Excitable Cells and Endocrine Systems

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Questions and Answers

What is the term used for electrical signals that might or might not cause an action potential?

  • Resting Membrane Potential
  • Graded Potential (correct)
  • Action Potential
  • Threshold Potential

What is the main ion responsible for establishing the resting membrane potential?

  • Sodium
  • Chloride
  • Calcium
  • Potassium (correct)

How does an increase in extracellular potassium concentration affect the resting membrane potential?

  • It makes the cell more positive (correct)
  • It makes the cell more permeable to sodium
  • It has no effect on the resting membrane potential
  • It makes the cell more negative

What is the impact of low calcium levels on the threshold potential?

<p>Threshold potential decreases (becomes more negative) (B)</p> Signup and view all the answers

How does increasing the extracellular potassium concentration affect the cell's excitability?

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

What is the primary mechanism by which beta blockers lower blood pressure?

<p>Decreasing calcium levels (A)</p> Signup and view all the answers

What is the theoretical equilibrium potential for potassium (E_K)?

<p>-90 mV (B)</p> Signup and view all the answers

Which of the following is NOT a strategy to decrease the excitability of brain regions during a seizure?

<p>Increase calcium levels (A)</p> Signup and view all the answers

A patient is prescribed a prednisone pack for 2 weeks but stops taking the full dose after 4 days. Which of the following symptoms would they likely experience due to low cortisol levels?

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

Which of the following is a cause of secondary hyperaldosteronism?

<p>High activity of the RAAS (D)</p> Signup and view all the answers

Which of the following is NOT a symptom of primary hyperaldosteronism?

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

What is the primary symptom of Cushing's syndrome, caused by hypersecretion of cortisol?

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

Which of the following is a symptom associated with the excessive DHEA production in females?

<p>Irregular menstrual periods (C)</p> Signup and view all the answers

What is the primary cause of hyperpigmentation in Addison's disease?

<p>Increased levels of ACTH, POMC, and MSH (A)</p> Signup and view all the answers

What is the main difference between primary and secondary adrenocortical insufficiency?

<p>Primary is caused by an adrenal gland issue, secondary is caused by a pituitary issue. (A)</p> Signup and view all the answers

Which of the following is NOT a potential cause of secondary adrenocortical insufficiency?

<p>High levels of cortisol (D)</p> Signup and view all the answers

Which of the following is a potential side effect of long-term cortisol use?

<p>Suppression of the HPA axis (A)</p> Signup and view all the answers

Which of the following hormones contributes to vasoconstriction and helps sustain blood pressure during acute plasma volume loss?

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

In the context of adrenocortical insufficiency, what is the relationship between ACTH and cortisol levels?

<p>ACTH levels are low, cortisol levels are low. (B)</p> Signup and view all the answers

Which of the following is a common symptom of Addison's disease?

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

What is the typical signalment for Addison's disease?

<p>30-50 year old female (B)</p> Signup and view all the answers

What is the primary role of the thyroid gland in the body?

<p>Regulation of metabolism and energy expenditure (C)</p> Signup and view all the answers

Which of the following is TRUE about the thyroid gland's role in metabolism?

<p>Thyroid hormones increase the production of heat. (B)</p> Signup and view all the answers

What is the precursor molecule for the synthesis of thyroid hormones?

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

Which of the following hormones is released from the anterior pituitary gland and acts on the thyroid gland?

<p>Thyroid-stimulating hormone (TSH) (D)</p> Signup and view all the answers

What is the active form of thyroid hormone?

<p>Triiodothyronine (T3) (C)</p> Signup and view all the answers

Identify the correct sequence of events in the regulation of thyroid hormone secretion.

<p>TRH → TSH → T3/T4 (C)</p> Signup and view all the answers

What is the role of the colloid-filled lumen within the thyroid follicular cells?

<p>Storage of thyroid hormone precursors (D)</p> Signup and view all the answers

What is the role of the adrenal medulla in the body?

<p>Production of catecholamines, such as epinephrine and norepinephrine (A)</p> Signup and view all the answers

Which of the following hormones are glycoproteins?

<p>TSH, FSH, and LH (B)</p> Signup and view all the answers

What is the primary function of the suprachiasmatic nucleus (SCN)?

<p>To control the body's circadian rhythms (B)</p> Signup and view all the answers

Which of the following is NOT an example of a negative feedback loop in the Hypothalamic-Pituitary Axis?

