Hormone Signaling Pathways Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the initial step in turning off the signal in the cAMP second messenger system?

Hydrolysis of GTP to GDP by Ga (correct)

Reactivation of the inhibitory bg complex

Conversion of cAMP to AMP by phosphodiesterases

Phosphorylation of adenylate cyclase

Which of the following describes the role of phosphodiesterases in the cAMP signaling pathway?

They stimulate the production of GTP

They bind to the bg complex

They activate adenylate cyclase

They hydrolyze cAMP to AMP (correct)

Which receptors are associated with intrinsic tyrosine kinase activity?

Steroid hormone receptors

Ion channel receptors

Receptor tyrosine kinases (correct)

G protein-coupled receptors

What happens to Ga once GDP binds to it after GTP hydrolysis?

It rebinds to the bg complex Signup and view all the answers

Which hormone receptors are specifically mentioned for their action through a nuclear receptor?

Thyroid hormone receptors Signup and view all the answers

What characterizes chronic hormone secretion?

Hormone levels remain relatively constant. Signup and view all the answers

What is the primary reason for down-regulation of hormone receptors?

Prolonged exposure to high hormone levels. Signup and view all the answers

Which of the following best explains up-regulation of receptors?

Increased synthesis of receptors. Signup and view all the answers

What is the location of receptors for protein and peptide hormones?

On the plasma membrane. Signup and view all the answers

What is the role of the extracellular domains of hormone receptors?

To interact with and bind the hormone. Signup and view all the answers

What effect can prolonged hormone exposure have on receptor numbers?

It can decrease the synthesis of receptors. Signup and view all the answers

What defines acute hormone secretion?

Hormone release triggered by specific internal or external stimuli. Signup and view all the answers

Which domain of a receptor is responsible for generating second messengers?

Cytoplasmic or intracellular domain. Signup and view all the answers

What percentage of steroid hormones are typically found in a free form in the blood?

1-10% Signup and view all the answers

Which type of binding proteins has high affinity but low capacity?

Corticosteroid Binding Globulin (CBG) Signup and view all the answers

What is the primary consequence of hormones being bound to transport proteins?

Blunts hormone response potential. Signup and view all the answers

What is the usual role of non-specialized binding proteins like plasma albumins?

To bind steroids and thyroid hormones with low affinity but high capacity. Signup and view all the answers

Which hormone concentration is typically found at significantly lower levels in the blood compared to others?

Aldosterone Signup and view all the answers

How do binding proteins affect the hormone levels in the bloodstream?

Prevent fluctuations in active hormone levels. Signup and view all the answers

Which of the following hormones typically has a concentration level greater than $10^{-7}M$ in the blood?

Cortisol Signup and view all the answers

What kind of bonds are primarily responsible for the binding of steroid hormones to carrier proteins?

Weak chemical bonds Signup and view all the answers

Which of the following is NOT a major class of eicosanoids?

Neuropeptides Signup and view all the answers

What is one of the effects of eicosanoids?

Smooth muscle contraction Signup and view all the answers

In the patient profile, what was one of John Smith's elevated plasma eicosanoids?

Prostaglandin E2 Signup and view all the answers

Which treatment is NOT considered for managing John Smith's condition?

Antibiotics Signup and view all the answers

What condition does John Smith likely have based on his symptoms?

Rheumatoid arthritis Signup and view all the answers

Which lifestyle change could help modulate inflammation in John Smith?

Increasing omega-3 fatty acids Signup and view all the answers

What could be a potential clinical relevance of elevated eicosanoids?

Contributing to inflammation Signup and view all the answers

Which of these drug types is categorized under DMARDs?

Methotrexate Signup and view all the answers

Study Notes

Major Classes of Eicosanoids

Prostaglandins
Thromboxanes
Prostacyclins
Leukotrienes
HETEs

Synthesis of Eicosanoids

Arachidonic acid is a precursor for eicosanoids
Lipoxygenase is one of the enzymes that convert arachidonic acid into other substances leading to the synthesis of leukotrienes.
Cyclooxygenase (COX-1 and COX-2) enzymes convert arachidonic acid into prostaglandins, thromboxanes, and prostacyclins.

Effects of Eicosanoids

Induce inflammation
Mediate pain signals
Induce fever
Cause smooth muscle contraction (including uterine contractions)
Cause smooth muscle relaxation
Protect the stomach lining
Stimulate platelet aggregation
Inhibit platelet aggregation
Cause sodium and water retention

Clinical Relevance

Elevated eicosanoids can contribute to inflammation and pain, possibly indicating inflammatory arthritis.
Nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids might be used to reduce inflammation.
Disease-modifying antirheumatic drugs (DMARDs) such as methotrexate might be considered.
Lifestyle modifications, such as increasing omega-3 fatty acids intake, can help to modulate eicosanoid pathways.

