Histology - Lecture 4 - Functions of Testes and Spermatogenesis

Histologically what will a Leydig cell look like?

It will be in the interstitial around the seminiferous tubules. Zoomed in, usually TEM, the Leydig cells will have lots of mito, SER, and lipid droplets. This makes sense since the Leydig cells are specialized for testosterone synthesis. Given the lipid droplets it should make the cells look vaculated.

Describe the Sertoli cells.

Large, complex, columnar cells located WITHIN the seminiferous epithelium. Extend from basal lamina to lumen of seminiferous tubule. Large nucleus with prominent nucleolus. Sertoli cells are bound to one another by TIGHT JUNCTIONS, which form a BARRIER that separates the seminiferous epithelium into 2 COMPARTMENTS: 1. BASAL COMPARTMENT: closest to the basal lamina and contains SPERMATOGONIA. 2. ADLUMINAL COMPARTMENT: closest to the lumen of the duct. Contains SPERMATOCYTES and developing SPERMATIDS.

In response to what do Leydig cells secrete testosterone?

Leydig cells remain quiescent through prepubertal period, then commence testosterone synthesis in response to luteinizing hormone (LH) secreted by the pituitary.

Note. Make sure you know the learning objectives.

Major functions of the male reproductive system Basic function and structure of each of the major components of the male reproductive system Structure of the testis and intratesticular ducts Endocrine function of the Interstitial Cells of Leydig Structure and cell types of the seminiferous tubules Functions of Sertoli cells Process of spermatogenesis Basic structure of spermatozoa

Describe the Acrosomal phase of the spermatid phase.

NUCLEUS and CHROMOSOMES CONDENSE. MICROTUBULES assemble to form a transient cylindrical structure called the MANCHETTE (place assumed later by ANNULUS), which aids in the elongation of the spermatid. A cylindrical bundle of microtubules, called the manchette, limits the nucleus laterally. MITOCHONDRIA orient themselves into a sheath around the proximal portion of the flagellum, which will go on to become the MIDDLE PIECE of the sperm tail. So this is the phase in which you get elongated and put the engine into the tail.

Describe primary spermatocytes.

Primary spermatocytes are spermatocytes in Meiosis I. Thy are LARGE CELLS. Since Prophase I takes ~ 22 days, the majority of spermatocytes seen in sections will be PRIMARY SPERMATOCYTES = TQ. Present in the adluminal compartment of the seminiferous epithelium.

Describe the spermatid phase.

Process of cytodifferentiation in which SPERMATIDS shed cytoplasm and differentiate into SPERMATOZOA. THERE IS NO CELL DIVISION DURING THE SPERMATID PHASE. Instead, the SPERMATIDS undergo BIOCHEMICAL AND MORPHOLOGICAL CHANGES. Note: on a histological slide you can identify a spermatid since it will have a cone shape to it.

Describe the testicular lobules.

Pyramidal, interconnecting compartments (TESTICULAR LOBULES) separated by incomplete SEPTA. The septa originate from the mediastinum testis. Each LOBULE contains 1-4 SEMINIFEROUS TUBULES, along with a loose connective tissue stroma (TUNICA VASCULOSA).

What does the acrosomal cap do and what layers does it go through?

The ACROSOMAL CAP contains ENZYMES that digest proteins and other molecules, and it is important during fertilization of the oocyte for 2 reasons: (1) PENETRATION of the ZONA PELLUCIDA by sperm. (2) Initiating the ACROSOMAL REACTION.

What are the principal endocrine cells of the testes? What do they synthesize?

The Leydig cells, which synthesize testosterone.

What are the rete testis?

The SEMINIFEROUS TUBULES are continuous with a channel system in the MEDIASTINUM testis called the RETE TESTIS. Rete testis leads into the various excretory ducts (efferent ductules, ductus epididymis, ductus deferens) of male reproductive tract.

Describe the tunica propria.

The TUNICA PROPRIA envelopes the seminiferous tubules; contains several layers of FIBROBLASTS. The layer next to basal lamina consists of flattened MYOID CELLS.

What forms the blood-testis barrier? What is the function of this barrier?

The blood-testis barrier is formed by tight junctions between Sertoli cells (zonulae occludentes = tight junction). The function is to prevent immune system from "seeing" spermatids and mature sperm which might be recognized as "foreign" or "non-self" due to unique surface antigens. Impaired fertility in men with high levels of anti-sperm antibodies. Occluding junctions form a barrier to the transport of large molecules. Thought to "protect" cells in advanced stages of spermatogenesis from blood-borne noxious agents.

Describe the seminiferous tubules.

These consist of a thick seminiferous (spermatogenic) epithelium and surrounding CT capsule, which is called the tunica propria.

Describe the spermatocyte phase.

