Lecture 2: Hypothalamic-Pituitary Relationships Flashcards
(76 cards)
1
Q
Which are faster: hormones or neurohormones?
A
Neurohormones
2
Q
How is a neurohormone released? In what quantity?
A
Action potential in a neuron releases a neurohormone in the blood stream Very small quantities
3
Q
What hormones travel between the hypothalamus and the pituitary?
A
Neurohormones
4
Q
What are the general name of the neurohormones secreted by the hypo for the pit?
A
Releasing OR Inhibiting factors
5
Q
What are the 3 main benefits of the neuroendocrine system?
A
- Fast
- Amplified response
- Extended reponse
6
Q
What are the 3 types of hormone receptors in a cell?
A
- Membrane 2. Intracellular 3. Nuclear
7
Q
What is a hypothalamic nucleus?
A
Group of neurons of the hypo that perform the same function
8
Q
Label the hypo nuclei!
A
9
Q
Hormone released by medial preoptic nucleus?
A
GnRH = LHRH
10
Q
Hormone released by anterior hypothalamic area?
A
TRH
11
Q
4 hormones released by paraventricular nucleus?
A
- Oxytocin 2. Vasopressin 3. CRH 4. TRH
12
Q
What does TRH stand for?
A
Thyrotropin releasing hormone
13
Q
What does CRH stand for?
A
Corticotropin releasing hormone
14
Q
2 hormones released by supraoptic nucleus?
A
- Oxytocin 2. Vasopressin
15
Q
Which 2 nuclei are sisters?
A
- Paraventricular 2. Supraoptic
16
Q
Hormone released by ventromedial area?
A
GHRH
17
Q
What does GHRH stand for?
A
Growth hormone releasing hormone
18
Q
3 hormones released by the arcuate nucleus?
A
- GHRH 2. GnRH 3. Dopamine
19
Q
Hormone released by periventricular nucleus?
A
Somatostatin
20
Q
What connects the hypo to the pit? 2 names
A
Pituitary stalk = infundibulum
21
Q
What are the 2 parts of the pit called? 4/3 names for each.
A
- Posterior pit = neurohypophysis = neural lobe = infundibular process 2. Anterior pit = adenohypophysis = pars distalis
22
Q
What is the pit encased in?
A
Sphenoid bone
23
Q
What is the sella turcica?
A
The area where the pit sits in the sphenoid bone
24
Q
What is the median eminence?
A
The area where the hypo neurons terminate and release neurohormones into the pit blood supply
25
Describe the blood supply of the anterior pit.
1. 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
26
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
27
Describe the blood supply of the posterior pit.
Receives blood from inferior hypophyseal artery
28
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
29
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
30
What hormones do the 2 most common pit tumors overproduce?
Most common one: prolactin Second most common: growth hormone
31
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)
32
What is the blood-brain barrier?
Highly selective barrier that separates circulating blood from the CNS
33
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:
1. Organum vasculosum of the lamina terminalis (OVLT) = anterior demarcation of hypo
2. Posterior pit
3. Median eminence
4. Subfornical organ (above hypo) (SFO)
PURPOSE: negative and positive feedback
34
What effect does GHRH have on pit?
+GH
35
What effect does SS have on pit?
-GH -TSH
36
What does SS stand for?
Somatostatin
37
What effect does TRH have on pit?
+TSH +PRL
38
What does PRL stand for?
Prolactin
39
What effect does DA have on pit?
-PRL
40
What does DA stand for?
Dopamine
41
What effect does GnRH have on pit?
+LH +FSH
42
What effect does CRH have on pit?
+ACTH
43
What is the pit somatotroph hormone?
GH
44
What is a long feedback loop?
Pit hormone --\> target organ --\> hormone X --\> travels to pit/hypo to provide feedback
45
What is a short feedback loop?
Pit hormone directly provides feedback to hypo
46
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
47
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
48
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
49
What are hormones produced and secreted by?
Ductus glands
50
What is a paracrine hormonal action? 5 examples?
Hormonal action on neighboring cell via interstitial space or blood stream
Eg:
1. Testosterone synthesized in Leydig cells and acts on seminiferous tubules
2. Insulin in beta cells acting on alpha cells
3. Histamine released by mast cells acting locally on blood vessels
4. NTs
5. Prostaglandins released during inflammation
51
What are the 3 differences between hormones and neurohormones?
1. Releasing cell (neuron vs ductus gland) 2. Quantity released (small vs large) 3. Duration of effect (short: seconds/minutes vs long: hours/days)
52
What is autocrine hormonal action? 2 examples?
Self-regulating hormonal action on releasing cell via interstitial space or blood stream
Eg:
1. Growth factors
2. Thromboxane action on platelets
53
What kind of ligands bind membrane receptors?
Peptides and biogenic amines = water soluble hormones
54
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
55
What kind of ligands bind nuclear receptors?
Thyroid hormones and some steroid hormones
56
What are 2 biogenic amine hormones?
Epi and norepi
57
What effect do ligands that bind to membrane receptors usually produce intracellularly? Examples?
Second messengers: cAMP, Ca2+
58
Where is the median eminence located in regards to the hypo?
Below it
59
Where is the arculate nucleus?
Arched below the ventromedial nucleus
60
What is the third ventricle of the hypo filled with?
Cerebrospinal fluid
61
Where is the periventricular nucleus located?
Surrounds the third ventricle of the hypo
62
Which hypo nucleus does not release hormones?
Posterior hypo nucleus
63
What is the significance of the mammillary body to the nuclei?
1. Demarcates its posterior end 2. Acts as a weigh station for other parts of the brain to bring info to hypo
64
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)
65
What are the 2 ways for a surgeon to access the pit?
1. Transfrontal approach (through nose) 2. Transinoidal approach (through palet)
66
How does the pressure of the posterior blood supply change as it gets to anterior pit?
Decreases
67
Difference in ant and post pit blood supply?
Anterior: venous blood supply = low pressure and HIGHLY vascularized Posterior: arterial blood supply = high pressure
68
What do the fenestrations in endothelial cells of the capillaries of the blood brain barrier resemble?
Gap junctions
69
What second messenger is involved in GH secretion from pit? Increase causes what?
cAMP: increase causes increase in GH
70
In what pit gland are all of the hormones discussed in this chapter located?
Anterior pit
71
What is a tropic hormone?
Hormones that have other endocrine glands as their target
72
From what germ layers are the anterior and posterior pituitary made of?
Anterior Pit: surface ectoderm (endothelial cells)
Posterior Pit: neural ectoderm (neural tissue)
73
Which 7 hormones stimulate SS?
1. GH
2. IGF-1
3. T3/T4
4. Cortisol
5. Testosterone
6. Estrogen
7. CRH
74
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)
75
Does the pituitary have ultra short feedback loops?
No because it does not have neurons (except the hypo magnocellular ones)
76
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
