Histology - Lecture 26 - Male Reproductive System Flashcards
When do the testes descend into scrotum? How?
7-month-old fetus via the inguinal canal 3 phases:1. Testes attachment to the cranial suspensory ligament is severed + gubernaculum contracts (both hormone induced) 2. Transabdominal descent brings testes down to inguinal ring located cranially to the scrotum3. Transinguinal descent brings testes into scrotum
When do the testes develop embryologically? What is concurrent?
Around 13 weeks when kidney development begins
What is the gubernaculum testis?
Connective tissue extending from testis to what will become scrotum
Does the gubernaculum grow as the body grows? Consequence?
NOPEAs the fetus grows the gubernaculum holds the testis in a lower abdominal position
What is cryptorchidism? Consequences? Treatment?
Undescended testis (or both)Consequences: sterility (due to higher temperature inhibiting spermatozoa production) or cancerTreatment: surgery = orchidopexy
What is an inguinal hernia?
Hernia allowing a loop of intestine to descend into the scrotal area
What disease manifests as referred pain to the testes? Why?
Kidney disease because kidney has related embryological origin
What is the testicular capsule?
Connective tissue enclosing the testis
3 layers of the testicular capsule? List from inner to outer. Which is thickest?
- Tunica vasculosa2. Tunica albuginea** 3. Visceral tunica vaginalis
What is the visceral tunica vaginalis?
Mesothelial cuboidal cell layer
What does the tunica albuginea of the testes consist of?
- Collagen fibers2. Fibroblasts3. Nerve endings4. Smooth muscle cells
How are testis divided?
Divided into ~250 lobules by septa branching from the tunica albuginea
What is the mediastinum of the testis?
Thickening of the tunica albuginea along the posterior border of testis that supports the rete testis cavities
What is the rete testis?
Anastomosing network of delicate tubules located in the hilum of the testicle that carries sperm from the seminiferous tubules to the efferent ducts
Where is the interstitium of the testis? What does it contain?
Between the seminiferous tubules composed of clusters of: 1. Leydig cells2. Lymphatics3. Blood vessels4. Nerves5. Components of loose connective tissue6. Lymphocytes7. Mast cells 8. Macrophages
Role of Leydig cells?
Produce testosterone
4 roles of testosterone?
- Maintains spermatogenesis 2. Maintains accessory glands of reproduction3. Maintains secondary sex characteristics4. Maintains libido
What stimulates the Leydig cells to produce testosterone?
LH
What do human Leydig cells contain?
Characteristic structures = crystals of Reinke
How many seminiferous tubules in each testis lobule?
1-4
Describe the seminiferous tubules of the testis.
Looped structures that join, at both ends, with the rete testis
What is each seminiferous tubule surrounded by?
Tunica propria
Describe the layers of seminiferous tubules.
- Complex stratified epithelium: germ cells and Sertoli cells 2. Basement membrane: basal lamina + lamina reticularis
What is the transitional zone of the seminiferous tubule? Other name? What is the next section?
End of seminiferous tubule devoid of germs cells (Sertoli cells only)= terminal segment Then, there is the tubulus rectus connecting the transitional zone to the rete testis
What is special about the Sertoli cells of the seminiferous tubules?
- Only cells to extend from base of seminiferous tubule to the lumen 2. Oval shaped nucleus3. Infolding of nuclear membrane
Genome of Sertoli cells?
Diploid and non-proliferative in adult
How can you recognize Sertoli cells?
Lobulated nucleus and indented nuclear membrane
Why are Sertoli cells sustentacular?
They support surrounding germ cells in the seminiferous tubule epithelium by providing them with nutrients
What stimulates the Sertoli cells to conduct their function?
FSH
What is the morphological basis of the blood-testis barrier? What does this mean?
Tight junctions between adjacent Sertoli cells Means that blood proteins cannot penetrate so the Sertoli cells regulate the transport of compounds from the blood to the adluminal compartment (actually add compounds of their own to it)
What are the 2 functional compartments of the seminiferous tubule epithelium? Describe each. What are they divided by?
