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Biol 432 > Hypothalamus and Pituitary > Flashcards

Hypothalamus and Pituitary Flashcards

1
Q

the nuclei

that are bundles of __ in the hypothalamus that secrete hormones into ____

A

the nuclei

that are bundles of neurons in the hypothalamus that secrete hormones into pituitaries

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2
Q

Hypothalamus integrates many signals

e.g. ___

A

Hypothalamus integrates many signals
e.g. temperature, light, thirst/food,
cytokines responding to infection

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3
Q

Hypothalamus-Pituitary Axis work together = Neuroendocrine Paradigm

Pituitary =____

A

Pituitary = Hypophysis

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4
Q

Hypothalamus-Pituitary Axis work together = Neuroendocrine Paradigm

Anterior pituitary = ___

A

Anterior pituitary = Adenohypophysis

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5
Q

Hypothalamus-Pituitary Axis work together = Neuroendocrine Paradigm

Posterior pituitary = ___

A

Posterior pituitary = Neurohypophysis

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6
Q 
Specialized regions around
Hypothalamus lack \_\_\_\_ so brain can
interact directly with
hormones in the blood e.g.
GH (growth hormone)
\_\_\_  feedback
A 
Specialized regions around
Hypothalamus lack bloodbrain barrier so brain can
interact directly with
hormones in the blood e.g.
GH (growth hormone)
negative feedback
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7
Q

Secretion of Hypothalamic Hormones

Anterior Pituitary:

A 
Anterior Pituitary:
Hypothalamic hormones
secreted by neurons through
portal hypophysial vessel;
then specific cell types of the
anterior pituitary release
hormones into the blood or
get inhibited; balance of
activation and deactivation
both hypothalamic and
pituitary hormones are
released in pulses (pulsatile)
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8
Q

Secretion of Hypothalamic Hormones

Intermediate Pituitary:

A

Intermediate Pituitary
Mostly cells called melanotrophs
that produce melanocytestimulating hormone (MSH); thin
layer in between AL and PL

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9
Q

Secretion of Hypothalamic Hormones

Posterior Pituitary:

A 
Posterior Pituitary:
Neurons originate in
Hypothalamus and
project into posterior
pituitary; neurons
deliver hormones; then
released from post pit
into blood
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10
Q

Hypothalamus Connects nervous system to endocrine system: ____

A

Connects nervous system to endocrine system: stimulates many

endocrine glands – thyroid, adrenals, gonads etc. mostly through pituitary

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11
Q

Hypothalamus

Controls___

A

Controls: Temperature, appetite, thirst, fatigue, behavior, defense reactions,
circadian cycle, blood pressure

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12
Q 
Hypothalamus
Inputs (external and internal):
A 
light
smell 
autonomic (neural) inputs
hormones (steroids & thyroid H, blood borne peptides)
blood borne inputs
stress
immune stimuli…
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13
Q

Hypothalamic Outputs: (1)

A 
1) direct innervation to adrenal medulla, kidney, parathyroid gland,
pancreatic islets (fast)
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14
Q

Hypothalamic Outputs: (2)

A

2) neurosecretion = hormones secreted by hypothalamic nuclei;
hypothalamic hormones are mostly small peptides and act via
GPCR surface receptors; the hormones act on anterior or posterior
pituitary causing the pituitary to release hormones in turn (may be
fast or slower acting depending on pathway activated)

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15
Q

Hypothalamic Outputs:

Timing and Type of Hormone Response Highly Variable:

A

Some things must be fast (e.g. fight or flight, adrenaline, cortisol)
but some things must be slow (e.g. brain development via thyroid
hormone (TH) or bone growth via growth hormone (GH) and
insulin-like growth factor 1 (IGF-1 )

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16
Q

Hypophysiotropic H

A

Hypophysiotropic H – regulate release of anterior pituitary hormones; pulsatile

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17
Q

main function

Thyrotropin-releasing hormone (TRH)

A

regulation of thyroid stimulating hormone

TSH

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18
Q

Main function
Gonadotropin-releasing hormone
(GnRH)

