Hypothalamic-Pituitary Axis Overview
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Questions and Answers

Which hormone is primarily secreted by somatotropes?

  • Growth hormone (GH) (correct)
  • Luteinizing hormone (LH)
  • Adrenocorticotropic hormone (ACTH)
  • Thyroid-stimulating hormone (TSH)

What is a primary function of thyrotropes in the adenohypophysis?

  • Inhibiting insulin release
  • Regulating cortisol secretion
  • Promoting thyroid hormone production (correct)
  • Stimulating the production of testosterone

What triggers the secretion of adrenocorticotropic hormone (ACTH) from the adenohypophysis?

  • Elevated plasma osmolality and stress (correct)
  • Stress and low blood sugar
  • Insulin levels in the blood
  • High levels of thyroid hormones

Which of the following hormones is primarily associated with the regulation of gonadal functions?

<p>Luteinizing hormone (LH) (D)</p> Signup and view all the answers

What primarily stimulates the release of anti-diuretic hormone (ADH)?

<p>Increase in plasma osmolality (C)</p> Signup and view all the answers

What role does thyroid stimulating hormone (TSH) primarily serve in the body?

<p>Regulates thyroid function via TSH receptors (A)</p> Signup and view all the answers

Which hormones are responsible for regulating the function of the gonads?

<p>Follicle stimulating hormone and luteinising hormone (C)</p> Signup and view all the answers

What is the primary function of adrenocorticotropic hormone (ACTH)?

<p>Stimulates the adrenal cortex to produce cortisol (B)</p> Signup and view all the answers

How does growth hormone (GH) primarily regulate metabolism?

<p>Through its receptor in the liver (D)</p> Signup and view all the answers

What is the feedback mechanism of insulin-like growth factor-1 (IGF-1) on growth hormone (GH)?

<p>IGF-1 negatively feeds back to inhibit GH production (D)</p> Signup and view all the answers

What is the significance of the diurnal pattern observed in the release of adrenocorticotropic hormone (ACTH)?

<p>It helps regulate cortisol levels in a time-dependent manner (C)</p> Signup and view all the answers

Which of the following receptors are associated with hormone regulation in the adrenal cortex?

<p>MC2R for adrenocorticotropic hormone (B)</p> Signup and view all the answers

Which layer of the hypothalamus is involved in the release of hypophysiotropic hormones?

<p>Parvicellular neuronal cell bodies (B)</p> Signup and view all the answers

What physiological action is stimulated by thyrotropin-releasing hormone (TRH)?

<p>Stimulates production of thyroid hormones (A)</p> Signup and view all the answers

Which hormone is primarily responsible for stimulating the development of ovarian follicles in females?

<p>Follicle-stimulating hormone (FSH) (A)</p> Signup and view all the answers

Which condition is associated with abnormally low circulating levels of anti-diuretic hormone (ADH)?

<p>Diabetes insipidus (A)</p> Signup and view all the answers

Which hormone stimulates the secretion of breast milk in lactating females?

<p>Oxytocin (A)</p> Signup and view all the answers

What is a physiological effect of abnormally high levels of circulating ADH?

<p>Oedema due to high plasma volume (D)</p> Signup and view all the answers

What primary action does gonadotropin-releasing hormone (GnRH) perform at the anterior pituitary?

<p>Stimulates secretion of follicle-stimulating hormone (FSH) and luteinising hormone (LH) (A)</p> Signup and view all the answers

How does thyroid-stimulating hormone (TSH) affect the thyroid gland?

<p>Stimulates production of thyroid hormones and maintains the size of follicular cells (B)</p> Signup and view all the answers

Which hormone regulates metabolic rate and is produced by the thyroid gland?

<p>Thyroid hormones (B)</p> Signup and view all the answers

What is the effect of low levels of growth hormone during development?

<p>Dwarfism (C)</p> Signup and view all the answers

Which hormone is responsible for regulating spermatogenesis in males?

<p>Luteinizing hormone (LH) (D)</p> Signup and view all the answers

What is the primary function of adrenocorticotropic hormone (ACTH)?

<p>Stimulates secretion of glucocorticoids and androgens (B)</p> Signup and view all the answers

Which hormone stimulates ovulation and the formation of the corpus luteum in females?