- Basal compartment: contains spermatogonia and early primary spermatocytes (preleptotene, leptotene)2. Adluminal compartments: contains later primary spermatocytes (zygotene, pachytene, diplotene), secondary spermatocytes, and differentiating spermatids Divided by tight junctions between Sertoli cells
What is spermatogenesis?
Process of spermatozoa formation from diploid spermatogonia to haploid spermatozoa
Describe the 12 steps of spermatogenesis.
- Primitive type A spermatogonia containing 46 chromosomes (2n DNA) divide to yield type B spermatogonia2. The diploid (2n) type B spermatogonia divide by mitosis to yield tetraploid (4n) primary spermatocytes3. Preleptotene spermatocytes in prophase duplicate their DNA in preparation for the first meiotic division4. During meiotic prophase there is extensive rearrangement of chromatin as the cells pass through leptotene, zygotene, pachytene, and diplotene stages5. At the end of diplotene, the first reduction division occurs giving rise to 2 secondary spermatocytes (2n each) 6. The secondary spermatocytes are short lived (8 hours) and rapidly undergo the second reduction division to yield 2 spermatids each containing the haploid complement of DNA (1n) of 23 single stranded chromosomes 7. Within nascent spermatids the Golgi apparatus and the acrosomal granules migrate to one end of the nucleus where the acrosomal granules abut the nucleus forming the acrosomal cap 8. A pair of centrioles migrates to the opposite end of the spermatid from the acrosomal cap, lying perpendicular to each other9. From the distal centriole microtubules form, which in turn form the axoneme of the sperm 10. Mitochondria migrate to the base of the tail and surround it forming the mid-piece11. The manchette, a cylindrical band of microtubules, forms around the sperm nucleus as it elongates and condenses to form the sperm head12. Excess cytoplasm is shed as a residual body, which is phagocytosed by adjacent Sertoli cells
What is spermiogenesis?
Process whereby newly formed round spermatids differentiate to form spermatozoa
How does the reduction division from 2n to 1n occur during spermatogenesis?
Because no DNA synthesis takes place between the first and second meiotic divisions in secondary spermatocytes
What does the acrosomal cap of a spermatid contain? Purpose?
Enzymes (acrosin, hyaluronidase, neuraminidase) that facilitate penetration of the zona pellucida during fertilization
Describe microtubule arrangement of the axoneme of spermatids?
Characteristic 9+2 doublet of microtubules
How long does the ENTIRE spermatogenesis take?
74 days
What is Sertoli cell only syndrome?
Cause of infertility caused by aspermatogenesis. i.e., an absence of germ cells
What can lead to complete LOSS of germ cells and infertility?
Irradiation of the testes by cancer treatment or nuclear accident
4 parts of the spermatozoa?
- Head2. Mid-piece3. Principal piece4. End-piece
Describe the head of the spermatozoa. Size?
5µm, composed primarily of a condensed nucleus with the acrosomal cap over the anterior 2/3 of the nucleus The neck region contains the paired centrioles from which emerges the 9+2 doublet of microtubules
Describe the mid-piece of the spermatozoa. Size?
5µm, composed of the 9+2 doublet of microtubules (the axoneme) surrounded by an outer circumferentially arranged layer of 9 course fibersAround the course fibers is the cylindrical layer of mitochondria that supply the energy for motilityAttached to the mid-piece is a cytoplasmic droplet, a remnant of cytoplasm from spermatid condensation and differentiation
Describe the principal piece of the spermatozoa. Size?
50µm, consists of the axoneme surrounded by the 9 course fibersIn place of mitochondria, a circumferentially arranged fibrous sheath + plasma membraneNote: number of course fibers decline from 9 to 0 from the juxta-mid-piece region to the end-piece
Describe the end-piece of the spermatozoa.
Axoneme surrounded by the plasma membrane
What are the 6 stages of spermatogenesis? What do we call this?
In any cross-section of a seminiferous tubule certain types of germ cells will always be found in association with each other, so these cell associations or stages are classified in man as the 6 stages of spermatogenesis => cycle of seminiferous epithelium = sequential temporal succession of these associations up to the reappearance of the first stage
Purpose of temperature in scrotum being 2 degrees lower than in abdomen?
- Increased O2 diffusion2. Decreased metabolic rate of sperm=> greater concentration of sperm can be stored in the epididymis
Relationship between kidney development and male reproductive system development?
