(16) Male - spermatogenesis

Question 1

(Male Reproductive Physiology)

The Testes consist of….

1. seminiferous tubules… where what happens?
2. Interstitial tissue, located where?

contain which cell resposible for testosterone prduction?

3. Sperm transport duct system

consits of what three parts?

Answer 1

1. sperm is made ((~85% of total volume in ruminants, 72% horse, 65% boar))
2. between tubules

(blood vessels, nerves, lymphatics, macrophages and mast cells)

Leydig cells

23. straight tubules, rete testis, efferent ducts

Question 2

(Seminiferous Tubules)

(~ 3000 meters/testis in ram; stallion: 2 years ~2,000 meters/testis, 15 years ~2,800)

1. Convoluted, hollow, fluid filled, tubes open at both ends - empty into what?
2. penetrated by blood vessels or lymphatics?
3. Basement membrane with myoid cells around outside - what move fluid and sperm?
4. inside tubule: what makes us seminiferous epithelium?

Answer 2

1. rete testis
2. no
3. peristaltic contractions
4. sertoli cells and germ cells

Question 3

(Semniferous Epithelium = Sertoli cells and germ cells)

1. Germ cells at various stages of development occupy all levels of the epithelium,

least differentiated where?

most differentiated where?

2. Individual Sertoli cells extend from the basement membrane to the lumen. They totally surround and serve to do what?
3. While the germ cells divide and become more differentiated, they are moved gradually away from the basement membrane towards the lumen of the tubule (and apex of the Sertoli cell) as new generations commence development below them. The germ cells (within the same stage/generation) develop as a clone, all joined together by intercellular bridges. This keeps them developing synchronously.

Answer 3

1. at basement membrane (spermatogonia)

near the lumen (spermatids) (into which sperm will be released as they finish development.)

2. nurture the developing germ cells

Question 4

(Formation of Sperm)

Spermatogenesis is the process that results in formation of a highly specialized cell, the spermatozoa.

1-3. It consists of what three stages?

These 3 stages are associated with differently named intermediate cell types

1. Proliferaion -
2. meiosis -
3. differentiation -

Answer 4

1. cell proliferation (mitosis)
2. meiosis with chromosome duplication –> genetic recombination by crossing over –> meiotic reduction divisions –> haploid spermatids
3. terminal differentiation of spermatids to spermatozoa
4. spermatogonia
5. spermatocytes
6. spermatids

Question 5

(Proliferation: Mitosis)

1. The germ cells adjacent the basement membrane are termed what?
2. The most primitive of these can divide without limits, but they only undergo division when?
3. When one of these cells divides one of the daughter cells stays on the basement membrane to do what?
4. The other daughter cell becomes committed to spermatogetic pathway - once it does this the course is irreversible. This cell continues to divide by mitosis and all of the resulting cells in each generation remain linked - thus allowing what?
5. Usually they will go through several divisions multiplying their numbers each time (A1-A4) before becoming a type B spermatogonia - which is what?

Answer 5

1. type A spermatogonia
2. when signalled to do so (remain dormant between signals)
3. keep renewing (replacing) the resting reserve
4. so they communicate and keep dividing synchronously
5. the last one that divides by mitosis to produce the pre-leptotene spermatocyte and entry to meiosis

Question 6

(Proliferation: Mitosis) cont

1. Once cells in this “clone” enter meiosis, the resting spermatogonia on the basement membrane is signaled to do what?
2. This new clone pushes the cells of the previous clone closer to the lumen
3. This precise interval of division gives a timed repeat of different cell type associations as you go from basement membrane to lumen - every time you have an A2 spermatogonia next to the basement then you will have cell types w,x,y,z, above it in order, and whenever you have an A3 spermatogonia then above it you will have l,m,n,o and so on. This orderly entry into division and steady clonal progression gives what is called the what?
4. To complete the cycle (from A2,w,x,y,z to the next A2,w,x,y,z cell association at the same location of the seminiferous epithelium) takes how long
5. And depending on species it will take how many of these cycles to be relased as sperm?

Answer 6

1. divide by mitosis and the process starts again
2. spermatogenic cycle (a timed repeat of cell associations)
3. a specific number of days
4. 4-5

Question 7

(Meiosis)

1. Each 2N primary spermatocyte undergoes meiosis at the end of which it will have generated what?
2. The first meiosis is long and results in what?
3. The second meiosis is quicker giving what?

