histology: male reproductive system

this unit looks at the male reproductive system, focusing on spermiogenesis and the tubular architecture out to the penis. spermiogenesis occurs in the seminiferous tubules of the testis, which are covered on the outside by the tunica vaginalis layer, which is an invagination of the parietal peritoneum, followed by a thick CT tunica albuginea layer which sends CT partitions inwards, dividing the testis into lobes with 1-4 seminiferous tubules each. inside the seminiferous tubules, which are approximately 200um in diameter and 50cm long (but highly convoluted), spermiogenesis begins: type a spermatogonia are the undifferentiated stem cells that reside near the edges of the seminiferous tubules and provide a reserve of potential sperm cells. type b spermatogonia are the cells that have begun differentiating into spermatocytes. spermatocytes begin the process of meoisis, whereby the cell divides into two and halves its chromosomes-- primary spermatocytes are "4N" and secondary spermatocytes are "quasi 2N" that have undergone the first meotic division. spermatids are spermatocytes that have completed meoitic division and are now ready for morphological differentiation. spermatozoans are completed sperm cells that have been morphologically differentiated for swimming and fertilization. thus the order is type a spermatogonia => type b spermatogonia => primary spermatocyte => secondary spermatocyte => spermatid => spermatozoan.

the spermatozoans then swim out of the seminiferous tubules into a series of converging tubules out of the testis into the ductus epididymus, which is a singularly convoluted tubule (50 meters long scrunched up into 50cm) which serves as a maturation and storage site for the spermatozoans, as well as absorbing any excess fluids from spermiogenesis. it then flows upwards through a tube called the ductus deferens, which is straight and has a much thicker muscularis layer (inner longitudinal, middle circular, outer longitudinal) which is responsible for the peristaltic waves during ejaculation. after passing through the prostatic region, the ductus deferens changes into the urethra, which is a common pathway for the urinary and reproductive tract. it is housed in the corpus spongiosum on the dorsal side of the penis, which is one of the three fibroelastic erectile tissues- the other two being two columns of corpus cavernosum on the ventral side. as the urethra goes from the prostatic region to the tip of the penis, it undergoes epithelial transitions from transitional to stratified columnar to stratified squamous.

questions
1. how long does spermatogenesis take to complete and how many sperm are produced per day?
2. where does spermatogenesis take place?
3. what is the testis covered by?
4. describe the rough dimensions of a seminiferous tubule.

5. what are spermatogonia? what are type a and type b spermatogonia?
6. what are spermatocytes? what are primary and secondary spermatocytes?
7. what are spermatids?
8. what are spermatozoans?

9. what are Leydig's cells?
10. what is the ductus epididymis? what is its function?
11. what are the layers of the ductus epididymus?
12. what is the ductus deferens?
13. what are the layers of the ductus deferens?
14. what are the accessory glands?

15. what is erectile tissue?
16. what are the three columns of erectile tissue in the penis?
17. describe the epithelial transitions in the urethra.

answers
1. 75 days, 200,000 sperm produced per day
2. in the stratified cuboidal epithelium of the seminiferous tubules in the testis.
3. tough CT layer called tunica albuginea which sends partitions inwards to form lobules, and a tunica vaginalis on the outside, which is an invagination of the parietal peritoneum.
4. 200um diameter pipe, about 50cm long

5. reserve cells that pool along the back of the seminiferous tubules. type a are stem cells that maintain the stock and type b differentiate into spermatocytes.
6. spermatocytes are spermatogonia that have begun meiotic division, moving towards the lumen of the tubule as they divide. primary spermatocytes are 4N and secondary spermatocytes are quasi-2N cells that have undergone the first meiotic division.
7. spermatids are haploid (2N) cells and are ready to morphologically differentiate.
8. spermatozoans are sperm cells that have completed spermiogenesis and is now specialized morphologically for swimming and fertilization.

9. special endocrine cells within the between the seminiferous tubules that secrete testosterone, promoting spermatogenesis and secondary sex characteristics.
10. the long convoluted duct that leads out of the testis and serves as a maturation / storage site for spermatozoa, and absorbs excess fluids from spermatogenesis.
11. the layers are: PSCC, thin CT lamina propria, muscularis, serosa.
12. the thick, muscular tube leading from the epididymus back to the body which is responsible for the peristaltic waves during ejaculation.
13. PSCC, lamina propria (thin CT, rich in elastic fibers), thick and well developed muscularis (with inner longitudinal, middle circular, outer longitudinal layers), and adventitia.
14. glands that promote sperm survival and transport by adding "seminal fluids", such as the seminal vescicle and prostate.

15. fibroelastic CT mixed with endothelially lined spaces that can accumulate blood.
16. 2 dorsal columns of corpus cavernosum and 1 ventral column of corpus spongiosum.
17. in the prostatic area there is a change from transitional epithelium to stratified columnar, and near tip of the penis another change to stratified squamous.