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Endocrinology > Pituitary Gland > Flashcards

Pituitary Gland Flashcards

1
Q

What is a hormone?

A

A signalling molecule produced by glands - transported in the blood stream to distant organs where they regulate physiology and behaviour

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2
Q

What are the 2 types of hormones?

A

Peptide and steroid hormones

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3
Q

What is the difference between the synthesis of peptide and steroid hormones?

A

Peptide are synthesised as prohormones and so to be activated they require further processing such as cleavage to activate. E.g. insulin

Steroid hormones are synthesised from the precursor cholesterol

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4
Q

What is regulatory secretion?

A

Peptide hormones are stored in vesicles and secreted when needed. (Vesicles fuse w cell membrane in response to a stimulus)

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5
Q

What is constitutive secretion?

A

Steroid hormones released as soon as they are made.

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6
Q

How do peptide hormones bind?

A

They bind to receptors on cell membrane and transduce signals using second messenger systems

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7
Q

How do steroid hormones bind?

A

They bind to intracellular receptors to change gene expression directly

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8
Q

Where is the pituitary gland located?

A

Sella tursica of sphenoid bone

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9
Q

What is directly above the pituitary gland and what connects the two together ?

A

Hypothalamus
Median eminence
(It hangs from pituitary stalk)

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10
Q

What is the structure above the pituitary that has an impact on eye sight and what happens there?

A

Optic chiasm:

the fibers of the nasal retina (i.e., the temporal visual field) of each eye cross

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11
Q

What would happen if a pituitary tumour/suprasellar tumour was compressing the optic chiasm?

A

It would cause it to stretch over the tumour and possibly result in ‘bitemporal hemianopia’ which is a type of partial blindness where vision is missing in the temporal regions (the sides).

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12
Q

What are hypothalamic parvocellular neurones and what do they do ?

A

Short neurones which terminate on the median eminence.
Release hypothalamic releasing/inhibiting factors into the capillary plexus
Diffuse into leaky blood vessels part of the portal circulation
Carried down pituitary stalk
Released and so cause the release or inhibition of a pituitary hormone.
They regulate anterior pituitary function

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13
Q

How do hypothalamic parvocellular neurones do their job?

A

Release hypothalamic releasing/inhibitory factors into the capillary plexus in median eminence. These are carried by portal circulation to anterior pituitary (the blood vessels are fenestrated/leaky).

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14
Q

Is the anterior pituitary of the hypothalamus?

A

No, it is anatomically distinct from it

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15
Q

What is the Anterior pituitary made up of?

A 
Endocrine cells (not neuronal):
Somatotrophs
Lactotrophs
Corticotrophs
Thyrotrophs
Gonadotrophs
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16
Q

How is the anterior pituitary regulated?

A

By hypothalamic releasing/inhibiting factors via hypophyseal pituitary portal system (blood vessels)

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17
Q

What is the mechanism of the hypothalamo-pituitary portal system?

A
  1. Axon terminals of hypothalamic neurosecretory cells release hormones ( could be releasing hormones or inhibiting hormones) into hypothalamo-hypophysial portal system
  2. RHS and IHs travel in the portal system to anterior pituitary
  3. RHS / IHs bind to receptors then stimulate/inhibit the release of hormones from anterior pituitary cells
  4. The anterior pituitary hormones leave gland via blood
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18
Q

What is the hormone that axon terminals release to regulate thyroid hormone production?

A

Thyrotropinn Releasing Hormone (TRH)

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19
Q

What does TRH stimulate the release of?

A

Thyroid Stimulating Hormone (thyrotropin) from anterior pituitary thyrotrophs

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20
Q

What does TSH do after leaving the anterior pituitary via the blood?

A

Travels to the thyroid gland to stimulate thyroid hormone release (thyroxine)

21
Q

Which of the anterior pituitary cells synthesise both releasing and inhibiting hormones and what are they?

A 
SOMATOTROPHS
-growth hormone = somatrophin ( releasing)
Also somatostatin (inhibiting, stops growth)
22
Q

What hormone do Lactotrophs synthesise ? And what is this stimulated by?

A

Prolactin

Stimulated by an inhibiting factor = dopamine so as dopamine decreases, prolactin increases and vice versa.

23
Q

By what cells is thyroid-stimulating hormone synthesised by and what is this stimulated by?

A

Thyrotrophs

-thyrotrophin releasing hormone (TRH) from hypothal

24
Q

What hormones do gonadotrophs and corticotrophs synthesise? State whether these are releasing or inhibiting and where they have an effect

A

Gonadotrophs- Luteinising hormone (LH), Follicle Stimulating Hormone (FSH) (male&female - testes and ovaries)
by gonadotrophin-releasing hormone(h)
Corticotrophs - Adrenocorticotrophic hormone (ACTH, corticotrophin) (adrenal cortex)
by corticotrophin releasing hormone (h)

25
Q

Describe the neuroendocrine reflex arc for milk PRODUCTION

A
  1. Mechanical stimulation of nipple and surrounding area leads to activation of afferent pathways
  2. Afferent signals in hypothalamus - inhibit dopamine release from dopaminergic neurones
  3. Less dopamine in hypothalamic-pituitary portal system = less inhibition of lactotrophs = increased prolactin in plasma = increases milk secretion in mammary glands
26
Q

What is GH?

