Physiology Endocrine

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What is the function of calcitonin in the intestine?

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Calcitonin inhibits calcium absorption in the intestine.

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Actions and Disorders of Growth Hormone

What is the function of calcitonin in the intestine?

Calcitonin inhibits calcium absorption in the intestine.

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Actions and Disorders of Growth Hormone

What is the drug form of PTH and its characteristics?

The drug form of PTH is Teriparatide, which is a protein hormone consisting of 84 amino acids and is secreted from the chief cells of the parathyroid gland.

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Types of Cell Membrane Receptors

What are the types of Tyrosine Kinase Receptors and their associated growth factors?

ReceptorAssociated Growth Factor
TRK ANerve Growth Factor
TRK BBrain Derived Growth Factor
TRK CNeurotrophin
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Types of Cell Membrane Receptors

What are the main types of cell membrane receptors?

The main types of cell membrane receptors include:

  • G-Protein Coupled Receptors (GPCRs)
  • Receptor Tyrosine Kinase (e.g., Insulin)
  • Cytokine Family Receptors (e.g., GH, Leptin, Erythropoietin)
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Cytoplasmic Receptors and Their Mechanism

What is the inactive state of cytoplasmic steroid hormone receptors?

In the inactive state, steroid hormone receptors are located in the cytoplasm and are bound to heat shock proteins. When a hormone binds to the receptor, it activates the complex, allowing it to enter the nucleus.

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Nuclear Receptors and Their Functions

What are some examples of nuclear receptors?

Examples of nuclear receptors include:

  • Estrogen Receptor
  • Retinoic Acid Receptor (RAR)
  • Progesterone Receptor
  • Thyroid Hormone Receptors
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G-Protein Coupled Receptors (GPCRs)

What is the mechanism of action of G-Protein Coupled Receptors (GPCRs)?

The mechanism of action of GPCRs involves the following steps:

  1. Hormone binds to the receptor.
  2. The α subunit of the G protein separates.
  3. The receptor is activated.
  4. Secondary messengers are triggered to enter the cell, leading to a cellular response.
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Second Messengers in Hormonal Action

What are some functions of second messengers in hormonal action?

Functions of second messengers include:

Second MessengerHormoneFunction
cAMPVasopressin (va)Water reabsorption
GlucagonMetabolism
SecretinElectrolyte (HCO3-) secretion
Calcium (IP3 - DAG)Vasopressin (vi), EndothelinVasoconstriction
OxytocinUterine contraction
-Exocytosis
cAMPNitric OxideVasodilatation
Natriuretic PeptidesRelaxation
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Hypothalamic and Pituitary Hormones

What is the role of leptin as a permissive hormone in early puberty?

Leptin plays a crucial role in signaling energy status to the hypothalamus, which is essential for the onset of puberty. It influences the secretion of gonadotropin-releasing hormone (GnRH), thereby affecting the development of secondary sexual characteristics.

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Hypothalamic and Pituitary Hormones

What are the main functions of prolactin in lactation?

Prolactin is responsible for the initiation of milk secretion (lactogenesis) and the maintenance of lactation (galactopoiesis). It stimulates mammary gland development and milk production in response to suckling.

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Hypothalamic and Pituitary Hormones

What hormones are released by the anterior pituitary and their corresponding cell types?

Cell TypeHormone(s)
SomatotropeGrowth Hormone
LactotropeProlactin
GonadotropeFSH, LH
ThyrotropeTSH
CorticotropeACTH
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Endocrine Physiology and Feedback Mechanisms

What is the significance of negative feedback in endocrine hormone release?

Negative feedback is a regulatory mechanism that helps maintain homeostasis in the endocrine system. It involves the inhibition of hormone release by the effects of the hormone itself or by the hormones produced by target glands, ensuring that hormone levels remain within a normal range.

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Hypothalamic and Pituitary Hormones

What are the effects of ACTH on the body, particularly in relation to Addison's disease?

