Male Reproductive System Flashcards
What type of gland is the exocrine component of the testes? What is the mechanism of sperm secretion?
Compound tubular gland which secretes sperm via holocrine secretion (production of residual bodies)
What is the name of the dense irregular connective tissue capsule around the testes?
Tunica albuginea
What is the innermost layer of the testes capsule called and what does it contain?
Tunica vasculosa - contains loose connective tissue with blood vessels called tunica vasculosa
What happens to the tunica albuginea posteriorly?
Thickens to form mediastinum testis. The septae will divide each testis into lobules.
What is the organization of a lobule of the testes?
Each lobule contains 1-4 seminiferous tubules, beginning and ending near the mediastinum testes
What is contained in the interstitial connective tissue / stroma?
Lymphatic vessels, blood vessels, and nerves
How can Leydig cells be identified? Why is their cytoplasm acidophilic?
Leydig cells can be identified as the largest cells of the interstitium, with eosinophilic cytoplasm, vesicular nucleus, prominent nucleolus, and a cytoplasm of lipid droplets.
They are acidophilic due to their mitochondria with tubulo-vesicular cristae + smooth ER
What is the function of Leydig cells and what is the function of their product?
They produce testosterone via stimulation by LH. Testosterone is important for development, secondary male sex characteristics, reproductive tract function, and maturation / maintenance of gamete production.
What is the tunica propria and what cell type does it contain? What is the function of this cell type?
Layer of dense connective tissue surrounding the seminiferous tubule. Contains contractile myoid cells which have characteristics of smooth muscle cells and fibroblasts. Contracts to propel secreted spermatozoa along seminiferous tubule.
What separates the tunica propria from the seminiferous epithelium?
A basal lamina
What is a primary cause of male infertility?
Sperm production must happen at 34-35 degrees C, which is 2-3 degrees below body temperature. Undescended testicles may lead to elevated temperature of testes and infertility. Also, mutagens, steroids, infections, and radiation can cause this.
What are Sertoli cells and what is their function?
They are part of the seminiferous epithelium. They function to form compartments to organize the spermatogenic cells, and have microenvironments needed for the development of the different types of cells.
How can Sertoli cells be identified?
They are columnar and stretch from basal lamina to lumen of tubule. 3 main characteristics
- Indistinct plasma membrane boundaries
- Vesiculated nucleus - pale staining center
- Prominent nucleolus
What type of junctions create the blood-testis barrier and why is this important?
Sertoli-Sertoli cell junctions. This is important because developing sperm may be recognized as foreign by immune cells and must be kept separate from the blood (much like the thymus)
What are the two compartments of the seminiferous epithelium and what is contained in them? What divides these two compartments?
The two compartments are divided by the projections of interconnecting Sertoli-Sertoli junctions.
Basal: Spermatogonium, and briefly primary spermatocytes
Adluminal: Spermatocytes and spermatids
What is the function of the Sertoli-spermatid junctions?
Sertoli cells bind spermatids within the seminiferous epithelium to help anchor the spermatid to the Sertoli cell during sperm development
How do Sertoli cells function to keep high levels of testosterone for spermatogenesis?
They produce testosterone binding protein under the control of FSH to keep testosterone levels about 200x higher than normal blood levels
What do Sertoli cells secrete other than testosterone binding protein and what is its function?
Fluid which functions to help move spermatozoa along the lumen of the seminiferous tubule
What are two mechanisms of autoimmunity to sperm?
- If Sertoli-Sertoli junctions are compromised, immune system may detect foreign particles of spermatozoa since they have different genetic makeup from host.
- Vasectomy allows sperm to leak out of reproductive tract and can have autoimmunity to their sperm
What are the three phases of spermatogenesis and how long does it take?
65-75 days in humans.
- Spermatogonial phase - mitosis & spermatocyte production via spermatogonia
- Spermatocyte phase - meiosis 1 and 2 to make haploid
- Spermatid phase - differentiate of sperm to give mature structure
What are the three types of spermatogonia and where do they reside? How can they be identified?
Ad(ark) -> Ap(ale) -> B, do not have to distinguish between them.
They are next to the basal lamina in the basal compartment. They are identified as any cell resting on basal lamina but lacking Sertoli cell morphology.
What are Ad cells and what are their possible fate?
A-dark spermatogonia. They are the stem cells. They divide by mitosis to become either two Ad or two Ap
What are type Ap spermatogonia and what is a cohort?
Spermatogonia formed by Ad which are now committed to becoming sperm. They will do several rounds of mitosis, but all remained linked by cell bridges and are called a cohort. These cells develop together.
They will differentiate to become B type spermatogonia.
What do type B spermatogonia become and how do they move to the adluminal compartment?
They divide by mitosis to produce preleptotene primary spermatocytes. They move into the adluminal compartment when Sertoli-Sertoli junctions break, and new ones form beneath them, pushing them up.
What cells have the largest nuclei in the seminiferous epithelium and why?
