The Endocrine System: Hormones and Control

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Questions and Answers

How does the endocrine system primarily influence cellular activities?

  • Via mechanical forces exerted on target tissues.
  • Through electrical impulses that directly stimulate cells.
  • By releasing hormones that alter metabolic activity. (correct)
  • Through direct physical connections between organs.

Which of the following is a characteristic of hormones?

  • They act as signaling molecules that regulate cell activity. (correct)
  • They always inhibit the growth of target tissues.
  • Their effects are immediate, lasting only seconds.
  • They exert effects only on the organs that produce them.

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

  • To regulate body temperature through sweat glands.
  • To directly control muscle contractions.
  • To produce digestive enzymes.
  • To serve as the major endocrine system controller. (correct)

Which of the following is a characteristic of local-acting hormones?

<p>They are produced close to the site of action. (D)</p> Signup and view all the answers

Which of the following is an example of an autocrine function?

<p>The release of prostaglandin by smooth muscle cells causing vasoconstriction. (B)</p> Signup and view all the answers

Which gland type secretes substances through excretory ducts directly into adjoining areas?

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

Hormones can be classified based on their chemical structure. Which of the following is a major class of hormones?

<p>Amino acid-based hormones (B)</p> Signup and view all the answers

Which type of hormone can readily pass through cell membranes due to its lipid-soluble nature?

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

What is the direct effect of hormones on target cells?

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

How do steroid and peptide hormones differ in their mechanisms of action on target cells?

<p>Steroid hormones directly stimulate transcription, while peptide hormones use a secondary messenger system. (C)</p> Signup and view all the answers

How can a single cell respond to multiple hormone signals simultaneously?

<p>By expressing several different hormone receptor types. (B)</p> Signup and view all the answers

Where are thyroid hormone receptors typically located?

<p>Nearly all body cells, including the adrenal cortex. (B)</p> Signup and view all the answers

What is the significance of the blood-brain barrier in the context of hormone action?

<p>It prevents certain hormones from affecting the brain. (D)</p> Signup and view all the answers

What is a key factor that controls target cell activation by a hormone?

<p>The hormone-receptor affinity. (A)</p> Signup and view all the answers

How does down-regulation affect target cell sensitivity to hormones?

<p>It decreases the number of receptors, desensitizing target cells. (B)</p> Signup and view all the answers

Flashcards

Endocrine System

Integrated system of small organs exerting large effects on cell metabolic activity, controlling it by hormonal means.

Hormones

Bloodborne chemical substances functioning as signaling (messenger) molecules that regulate cell activity.

Hypothalamus

A neuroendocrine organ that produces/releases several hormones and is the major endocrine controller.

Local-acting hormones

Hormones produced by several tissues that act close to where they are produced.

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Autocrines

Exert effects on the SAME cells secreting them

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Paracrines

Exert effects on NEARBY cells close to those secreting them

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Exocrine Gland

Glands that secrete substances through excretory ducts directly into adjoining areas.

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Endocrine Gland

Glands that release hormones into local interstitial fluid and are transported through the bloodstream.

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Mixed Gland

Glands with both exocrine and endocrine functions.

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Hormone characteristics

Regulate metabolic activity of other cells with prolonged effects that exhibit lag times.

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Amino acid-based hormones

Hormones that are water soluble so they cannot pass through cell membranes, except for thyroid hormone

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Steroid hormones

Hormones that are lipid soluble and can readily pass directly through target cell membranes.

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Cellular Action

Hormones alter cellular activity for growth, maintenance and/or repair.

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Peptide/steroid hormone

The hormone target cell activation mechanism differs due to membrane permeability/receptor location

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Up-regulation

Persistently low hormone levels cause an increase in membrane receptor numbers.