ACTH stimulates the adrenal cortex to produce cortisol. In Addison's disease, there is an underproduction of cortisol, leading to increased levels of ACTH. This can result in symptoms such as hyperpigmentation due to the excess ACTH mimicking the action of melanocyte-stimulating hormone (MSH).

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Hypothalamic and Pituitary Hormones

What are the hypothalamic releasing hormones and their corresponding hormones released from the anterior pituitary?

Hypothalamic HormoneAnterior Pituitary Hormone(s)
Thyrotropin-releasing hormone (TRH)TSH, Prolactin
Corticotropin-releasing hormone (CRH)ACTH
Gonadotropin-releasing hormone (GnRH)LH, FSH
Growth hormone-releasing hormone (GHRH)GH
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Hypothalamic and Pituitary Hormones

What are the roles of hypothalamic inhibiting hormones in the anterior pituitary?

Hypothalamic Inhibiting HormoneRole in Anterior Pituitary
Prolactin release-inhibiting hormone (PIH)/dopamineInhibits prolactin release
Growth hormone release-inhibiting hormone/somatostatinInhibits GH release
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Actions and Disorders of Growth Hormone

What factors increase and inhibit growth hormone secretion?

Factors Increasing GH SecretionFactors Inhibiting GH Secretion
HypoglycemiaSomatostatin
ExerciseIncreased blood glucose (e.g., infusion)
FastingREM sleep
Stress
Starvation
Deep sleep (NREM stage 3 & 4)
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Actions and Disorders of Growth Hormone

What are the direct actions of growth hormone?

  • Decreased insulin sensitivity
  • Protein synthesis
  • Sodium retention
  • Lipolysis
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Actions and Disorders of Growth Hormone

What are the direct actions of Growth Hormone (GH) mediated by the JAK-STAT pathway?

The direct actions of GH mediated by the JAK-STAT pathway include:

  1. Lipolysis
  2. Bone growth: Conversion of prechondrocytes to chondrocytes.
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Actions and Disorders of Growth Hormone

What are the indirect actions of Growth Hormone (GH) mediated by IGF-1?

The indirect actions of GH mediated by IGF-1 primarily involve:

  • Bone Growth: All remaining actions at the level of bone.
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Actions and Disorders of Growth Hormone

What disorders are associated with abnormal levels of Growth Hormone (GH) in children?

In children, disorders associated with abnormal levels of GH include:

  • ↑GH: Gigantism
  • ↓GH: Dwarfism
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Actions and Disorders of Growth Hormone

What are the features of Acromegaly in adults?

Features of Acromegaly include:

  • Bony overgrowth: Frontal bossing
  • Increased hand and foot size
  • Prognathism: Mandibular enlargement
  • Increased heel pad thickness (due to soft tissue overgrowth)
  • Carpal tunnel syndrome
  • Sleep apnea (due to upper airway obstruction)
  • Diabetes mellitus
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Actions and Disorders of Growth Hormone

What are the treatment options for Acromegaly?

Treatment options for Acromegaly include:

Surgical Treatment:

  1. Trans-sphenoidal resection of microadenoma

Pharmacological Treatment:

  1. Somatostatin analogues: Octreotide
  2. GH receptor antagonist: Pegvisomant
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Actions and Disorders of Growth Hormone

What is Laron dwarfism and its etiology?

Laron dwarfism, also known as GH insensitivity syndrome, is characterized by:

  • Etiology: Defective receptors
  • Hormone levels: Increased GH with decreased plasma levels of IGF-1
  • Treatment: Mecasermin (recombinant form of IGF-1)
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Actions and Disorders of Growth Hormone

What are the uses of Recombinant Human Growth Hormone?

Recombinant Human Growth Hormone is used in:

  • Treatment of dwarfism
  • Treatment of muscle wasting in AIDS patients (increases lean body mass and muscle mass)
  • Anti-aging treatment
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Actions and Disorders of Growth Hormone

What are the primary effects of prolactin on the body?

