Origin of the Gametes Flashcards
What are the starting cells in the process of spermatogenesis? Where are they found?
Spermatogonia - the stem cells of spermatogensis. Found in the seminiferous tubules
Maintained by mitosis
What is produced from the stem cells and what happens to them?
A1 spermatogonia which divide a fixed number of times by mitosis to form clone cells. These are the primary spermatocytes.
What do the primary spermatocytes look like?
They are linked by a bridge of cytoplasm
When does meiosis begin?
In the primary spermatocytes. Each one produces four haploid spermatids, moving towards the lumen as this happens.
What happens to the spermatids?
Released and remodel as they pass down the tubule through the rete testis, ducti efferentes and epididymis to form spermatozoa.
How many spermatids does each A1 spermatogonium produce?
256
What role do the Sertoli cells have?
Produce fluid which washes sperm down the rete testis.
How long does spermatogenesis take?
About 70 days
What is the spermatogenic wave of production?
Different parts of the seminiferous tubule begin spermatogensis at different times so production is continuous
How much ejaculate is released typically and how many sperm will be in there?
3.5 ml
350 million sperm
What is the spermatogenic cycle?
Development of the A1 spermatogonia to 256 sperm. So the amount of time taken for reappearance of the same stage of the cycle within a given segment of the tubule.
Where are sperm stored and matured?
Epididymis
What do the seminal vesicles produce?
Thick alkaline fluid rich in fructose and a coagulating agent. Forms 60% of the volume of semen.
Where does the duct of the seminal gland go?
Joins the vas deferens to form the ejaculatory duct
What percentage of the volume of semen do secretions from the prostate make up?
20%
Where are the bulbourethral glands found?
Posterolateral to the intermediate part of the urethra, embedded in the external urethral sphincter.
Where do the ducts of the bulbourethral glands open into?
Proximal part of the spongy urethra
When do female gametes start being produced?
During fetal development
How do female gametes begin development?
Germ cells colonise the gonadal cortex and become oogonia. Oogonia proliferate rapidly by mitosis.
What happens to the 7 million oogonia produced?
Most die during gestation.
Remaining 2 million enter meiosis before birth. Entry to meiosis is stimulated by surrounding cells.
Meiosis stops at an early stage and a primary oocyte is formed
What surrounds the primary oocyte?
Single layer of granulosa cells to form the primordial follicle.
When does the primordial follicle develop further?
From puberty onwards. Most die but each month one or two complete development.
After ovulation, how long is the female fertile for?
About 36 hours
What happens after ovulation?
Period of waiting.
If fertilised, conceptus is initially too small to signal its presence. Further production of gametes is suspended until pregnancy can be confirmed by secretion of placental hormone.
When does the menstrual cycle begin?
On the first day of bleeding
When does ovulation occur
Day 12-14
Which days is the preparation phase?
0-12
aka follicular/proliferative phase
Which days is the waiting phase?
14-28
Aka luteal/secretory phase
How is the ovum produced?
At start of cycle, small no. of gametes that have already started development develop further.
Primordial follicles develop to pre-antral follicles - independent of hormones
What is in pre-antral follicles?
Zona pellucida
Granulosa cell layers
Theca interna and externa
An antrum also develops (fluid-filled space)
How does ovulation occur?
LH and FSH cause half of follicles to grow to 20mm
Theca secretes increasing amount of oestrogen
LH surge triggers rupture of follicle to release ovum
What happens just before ovulation?
Meiosis restarts
Second division isn’t until after fertilisation
What happens to the follicle after ovulation?
Re-organises to form a corpus luteum.
This grows under influence of LH.
Secretes oestrogen and progesterone.
Dies after 14 days.
