Molecular Signaling Pathways

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Questions and Answers

What is an antagonist in the context of hormones?

A hormone that is broken down rapidly

An agent that binds to the receptor like the desired hormone, but does not stimulate the receptor (correct)

A hormone that stimulates the receptor

A hormone that is released by the pituitary gland

What is the main control point for hormone synthesis and release?

Hypothalamus

Pituitary gland

Endocrine tissues

Central nervous system (correct)

What is the function of tropic hormones?

To control the secretion of releasing factors

To produce regulatory hormones in response to CNS messages

To regulate the activity of other tissues or glands (correct)

To stimulate the receptor

What is the function of JAKs in signal transduction?

To phosphorylate and activate STAT proteins Signup and view all the answers

What is the purpose of feedback control in hormone regulation?

To control hormone production by changing secretion of releasing factors Signup and view all the answers

What is the term for the periodic occurrence of a biological event?

Biological rhythm Signup and view all the answers

Which type of receptors are involved in the transmission of messages from arterial natriuretic factor (ANF)?

Guanylyl cyclase receptors Signup and view all the answers

What is the term for the rhythm that occurs during 24 hours?

Circadian rhythm Signup and view all the answers

How do thyroid, steroid, and retinoic acid hormone receptors enter the cell?

Through simple diffusion Signup and view all the answers

What controls the secretion of pituitary hormones?

Hypothalamic factors Signup and view all the answers

What is the result of desensitization of receptors?

Decreased responsiveness to hormones Signup and view all the answers

What is the effect of upregulation of receptors?

Increased sensitivity of target cells Signup and view all the answers

What type of control can feedback control be?

Both negative and positive Signup and view all the answers

What is the function of an agonist in pharmacological interventions?

To mimic the action of a hormone Signup and view all the answers

Which of the following hormones is an example of a hormone that acts through intracellular receptors?

Thyroid hormone Signup and view all the answers

Where is oxytocin release triggered in response to suckling?

Hypothalamus Signup and view all the answers

What is the result of covalent modification of receptors by phosphorylation?

Decreased transmission of the message into the cell Signup and view all the answers

What can bypass the neurogenic pathway to trigger oxytocin secretion?

Psychological stimuli Signup and view all the answers

What can inhibit oxytocin secretion?

Stressful situations Signup and view all the answers

What is the half-life of oxytocin?

3 to 5 minutes Signup and view all the answers

Where is AVP (ADH) synthesized?

Paraventricular and supraoptic nuclei of the hypothalamus Signup and view all the answers

What stimulates the V2 receptors on principal epithelial cells in the kidney?

ADH Signup and view all the answers

What is the primary function of ADH?

Maintaining osmotic homeostasis Signup and view all the answers

At what serum osmolality is ADH secretion maximally stimulated?

295 mOsm/kg Signup and view all the answers

What is characterized by a euvolemic hypoosmolar hyponatremia associated with hyperosmolar urine?

Syndrome of Inappropriate Secretion of ADH (SIADH) Signup and view all the answers

What is the function of dopamine produced by the hypothalamus?

Inhibits prolactin secretion Signup and view all the answers

What is the normal reference value for serum prolactin in women?

1-25 ng/mL Signup and view all the answers

What is the typical manifestation of hyperprolactinemia in women?

Luteal phase abnormalities, oligomenorrhea, or frank amenorrhea Signup and view all the answers

What is a common cause of hyperprolactinemia?

Pituitary adenomas Signup and view all the answers

What is the effect of hyperprolactinemia on GnRH secretion?

Inhibition Signup and view all the answers

What is the typical manifestation of hyperprolactinemia in men?

Hypoandrogenemia, decreased libido, and impotence Signup and view all the answers

What can lead to disinhibition of prolactin secretion?

Any sellar or parasellar process that compresses the pituitary stalk Signup and view all the answers

What is the correlation between the height of elevation of serum PRL levels and the presence of a pituitary tumor?

Direct correlation Signup and view all the answers

What is another important cause of hyperprolactinemia?

Hypothyroidism Signup and view all the answers

What stimulates PRL secretion in addition to TSH secretion?

TRH Signup and view all the answers

What is usually done to return PRL levels to normal in patients with hyperprolactinemia due to hypothyroidism?

Thyroid hormone replacement therapy Signup and view all the answers

What is measured in addition to PRL in patients with acromegaly?

