to the posterior pituitary.

Receptors, Target Cells, Activities, Steroids, Amino Acids, Negative Feedback, Pituitary, Releasing/Inhibiting Hormones, Hypothalamus, Neuroendocrine

  • Receptors on target cells bind to hormones, initiating changes in cell activity.
  • Hormonal activity can stimulate new or unusual activity within cells.
  • Hormones can be steroid or amino acid based.
  • Negative feedback mechanisms regulate hormone secretion.
  • The pituitary gland is a key component of the endocrine system.
  • Releasing or inhibiting hormones from the hypothalamus control pituitary hormone release.
  • The hypothalamus is a critical neuroendocrine structure.

Corticotropin-Releasing Hormone (CRH) and Cortisol Feedback Loop

  • Corticotropin-releasing hormone (CRH) is released from the hypothalamus in response to low blood glucose levels or stress.
  • CRH binds to and stimulates cells in the anterior pituitary to secrete adrenocorticotropic hormone (ACTH).
  • ACTH travels in the blood to the adrenal cortex and stimulates the secretion of cortisol.
  • Cortisol acts on target tissues, increasing fat and protein breakdown and blood glucose levels.
  • Cortisol has a negative feedback effect on the hypothalamus and anterior pituitary, inhibiting CRH and ACTH release.

Oxytocin in Childbirth

  • Stretch of the uterus and cervix or stimulation of the nipples triggers the hypothalamus.
  • Signals in the form of action potentials are sent from the hypothalamus to the posterior pituitary.
  • The posterior pituitary receives the action potentials and releases oxytocin into the blood circulation.
  • Circulating oxytocin increases uterine contractions and milk ejection.
  • As oxytocin levels rise, the hypothalamus and pituitary continue to be stimulated until a significant change occurs.

Growth Hormone

  • Stimulates amino acid uptake and protein synthesis (muscle growth).
  • Stimulates fat breakdown for energy.
  • Promotes bone and cartilage growth.
  • Regulates blood nutrient levels after a meal.
  • Stimulates the liver and skeletal muscle to produce IGF-1.
  • Levels peak during deep sleep.

Thyroid-Stimulating Hormone (TSH), T3 and T4

  • Regulated by the hypothalamus, which secretes thyroid-releasing hormone.
  • Thyroid-releasing hormone acts on the anterior pituitary to produce TSH.
  • TSH, a tropic hormone, stimulates the thyroid gland to secrete T3 and T4.
  • T3 and T4 increase metabolism, body temperature, growth, and development.
  • The hypothalamus exerts negative feedback on the anterior pituitary and thyroid gland.

Thyroid Gland

  • One of the largest endocrine glands.
  • Highly vascular.
  • The only gland that stores hormones.
  • Composed of follicles with follicular cells surrounding thyroglobulin/thyroid hormones.
  • Iodine and tyrosine are essential for T3 and T4 production.
  • Increases glucose, fat, and protein metabolism in many tissues, raising body temperature.
  • Promotes normal growth for many tissues.
  • T3 is triiodothyronine.
  • T4 is thyroxine (tetraiodothyronine).

ACTH (Adrenocorticotropic Hormone)

  • Adrenal glands are located near the kidneys, consisting of an inner medulla and outer cortex.
  • Corticotropin-releasing hormone from the hypothalamus stimulates ACTH release from the anterior pituitary.
  • ACTH stimulates cortisol secretion from the adrenal cortex (a glucocorticoid).
  • Cortisol regulates blood glucose levels, metabolism, and stress response.
  • ACTH also stimulates aldosterone secretion from the adrenal cortex (a mineralocorticoid), controlling sodium and water balance.
  • ACTH causes androgen secretion (weak sex hormones) from the adrenal cortex.

Adrenal Medulla

  • Stress, physical activity, and low blood glucose levels stimulate the hypothalamus, increasing sympathetic nervous system activity.
  • Increased action potential frequency in the sympathetic division stimulates the adrenal medulla to secrete epinephrine (adrenaline) and norepinephrine (noradrenaline) into the circulatory system, resulting in:
    • Increased glucose release from the liver.
    • Increased fatty acid release from adipose tissue.
    • Increased heart rate.
    • Decreased blood flow to internal organs.
    • Increased blood flow to heart and skeletal muscles.
  • These hormone secretions prepare the body for physical activity (short-lived response).

Melanocyte-Stimulating Hormone (MSH)

  • Acts on skin cells (melanocytes) to stimulate melanin (skin pigment) production.
  • MSH also plays a role in regulating appetite and sexual behavior.
  • Its function is not fully understood.

Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)

  • Gonadotropin-releasing hormone from the hypothalamus stimulates LH and FSH secretion from the anterior pituitary.
  • LH and FSH, gonadotropins, promote growth and function of the gonads.
  • LH and FSH regulate gamete production and reproductive hormone secretion:
    • Testes: testosterone production and spermatogenesis.
    • Ovaries: estrogen and progesterone production, and oogenesis.

Prolactin

  • A non-tropic hormone.
  • Responsible for breast milk production.
  • Supply is dependent on demand: a positive feedback loop.
  • Secreted from the anterior pituitary.
  • Prolactin release is regulated by prolactin-releasing factor and prolactin-inhibiting factor from the hypothalamus.

Oxytocin (Posterior Pituitary)

  • A non-tropic hormone.
  • Involved in positive feedback.
  • Stimulates breast milk release (let-down).
  • Supply is based on demand.

Anti-Diuretic Hormone (ADH) (Vasopressin)

  • Reduces urine formation.
  • Retains water in the body.
  • Increases blood volume and pressure.
  • Secreted in response to dehydration or hot environments.
  • Diuretics like tea, coffee, or alcohol suppress ADH secretion.

