MALE REPRODUCTIVE SYSTEM

Department of the Histology, Cytology and Embryology

Tatiana Globa

State University of Medicine and Pharmacy “Nicolae Testemitanu”

Functions

The male reproductive system is responsible for:

1. Continuous production, nourishment, and temporary storage of the haploid male gamete (sperm).

2. The synthesis and secretion of male sex hormones (androgens).

MALE REPRODUCTIVE SYSTEM

Consists of:1. The testis, which produce sperm and synthesis and

secrete androgens2. The epididymis, vas deferens, ejaculatory duct, and

a segment of the male urethra, which form the excurrent duct system responsible for the transport of spermatozoa to the exterior

3. Accessory glands, the seminal vesicle, the prostate gland, and the bulbourethral glands, whose secretions form the bulk of the semen and provide nutrients to ejaculated spermatozoa

4. Penis, the copulatory organ, formed of erectile tissue

Testes• are paired oval shaped organs, located

in the scrotum, outside the abdominal cavity (Sperm development: 2°F below body temp)

• Scrotum:– Cremaster muscle: skeletal, tenses scrotum and

pulls testes closer to body• During sexual arousal and temp change

• Functions: - spermatogenesis- endocrine

• Each testis is surrounded by a thick capsule of dense fibrous connective tissue called the tunica albuginea.This capsule is thin on the anterior side and thick on the posterior, to form the mediastinum, where rete testis is located

Testes• Fibrous septa from the

mediastinum project into the testicular mass, dividing the tissue into 250 to 300

• Each lobule contains 1 to 4 seminiferous tubules, where spermatogenesis occurs (make sperm)

– To straight tubule to rete testis to efferent ductulesto epididymus

– To ductus deferens

Fig 27.4

TestesEach seminiferous tubule consists of a central lumen lined by a specialized epithelium containing two distinct cell populations: 1. the Sertoli cells2. the spermatogenic cells

The seminiferous epithelium is encircled by a basement membrane and a wall formed by collagenous fibers, fibroblasts and contractile myoid cells(responsible for te rhytmic contractile activity that propels the nonmotile sperm to the rete testis).The space around the seminiferous tubules is occupied by blood vessels and the interstitial cells or Leydig cells (make testosterone in response to LH, stimulate spermatogenesis)

Sertoli Cells

Leydig Cells

Sertoli Cells• Are columnar cells extending from the basal

lamina to the lumen of the seminiferous tubule• The apical and lateral plasma membranes of

Sertoli cells have an irregular outline because they provide crypts to house the developing spermatogenic cells

• At their basolateral domain, Sertoli cells form occluding junctions (blood-testis barrier, which protects developing spermatocytes and spermatids from autoimmune reactions)

• Occluding junctions subdivide the seminiferous epithelium into a basal compartment (below the junctions) and an adluminal compartment(above the junctions )

• Spermatogonia are located in the basal compartment and Spermatocytes, Spermatidsand Spermatozoa occupy the adluminal position

Sertoli Cellsa. This is a diploid somatic cell (not part of the germ cell

lineage).b. These cells provide nutrients to and remove wastes from the

developing gametes.c. They also phagocytose and digest cytoplasm that is shed by

the developing spermatids, thus recycling nutrients.d. They secrete fluid to carry mature sperm out of

seminiferous tubules.e. They secrete hormones such as activin and inhibin.f. They respond to follicle-stimulating hormone (FSH)

stimulation, which regulates the synthesis and secretion of androgen-binding protein (ABP) - secretory protein with high binding affinity for the testosterone.

j. They act to compartmentalize the developing gametes, separating them from the body’s immune system and the effects of certain hormones.

Stages and cell types of spermatogenesis

• spermatogonia - diploid cells in terms of genetic content and chromosome number - divide by mitosis.

• primary spermatocytes - diploid cells in terms of genetic content and (prior to chromosome replication in preparation for division) chromosome number - divide during first meiotic division.

