Physiology and Anatomy II - Endocrine System
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Questions and Answers

Which type of hormone acts primarily through intracellular receptors located in the cytoplasm or nucleus?

  • Vitamin C derivatives
  • Steroid hormones (correct)
  • Protein and polypeptide hormones
  • Tyrosine derivatives

How do protein-bound hormones differ from free hormones in the blood?

  • They represent the storage form of hormone (correct)
  • They bind directly to receptors
  • They are smaller in size
  • They can be filtered in urine

What happens to target cell receptors during chronic high levels of a hormone in the blood?

  • Receptors are inactivated gradually
  • The total number of receptors decreases (correct)
  • The total number of receptors increases
  • Receptors are synthesized continuously

What is the correct sequence of events in the hormone signaling mechanism initiated by a hormone?

<p>Hormone binding, receptor activation, cell response (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of hormone receptors?

<p>They are always static components (D)</p> Signup and view all the answers

Which hormones primarily use the phospholipid membrane pathway for signaling?

<p>Steroid and thyroid hormones (D)</p> Signup and view all the answers

What effect does chronic low hormone levels have on hormone receptors?

<p>Increased total number of receptors (B)</p> Signup and view all the answers

Why are steroid hormones effective at binding to their receptors?

<p>They can cross the plasma membrane (C)</p> Signup and view all the answers

What is the result of the hormone binding to its receptor in membrane pathways?

<p>It activates G protein, leading to the production of second messengers. (A)</p> Signup and view all the answers

Which mechanism is described as rapid and transient?

<p>Surface membrane receptor pathway activating already formed proteins. (D)</p> Signup and view all the answers

What is the role of cAMP in the adenylate cyclase pathway?

<p>It phosphorylates proteins, altering their activity. (D)</p> Signup and view all the answers

In the calcium-calmodulin pathway, what is the first step after hormone binding?

<p>Activation of the G protein. (C)</p> Signup and view all the answers

Why is the intracellular receptor pathway considered slow?

<p>It involves the synthesis of new proteins. (B)</p> Signup and view all the answers

Which type of hormones primarily act through membrane receptor pathways?

<p>Protein and polypeptide hormones. (B)</p> Signup and view all the answers

What physiological action results from the phosphorylation of proteins in the adenylate cyclase pathway?

<p>Modification of enzymatic activity. (D)</p> Signup and view all the answers

What is the main purpose of second messengers in hormone signaling pathways?

<p>To amplify the hormonal signal within the cell. (C)</p> Signup and view all the answers

What occurs after the hormone binds to its receptor in the membrane during the phospholipid membrane pathway?

<p>The receptor activates a G protein. (C)</p> Signup and view all the answers

What is the role of inositol triphosphate (IP3) in the phospholipid membrane pathway?

<p>It triggers the release of calcium from the endoplasmic reticulum. (C)</p> Signup and view all the answers

Which molecule produced during the phospholipid membrane pathway activates protein kinase C?

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

What are the final products of protein kinase C activity in the phospholipid membrane pathway?

<p>Phosphorylation of target proteins. (C)</p> Signup and view all the answers

What is the primary action of the active G protein in the phospholipid membrane pathway?

<p>Activation of phospholipase C. (B)</p> Signup and view all the answers

Which step involves the liberation of diacylglycerol during the phospholipid membrane pathway?

<p>Activation of phospholipase C. (A)</p> Signup and view all the answers

How does calcium function in the phospholipid membrane pathway?

<p>It binds to calmodulin and activates additional pathways. (A)</p> Signup and view all the answers

What is the initial event triggered by hormone binding in the phospholipid membrane pathway?

<p>Activation of a receptor. (D)</p> Signup and view all the answers

Flashcards

Adenylate Cyclase Pathway

Hormone binds to a receptor on the cell membrane, activating it. This activates a G protein, which in turn activates adenylate cyclase. Adenylate cyclase converts ATP to cAMP, a second messenger. cAMP activates protein kinases, leading to phosphorylation and alteration of protein activity.

Cell Membrane Receptor Pathways

Hormones bind to receptors on the cell membrane and trigger intracellular signaling pathways. These pathways use second messengers, such as cAMP, to amplify and convey the signal.

Intracellular Receptor Pathway

Specific proteins bind to DNA and regulate gene expression. This process involves the activation of a receptor, exposure of a DNA-binding domain, and initiation of transcription.

Conformational Change

A change in the three-dimensional structure of a molecule, often due to binding with another molecule.

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Membrane Receptor

A protein that acts as a gatekeeper, controlling the passage of molecules through cell membranes.

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DNA-binding Domain

A protein that binds to DNA and regulates gene expression. Think of a switch that turns genes on or off.

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Hormone

A chemical messenger that is released by a cell and travels to target cells to elicit a response.

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Ligand

A molecule that binds to a receptor and activates it, initiating a cellular response.

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G protein

A protein that acts as a switch, activated by hormone-receptor complex, triggering a cascade of events within the cell.

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Diacylglycerol

A messenger molecule inside the cell, created by the breakdown of membrane phospholipids.

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Inositol triphosphate ( IP3 )

A second messenger that increases intracellular calcium levels, leading to various cellular processes.

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Protein kinase C

A protein that phosphorylates other proteins, altering their activity and leading to physiological effects.

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Negative feedback

A process where the product of a pathway inhibits its own production, ensuring a balanced response.