A

regulation pituitary gonadotropins LH and
FSH (luteinizing hormone and follicular
stimulating hormone)

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19
Q

Main function

Somatostatin

A

inhibition of growth hormone (GH), TSH,

insulin, glucagon, and others

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20
Q

Main function
Growth hormone-releasing hormone
(GHRH)

A

stimulation of GH (GHRH tropic effect on
GH)
Also GHRH is trophic for somatotrophs
(helps them grow/thrive)

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21
Q

Main function
Prolactin-inhibiting hormone
(PIH, exactly the same as dopamine)

A

inhibits prolactin (PRL)

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22
Q

Main function
Corticotropin-releasing hormone
(CRH)

A

regulation of adrenocortical function,
adrenocorticotropic hormone (ACTH)
release, regulate appetite, sympathetic
nervous system and adrenal medulla

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23
Q

Cells of the Anterior Pituitary

Different cell types of anterior pituitary secrete different hormones controlled by
the ___ hypothalamic hormones for each___

A

Different cell types of anterior pituitary secrete different hormones controlled by
the upstream hypothalamic hormones for each axis

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24
Q

Cells of the Anterior Pituitary

Somatotrophs

A

Somatotrophs = GH growth hormone

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25
Cells of the Anterior Pituitary | Lactotrophs
Lactotrophs = PRL prolactin
26
Cells of the Anterior Pituitary | Thyrotrophs
Thyrotrophs = TSH thyroid-stimulating hormone
27
Cells of the Anterior Pituitary | Corticotrophs
Corticotrophs = ACTH adrenocorticotropic hormone
28
Cells of the Anterior Pituitary | Gonadotrophs
Gonadotrophs = LH luteinizing hormone and FSH follicular stimulating hormone
29
GnRH Receptor:
: GPCR Gαq – stim. PLC receptors found in pituitary, brain, placenta, ovary, testis - it uses a GPCR; receptors found in reproductive tissues, but main effect is in pituitary release of LH and FSH
30
``` GnRH Main functions (3) ```
Main Functions: 1. Stimulate release and synthesis of pituitary hormones, LH (luteinizing hormone) & FSH (follicle stimulating hormone) from gonadotroph cells 2. Some axons branch to other parts of brain, limbic system (emotions) neuromodulator 3. Placenta and ovaries make GnRH – acts locally (receptors found there);
31
Gonadotrophs | • Release Luteinizing Hormone (LH) and Follicular Stimulating Homone (FSH) (4)
- Both glycoproteins (structurally related) – The effects of FSH and LH are sex specific – In general, they bind to receptors in the ovary and testis and regulate gonadal function by promoting sex steroid production and gametogenesis. – Stimulated by GnRH (Gonadotropin-Releasing Hormone)
32
The Hypothalamic-Pituitary-Gonadal Axis (HPG)
``` The hypothalamus must integrate many signals and produce an appropriate response including stimulating or inhibiting endocrine glands Note that hormones downregulate themselves using negative feedback loops Note that GnRH must be pulsatile otherwise LH and FSH become desensitized ```
33
CRH
Corticotropin-Releasing Hormone
34
ACTH
Adrenocorticotropic Hormone (ACTH)
35
CRH main function
Main Function: CRH is secreted in response to stress. Stimulates secretion of products derived from proopiomelanocortin (POMC) like adrenocorticotropic hormone (ACTH) from corticotroph cells of ant pit
36
``` Vasopressin (VP) and angiotensin act synergistically with ____ to mediate ____ release (so VP positive regulator of _____) ```
``` Vasopressin (VP) and angiotensin act synergistically with CRH to mediate ACTH release (so VP positive regulator of ACTH) ```
37
Oxytocin (OT) inhibits the ___ mediated release of ___ (so OT negative regulator of ____)
Oxytocin (OT) inhibits the CRH mediated release of ACTH (so OT negative regulator of ACTH)
38
CRH is also secreted from the ____
CRH is also secreted from the placenta
39
