Endocrine System Overview

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Questions and Answers

Which of the following substances can directly stimulate hormone secretion?

  • Neurotransmitters
  • Circulating Hormones
  • Metabolites
  • All of the above (correct)

Which layer of the adrenal cortex is responsible for secreting aldosterone?

  • Medulla
  • Reticularis
  • Fasciculata
  • Glomerulosa (correct)

Which hormone is primarily secreted in an episodic pattern?

  • Cortisol
  • Growth Hormone (correct)
  • Thyroid Hormone
  • Insulin

What is the primary function of the hypothalamus in relation to hormone secretion?

<p>Regulating the release of hormones from the pituitary gland (B)</p> Signup and view all the answers

Which hormone exhibits a circadian secretion pattern, peaking in the morning?

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

Which of the following is NOT a typical factor that influences hormone secretion patterns?

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

What is the term for hormone secretion that occurs locally within a gland to regulate neighboring cells?

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

The adrenal gland is located on top of which organ?

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

What type of feedback mechanism is responsible for the regulation of growth hormone (GH) secretion?

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

Which of the following correctly describes the role of the hypothalamus in the HPT axis?

<p>The hypothalamus secretes TRH, which stimulates the anterior pituitary to secrete TSH. (D)</p> Signup and view all the answers

Which anterior pituitary hormone is responsible for stimulating the adrenal gland to produce cortisol?

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

Which of the following is NOT a direct effect of growth hormone (GH)?

<p>Increased thyroid hormone production (A)</p> Signup and view all the answers

Which of the following accurately describes the role of the pituitary gland in the endocrine system?

<p>The pituitary gland acts as a relay center, receiving signals from the hypothalamus and releasing hormones that regulate other endocrine glands. (D)</p> Signup and view all the answers

Which hormone is responsible for stimulating the release of both LH (luteinizing hormone) and FSH (follicle-stimulating hormone) from the anterior pituitary?

<p>GnRH (Gonadotropin-releasing hormone) (C)</p> Signup and view all the answers

What is the primary difference between the long loop and short loop feedback mechanisms in hormone regulation?

<p>The long loop involves the target gland, while the short loop involves the pituitary. (D)</p> Signup and view all the answers

Which of the following is an example of positive feedback in hormone regulation?

<p>Estrogen stimulates the release of LH and FSH. (B)</p> Signup and view all the answers

Which of the following is a characteristic of a primary endocrine disorder?

<p>Dysfunction of the target gland. (D)</p> Signup and view all the answers

What is the primary function of the hypothalamus in the endocrine system?

<p>To act as the primary control center for the endocrine system, regulating the pituitary gland. (A)</p> Signup and view all the answers

Flashcards

Hormone secretion signals

Signals that stimulate hormone secretion include neurotransmitters, hormones, metabolites, and paracrine factors.

Neurotransmitters

Chemicals that transmit signals across a synapse, stimulating hormone secretion.

Neural hormones

Hormones released by the hypothalamus that stimulate the pituitary gland.

Circulating hormones

Hormones that act as signals while traveling in the bloodstream, such as LH and TSH.

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Paracrine secretion

Hormone release that affects neighboring cells within the same gland.

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Adrenal cortex layers

The adrenal cortex has three layers: Glomerulosa (aldosterone), Fasciculata (cortisol), Reticularis (androgens).

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Circadian secretion

Hormone secretion that varies according to the time of day, like cortisol peaking in the morning.

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Episodic secretion

Hormone release occurring in bursts, varying in frequency, such as growth hormone during sleep.

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Hypothalamus function

Integrates information from various body systems to maintain homeostasis and secrete hormones affecting the pituitary gland.

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HPG Axis

Hypothalamus-Pituitary-Gonads axis that regulates reproductive hormones; hypothalamus releases GnRH to stimulate pituitary.

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HPA Axis

Hypothalamus-Pituitary-Adrenal axis controlling stress response; CRH stimulates cortisol secretion from adrenal glands.

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HPT Axis

Hypothalamus-Pituitary-Thyroid axis that regulates metabolism; TRH stimulates the secretion of TSH which affects thyroid activity.

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Negative Feedback Regulation

Hormones from target organs inhibit secretion of hypothalamus/pituitary hormones to maintain balance.

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Positive Feedback Regulation

Target organ hormones stimulate secretion of hypothalamus/pituitary hormones, enhancing responses like during childbirth.

