Lecture 5 - Male Reproductive System

What are the basic components of the male reproductive system and what are their functions?

-Testes: spermatogenesis and testosterone synthesis

-Ducts: secrete seminal fluid

What is spermatogenesis?

Production of sperms by the testes

What are the components of the testis?

-Testicular capsule

-Parenchyma: cellular mass w/ dense CT

-Rete tubules: channels that help sperm leave testis

What determines the testis size? What does it mean if there's a decrease in testis size?

-Seminiferous tubules

-It means there is a spermatogenesis problem

What is the structure and function of the testicular capsule?

-Made of connective tissue and smooth muscle fibers

-Facilitates movement of spermatozoa into rete tubules and efferent ducts

What are the 2 components of the parenchyma?

-Seminiferous tubules

-Interstitial tissue

What is found in the seminiferous tubules?

Sertoli cells and germ cells

What is found in the interstitial tissue?

Leydig cells, capillaries, lymphatic vessels

What is the function of Sertoli cells?

-Blood-testis barrier

-Produce a variety of substances needed for germ cell development (ABP, transferrin)

-Produce inhibin which has a negative feedback on FSH secretion

What is the blood-testis barrier?

Tight junctions to prevent immunoglobulins from accessing germ cells because they are foreign to the body during development

What is the functional of leydig cells?

Production of testosterone

What are the 3 phases of spermatogenesis? When do they occur?

-Proliferation, meiotic, and differentiation phase

-All occur after puberty

What occurs during the proliferation phase?

Stem cells undergo mitosis and replenish the stem cell pool

What occurs during the meiotic phase?

Meiosis, produce haploid spermatids

What occurs during the differentiation phase?

No cell division, cells go from round to an elongated head and tail

What is spermiogenesis?

Process by which spermatids are transformed into mature spermatozoa that are capable of motility and fertilization

What are the 4 phases of spermiogenesis?

1. Golgi phase

2. Cap phase

3. Acrosome phase

4. Maturation phase

What happens in the Golgi phase?

The golgi complex breaks down into small vesicles

What happens in the cap phase?

Vesicle forms acrosome (cap)

What happens in the acrosome phase?

Acrosome becomes elongated

What happens in the maturation phase?

Cytoplasmic droplet forms, sperm is mature

What are the rete tubules?

-Tiny channels through which spermatozoa are transported out of the testis

-Simple cuboidal epithelium and dense CT

What is the function of efferent ducts?

Transport newly formed spermatozoa and tubular fluid into the epididymal duct

What are the four function of the epididymis?

1. Provide the environment for final maturation of spermatozoa

2. Serves as a storage reservoir for spermatozoa

3. Has cytoplasmic droplets that helps sperm acquire more motility

4. Cells coat sperm heads with proteins that are important for binding to zona pellucida

What are the three regions of the epididymus?

1. Caput (head)

2. Corpus (body)

3. Cauda (tail)

What is involved in the endocrine control of the male repro system?

-Secretion of GnRH from the hypothalamus

-FSH and LH secretion from the anterior pituitary

-Secretion of gonadal steroids (testosterone and estrogen)

Explain the hormonal profile in the male.

-GnRH is secreted tonically (no surge center)

-FSH has a lower level of secretion (because of inhibin from Sertoli cells) and it has a longer half life

-Testosterone is secreted after LH

How does LH act in the male?

Binds to leydig cells which stimulate them to produce testosterone that is transported to Sertoli cells and adjacent vasculature

What happens to testosterone when it enters the Sertoli cell?

-Converted to estrogen by aromatase

-Converted to dihydrotestosterone (DHT) by 5-alpha reductase

What happens when testosterone, DHT, and estrogen get into the bloodstream?

They have a negative feedback on GnRH neurons in hypothalamus

How does FSH act in the male?

Binds to sertoli cells and influences sperm cell development

How are testosterone levels different in the Sertoli cells versus circulation? Why?

Testosterone is high in the cells for spermatogenesis but low in circulation, because it inhibits GnRH