Reproductive System 2 - Introduction to Reproductive Hormones

Question 1

The Endocrine System

Answer 1

A collection of glands located throughout the body that manufacture and secrete hormones to regulate physiological function
generally act in a paracrine or endocrine manner

Question 2

What are hormones?

Answer 2

A chemical substance produced by ductless glands within the endocrine system

Question 3

The major endocrine glands are:

Answer 3

Adrenal glands
Hypothalamus
Ovaries and testes
Pancreas
Thyroid and parathyroid
Pineal gland
Pituitary gland
Thymus gland

Question 4

What are the classes of hormones?

Answer 4

Three general classes
Hormones derived from amino acids
Dopamine, epinephrine (tyrosine precursor)
Proteins and peptides
Insulin (peptide), growth hormone (protein)
Hormones derived from lipids
Prostaglandins (derived from phospholipids)
Steroids (derived from cholesterol)
Most RH steroids but stimulated by other classes

Question 5

Cholesterol

Answer 5

Large molecule
4 cycloalkane rings
Large hydrocarbon chain
Essential component of all cellular membranes
Source?
Diet and de-novo

Sex steroids / hormones
Oestrogens
Progestogens
Androgens

Precursor for:
Steroid hormones
Adrenal steroids
Glucocorticoids
Mineralcorticoids

Question 6

Reproductive hormones

Answer 6

Commonly called sex steroids or steroid hormones
Produced mainly by the gonads (ovaries and testes)

Question 7

3 classes of reproductive hormones:

Answer 7

Oestrogens
Androgens
Progestogens

Question 8

Oestrogens

Answer 8

Oestradiol
Oestrone
Oestriol

Question 9

Androgens

Answer 9

Testosterone

5a-dihydrotesterone

androstenedione

dehydroepiandrosterone

Question 10

Progestogens

Answer 10

progesterone

Question 11

Overview of major functions of reproductive hormones

Answer 11

Bind to specific receptors in target tissues
AR, ER, PR
Exert a range of effects on both organs and the body as a whole
Primary role: maturation of reproductive organs, fertility and pregnancy
Secondary role: development of physical characteristics

Question 12

Testes anatomy: sites of testosterone production

Answer 12

Testosterone is produced in Leydig cells

Question 13

Ovarian anatomy: sites of steroid hormone production

Answer 13

label ovary

Question 14

Ovarian anatomy: sites of steroid hormone production

Answer 14

Oestrogens: ovarian granulosa cells
Androgens: ovarian theca cells
Progesterone: corpus luteum

Question 15

Reproductive hormones: molecular action

Answer 15

Generic mechanism of action
Hormones enter cells
Hormones bind to intracellular receptor
Conformation change and translocation
DNA binding (HRE’s)
Gene expression (or repression)

Question 16

Regulation of gonadal steroidogenesis

Answer 16

Endocrine function of gonads is regulated by HPG axis
Hypothalamus
Pituitary
Gonad

Question 17

Hypothalamus

Answer 17

Small structure at base of forebrain
Hypothalamus releases GnRH (Gonadotrophin Releasing Hormone)
Peptide hormone
Released into blood
Reach pituitary

Question 18

Pituitary

Answer 18

Pea-sized gland located at the base of the skull ventral to the hypothalamus
Comprised of two elements
Posterior and anterior lobes
Anterior pituitary contains specialised cells (gonadotropes)
GnRH stimulates gonadotropes to
Produce gonadotrophins
glycoproteins
FSH (follicular stimulating hormone)
LH (Lutenising hormone)
hCG (human chorionic gonadotrophin)

Question 19

Gonadotrophins

Answer 19

LH and FSH
Mechanism of action
bind to different receptors expressed on cells within ovary and testes

LH main functions
♀ acts on ovarian follicle inducing ovulation
♂ acts on testes producing testosterone
FSH main functions
♀ promotes ovarian follicle development & oestrogen production
♂ stimulates spermatogenesis in testes

Question 20

HPG axis

Answer 20

Hypothalamus > Pituitary > Gonads (release pf the sex hormones)

Question 21

Reproductive hormones are subject to feedback control

Answer 21

Both positive and negative – different stages of the cycle
Negative feedback
decreases level of signal and maintains homeostasis
Direct negative feedback
Steroid hormones (testosterone/oestrogen) decrease secretion of gonadotrophins (FSH, LH)
Indirect negative feedback
Steroid hormones inhibit their own production indirectly by inhibiting hypothalamus GnRH
> decreased pituitary gonadotrophin secretion
> reduced steroid hormone production

Question 22

GnRH get released by the

Answer 22

hypothalamus

Question 23

Where is the pituitary?

Answer 23

just below the hypothalamus

Question 24

Negative regulation of steroidogenesis by inhibin

Answer 24

Inhibin
Protein hormone
In females, released by granulosa cells in response to FSH
In males, produced by Sertoli cells in response to androgens
Negative regulator of FSH

Question 25

Positive feedback of reproductive hormones

Answer 25

Positive feedback
leads to an increase in hormone level
Occurs within follicular phase of uterine (menstrual) cycle
Oestrogen-induced LH to trigger ovulation

Question 26

Detailed representation of the HPG axis:

Answer 26

Hypothalamus
(Hypothalmic neurons) secreting GnRH > onto Pituitary Gland (anterior gondotrophs) > LH and FSH gets released and reproductive hormone synthesis > physiological effects