Lecture 2: Hypothalamic-Pituitary Relationships Flashcards
Which are faster: 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 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
- Amplified response
- Extended reponse
What are the 3 types of hormone receptors in a cell?
- Membrane 2. Intracellular 3. Nuclear
What is a hypothalamic nucleus?
Group of neurons of the hypo that perform the same function
Label the hypo nuclei!
Hormone released by medial preoptic nucleus?
GnRH = LHRH
Hormone released by anterior hypothalamic area?
TRH
4 hormones released by paraventricular nucleus?
- Oxytocin 2. Vasopressin 3. CRH 4. TRH
What does TRH stand for?
Thyrotropin releasing hormone
What does CRH stand for?
Corticotropin releasing hormone
2 hormones released by supraoptic nucleus?
- Oxytocin 2. Vasopressin
Which 2 nuclei are sisters?
- Paraventricular 2. Supraoptic
Hormone released by ventromedial area?
GHRH
What does GHRH stand for?
Growth hormone releasing hormone
3 hormones released by the arcuate nucleus?
- GHRH 2. GnRH 3. Dopamine
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 2. 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
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.
- Carotid artery 2. Superior hypophyseal artery (ramifying near median eminence) 3. Primary capillary plexus = complex network of capillaries 4. Long portal veins 5. Secondary capillary plexus 6. 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 hypo axons terminals right on it that connect to its vasculature
Describe the blood supply of the posterior pit.
Receives blood from inferior hypophyseal artery
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 = hypophysectomy
What hormones do the 2 most common pit tumors overproduce?
Most common one: prolactin Second 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 pharmaco treatment: somatostatin (hormone usually secreted by hypo)
What is the blood-brain barrier?
Highly selective barrier that separates circulating blood from the CNS
What are the 4 holes of the blood-brain barrier? What are they called? What is their purpose?
Circumventricular organs with fenestrations in endothelial cells the capillaries of:
- Organum vasculosum of the lamina terminalis (OVLT) = anterior demarcation of hypo
- Posterior pit
- Median eminence
- Subfornical organ (above hypo) (SFO)
PURPOSE: negative and positive feedback
What effect does GHRH have on pit?
+GH
What effect does SS have on pit?
-GH -TSH
What does SS stand for?
Somatostatin
What effect does TRH have on pit?
+TSH +PRL
What does PRL stand for?
Prolactin
What effect does DA have on pit?
-PRL
What does DA stand for?
Dopamine
What effect does GnRH have on pit?
+LH +FSH
What effect does CRH have on pit?
+ACTH
What is the pit somatotroph hormone?
GH
What is a long feedback loop?
Pit hormone –> target organ –> hormone X –> travels to pit/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 cannot provide feedback to hypo so PRL stimulates hypo to produce dopamine
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 NT 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
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
Eg:
- Testosterone synthesized in Leydig cells and acts on seminiferous tubules
- Insulin in beta cells acting on alpha cells
- Histamine released by mast cells acting locally on blood vessels
- NTs
- Prostaglandins released during inflammation
What are the 3 differences between hormones and neurohormones?
- Releasing cell (neuron vs ductus gland) 2. Quantity released (small vs large) 3. Duration of effect (short: seconds/minutes vs long: hours/days)
What is autocrine hormonal action? 2 examples?
Self-regulating hormonal action on releasing cell via interstitial space or blood stream
Eg:
- Growth factors
- Thromboxane action on platelets
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 are 2 biogenic amine hormones?
Epi and norepi
What effect do ligands that bind to membrane receptors usually produce intracellularly? Examples?
Second messengers: cAMP, Ca2+
Where is the median eminence located in regards to the hypo?
Below it
Where is the arculate nucleus?
Arched below the ventromedial nucleus
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
Which hypo nucleus does not release hormones?
Posterior hypo nucleus
What is the significance of the mammillary body to the nuclei?
- Demarcates its posterior end 2. Acts as a weigh station for other parts of the brain to bring info to hypo
How do the hypo and pit connect during embryologic development?
Cluster of neurons grow from supraoptic and paraventricular nuclei to median eminence to pit to create posterior pituitary carrying oxytocin and vasopressin. Then, neural tissue grows down and triggers movement from epithelial cells from upper soft tissue palet moving up to join posterior pit to create anterior pit gland. Cells convert to hormone producing cells (not neural cells)
What are the 2 ways for a surgeon to access the pit?
- Transfrontal approach (through nose) 2. Transinoidal approach (through palet)
How does the pressure of the posterior blood supply change as it gets to anterior pit?
Decreases
Difference in ant and post pit blood supply?
Anterior: venous blood supply = low pressure and HIGHLY vascularized Posterior: arterial blood supply = high pressure
What do the fenestrations in endothelial cells of the capillaries of the blood brain barrier resemble?
Gap junctions
What second messenger is involved in GH secretion from pit? Increase causes what?
cAMP: increase causes increase in GH
In what pit gland are all of the hormones discussed in this chapter located?
Anterior pit
What is a tropic hormone?
Hormones that have other endocrine glands as their target
From what germ layers are the anterior and posterior pituitary made of?
Anterior Pit: surface ectoderm (endothelial cells)
Posterior Pit: neural ectoderm (neural tissue)
Which 7 hormones stimulate SS?
- GH
- IGF-1
- T3/T4
- Cortisol
- Testosterone
- Estrogen
- CRH
What is human chorionic somatomammotropin (HPL) and what is its effect on the anterior pituitary?
Growth hormone like hormone secreted by the placenta that exerts a short loop negative feedback on GH secretion by the pituitary (short loop because it resembles GH)
Does the pituitary have ultra short feedback loops?
No because it does not have neurons (except the hypo magnocellular ones)
How does the amplified effect of the neuroendocrine system affect the half lives of the neurohormones/hormones release?
Each subsequent hormone/neurohormone has a longer half-life than the previous one
