Mrs. Ofelia Solano SaludarDepartment of Natural Sciences

University of St. La Salle

Male genital tract is designed to: produce, store, and release sperm as required, add fluid and regulatory

components to sperm. Recent scientific evidence indicates that the foreskin contains receptors for the HIV virus,

thus making uncircumcised males more susceptible to developing AIDS. The cells from the foreskin have also proven to be very valuable for study on cell function in

humans.

HISTOLOGY OF THE TESTIS

Male Hypothalamus (Hypothalamic releasing factors)

Hypophysis

FSH LH (ICSH)- released in pulses of 90 min. intervals at night

Sertoli cells Leydig cells

Inhibin (inhibits HH axis) Testosterone Estrogen Prostate, seminal vesicle, Leydig-stimulatory factor epididymis, ductusAndrogen-binding proteins deferens, penis,scrotum

secondary sexual characteristics

Germ Cells

MALE REPRODUCTIVE

ENDOCRINOLOGY

Model of FSH and LH action on Sertoli and Leydig cellsFSH stimulates:

cAMP-mediated production of ABP

transport of testosterone into semineferous tubules and epididymis for sperm maturation.

conversion of testosterone to DHT in Sertoli.

inhibin secretion by Sertoli cells, to inhibit further FSH secretion.

LH increases cAMP and stimulates steroidogenesis in Leydig cells. FSH

acts synergistically with LH on Leydig cells.

http://highered.mcgraw-hill.com/olc/dl/120112/anim0043.swf

1. Mitotic multiplication

• At birth, germ cells are recognized in sex cords of human testis as pale cells surrounded by Sertoli cells.

• Before puberty, sex cords acquire a lumen and become seminiferous tubules.

• At puberty, PGCs known as spermatogonia synthesize BMP8B. Mice lacking BMP8B do not initiate spermatogenesis at puberty.

• They become subdivided into Type A (mitotic stem-cell), & type B (sperm-producing cells or preleptotene spermatocytes) spermatogonia.

2. Meiosis• One type B cell

commits to become 10 spermatocyte (1st division, several weeks); 20 spermatocyte (2nd division, 8 hrs.); spermatids.

• This maturation cycle is completed in humans in approximately 65 days.

Protamine mRNAs are synthesized, but are translated only at the spermatid stage resulting to condensation of chromosomes;

If this takes place earlier, sterility results.

Cells are connected to each other by intercellular bridges of cytoplasm (bodies of Regnaud) which facilitates synchronous division and differentiation of sperm-producing cells.

The spermatogenic germ cells are bound to the Sertoli cells by N-cadherin molecules on both cell surfaces and by galactosyltransferase molecules on the spermatogenic cells that bind a carbohydrate receptor on the Sertoli cells. As such, these cells have numerous functions:

1.They nourish and protect the developing sperm cells, and spermatogenesis occurs in the recesses of the Sertoli cells.2.Synchronize and regulate the events of spermatogenesis

3.Secrete critical proteins (e.g., growth factors, androgen-binding protein, inhibin) that are important for testes function and spermatogenesis

4.Secretion of tubule fluid

Phagocytosis of residual bodies so cellular constituents can be recycled.

Control release of sperm cells. Processes of adjacent Sertoli cells are connected via tight

junctions, forming the immunological blood-testis barrier (autoimmune infertility results if this barrier is broken down).

3.Spermiogenesis (spermatid metamorphosis)

a. Formation of the acrosome Derived from Golgi bodies; acrosomal

granule which contains enzymes to dissolve egg envelopes during fertilization enlarges and acrosomal cap forms from walls of vacuole

In other animals, acrosomal cone forms rudiment of acrosomal filament.

As acrosomal cap forms, nucleus rotates to face basal membrane of tubule.

b.Condensation of the nucleus

• Loss of water and other nuclear structures except condensed chromatin

• Head may present varied shapes: ovoid and flattened from sides (man), with pointed tip (rodents), corkscrew (birds), round (molluscs)

• About 10% of sperms are abnormal with defective heads or tails, and variability in head size; greater than 20% may result to reduced fertility.

http://www.pennmedicine.org/encyclopedia/em_DisplayAnimation.aspx?gcid=000120&ptid=17

Double headed spermMisshapen head along with 4 normal sperm  Elongaged head

Pyriform head; bent, abnormal midpiece

Coiled tail 

Coiled and proximal droplet in sperms

Detached head

Bent tail or midpiece

Misshapen head and proximal droplet 

c.Formation of neck, middle piece, and tail

• A proximal centriole is located at the posterior surface of nucleus, and the distal centriole gives rise to axial filament of flagellum.

• The distal centriole and axial filament in midpiece are surrounded by fused mitochondria.

• A critical molecule for flagellar function is dynein, a protein attached to microtubules. Lack of this protein causes male sterility in Kartagener’s syndrome.

d.Shedding of most of the cytoplasm

Sertoli cells degrade residual cytoplasm shed during spermatogenesis

They also facilitate release of mature spermatozoa from seminiferous tubules.

