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Endocrine System > The Pituitary Gland > Flashcards

The Pituitary Gland Flashcards

1
Q

What two structures are the principal organisers of the endocrine system?

A

Hypothalamus and pituitary

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2
Q

How are the hypothalamus and pituitary gland connected?

A

Via a stalk called the infundibulum

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3
Q

How do the hypothalamus and pituitary communicate?

A

Neural (to the posterior pituitary) and endocrine (to the anterior pituitary) hence it’s neuroendocrine function

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4
Q

What are the features of the hypothalamus?

A
  • Integration centre for endocrine systems
  • Located at the base of the brain, below the thalamus,
  • Connected to the pituitary via a stalk (infundibulum)
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5
Q

What are the features of the pituitary gland?

A
  • Bean-shaped and bean-sized endocrine gland (~14 mm diameter)
  • Located in a pocket in the sphenoid bone, directly below the hypothalamus
  • Contains 2 distinct types of tissue – anterior and posterior pituitary
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6
Q

What are tropic neurohormones?

A
  • Neurohormones secreted into capillaries travelling to anterior pituitary
  • Govern the release of another hormone
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7
Q

What type of hormones are released by the hypothalamus?

A

Neurohormones

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8
Q

What type of hormones are released by the posterior pituitary?

A

Neurohormones

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9
Q

What type of hormones are released by the anterior pituitary?

A

Endocrine hormones

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10
Q

What are the two classifications of hormones that are released by the hypothalamus and anterior pituitary gland?

A

Tropic and non-tropic

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11
Q

What are the two forms of hypothalamic neurohormones?

A

Tropic and non-tropic

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12
Q

What are non-tropic neurohormones?

A

Neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood

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13
Q

What are the actions of the tropic neurohormones?

A

Bind to receptors on anterior pituitary and stimulate/inhibit release of anterior pituitary hormones

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14
Q

What are five tropic hypothalamic “releasing hormones”?

A
  • Thyrotropin Releasing Hormone (TRH)
  • Corticotropin Releasing Hormone (CRH)
  • Growth Hormone Releasing Hormone (GHRH)
  • Gonadotropin Releasing Hormone (GnRH)
  • Prolactin Releasing Hormone (PRH)

All peptides

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15
Q

What are two tropic hypothalamic “inhibiting hormones”?

A
  • Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin (peptide)
  • Dopamine aka Prolactin Inhibiting Hormone (PIH) - non peptide
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16
Q

What is the hypothalmo-hypophyseal portal system?

A

Network of tiny vessels which transfer trophic hormones from hypothalamus to anterior pituitary

Two capillary beds connected in series

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17
Q

Describe the effect of neurohormones in the hypothalmo-hypophyseal portal system

A
  • Small numbers of neurosecretory neurons sufficient for control
  • Hormones released from neurosecretory neurons at the median eminence
  • Very small amounts of hormones required
  • Short distance – very rapid and dynamic
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18
Q

What are the features of the anterior pituitary?

A 
• True endocrine tissue
epithelial origin
• Connected to hypothalamus via capillary portal system
• Also called adenohypophysis
• Makes up 2/3rds of the gland
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19
Q

What are the features of the posterior pituitary?

A
  • Neuroendocrine tissue
  • Neural tissue origin
  • Neural connection to hypothalamus
  • Secretes neurohormones made in hypothalamus
  • Also called neurohypophysis
  • Makes up 1/3rd of the gland
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20
Q

What controls the production of anterior pituitary hormones?

A

Hypothalamus

21
Q

How does the hypothalamus control the production of anterior pituitary hormones?

A

Produces “releasing” or “inhibiting” trophic hormones, (sometimes called factors), that stimulate or inhibit hormone production from the anterior pituitary e.g. Thyrotropin Releasing Hormone (TRH) stimulates AP to secrete Thyroid Stimulating Hormone (TSH).

22
Q

How many hormones are released from the anterior pituitary gland?

A

6 hormones, all peptides (5 of these are tropic hormones)

23
Q

Name 6 anterior pituitary hormones

A
  • Thyroid Stimulating Hormone (TSH) aka thyrotropin
  • Adrenocorticotrophic Hormone (ACTH) aka corticotropin
  • Follicle Stimulating Hormone (FSH)
  • Luteinising Hormone (LH)
  • Growth Hormone (GH)
  • Prolactin

1-5 control secretion of other endocrine glands and have direct or indirect effects in promoting growth = tropic hormones

Prolactin directly stimulates milk production from the breast during lactation

24
Q

Describe pathway of hypothalmo-hypophyseal portal system

A
  1. Neurons synthesizing trophic hormones release them into capillaries of the portal system
  2. Portal vessels carry trophic hormones directly to the anterior pituitary
  3. Endocrine cells release their hormones into the second set of capillaries for distribution to the rest of the body
25
Q

What is the action of prolactin (anterior pituitary hormone)?