  • Proliferation of lobulo-alveolar epithelial cells in the breast leading to milk production.
  • Acts as a negative regulator of reproductive functions by inhibiting GnRH, which in turn inhibits FSH and LH, resulting in lactational amenorrhea in females and decreased libido in females and spermatogenesis in males.
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Actions and Disorders of Growth Hormone

What factors increase prolactin secretion?

Factors increasing prolactin secretion include:

  1. Marked increase during pregnancy and lactation
  2. Sexual intercourse
  3. Dopamine blockers
  4. Exercise
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Actions and Disorders of Growth Hormone

What factors inhibit prolactin secretion?

Factors inhibiting prolactin secretion include:

  1. Somatostatin
  2. Dopamine agonists (like Bromocriptine)
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Hypothalamic and Pituitary Hormones

How does the hypothalamus regulate prolactin secretion?

The hypothalamus regulates prolactin secretion by releasing Thyrotrophin releasing hormone (TRH) which stimulates lactotrophs in the anterior pituitary to produce prolactin. Additionally, glucocorticoids and thyroid hormones inhibit prolactin secretion, as does the prolactin inhibiting factor (Dopamine).

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Thyroid Hormone Synthesis and Regulation

What are the raw materials required for thyroid hormone synthesis?

The raw materials required for thyroid hormone synthesis are:

  • Tyrosine: Derived from thyroglobulin (Tg).
  • Iodine: Present as iodide in the diet.
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Thyroid Hormone Synthesis and Regulation

What is the function of the Sodium Iodide Symporter (NIS) in thyroid hormone synthesis?

The Sodium Iodide Symporter (NIS) is located at the basolateral end of follicular cells and functions in iodide trapping through 2º active transport. It is also found in other locations such as the salivary gland, mammary gland, and placenta.

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Thyroid Hormone Synthesis and Regulation

What is the wolf-Chaikoff effect and its clinical use?

The wolf-Chaikoff effect is the phenomenon where excess iodide, through the sodium-iodide symporter (NIS), inhibits the organification of iodide, leading to decreased synthesis of thyroid hormones T3 and T4. Clinically, it is used in the treatment of patients with hyperthyroidism by administering Lugol's iodine prior to thyroid surgery.

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Thyroid Hormone Synthesis and Regulation

What are the consequences of mutations in the iodide-chloride antiporter/pendrin?

Mutations in the iodide-chloride antiporter/pendrin can lead to:

  • Goiter: Enlargement of the thyroid gland due to impaired iodide transport.
  • Sensorineural hearing loss: A condition associated with Pendred syndrome, which is characterized by both thyroid dysfunction and hearing impairment.
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Thyroid Hormone Synthesis and Regulation

What is the function of Thyroid Peroxidase (TPO) in thyroid hormone synthesis?

Thyroid Peroxidase (TPO) is an enzyme that catalyzes the oxidation of iodide to iodine, which is essential for the synthesis of thyroid hormones T3 and T4. It plays a crucial role in the organification of iodide, which is necessary for the production of these hormones.

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Thyroid Hormone Synthesis and Regulation

What is the role of binding proteins in the transport of thyroid hormones?

Thyroid hormones T3 and T4 are predominantly bound to binding proteins in the blood, with 99% of them being bound and only 1% free, which is responsible for their biological actions. The main binding proteins include:

  • Thyroid Binding Globulin (TBG): Has the highest affinity for T3 and T4.
  • Albumin: Binds a smaller fraction of thyroid hormones.
  • Pre Albumin/Transthyretin: Binds T3, T4, and vitamin A.
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Nuclear Receptors and Their Functions

How do T3 and T4 enter target cells and what is their mechanism of action?

T3 and T4 enter target cells through transporters such as monocarboxylate transporter (MCT) and organic anion transporting polypeptide (OATP). Once inside the cell, they bind to nuclear receptors in the nucleus, where they regulate gene expression and influence metabolic processes.

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Thyroid Hormone Synthesis and Regulation

What are the differences in potency and half-life between Triiodothyronine (T₃) and Thyroxine (T₄)?