There are 3 kidneys during development:1. Pronephros: very primitive2. Mesonephros: large kidney 3. Metaphrenic kidneyMesonephric duct and tubules are co-opted during embryological development to give rise to the excurrent duct system of the male reproductive system, which makes sense as their main function is fluid reabsorbtion to concentrate sperm (just like the kidney) => this includes: seminal vesicles, ejaculatory ducts, ductus deferens, epididymis, and efferent ducts
Other name for mesonephros?
Middle kidney
2 other names for efferent ducts of the testis?
Ductuli efferentes = vasa efferentia
What do the efferent ducts of the testis give rise to?
Epididymis
Embryological origin of seminiferous tubules, straight tubules, and rete testis?
Indifferent gonads
Embryological origin of prostate?
Pelvic urethra
What is the pampiniform plexus?
Plexus of testicular veins + testicular artery in the spermatic cord that serves as a countercurrent heat exchange system to cool abdominal arterial blood passing to the testis and epididymis and to heat venous blood returning from the testis and epididymis to the abdomen
Treatment for testicular torsion?
Surgery
What does the tunica vasculosa consist of?
Vascular layer consisting of a plexus of blood vessels, held together by delicate connective tissue
What hormone do Sertoli cells produce? Role?
Inhibin => feedback to anterior pit to reduce FSH secretion
What are typical steroid producing cells characterized by?
- Smooth ER2. Lipid droplets3. Mitochondria with tubular cristae
What happens to spermatogenesis in the absence of testosterone?
Regression and seminiferous tubules and cessation of spermatogenesis
What are the accessory glands of reproduction maintained by testosterone? What happens to them without testosterone?
- Seminal vesicles 2. Prostate gland3. Bulbo-urethral glands They would shrink
What are male secondary sex characteristics?
- Facial hair 2. Musculature
What is dihydrotestosterone (DHT)?
More potent testosterone (binds to receptors with 50 times the affinity) that can be produced within target tissues
Can testosterone act directly on target tissues?
YUP
How do testosterone and DHT exert androgenic effects on tissues?
Via androgen receptors
What does androgen receptor defect lead to? Treatment?
Androgen insensitivity syndrome: male genotype (XY) but female phenotype, tall (because no effect of testosterone to close epiphyseal plate), gynecomastia (excess androgens converted to estrogen by adipose tissue aromatase) and infertility with undescended testes Treatment for undescended testes: after puberty to allow for hormones to contribute to changes in puberty + can increase size of vaginal pouch so penetrativeintercourse can be enjoyed + ensure other steroid needs are not compromised
Precursor to testosterone?
Cholesterol
What are the tubulus rectus and the rete testis lined by in the testis?
Simple cuboidal epithelial cells with microvilli and occasional cilia/flagella
Purpose of blood-testis barrier?
During meiosis some very unique proteins are being expressed on the germ cells, so if the immune system had access, this would mount an immune response - the barrier prevents this
Other name for type A spermatogonia?
Stem cells
Other name for type B spermatogonia?
Progenitor cells
Which cells are the largest during spermatogenesis?
Primary spermatocytes because 4n
Purpose of spermiogenesis?
- Reduced nucleus volume for greater motility and to protect genome from damage while transit to egg2. Rest of spermatozoa arranged to promote motility
Other name for neck region of the spermatocyte?
Connecting piece
Other name for course fibers of the spermatocyte?
Outer dense fibers
What is the cycle of the seminiferous epithelium facilitated by?
Incomplete cytokinesis between germ cells connecting them by cytoplasmic bridges, which make them develop synchronously
Describe the arrangement of cellular associations in seminiferous tubules in humans.
Helical distribution, so that a cross-section displays more than 1 cellular association
How many efferent ducts per testis?
20 bundled together
What is the main role of the efferent ducts of the testis?
Reabsorb 95% of the fluid leaving the testis to concentrate the sperm 20 fold
Effect of excessive temperature of spermatogenesis?
Prevents it
For what men are testicular cancers more prevalent?
Men under 40
Can testicular cancers be cured? What to note?
Yes in 90% of cases and are almost always malignant
How many spermatocytes produced per second?