Primary spermatocytes. This is because they have strands of condense and very basophilic chromatin, and have twice the total amount of DNA compared to interphase cells since they are about to undergo the reductional division of meiosis 1, and each chromosome has a sister chromatid
When does crossing over occur and how long does this take?
Four chromatids form tetrads (two homologous chromosomes with sister chromatids). This takes 2 weeks during the extended prophase of meiosis 1.
Why will meiosis I produce secondary spermatocytes with the same amount of DNA as the parent cell?
There are now only 23 chromosomes; however, they now have 2 sister chromatids, which is the same amount of DNA as the 46 chromosomes of the parental primary spermatocyte prior to the DNA replication before prophase I.
Why is it unlikely to see any secondary spermatocytes in a histological section?
The equatorial division, Meiosis II, happens in only a few hours, whereas Meiosis I takes weeks.
What does each diploid type B spermatogonium yield?
A preleptotene spermatocyte which will form four haploid, genetically distinct spermatids which have 1/2 the DNA of this parental cell
How do early spermatids appear and what process do they still need to undergo?
They appear as small and round with a fairly dark staining basophilic nucleus, with no condense strands of chromatin.
They still need to undergo a series of biochemical and morphological changes during spermiogenesis
What are the four stages of spermiogenesis?
- Golgi phase
- Cap phase
- Acrosome phase
- Maturation phase
What happens during the Golgi phase of spermiogenesis?
- Acrosomal vesicle is produced, which is a membrane-bound vesicle near the nuclear envelop.
- Microtubules of the axoneme tail begin to form
What is the function of the acrosomal vesicle?
Contains hydrolytic enzmes, including hyalurinidase, acrosin, and neuraminidase which are needed to penetrate the coverings of the ovum and zona pellucida
What happens during the cap phase of spermiogenesis?
Acrosomal vesicle flattens against the round spermatid nucleus to form a cap sometimes seen by LM, and the tail elongates
What happens during the acrosome phase of spermiogenesis?
- Acrosome vesicle condenses
- Nucleus condenses and elongates to give the sperm head a pointed, flattened appearance
- Mitochondria migrate to the initial portion of the axoneme adjacent to the neck to make the “middle piece” of the spermatozoan
This gives the elongated appearance of the late spermatid
What happens during the maturation phase of spermiogenesis?
Excess cytoplasm is extruded into a residual body which is phagocytized by a nearby Sertoli cell (holocrine)
When does the late spermatid become a spermatozoan and how does it move into the seminiferous tube lumen?
When it is shed from the seminiferous epithelium. At this point it is morphologically mature, but non-motile and incapable of fertilization.
The spermatozoa are moved passively along the seminiferous tube lumen via Sertoli fluids and contractions of myoid cells in tunica propria
What are straight tubules and what lines them?
First component of excretory duct system, they are an intratesticular duct which receives sperm from seminiferous tubules and dumps into rete testis in mediastinum testis.
Lined by simple cuboidal epithelium
What is the rete testis?
Intratesticular duct system within the connective tissue of the mediastinum testis. Same lining as straight tubules: simple cuboidal. It is a number of interconnecting channels.
What does the rete testis drain into? What will these do?
They merge to form 6-10 efferent ductules, the first part of the extratesticular duct system. They will form a bridge between the testes and the head of the epididymis (formed by efferent ductules)
What type of epithelium lines efferent ductules and what are the cell types? What are their functions?
Pseudostratified columnar
3 types:
1. Tall, ciliated columnar cells - facilitate sperm movement
2. Non-ciliated cuboidal cells - reabsorb testicular fluid
3. Incomplete layer of basal cells - regenerative
How does sperm move through the efferent ductules?
Via joint action of the ciliated cells and the contraction of the thin layer of smooth muscle around the duct
What forms the epididymal duct and what are the two main cell types present?
The efferent ductules combine to form one highly-coiled tube about 5-6 meters long.
- Principle cells - covered with non-motile, branched stereocilia
- Basal cells
What are the functions of the principle cells of the epididymal duct?
- Absorb testicular fluid not absorbed by cuboidal cells of efferent ductules, mainly in the head.
- Phagocytosis of abnormal spermatozoa + residual bodies
- Secretion of glycerylphosphorylcholine (GPC), glycoproteins, and other molecuels to help sperm mature so they are motile and can fertilize the oocyte
Where are mature sperm stored?
The tail of the epididymis
What is the function of the basal cells of the epididymis?
May be precursors of principle cells, also regulate electrolyte and water transport by principal cells
How does the smooth muscle change in the epididymis?
Gets progressively thicker, until the tail region where it has three layers, the same as ductus deferens
What are the characteristics of the mucosa of the ductus deferens?
- Epithelium similar to pseudostratified columnar epithelium lining epididymal duct
- Contains stereocilia to the level of the ampulla
- Lamina propria containing elastic fibers
What is the muscularis layer of the vas deferens and what is its function?
