Lecture 8 - The Gonads 1 Flashcards
How do the gonads develop in males and females?
Males - testes Females - ovaries
What differentiates the ovaries from testes in embryogenesis?
The SRY gene on Y chromosome makes gonad develop into testes
When does spermatogenesis begin?
In puberty
When does oogenesis begin?
Reach 6-7 million oogonia at 24 weeks and cells begin deteriorating (atresia) and when puberty is reached 400,000 and by the time menopause is reached, 300-400
What are the functions of the gonads?
Production of gametes - gametogenesis Steroidogenesis - Androgens (MALES, females) and Oestrogens/Progesterones (FEMALES males)
Describe the process of Spermatogenesis:
Germ cell (diploid) > spermatogonia (mitotic, ^ testosterone) > 1ry spermatocytes (1st meiotic) > 2ry spermatocytes (2nd meiotic/HAPLOID) > Spermatids > Spermatozoa
How long does spermatogenesis take?
Around 70 days
How do males retain some spermatogenic capability throughout life?
A pool of spermatogonia remain for subsequent cycles
At what rate is sperm produced?
300-600 sperm/gm in testis/second
Describe the process of oogenesis:
Germ cell (diploid) > Oogonia (mitotic) > 1ry oocyte (1st meiotic) > 2ry oocyte (HAPLOID, 2ry meiotic and takes both cytoplasms, so 1st polar body dies - occurs during ovulation) > Ovum (with 2nd polar body)
What happens to primordial follicles?
They are arrested in development and enter atresia - cell degradation then death
Key features of testes:
Coiled seminiferous tubules - spermatogenesis Rete testis, Vasa efferentia Epididymis - stores sperm and sperm gain motility Vas deferens - surrounded by smooth muscle, propels sperm to urethra and other secretions added
Key features of seminiferous tubules:
Leydig cells - close to ST Sertoli cells - Sperm develop in folds of sertoli cells, where they then move into tubule lumen - connected very tightly leading to blood-testes barrier
What are Sertoli cells?
Form seminiferous tubules Synthesise FSH and androgen receptors (ABG) In response to FSH - INHIBIN produced Associated with developing spermatocytes
What are Leydig cells?
Lie outside ST Synthesise LH receptors In response to LH are the main source of testicular androgens - testosterone (testosterone in testicles is 1000x higher than in blood)
Key features of ovaries:
GRAFFIAN FOLLICLE: Ovum, Follicular fluid, Granulosa cells, Thecal cells
Ovarian stroma
Follicles undergoing atresia
Remnants of last corpus luteum
What is the precursor molecules to steroids?
Cholesterol
How do we differentiate between which steroid produced?
Different enzymes present in each target tissue
How is Dihydrotestosterone formed?
Chol > preg > prog > 17 OH prog > androstenedione > testosterone > DHT
How is 17 beta oestradiol formed?
Chol > preg > prog > 17 OH prog > androstenedione > EITHER a) testosterone > oestrone > 17BO OR b) Oestrone > 17BO
How long does the menstrual cycle last?
Between 20-35 days, usually 28
When does MC begin?
On first day of menstruation
What is menstruation?
Loss of blood and cellular debris from necrotic uterine epithelium
When does ovulation occur?
Around day 14
What does the menstrual cycle consist of?
Ovarian cycle and Endometrial cycle
What is the process of the menstrual cycle?
Follicular phase (OC) > 17BO > Proliferative phase (EC) (thickening of endometrium) & Ovulation (OC) > Luteal phase (OC) > Prog (stimulates secreation of hormones) and 17BO > Secretory phase (EC)
When does 17BO secretion begin?
When follicles increase in growth and when dominant follicle secretes ^ oestrogen levels - maintaining it for 36 hrs where -ve feedback turns to +ve feedback, surging LH and FSH causing ovulation
What is the ovarian cycle?
Pre-antral follicle > Early antral follicle > late antral follicle > Graffian follicle > OVULATION + LUTEAL PHASE (release of ovum and corpus luteum)
How is the ovum chosen?
They’re selected sporadically for development and the most highly developed can then survive on its own, so the others undergo atresia
What hormones are produced during the ovarian cycle by the follicle?
The late antral follicle produces 17BO in granulosa cells from androgens (contain aromatase) FSH and LH are secreted to the follicle Thecal cells have LH receptors and synthesise androgens from LH, which then diffuse to granulosa cells
What hormones are produced during ovarian cycle by the corpus luteum?
Androgens converted into 17BO and progesterone under LH and FSH influence
What is the dominant hormone in the proliferative phase?
Oestrogen
What happens to the endometrium during the early and late phase of the proliferative phase?
Early: thin Late: thickens - mitosis
What happens to the glands during early and late phases of proliferative phase?
Early: Straight Late: Enlarge, coil, increased blood supply to endomentrium
What happens to endometrium and glands during secretory phase?
Endom: becomes secretory Glands: secrete glycogen, mucopolysaccharides; mucosa engorged with blood
What is the dominant hormone in the secretory phase?
Progesterone (small oestrogen influence)
What days correspond to each part of the cycle?
1-5 = Menstruation 6-14 = Proliferative phase 14-15 = Ovulation 15-28 = Secretory phase
