1 / 22

Endocrine Physiology

Endocrine Physiology. Dale Buchanan Hales, PhD Department of Physiology & Biophysics. Regulation of hormone secretion.

clint
Download Presentation

Endocrine Physiology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Endocrine Physiology Dale Buchanan Hales, PhD Department of Physiology & Biophysics

  2. Regulation of hormone secretion • Sensing and signaling: a biological need is sensed, the endocrine system sends out a signal to a target cell whose action addresses the biological need. Key features of this stimulus response system are: ·        receipt of stimulus ·        synthesis and secretion of hormone ·        delivery of hormone to target cell ·        evoking target cell response ·        degradation of hormone

  3. Control of Endocrine Activity • The physiologic effects of hormones depend largely on their concentration in blood and extracellular fluid. • Almost inevitably, disease results when hormone concentrations are either too high or too low, and precise control over circulating concentrations of hormones is therefore crucial.

  4. Control of Endocrine Activity • The concentration of hormone as seen by target cells is determined by three factors: • Rate of production • Rate of delivery • Rate of degradation and elimination

  5. Control of Endocrine Activity Rate of production: Synthesis and secretion of hormones are the most highly regulated aspect of endocrine control. Such control is mediated by positive and negative feedback circuits, as described below in more detail.

  6. Control of Endocrine Activity • Rate of delivery: An example of this effect is blood flow to a target organ or group of target cells - high blood flow delivers more hormone than low blood flow.

  7. Control of Endocrine Activity • Rate of degradation and elimination: Hormones, like all biomolecules, have characteristic rates of decay, and are metabolized and excreted from the body through several routes. • Shutting off secretion of a hormone that has a very short half-life causes circulating hormone concentration to plummet, but if a hormone's biological half-life is long, effective concentrations persist for some time after secretion ceases.

  8. Feedback Control of Hormone Production Feedback loops are used extensively to regulate secretion of hormones in the hypothalamic-pituitary axis. An important example of a negative feedback loop is seen in control of thyroid hormone secretion

  9. Inputs to endocrine cells

  10. Neural control • Neural input to hypothalamus stimulates synthesis and secretion of releasing factors which stimulate pituitary hormone production and release

  11. Hormonal control • Hypothalamus regulates anterior pituitary hormone production and release. • Hormones from anterior pituitary glands stimulate other glands in endocrine system to release hormones.

  12. Chronotropic control • Endogenous neuronal rhythmicity • Diurnal rhythms, circadian rhythms (growth hormone and cortisol), Sleep-wake cycle; seasonal rhythm

  13. Episodic secretion of hormones • Response-stimulus coupling enables the endocrine system to remain responsive to physiological demands • Secretory episodes occur with different periodicity • Pulses can be as frequent as every 5-10 minutes

  14. Episodic secretion of hormones • The most prominent episodes of release occur with a frequency of about one hour—referred to as circhoral • An episode of release longer than an hour, but less than 24 hours, the rhythm is referred to as ultradian • If the periodicity is approximately 24 hours, the rhythm is referred to as circadian • usually referred to as diurnal because the increase in secretory activity happens at a defined period of the day.

  15. Circadian (chronotropic) control

  16. Circadian Clock

  17. Physiological importance of pulsatile hormone release • Demonstrated by GnRH infusion • If given once hourly, gonadotropin secretion and gonadal function are maintained normally • A slower frequency won’t maintain gonad function • Faster, or continuous infusion inhibits gonadotropin secretion and blocks gonadal steroid production

  18. Clinical correlate • Long-acting GnRH analogs (such as leuproline) have been applied to the treatment of precocious puberty, to manipulate reproductive cycles (used in IVF), for the treatment of endometriosis, PCOS, uterine leiomyoma etc

  19. Feedback control • Negative feedback is most common: for example, LH from pituitary stimulates the testis to produce testosterone which in turn feeds back and inhibits LH secretion • Positive feedback is less common: examples include LH stimulation of estrogen which stimulates LH surge at ovulation

  20. Negative feedback effects of cortisol

  21. Nonhormonal control • Glucose and insulin: as glucose increases it stimulates the pancreas to secrete insulin

  22. Feedback control of insulin by glucose concentrations

More Related