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Lily BRS Endo > The Pituitary Gland > Flashcards

The Pituitary Gland Flashcards

1
Q

What is a hormone?

A

A messenger

Carried in the blood from the organ where they are produced to their effector organ

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2
Q

What are the two classes of hormones?

A

Peptide

Steroid

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3
Q

What are some properties of peptide hormones? (Synthesis, storage, receptors)

A

Synthesised as pro hormones that require further processing (cleavage) to activate

Stored in vesicles (regulatory secretion)

Bond to receptors on cell membrane and transducer signals using second messenger systems

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4
Q

What are some properties of steroid hormones? (Synthesis, storage, receptors)

A

Synthesised from cholesterol

Released immediately (constitutive secretion)

Bind to intracellular receptors to change gene expression directly

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5
Q

Where is the pituitary found?

A

Beneath the optic chiasm

Sits in the sella turcica of the sphenoid bone

Hangs from the pituitary stalk below the hypothalamus

It is roughly the size of a thumb nail

Split into the anterior and posterior pituitary

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6
Q

Which cells regulate the anterior pituitary function? And what are their properties?

A

Hypothalamic parvocellular neurones

Short, terminate on median eminence

Release hypothalamic releasing/inhibitory factors (hormones) into capillary plexus in median eminence

These regulatory factors are carried in the blood to the anterior pituitary by the hypothalamo-pituitary portal system

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7
Q

Which cells make up the anterior pituitary (adenohypophysis)?

A

Endocrine cells:

Somatotrophs

Lactotrophs

Corticotrophs

Thyrotrophs

Gonadotrophs

The anterior pituitary is anatomically different from the hypothalamus

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8
Q

How does the hypophyseal-pituitary portal system work?

A
  1. Axon terminals of hypothalamic neurosecretory cells release hormones (releasing and inhibitory hormones) into the portal system
  2. The RHs and IHs travel in the portal system to the anterior pituitary
  3. In the pituitary the RHs and IHs stimulate or inhibit the release of hormones from anterior pituitary cells
  4. Anterior pituitary hormones leave the gland via the blood

The portal system contains fenestrated blood vessels making them leaky so the regulatory hormones can diffuse out

Eg. Thyrotrophin releasing hormone (TRH) released from hypothalamus. Travels through portal system to anterior pituitary. TRH stimulates the release of TSH (theo is stimulating hormone) from thyrotrophs. TSH leaves the pituitary to go to the thyroid gland to stimulate the release of thyroxine

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9
Q

What are the 5 anterior pituitary cells and what hormone do they release?

A

Somatotrophs - growth hormone (somatotropin)

Lactotrophs - prolactin

Thyrotrophs - thyroid stimulating hormone

Gonadotrophs - LH and FSH

Corticotrophs - adrenocorticotrophic hormone (ACTH/ corticotropin)

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10
Q

What are the regulatory hormones of somatotrophs?

A

Growth hormone releasing hormone - releasing

Somatostatin - inhibitory

Relates to growth hormone

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11
Q

What is the regulatory hormone of lactotrophs?

A

Dopamine - inhibitory

Relates to prolactin

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12
Q

What is the regulatory hormone of thyrotrophs?

A

Thyrotropin releasing hormone (TRH) - releasing

Relates to TSH

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13
Q

What is the regulatory hormone of gonadotrophs?

A

Gonadotropin releasing hormone - releasing

Relates to LH and FSH

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14
Q

What is the regulatory hormone of corticotrophs?

A

Corticotropin releasing hormone - releasing

Relates to adrenocorticotropic hormone (ACTH)

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15
Q

What are the effector organs of each cell in the anterior pituitary?

A

Somatotrophs - growth hormone - the liver and all body tissues

Lactotrophs - prolactin - breasts of lactating women

Thyrotrophs - TSH - thyroid

Gonadotrophs - LH and FSH - gonads (ovaries and testes)

Corticotrophs - ACTH - adrenal cortex

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16
Q

How might a pituitary tumour affect the visual field?

