S2 L1 Physio

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Questions and Answers

Which of the following hormones is NOT a steroid hormone?

Epinephrine (correct)

Aldosterone

Cortisol

Testosterone

What is the primary purpose of protein hormones being initially synthesized as preprohormones?

To protect the hormone from being degraded before reaching its target cells.

To provide a precursor molecule that can be modified into the active hormone. (correct)

To ensure the hormone can easily travel through the bloodstream.

To allow for the hormone to be folded correctly into its active conformation.

How are steroid hormones typically stored?

Bound to carrier proteins in the bloodstream.

Stored in specialized organelles like the Golgi apparatus.

In large quantities within secretory vesicles.

In small quantities within their producing cells. (correct)

What is the role of the Golgi apparatus in the synthesis and secretion of protein hormones?

Packaging of the active hormone into secretory vesicles. (B) Signup and view all the answers

Which of the following is NOT a characteristic of the feedback control mechanism for hormone secretion?

It is always controlled by the nervous system. (B) Signup and view all the answers

Which type of hormone acts on specific target tissues?

Local hormones (A) Signup and view all the answers

What is the difference between a prohormone and a preprohormone?

A prohormone has undergone more cleavage than a preprohormone. (A) Signup and view all the answers

How is the secretion of norepinephrine and epinephrine regulated?

By direct stimulation from the nervous system. (B) Signup and view all the answers

What is the primary function of negative feedback in hormone regulation?

To prevent oversecretion of hormones and overactivity at target tissues. (B) Signup and view all the answers

Which of the following examples illustrates a positive feedback mechanism in hormone regulation?

Luteinizing hormone (LH) secretion before ovulation. (C) Signup and view all the answers

How does a negative feedback mechanism affect the secretion of a hormone?

Decreases the secretion rate of the hormone. (B) Signup and view all the answers

What is the main difference between membrane receptors and cytoplasmic receptors in terms of hormone binding?

Membrane receptors bind to peptide hormones, while cytoplasmic receptors bind to steroid hormones. (A) Signup and view all the answers

Why are bound hormones physiologically inactive?

They cannot diffuse across capillaries and reach target tissues. (C) Signup and view all the answers

What is up-regulation in the context of hormonal action?

Increasing the number of receptors in a target cell. (A) Signup and view all the answers

How do ion channel-linked receptors mediate hormone action?

By changing the permeability of the cell membrane to specific ions. (A) Signup and view all the answers

What is the metabolic clearance rate of a hormone?

The rate at which a hormone is removed from the blood. (B) Signup and view all the answers

What is the role of cAMP in the signal transduction pathway?

cAMP activates protein kinases, which phosphorylate target proteins, leading to changes in cellular activity. (D) Signup and view all the answers

Which of the following hormones is NOT a known activator of the cAMP second messenger system?

Insulin (C) Signup and view all the answers

What is the function of calmodulin in the calcium-calmodulin second messenger system?

Calmodulin acts as a calcium-binding protein, undergoing conformational change upon binding calcium, activating various enzymes. (D) Signup and view all the answers

What are the two main breakdown products of phosphatidylinositol biphosphate (PIP2) by phospholipase C?

Inositol triphosphate (IP3) and diacylglycerol (DAG) (B) Signup and view all the answers

How does the activation of protein kinase C (PKC) impact cellular function?

PKC promotes cell division and proliferation. (A) Signup and view all the answers

Which of the following hormones is NOT a known activator of the phospholipid second messenger system?

Epinephrine (A) Signup and view all the answers

What is the key difference between G protein-linked hormone receptors and enzyme-linked hormone receptors?

G protein-linked receptors utilize second messengers to activate intracellular enzymes, while enzyme-linked receptors activate intracellular enzymes directly. (C) Signup and view all the answers

How do steroid hormones exert their effects on gene expression?

Steroid hormones bind to intracellular receptors, forming a complex that activates gene transcription. (D) Signup and view all the answers

Study Notes

Introduction to Endocrine Physiology

Endocrine physiology is the study of the hormonal control systems in the body
Hormones are secreted from groups or single cells
Hormones regulate various functions like chemical reactions, transport of substances, growth and development, water and electrolyte balance, and secretion

Learning Objectives

Classify hormones by structure
Describe hormone synthesis, secretion, and transport
Explain the mechanism of hormone action

Nature of Hormones

Some hormones act locally (e.g., acetylcholine)
Some hormones act on all cells (e.g., growth hormone)
Other hormones act on specific target tissues (e.g., adrenocorticotropic hormone on adrenal cortex)

