Physiology - Hypothalamic Pituitary Relationships Flashcards
Which are faster-acting: hormones or neurohormones?
Neurohormones
How is a neurohormone released? In what quantity?
Action potential in a neuron releases a neurohormone in the blood stream
Very small quantities
What type of hormones travel between the hypothalamus and the pituitary?
Neurohormones
What are the general name of the neurohormones secreted by the hypo for the pit?
Releasing OR Inhibiting factors
What are the 3 main benefits of the neuroendocrine system?
- Fast-acting
- Amplified response
- Extended reponse
What are the 3 types of hormone receptors in a cell?
- Membrane
- Intracellular
- Nuclear
What is a hypothalamic nucleus?
Group of neurons of the hypo that perform the same function (i.e. secrete the same factors)
Label the hypo nuclei!
Hormone released by medial preoptic nucleus? 2 names
GnRH = LHRH
Hormone released by anterior hypothalamic nucleus?
TRH
4 hormones released by paraventricular nucleus?
- Oxytocin
- Vasopressin
- CRH
- TRH
What does TRH stand for?
Thyrotropin releasing hormone
What does CRH stand for?
Corticotropin releasing hormone
2 hormones released by supraoptic nucleus?
- Oxytocin
- Vasopressin
Which 2 nuclei are sisters?
- Paraventricular
- Supraoptic
Hormone released by ventromedial area?
GHRH
What does GHRH stand for?
Growth hormone releasing hormone
3 hormones released by the arcuate nucleus?
- GHRH
- GnRH
- Dopamine
What is the third ventricle of the hypo filled with?
Cerebrospinal fluid
Where is the periventricular nucleus located?
Surrounds the third ventricle of the hypo
Hormone released by periventricular nucleus?
Somatostatin
What connects the hypo to the pit? 2 names
Pituitary stalk = infundibulum
What are the 2 parts of the pit called? 4/3 names for each.
- Posterior pit = neurohypophysis = neural lobe = infundibular process
- Anterior pit = adenohypophysis = pars distalis
What is the pit encased in?
Sphenoid bone
What is the sella turcica?
The area where the pit sits in the sphenoid bone
Where is the median eminence located in regards to the hypo?
Below it
What is the median eminence?
The area where the hypo neurons terminate and release neurohormones into the pit blood supply
Describe the blood supply of the anterior pit.
- Internal carotid artery
- Superior hypophyseal artery (ramifying near median eminence)
- Primary capillary plexus = complex network of capillaries with fenestrations at the median eminence
- Long portal veins
- Secondary capillary plexus
- Sinusoids filled with blood with hypothalamic factors
What part of the pit receives blood supply with hypo neurohormones? How is the other part stimulated?
The ANTERIOR pit receives blood and the posterior pit has hypothalamic axons terminals right on it that connect to its vasculature
Describe the blood supply of the posterior pit.
Receives blood from inferior hypophyseal artery
Difference in ant and post pit blood supply?
Anterior: venous blood supply = low pressure and HIGHLY vascularizedPosterior: arterial blood supply = high pressure
How can a pit tumor affect vision?
The optic nerve and tract are directly superior to the pit so the tumor can push up on the nerve and damage vision
What is a macroadenoma? Treatment?
Greater than 10 mm in diameter pit tumor which causes the overproduction of hormones and that is so large that it is mechanically destructive to neighboring pit cells: could destroy them.
Treatment: surgical removal and potential hormone replacement therapy
What hormones do the 2 most common pit tumors overproduce?
Most common one: prolactinSecond most common: growth hormone
What is a microadenoma? Treatment?
Tumor less than 10 mm in diameter
Overproducing hormones but not causing damage to neighboring cell types
Treatment: No surgery, but pharmacological treatment
What is the blood-brain barrier?
Highly selective barrier that separates circulating blood from the CNS
What are the 3 holes of the blood-brain barrier? What are they called? What is their purpose?
Circumventricular organs with fenestrations in endothelial cells of their capillaries:
- Organum vasculosum of the lamina terminalis (OVLT) = anterior tip of hypothalamus
- Posterior pituitary
- Median eminence
PURPOSE: negative and positive feedback by blood contents
What effect does GHRH have on anterior pit?
+ GH
Name of cells that secrete GH in the anterior pituitary?
Somatotrophs
What second messenger is involved in GH secretion from pit? Increase causes what?
cAMP: increase causes increase in GH
What effect does SS have on anterior pit?