Synthesis of Hormone Derivatives of Tryptophan

L-Tryptophan is a precursor to serotonin and melatonin.
The enzymes tryptophan-5-hydroxylase, 5-Hydroxytryptophan decarboxylase, serotonin N-acetyltransferase, and hydroxindole-0-methyltransferase catalyze these transformations.

Synthesis of Hormone Derivatives of Tyrosine

Tyrosine is a precursor for dopamine, norepinephrine, epinephrine
The key enzymes include tyrosine hydroxylase (TH), dopa decarboxylase (DDC), dopamine beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT).
The synthesis of thyroid hormones (thyroxine (T4), triiodothyronine (T3)) involves the iodination of tyrosine molecules.

Transport of Hormones

Peptide/protein hormones dissolve readily in plasma but may still be bound to carrier proteins.
Steroid/amine hormones are largely insoluble in plasma; therefore, they usually bind to carrier proteins (mainly albumin) for transport–resulting in a high bond affinity.
Only the unbound (free) form of hormone is physiologically active.

Binding Proteins

Specialized binding proteins have high affinity but low capacity, and non-specialized binding proteins have low affinity but high capacity.

Consequences of Hormone Binding

Preventing hormone action from overwhelming the system.
Prolonging hormone effect
Inactivation in liver or excretion in urine are delayed
Increase total amount of hormone carrying capacity in blood
Prevent fluctuations in active hormone levels.
Increases reservoir of hormone available.
Maintains equilibrium between bound and free hormone forms.

Hormone Concentration in Blood

Peptide hormone concentrations are typically low, while steroid hormone concentrations are markedly higher, including cortisol, steroid sex hormones, with aldosterone being an exception.

Patterns of Hormone Secretion

Chronic secretion shows relatively constant hormone levels over time.
Acute secretion is a rapid response to a stimulus, with hormone levels rising and quickly returning to baseline.
Episodic (cyclic) secretion shows varying hormone levels at different times (for example, daily or seasonal fluctuations in some hormones).

Hormone Specificity

Receptors for hormones are found on or in cells, and their presence is not constant; they are degraded and replaced.
Down-regulation is a decrease in the synthesis of receptors, occurring with chronic hormone exposure.
Up-regulation is an increase in receptor synthesis, increasing cellular sensitivity to the hormone.

Receptor Location

Protein/peptide hormones are too large or charged to pass the plasma membrane directly.
Receptors are located on the plasma membrane in this situation.
Extracellular domains enable interaction and binding of hormone ligands, while membrane-spanning domains anchor the receptor to the membrane.
Cytoplasmic or intracellular domains interact with other intracellular molecules and trigger secondary messenger signalling cascades.

cAMP Second Messenger System

Hormones bind to receptors, initiating a cascade of events culminating in an intracellular second messenger, cAMP.
This activates protein kinases, triggering responses in the target cell.

Turning Off the Signal

GTP hydrolysis on Gα protein turns the signaling pathway off.
Phosphodiesterases catalyze the hydrolysis of cAMP to AMP.

Various Cellular Responses from cAMP

Cellular responses from cAMP are varied and depend on the specific target cell and pathway.
cAMP-dependent protein kinases can activate or inhibit many enzymes or processes

Amplification

The initial binding of a hormone molecule triggers a specific cascade in a target cell.
The cascade triggers many molecules to amplify the signaling process as it propagates through the cell and beyond.

PI Second Messenger System

Hormones binding to surface receptors trigger a cascade of events leading to the release of second messengers.
These trigger responses within the cell like controlling the release of various products via exocytosis.

Other Protein Hormone Receptors

Transmembrane receptors with intrinsic tyrosine kinase activity, including receptors for insulin and growth factors, have intracellular domains.
Receptors are activated via signal molecule dimerization and subsequent autophosphorylation of their intracellular domains.
Activated signaling proteins transmit signals inside the cytoplasm and initiate downstream effects.

Steroid Hormone Action

Steroid hormones diffuse directly through cell membranes, interacting with cytoplasmic or nuclear receptors.
These actions lead to changes in gene expression and ultimately protein synthesis.

Thyroid Hormone Nuclear Receptor

Thyroid hormones interact with nuclear receptors, directly activating specific genes and impacting RNA synthesis resulting in a thyroid hormone-specific response.

Known to Act Via cAMP

List of hormones that use the cAMP second messenger system.

Known to Act Via cGMP

List of hormones that use the cGMP second messenger system.

Known to Act Via Tyrosine Kinase/Phosphatase

List of hormones that use the Tyrosine Kinase/Phosphatase cascade pathway.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge of hormone signaling mechanisms, including cAMP pathways, receptor functions, and the effects of hormone exposure on receptor regulation. This quiz covers key concepts related to hormone receptors and their roles in cell signaling.