HormonePotencyHalf-life
T₃Most potent1 day
T₄Least potent7 days
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Thyroid Hormone Synthesis and Regulation

How do T₃ and T₄ differ in their plasma protein binding and action duration?

HormonePlasma Protein BindingAction Duration
T₃LessActs rapidly
T₄MoreLong-lasting
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Thyroid Hormone Synthesis and Regulation

What are the physiological effects of thyroid hormones on the heart?

Thyroid hormones have a chronotropic and inotropic effect on the heart by increasing the number of β-adrenergic receptors, mediated by norepinephrine.

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Thyroid Hormone Synthesis and Regulation

How do thyroid hormones affect adipose tissue and muscle?

Thyroid hormones stimulate lipolysis in adipose tissue (catabolic effect) and increase proteolysis in muscle (catabolic effect).

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Thyroid Hormone Synthesis and Regulation

What developmental effects do thyroid hormones have on the CNS and bone?

Thyroid hormones promote brain growth through increased myelination in the CNS and support normal growth and skeletal development in bones.

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Thyroid Hormone Synthesis and Regulation

What is the impact of T₃ on glycosaminoglycans (GAGS) and what condition can result from hypothyroidism?

T₃ prevents the accumulation of GAGS, while hypothyroidism leads to their accumulation, resulting in myxedema and puffiness of the face.

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Thyroid Hormone Synthesis and Regulation

What are the consequences of congenital hypothyroidism on mental and physical development?

Congenital hypothyroidism can lead to mental retardation (most common reversible cause) and stunted growth.

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Thyroid Hormone Synthesis and Regulation

How does T₃ affect respiration and oxygen consumption in the lungs?

T₃ increases metabolism and oxygen consumption, leading to hypoxia and a right shift of the oxygen dissociation curve, which stimulates respiration and increases respiratory rate.

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Thyroid Hormone Synthesis and Regulation

What is the role of T4 deiodinase in the conversion of T4 to T3?

T4 deiodinase catalyzes the conversion of T4 (thyroxine) to T3 (triiodothyronine) and contains the amino acid selenocystine.

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Thyroid Hormone Synthesis and Regulation

How does T3 influence thermogenesis in the body?

T3 stimulates uncoupling protein I (UCPI), leading to heat dissipation and thermogenic action, which increases heat production in the body.

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Thyroid Hormone Synthesis and Regulation

What are the effects of hyperthyroidism and hypothyroidism on heat generation?

Hyperthyroidism results in increased heat generation and heat intolerance, while hypothyroidism leads to no heat generation and cold intolerance.

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Endocrine Physiology and Feedback Mechanisms

What are the secretions of the different cell types in the endocrine pancreas?

Cell typeSecretion
A cells (Alpha)Glucagon
B cells (Beta)Insulin, Amylin, C peptide
D cells (Delta)Somatostatin
F cellsPancreatic polypeptide
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Endocrine Physiology and Feedback Mechanisms

What are some properties of insulin?

  • Insulin is a large protein hormone composed of si amino acids.
  • It was the first protein to be completely sequenced by Sanger.
  • Insulin is produced using recombinant DNA technology.
  • Zinc stabilizes the structure of insulin.
  • Mutations in Hepatocyte Nuclear Factor (HNF) can lead to Maturity Onset Diabetes of the Young (MODY).
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Endocrine Physiology and Feedback Mechanisms

What are the steps involved in the release of insulin from beta cells of the pancreas?

  1. Glucose enters the beta cells via GLUT-2.
  2. Increased glucose leads to ATP accumulation, causing the ATP-sensitive K+ channels to close.
  3. This closure causes depolarization of the cell membrane, opening voltage-sensitive Ca2+ channels (VSCC).
  4. Calcium influx triggers exocytosis of insulin, amylin, and C peptide from secretory granules.
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Endocrine Physiology and Feedback Mechanisms

What are the sites of insulin-dependent glucose uptake?