<p>Luteinizing hormone (LH) (B)</p> Signup and view all the answers

Which hormone is released by somatotropes in the anterior pituitary?

<p>Growth hormone (GH) (C)</p> Signup and view all the answers

What effect does growth hormone (GH) have on the body?

<p>Stimulates growth and lipolysis (A)</p> Signup and view all the answers

Which hormone stimulates the production of testosterone in males?

<p>Luteinizing hormone (LH) (D)</p> Signup and view all the answers

What role does corticotropin-releasing hormone (CRH) play in the endocrine system?

<p>Stimulates secretion of adrenocorticotropic hormone (ACTH) (A)</p> Signup and view all the answers

Which hormone is primarily involved in the regulation of insulin-like growth factor?

<p>Growth hormone (GH) (C)</p> Signup and view all the answers

What is a key function of glucocorticoids produced by the adrenal cortex?

<p>Regulate metabolism and inflammation (A)</p> Signup and view all the answers

Which hormone counters some actions of insulin?

<p>Growth hormone (GH) (B)</p> Signup and view all the answers

What primary role does IGF-1 play in the endocrine system?

<p>Provides negative feedback in hormone regulation (B)</p> Signup and view all the answers

Which hormone is responsible for stimulating breast milk production?

<p>Prolactin (C)</p> Signup and view all the answers

What is a characteristic symptom of gonadotropin-secreting adenomas?

<p>Headaches (C)</p> Signup and view all the answers

Which hormone is NOT coordinated by the adenohypophysis?

<p>Antidiuretic hormone (B)</p> Signup and view all the answers

What type of feedback is primarily involved in the regulation of the HPA axis?

<p>Negative feedback (A)</p> Signup and view all the answers

Which hormone is secreted by the neurohypophysis?

<p>Oxytocin (A)</p> Signup and view all the answers

What can occur as a result of hypopituitarism?

<p>Visual field defects (A)</p> Signup and view all the answers

Which of the following hormones is NOT released from the adenohypophysis?

<p>Antidiuretic hormone (B)</p> Signup and view all the answers

Gonadotropin-secreting adenomas typically result in low levels of which two hormones?

<p>FSH and LH (D)</p> Signup and view all the answers

Which structure is classified as true endocrine tissue?

<p>Adenohypophysis (D)</p> Signup and view all the answers

Flashcards

Growth Hormone Inhibitory

Substance that reduces the release of growth hormone.

Somatotropes

Cells in the anterior pituitary that produce growth hormone.

Hypophysiotropic hormones

Hormones made in the hypothalamus and regulating the pituitary hormones secretion.

Tropic hormone

Hormones that stimulate other glands to produce hormones.

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Thyroid Stimulating Hormone (TSH).

A tropic hormone that controls thyroid function.

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Follicle Stimulating Hormone (FSH)

Hormone influencing gonads' functions.

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Adrenocorticotropic Hormone (ACTH)

Hormone stimulating adrenal cortex to release cortisol, having diurnal pattern.

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Growth Hormone (GH)

A hormone that affects metabolism and growth by acting on the liver.

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LH hormone

Stimulates spermatogenesis in males and ovulation/corpus luteum formation in females, plus oestrogen and progesterone production.

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ACTH

Stimulates glucocorticoids and androgens in the adrenal cortex.

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GHRH

Stimulates growth hormone (GH) secretion and IGF production.

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Spermatogenesis

The process of sperm production.

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Ovulation

Release of an egg from the ovary.

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Corpus Luteum

Structure that forms after ovulation, producing hormones.

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Glucocorticoids

Hormones produced by the adrenal cortex, related to blood sugar.

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Androgens

Hormones related to male characteristics.

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Growth Hormone

Stimulates body growth, IGF release, and lipolysis.

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Pituitary – adrenal axis

The interaction between the pituitary gland and adrenal glands.

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Negative Feedback (Endocrine)

A mechanism in which the release of a hormone is inhibited by its effect or the effect of hormones it stimulates.

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IGF-1

Insulin-like growth factor 1, a hormone that influences growth and metabolism.

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Somatostatin

A hormone that inhibits growth hormone release, among other functions.

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Prolactin

A hormone that stimulates milk production in the breasts.

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Dopamine

A neurotransmitter that inhibits prolactin release.