- GH
- TSH
What does SS stand for?
Somatostatin
What hormone causes a decrease in cAMP levels of anterior pituitary somatotrophs?
SS
What effect does TRH have on anterior pit?
+TSH
+PRL
Does TRH have a physiological inhibition of PRL secretion by anterior pituitary?
Nope, only pharmacological effect
What is the name of the ant pit cells that secrete TSH?
Thyrotrophs
What does PRL stand for?
Prolactin
What effect does DA have on pit?
-PRL
What kind of substance is dopamine?
A bioaminergic amine
What does DA stand for?
Dopamine
What are lactotrophs?
Cells of ant pit that secrete PRL
What effect does GnRH have on pit?
+LH
+FSH
What is the name of the ant pit cells that secrete LH and FSH?
Gonadotrophs
What effect does CRH have on pit?
+ACTH
What are corticotrophs?
Cells of the ant pit that secrete ACTH
What is a hypothalamic-pituitary long feedback loop?
Hypo neurohormone –> pit hormone –> target organ –> hormone X in blood –> travels to pit AND hypo to provide feedback
What is a short feedback loop?
Pit hormone directly provides feedback to hypo
What is an example of a short feedback loop?
Milk produced by prolactin stimulation of the breasts cannot provide feedback to hypo (does not enter blood stream) so PRL stimulates hypo to produce dopamine (which inhibits prolactin release by ant pit)
What is an ultra short feedback loop?
Recurrent collateral neuron loops back on each hypo neuron and releases neurohormones directly onto hypo acting as an neurotransmitter to inhibit the release of further NHs = autoinhibitory
What is the purpose of ultra short feedback loops on the hypo?
For hormone pit release to be pulsatile = episodic so that receptors do not get desensitized by constant hormone release
What are hormones produced and secreted by?
Ductus glands
What is a paracrine hormonal action? 5 examples?
Hormonal action on neighboring cell via interstitial space or blood stream
What are the 3 differences between hormones and neurohormones?
- Releasing cell (neuron vs ductus gland)
- Quantity released (large vs small)
- Duration of effect (longer vs shorter)
What is autocrine hormonal action? 2 examples?
Self-regulating hormonal action on releasing cell via interstitial space or blood stream
What kind of ligands bind membrane receptors?
Peptides and biogenic amines = water soluble hormones
What kind of ligands bind intracellular receptors? How does this work?
Steroid hormones enter down their concentration gradient and bind an intracellular receptor. The complex will then bind a nuclear receptor
What kind of ligands bind nuclear receptors?
Thyroid hormones and some steroid hormones
What effect do ligands that bind to membrane receptors usually produce intracellularly? Examples?
Second messengers: cAMP, Ca2+
Does the hypothalamus only receive input from the blood stream to regulate its activity?
NOPE
It also receives input from other brain centers
What do the fenestrations in endothelial cells of the capillaries of the blood brain barrier resemble?
Gap junctions
What is a tropic hormone?
Hormones that have other endocrine glands as their target and maintain their integrity (eg: size)
From what germ layers are the anterior and posterior pituitary made of?
Anterior Pit: surface ectoderm (endothelial cells)
Posterior Pit: neural ectoderm (neural tissue)
Does the pituitary have ultra short feedback loops? Why?
No because it does not have neurons (except the hypo magnocellular ones)
Effect of vasopressin on the kidneys?
Increases water reabsorption by the kidneys
6 stimulators of vasopressin secretion by posterior pituitary?
- Increase in extracellular fluid osmolality
- Blood volume increase
- Blood pressure increase
- Pain
- Stress
- Temperature increase
Reason why pain and stress stimulate vasopressin release by the posterior pit?
Because ADH is a stress hormone and during a fight/flight response you need higher blood pressure to increase tissue oxygenation
Reason why temperature increase stimulates vasopressin release by the posterior pit?
Because an increasein blood volume will favor perspiration which will allow for cooling down
3 inhibitors of vasopressin release by the posterior pituitary?
- Temperature decrease
- Alcohol
- Cortisol
Reason why cortisol inhibits vasopressin release by posterior pit? What is this called?
Vasopressin stimulates the secretion of ACTH by the anterior pituitary, which then stimulates cortisol secretion by the adrenal glands
Negative feedback loop
Which feedback loops are blood-borne mediated?
Short and long (not ultra-short)