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Study Notes

  • Topics include the Endocrine system overview, Hormone types, chemistry and control, Target cell action and properties, Signaling mechanisms and Target cell activation

Endocrine System Overview

  • An integrated system of small organs exerts significant effects on cell metabolic activity and controls cell activity through hormones
  • Hormones are bloodborne chemical substances that act as signaling messengers, regulating cell activity with effects felt far from the release site, stimulating or inhibiting tissue growth and function for seconds to days
  • The hypothalamus is the primary neuroendocrine controller releasing various hormones and influencing the autonomic nervous system

Local-Acting Hormones

  • Produced by various tissues, not considered true hormones due to their effect close to the production site
  • These include adipose cells, the small intestine, the stomach, kidneys, and heart
  • Autocrines exert effects on the same cells that secrete them, using autocrine receptors, illustrated by prostaglandin release causing vasoconstriction
  • Paracrines affect nearby cells using paracrine receptors like pancreatic somatostatin which inhibits insulin and glucagon release from beta and alpha cells respectively

Hormone Control and Glands

  • Body cells targeted by hormones regulate growth, maintenance and repair through processes like reproduction, development, electrolyte and water balance, cell metabolism, nutrient management, energy output, and immune responses
  • Exocrine glands secrete sweat, saliva, and digestive enzymes, moved through ducts to adjoining areas
  • Endocrine glands, including the pituitary, thyroid, parathyroid, adrenal, and pineal glands, release hormones into interstitial fluid and bloodstream, binding to target organ receptors
  • Mixed glands, such as the pancreas, gonads, and placenta, perform both exocrine and endocrine functions, like the pancreas producing insulin and digestive enzymes

Hormones- General Characteristics

  • Hormones regulate metabolic activity, show a delayed response lasting seconds to hours, with prolonged effects
  • Amino acid-based hormones are proteins, including amines, short peptides, and long polypeptides
  • Steroids are cholesterol-based
  • Eicosanoids consist of biologically active lipids such as leukotrienes and prostaglandins, released by nearly all cell membranes

Hormone Chemistry

  • Amino acid-based hormones are water-soluble and can not pass through cell membranes, except for thyroid hormone which has to relay an external signal through an internal pathway
  • Steroid hormones, being lipid-soluble pass through cell membranes
  • A hydrophobic cholesterol base helps steroid hormones penetrate the hydrophobic phospholipid layers
  • Variations in receptors and target cell types determine the exact cellular response to hormones which then alter cell activities

Hormone Action on Target Cells

  • Hormones signal changes in cellular action, shifting protein output, activating enzymes, adjusting ion channels, and controlling secretion
  • Target cell effects include altering plasma membrane permeability, stimulating protein production, activating or deactivating enzyme systems, inducing secretion, and promoting mitosis, which supports cell maintenance, growth, and repair

Hormones Signaling

  • Whether peptide or steroid, a target cell’s activation depends on membrane permeability and receptor location
  • Steroid hormones enter the cell, bind to chaperone proteins, migrate to the nucleus, and bind to an internal (DNA) receptor, changing cell activity by stimulating transcription (direct mechanism)
  • Peptide hormones bind to an extracellular receptor, triggering signal transduction, producing cAMP, and activating enzymes through an indirect mechanism

Peptide Hormones- Target Cell Properties

  • Hormones circulate to all body tissues except the brain, protected by the blood-brain barrier
  • Hormones affect cells with specific receptors, activating a pre-programmed function
  • A single cell can have different types of hormone receptors
  • Receptor location, amount, and type of vary among cells with ACTH receptors found only on adrenal cortex cells and thyroid hormone receptors on nearly all body cells

Peptide Hormones- Target Cell Activation

  • Hormone action is controlled by hormone blood levels, how many target cell receptors there are, and the binding strength
  • Receptor number is a dynamic, regulated process
  • Up-regulation happens when a cell increases receptor numbers in response to low hormone levels
  • Down-regulation occurs when high hormone levels cause a reduction in receptor numbers, desensitizing the cell to the hormone

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