Physiology - Endocrine - Principles

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  1. Endocrine means ________.
    to secrete internally
  2. The endocrine system is composed of _______ that secrete __________, i.e. _______, into _______ and function by _____________ at ________.
    • ductless endocrine glands
    • chemical messengers
    • hormones
    • the blood
    • affecting other cells and organs
    • distant sites
  3. In addition to specialized endocrine glands, some cells with other functions can also secrete hormones into the blood, giving them a _________.
    secondary endocrine function
  4. The nerve terminals of certain neurons secrete hormones directly into the blood, giving rise to _______________.
    neuroendocrine (neurocrine) signals
  5. Endocrine signaling allows ________ cells to __________ cells. It also allows ___________ of the functions of multiple types of cell or tissue. An example of coordinated hormone action is epinephrine surge during "fight or flight" responses.
    • a small number of
    • influence the behavior of many target
    • coordination
  6. Some receptors respond to more than one hormone. Some hormones bind more than one type of receptor, each commonly couples to a distinct intracellular signal transduction pathway.
  7. The catecholamines epinephrine and norepinephrine:
    • overlapping affinity for the same types of receptor.
    • GPCRs, α1‐, α2‐ and ß‐adrenergic receptors.
    • distinct intracellular signal transduction pathways.
  8. The α1‐Adrenergic receptor is normally coupled to _________.
    Gq, IP3 formation and calcium mobilization
  9. The α2‐Adrenergic receptor is normally coupled to _________.
    Gs, inhibition of cAMP formation
  10. The ß‐Adrenergic receptor is normally coupled to ________.
    Gq, cAMP formation
  11. ACh actions on heart, skeletal muscle, and salivary gland cells
    • Cardiac nodes: Muscarinic M2 -> Gi -> (-) cAMP; decrease heart rate and contraction force
    • Skeletal muscle: Nicotinic; ligand-gated ion chan; contraction
    • Salivary acinar cells: muscarinic M3 -> Gq -> IP3 & Ca2+; secretion
  12. Hypothalamus (neurocrine) – _______.
    controls pituitary endocrine secretions.
  13. Pituitary –
    controls other endocrine glands and has direct effects on peripheral tissues.
  14. Pineal –
    regulates circadian rhythm.
  15. Thyroid –
    controls metabolic rate and growth.
  16. Parathyroid –
    regulates calcium and phosphorous homeostasis.
  17. Adrenal (cortex & medulla) –
    regulate metabolism, mineral balance and stress responses.
  18. Pancreatic islets of Langerhans –
    regulate metabolism and energy balance.
  19. Ovaries & Testes –
    control maturation and development, sexual function and pregnancy.
  20. Examples of hormones secreted from tissues with secondary endocrine functions
    • adipose tissue -> leptin
    • CCK, secretin, gastrin
  21. Endocrine signaling involves 4 steps.
    • 1. Extracellular chemical messengers = hormones.
    • 2. Cell surface or intracellular receptors.
    • 3. Signal transduction pathways.
    • 4. Mechanisms to change cell function.
  22. Hormones that act in the endocrine system fall into one of four major classes:
    • Peptides: insulin
    • Steroids: E2
    • Thyroid hormones
    • Catecholamines and other biogenic amines: E
  23. Peptides – Encoded by specific genes and synthesized using the normal protein synthesis machinery. Undergo extensive ____________ and follow __________ pathway. Stored in ________ and released when needed.
    • post‐translational modification
    • the secretory protein
    • secretory granules
  24. Steroids – Synthesized through a series of enzyme steps from ________. ___phylic and released _________.
    • cholesterol
    • Lipo
    • directly from cells when synthesized (generally not stored)
  25. Thyroid hormones – Synthesized from ______ that is stored in a _____ form in ______. Release occurs by _______.
    • tyrosine residues of a protein precursor
    • colloidal
    • the thyroid gland
    • proteolysis of the precursor
  26. Catecholamines and other biogenic amines – Synthesized from ______. Stored in _______ and released when needed.
    • various amino acids and other small molecule biochemical precursors
    • secretory granules
  27. Secretion of hormones occurs through ______ from secretory vesicles. Secretion is initiated by an external stimulus, usually leading to an increase in the cytosolic ____. Secretory granules associate with the _______ and translocate to the plasma membrane.
    • exocytosis
    • [Ca2+] or cAMP
    • cytoskeleton
  28. _______ hormones are lipophylic, and therefore cannot dissolve at significant concentrations in blood plasma. They travel through the blood stream bound to ________: Specific binding globulins (proteins) with high _____ for an individual hormone. (eg. _______ carries thyroid hormones). Nonspecific lower affinity proteins that are present in _____ amounts also carry significant quantities of hormones. Most important amongst these is ______.