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Hypo-secretion

Low secretion of target hormones due to gland damage or dysfunction in hypothalamus/pituitary.

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Hyper-secretion

Excess hormone production usually due to gland overactivity or stimulation by the pituitary/hypothalamus.

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Hypo-responsiveness

Reduced sensitivity to hormones, such as insulin resistance in type 2 diabetes.

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Endocrine disorders

Conditions resulting from abnormal hormone levels, including hypo-secretion, hyper-secretion, hypo-responsiveness, and hyper-responsiveness.

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Study Notes

Hormone Secretion Stimuli

  • Various signals stimulate hormone secretion, including:
    • Neurotransmitters: Examples like glutamate, GABA, dopamine, epinephrine, norepinephrine, histamine, serotonin
    • Neural Hormones: Hypothalamic hormones stimulating the pituitary
    • Circulating Hormones: Hormones from other glands (e.g., gonads responding to LH/FSH; thyroid responding to TSH)
    • Paracrine Hormones: Local regulation within a gland (e.g., testosterone stimulating sperm production)
    • Metabolites: Substances like glucose, amino acids, calcium influencing hormone release (e.g., glucose/amino acids stimulating pancreas; calcium regulating PTH)

Adrenal Gland Structure and Function

  • Located atop the kidneys, with two parts:
    • Medulla: Inner part
    • Cortex: Outer part, further divided into:
      • Glomerulosa (orange): Stimulated by angiotensin II to secrete aldosterone
      • Fasciculata (blue): Stimulated by ACTH to secrete cortisol
      • Reticularis (green): Stimulated by ACTH to secrete androgens

Hormone Secretion Patterns

  • Circadian Secretion: Daily cycle, e.g., cortisol peaking in the morning, helping prepare the body.
  • Episodic Secretion: Bursts of varying duration/frequency; common in hypothalamic and pituitary hormones. Example: Growth hormone is secreted episodically, primarily at night during sleep.

The Hypothalamus

  • Crucial integration center, receiving input from various sources (thalamus, limbic system, sensory systems, visceral system; hormonal and environmental stimuli like light, temperature, sleep, mood, activity, and glucose).
  • Processes input and controls pituitary gland to maintain homeostasis.
  • Acts as central control point for the endocrine system.

Hypothalamus-Pituitary Endocrine Axis

  • The hypothalamus controls the pituitary gland, which in turn regulates target organs.
  • Example axes:
    • HPG (Hypothalamus-Pituitary-Gonads): GnRH → LH/FSH → Gonadal hormones (estrogen, androgen, progesterone)
    • HPA (Hypothalamus-Pituitary-Adrenal): CRH → ACTH → Cortisol/Aldosterone
    • HPT (Hypothalamus-Pituitary-Thyroid): TRH → TSH → T3/T4
  • Other hypothalamic hormones:
    • GHRH: Stimulates growth hormone (GH), influencing metabolism and IGF production.
    • Somatostatin: Inhibits GH and TSH secretion.
    • Dopamine and TRH: Stimulate prolactin production.

Anterior Pituitary Hormones

  • Hormone | Cell Type | Structure
  • ---|---|---
  • ACTH | Corticotroph | 39 amino acids
  • TSH | Thyrotroph | α subunit shared with LH/FSH; unique β subunit
  • LH | Gonadotroph | α subunit shared with TSH/FSH; unique β subunit
  • FSH | Gonadotroph | α subunit shared with TSH/LH; unique β subunit

Regulation of Hormone Secretion

  • Negative Feedback: Target organ hormones inhibit pituitary/hypothalamic hormones (e.g., long, short, ultra-short loops).
  • Positive Feedback: Target organ hormones stimulate pituitary/hypothalamic hormones (e.g., estrogen stimulating follicle maturation).
  • Product Regulation: Hormone products (e.g., sodium, calcium, glucose) influence hormone secretion.

Endocrine Disorders

  • Hypo-secretion: Low hormone levels, due to target gland, pituitary, or hypothalamic dysfunction.
  • Hyper-secretion: High hormone levels, due to target gland, pituitary, or hypothalamic hyperactivity.
  • Hypo-responsiveness: Reduced hormone response (e.g., type 2 diabetes).
  • Hyper-responsiveness: Enhanced hormone response (e.g., overgrowth).

Example: Cortisol

  • Secretion governed by the HPA axis
  • Peaks in the morning, preparing the body.
  • Suppression by long-term exogenous cortisol medication suppresses the HPA axis and ACTH.

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