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Hypophysiotropic Hormone

Hormones released into the bloodstream to regulate hormones from the pituitary gland.

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HPA Axis

The hypothalamic-pituitary-adrenal axis, a major endocrine system controlling stress response.

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Tropic Hormones

Hormones that stimulate other endocrine glands to release hormones.

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Gonadotropin-secreting adenomas

Rare pituitary tumors that produce too little FSH and LH.

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Hypopituitarism

A condition where the pituitary gland doesn't produce enough hormones.

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Adenohypophysis

The anterior pituitary, an endocrine tissue with different cell types that release hormones.

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Neurohypophysis

The posterior pituitary, neural tissue storing hormones made in the hypothalamus.

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Hypothalamic-hypophyseal portal system

A specialized blood vessel network connecting the hypothalamus and anterior pituitary.

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Anti-diuretic hormone (ADH)

A hormone that regulates water reabsorption in the kidneys, controlled by blood osmolarity, pressure, stress, and pain.

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Pituitary hormones

Hormones released by the pituitary gland that regulate many bodily functions, like growth, metabolism, and reproduction.

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ADH High Levels

High Anti-diuretic Hormone (ADH) leads to high urine osmolality, edema (excess fluid in tissues), and low blood osmolality.

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ADH Low Levels

Low ADH causes diabetes insipidus, a condition characterized by excessive urination.

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Oxytocin Stimulation

Oxytocin release is triggered by breast-feeding (suckling), labor (vaginal/cervical stimulation), and crying.

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Oxytocin Effects

Oxytocin stimulates milk release in nursing mothers and might aid in childbirth.

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TRH Function

Thyrotropin-releasing hormone (TRH) stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary.

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GnRH Function

Gonadotropin-releasing hormone (GnRH) stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary.

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TSH Effect (on Thyroid)

Thyroid-stimulating hormone (TSH) stimulates the thyroid glands to produce thyroid hormones and regulates the follicular cell size.

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FSH Effect (on Females)

Follicle-stimulating hormone (FSH) in females promotes ovarian follicle development.

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Anterior Pituitary

The front part of the pituitary gland.

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Hypophysiotropic Hormones

Hormones made in the hypothalamus that control pituitary hormone release

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Study Notes

Hypothalamic-Pituitary Axis (HPA)

  • The HPA is the most important part of the endocrine system
  • It controls the thyroid, adrenal, and reproductive glands
  • It regulates somatic growth, lactation, milk secretion, and water metabolism

Learning Outcomes

  • Understand the structure and anatomy of the HPA
  • Compare anterior and posterior pituitary regarding cell types, vascular supply, and hypothalamic innervation
  • Identify the six key anterior pituitary hormones, their target tissues, and functions
  • Identify and understand the functions of two key posterior pituitary hormones
  • Understand how pituitary tumors affect pituitary function and physiology
  • Endocrine and Reproductive Physiology, 4th Edition, Elsevier, Chapter 5 (pp. 99-129)
  • Salhadar, K., et al. (2021). Phosphoproteomic identification of vasopressin/cAMP/protein kinase A-dependent signaling in kidney. Molecular Pharmacology, 99, 358-369. (https://doi.org/10.1124/mol.120.119602)
  • Arrowsmith, S., and Wray, S. (2014). Oxytocin: Its mechanism of action and receptor signaling in the myometrium. Journal of Neuroendocrinology, 26, 356-369. (https://doi.org/10.1111/jne.12154)
  • BS21002 - Cellular communication - Steroid hormones
  • BS21002 - Cellular communication - Peptide hormones

Anatomy of the Pituitary Gland

  • The pituitary gland has two parts: anterior and posterior
  • The anterior pituitary is derived from oral ectoderm
  • The posterior pituitary is derived from the forebrain
  • The hypothalamus regulates hormone release by the pituitary gland.