    • Steroid and thyroid
    • binding proteins
    • affinity
    • Thyronine binding globulin [TBG]
    • larger
    • albumin
  29. Advantages of hormone binding to plasma proteins
    • 1. Enhances distribution to all body compartments (otherwise would accumulate in lipid environments).
    • 2. Provides a reservoir of readily available hormone, making the blood serve as the storage site.
    • 3. Protects the hormone from degradation and excretion, thereby increasing half‐life in the circulation.
    • 4. Limits rapid fluctuations.
  30. Rates relevant to hormone action on/off
    • rate of release
    • rate of blood transport
    • intracellular signal transduction rate in the target cell
    • Off‐rates for signaling cascades
    • rate of removal of the hormone
  31. The half‐life of a hormone in the blood is determined by its rate of elimination via:
    • Reuptake by secretory cell
    • Internalization of receptor‐coupled hormone by target cell
    • Metabolic degradation (can occur in target cell, other cells or by action of extracellular enzymes).
    • Excretion, primarily in urine
  32. rate of response and T50 for Catecholamines, Peptide hormones, and Steroid/thyroid hormones:
    • Catecholamines: within seconds; 1‐3 minutes.
    • Peptide hormones: seconds to minutes; 2 min to several hours.
    • Steroid/thyroid hormones: hours to days; 30 min to many hrs or days.
  33. secretion of Steroids, Thyroxine, Peptides and Proteins, Catecholamines
    • Diffusion through plasma membrane
    • Proteolysis of thyroglobulin
    • Exocytosis of storage vesicles
    • Exocytosis of storage vesicles
  34. Steroids, Thyroxine, Peptides and Proteins, Catecholamines: bind to plasma proteins
    • Yes
    • Yes
    • Rarely
    • No
  35. Steroids, Thyroxine, Peptides and Proteins, Catecholamines: Lifetime
    • Hours
    • Days
    • Minutes
    • Seconds
  36. Steroids, Thyroxine, Peptides and Proteins, Catecholamines: Time course of action
    • Hours to days
    • Days
    • Minutes to hours
    • Seconds or less
  37. Steroids, Thyroxine, Peptides and Proteins, Catecholamines: Receptors
    • Cytosolic or nuclear
    • Nuclear
    • Plasma membrane
    • Plasma membrane
  38. Steroids, Thyroxine, Peptides and Proteins, Catecholamines: Mechanism of action
    • Controls transcription and stability of mRNAs
    • Controls transcription and stability of mRNAs
    • Synthesis of cytosolic second messengers or direct protein kinase activation
    • Change in membrane potential or synthesis of cytosolic second messengers
  39. It is the _______ that determines which cells respond to a given hormone. Only cells with the appropriate receptor will respond to the ________.
    • receptor
    • cognate hormone
  40. The _________ of hormone receptors are important determinants of the magnitude of cellular response to a given dose of hormone
    affinity and number
  41. Hormone dose‐response curves are determined by _________ for hormone
    receptor binding affinity
  42. _________ is the largest possible effect obtained with a _______hormone dose.
    • Maximal response
    • saturating
  43. Sensitivity is usually measured as the hormone dose giving _________.
    a half‐maximal response (EC50)
  44. Threshold is the hormone dose giving ________.
    the minimum detectable response
  45. Hormone responses can be modulated by __________, which usually happen _______ (how and when)
    • decreasing the maximal responsiveness or the sensitivity
    • hand-in-hand
    • after prolonged exposure to hormone
  46. Decreased (maximal) hormone responsiveness often occurs by ________ as a result of ________. It may also be due to _________.
    • receptor down‐regulation
    • receptor internalization or degradation
    • decreased activity of the intracellular signaling pathway
  47. Decreased hormone sensitivity can occur through _________. It can also result from ________.
    • changes in receptor affinity for binding the hormone
    • the receptor down‐regulation
  48. Mechanisms by which the number and/or affinity of hormone receptors can be modulated
    • Receptor Degradation
    • Receptor Internalization
    • Receptor Phosphorylation
  49. Negative feedback is the key to homeostatic regulation by hormones to correct/prevent hormone excess and product deficiency
    • hormone excess: high hormone secretion -> greater output of product from target cell -> suppress the gland of further hormone secretion
    • product deficiency: low in product -> relieves inhibition of hormone secretion -> more output of product
    • For example:
    • Glucagon high -> plasma glucose even higher -> inhibits glucagon secretion
    • glucose low -> negative feedback is released for glucagon secretion -> glucose increases
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Physiology - Endocrine - Principles
2016-03-05 17:29:06
Physiology - Endocrine - Principles
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