  • Heart
  • Skeletal muscle (upregulates GLUT-4 to decrease serum glucose)
  • Adipose tissue

Note: Exercise activates the AMP-activated kinase pathway, which also increases GLUT-4 independently of insulin, benefiting diabetics.

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Endocrine Physiology and Feedback Mechanisms

What are the rapid and long-term actions of insulin?

Rapid actions (within seconds):

  • Decrease in blood glucose via GLUT-4.
  • Decrease in K+ levels (used in treatment of hyperkalemia with insulin + dextrose).

Long-term actions (in days):

  • Major anabolic hormone promoting storage of nutrients.
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Endocrine Physiology and Feedback Mechanisms

What are the two main signaling pathways activated by insulin and their functions?

  1. PI3 Kinase pathway (PI3K):

    • Mediates growth-promoting and anabolic functions.
    • Upregulates GLUT-4.
  2. MAP Kinase pathway (MAPK):

    • Also involved in growth promotion and metabolic actions.
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Endocrine Physiology and Feedback Mechanisms

What is the clinical significance of insulin in relation to blood glucose levels?

Insulin is a hypoglycemic hormone; a decrease in blood glucose levels can lead to coma if levels drop below 30 mg/dl. It plays a crucial role in maintaining glucose homeostasis, especially after protein meals where insulin and glucagon levels increase.

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Endocrine Physiology and Feedback Mechanisms

What factors increase insulin secretion?

Factors that increase insulin secretion include:

  • High blood glucose
  • Glucagon
  • Amino acids like arginine and leucine
  • Acetylcholine (Parasympathetic ANS)
  • β receptor mediated (Sympathetic ANS)
  • Gastrin, cholecystokinin, secretin
  • Incretin hormones such as GLP-1 and GIP, which enhance insulin secretion more from oral glucose than from IV glucose.
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Endocrine Physiology and Feedback Mechanisms

What factors decrease insulin secretion?

Factors that decrease insulin secretion include:

  • Epinephrine
  • Somatostatin
  • Toxins such as streptozocin and alloxan
  • α adrenergic receptor mediated (Sympathetic ANS, dominant effect)
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Endocrine Physiology and Feedback Mechanisms

What are the metabolic pathways stimulated and inhibited by insulin?

Pathways Stimulated by InsulinPathways Inhibited by Insulin
↑ Glycolysis↓ Glycogenolysis
↑ Glycogenesis↓ Gluconeogenesis
↑ Lipogenesis↓ Lipolysis
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Endocrine Physiology and Feedback Mechanisms

What hormones mediate ketogenesis in response to hyperglycemia?

Ketogenesis is mediated by hyperglycemic/counter-regulatory hormones, which include:

  • Cortisol
  • Growth hormone
  • Glucagon
  • Epinephrine
  • Thyroid hormones
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Endocrine Physiology and Feedback Mechanisms

What are the main secretions of the adrenal gland?

The adrenal gland has different zones that secrete various hormones:

  • Zona glomerulosa: Secretes mineralocorticoids (e.g., aldosterone)
  • Zona fasciculata: Secretes glucocorticoids (e.g., cortisol)
  • Zona reticularis: Secretes sex steroids
  • Adrenal medulla: Secretes catecholamines (90% epinephrine, 10% norepinephrine)
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Actions and Disorders of Growth Hormone

What is the major source of testosterone in the body?

The major source of testosterone is the testis.

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Endocrine Physiology and Feedback Mechanisms

What is the role of the hypothalamic-pituitary-adrenal (HPA) axis in hormone synthesis?

The HPA axis regulates hormone synthesis through a feedback loop where the hypothalamus releases corticotropin-releasing hormone, stimulating the anterior pituitary to release adrenocorticotropic hormone, which in turn stimulates the adrenal cortex to produce cortisol, aldosterone, and adrenal sex steroids.

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Actions and Disorders of Growth Hormone

What is the half-life of aldosterone and its significance?

