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ESA 4 - Reproductive System > HPG Axis > Flashcards

HPG Axis Flashcards

1
Q

What does successful reproduction require?

A
  • Fertilisation
  • Support of conceptus, embryo, and fetus
  • Birth at the right time
  • Support of the neonate
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2
Q

What is crucial to all the steps of successful reproduction?

A

Hormones of the hypothalmic-pituitary-gonadal (HPG) axis

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3
Q

What does the output of the hypothalamus-pituitary unit regulate the function of?

A
  • Thyroid
  • Adrenals
  • Reproductive glands
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4
Q

What does the hypothalamic-pituitary unit control?

A
  • Somatic growth
  • Lactation
  • Milk secretion
  • Water metabolism
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5
Q

What does the hypothalamus always produce, regarding hormone cascades?

A

A releasing hormone that is specific to the hormone cascade that it follows

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6
Q

What are the common features of the releasing hormones produced by the hypothalamus?

A
  • Secretion in pulses tied to internal biological clock
  • Act on specific membrane receptors
  • Transduce signals via second messengers
  • Stimulate release of one or more pituitary hormones
  • Stimulate synthesis of pituitary hormones
  • Stimulates hyperplasia and hypertrophy of target cells
  • Regulates its own receptor
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7
Q

Does the hypothalamus produce any hormones other than releasing hormones?

A

No

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8
Q

Give 7 hypothalamic releasing hormones

A
  • Corticotrophin releasing hormone
  • Thyrotropin releasing hormone
  • Growth hormonne releasing hormone
  • Somatostatin
  • Gonadotropin releasing hormone
  • Prolactin releasing hormone
  • Prolactin inhibiting hormone
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9
Q

What is the effect of corticotrophin releasing hormone on the pituitary?

A

Stimulates ACTH release

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10
Q

What is the effect of thyrotropin releasing hormone on the pituitary?

A

Stimulates TSH and prolactin secretion

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11
Q

What is the effect of growth hormone releasing hormone on the pituitary?

A

Stimulates GH secretion

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12
Q

What is the effect of somatostatin on the anterior pitutiary?

A

Inhibits GH (and other hormone) secretion

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13
Q

What is the effect of gonadotrophin releasing hormone (GnRH) on the pituitary?

A

Stimulates LH and FSH secretion

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14
Q

What is the effect of prolactin releasing hormone on the pituitary?

A

Stimulates PRL secretion

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15
Q

What is the effect of prolactin inhibiting hormone on the pituitary?

A

Inhibits PRL secretion

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16
Q

What is the pituitary gland also known as?

A

Hypophysis

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17
Q

Where does the pituitary gland lie?

A

In depression of base of skull known as pituitary fossa, or sella turcica

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18
Q

What does the pituitary gland resemble in terms of size and shape?

A

A bean

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19
Q

What seperates the anterior and posterior pituitary?

A

Lumen of Rathke’s pouch

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20
Q

What is the anterior pituitary also known as?

A

Adrenohypophysis

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21
Q

Is the adrenohypophysis made of nervous tissue?

A

No

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22
Q

How is the adrenohypophysis connected to the hypothalamus?

A

By the superior hypophyseal artery

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23
Q

What is the anterior pituitary made up of?

A

Collection of hormone producing glandular cells

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24
Q

What are the hormone producing cells of the anteiror pituitary under the control of?

A

The hypothalamus

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25
Q

How does the hypothalamus control the hormones produced by the anterior pituitary?

A

The hypothalamus tells the pituitary which hormone is needed with specific releasing hormone

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26
Q

What are the cell types of the anterior pituitary?

A
  • Thyrotrophic cells
  • Mammotrophic cells
  • Corticotrohic cells
  • Somatotrophic cells
  • Gonadotrophic cells
  • Pars intermedia cells
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27
Q

What hormone do thyrotrophic cells produce?

A

Thyroid stimulating hormone

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28
Q

What does thyroid stimulating hormone act on?

A

The thyroid gland

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29
Q

What hormone do mammotrophic cells produce?

A

Prolactin

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30
Q

What does prolactin act on?

A
  • Mammary glands
  • Testes
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31
Q

What hormone do corticotrophic cells produce?

A

ACTH

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32
Q

What does ACTH act on?

A

Adrenal cortex

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33
Q

What hormone do somatotrophic cells produce?

A

Growth hormone

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34
Q

What does growth hormone act on?

A

All body tissues, especially;

  • Bone
  • Muscle
  • Connective tissue
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35
Q

What % of AP cells are gonadotrophic cells?

A

5-10%

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36
Q

What hormones do gonadotrophic cells produce?

A
  • FSH
  • LH
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37
Q

What do FSH and LH act on?

A

Gonads- testes and ovaries

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38
Q

What hormone do the pars intermedia cells produce?

A

Melanocyte-stimulating hormone (MSH)

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39
Q

What does MSH act on?

A

Melonocytes in epidermis

40
Q

What anterior pituitary hormones are involved in reproduction?

A

All involved in some way, but LH, FSH, and prolactin are most significant

41
Q

What is the posterior pituitary also known as?

A

Pars nervosa

42
Q

What is the posterior pituitary?

A

An outgrowth of the hypothalamus

43
Q

How can the posteiror pituitary be distinguished from the anterior histologically?

A

Stains lighter

44
Q

What is the posterior pituitary made of?

A

Nervous tissue

45
Q

Describe the relationship between the nerves of the hypothalamus and the posterior pituitary

A

Hypothalamic neurones pass through neural stalk and end in posterior pituitary

46
Q

What is the median eminence?

