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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
Q

Cells of the Anterior Pituitary

Lactotrophs

A

Lactotrophs = PRL prolactin

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26
Q

Cells of the Anterior Pituitary

Thyrotrophs

A

Thyrotrophs = TSH thyroid-stimulating hormone

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27
Q

Cells of the Anterior Pituitary

Corticotrophs

A

Corticotrophs = ACTH adrenocorticotropic hormone

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28
Q

Cells of the Anterior Pituitary

Gonadotrophs

A

Gonadotrophs = LH luteinizing hormone and FSH follicular stimulating hormone

29
Q

GnRH Receptor:

A

: 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
Q 
GnRH 
Main functions (3)
A

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
Q

Gonadotrophs

• Release Luteinizing Hormone (LH) and Follicular Stimulating Homone (FSH) (4)

A
  • 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
Q

The Hypothalamic-Pituitary-Gonadal Axis (HPG)

A 
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
Q

CRH

A

Corticotropin-Releasing Hormone

34
Q

ACTH

A

Adrenocorticotropic Hormone (ACTH)

35
Q

CRH main function

A

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
Q 
Vasopressin (VP) and angiotensin act synergistically with \_\_\_\_ to mediate
\_\_\_\_ release (so VP positive regulator of \_\_\_\_\_)
A 
Vasopressin (VP) and angiotensin act synergistically with CRH to mediate
ACTH release (so VP positive regulator of ACTH)
37
Q

Oxytocin (OT) inhibits the ___ mediated release of ___ (so OT negative
regulator of ____)

A

Oxytocin (OT) inhibits the CRH mediated release of ACTH (so OT negative
regulator of ACTH)

38
Q

CRH is also secreted from the ____

A

CRH is also secreted from the placenta

39
Q

Corticotrophs

  • Release derivatives of pro-opiomelanocortin (POMC)
A

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
Q

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 \_\_\_
A 
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
Q 
Negative feedback
Short - 
Long - 
- fast (nonnuclear) 
- slow (nuclear)
A 
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
Q

A negative feedback loop of ____ on the

secretion of ___ also exists.

A

A negative feedback loop of ACTH on the
secretion of corticotropin-releasing
hormone (CRH) also exists.

43
Q

ACTH followed by a cortisol ___ before
waking and ___ as the day progresses;
stress may stimulate ____ (mediated by __ and ___); low while sleeping

A

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
Q 
Lactotrophs
Release Prolactin (PRL)
A

-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
Q

Dopamine (aka Prolactin Inhibitory Hormone) Regulates Milk Production via Inhibiting PRL

Dopamine Receptors:

A

Gαi - inhibits AC, ↓ cAMP levels

46
Q

Dopamine (aka Prolactin Inhibitory Hormone) Regulates Milk Production via Inhibiting PRL

Main Function

A

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
Q

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)

A

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
Q

___ regulation by breast feeding infant
stimulates nipple ___ that
tell hypothalamus to increase ___

A

Positive regulation by breast feeding infant
stimulates nipple mechanoreceptor that
tell hypothalamus to increase PRL

49
Q

TRH Receptor:

main function

A

TRH Receptor: GPCR

Main Function: Stimulates release of thyroid stimulating hormone (TSH)
from thyrotroph cells of anterior pituitary

50
Q

Thyrotrophs

Release Thyroid Stimulating Hormone (TSH) (4)

A

-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
Q

Regulation of TH Axis

step 1

A 
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
Q

Regulation of TH Axis

Step 2

A 
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
Q

Regulation of TH Axis

Step 3

A

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
Q

Regulation of TH Axis

Step 4

A

4) TH transported into cells of

target tissue

55
Q

Regulation of TH Axis

Step 5a

A

5a) Negative Feedback: serum T3 and T4

levels regulate TRH and TSH

56
Q

Regulation of TH Axis

Step 5b

A

5b) Negative Feedback:
excess iodide inhibits (iodide
required for TH; is also a
regulator)

57
Q

Somatostatin Regulates the Growth, Thyroid and Insulin Axes by Inhibition

Somatostatin Receptor:

A

: GPCR Gαi – inhibits AC, ↓ cAMP levels,↓GH and
↓TSH secretion (binds to cell surface receptors on somatotrophs and
thyrotrophs)

58
Q

Somatostatin Regulates the Growth, Thyroid and Insulin Axes by Inhibition

Main Functions

A

: Inhibits secretion of GH and TSH from pituitary, also made

in pancreas, gut and thyroid

59
Q

Somatostatin Regulates the Growth, Thyroid and Insulin Axes by Inhibition

Two forms

A

Two forms: SS14 in hypothalamus and SS28 (N-term extended) in gut;
differential processing in different tissues allows different function of SS

60
Q

Growth Hormone-Releasing Hormone (GHRH) Regulates Growth Axis via ____

A

Growth Hormone-Releasing Hormone (GHRH) Regulates Growth Axis via Growth
Hormone (GH)

61
Q

GHRH Receptor:

A

GPCR Gαs – activates AC which then produces cAMP, ↑GH secretion

62
Q

GHRH Characteristics:

A

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
Q

Somatotrophs

• Release Growth Hormone (GH) (5)

A

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
Q

GHRH and Somatostatin are Reciprocal hormones (2)

A
  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
Q

Both ____ (GHRH) and ____ (SS) act on
same somatotroph cells via ____ and stimulate or inhibit
synthesis and secretion of GH by increasing or decreasing ____.

A

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
Q

Tropic H

A

Tropic H – hormone that stimulates a specific target

gland to secrete a different set of hormones

67
Q

Trophic H

A

Trophic H – affect the growth, nutrition, or function of

another endocrine gland/cell

68
Q

GHRH has a ___ effect on GH causing its production
and release; but GHRH is ___ for somatotrophs by
helping them grow/thrive

A

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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