2,000
Can sperm released from the testis fertilize an ova? Explain.
NOPE because that ability will be acquired through the transit through the excurrent duct system via morphological, physiological, and biochemical modifications, aka sperm maturation
Is sperm maturation intrinsic only?
NOPE also extrinsic via interaction with excurrent duct system (secretion/resorption)
6 histologically distinct regions of the excurrent ducts? Which ones are intratesticular?
- Tubulus rectus2. Rete testis3. Ductuli efferentes (*first part is intratesticular)4. Ductus epididymidis 5. Ductus deferens6. Ampulla
What layer surrounds the epithelium of the rete testis?
Very dense layer of connective tissue with very few blood or lymphatic vessels
Other name for intra-testicular efferent ducts?
Trans-capsule channels
Describe the transition from intra to extra efferent ducts?
Several intratesticular efferent ducts continuous with the cavity of the rete testis pass through the tunica albuginea to become the extra-testicular efferent ducts
How many extra-testicular efferent ducts are there per testis?
~10-20
What are extra-testicular efferent ducts lined by? Describe roles.
Simple columnar epithelial with:1. Principal cells with microvilli: reabsorb fluid 2. Ciliated cells: help move sperm through the ducts
Where does most fluid reabsorption occur in the excurrent duct system? What facilitates this?
Efferent ducts High degree of vascularization facilitates fluid reabsorption
By what 3 mechanisms does fluid containing sperm move through the efferent ducts?
- Hydrostatic pressure generated from the testis2. Beating of cilia on ciliated cells 3. Peristaltic contractions of a thin layer of periductal smooth muscle layer around the ducts
3 parts of the epididymis? 2 names for each.
- Caput = head2. Corpus = body3. Cauda = tail
What is the epididymis? What is it lined by?
Single, highly coiled duct, 7 meters long in man lined by a highly pseudostratified columnar epithelium composed of principal cells and several other cell types
What characterizes the principal cells of the epididymis?
Very prominent Golgi (to glycosylate secretory proteins), numerous vesicles, mitochondria, RER, and long stereocilia
Role of principal cells of epididymis?
- Protein secretion associated with sperm maturation2. Resorption of fluid and compounds from the lumen of the ductus epididymidis
How does sperm move along the epididymis? What to note?
Peristaltic contractions of a layer of periductal smooth muscle layer around the ductsNote: cauda contains additional layers of periductal muscle
In what part of the epididymis are sperm stored?
Cauda due to wider lumen
What issue with the epididymis may lead to infertility?
Breakdown in one or more of the interactive components of sperm maturation
Describe infection of the epididymis.
Common after puberty and can be cause by gonococcal or nonspecific infection usually following retrograde spreading of the infection from the urethra
What is the vas deferens lined by? What to note?
Pseudostratified columnar epithelium with stereocilia with longitudinal folds protruding into the lumen + lamina propria Note: folds increase in height and become branched toward the ampulla
What is the vas deferens surrounded by?
3 layers of smooth muscle and adventitia:1. Inner longitudinal2. Middle circular3. Outer longitudinal
What is the ampulla?
Terminal dilated region of the vas deferens
Where is the ampulla located? What does it connect to?
Posterior to the bladder and joins the duct of the seminal vesicle to form the ejaculatory duct that enters the prostatic urethra
Role of ampulla?
Mixes sperm from epididymis with secretions from accessory organs
What are the seminal vesicles?
Paired with each a highly convoluted duct enclosed within a lamina propria with elastic fibers, smooth muscle, and loose connective tissue
Lining of seminal vesicles?
Pseudostratified/simple columnar with folds to increase the surface area for secretion
Why is the term “seminal vesicle” a misnomer?
They do not store sperm, they are secretory glands
Role of seminal vesicles?
During ejaculation secretions within the vesicles are expelled by contraction of smooth muscle cells in the lamina propria (inner circular and outer longitudinal)The secretion contains:1. Prostaglandins to increase uterine contractions and raise cAMP levels for sperm motility 2. Vitamin C: metabolite for sperm motility3. Fructose: metabolite for sperm motility
What is the prostate enclosed by?
Fibro-elastic capsule
Organization of prostate?