A

Growth hormone aka human growth hormone (hGH) or somatotropin regulates growth of bone, muscles etc. by binding to receptors.

It is a peptide hormone that stimulates growth, cell production and cell regeneration

27
Q

Where are GH receptors found?

A

Muscle, bone and liver

28
Q

What hormone is stimulated by GH?

A

GH binds to the liver and causes the production of insulin-like growth factor/somatomedin - IGF-1 in adults & children, IGF-2 in the foetus
(also has receptors on muscle and bone)
It increases glucose and free fatty acid concentration

29
Q

How does growth hormone cause growth?

A

Somtrophs/somatotropic cells in the anterior pituitary gland produce growth hormone, travels in bloodstream either to muscles, bones directly and binds to receptors there causing growth OR binds to liver receptors to prod IGF-1 which also has receptors on muscle and bone tissue and binds to cause growth

30
Q

What is acromegaly and how is it often caused?

A

Too much growth hormone in adults/post-puberty and is often due to a pituitary tumour

31
Q

What is it called if there is too much growth hormone in children/ pre puberty

A

Gigantism

32
Q

Can people with acromegaly grow in height, why/why not?

A

No because their epiphyseal plates (growth plates) have fused so cannot whereas people with gigantism can as their plates have not fused

33
Q

What are the main symptoms of acromegaly?

A 
Coarsening of facial features 
Macro gloss is (unusually large tongue)
Prominent nose
Large Jaw (prognathism) - enlargement of mandible
Increased hand and feet size (ring no longer seems to fit or shoe size changed)
Sweatiness
Headaches
Larger lips
Sleep apnea - disturbed sleep
34
Q

What is the role of IGF-1 in acromegaly?

A

Increased growth hormone means increased IGF-1 and so lots of glucose. This can lead to insulin resistance and can result in diabetes/ diabetes like symptoms such as polyuria, polydispsia, and increased tiredness

35
Q

How can you diagnose acromegaly?

A

An adapted version of the oral glucose tolerance test can be used. If you give a pt glucose and their GH levels don’t decrease = acromegaly

36
Q

What is the posterior pituitary made of?

A

Neuronal cells (NOT endocrine)

37
Q

What are the hormones that the posterior pituitary contains?

A 
Arginine Vasopressin (AVP) also known as ADH - antidiuretic hormone 
Oxytocin
38
Q

Where is AVP produced?

A

Supraoptic hypothalamic magnocellular neurones (long neurones at the base of the hypothalamus)

39
Q

Where is oxytocin formed?

A

In the paraventricular hypothalamic magnocellular nuclei (long neurones at base of hypothalamus)

40
Q

What is the path of the hormones of the posterior pituitary ?

A

The posterior pituitary is anatomically continuous with the hypothalamus so:
Nuclei-> stalk (no blood supply here) -> posterior pituitary -> blood capillaries-> bloodstream

41
Q

In what other conditions can macroglossia occur?

A

Down syndrome
Hypothyroidism
Amyloidosis

42
Q

What does ADH / AVP do?

A

Prevents the production of urine - stimulates water reabsorption in the renal collecting duct
(Also a vasoconstrictor via V1 receptor
stimulates ACTH release from the anterior pituitary)

43
Q

What is the mechanism of action of ADH?

A

AVP/ADH in the plasma binds to the v2 receptor on the collecting duct cells.
Binding results in an intracellular signalling cascade
(This leads to G protein production) which activates a cascade by binding to Adenylate cyclase
cAMP is then formed -> protein kinase A-> binds to aquaporin2
results in movement of aquaporin 2 molecules /channels to the apical membrane which is in contact w the urine, water is reabsorbed via the aquaporin 2 and then transported to an aquaporin 3 channel by which it is reabsorbed into the plasma

44
Q

What is oxytocin used for?

A

Milk ejection and delivery of baby

45
Q

What is pathway of oxytocin during labour?

A

uterus at parturition - stimulates myometrial cells to contract powerfully and that allows the delivery of the baby

46
Q

What stimulates the release of growth hormone?

A

Growth hormone-releasing hormone (GHRH)

47
Q

What inhibits the release of growth hormone?

A

somatostatin

48
Q

What does it mean if a tumour is suprasellar?

A

grown outside(above) of the sella turscia

49
Q

The mechanism for milk ejection?

A

Mechanical stimulation of nipple & surrounding area activates afferent pathways.
Afferent signals integrated into the hypothalamus- stimulate oxytocin releasing neuron activity
action potential travel down oxytocin neurones and oxytocin secreted into the bloodstream
increased plasma oxytocin increased milk ejection in mammary glands
Myoepithelial cells in breast contract in response to oxytocin and then expel milk from the breast.

Endocrinology (8 decks)

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