HPG Axis Flashcards Preview

ESA 4 - Reproductive System > HPG Axis > Flashcards

Flashcards in HPG Axis Deck (95):
1

What does successful reproduction require? 

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

 

2

What is crucial to all the steps of successful reproduction? 

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

3

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

  • Thyroid
  • Adrenals
  • Reproductive glands

 

4

What does the hypothalamic-pituitary unit control? 

  • Somatic growth
  • Lactation 
  • Milk secretion
  • Water metabolism 

 

5

What does the hypothalamus always produce, regarding hormone cascades

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

6

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

  • 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

 

7

Does the hypothalamus produce any hormones other than releasing hormones? 

No 

8

Give 7 hypothalamic releasing hormones

  • Corticotrophin releasing hormone
  • Thyrotropin releasing hormone
  • Growth hormonne releasing hormone 
  • Somatostatin 
  • Gonadotropin releasing hormone
  • Prolactin releasing hormone
  • Prolactin inhibiting hormone 

 

9

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

Stimulates ACTH release

10

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

Stimulates TSH and prolactin secretion 

11

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

Stimulates GH secretion 

12

What is the effect of somatostatin on the anterior pitutiary? 

Inhibits GH (and other hormone) secretion 

13

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

Stimulates LH and FSH secretion 

14

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

Stimulates PRL secretion 

15

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

Inhibits PRL secretion 

16

What is the pituitary gland also known as? 

Hypophysis 

17

Where does the pituitary gland lie? 

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

18

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

A bean 

19

What seperates the anterior and posterior pituitary? 

Lumen of Rathke's pouch 

20

What is the anterior pituitary also known as? 

Adrenohypophysis

21

Is the adrenohypophysis made of nervous tissue? 

No

22

How is the adrenohypophysis connected to the hypothalamus? 

By the superior hypophyseal artery 

23

What is the anterior pituitary made up of? 

Collection of hormone producing glandular cells 

24

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

The hypothalamus 

25

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

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

26

What are the cell types of the anterior pituitary? 

  • Thyrotrophic cells
  • Mammotrophic cells
  • Corticotrohic cells
  • Somatotrophic cells
  • Gonadotrophic cells
  • Pars intermedia cells

 

27

What hormone do thyrotrophic cells produce? 

Thyroid stimulating hormone 

28

What does thyroid stimulating hormone act on? 

The thyroid gland 

29

What hormone do mammotrophic cells produce? 

Prolactin 

30

What does prolactin act on? 

  • Mammary glands
  • Testes

 

31

What hormone do corticotrophic cells produce? 

ACTH

32

What does ACTH act on? 

Adrenal cortex

33

What hormone do somatotrophic cells produce? 

Growth hormone

34

What does growth hormone act on? 

All body tissues, especially; 

  • Bone
  • Muscle
  • Connective tissue

 

35

What % of AP cells are gonadotrophic cells? 

5-10%

36

What hormones do gonadotrophic cells produce?

  • FSH
  • LH

 

37

What do FSH and LH act on? 

Gonads- testes and ovaries 

38

What hormone do the pars intermedia cells produce?

Melanocyte-stimulating hormone (MSH)

39

What does MSH act on? 

Melonocytes in epidermis 

40

What anterior pituitary hormones are involved in reproduction? 

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

41

What is the posterior pituitary also known as? 

Pars nervosa 

42

What is the posterior pituitary? 

An outgrowth of the hypothalamus 

43

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

Stains lighter

44

What is the posterior pituitary made of? 

Nervous tissue 

45

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

Hypothalamic neurones pass through neural stalk and end in posterior pituitary

46

What is the median eminence? 

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

47

What kind of gland is the neurohypophysis? 

Neuro-secretory gland

48

What does the neurohypophysis secrete? 

  • ADH
  • Oxytocin 

 

49

What is oxytocin important in? 

Reproduction 

50

What does the HPG axis comprise of? 

Interaction between hypothalamus, pituitary gland, and gonads

51

What does the HPG axis work together to do? 

Regulate; 

  • Development
  • Reproduction 
  • Aging
  • Many other body processes

 

52

What does the regulation of the HPG axis rely on? 

A number of complex positive and negative feedback loops

53

Why is it important that the HPG axis is regulated? 

Don't want the system to run away with itself 

54

What regulates the HPG axis? 

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

55

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

Disease

56

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

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

57

What does GnRH do? 

Stimulates the anterior pituitary gland to secrete two gonadotrophic hormones;

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

 

58

What produces LH and FSH?

Gonadotrophs 

59

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

Little or none

60

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

They are very sensitive to pulsatile nature and concentration 

61

Describe a GnRH molecule

10aa peptide

62

Of what nature is the release of GnRH? 

Every 1-3 hours, in a discrete pulse

63

What is the intensity of GnRH stimulus affected by? 

Frequency of release

64

What does LH release mirror? 

The pulsatile nature 

65

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

Loose LH completely

66

Does FSH mirror the pulsatile nature of GnRH?

No, it is more generally released

67

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

Increased FSH

68

How does GnRH travel to the pituitary? 

In the hypophysial portal system

69

What control is gonadotroph synthesis and release under? 

Positive and negative feedback by gondal steriods and gondal peptides 

70

How do gonadal hormones decrease gonadotrophin release? 

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

 

71

Draw a diagram illustrating the HPG axis

72

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

Via G-alphaPCR affecting adenylate cyclase 

73

Where does LH act in the male? 

On the Leydig cells of the testis 

74

What does LH stimulation of the Leydig cells cause? 

The cells to release testosterone 

75

What controls testesterone release from the Leydig cells by LH? 

Negative feedback

76

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

  • Testosterone releases LH from AP 
  • Testosterone reduces GnRH secretion 

 

77

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

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

78

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

They are constant

79

Why are testosterone levels not constant in the short term? 

  • Circadian rhythm
  • Effects of environmental stimuli 

 

80

What time of day are testosterone levels highest? 

In the morning

81

Where does FSH act in the male? 

On Sertoli cells of the seminiferous tubules 

82

What does the stimulation of Sertoli cells by FSH cause? 

  • Sertoli cells to grow and secrete spermatogenic substances 
  • Sertoli cells to secrete ABG and inhibin

 

83

What is also needed for the function of Sertoli cells? 

Testosterone 

84

How does testosterone get to the Sertoli cells? 

It diffuses into the seminiferous tubules

85

What does ABG do? 

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

86

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

Reduce FSH secretion selectively 

87

Where is inhibin imoprtnat in males? 

In spermatogenesis

88

What is the function of inhibin in spermatogenesis? 

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

89

Draw a diagram illustrating the HPG axis in the male 

90

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

Primarily via G-alphas PCR affecting adenylate cyclase 

91

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

Ovarian granulose cells and theca interna 

92

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

  • Stimulate sex hormone synthesis
  • Control gamete production 

 

93

What sex hormones are produced in the female? 

  • Oestrogen
  • Progesterone
  • Inhibin

 

94

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

Folliculogenesis and ovulation 

95

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

Because release of gametes is pulsatile over 28 days