This is where you have meiosis. PRIMARY SPERMATOCYTES replicate their DNA [to 4N DNA] and enter the first meiotic division. Prophase of this division takes ~ 22 days. THEREFORE, THE MAJORITY OF SPERMATOCYTES SEEN IN SECTIONS WILL BE PRIMARY SPERMATOCYTES. Primary spermatocytes are the largest cells in the spermatogenic lineage; characterized by chromosomes in various stages of coiling. The 2 daughter cells of the first meiotic division are called SECONDARY SPERMATOCYTES (2N DNA). SECONDARY SPERMATOCYTES enter the second meiotic division. Resulting daughter cells are HAPLOID SPERMATIDS (1N, haploid).

What are the subclassifications of Type A spermatogonia?

Type A SPERMATOGONIA can be sub-classified as: Type A dark (Ad) -- flattened nucleus stains darkly but uniformly, due to abundant HETEROCHROMATIN; mitotically inactive). Type A pale (Ap) -- flattened nucleus is relatively pale (EUCHROMATIN); mitotic divisions induced by testosterone.

Describe type B spermatogonia.

Type B SPERMATOGONIA: Round nucleus with clumped chromatin Divide mitotically to give rise to PRIMARY SPERMATOCYTES.

Describe how spermatogenesis is regulated by the hypothalamic-pituitary axis.

GnRH production by neurons of the hypothalamus induces GONADOTROPHS of the ADENOHYPOPHYSIS to secrete LH and FSH. LH stimulates LEYDIG CELLS to produce TESTOSTERONE. FSH promotes the synthesis of Androgen-Binding Protein by SERTOLI CELLS. TESTOSTERONE is necessary for development of male germ cells and secondary sex characteristics. ABP BINDS TESTOSTERONE and maintains it at high concentration in the seminiferous tubule (testosterone promotes spermatogenesis).

How long does it take to go from the spermatogonial stage to the mature spermatozoa?

64 days.

What is a Seminoma?

A germ cell neoplasm. Germ cell neoplasms are the most common types of testicular neoplasm. They are most common in men under 40, and are the most common cancer of men between the ages of 20 to 34. (Think of Tom Green Show).

Describe the cellular stages in sperm differentiation.

(1) SPERMATOGONIA (Diploid stem cells; undergoing mitotic divisions) TYPE A (also subdivided into dark and pale) TYPE B (divide to give rise to primary spermatocytes) (2) SPERMATOCYTES (undergo meiotic divisions) PRIMARY SPERMATOCYTES (Diploid -- 4N DNA; undergo Meiosis I to form secondary spermatocytes) SECONDARY SPERMATOCYTES (2N DNA; undergo Meiosis II) (3) SPERMATIDS (no cell division; haploid cells [1N DNA]) that undergo post-meiotic differentiation) (4) SPERMATOZOA the differentiated male gametes

When are androgen important?

1. During embryonic development for the normal development of the male reproductive tract. 2. During puberty, testosterone is important for the initiation of sperm production and the development of secondary sex characteristics. 3. During adulthood, testosterone is important for the maintenance of sexual functions.

What are the three major functions of the male reproductive system?

1. Gametogenesis - Production of spermatozoa. 2. Exocrine function - Production of fluid secretions of the sexual ducts. These secretions participate in sperm growth and capacitation/maturation. 3. Endocrine function - Production of androgens. Androgens are male sex steroid hormones. The most important androgen produced by the testes is testosterone.

What are the functions of Sertoli cells?

1. General nutritive function of the developing sperm cells. This is why Sertoli cells are called nursemaid cells. 2. Phagocytosis of residual cytoplasm of spermatozoa during the last stage of spermatogenesis. This is important in the differentiation of spermatozoa. To do this the Sertoli cells contain an extensive lysosomal digestive system. 3. Secrete a number of proteins: -Inhibin, which feeds back to inhibit FSH section. -Androgen-binding proteins, which allows the Sertoli cells to concentrate testosterone in the lumen of the seminiferous tubules. -Anti-mullerian hormone - which is secreted during fetal development.

What are the four sub-phases of the spermatid phase?

1. Golgi phase. 2. Cap phase. 3. Acrosomal phase. 4. Maturation phase.

Describe the six structural components of the mature spermatozoon.

1. HEAD: Nucleus with 23 chromosomes: 22 autosomes plus an X or a Y. 2. ACROSOME: contains hydrolytic enzymes whose release is termed the ACROSOMAL REACTION. 3. NECK: Centrioles, which nucleated microtubule formation. CONNECTING PIECE, which is where the 9 OUTER DENSE FIBERS of the TAIL SHEATH are attached. 4. MIDDLE PIECE (TAIL). Extends from NECK TO ANNULUS. Contains AXONEME and MITOCHONDRIA. 5. PRINCIPAL PIECE (TAIL): contains axoneme surrounded by dense fibers and fibrous sheath. 6. END PIECE: consists of axoneme and surrounding cell membrane. Note: The AXONEMAL COMPLEX consists of 2 central singlet microtubules surrounded by 9 doublet microtubules. (9+2 setup).

