Lecture 39

Question 1

Spermatozoa pathway - general male system

Answer 1

Spermatozoa mature and stored in epidiymis. During ejaculation, it travels through vas deferens and enters urethra.

On the way, there are seminal vesicle, prostate gland, bulbourethral gland that produce seminal fluid that is important for spermatozoa function, also producing a medium for ejaculation

Question 2

Spermatozoa pathway in testis

Answer 2

Seminiferous (carrying spermatozoa) tubules are U-shaped, highly coiled, that has both openings towards one side of the testis called rete testis.
- Spermatozoa are made in seminiferous tubules and travel to rete testis

The testis are divided into several lobes and lobules, up to 300 of them, that are separated by CT. Each lobule has up to 4 of
these U shaped coiled seminiferous tubules. all of them open up into a passageway of rete testis.

Rete testis then feed the spermatozoa into several tubules called ductuli efferentes or efferent ductules that then merge into 1 highly coiled long tube called epididymis (divided into head and body portion). Spermatozoa are held here until ejaculation

Every second, 1500 spermatozoa are made. several millions made a day. We need a high ep surface where the spermatozoa production takes place

Question 3

Tunica albuginea

Answer 3

The testis is enclosed by a dense connective tissue capsule (Tunica Albuginea) and contains 250-300 lobules with one to four seminiferous tubules each.

Tunica albuginea is white covering irl around seminiferous tubules

Question 4

Seminiferous tubules are surrounded by…

Answer 4

Each tubule has layer of CT, there are contractile myoid cells here. These tubules are separated by interstitial tissue. There is CT but also some hormone-producing cells called leydig cells that make testosterone

Question 5

Sertoli cells

Answer 5

Sertoli cells are connected to one another by
cellular processes. These are ep cells that reach from basement membrane to the apical surface that encircles the lumen

Distinguished by their oval nucleus. Usually the largest nuclei that are not round. Sertoli cells have large nucleolus, which indicates protein production.

Question 6

Leydig cells

Answer 6

In bw the cross sec of seminiferous tubules and outside of tubule are interstitial cells called leydig cells. These cells make testosterone

Question 7

Clonal nature of spermatogenesis

Answer 7

Stem cells migrate from yolk sac into seminiferous tubule during development, then sit on basement membrane. Stem cells are called spermatogonia. Type A spermatogonia become type B spermatogonia, they undergo mitosis

Type B spermatogonia divide to become primary spermatocytes, which do not reside on basement membrane, they are pushed towards lumen. Primary spermatocytes undergo meiosis I. Primary spermatocytes become secondary spermatocyte, which does meiosis II.

Meiosis I and II are the last step of cell division within spermatogenesis. The resulting cells are early spermatids. Then there are late spermatids. Spermatids undergo transformation to form spermatozoa. No cell division any further

Type B cells are connected by cytoplasmic bridge. The clones that develop from stem cells remain connected throughout until the
spermatozoa are released into the lumen. Which means there are sets of cells being clonally expanded and always communicate with each other due to cytoplasmic connection.

Question 8

Spermiogenesis vs spermatogenesis

Answer 8

Spermatogenesis: stem cell to spermatozoa

Spermiogenesis: is part of spermatogenesis and goes from early spermatid to spermatozoa

Question 9

Myoid cells

Answer 9

Next to basement membrane are myoid cells on CT side bc they are contractile and are CT cells that have fibroblast-like origin and can
contract and squeeze ep to release spermatozoa into the lumen.

Question 10

Spermatogonia

Answer 10

Round nuclei with prominent nucleolus. Always found on basement membrane. Attachment to basement membrane keeps them in undifferentiated state. They divide and multiply

Question 11

Primary spermatocyte

Answer 11

No well defined nuclear envelope, all you
see are wiggly chromosomes. This is the first meiotic division. They divide into secondary spermatocytes (cant identify them bc short
lived)

Question 12

Early spermatids

Answer 12

All other round nuclei close to lumen of tubule. If you have round homogenous nuclei, the color of nuclei is homogenous
and smaller than primary spermatocytes

Undergo transformation to get rid of cytoplasm (most of it). The nucleus will condense to be smaller to form late spermatids

Question 13

Late spermatids

Answer 13

Are nuclei that are oddly shaped, dense but still attached to ep. They release cytoplasm.

Question 14

Spermatozoa

Answer 14

Eventually, spermatozoa are released into lumen and identified by small apple seed dark nucleus and cytoplasmic tail

Question 15

Blood-testis barrier

Answer 15

Sertoli cells form a layer. It is a platform of
cellular processes where the cells form tight junctions.

Basal compartment at bottom and apical
compartment at the top are separated by blood-testis barrier. The 2 compartments are biochemically diff in hormones, cytokines and
mediators. Most of spermatogenesis is in apical compartment.