Corticotrophs - Release derivatives of pro-opiomelanocortin (POMC)
POMC: a polypeptide of 134 AA –its tissue specific processing, and its biologically active peptides ACTH and MSH – Stimulated by Corticotropin-Releasing Hormone (CRH)
40
Regulation of ACTH (and Cortisol): The Hypothalamus - Pituitary - Adrenal (HPA) Axis ``` Cortisol helps the body respond to stress (restore homeostasis) by maintaining ___ and cardiovascular function, reduce___ responses, maintain blood ____ levels and regulate the metabolism of ___, ____, and ___ ; regulated mainly by circadian rhythm (___release), stress, feedback inhibition by ____ and ___ ```
``` Cortisol helps the body respond to stress (restore homeostasis) by maintaining blood pressure and cardiovascular function, reduce immune responses, maintain blood glucose levels and regulate the metabolism of proteins, carbohydrates, and fats; regulated mainly by circadian rhythm (ACTH release), stress, feedback inhibition by cortisol and ACTH ```
41
``` Negative feedback Short - Long - - fast (nonnuclear) - slow (nuclear) ```
``` Negative feedback Short - ACTH inhib own secretion Long - Cortisol can act on the pituitary or hypothalamus to decrease ACTH synthesis and can be: - fast (nonnuclear) and depends on the rate of change of cortisol levels - slow (nuclear) and depends on the absolute levels cortisol and involves transcription ```
42
A negative feedback loop of ____ on the | secretion of ___ also exists.
A negative feedback loop of ACTH on the secretion of corticotropin-releasing hormone (CRH) also exists.
43
ACTH followed by a cortisol ___ before waking and ___ as the day progresses; stress may stimulate ____ (mediated by __ and ___); low while sleeping
ACTH followed by a cortisol peak before waking and declines as the day progresses; stress may stimulate ACTH (mediated by VP (vasopressin; cover next in posterior pituitary) and CRH); low while sleeping
44
``` Lactotrophs Release Prolactin (PRL) ```
-A 198 aa protein –During pregnancy it helps in the preparation of the mammary glands for future milk production. –Following birth, stimulates the production of milk products (protein and lactose synthesis, water excretion and sodium retention) –Dopamine aka PIH (prolactin inhibiting hormone) inhibits PRL, so main regulatory hypothalamic hormone is inhibitory –Stimulated by sleep and stress, but mainly suckling stimulation by baby nursing at breast –Important in men and women for sexual gratification –In women who aren’t pregnant, prolactin helps regulate the menstrual cycle –In men, prolactin affects sperm production
45
Dopamine (aka Prolactin Inhibitory Hormone) Regulates Milk Production via Inhibiting PRL Dopamine Receptors:
Gαi - inhibits AC, ↓ cAMP levels
46
Dopamine (aka Prolactin Inhibitory Hormone) Regulates Milk Production via Inhibiting PRL Main Function
Role is inhibitor of prolactin by binding receptor on lactotrophs, so disruption or inhibition of dopamine leads to an increase in prolactin (for milk) Dopamine is an amino acid derivative
47
Prolactin Axis PRL stimulates breast development and milk production; inhibits ___ synthesis thus inhibiting ___ in females and ___ in males (decreases ___ as a response), and increases ___ secretion (negative feedback)
PRL stimulates breast development and milk production; inhibits GnRH synthesis thus inhibiting ovulation in females and spermatogenesis in males (decreases FSH/LH as a response), and increases dopamine secretion (negative feedback)
48
___ regulation by breast feeding infant stimulates nipple ___ that tell hypothalamus to increase ___
Positive regulation by breast feeding infant stimulates nipple mechanoreceptor that tell hypothalamus to increase PRL
49
TRH Receptor: main function
TRH Receptor: GPCR Main Function: Stimulates release of thyroid stimulating hormone (TSH) from thyrotroph cells of anterior pituitary
50
Thyrotrophs Release Thyroid Stimulating Hormone (TSH) (4)