Aldosterone has a half-life of 20 minutes and is considered a life-saving steroid hormone due to its critical role in regulating sodium and potassium levels in the body.

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Cytoplasmic Receptors and Their Mechanism

What are the sites of mineralocorticoid receptor (MR) action in the body?

The mineralocorticoid receptor (MR) is found in the kidneys, colon, hippocampus, salivary glands, and sweat glands.

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Types of Cell Membrane Receptors

What is the significance of enzyme deficiencies in adrenal hormone synthesis?

Deficiencies of enzymes involved in adrenal hormone synthesis can lead to Congenital adrenal hyperplasia, a condition that affects hormone production and can have significant clinical implications.

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Endocrine Physiology and Feedback Mechanisms

What is the primary action of aldosterone in the kidneys?

Aldosterone primarily promotes the reabsorption of sodium (Na⁺) through epithelial sodium channels (ENaC) and facilitates the excretion of potassium (K⁺) via renal outer medullary potassium channels (ROMK).

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Endocrine Physiology and Feedback Mechanisms

What is Liddle's syndrome and how is it related to aldosterone?

Liddle's syndrome is characterized by a gain of function mutation of ENaC, leading to increased sodium reabsorption, which results in hypertension as a key manifestation.

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Endocrine Physiology and Feedback Mechanisms

What is the significance of aldosterone escape in hyperaldosteronism?

Aldosterone escape refers to the phenomenon where an increase in extracellular fluid (ECF) does not lead to edema despite hyperaldosteronism, which results in increased sodium (Na⁺) levels.

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Endocrine Physiology and Feedback Mechanisms

How does aldosterone affect potassium levels in the body?

Aldosterone facilitates the excretion of potassium (K⁺) through renal outer medullary potassium channels (ROMK), which helps regulate potassium levels in the body.

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Endocrine Physiology and Feedback Mechanisms

What role does atrial natriuretic peptide play in relation to aldosterone?

Atrial natriuretic peptide promotes natriuresis, which is the excretion of sodium in urine, counteracting the effects of aldosterone and preventing edema.

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Endocrine Physiology and Feedback Mechanisms

What stimulates aldosterone release in the body?

Hyperkalemia stimulates aldosterone release, while ACTH increases aldosterone levels transiently.

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Actions and Disorders of Growth Hormone

What are the clinical features of Conn's syndrome associated with hyperaldosteronism?

The clinical features of Conn's syndrome include:

  1. Metabolic alkalosis due to H+ excretion.
  2. Hypokalemia leading to muscle cramps, interstitial atony, and nephropathy.
  3. Hypertension due to Na+ and H₂O retention, increasing extracellular fluid and blood pressure without edema.
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Endocrine Physiology and Feedback Mechanisms

What is aldosterone escape and how does it occur?

Aldosterone escape refers to the phenomenon where there is Na+ and H₂O excretion despite increased aldosterone levels, due to:

  • Pressure diuresis caused by increased blood pressure.
  • Atrial natriuretic peptide promoting natriuresis. This results in no edema despite high aldosterone levels.
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Actions and Disorders of Growth Hormone

What are the features of Addison's disease related to hypoaldosteronism?

FeatureDescription
HyponatremiaLow sodium levels
Postural hypotensionDrop in blood pressure on standing
HyperkalemiaHigh potassium levels
MicrocardiaSmall heart size
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Actions and Disorders of Growth Hormone

What are the main functions of sex steroids?

The main functions of sex steroids include:

  • Axillary hair growth
  • Pubic hair growth
  • Libido
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Actions and Disorders of Growth Hormone

What are the causes of increased adrenal androgens in disorders?

CauseDescription
Adrenocortical tumorsTumors of the adrenal cortex
Congenital adrenal hyperplasiaEnzyme deficiency in adrenal hormone synthesis
Adrenogenital syndromeExcess androgen production
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Actions and Disorders of Growth Hormone

What are the pathological effects of Cushing's syndrome due to cortisol excess?

