Physiology - Hypothalamic Pituitary Relationships Flashcards
1
Q
Which are faster-acting: 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 type of 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-acting
- Amplified response
- Extended reponse
6
Q
What are the 3 types of hormone receptors in a cell?
A
- Membrane
- Intracellular
- Nuclear
7
Q
What is a hypothalamic nucleus?
A
Group of neurons of the hypo that perform the same function (i.e. secrete the same factors)
8
Q
Label the hypo nuclei!
A
9
Q
Hormone released by medial preoptic nucleus? 2 names
A
GnRH = LHRH
10
Q
Hormone released by anterior hypothalamic nucleus?
A
TRH
11
Q
4 hormones released by paraventricular nucleus?
A
- Oxytocin
- Vasopressin
- CRH
- 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
- Vasopressin
15
Q
Which 2 nuclei are sisters?
A
- Paraventricular
- 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
- GnRH
- Dopamine
19
Q
What is the third ventricle of the hypo filled with?
A
Cerebrospinal fluid
20
Q
Where is the periventricular nucleus located?
A
Surrounds the third ventricle of the hypo
21
Q
Hormone released by periventricular nucleus?
A
Somatostatin
22
Q
What connects the hypo to the pit? 2 names
A
Pituitary stalk = infundibulum
23
Q
What are the 2 parts of the pit called? 4/3 names for each.
A
- Posterior pit = neurohypophysis = neural lobe = infundibular process
- Anterior pit = adenohypophysis = pars distalis
24
Q
What is the pit encased in?
A
Sphenoid bone
25
What is the sella turcica?
The area where the pit sits in the sphenoid bone
26
Where is the median eminence located in regards to the hypo?
Below it
27
What is the median eminence?
The area where the hypo neurons terminate and release neurohormones into the pit blood supply
28
Describe the blood supply of the anterior pit.
1. Internal carotid artery
2. Superior hypophyseal artery (ramifying near median eminence)
3. Primary capillary plexus = complex network of capillaries with fenestrations at the median eminence
4. Long portal veins
5. Secondary capillary plexus
6. Sinusoids filled with blood with hypothalamic factors
29
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
30
Describe the blood supply of the posterior pit.
Receives blood from inferior hypophyseal artery
31
Difference in ant and post pit blood supply?
Anterior: venous blood supply = low pressure and HIGHLY vascularizedPosterior: arterial blood supply = high pressure
32
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
33
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
34
What hormones do the 2 most common pit tumors overproduce?
Most common one: prolactinSecond most common: growth hormone
35
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
36
What is the blood-brain barrier?
Highly selective barrier that separates circulating blood from the CNS
37
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:
1. Organum vasculosum of the lamina terminalis (OVLT) = anterior tip of hypothalamus
2. Posterior pituitary
3. Median eminence
PURPOSE: negative and positive feedback by blood contents
38
What effect does GHRH have on anterior pit?
+ GH
39
Name of cells that secrete GH in the anterior pituitary?
Somatotrophs
40
What second messenger is involved in GH secretion from pit? Increase causes what?
cAMP: increase causes increase in GH
41
What effect does SS have on anterior pit?
- GH
- TSH
42
What does SS stand for?
Somatostatin
43
What hormone causes a decrease in cAMP levels of anterior pituitary somatotrophs?
SS
44
What effect does TRH have on anterior pit?
+TSH
+PRL
45
Does TRH have a physiological inhibition of PRL secretion by anterior pituitary?
Nope, only pharmacological effect
46
What is the name of the ant pit cells that secrete TSH?
Thyrotrophs
47
What does PRL stand for?
Prolactin
48
What effect does DA have on pit?
-PRL
49
What kind of substance is dopamine?
A bioaminergic amine
50
What does DA stand for?
Dopamine
51
What are lactotrophs?
Cells of ant pit that secrete PRL
52
What effect does GnRH have on pit?
+LH
+FSH
53
What is the name of the ant pit cells that secrete LH and FSH?
Gonadotrophs
54
What effect does CRH have on pit?
+ACTH
55
What are corticotrophs?
Cells of the ant pit that secrete ACTH
56
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
57
What is a short feedback loop?
Pit hormone directly provides feedback to hypo
58
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)
59
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
60
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
61
What are hormones produced and secreted by?
Ductus glands
62
What is a paracrine hormonal action? 5 examples?
Hormonal action on neighboring cell via interstitial space or blood stream
63
What are the 3 differences between hormones and neurohormones?
1. Releasing cell (neuron vs ductus gland)
2. Quantity released (large vs small)
3. Duration of effect (longer vs shorter)
64
What is autocrine hormonal action? 2 examples?
Self-regulating hormonal action on releasing cell via interstitial space or blood stream
65
What kind of ligands bind membrane receptors?
Peptides and biogenic amines = water soluble hormones
66
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
67
What kind of ligands bind nuclear receptors?
Thyroid hormones and some steroid hormones
68
What effect do ligands that bind to membrane receptors usually produce intracellularly? Examples?
Second messengers: cAMP, Ca2+
69
Does the hypothalamus only receive input from the blood stream to regulate its activity?
NOPE
It also receives input from other brain centers
70
What do the fenestrations in endothelial cells of the capillaries of the blood brain barrier resemble?
Gap junctions
71
What is a tropic hormone?
Hormones that have other endocrine glands as their target and maintain their integrity (eg: size)
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
Does the pituitary have ultra short feedback loops? Why?
No because it does not have neurons (except the hypo magnocellular ones)
74
Effect of vasopressin on the kidneys?
Increases water reabsorption by the kidneys
75
6 stimulators of vasopressin secretion by posterior pituitary?
1. Increase in extracellular fluid osmolality
2. Blood volume increase
3. Blood pressure increase
4. Pain
5. Stress
6. Temperature increase
76
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
77
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
78
3 inhibitors of vasopressin release by the posterior pituitary?
1. Temperature decrease
2. Alcohol
3. Cortisol
79
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
80
Which feedback loops are blood-borne mediated?
Short and long (not ultra-short)