Pancreas

  • Located along and near the stomach and intestine.
  • Exocrine gland: Produces pancreatic digestive juices.
  • Endocrine gland: Composed of pancreatic islets.
  • Alpha cells secrete glucagon.
  • Beta cells secrete insulin.
  • These hormones regulate blood sugar levels.

Growth Hormone

  • Stimulates amino acid uptake and protein synthesis for muscle growth.
  • Breaks down fats for energy.
  • Promotes bone and cartilage development.
  • Regulates blood nutrient levels after meals.
  • Stimulates IGF-1 production in liver and skeletal muscle.
  • Peaks during deep sleep.

Thyroid-Stimulating Hormone (TSH), T3, and T4

  • Hypothalamus releases thyroid-releasing hormone (TRH) which stimulates TSH production in the anterior pituitary.
  • TSH acts on the thyroid gland, a negative feedback mechanism controls its release.
  • T3 and T4 increase metabolism, body temperature, growth, and development.

Thyroid Gland

  • Largest endocrine gland.
  • Highly vascular.
  • Unique in storing hormones.
  • Composed of follicles containing thyroglobulin and thyroid hormones.
  • Requires iodine and tyrosine for T3 and T4 production.
  • Increases glucose, fat, and protein metabolism, raising body temperature.
  • Essential for normal tissue growth.

ACTH (Adrenocorticotropic Hormone)

  • Adrenal glands are located near the kidneys, with an inner medulla and outer cortex.
  • Hypothalamic corticotropin-releasing hormone (CRH) causes ACTH release from the anterior pituitary, stimulating cortisol secretion by the adrenal cortex.
  • ACTH also promotes aldosterone secretion from the adrenal cortex (mineralocorticoid), regulating sodium and water balance.
  • It leads to androgen production (weak sex hormones).

Adrenal Medulla

  • Stimulated by stress, physical activity, and low blood glucose levels through increased sympathetic nervous system activity.
  • Releases epinephrine and norepinephrine into the circulatory system, preparing the body for "fight or flight."

Basics of Chemical Communication

  • Autocrine: Local effect on same cell type that released the signal.
  • Paracrine: Local effect on other cell types without blood transport.
  • Neurotransmitter: Secreted by neurons from presynaptic terminals, affects postsynaptic cells over short distances.
  • Endocrine: Secreted by endocrine glands, travels via blood to distant cells.

Characteristics of the Endocrine System

  • Body control system prioritizing duration over speed.
  • Secretes hormones into the circulatory system.
  • Hormones are produced in small quantities, travel significant distances, and act on targeted tissues.

Functions of the Endocrine System

  • Metabolism.
  • Food intake and digestion control.
  • Tissue maturation.
  • Ion regulation.
  • Water balance.
  • Heart rate and blood pressure control.
  • Blood glucose and nutrient regulation.
  • Reproductive function (gametogenesis and pregnancy).
  • Uterine contractions and milk release.

Posterior Pituitary Hormones

  • Antidiuretic Hormone (ADH): Increases water reabsorption from nephrons, resulting in concentrated urine. Also known as vasopressin, it constricts blood vessels, raising blood pressure.
  • Oxytocin: Stimulates uterine contractions during childbirth and milk ejection (let-down reflex) from lactating breasts.

Control of Hormone Secretion

  • Negative Feedback: A hormone from a target endocrine cell inhibits the release of tropic hormones from the hypothalamus and anterior pituitary.
  • Positive Feedback: A hormone from a target endocrine cell enhances the release of tropic hormones from the hypothalamus and anterior pituitary.

Epinephrine and Norepinephrine

  • Released from the adrenal medulla in response to stress.
  • Prepare the body for physical activity by increasing glucose release, fatty acid release, heart rate, and blood flow to muscles while diverting blood from internal organs.

Melanocyte-Stimulating Hormone (MSH)

  • Acts on melanocytes in the skin, stimulating melanin production.
  • Also plays a role in appetite and sexual behavior, but its function is poorly understood.

LH and FSH (Luteinizing Hormone and Follicle-Stimulating Hormone)

  • Released by the anterior pituitary under the influence of gonadotropin-releasing hormone from the hypothalamus.
  • Regulate the production of gametes and reproductive hormones in the gonads:
    • Testes: Testosterone – spermatogenesis and secondary sex characteristics.
    • Ovaries: Estrogen and progesterone – sex organ development, menstrual cycle, and pregnancy.

Prolactin

  • Non-tropic hormone secreted by the anterior pituitary.
  • Responsible for breast milk production.
  • Subject to positive feedback, increasing with the demand for milk (sucking).
  • Regulated by prolactin-releasing factor and prolactin-inhibiting factor from the hypothalamus.

Oxytocin

  • Non-tropic hormone released by the posterior pituitary.
  • Functions under positive feedback.
  • Stimulates milk ejection during lactation based on demand.

Antidiuretic Hormone (ADH) (Vasopressin)

  • Reduces urine formation, conserving water in the body.
  • Increases blood volume and blood pressure.
  • Secretion is high when dehydrated or exposed to hot conditions.

Pancreas

  • Located near the stomach and intestines.
  • Exocrine function: Secretes digestive juices.
  • Endocrine function: Islets of Langerhans secrete hormones:
    • Alpha cells: Glucagon – raises blood glucose.
    • Beta cells: Insulin – lowers blood glucose.

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Explore the fascinating roles of neurohormones and the functioning of posterior pituitary hormones like ADH and oxytocin. This quiz covers the mechanisms of hormone secretion and regulation, emphasizing the critical feedback loops involved. Test your knowledge on how these hormones affect various bodily processes.

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