Cells that are destined to be spermatozoa need to transfer from basal compartment to apical compartment and cross the blood-testis barrier

Capillaries surround tubules and our blood has lots of antibodies. During spermatogenesis, the spermatozoa will get new genetic material and they need to be protected from our immune system. We dont want our antibodies to attack genetically diff cells, so this is why we have blood testis barrier

Question 16

Sertoli cell functions

Answer 16

1. Separate seminiferous tubules into biochemically distinct luminal and abluminal compartments.
2. Form Blood/Testis barrier.
3. Secrete fluid containing Androgen Binding Protein (ABP) enriching testosterone in tubular fluid.
   - ABP sequesters testosterone. Need high conc of testosterone in tubules and also
   in the remainder of the male reproductive tract.
   - ABP binds testosterone and delivers that throughout male reproductive tract and this is made by sertoli cells.
   - This is delivered in a tubular fluid that contains testosterone, ABP and spermatozoa.
4. Provide metabolic support to spermatogenic cells.
5. Facilitate translocation of spermatogenic cells toward the lumen of seminiferous tubules.
   - there are cytoplasmic structures that contain a lot of proteins that bind to the spermatogenic cells and providing a
   transport system, and this includes microtubules and motor proteins
6. Phagocytose residual bodies.

Question 17

Problem with tight junction of Sertoli cells

Answer 17

Sertoli cells form cellular processes that make a gate composed of tight junction

Basal compartment keeps the spermatogonia in a diff biochemical or
molecular location compared to spermatocytes. The luminal compartment
facilitates differentiation of spermatocytes into spermatozoa

Sertoli cells form claudin 11- containing tight junctions that keep early spermatocytes away from the luminal (upper) compartment.

As spermatogonium divides, how does it push the progeny cell (primary
spermatocyte) into other compartment without compromising the junction?
- answer: the cell makes new tight junction under the spermatocytes and the new
junction has claudin 3.

Question 18

Spermiogenesis - details

Answer 18

Flagellum arise from microtubules generated by the centrioles. Surrounding the base of flagellum, mitochondria
accumulate and make spiral arrangement close to the nucleus of the flagellum. These mitochondria will provide ATP and energy for the movement of the flagella.

Golgi apparatus moves opposite to where flagellum develops and makes cap-like structure over nucleus and is called acrosomal vesicle

• all golgi membranes fuse to make vesicle and golgi apparatus is involved in cells in secretory processes.
• this acrosomal vesicle, later called acrosome, contains hydrolytic enzymes that are important in the fertilization process of oocytes.

Question 19

Components of sperm

Answer 19

After getting rid of extra cytoplasm called residual body (phagocytosed by sertoli cells), we have spermatozoa that have…

• head with nucleus, highly condensed chromatin
• acrosome
• middle piece with mitochondria
• principal piece with microtubules of
  the flagellum
• end piece is a bit of cytoplasm that lacks
  microtubules

Question 20

Sperm on oocyte surface

Answer 20

As spermatozoa matures and find themselves within the reproductive tract, their job is to deliver genetic info within the
nucleus to the oocyte

There are receptors that bind to molecules on oocyte surface. This binding triggers an acrosome reaction where the enzymes within the acrosome are released, which ensures that the protective coating of the oocyte is dissolved. Allowing fusion of the
membrane of spermatozoa with the PM of oocyte, and the nucleus can enter the oocyte

Question 21

Testosterone made by….

Answer 21

Steroid hormone made by leydig cells

Not much leydig cells, they are in the intersitium. They secrete testosterone to capillaries, but also towards seminiferous tubules.

Testosterone binds to ABP and takes part in process of spermatogenesis

Leydig cells make 18000 testosterone per second

• in males, this is the main source of androgens
• second source of androgens, also in females, is zona reticularis of adrenal cortex.

Question 22

Testosterone functions

Answer 22

Promotes spermatogenesis and sperm life
- involved in spermatozoa production in seminiferous tubules

In circulation, reaches other structures too. Not just male reproductive system

Maintains accessory organs:
epididymis, vas deferens, ejaculatory ducts, seminal vesicle, urethra, prostate gland, bulbourethral glands, and seminal vesicles

Secondary sexual characteristics
•Muscle growth
•Libido

Feedback to Pituitary and Hypothalamus

• controlled by feedback mechanism by pituitary gland and via hypothalamus
• hypothalamus contains a nuclei that makes gonadotropin releasing hormone
• gonadotropins affect cells in anterior pituitary gland to make FSH and LH

Question 23

H and E: leydig cells

Answer 23

• store cholesterol in lipid droplets for steroid hormone (testosterone) production
• identified by containment of lipid droplets in cytoplasm

Question 24

What occurs in leydig cells?

Answer 24

Mitochondria and smooth ER are the main cytoplasmic components involved in steroid hormone production. It depends on cholesterol that is stored in cytoplasm in lipid droplets

Prolactin induces LH receptor expression. LH is the main pitutiary gland regulator that induces testosterone production by leydig cells
- Testosterone feeds back to hypothalamus to downregulate GNRH production
- Level of testosterone is regulated by LH and GNRH by pituitary gland and hypothalamus
- GNRH from hypothalamus also induces FSH production by anterior pitutiary gland. FSH binds to receptors on sertoli cells, making ABP
- ABP and testosterone form a complex that then travels through male reproductive
tract and ensures that testosterone is present in all diff regions
- feedback loop

Cholesterol needs to be transported into michondria to start testosterone production process. So there are other proteins involved. Steroidergenic regulatory proteins. Steroidergenic acute regulatory proteins.

Cholesterol to pregnenolone to progesterone to androstenedione to testosterone