IGF-1 Signup and view all the answers

What is the consequence of complete PRL deficiency in women?

Menstrual disorders and infertility Signup and view all the answers

What hormone is secreted by the somatotrophs of the pituitary gland?

GH Signup and view all the answers

What inhibits GH synthesis and release?

Somatostatin Signup and view all the answers

Study Notes

Receptors and Hormone Signaling

JAKs (Janus kinases) and STAT (signal transducer and activator of transcription) are involved in hormone signaling, with examples including growth hormone and prolactin.
Guanylyl cyclase receptors transmit messages, with an example being arterial natriuretic factor (ANF).

Intracellular Receptors

Thyroid, steroid, and retinoic acid hormone receptors exist in soluble form inside cells, with hormones passing through the cell membrane by simple diffusion.
The receptor-hormone complex is transported into the nucleus, binding to specific hormone response elements and stimulating gene transcription.

Regulation of Receptor Activity

Desensitization occurs through decreased responsiveness to increased hormone amounts, reduced receptor numbers or affinity, downregulation, and covalent modification by phosphorylation.
Upregulation increases target cell sensitivity, with examples including prolactin and angiotensine II.

Hormone Regulation

Hormone amounts in blood circulation are controlled by synthesis, release, breakdown, and removal processes.
The hypothalamic-pituitary regulatory system integrates messages from internal and external sensory receptors to control hormone production.
Feedback control involves hormones released from target glands regulating production by changing hypothalamic and pituitary hormone secretion.

Biological Rhythms

Biological rhythms refer to periodic biological events, with examples including circadian rhythms in pituitary hormone secretion.
Oxytocin has a circadian rhythm and is released in response to suckling, neurogenic stimuli, and psychological stimuli, with inhibition by stressful situations.

Oxytocin

Oxytocin has a half-life of 3-5 minutes and is rapidly degraded by oxytocinase.
Pathologic conditions associated with oxytocin excess or deficiency are rare.

Arginine Vasopressin/Antidiuretic Hormone (ADH)

ADH is synthesized in the paraventricular and supraoptic nuclei of the hypothalamus.
ADH regulates water balance and osmotic homeostasis by stimulating V2 receptors in the kidney, increasing water permeability and reabsorption.
ADH secretion is modulated by changes in serum osmolality and intravascular volume, with detection by osmoreceptors in the anterior hypothalamus.

Syndrome of Inappropriate Secretion of ADH (SIADH)

SIADH is characterized by euvolemic hypoosmolar hyponatremia with hyperosmolar urine.

Hypothalamus and Pituitary Gland

The hypothalamus communicates with the anterior pituitary gland by secreting trophic hormones specific for each cell population.
Prolactin (PRL) is produced by the lactotrophs of the pituitary gland, responsible for lactation initiation and maintenance.

Prolactin

PRL secretion is normally kept low by dopamine produced by the hypothalamus.
PRL is secreted in a circadian fashion, with highest levels during sleep and a nadir between 10 am and noon.
Reference values for serum PRL are 1-25 ng/mL for women and 1-20 ng/mL for men.
PRL levels are increased by physiologic and pathologic factors, as well as by medications.

Hyperprolactinemia

Hyperprolactinemia leads to inhibition of GnRH secretion, manifesting as sexual dysfunction and infertility in both men and women.
Pituitary adenomas are an important cause of hyperprolactinemia, with elevation of serum PRL levels correlating with the likelihood of a pituitary tumor.
Hypothyroidism is another important cause of hyperprolactinemia, with thyroid hormone replacement therapy usually returning PRL levels to normal.

Hypoprolactinemia

PRL deficiency can be seen with pituitary necrosis or infarction, and in some cases of pseudohypoparathyroidism.
In women with complete PRL deficiency, menstrual disorders and infertility have been found.

Growth Hormone (GH)

GH is a single-chain polypeptide synthesized, stored, and secreted by the somatotrophs of the pituitary gland in response to GHRH secretion by the hypothalamus.
Somatostatin, also produced by the hypothalamus, inhibits GH synthesis and release.

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Description

This quiz covers different molecular signaling pathways, including JAK-STAT, guanylyl cyclase receptors, and intracellular receptors. Examples of signaling molecules include growth hormone, prolactin, and thyroid hormone.