They are joined by secretions from the seminal vesicles (fructose-rich alkaline fluid) and prostate gland (citric acid, acid phosphatase, zinc and magnesium ions) to form semen.

2-6mL of semen (pH 7-8.3) is ejaculated. At ovulation, cervical mucus becomes watery and

its mucin strands assume a parallel orientation. This state apparently greatly facilitates passage of sperm through the cervical canal.

SPERM TRANSPORT Spermatozoa exit slowly from

the tubules, and functionally mature (12 days) in the epididymis, where cells undergo biochemical maturation. 40-250 million sperms are ejaculated (only 25-30 million is needed for fertility).

Initial rapid transport of spermatozoa due to muscular movements of female reproductive tract enables them to reach uterine tubes within 5-20 min. after ejaculation.

Active swimming takes place in the cervix at the rate of 2-3 mm/hr, reaching the uterine tubes where they undergo capacitation 2-4 days later.

Spermatozoa remain viable in the tract for about 80 hours (unprotected sex based on the timing of the menstrual cycle can still lead to pregnancy!)

Buffering effect of the 2-6 ml seminal fluid changes vaginal pH from 4.3 to 7.2 (pH for fertilization = 6.0-6.5).

Majority of ejaculated sperm are lost are various points between the cervix and oviduct --- “Life is tough, and then you die.” A few exhausted semifinalists make it to the site of fertilization.

SPERM CAPACITATION occurs during transport in the female genital tract in approximately 7 hours, rendering them capable of fertilizing an egg:

1. Changes in the sperm cell membrane: Changes in surface glycoproteins caused by

secretions of the female genital tract. Cholesterol is removed possibly leading to an

increase fluidity of the sperm cell membrane. Glycoproteins are lost which may expose the zona

binding proteins. Proteins are phosphorylated.

Signal Transduction Events during Capacitation In humans, capacitation is triggered by

bicarbonate ions in the vagina, which enter the sperm and directly activate a soluble adenylyl cyclase enzyme in the cytosol.

The cyclase produces cyclic AMP which helps to initiate the changes associated with capacitation. 

Elevated cAMP levels lead to changes in sperm motility and reorganization of membrane components, changes that are essential for sperm binding and penetration of the egg coat, as well as for subsequent fusion with the egg plasma membrane.

Certain proteins are phosphorylated by tyrosine kinases under the influence of cAMP which has been shown to be absolutely required for human sperm cell capacitation

Effects of Capacitation on Sperm Increased rate of metabolism Hyperactivation: flagellum beats

more rapidly Changes in sperm glycoproteins

allow sperm-egg binding Pro-acrosin (inactive) is

converted to acrosin (active). Once a capacitated sperm has penetrated the

layer of follicle cells, it binds to the ZP. Binding proteins in the acrosomal matrix, e.g.

sperm protein 56 (sp56), are released to the sperm surface only during capacitation.

Hence, uncapacitated mammalian sperm are unable to bind to the unfertilized egg ZP.

Spermatozoa Statistics- based on normal human male values for reproductive ages between 20 to 50 years: 45 to 207 million spermatozoa are produced per

day in each testicle; OR approximately 2,000 spermatozoa per second each day (adult human RBC production is about 250,000 million per day)

182 million spermatozoa are stored in epididymal reserves. 23 million spermatozoa per gram are in testicular parenchyma.

Unused sperm are either resorbed or passed out of the body in urine or during wet dreams.

TESTICULAR DYSGENESIS

Excess alcohol induces aromatase to convert testosterone to estrogens by adipose cells.

The elevated estrogens can suppress gonadotropin secretion.

Alcohol causes Leydig cell damage and loss of testosterone receptors.

Alcohol decreases cAMP levels in Leydig cells. Prolonged cannabinoid intake also leads to

diminished spermatogenesis.

The lifting of the selection pressure on fertility means that those endowed with genes for high fecundity have lost their advantage over those without. As a result, future generations are bound to experience a further decline in semen quality and human fertility.

Over the past 300 million years, gene deletions on the long arm of the male sex-determining Y chromosome and oxidative stress, have caused it to retain only about 50 genes (for sex determination and spermatogenesis), whereas it originally contained approximately 1500 genes.

Overall, this gives an inactivation rate of five genes per million years. The presence of pseudogenes on the Y chromosome indicates that this process of attrition is continuing. At the present rate of decay, the Y chromosome will self-destruct in approximately 10 million years.

This has already occurred in the mole vole, in which the Y chromosome has been completely lost from the genome.

ON THE VULNERABILITY OF THE Y CHROMOSOME

The presence of TDF induces the expression of the transcription factor Sox9 which in turn leads to an increased expression of fibroblast growth factor 9 (FGF9) and the down regulation of Wnt4 expression. These events are part of the

signaling pathways that underlie the development of the testis. In contrast, the lack of Sox9 expression in female embryos allows expression of the secreted protein Wnt4

leading to ovary development. There are more genes involved in the final development of the ovaries and testes but Wnt,

Sox9 and FGF9 are central.