-glycoprotein – Stimulates all aspects of thyroid gland function - including thyroid hormone synthesis and release. TSH also causes an increase in thyroid gland size and vascularization. – Stimulated by thyrotropin-releasing hormone (TRH); inhibited by somatostatin both from the hypothalamus – also inhibited by thyroid hormone (TH, T3 and T4 ) negative feedback loop
51
Regulation of TH Axis | step 1
``` 1) Neurons from hypothalamus secrete thyrotropin-releasing hormone (TRH) into portal veins that provide a direct route for TRH to the anterior lobe cells ```
52
Regulation of TH Axis | Step 2
``` 2) Thyrotrophs in anterior pituitary are stimulated by TRH and secrete TSH (thyroid-stimulating hormone) into the pituitary venous system; inhibited by somatostatin from hypothalamus ```
53
Regulation of TH Axis | Step 3
3) Cells in thyroid are stimulated by TSH and secrete thyroid hormone (TH) into the capillaries for transport to target tissues or via blood stream back to hypothalamus and pituitary. TH uses iodide – critical to structure and iodide (I) acts as regulator too
54
Regulation of TH Axis | Step 4
4) TH transported into cells of | target tissue
55
Regulation of TH Axis | Step 5a
5a) Negative Feedback: serum T3 and T4 | levels regulate TRH and TSH
56
Regulation of TH Axis | Step 5b
5b) Negative Feedback: excess iodide inhibits (iodide required for TH; is also a regulator)
57
Somatostatin Regulates the Growth, Thyroid and Insulin Axes by Inhibition Somatostatin Receptor:
: GPCR Gαi – inhibits AC, ↓ cAMP levels,↓GH and ↓TSH secretion (binds to cell surface receptors on somatotrophs and thyrotrophs)
58
Somatostatin Regulates the Growth, Thyroid and Insulin Axes by Inhibition Main Functions
: Inhibits secretion of GH and TSH from pituitary, also made | in pancreas, gut and thyroid
59
Somatostatin Regulates the Growth, Thyroid and Insulin Axes by Inhibition Two forms
Two forms: SS14 in hypothalamus and SS28 (N-term extended) in gut; differential processing in different tissues allows different function of SS
60
Growth Hormone-Releasing Hormone (GHRH) Regulates Growth Axis via ____
Growth Hormone-Releasing Hormone (GHRH) Regulates Growth Axis via Growth Hormone (GH)
61
GHRH Receptor:
GPCR Gαs – activates AC which then produces cAMP, ↑GH secretion
62
GHRH Characteristics:
Released in pulses (like the other hypothalamic hormones) -this leads to pulsatile increases of GH in circulation when stimulates somatotroph cells of anterior pituitary
63
Somatotrophs • Release Growth Hormone (GH) (5)
A 191 AA protein; mainly non-glycosylated – Stimulates the production of insulin-like growth factor 1 (IGF-1), a mediator of the indirect growth promoting effects of GH – Also exerts direct effects on lipolysis, AA uptake in various tissues, protein synthesis in the liver, and opposes insulin actions – Stimulated by growth hormone-releasing hormone (GHRH) from hypothalamus; inhibited by somatostatin – Negative feedback on somatotrophs to regulate self = autocrine
64
GHRH and Somatostatin are Reciprocal hormones (2)
1. Growth Hormone Releasing Hormone (GHRH) stimulates synthesis and secretion of GH by increasing cAMP. 2. Somatostatin (SS) inhibits GH release by decreasing cAMP
65
Both ____ (GHRH) and ____ (SS) act on same somatotroph cells via ____ and stimulate or inhibit synthesis and secretion of GH by increasing or decreasing ____.
Both Growth Hormone Releasing Hormone (GHRH) and Somatostatin (SS) act on same somatotroph cells via adenylyl cyclase enzyme (AC) and stimulate or inhibit synthesis and secretion of GH by increasing or decreasing cAMP.
66
Tropic H
Tropic H – hormone that stimulates a specific target | gland to secrete a different set of hormones
67
Trophic H
Trophic H – affect the growth, nutrition, or function of | another endocrine gland/cell
68
GHRH has a ___ effect on GH causing its production and release; but GHRH is ___ for somatotrophs by helping them grow/thrive
GHRH has a tropic effect on GH causing its production and release; but GHRH is trophic for somatotrophs by helping them grow/thrive

Biol 432 (8 decks)

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