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Feedback control

The mechanism by which hormones regulate the activity of other hormones, often maintaining hormone levels within a specific range.

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Nervous control

The regulation of hormone secretion by nerve signals, responding to external and internal stimuli.

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Hormone Forms in Blood

Hormones can exist in two forms in the blood: free (not bound to proteins) and protein-bound (attached to proteins).

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Hormone Receptors

These receptors are specialized proteins that bind to specific hormones. They are found in the cell membrane, nucleus, or cytoplasm.

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Signal Transduction Pathways

When a hormone binds to its receptor, it triggers a chain reaction within the cell. This series of events is called a signal transduction pathway.

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Lipid-Soluble Hormones

Some hormones, like steroid and thyroid hormones, can easily pass through the cell membrane due to their lipid solubility.

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Down-Regulation of Receptors

If there is consistently a high level of a hormone in the blood, the target cells may reduce the number of their receptors. This is called down-regulation.

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Up-Regulation of Receptors

If there is persistently a low level of a hormone in the blood, the target cells may increase the number of their receptors. This is called up-regulation.

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Hormone Classification

Hormones can be categorized based on their chemical composition. Three main categories are: protein and polypeptide hormones, steroid hormones, and tyrosine derivatives.

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Study Notes

Physiology and Anatomy II - Endocrine System

Grade Distribution

  • Final exam: 40%
  • Midterm exam: 30%
  • Quizzes: 20%
  • Student activities (class work & essay): 10%

Competency Objectives

  • Demonstrate the anatomy of the endocrine system.
  • Define endocrine glands and hormones.
  • Describe the chemical nature of hormones.
  • Compare the two forms of hormones in blood.
  • Define hormone receptors, describing their site, characteristics, and regulation.
  • Explain hormone action mechanisms (signal transduction pathways).
  • Demonstrate the different regulatory mechanisms of hormone action.

Anatomy of the Endocrine System

  • Pituitary gland: A small gland (1/2 g) located in a fossa at the base of the skull, below the brain.
  • Thyroid gland: Butterfly-shaped gland in front of the lower larynx and upper trachea, connected by an isthmus, moves with larynx movement.
  • Parathyroid glands: Four small yellowish glands embedded behind the thyroid.
  • Suprarenal (Adrenal) glands: Two triangular glands on top of the kidneys, with cortex and medulla.
  • Pancreas: A mixed endocrine and exocrine gland, located transversely on the posterior abdominal wall, extending from the duodenum to the spleen.
  • Gonads: Two testes in males, two ovaries in females.

The Endocrine Glands

  • Ductless glands secreting hormones into interstitial spaces, absorbed into the bloodstream for distribution to target tissues.

Hormones

  • Definition: Specific chemical substances secreted in small amounts by endocrine glands, affecting nearby or distant target cells; chemical messengers.
  • Chemical Nature: Classified into protein/polypeptide (hypothalamic, pituitary, pancreatic, parathyroid), steroid (adrenocortical, gonadal, active vitamin D), and tyrosine derivatives (thyroid, adrenal medullary).

Forms in the Blood

  • Free: Not bound to proteins, directly bind to receptors, small size, filtered in urine.
  • Protein-bound: Carried by plasma proteins, inactive, large size, not filtered in urine; storage form.

Hormone Receptors

  • Located on cell membranes, cytoplasm, or nucleus.
  • Characterized by being proteins, specific, and dynamic (number changes based on physiological conditions).
  • Regulation: Occurs through:
    • Downregulation: Chronic high hormone levels lead to fewer receptor sites.
    • Upregulation: Chronic low levels result in more receptor sites.

Mechanisms of Hormone Action (Signal Transduction Pathways)

1. Pathways Initiated by Intracellular Receptors

  • Mechanism: For steroid and thyroid hormones (lipid soluble) that pass through the cell membrane.
  • Steps:
    • Hormone diffuses through the membrane.
    • Binds to intracellular receptor, activating it.
    • H-R complex binds to DNA influencing transcription.
    • mRNA is produced directing protein synthesis producing physiologic effects.
    • Slow process due to protein synthesis.

2. Pathways Initiated From Cell Membrane Receptors

  • Mechanism: Used by peptide and protein hormones.
  • Types:
    • A. Adenylate cyclase pathway: Activation of G proteins, cAMP production, activating protein kinase A, phosphorylating enzymes, and altering cell activity.
    • B. Calcium-calmodulin pathway: Activation of G proteins, releasing intracellular calcium, calcium-calmodulin binding, initiating protein kinase activation and physiologically important effects.
    • C. Membrane phospholipid pathway: Activates G protein, activating phospholipase C, releasing diacylglycerol and IP3, increasing intracellular calcium, activating protein kinase C, and producing physiologic actions.

Mechanism of Action of Different Hormones

  • Tables displaying hormones and mechanisms (e.g., cAMP, IP3, steroid hormone).

Regulation of Hormone Secretion

  • Nervous control: External or internal stimuli affect hormone secretion, either directly or via hypothalamic releasing/inhibiting hormones.
  • Feedback control:
    • Negative feedback: Hormone levels influence gland function, influencing increase or decrease in secretion (most common).
    • Positive feedback: High hormone levels stimulate further production to maintain a high level. (less common)

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Description

This quiz covers the anatomy and physiology of the endocrine system as outlined in the course. You'll be tested on endocrine glands, hormones, and their mechanisms of action. Prepare to demonstrate your understanding of how hormones regulate various bodily functions.

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