Pathological EffectDescription/Manifestation
Muscle weakness & proximal myopathySteroid myopathy
Glucose intolerance & diabetes mellitusAdrenal diabetes
DyslipidemiaAbnormal lipid levels
Buffalo hump & moon faceFat redistribution
Increased susceptibility to infectionsImmunosuppression
EosinopeniaLow eosinophil count
Hypercoagulable stateIncreased risk of thrombosis
Irritability & psychosisNeuropsychiatric symptoms
Hypertension & atherosclerosisHigh blood pressure & arterial disease
Hypercalciuria & renal stonesIncreased calcium in urine, kidney stones
Peptic ulcerIncreased gastric acid
Amenorrhea, loss of libido, infertilityReproductive dysfunction
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Actions and Disorders of Growth Hormone

How does cortisol affect carbohydrate metabolism?

Cortisol acts as a 'hyperglycemic hormone' by increasing gluconeogenesis, which raises blood glucose levels.

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Actions and Disorders of Growth Hormone

What is the effect of cortisol on protein metabolism?

Cortisol has a catabolic effect in muscle, leading to proteolysis, while it has an anabolic effect in the liver, increasing the synthesis of plasma proteins.

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Actions and Disorders of Growth Hormone

What is the role of cortisol in fat metabolism?

Cortisol is lipolytic, meaning it promotes the breakdown of fats.

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Actions and Disorders of Growth Hormone

How does cortisol influence the immune system?

Cortisol acts as an anti-inflammatory agent, reducing inflammation and immune responses.

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Actions and Disorders of Growth Hormone

What changes in blood cell levels are caused by cortisol?

Cortisol decreases the blood levels of eosinophils and lymphocytes while increasing the levels of neutrophils, platelets, and red blood cells (RBCs).

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Actions and Disorders of Growth Hormone

What effects does cortisol have on the nervous system?

Cortisol alters mood and behavior and increases appetite.

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Actions and Disorders of Growth Hormone

How does cortisol affect kidney function?

Cortisol increases the glomerular filtration rate and calcium excretion in the kidneys.

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Actions and Disorders of Growth Hormone

What impact does cortisol have on bone health?

Cortisol increases bone resorption by enhancing the activity of osteoclasts, which can lead to bone loss.

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Actions and Disorders of Growth Hormone

What is the effect of cortisol on connective tissues?

Cortisol inhibits fibroblast proliferation and collagen formation, which can delay wound healing and cause purple striae on the skin.

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Actions and Disorders of Growth Hormone

How does cortisol influence the gastrointestinal tract?

Cortisol increases gastric acid secretion, which can lead to peptic ulcers.

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Actions and Disorders of Growth Hormone

What reproductive effects does cortisol have?

Cortisol inhibits GnRH, leading to amenorrhea, loss of libido, and infertility.

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Actions and Disorders of Growth Hormone

What are the main adrenal sex steroids found in both males and females?

SteroidDescription
Dehydroepiandrosterone (DHEA)Precursor to androgens/estrogens
Dehydroepiandrosterone sulfate (DHEAS)Sulfated form of DHEA
AndrostenedionePrecursor to testosterone/estrogens
Testosterone (small amounts)Main male sex hormone (minor from adrenals)
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Calcium Homeostasis

What are the normal serum calcium levels?

Normal serum calcium levels range from 9 to 11 mg/dL.

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Calcium Homeostasis

What is the relationship between ionized calcium and protein-bound calcium?

Ionized calcium and protein-bound calcium each make up 50% of total calcium in the serum, with ionized calcium being the physiologically active form and protein-bound calcium being the inactive form.

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Calcium Homeostasis

How does respiratory alkalosis affect calcium levels?

In respiratory alkalosis, the decrease in H⁺ ions causes calcium to bind to albumin, increasing the bound form of calcium and decreasing the free form, which can lead to hypocalcemic tetany.

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Distribution & Absorption of Ca²+

What are the three forms of calcium distribution in the body and their respective percentages?

