The Gonads Flashcards
where do the testes and ovaries develop from
Gonads
What are the functions of the gonads
Production of gametes and steroid hormones
How is gametogenesis specific to sex
Males = spermatogenesis Females = Oogenesis
How is steroidogenesis specific to sex
Males = androgens - oestrogen, progestogens
Females - oestrogen, progestogens
Describe the process of spermatogenesis
- Germ cell proliferates via mitosis to produce spermatogonia
- Spermatogonia undergoes the first meiotic division
- primary spermatocytes undergo second meiotic division to produce spermatids
- Maturation into spermatozoa
How long does spermatogenesis take
70 days
Describe the process of oogenesis
- Germ cell divides by mitosis
- Oogonia undergo the first meiotic division to produce primary oocytes
- Meiotic arrest in prophase of meiosis 1
- At puberty meiosis 1 finishes to produce the secondary oocytes and a polar body
- secondary oocytes enter the second meiotic division at fertilisation
- Production of the ovum and a second polar body
How long may meiotic arrest occur for
12-50 years
Where does spermatogenesis occur
Testes - Sertoli cells
How does testes production/development occur
Development in the abdomen and descent into the scrotum
Describe the anatomy of the testes
Lumen surrounded by Sertoli cells which contain the spermatogonia
What is the function of the Sertoli cells
Spermatogenesis + development
Location of the spermatogonia
Forms the seminiferous tubules
What is the relationship of there Sertoli cells with FSH
Stimulated by FSH to release inhibit which has a negative feedback effect on FSH release
Where are the Leydig cells located
Outside of the seminiferous tubules
What is the function of Leydig cells
Synthesis of testosterone in response to LH to have a -ve feedback effect
Source of testicular androgens. mainly testosterone
Describe the anatomy of the ovaries
Graafian follicle: Ovum granulosa cells Follicular fluid Thecal cells
Follicles that are under different stages of development in the stroma e.g. follicles undergoing atresia
How long does the menstrual cycle take
28 days
When does ovulation occur
Day 14
What are the two cycles occurring during the menstrual cycle
Ovarian and Endometrial
What are the 3 stages of the ovarian cycle
Follicular phase, ovulation, luteal phase
What are the 2 stages of the endometrial cycle
Proliferative phase - oestrogen dominant
secretory phase - progesterone dominant
How does basal body temperature change during menstruation
Slight increase in the second half due to the increase in progesterone
Describe how cholesterol is converted to androstenedione
Cholesterol Pregnenolone Progesterone 17-OH progesteron Androstenedione
What is testosterone and oestrone converted to
dihydrotestosterone
17β-Oestradiol
What can testosterone be converted to
reduction to dihydrotestosterone or aromatisation to oestrogen
What is testosterone bound to in seminiferous fluid
androgen binding globulin (ABG)
How does testosterone travel in the blood
60% - sex hormone binding globulin (SHBG)
38% - albumin
2% - free
What are the actions of androgen
fetus - development of male internal and external genitalia
fetal growth
adult - spermatogenesis
growth and development of male genitalia
protein and bone anabolism
sexual behaviour
pubertal growth spurt
Describe oestrogens
any substance which induces mitosis in the endometrium
e.g. 17β-Oestradiol, oestrone, oestriol
Give the actions of oestrogen
stimulates proliferation in the endometrium to thicken the womb
triggers an LH surge for ovulation
secretions from vagina and cervix
Stimulated growth of the ductile system in the breasts
Decreases sebaceous gland secretion in the skin
Feedback regulation of GnRH
Stimulation of osteoblasts
Metabolic actions
Behavioural effects
Increases salt and water reabsorption
Increases plasma protein synthesis
Influences the release of other hormones e.g. prolactin thyrotrophin
Describe progestogens
Any substance including secretory changes in the endometrium
e.g. progesterone, 17𝛼-hydroxyprogesterone
What are the actions of progestogens
Stimulates secretory activity in the endometrium and cervix
Negative feedback on hypothalamic GnRH
Increase in basal body temperature
Decease in sodium chloride re-absorption in the kidney
Stimulated growth of alveolar system in the breast.
What is the difference between LH and FSH action
LH - stimulates hormones
FSH - stimulates gametes
Describe the process of endocrine control of testicular function
- GnRH is released in pulses every hour, triggering pulses of LH and FSH
- LH stimulated the Leydig cells to synthesise testosterone
- FSH stimulates the Sertoli cells (lining of the seminiferous tubules) to support spermatogenesis
- Testosterone is used in the final stage of spermatogenesis
- Testosterone has a -ve feedback effect on the hypothalamus + adenohypophysis (OH/LH)
Inhibin produced buy the Sertoli cells 4 -ve inhibits LH and FSH
What are the 5 phases of the menstrual cycle
Early follicular phase Early mid follicular phase mid follicular phase late follicular phase luteal phase
When is progesterone produced in the menstrual cycle
second half of the cycle or when pregnant
How is LH and FSH controlled in females
Oestrodiol produces the -ve feedback
Describe what occurs in the early follicular phase
FSH causes the ovaries’ follicles to enlarge/grow
5-10 eggs grow under the influence of FSH
The follicles begin to produce oestradiol (and little progesterone)
Describe what occurs in the early mid follicular phase
LH and FSH remain the same form early follicular phase
More oestradiol as the follicles grow larger
1 egg grows more than the rest (Graafian follicle)
Positive feedback as the increase in oestrogen from the Graafian follicle stimulates the surrounding granulosa cells to grow which in turn allows for increased oestrogen production etc.
Describe what occurs in the mid follicular phase
As the oestrogen levels increase, it causes a -ve feedback effect on the adenohypophysis so LH and FSH levels decrease, causing the other follicles in the ovary die
Describe what occurs in the late follicular phase
High oestrogen levels triggers a +ve feedback (hypothalamus and pituitary) to cause an LH surge
Ovulation as the follicle breaks open and egg moves to the uterus
Describe what occurs in the luteal phase
Once the follicle has broken the corpus luteum is left, which produces progesterone
Progesterone prepares the endometrium for implantation (secretory lining)
No fertilisation with high levels of oestradiol, inhibin and progesterone causes a decline in LH and FSH which leads to menstruation
What is the Graafian follicle
The largest follicle that no longer requires FSH to develop and proliferate
Keeps growing and producing large amounts of E2
What is amenorrhoea and oligomenorrhoea
Amenorrhoea = The absence of menstrual cycles Oligomenorrhoea = infrequent cycles primary = if a women has never had a period secondary = periods that hone stop
What is infertility defined as
The inability to become pregnant after 12 months of unprotected sex
What are the causes of infertility
Pituitary failure
Prolactinoma
Testicular failure e.g. mumps, Klinefelter’s syndrome
Ovarian failure e.g. Turner’s syndrome
Polycystic ovarian syndrome (most common metabolic disorder in women)
Infrequent periods
Hyper-androgenaemia e.g. increased male pattern hair, acne
Polycystic ovaries (increased number of enlarging ovarian follicles)
Describe the blood-testes barrier
Sertoli cells are connected via tight junctions to form a blood-testes barrier
Prevents large molecules from entering the testes
What are thecal cells
Surrounds the ovum in the ovaries
Has LH receptors which allows stimulation of steroidogenesis
Describe the pathway of spermatids through the testes
- Spermatogenesis in the seminiferous tubules
- Spermatids enter the lumen of the tubules and collected in the Rete testis
- Drainage into the Vasa efferentia
- Drainage into the epididymis
- +nutrient secretion to mature and gain motility
- Expelled by the vas deference