Answer 7

1. 4 haploid spermatids
2. th 1N2C secondary spermatocyte
3. haploid spermatid (that still looks fairly much like a regular cell)

Question 8

(Differentiation)

1. where the newly formed haploid round spermatid undergoes dramatic cellular changes to form what?
2. what happens to nuclues?

chromatin?

3. The Golgi apparatus produces small granules that do what?
4. The pair of centrioles migrate to the nucleus (opposite pole to the acrosome) and bind to it, while at the same time forming the what?
5. Mitochondria migrate to the proximal part of the developing tail, line-up and later condense and form the what?
6. The spermatid loses large amounts of its cytoplasm during this stage. This forms the what?

Answer 8

1. the spermatozoa
2. elongates

condenses

(Final nucleus shape is species specific and largely determines the shape of the sperm head)

3. coalesce to form a large acrosomic vesicle that moves over the nucleus to form the acrosome (full of enzymes that have a role in fertilization)
4. axoneme (which rapidly elongates to form the core of the tail)

Other cytoskeletal elements migrate to the tail to give the characteristic structure

5. spiral pattern of the midpiece region.(help provide energy for sperm motility)
6. residual body (which is phagocytosed by the Sertoli cell)

(The developing spermatid is tethered to its residual body by cytoplasmic stalks attached to its neck region.)

Question 9

(Release of Spermatids - Spermiation)

1. The release of the spermatid from its tether is known as what?

the released cell is now a what?

The remnant of cytoplasm where it was attached is located in the mid-piece region and is known as the what?

Answer 9

1. spermiation

spermatozoa

cyctoplasmic droplet

Question 10

(How Many Sperm Are produced?)

The combined production (completed sperm) from the two testicles of an adult stallion during the breeding season is estimated at 70,000 per second. For an adult human the figure is approximately 200 million/day, or 2,300 per second. This represents only a fraction of the theoretical production potential. Since you may have 5 or 6 rounds of mitotic division (25: 1 cell becomes 32) and then each of these forms 4 haploid cells at meiosis, you could wind up with 128 sperm from each division of the a single resting spermatogonia. In reality many are lost along the way to apoptosis and this loss occurs at all stages of development.

1-2. Apoptosis has two functions - what are they?

How many germ cells a single Sertoli cell can support at one time probably varies with species (and other factors like season for seasonal breeders), but figures of approximately 30 are bandied about (this is the combined total of germ cells at all stages).

3. the bulk of loss apparently occurs when?
4. check points exist at what level?

Answer 10

1. keeping the number of germ cells to a number Sertoli cell can support
2. removal of defective sperm
3. during mitosis (75% lost)
4. spermatocyte level (to remove cells that have undergone faulty meiosis;)

and during differentation of spermatids

Question 11

(Functions of the Seroli cell)

1-3. what three functions?

4. they secrete controlling factors that regulate what?
5. The maximum number of germ cells that can be supported by each Sertoli cell is fixed for each species as is the number of Sertoli cells per testis, but the latter is highly heritable.
6. Produce androgen-binding protein that is secreted into the lumen of the seminiferous tubule where it binds what?
7. They form the tight junctions that form what?

they are the major source of what?

Answer 11

1. organize the clones of germ cells in the seminiferous epithelium
2. support the cells
3. ensure their timely release as spermatozoa
4. germ cell differentiation and maturation and phagcytose degnerating cells
5. androgens (trapping them for local and downstream use (eg epididymis) - This complex may be important in regulating epididymal function.
6. the blood-testis barrier

estrogen in males

Question 12

(Hypothalamo-pituitary testicular axis)

1. Hypothalamic GnRH releases LH and FSH from the anterior pituitary.
2. LH acts on leydig cells to do what?
3. FSH acts on Sertolli cells and does what?

also promotes conversion of testosterone to what in Sertoli cells?

Answer 12

2. increase testosterone synthesis and secretion

(Some species, e.g. stallions, actually produce more estrogens then testosterone (unlike their female counterpart the theca cell, Leydig cells can also produce estrogen).

3. stimulates them in their supporting role for the developing germ cells, promotes seminiferous tubule growth, and androgen-binding protein (ABP) production by Sertoli cells

estradiol (role unknown)

Question 13

(Hypothalamo-pituitary testicular axis) cont

1. Testosterone secretion has a basal component on which is imposed additional pulses in response to what?
2. In Sertoli cells testosterone is also converted to what?

Both T and DHT can bind to ABP which serves to do what?

3. Testosterone and estradiol feedback on the hypothalamus to do what to GnRH secretion?
4. Testicular inhibin acts directly at the level of the pituitary to do what?