1mm thick with 3 layers of smooth muscle:
- Inner longitudinal
- Middle circular
- Outer longitudinal
Peristalsis acts to propel sperm during ejaculation
What defines the adventitia of the vas deferens?
Loose elastic connective tissue which blends with the connective tissue structures within the spermatic cord
What is the ampulla of the vas deferens?
Dilated region adjacent to the prostate and seminal vesicle. Its epithelium becomes folded and resembles the seminal vesicle, and may have a secretory function
What are accessory glands and what are their dependent on for full morphological development and physiological activity?
Secretory glands to nourish and support the spermatozoa, making the bulk of semen.
Dependent on testosterone
What type of glands are the seminal vesicles, and what is their mucosal morphology?
They are highly folded, branched tubular glands to increase surface area for secretion. The epithelium is pseudostratified columnar but varies with testosterone levels, and the lamina propria is loose vascularized elastic connective tissue.
What is the function of the seminal vesicles?
Epithelium secretes components making up 50-70% of semen volume.
Secretion is primarily fructose, the principle substrate for sperm. Also includes, bicarbonate, prostaglandins, proteins, and amino acids.
What layers of smooth muscle cause secretion of seminal vesicles? What is the adventitia?
Inner circular and outer longitudinal, like the intestine. The adventitia is collagenous connective tissue with elastic fibers
What forms the ejaculatory duct?
Short excretory duct from seminal vesicle + ampulla of ductus deferens
What is the largest accessory gland and what does it surround?
Prostate gland - surrounds prostatic segment of urethra which has transitional epithelium
What type of gland is the prostate gland and what epithelium type?
It is a compound tubuloalveolar duct which has simple columnar or pseudostratified columnar epithelium depending on the levels of testosterone
What are the three zones of the prostate gland?
- Peripheral zone - on the outside, the main prostatic glands
- Central zone - submucosal glands
- Transitional zone - mucosal glands. This contains the prostatic urethra.
All of these zones have ducts which converge to drain into the prostatic urethra
What are the secretions of the prostate? What do they do?
- Citric acid
- Fibrolysin - liquefies semen
- Prostate-specific acid phosphatase
- Prostate specific antigen - protease (PSA marker)
- Amylase
What is the diagnostic feature of the prostate gland and how does it stain?
Prostatic concentrations - much like the brain sand of the pineal gland.
Stain red/pink with eosin dye, or blue/green using trichrome.
What defines the stroma of the prostate gland and what is it called?
Infiltrated with smooth muscle fibers, it is a combination of smooth muscle cells, fibroblasts, elastic and collagen fibers.
Called: Fibromuscular stroma
What is benign prostatic hyperplasia and what causes it?
Hypertrophy of mucosal and submucosal glands in the transitional + central zones + hypertrophy of stroma. This is due to stromal convertion of testosterone to dihydrotestosterone. DHT has autocrine function on stromal cells and paracrine function on epithelium to make growth factors.
Reduces lumen of urethra and affects most men by age 85.
What is the frequency of prostate cancer and where does it normally develop? Why is this problematic?
Affects about 30% of population over age 75. Affects main (peripheral) glands most often, which is a problem because it does not impinge on urethra and will thus not be symptomatic. These carcinoma can enter circulation and metastasize to bone.
What are good markers for prostate cancer?
Prostate carcinoma will show increased blood levels of both prostate-specific antigen (PSA) and prostate-specific acid phosphatase
Where is the bulbourethral gland found and where does it empty?
Found in UG diaphragm and open into the penile urethra
What type of secretion does the bulbourethral gland have?
All mucous - same as glands of Littre. They function to protect semen against acidic urine
What type of skin covers the penis and what is right beneath it?
Thin skin, a subcutaneous layer of smooth muscle is right beneath it.
What is the morphology of the penile urethra epithelium, and what are its outpouchings?
Stratified or pseudostratified columnar most often, running within the corpus spongiosum.
The outpouchings are glands of Littre, which are mucous secreting glands. They are more numerous in males.
What two things make up erectile tissues?
- Trabeculae - consisting of dense connective tissue and smooth muscle
- Lacunae - vascular spaces lined by endothelium
How is erection produced?
Acetylcholine is released by PANS to the nerve in the penis or clitoris. This acts on the endothelium of the erectile tissue to produce nitric oxide (NO). NO spreads to the smooth muscle trabeculae and helicine arteries to make guanylate cyclase produce cGMP, relaxing the smooth muscle.
Relaxation of smooth muscle increases blood flow through helicine arteries, filling the lacunae.
What counteracts / stops erection?
The production of a phosphodiesterase that breaks down cGMP to constrict smooth muscle in the trabeculae, so helicine arteries cannot supply the lacunae
What is the mechanism of Viagra / sildenafil citrate?
Phosphodiesterase inhibitor, prevents destruction of cGMP, which is the primary smooth muscle relaxant of the trabeculae. This allows erection to take place.