What are the three phases of Spermatogenesis?

1. Spermatogonial phase. - Have mitotic division of spermatogonia to give rise to primary spermatocytes. 2. Spermatocyte phase (meiosis). - Have meiotic divisions of spermatocytes to give spermatids. Primary spermatocyte is 4N. Secondary Spermatocyte is 2N). 3. Spermatid phase. - have transformation of spermatids (haplod, 1N) into spermatozoa. No cell divisions. Have most-meiostic differentiation.

Describe spermatogenesis steps.

1. Spermatogonium. (mitosis) 2. Primary spermatocyte. (meiosis 1) 3. Secondary spermatocyte. (meiosis 2) 4. Spermatids. 5. Functional spermatozoids.

What are the four major functional components of the male reproductive system?

1. Testes (primarily endocrine function). The testes produce spermatozoa and androgens. 2. Duct system - consists of efferent ductules, epididymis, ductus deferens and the ejaculatory ducts. The ejaculatory ducts converge on the urethra. 3. Two main exocrine glands - the seminal vesicles and the prostate gland. These secrete seminal fluid. 4. Penis.

Describe the testicular tunicae.

1. Tunica vaginalis - When the testes descend into the scrotum shortly before birth, they carry an extension of the peritoneum (processus vaginalis) that remains associated with their anterolateral surface as a double layer of mesothelium enclosing a serous space; this double lining is called the TUNICA VAGINALIS. 2. Tunica albuginea - Each TESTIS is covered by a thick, fibrous connective tissue capsule, the TUNICA ALBUGINEA. Tunica albuginea is lined by a highly vascular layer of loose connective tissue called the TUNICA VASCULOSA. 3. Mediastinum testis - Along the posterior surface, the tunica albuginea thickens to form the MEDIASTINUM TESTIS. The MEDIASTINUM projects inward into the testis to form incomplete SEPTA, which separate the testis into LOBULES.

Describe the Cap phase of the spermatid phase.

ACROSOMAL VESICLE increases in size and partially encloses nucleus. Then known as the ACROSOMAL CAP.

Describe the Maturation phase of the spermatid phase.

Excess cytoplasm (RESIDUAL BODIES) is shed and phagocytosed by SERTOLI CELLS. Nonmotile SPERMATOZOA are released into lumen of the seminiferous tubule -- SPERMIATION.

Where are androgens produced in the testis?

In the interstitial cells of the testis called the Leydig cells.

Describe the spermatogonial phase.

Note: Takes place in the basal compartment of the epithelium. SPERMATOGONIA: Diploid germ cells that undergo mitotic divisions. TYPE A SPERMATOGONIA divide mitotically to replace themselves and to generate TYPE B SPERMATOGONIA. TYPE B SPERMATOGONIA divide mitotically to give rise to PRIMARY SPERMATOCYTES. As soon as primary spermatocytes are formed, they migrate from the basal compartment into the adluminal compartment

Describe the Golgi phase of the spermatid phase.

PREACROSOMAL GRANULES (contain hydrolytic enzymes) form in the Golgi complex. Granules coalesce into ACROSOMAL VESICLE, which determines anterior pole. CENTRIOLES migrate to posterior region and initiate formation of the FLAGELLAR AXONEME (core of longitudinally arranged microtubules).

Where are Sertoli cells and interstitial cells of Leydig contained?

SEMINIFEROUS TUBULES, which contain SPERMATOGENIC CELLS and SERTOLI CELLS, are located within a connective tissue stroma known as the TUNICA VASCULOSA. Recall that the seminiferous tubules are within the tunica vasculosa. Dispersed within the tunica vasculosa are clumps of specialized endocrine cells called LEYDIG CELLS. This is an important slide to make sure you have your anatomy correct.

What is the technical composition of semen?

Seminal fluid + spermatozoa + some desquamated duct lining cells.

Describe the significance that cytokinesis is incomplete during the mitotic and meiotic divisions that occur during spermatogenesis.

Since cytokinesis is incomplete during the mitotic and meiotic divisions CYTOPLASMIC BRIDGES remain between daughter cells of dividing spermatogonia. Bridges connect cells through all stages of spermatogenesis -- development of connected cells is thus SYNCHRONIZED. The connections remain until the FINAL STAGE of SPERMATID MATURATION, when the residual bodies are shed and the spermatozoa are released.

What does the tunica vasculosa contain?

Tunica vasculosa contains blood and lymphatic vessels, nerves, and the INTERSTITIAL CELLS OF LEYDIG. = TQ.