Answer 13

1. pulses of LH (thus levels vary throughout the day)
2. dihydrotestosterone (DHT)

maintain high levels of these hormones in the seminiferous tubule

3. reduce
4. reduce FSH secretion

Question 14

(Hormonal Control of Spermatogenesis)

1. Testosterone levels in the testicular interstitial fluid and the seminiferous tubule are far higher than in peripheral blood (25-30 fold higher).
2. High levels of testosterone are required in the testicle (at least 10 fold greater than peripheral blood) for what?
3. What cells are particularly vulnerable to low testosterone?
4. It appears that testosterone works through its action on what?

appears to be a synergistic role for what in this process?

In the absence of this binding the developing germ cells do what?

Answer 14

2. normal spermatogenesis
3. Cells at the pachytene spermatocyte and early spermatid stages
4. Sertoli cells - by maintaining binding of the Sertoli cell to these developing sperm cell stages

FSH

DIE

Question 15

(Hormonal Control of Spermatogenesis)

(cont)

1. What is required for the initiation of spermatogenesis at puberty?
2. It appears that FSH is able to maintain spermatogenesis by doing what?

but can’t do what?

3. FSH and testosterone also prevent apoptosis

Answer 15

1. FSH

(Whether it is required for continued spermatogenesis after this if testosterone levels are normal is under debate)

(It is required if testosterone levels drop, but if they drop too far FSH can’t do it alone)

2. increasing the number of spermatogonia and promoting maturation through meiosis to the round spermatid stage

take them beyond this point alone (i.e. can’t do spermiogenesis). Testosterone is required to complete this process.

Question 16

(Blood Testis barrier)

1. Fluid within the seminiferous tubules and rete testis is vastly different to blood plasma or interstitial fluid.
2. the more developed spermatozoa express protein antigens that the immune system does not recognize as self (because these advanced sperm stages are first produced after puberty).
3. To maintain these fluid differences and the immune compartmentalization, there is the blood- testis barrier
4. It is formed by what?

divide seminiferous epithelium into what?

5. As germ cells divide and enter meiosis on their pathway to becoming sperm, they progressively move away from the basement membrane towards the lumen of the tubule. Stages up to preleptotene spermatocyctes are in what compartment?

stages from pachytene spermatocytes on to spermatids and spermatozoa are in?

6. Leptotene spermatocytes pass through the tight junction barrier, somewhat like a boat going through a lock - new junctions form on their basal side and then those on the luminal side open up.
7. the barrier blocks antibodies - so what plays macrophage role?

Answer 16

4. tight junctions between adjacent Sertoli cells

basal and adluminal compartments

5. the basal compartment

the adluminal compartment

7. Sertolli cells

Question 17

(Testicular temperature control)

1. need to keep balls cool in most species
2. several other features keep them cool other than location
3. the scrotal skin is free of what?
4. abundant what?
5. what smooth muscle can raise/lower the skin of scrotum to alter temp?
6. what can raise and lower the testicle quickly for sudden variations?
7. The arterial supply and vascular drainage of the testicle form a counter-current heat exchange system. The artery is very coiled after leaving the body, while the veins form a plexus (pampiniform plexus) of interconnected vessels. The relatively cool blood returning from the scrotum is used to cool the blood in the artery prior to it entering the testicle

Answer 17

3. hair (or sparse)
4. sweat glands
5. tunica dartos
6. cremaster muscles (significance of this in temp control is questionable)

Question 18

(effect of elevated temp on spermatogenesis)

1. All cells in semi epi are hurt by heat.

most sensitive?

2. what are more resistance - how do we know?
3. receovery depends on severity
4. Sperm already in the epididymis are fairly resistant to heat damage and these are the ones that appear in the ejaculate for the first week or so following the thermal insult - so initially you may see no adverse effect.
5. However after this, stages that were spermatids and subsequently those that were spermatocytes during the heating episode will be ejaculated and the deleterious effects will be obvious. If it was a relatively minor insult you might have to wait till the cells that were early spermatocytes at the time of heating appear in the ejaculate, a month after the incident.
6. By the same reasoning: in severe damage it may take the entire duration of spermatogenesis plus epididymal transit time to see healthy sperm in the ejaculate again.

Answer 18

1. spermatocytes and early round spermatids

(Other germ cell stages are also affected as are Sertoli cells, which may remain in the seminiferous epithelium but become dysfunctional.)

2. Leydig (keep secreting testosterone)