<p>The release of oxytocin from the posterior pituitary (A)</p> Signup and view all the answers

What is the role of angiotensin II in the Renin-Angiotensin-Aldosterone System (RAAS)?

<p>It causes vasoconstriction and stimulates aldosterone release (A)</p> Signup and view all the answers

What is the primary function of cortisol in the body?

<p>To regulate blood glucose levels (C)</p> Signup and view all the answers

Which of the following is NOT a direct effect of aldosterone?

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

Which of the following statements about receptor sequestration is TRUE?

<p>The signal molecule is pulled into the cell's endosome and remains there. (D)</p> Signup and view all the answers

What is the role of melanopsin in the regulation of circadian rhythms?

<p>It senses light changes and stimulates the SCN (D)</p> Signup and view all the answers

Which of the following hormones is responsible for the contraction of myoepithelial cells surrounding alveoli during breastfeeding?

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

What is the primary function of vasopressin (ADH)?

<p>To increase water reabsorption in the kidneys (D)</p> Signup and view all the answers

Which of the following describes the pattern of hormone secretion that is most common?

<p>Basal (D)</p> Signup and view all the answers

Which of the following statements about the release of oxytocin is TRUE?

<p>It plays a role in uterine contractions during childbirth. (A)</p> Signup and view all the answers

Which of the following hormones is produced by the adrenal medulla?

<p>Epinephrine (B)</p> Signup and view all the answers

Which of the following is a precursor to both aldosterone and cortisol?

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

Which of the following correctly describes the effect of bright late-night light on circadian rhythms?

<p>It advances the rhythm (A)</p> Signup and view all the answers

Which of the following is a common example of feed-forward signaling in the body?

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

What is the effect of increasing extracellular calcium concentration on the excitability of a cell?

<p>Decreased excitability due to an increase in threshold potential. (D)</p> Signup and view all the answers

What is the primary mechanism by which parasympathetic stimulation affects heart rate?

<p>Increasing acetylcholine release from postganglionic fibers. (A)</p> Signup and view all the answers

What is the role of the hypothalamus in the autonomic nervous system?

<p>It serves as the central control center for autonomic activity. (C)</p> Signup and view all the answers

Which of the following correctly describes the characteristics of sympathetic preganglionic fibers?

<p>Short, originate in the thoracolumbar spinal cord, release acetylcholine. (D)</p> Signup and view all the answers

Which of the following is NOT a characteristic of steroid hormones?

<p>Stored in secretory vesicles before release. (C)</p> Signup and view all the answers

What is the primary function of the second messenger cAMP in 7 transmembrane loop receptor signaling?

<p>It activates protein kinase A, which phosphorylates target proteins. (B)</p> Signup and view all the answers

Which of the following is an example of a neurohormone?

<p>Antidiuretic hormone released from the posterior pituitary. (C)</p> Signup and view all the answers

What is the primary difference between paracrine and endocrine signaling?

<p>Paracrine signaling involves the release of local mediators, while endocrine signaling involves the release of hormones into the bloodstream. (A)</p> Signup and view all the answers

What is the effect of sympathetic stimulation on blood vessels in skeletal muscle?

<p>Dilation due to the release of norepinephrine from postganglionic fibers. (C)</p> Signup and view all the answers

What is the primary function of the autonomic nervous system?

<p>Regulate the body's internal environment (homeostasis). (C)</p> Signup and view all the answers

Which of the following is true regarding the sympathetic and parasympathetic nervous systems?

<p>They can work antagonistically or synergistically depending on the target organ and context. (D)</p> Signup and view all the answers

Which of the following hormones is responsible for the development of Addison's disease?

<p>Cortisol. (A)</p> Signup and view all the answers

What is the primary role of transport proteins in the bioavailability of steroid hormones?

<p>They protect steroid hormones from degradation in the bloodstream. (D)</p> Signup and view all the answers

What is the primary difference between the nervous system and the endocrine system in terms of their response characteristics?

<p>The nervous system is rapid and short-lived, while the endocrine system is slower and longer-lasting. (B)</p> Signup and view all the answers

What is the primary mechanism by which the sympathetic nervous system increases heart rate?

<p>By releasing norepinephrine from postganglionic fibers. (C)</p> Signup and view all the answers

What is the primary function of the varicosities at the end of sympathetic postganglionic fibers?