Principle Endocrine Glands

Pituitary gland
Hypothalamus
Pineal gland
Thyroid gland
Parathyroid glands
Thymus gland
Pancreas
Kidney
Ovaries
Testes
Adrenal glands
Adipose tissue
Stomach
Small intestine

Chemical Structure of Hormones

Protein/polypeptide hormones (e.g., anterior and posterior pituitary, pancreatic hormones)
Steroid hormones (e.g., cortisol, aldosterone, testosterone, estrogen) derived from cholesterol
Amino acid derivatives (e.g., T3, T4, epinephrine, norepinephrine)

Synthesis, Storage, and Secretion of Hormones

Protein hormones are initially formed as inactive preprohormones, then cleaved to prohormones in the rough endoplasmic reticulum (ER).
Further processing in the Golgi apparatus produces the active hormone, packaged into secretory vesicles, and stored.
Specific signals trigger hormone secretion

Synthesis and Storage (Diagram)

Hormones are synthesized in the cell and packaged in secretory vesicles, then stored.
Secretion is triggered by a specific stimulus.

Steroid Hormones Storage

Steroid hormones are stored in smaller quantities.
Enzymes act on precursor molecules to synthesize hormones.
Thyroid hormones are stored as part of large protein Thyroglobulin in follicles of the thyroid gland.
Norepinephrine and epinephrine are stored in granules and secreted via exocytosis.

Feedback Control of Hormone Secretion

Hormone secretion is generally regulated by internal control mechanisms.
Negative feedback loops prevent oversecretion or overactivity at the target.

Negative Feedback Mechanism

Negative feedback controls hormone secretion.
The endocrine gland and the target cell both have a role in the feedback loop.

Positive Feedback Mechanism

Positive feedback mechanisms, like the LH surge before ovulation, are also observed.

Cyclical Variations

Hormone release can fluctuate due to seasonal changes, sleep cycles, or daily rhythms.
Growth hormone (GH) secretion is higher during the early stages of sleep and decreases as sleep progresses.

Transport of Hormones

Peptide hormones are often dissolved in plasma.
Steroid and thyroid hormones circulate bound to plasma proteins.
This binding makes them inactive, making them more regulated and less likely to diffuse away.

Clearance of Hormones

Hormone concentration in the blood is determined by secretion rate and metabolic clearance rate (hormone removal rate).

Mechanisms of Action of Hormones

Hormones generally act via specific receptors.
Hormone-receptor complex triggers cellular responses.
Different types of receptors exist (membrane, cytoplasmic, nuclear).
Receptor number can change through upregulation or downregulation.

Intracellular Signaling

Hormones often exert their effects by activating receptors, which triggers responses within the cell.
Membrane receptors, such as ion channel-linked receptors, can change membrane permeability.
Receptors on cell surface usually trigger signaling pathways to bring cellular responses

G Protein-Linked Hormone Receptors

Hormone binding to a receptor activates a G protein, initiating a cascade of events.

Enzyme-Linked Hormone Receptors

Hormone-receptor interactions activate intracellular enzymes, triggering physiological effects.

Activation of Intracellular Enzymes

Hormone binding activates enzymes.
AMP activates cellular reactions

By activating gene

Steroid and thyroid hormones bind intracellular receptors.
Hormone-receptor complex affects target genes in the nucleus.
Transcription and protein synthesis are initiated

Cyclic AMP (2nd Messenger)

Hormones bind to cell surface receptors.
The receptor activates adenylyl cyclase, leading to cAMP formation.
cAMP acts as a second messenger.

Calcium-Calmodulin (2nd Messenger System)

Changes in membrane potential or hormone binding open calcium channels.
Calcium binds to calmodulin, altering its activity.
Activated calmodulin activates other enzymes leading to various cellular responses

Phospholipid (2nd Messenger System)

Hormone activation triggers phospholipase C.
Phospholipase C cleaves PIP2, releasing IP3 and DAG as second messengers.
IP3 releases calcium causing cellular responses.
DAG activates protein kinase C, altering cellular activities

Learning Resources

Textbook: John E. Hall and Michael E. Hall, Textbook of Medical Physiology, 14th ed. Elsevier, 2021
ISBN: 978-0-323-59712-8, Chapter 75, Pages 915-927
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Description

This quiz explores the fundamentals of endocrine physiology, focusing on hormone classification, synthesis, and action mechanisms. You'll learn about the various endocrine glands and the roles hormones play in regulating bodily functions. Test your understanding of how hormones interact with target tissues and overall physiological processes.