Physiology 3120 Lecture Notes - Lecture 52: Growth Hormone–Releasing Hormone, Hypophyseal Portal System, Anterior Pituitary
15 May 2018
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Lecture 52 – Neuroendocrinology
Functional anatomy
- Acromegaly (pituitary disorder): too much growth hormone (GH) = very tall, bone
deficiencies, etc.
- Hypothalamus is superior to the pituitary and is a sensor
o Sense changes in fear, glucose, temperature, etc and relays it to the pituitary to
release hormones to deal with the stress
- Each region of the pituitary (anterior or posterior) target different hormones
- Both regions are innervated by the hypothalamus but in a different manner
Anterior pituitary:
- Receives signals from the hypothalamus via parvicellular neurons
- Parvicellular neurons are neuro endocrine cells in the hypothalamus and they have short
axons (not long enough to get into anterior pituitary)
- In response to stress that hypothalamus senses, short axons trigger the release of a
hypothalamic hormone which travels through the hypophyseal portal system to target the
anterior pituitary
- In the anterior pituitary, hormones act on an anterior pituitary cell which then produces an
anterior pituitary hormone which is secreted into blood to target another endocrine
gland/organ
- Parvicellular neurons target the anterior pituitary from hypothalamus and use the
hypophyseal portal system to carry the hormones from the hypothalamus into the target
Posterior pituitary
- Hypothalamus targets posterior pituitary through magnocellular cells which have long
axons and do not require the hypophyseal portal system (have direct release into post. pit)
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- In response to change in body, magnocellular cells directly secrete hormone into posterior
pituitary which is then secreted into circulation to act on a particular organ
- Magoncellular cells axons project to hormone secretory cells in posterior pituitary which
then secrete another hormone into the blood stream
Hypothalamic neurons and factors
- Posterior pituitary: vasopressin, oxytocin (target kidney, uterus, mammillary gland)
- Parvicellular neurons target anterior pituitary and influence it to produce trophic hormones
- Trophic hormones: ACTH (adrenocorticotropic hormone) TSH, GH, LH, FSH, prolactin)
o Produced by anterior pituitary and target adrenal, thyroid, liver and ovary
- Magnocellular and parvicellular neurons influence secretion of pituitary hormones
- Hypothalamus does not only have neuroendocrine cells and it also has regular neurons
involved in nervous system function (has nervous system functions too)
- Hypothalamus is not just an endocrine gland or part of the brain (other functions too)
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Paraventricular nucleus
- There are multiple hormones and peptides produced by magoncellular neurons,
parvicellular neurons and region of the brain called the arcuate nucleus
- There is overlap – some of the hormones in arcuate nucleus overlap with magnocelular cells
and parvicellular cells (e.g. neuropeptide Y)
- There are two spots in the hypothalamus that can produce hormones and other peptides
Episodic endocrine secretion
- Many hormones are regulated short term on a minute to minute basis or long term on a
daily basis
- Many hypothalamic and pituitary hormones are regulated on a circadian rhythm (once a
day)
- Diurnal rhythm: EXACTLY 24h (interchangeable with circadian)
- Hormones secreted once a day:
o Growth hormone releasing hormone (GHRH)
o Corticotropic releasing hormone (CRH) – stress system
o Cortisol
- On a daily basis we have an increase in cortisol production unless there is a stress which
activates CRH/cortisol secretion
- Cortisol is produced in a circadian manner (once a day)
o Everyday at 4am there is a peak in production (with daylight)
o Naps do not influence the rhythm
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find more resources at oneclass.com
Document Summary
Acromegaly (pituitary disorder): too much growth hormone (gh) = very tall, bone deficiencies, etc. Hypothalamus is superior to the pituitary and is a sensor: sense changes in fear, glucose, temperature, etc and relays it to the pituitary to release hormones to deal with the stress. Each region of the pituitary (anterior or posterior) target different hormones. Both regions are innervated by the hypothalamus but in a different manner. Receives signals from the hypothalamus via parvicellular neurons. Parvicellular neurons are neuro endocrine cells in the hypothalamus and they have short axons (not long enough to get into anterior pituitary) In response to stress that hypothalamus senses, short axons trigger the release of a hypothalamic hormone which travels through the hypophyseal portal system to target the anterior pituitary. In the anterior pituitary, hormones act on an anterior pituitary cell which then produces an anterior pituitary hormone which is secreted into blood to target another endocrine gland/organ.