<p>To store and release neurotransmitters. (B)</p> Signup and view all the answers

Flashcards

Action Potential Effects

The result of an action potential leads to neurotransmitter (NT) release.

NT Release Variation

Neurons do not release the same amount of NT; the amount affects signal strength.

Graded Potentials

Changes in membrane potential that may or may not trigger an action potential (AP).

Resting Membrane Potential (RMP)

RMP is typically negative due to more potassium inside the cell than outside.

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Calcium's Role in Threshold

Calcium levels determine the threshold for action potentials: low calcium lowers threshold, high calcium raises it.

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Nernst Equation

A formula to calculate equilibrium potential; E = 61 log ([outside]/[inside]). Potassium's E is -90mV.

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Extracellular Potassium Increase

An increase in extracellular potassium raises the concentration gradient, making the cell more excitable.

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Hyperexcitable Seizure Focus

Regions of the brain that are overly excitable due to being too close to threshold for firing.

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Low cortisol levels

Can lead to hypotension, shock, hypoglycemia, fatigue, vomiting, decreased appetite, and abdominal pain.

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Primary hyperaldosteronism

A condition characterized by excessive secretion of aldosterone, often due to idiopathic causes or adrenal adenomas.

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Cushing's syndrome

A disorder caused by excessive cortisol, leading to symptoms like fat accumulation and muscle wasting.

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Symptoms of adrenal gland disorders

Symptoms may include increased blood pressure, irregular menstruation, and changes in libido due to hormonal imbalances.

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Adrenal gland regions

The adrenal gland consists of zones including the zona glomerulosa, which is responsible for aldosterone production.

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Vasopressin

Hormone released by the posterior pituitary to conserve water and sodium.

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Cortisol

Hormone with anti-inflammatory and immunosuppressive properties, released by adrenal glands.

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Addison's Disease

Primary adrenocortical insufficiency leading to low adrenal hormone production.

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Secondary Adrenocortical Insufficiency

Condition caused by low ACTH due to a hypothalamic or pituitary defect.

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Symptoms of Addison's

Low blood pressure, hypoglycemia, changes in hair distribution, and hyperpigmentation.

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ACTH

Adrenocorticotropic hormone that stimulates cortisol production from the adrenal glands.

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Cortisol Side Effects

Can include high blood pressure, gastric ulcers, and increased infection risk.

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Hypothalamic-Pituitary-Adrenal Axis

A complex regulatory system for stress response, including hormone production.

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Adrenogenital syndrome

A condition causing excess androgen production due to cortisol deficiency.

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Polycystic ovary syndrome (PCOS)

A condition affecting 30% of women with excessive adrenal androgen production, causing various symptoms.

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Adrenal medulla

An endocrine part of the sympathetic nervous system, releasing catecholamines.

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Catecholamines

Hormones produced by the adrenal medulla, including epinephrine and norepinephrine.

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Epinephrine

A central hormone in fight or flight response, promoting glucose release and energy.

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Thyroid hormone (T3 and T4)

Hormones released by the thyroid gland, crucial for metabolism and growth.

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Thyroid-releasing hormone (TRH)

A hormone that stimulates the release of TSH from the pituitary gland.

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TSH (Thyroid Stimulating Hormone)

A hormone that stimulates the thyroid gland to produce T3 and T4.

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RMP (Resting Membrane Potential)

The electrical charge difference across a cell's membrane at rest.

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Threshold

The point at which an action potential is triggered in a neuron.

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Calcium's role in excitability

Calcium levels influence threshold and cell excitability; higher calcium decreases excitability.

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Potassium Permeability

Refers to how easily potassium ions can move in and out of a cell.

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Sodium Permeability

Indicates how much sodium can enter a cell, affecting excitability.

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Sympathetic Nervous System

Part of the autonomic nervous system responsible for 'fight or flight' responses.

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Parasympathetic Nervous System

Part of the autonomic nervous system that promotes 'rest and digest' responses.

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Dual Innervation

When an organ is regulated by both sympathetic and parasympathetic systems.

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Hormone Bioavailability

The degree to which a hormone is available to bind to its target receptor.

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Polypeptide Hormones

Hormones made of amino acid chains, synthesized in the rough ER.

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Steroid Hormones

Derived from cholesterol, can pass through membranes easily.

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Endocrine Signaling

Hormonal communication that occurs over long distances through the bloodstream.

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Paracrine Signaling

Cell signaling that occurs when a signaling molecule affects nearby cells.