A

Breast –> lactation (direct)

26
Q

What is the action of thyroid-stimulating hormone (anterior pituitary hormone)?

A

Thyroid –> TH release (tropic)

27
Q

What is the action of adrenocorticotropic hormone (anterior pituitary hormone)?

A

Adrenal cortex –> cortisol release (tropic)

28
Q

What is the action of growth hormone (anterior pituitary hormone)?

A

Liver –> IGF-1* release (tropic) + tissue metabolism (direct)

IGF-1 = insulin-like growth factor-1

29
Q

What is the action of luteinising hormone (anterior pituitary hormone)?

A

Gonads –> regulation of reproductive function (direct) + sex hormone release (tropic)

30
Q

What are the 3 integration centres involved in the anterior pituitary feedback control?

A
  1. Hypothalamus
  2. Anterior pituitary
  3. Target endocrine cell
31
Q

Describe the anterior pituitary feedback control

A
  • Hormones themselves act as negative feedback signal

* Each hormone feeds back to inhibit hormone secretion by integrating centres earlier in the reflex

32
Q

Name a short and a long loop feedback

A

• Feedback from endocrine target = long-loop feedback
- As signals hypo to stop producing trophic hormone and thus stops AP from releasing trophic hormone
• Feedback from anterior pituitary to hypothalamus = short-loop feedback
- Only needs to tell hypo to stop releasing trophic hormone

33
Q

What is the function of the posterior pituitary?

A

Stored and releases two peptide neurohormones:
• Vasopressin (aka anti-diuretic hormone; ADH)
• Oxytocin

34
Q

Where in the posterior pituitary are the peptide neurohormones formed?

A

Magnocellular neurons which have their cell bodies in specific areas of the hypothalamus

35
Q

Describe the magnocellular neurons of the posterior pituitary?

A
  • Different subsets make either vasopressin or oxytocin
  • Axons projects down the infundibulum to posterior pituitary
  • Do not synapse with other neurones, their terminals end directly on capillaries
  • Release of vasopressin or oxytocin directly into the blood stream at the posterior pituitary
36
Q

Describe how the posterior pituitary releases neurohormones

A
  1. Hormone made and packaged in the cell body of neurone (magnocellular)
  2. Vesicles are transported down the cell
  3. Vesicles containing hormone are stored in posterior pituitary
  4. Hormones are released into blood
37
Q

What is the action vasopressin (ADH)?

A

Regulates water balance

38
Q

What triggers the release of vasopressin (ADH)?

A
  • Increase plasma osmolarity

* Decrease plasma volume/blood pressure

39
Q

What is the site/mode of action of vasopressin (ADH)?

A
  • Kidney collecting ducts –> Increase water reabsorption

* Vascular smooth muscle –> increase blood pressure

40
Q

What is the function of oxytocin?

A

Milk ejection and uterine contraction

41
Q

What is oxytocin release triggered by?

A
  • Labour (baby’s head against cervix)

* Suckling

42
Q

What is the site/mode of action of oxytocin?

A

Milk duct smooth muscle:
• Contracts muscle, ejecting milk

Uterine smooth muscle:
• Child birth

43
Q

What can endocrine disorders be classified as?

A
  • Hyposecretion - too little hormone secreted
  • Hypersecretion
  • Hyporesponsiveness - reduced response of the target cell
  • Hyperresponsiveness
  • 1° disorders
  • 2° disorders
  • 3° disorders
44
Q

What are 1° disorders?

A

The defect is in the cells that secrete the hormone

45
Q

What are 2° disorders?

A

There is too little or too much trophic hormone from pituitary

46
Q

What are 3° disorders?

A

Relate to hypothalamic defects

47
Q

What could be a cause of hyporesponsiveness?

A

Relates to alterations in receptor for hormone, disordered post-receptor events or failure of metabolic activation of hormone, (where this is required for function).

48
Q

What could be a cause of hyperresponsiveness?

A

Could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis

Endocrine System (29 decks)

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