Lecture 39 Flashcards
Spermatozoa pathway - general male system
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
Spermatozoa pathway in testis
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
Tunica albuginea
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
Seminiferous tubules are surrounded by…
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
Sertoli cells
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.
Leydig cells
In bw the cross sec of seminiferous tubules and outside of tubule are interstitial cells called leydig cells. These cells make testosterone
Clonal nature of spermatogenesis
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.
Spermiogenesis vs spermatogenesis
Spermatogenesis: stem cell to spermatozoa
Spermiogenesis: is part of spermatogenesis and goes from early spermatid to spermatozoa
Myoid cells
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.
Spermatogonia
Round nuclei with prominent nucleolus. Always found on basement membrane. Attachment to basement membrane keeps them in undifferentiated state. They divide and multiply
Primary spermatocyte
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)
Early spermatids
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
Late spermatids
Are nuclei that are oddly shaped, dense but still attached to ep. They release cytoplasm.
Spermatozoa
Eventually, spermatozoa are released into lumen and identified by small apple seed dark nucleus and cytoplasmic tail
Blood-testis barrier
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
Sertoli cell functions
- Separate seminiferous tubules into biochemically distinct luminal and abluminal compartments.
- Form Blood/Testis barrier.
- 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. - Provide metabolic support to spermatogenic cells.
- 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 - Phagocytose residual bodies.
Problem with tight junction of Sertoli cells
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.
Spermiogenesis - details
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.
Components of sperm
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
Sperm on oocyte surface
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
Testosterone made by….
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.
Testosterone functions
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
H and E: leydig cells
- store cholesterol in lipid droplets for steroid hormone (testosterone) production
- identified by containment of lipid droplets in cytoplasm
What occurs in leydig cells?
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