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G-protein Coupled Receptors

Receptors that activate G-proteins, mediating various cellular responses.

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Second Messenger Systems

Intracellular signaling pathways activated by hormones via membrane receptors.

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Receptor Sequestration

Signal molecule is pulled into the cell endosome and remains there without destruction.

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Receptor Down-Regulation

Decrease in the number of receptors on a cell's surface, reducing its sensitivity to a signal.

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Pulsatile Hormone Secretion

Hormone is released in bursts or pulses, common in reproductive hormones.

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Basal Hormone Secretion

Constant, low-level hormone release typical in many bodily functions.

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Sustained Hormone Secretion

Continuous release of hormones, often in response to stress.

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Hypothalamic-Pituitary Axis

System where the hypothalamus releases hormones that regulate the pituitary gland's hormone secretion.

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Negative Feedback Loop

Process where the output of a system inhibits its own production to maintain balance.

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Oxytocin Function

Hormone that facilitates childbirth and lactation; promotes uterine contractions.

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Vasopressin (ADH)

Hormone that increases water reabsorption in kidneys and causes blood vessels to constrict.

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Circadian Rhythms

Biological processes that follow a 24-hour cycle, affected by light and dark.

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Melatonin Production

Hormone produced by the pineal gland that regulates sleep-wake cycles, increases in darkness.

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Renin-Angiotensin-Aldosterone System (RAAS)

Hormonal system that regulates blood pressure and fluid balance.

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Cortisol Functions

Stress hormone that regulates metabolism, increases glucose production, and manages stress responses.

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Prolactin

Hormone released from the anterior pituitary that stimulates milk production in mammals.

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Study Notes

Excitable Cells

  • Action potentials result in neurotransmitter (NT) release. NT release isn't always consistent in amount; more NT equals a stronger signal, less a weaker one.
  • Graded potentials may or may not trigger an action potential (AP).
  • Resting membrane potential (RMP) relies on potassium ion (K+) concentration differences across the membrane. High potassium can cause excitation, muscle spasms, and twitching.
  • Low potassium lowers the threshold for excitation.
  • High calcium raises the threshold for excitation; beta blockers lower heart rate by affecting calcium.
  • Equilibrium potential (E) calculation: E = 61 log ([outside]/[inside]). The permeability of the membrane to a specific ion factors into these calculations. Potassium has the greatest effect on RMP.
  • Increased extracellular potassium causes the cell to become more excitable.
  • Decreased extracellular potassium causes the cell to become less excitable.

Endocrine Systems (Hormones)

  • Hormones are classified as membrane-receptor binding or intracellular-receptor binding, based on how they bind to cells.
  • Different hormone classes include polypeptides (amino acid chains produced by the rough ER), and steroids (derived from cholesterol).
  • Hormones work through different ways such as paracrine neurotransmitters, endocrine hormones, and neurohormones.
  • The nervous system can induce rapid, brief effects, while endocrine responses are slower and have long-lasting effects.
  • Hormones often bind to receptors on the cell membrane (hydrophilic) or inside the cell (lipophilic).
  • Feedback loops regulate hormone release.
  • The hypothalamus-pituitary axis (HPA) is a crucial endocrine system component. It includes the hypothalamus, anterior pituitary, and various target endocrine organs and controls many physiological functions.

Circadian Rhythms

  • The pineal gland and suprachiasmatic nucleus (SCN) regulate circadian rhythms.
  • Melanopsin, part of retinal ganglion cells, senses light and regulates the SCN.
  • The SCN establishes a daily clock and the pineal gland responds to the SCN by releasing melatonin (regulates the light/dark cycle rhythm)
  • Light and dark cycles influence the SCN and endocrine organs, causing daily fluctuations in hormone production and other biological functions.

Thyroid and Growth

  • The thyroid gland is located below the larynx. It regulates metabolism.
  • The thyroid releases thyroid hormone (T3 and T4).
  • T3 and T4 increase metabolic rate and heat production, and enhance growth and central nervous system development.
  • T4 is converted to T3 before T3 can be utilized by most tissues.
  • Hormones are actively transported using carrier proteins.
  • Thyroid hormone effects depend on the tissue target and receptor types present.
  • Iodine deficiency can lead to goiter formation due to disruptions in thyroid hormone production.
  • A large set of processes regulates how the thyroid gland functions, including TSH production by the pituitary, feedback, and iodine import.

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