3 branched glands around urethra surrounded by fibromuscular stroma to aid in discharge of fluid:1. Main glands2. Submucosal glands3. Mucosal glands (from outer to inner)
How many prostatic glands empty into the urethra?
30-50
Lining of prostate?
Pseudostratified or simple columnar epithelium
What % of ejaculate is made of prostatic fluid?
30%
What is prostatic fluid made of?
- Proteolytic enzymes2. Zinc3. Citric acid4. Acid phosphatase5. PSA = prostate-specific antigen
What are corpora amylacea?
Prostatic concretions characteristic of the prostate gland, and occur in older men that can obstruct the lumen of the ducts
What does prostatic cancer arise from?
Prostatic epithelium in the peripheral zone
What men are at a higher risk of prostate cancer?
Blacks
What is BPH exactly?
Overgrowth of the stroma of the prostate and often with secondary reactivation of epithelial proliferation
What are bulbo-urethral glands enclosed in?
Thin smooth muscular sheath with both smooth and skeletal muscles in connective tissue
What type of gland are both the prostate and bulbo-urethral glands?
Tubulo-alveolar glands
What do bulbo-urethral glands secrete? Purpose?
Sialoglycoprotein (mucin) that acts as a lubricant of the penile urethra prior to ejaculation:1. Protects lining of urethra from acrosomal proteases2. Protects sperm from urine remnants
What is characteristic of the bulbo-urethral glands? Explain.
Skeletal muscle in the connective tissue stroma but cannot be voluntarily controlled
Other name for corpus spongiosum?
Corpus cavernosa of the urethra
What surrounds the corpus cavernosa of the penis? Purpose?
A dense fibroelastic connective tissue layer, the tunica albuginea which forms a septum in the midline that is incomplete in the distal region to allow equilibration of blood flow between the two corpora cavernosa
What surrounds the corpus spongiosum of the penis? Purpose?
Connective tissue layer with more elastic fibers (than the layer around corpus cavernosa) to allow the urethra to remain patent during ejaculation
What is impotence? What can cause this?
Inability to achieve erection Causes:1. Neurological dysfunction2. Emotional dysfunction3. Congenital circulatory disorders of the penis
Infections of the penis?
Venereal diseases aka STD
What is the external meatus of the penis?
Urethral opening on the glans
What is the male urethra lined by?
- Prostatic urethra: transitional epithelium2. Membranous and penile urethra: either stratified and/or pseudostratified columnar epithelium
Does the male urethra have glands?
YUP, in the submucosal connective tissue
Where can infections of the urethra spread?
- Bladder2. Seminal vesicles3. Epididymis
Are stereocilia true cilia?
NOPE, they contain actin instead of microtubules so are just really long and thin microvilli
How many lumens in seminal vesicle?
ONLY ONE
What is the veramontanum? What to note?
Region within prostate where urethra merges with ejaculatory duct Note: important imaging landmark because it can expand
What are the 4 different zones of the prostate? List them from inner to outer. Which ones typically give rise to BPH?
- *Periurethral zone2. *Transitional zone3. *Central zone4. Peripheral zone
Test for cancer and/or BPH?
PSA assayed in blood tests (if > 4) because it can leak out into the vasculature due to disruption of the normal architecture of the prostate
What is a unique feature of the prostate ONLY?
Corpora amylacea
What is the root of the penis?
Fixed end attached to body wall
What is the body of the penis?
Mobile tubular portion
What is the glans of the penis?
Expanded distal end around urethral orifice
What covers the glans of the penis? Other name?
Foreskin = prepuce
Purpose of penis?
Organ to conduct internal fertilization for greater survivability of offspring
What is male circumcision?
Removal of the foreskin
Cons of circumcision?
- Painful 2. Causes Peyronies disease in adults (curvature of the penis)3. Infections and poor surgical procedure can cause disfigurement and need for remedial surgery (or even amputation) 4. Loss of sensitivity5. Discoloration due to scar tissue6. Can be considered genital mutilation due to irreversibility 7. No informed consent8. Medically unnecessary
Can a man be fertile without seminal vesicles?
YUP but less fertile
Androgen insensitivity syndrome: 2 other names?
Androgen resistance syndrome = testicular feminization