• secondary spermatocytes - haploid cells in terms of genetic content, but diploid in terms of chromosome number -divide during second meiotic division.

• spermatids - immature spermatozoa - haploid cells in terms of genetic content and chromosome number.

Spermatogenesis can be divided into three stages:

a. Mitotic division of the spermatogonia that form various sub-types of spermatogonia and eventually many primary spermatocytes

b. Meiosis - two divisions

• * Meiosis I• * Meiosis II

c. Spermiogenesis (also called spermateleosis or spermatozoan metamorphosis) - cellular differentiation of the spermatids that are formed by the second meiotic division into mature spermatozoa.

Puberty: begin

Seminiferus TubuleLumen

Sertoli Cells

Leydig Cells

Testosterone directly stimulates spermatogenesis

Cytoplasmic bridges!! - syncytium

Spermiogenesis• The Golgi apparatus forms a membrane bound vesicle called the acrosomal

granule that eventually covers the anterior part of nucleus to form the acrosome.– The acrosome contains enzymes that help the sperm penetrate an acellular

layer surrounding the ovum that is called the zona pellucida• The centrioles of the spermatid migrate to the posterior end of this cell and give

rise to the flagellar axoneme that consist of a 9 + 2 structure of microtubules• The majority of the spermatid cytoplasm shifts to posterior region of the

maturing sperm.– This cytoplasm will eventually be shed as the residual body, a process that

helps streamline the body of the sperm.– The residual bodies are phagocytosed by Sertoli cells.

• The mitochondria of the spermatid organize around forming flagellum.– In humans these mitochondria fuse to form a spirally wound super

mitochondrion– This super mitochondrion produces ATP to power the sperms flagellum

• The spermatid nucleus condenses to small size.– This small nucleus is surrounded by a linear arrangement of microtubules

called the manchette.– The manchette may play a role in the elongation and flattening of the

nucleus.

Spermiogenesis

Spermatogenesis• The mature spermatozoa have lost the majority of its cytoplasm and has

become specialized for locomotion, penetration of the ovum, and transmission of genetic material to the next generation. In humans, the entire process from the first mitotic division of spermatogonial cell to fully formed spermatozoa takes about 64 days.

• As you examine the seminiferous tubules on your testes slide you'll note that the same combination of gamete stages is not present in every tubule section.

– This is the result of the spermatogonial cells dividing cyclically rather than continuously and at different times in different portions of the seminiferous tubules.

– The division cycle of a given spermatogonial cell in human males is every 16 +1 days.

In addition, in a given histological section (in humans), not all portions of the wall of the seminiferous tubules are in the same part of a given cycle.

a. Thus different parts of a given tubule will contain different associations of the various gamete stages.

b. Some regions may appear to contain mostly mature spermatozoa, while other regions will contain a mixture of primary and secondary spermatocytes and early spermatid stages.

spermatogonia

spermatocytes

spermatids

Leydig’s cells

spermatozoa

Epididymis• Head, body, tail

– Tail: storage• Composition of seminiferous

fluid• Phagocytoses damaged

spermatozoa• Stores spermatozoa• Maturation of spermatozoa

– Secretion to prevent premature capacitation

– Capacitation: become active, motile and fully functional

• Motile: from seminal vesicle secretions;

• Able to fertilize: conditions w/n female repro tract

Fig 27.7 a

Ductuli efferentes

Epididimal ducts

Ductus/Vas Deferens

• Tail of epididymis spermatic cordalong lat bladder into prostate gland

• Can store for months• Ejaculatory duct:

ampulla of VD and base of seminal vesicle– Into prostatic urethra

Spermatic cord: testicular artery, deferential artery, veins, Vas deferens

Vas Deferens

A straight tube with thick walls.

* Consists of narrow lumen surrounded by thick wall of smooth muscle (3 layers, inner longitudinal, middle circular, outer longitudinal).

* Mucosa of tube is in longitudinal folds.