A

Bitemporal hemianopia

Loss of the peripheral vision in both eyes

Due to compression of the optic chiasm above the pituitary

Fibres from the medial retinae (which have crossed from the lateral visual field) cross at the optic chiasm

The tumour prevents transmission of sensory information from the lateral visual field to the occipital lobe

17
Q

What is the reflex arc of anterior pituitary lactotrophs?

A
  1. Mechanical stimulation of nipple
  2. Afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurones
  3. Less dopamine in the hypothalamo-pituitary portal system causes less inhibition of anterior pituitary lactotrophs
  4. Increased plasma prolactin increases milk SECRETION in mammary glands
18
Q

What are the mechanisms of growth hormone action?

A

Growth hormone releasing hormone released from hypothalamus

Goes via hypothalaomo-pituitary portal to the anterior pituitary somatotrophs

Stimulates the release of growth hormone into the blood

GH goes to general body tissues and causes growth and development

GH also goes to liver and binds to GH receptors, stimulating the release of IGF-1 (insulin like growth factor 1)

IGF-1 binds to IGF-1 receptors on bone and muscle etc and causes growth

19
Q

What is the difference between gigantism and acromegaly?

A

Both may be caused by excess levels of growth hormone that could be caused by a pituitary tumour

Gigantism causes longer limbs and happens before/during puberty

Acromegaly does not result in increased height as it occurs after puberty. After the epiphyseal growth plates have fused.

20
Q

What are some symptoms of acromegaly?

A

Macroglossia

Prominent nose

Large jaw (prognathism)

Increased hand and feet size

Sweatiness

Headache

21
Q

What are the posterior pituitary hormones?

A

Arginine vasopressin (AVP) (anti diuretic hormone)

Oxytocin

22
Q

Which cells are found in the posterior pituitary?

A

Magnocellular neurones

These are long, originate in supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei

Nuclei —> stalk —> posterior pituitary

23
Q

What is the anatomical difference between the anterior and posterior pituitary?

A

Anterior is not confine with the hypothalamus, it is vascularised in the form of the portal

The posterior IS continuous with the hypothalamus as it’s is made completely of neuronal tissue and has no blood supply

24
Q

How does regulation of the posterior pituitary gland work?

A
  1. Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport them to the posterior pituitary
  2. Excitation of these hypothalamic magnocellular neurones stimulates release of AVP and oxytocin into the PP where they diffuse into the blood
  3. They then leave the pituitary via the blood
25
Q

What is the physiological action of arginine vasopressin?

A

Aka ADH

Duiresis = production of urine

Stimulates water reapsorbtion in the collecting ducts of the kidney

This concentrates urine

Acts through the V2 receptor in the kidney

Also a vasoconstrictor via the V1 receptor

Also stimulates adrenocorticotrophic hormone release from anterior pituitary

26
Q

How does vasopressin concentrate urine?

A

AVP binds to V2 receptors on basolateral section of collecting duct

Acts through a G protein coupled receptor

Moves aquaporin-2 vesicles to the apical membrane of the collecting duck where the aquaporins allow the diffusion of water back through the wall of the collections duct

Water goes into the blood plasma through aquaporin-4 channels

27
Q

What are the physiological actions of oxytocin

A
  1. Uterus at parturition (labour)

Myometrial (muscle) cells

Contraction

Delivery of baby

(Oxytocin analogues can be used to help progress labour)

  1. Breast during lactation

Myoepithelial cells

Contraction

Milk ejection

28
Q

What is the reflex arc or oxytocin relating to milk ejection?

A
  1. Mechanical stimulation of nipple
  2. Afferent signals integrated in the hypothalamus and stimulate oxytocin releasing neurone activity
  3. Action potentials travel down oxytocin neurones and oxytocin is secreted into the blood stream
  4. Increased plasma oxytocin increases milk ejection in mammary glands
29
Q

What is the difference between prolactin and oxytocin in terms of lactation?

A

Prolactin = produces milk

Oxytocin = ejection

Lily BRS Endo (10 decks)

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