Development of the Pituitary Gland

  • Neurohypophysis: downgrowth of the forebrain
  • Adenohypophysis: oral ectoderm of the roof of the stomatodeum

Cells of the Pituitary Gland

  • Adenohypophysis: endocrine tissue with distinct cell types for hormone release:
    • Somatotropes
    • Corticotropes
    • Thyrotropes
    • Gonadotropes
    • Lactotropes
  • Neurohypophysis: neural tissue for transport and storage of hypothalamic hormones

Vascular Supply of the Pituitary Gland

  • Hypothalamic neurons release hormones into the portal system
  • Superior hypophyseal artery supplies the portal system, which branches into the secondary plexus
  • Secondary plexus of the hypophyseal portal system supplies the adenohypophysis

Innervation of the Pituitary Gland

  • Hypothalamohypophysial portal system transports hypothalamic hormones to the anterior pituitary.
  • Posterior pituitary receives hormones directly from the hypothalamus via the hypothalamo-hypophyseal tract.

Neurohypophysis (Posterior Pituitary)

  • Supraoptic nuclei = antidiuretic hormone (ADH)
  • Paraventricular nuclei = oxytocin

Anti-diuretic Hormone (ADH) - Secretion

  • Stimulated by: increased plasma osmolality, decrease in blood pressure, stress, and pain.

Anti-diuretic Hormone (ADH) - Physiological Effects

  • ADH increases permeability of distal tubules and collecting ducts to water.
  • This increases water reabsorption and blood volume
  • ADH causes vasoconstriction and reduced cardiac output.
  • Independent of solute movement

Anti-diuretic Hormone (ADH) - Disorders

  • Abnormally high ADH: high urine osmolality, edema (high plasma volume)
  • Abnormally low ADH: diabetes insipidus

Oxytocin

  • Stimulates milk secretion in lactating females
  • Contributes to parturition

Oxytocin - Secretion

  • Stimulated by: suckling, vaginal/cervical stimulation, and crying

Oxytocin - Physiological Effects

  • Initiates milk letdown (myoepithelial cell contraction)
  • Increases milk production (prolactin)

Adenohypophysis (Anterior Pituitary)

  • Hypothalamus releases hormones via the hypophyseal portal system and these hormones reach the anterior pituitary (adenohypophysis)
  • Anterior pituitary is an endocrine gland that releases hormones directly into the bloodstream.

Adenohypophysis - Hypophysiotropic hormones

  • Hormones that stimulate the release of other hormones from the anterior pituitary

Summary - Adenohypophysis Hormones

  • Hypophysiotropic hormones (from hypothalamus) stimulate adenohypophysis hormones
  • Adenohypophysis hormones (tropic hormones) stimulate other endocrine glands to produce more hormones

Adenohypophysis Hormones (thyroid stimulating hormone (TSH))

  • Regulates thyroid function via TSH receptor on thyroid epithelial cells, and T3 and T4 support tropic effects on growth and metabolism

Adenohypophysis Hormones (Follicle stimulating hormone (FSH) and Luteinizing hormone (LH))

  • Regulate the function of the gonads (ovaries and testes) in both males and females via their target receptors

Adenohypophysis Hormones (Adrenocorticotropic hormone (ACTH))

  • Shows a diurnal pattern
  • Stimulates adrenal cortex via MC2R receptor to increase cortisol and adrenal androgen production
  • Cortisol inhibits ACTH secretion

Adenohypophysis Hormones (Growth hormone (GH))

  • Regulates metabolism via GH receptor in the liver
  • Results in the production of IGF-1 and negative feedback
  • Negative feedback inhibits GH secretion

Adenohypophysis Hormones (Prolactin)

  • Stimulates breast milk production via reduced dopamine release from parvicellular hypothalamic neurons

Feedback Loops in HPA Regulation

  • Tropic hormones provide negative feedback to regulate hormone release

Gonadotropin-secreting Adenomas

  • Rare pituitary tumors
  • Secrete low FSH and LH
  • Symptoms usually depend on tumor size (headaches, visual field defects)

Note on HPA

  • The most dominant part of the endocrine system
  • Pituitary (adenohypophysis & neurohypophysis) is embryologically different and has different structure and mechanisms

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BS31019 - Lecture 1.2 - The Hypothalamic-pituitary axis PDF

Description

Explore the Hypothalamic-Pituitary Axis (HPA) and its crucial role in the endocrine system. This quiz covers the anatomy of the HPA, the functions of anterior and posterior pituitary hormones, and the impact of pituitary tumors on physiology. Test your knowledge and understanding based on the recommended reading from Endocrine and Reproductive Physiology.

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