physiology of reproduction 1

Question 1

what determines fetal sex

Answer 1

male - ovum can only contribute an X chromosome, whereas half of the sperm produced during meiosis are X & half are Y

Question 2

sex until 6 weeks

Answer 2

primitive gonads (cortex, medulla) are identical

Question 3

sex after 6 weeks

Answer 3

o if Y chromosome (SRY gene) present: testes form, Mullerian development inhibited (by production of AMH & MIF from testis)
o If Y chromosome absent: ovaries form, Mullerian development occurs

Question 4

what are germ cells

Answer 4

• Specialised cells which develop into gametes

Question 5

how do germ cells migrate to genital ridge

Answer 5

amoeboid movement

Question 6

what happens to oocytes

Answer 6

• 5-10 million primary oocytes at 20 weeks
• Rapid cell deaths of oocytes from 20 weeks
• About 1 million primary oocytes left at birth

Question 7

what is the importance of meiosis

Answer 7

• Key step in germ-cell differentiation
• 2 meiotic divisions prevent polyploidy

• Genetic variability contributes to genetic or bio-diversity

Question 8

what happens during meiosis 1 of female

Answer 8

• Reduction division 46XX →23X + 23X
• Starts in-utero, before 12 weeks
• Homologous recombination & crossover
• Arrested at metaphase 1 until after puberty
• Resumption triggered by LH surge

Question 9

what happens in meiosis 2 of female

Answer 9

• Equational division 23X = 23X + 23X

* Arrested at metaphase 2 until fertilisation

Question 10

describe the embryology of the female genital tract

Answer 10

•	No gonadal (i.e. SRY gene or MIF) influence
•	Paramesonephric (Mullerian) duct develops:
o	Fallopian tubes, 
o	Uterus
o	Upper 2/3 of vagina
•	Mesonephric (Wolffian) duct regresses:
o	Lower vagina
o	Clitoris, labial majora and minora

Question 11

name some abnormalities of primary sex development

Answer 11

• Gonadal dysgeneses (turners & increased X chromosomes ect.)
• Intersex - Male pseudo-hermaphrodites
• Intersex - Female pseudo-hermaphrodites
• Abnormalities of Mullerian development

Question 12

hormonal control before puberty

Answer 12

• Low pulsatility amplitude of GnRH and
• GHRH secretion from Hypothalamus
• Low levels of (pituitary) FSH, LH and (gonadal) sex steroids

Question 13

hormonal control at pubertal age

Answer 13

•	Increased amplitude of GnRH and GHRH
•	Increased levels of FSH,LH and sex steroids
•	Increased levels of growth hormone (GH)
•	Depends on intact H-P-G axis
•	Influenced by many other factors
o	Nutrition (critical body mass)
o	Leptin and insulin
o	Socio-cultural
o	Genetic factors
o	Exercise

Question 14

causes of precocious puberty

Answer 14

gonadotrophin dependent e.g. hypothyroidism
gonadotrophin independent e.g. sex hormone secreting tumours
other variants e.g. premature thelarche

Question 15

treatment of precocious puberty

Answer 15

exclude lesions, infections, tumours
do nothing
inhibit puberty
treatment of premature adrenarche

Question 16

causes of delayed puberty

Answer 16

General:
•	Constitutional delay (most cases)
•	Malabsorption (coeliac ds., inflammatory bowel ds.)
•	Chronic disease/underweight
Gonadal failure
•	Turner syndrome; iatrogenic, polyglandular, autoimmune syndrome
Gonadotrophin deficiency
•	Kallman’s syndrome
•	Hypothalamic/pituitary lesions

Question 17

treatment of delayed puberty

Answer 17

• Exclude tumours/non-constitutional causes
• Sex hormone treatment
• Growth hormone therapy (occasionally needed)
• Treatment of associated infertility