FormPercentage
Free form50%
Bound form41%
Complex form9%
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Distribution & Absorption of Ca²+

What is the mechanism behind hypocalcemic tetany?

  • Na⁺ channels are affected by calcium levels.
  • A decrease in Ca²⁺ opens more Na⁺ channels, leading to:
    1. Increased depolarization
    2. Increased frequency of action potentials
    3. Resulting in hyperexcitability and hypocalcemic tetany.
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Distribution & Absorption of Ca²+

What are the signs of hypocalcemic tetany?

  1. Trousseau's sign: Eliciting carpopedal spasm by inflating a sphygmomanometer 20 mm Hg above SBP for 3 minutes.

  2. Chvostek's sign: Facial muscle twitching upon tapping the facial nerve at the angle of the jaw.

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Absorption of Ca²+

What is the role of parathyroid hormone (PTH) in calcium absorption?

  • Site: Secreted by the parathyroid glands.
  • Structure: Composed of 84 amino acids.
  • Actions: PTH acts on bone by stimulating osteoblasts, which in turn activate RANK ligand, leading to osteoclast differentiation and bone resorption, releasing calcium and phosphate into the bloodstream.
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Absorption of Ca²+

How does teriparatide affect bone metabolism?

  • Teriparatide is a drug form of PTH.
  • Continuous administration leads to bone resorption.
  • Intermittent administration promotes bone formation.
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Actions and Disorders of Growth Hormone

What is the overall action of PTH on the kidneys regarding calcium reabsorption?

PTH increases calcium reabsorption in the kidneys, specifically in the distal convoluted tubule (DCT) and proximal convoluted tubule (PCT). It also promotes phosphaturia through the Na+ PO4- cotransporter, leading to increased excretion of phosphate in urine.

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Endocrine Physiology and Feedback Mechanisms

How does PTH affect calcium absorption in the gastrointestinal tract?

PTH indirectly increases calcium absorption from the gastrointestinal tract by enhancing the synthesis of Vitamin D, which in turn promotes calcium absorption from the diet.

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Hypothalamic and Pituitary Hormones

What is the role of calcium sensing receptors (CaSR) in relation to PTH?

Calcium sensing receptors (CaSR) help regulate PTH secretion. A mutation in CaSR can lead to a condition where PTH is not suppressed, resulting in elevated levels of PTH and causing familial hypocalciuric hypercalcemia.

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Actions and Disorders of Growth Hormone

What is the source of calcitonin and its primary action?

Calcitonin is produced by the parafollicular C cells of the thyroid gland. Its primary action is to lower blood calcium levels by inhibiting osteoclast activity, thus reducing bone resorption.

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Actions and Disorders of Growth Hormone

What are the two types of bone markers and examples of each?

Bone markers are classified into two types:

  1. Bone formation markers:

    • Osteocalcin
    • Alkaline phosphatase
    • Pro-peptides of type I collagen
  2. Bone resorption markers:

    • TRAP (Tartrate resistant acid phosphatase)
    • MMP (matrix metalloproteinase)
    • Cathepsin K
    • NTX (N telopeptides of collagen crosslinks)
    • CTX (C telopeptides of collagen crosslinks)
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Extracellular and Intracellular Signaling

What are the facilitating and inhibiting factors for calcium absorption in the duodenum?

Facilitating factors for calcium absorption include gastric acid and a protein-rich diet. Inhibiting factors include phytates and oxalates, which form insoluble complexes that hinder absorption.

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Endocrine Physiology and Feedback Mechanisms

What is the overall effect of PTH, Vitamin D, and Calcitonin on serum calcium and phosphate levels?

HormoneSerum CalciumSerum Phosphate
PTH↑s. Ca²⁺↓s. phosphate
Vitamin D↑s. Ca²⁺↑s. phosphate
Calcitonin↓s. Ca²⁺-
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Hypothalamic and Pituitary Hormones

What is the role of PTH in the kidney?

PTH increases phosphate excretion by inhibiting the Sodium Phosphate cotransporter in the proximal convoluted tubule (PCT).

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