* Lined withpseudostratified columnar epithelium with stereocilia on surface.

Urethra• Urinary bladder to tip of

penis• Prostatic, which

receives the ejaculatory ducts and the ducts of the prostate

• Membranous, the shortest segment

• Penile, which receives the ducts of the bulbourethral glands

Accessory Glands

• Seminal vesicles• Prostate gland• Bulbourethral glands

• Activate spermatozoa• Nutrients for motility• Buffers for vaginal acidity

Seminal Vesicles• Are androgen-dependent organs• Consist of three components:

1. An outer connective tissue layer2. A middle circular and longitudinal

smooth muscle layer3. An inner folded mucosa lined by a

simple cuboidal-to-pseudostratified columnar epithelium

• 60% volume of the seminal fluid• Prostaglandins (sperm transport) • Clotting proteins• Fructose (make ATP)

– Discharged at emission from peristaltic contractions

– Spermatazoa beat flagella and are highly motile

Prostate Gland• Encircles prostatic urethra• Surrounded by thick, fibro-elastic

capsule; bilobed gland; lobes separated by thick fibromuscular stroma

• 3 separate groups of compound tubulo-acinar glands are arranged concentrically around urethra

– main prostatic glands (bulk of organ)– submucosal (outer periurethral) glands: – mucosal (inner periurethral) glands:

• 20-30% volume of semen• Prostatic fluid: alkaline, enzymes,

proteins, minerals– Neutralize vaginal acids and give

adequate physical environment for sperm survival in female reproductive tract

The glands are lined by simple or pseudostratified columnar epithelium.

The lumen contains prostatic concretions (corpora amylacea) rich in glycoproteins and,

sometimes, a site of calcium deposition.

Bulbourethral Glands

• Base of penis• Empty their contents into the

urethra. • These glands provide the first

fluids of ejaculation that act to lubricate the urethra for the passage of the semen that follows.

• Are lined by a mucus-secreting epithelium

• 5% of volume• Thick, sticky, alkaline mucus

– Neutralize acids in male urethra

Semen

• 2-5 ml fluid: ejaculate– Spermatozoa– Seminal fluid: secretions from seminal

vesicles, Sertoli cells, prostate, epididymus, bulbourethral glands

– Enzymes: protease (rid mucous secretions in female tract) and seminal plasmin (kills E. coli)

Penis

• Urine to exterior and semen into vagina

• Shaft: starts at bulb; movable, erectile tissue

• Glans: expanded distal end surrounding external urethral meatus

• Prepuce/foreskin: surrounds tip over glans that surrounds external urethral meatus

Structure of the penis• Contains three masses of spongy erectile tissue

plus the urethra.1. The two dorsal cylinders of erectile tissue

are called the corpora cavernosa• The dorsal corpora cavernosa are

surrounded by a thick layer of dense connective tissue called the tunica albuginea. This C.T. also surrounds the corpus spongiosum, but it’s not as well defined in this region.

• Internally they consist of an endothelium lined, anastomosing network of blood sinuses that receive blood from the coiledhelicene arteries that are also located in the corpora cavernosa.

• Engorgement of the blood sinuses by blood from the helicene arteries is what causes the male erection.

2. The ventral cylinder of erectile tissue surrounds the urethra and is called thecorpus cavernosum of the urethra or thecorpus spongiosum - also surrounded by tunica albuginea.

• This corpus spongiosum is dialated at its end to form the glans penis or head of the penis.

corpus cavernosa corpus cavernosa

Penile urethra

corpus spongiosumTunica albuginea

Ejaculation• Emission: sperm from epididymis to

ejaculatory duct– Done by rhythmic contractions of SM in VD– Sympathetic nerves– Also: prostate and seminal vesicles contract

• Ejaculation proper: rhythmic contraction of both bulbospongiosis muscles from base of penis (overlie corpus cavernosa)– Semen out of glans– ~100 million sperm/mL

• Below ¼ of this: sterility

Regulation of Spermatogenesis