A

The upper portion of the neural stalk that extends into the hypothalamus

47
Q

What kind of gland is the neurohypophysis?

A

Neuro-secretory gland

48
Q

What does the neurohypophysis secrete?

A
  • ADH
  • Oxytocin
49
Q

What is oxytocin important in?

A

Reproduction

50
Q

What does the HPG axis comprise of?

A

Interaction between hypothalamus, pituitary gland, and gonads

51
Q

What does the HPG axis work together to do?

A

Regulate;

  • Development
  • Reproduction
  • Aging
  • Many other body processes
52
Q

What does the regulation of the HPG axis rely on?

A

A number of complex positive and negative feedback loops

53
Q

Why is it important that the HPG axis is regulated?

A

Don’t want the system to run away with itself

54
Q

What regulates the HPG axis?

A

The product of the system- LH, FSH, and gonadal hormones

55
Q

What does the loss of the regulation of the HPG axis result in?

A

Disease

56
Q

What does a major share of the control of sexual functions in both male and female begin with?

A

Secretion of gonadotrophin-releasing hormone (GnRH) by the hypothalamus

57
Q

What does GnRH do?

A

Stimulates the anterior pituitary gland to secrete two gonadotrophic hormones;

  • Luteinising hormone (LH)
  • Follicle-stimulating hormone (FSH)
58
Q

What produces LH and FSH?

A

Gonadotrophs

59
Q

How much FSH and LH do gonadotrophs secrete in the absence of GnRH?

A

Little or none

60
Q

What is the result of gonadotrophs secreting little or no FSH or LH in the absence of GnRH?

A

They are very sensitive to pulsatile nature and concentration

61
Q

Describe a GnRH molecule

A

10aa peptide

62
Q

Of what nature is the release of GnRH?

A

Every 1-3 hours, in a discrete pulse

63
Q

What is the intensity of GnRH stimulus affected by?

A

Frequency of release

64
Q

What does LH release mirror?

A

The pulsatile nature

65
Q

What happens if we perfuse someone with constant level of GnRH?

A

Loose LH completely

66
Q

Does FSH mirror the pulsatile nature of GnRH?

A

No, it is more generally released

67
Q

What does an increased intensity of release of GnRH lead to?

A

Increased FSH

68
Q

How does GnRH travel to the pituitary?

A

In the hypophysial portal system

69
Q

What control is gonadotroph synthesis and release under?

A

Positive and negative feedback by gondal steriods and gondal peptides

70
Q

How do gonadal hormones decrease gonadotrophin release?

A
  • Decreasing GnRH release from hypothalamus
  • Affecting ability of GnRH to stimulate gonadotrophin secretion from the anterior pituitary
71
Q

Draw a diagram illustrating the HPG axis

A
72
Q

How do FSH and LH primarily act on the gonads in the male?

A

Via G-alphas PCR affecting adenylate cyclase

73
Q

Where does LH act in the male?

A

On the Leydig cells of the testis

74
Q

What does LH stimulation of the Leydig cells cause?

A

The cells to release testosterone

75
Q

What controls testesterone release from the Leydig cells by LH?

A

Negative feedback

76
Q

How does negative feedback control the release of testosterone from the Leydig cells?

A
  • Testosterone releases LH from AP
  • Testosterone reduces GnRH secretion
77
Q

What is the result of testosterone reduced LH and GnRH secretion?

A

Reduces LH and FSH secretion, as they are both released from the same cells

78
Q

What happens to testosterone levels in the medium/long term?

A

They are constant

79
Q

Why are testosterone levels not constant in the short term?

A
  • Circadian rhythm
  • Effects of environmental stimuli
80
Q

What time of day are testosterone levels highest?

A

In the morning

81
Q

Where does FSH act in the male?

A

On Sertoli cells of the seminiferous tubules

82
Q

What does the stimulation of Sertoli cells by FSH cause?

A
  • Sertoli cells to grow and secrete spermatogenic substances
  • Sertoli cells to secrete ABG and inhibin
83
Q

What is also needed for the function of Sertoli cells?

A

Testosterone

84
Q

How does testosterone get to the Sertoli cells?

A

It diffuses into the seminiferous tubules

85
Q

What does ABG do?

A

Binds testosterone and keeps some within the seminiferous tubules, to allow the Sertoli cells to work

86
Q

What is the function of inhibin produced by the Sertoli cells?

A

Reduce FSH secretion selectively

87
Q

Where is inhibin imoprtnat in males?

A

In spermatogenesis

88
Q

What is the function of inhibin in spermatogenesis?

A

Regulates production of sperm cells, so ensures spermatogenesis doesn’t continue all the time

89
Q

Draw a diagram illustrating the HPG axis in the male

A
90
Q

How do FSH and LH act on the gonads in the female?

A

Primarily via G-alphas PCR affecting adenylate cyclase

91
Q

What are the target cells for FSH and LH in the female?

A

Ovarian granulose cells and theca interna

92
Q

What do FSH and LH act to do in the female?

A
  • Stimulate sex hormone synthesis
  • Control gamete production
93
Q

What sex hormones are produced in the female?

A
  • Oestrogen
  • Progesterone
  • Inhibin
94
Q

What aspects of gamete production are controlled by the HPG axis?

A

Folliculogenesis and ovulation

95
Q

Why is the control of gamete production more complex in the female than the male?

A

Because release of gametes is pulsatile over 28 days

ESA 4 - Reproductive System (31 decks)

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