Male Reproductive Anatomy

Question 1

development of male reproductive anatomy

Answer 1

*bipotential fetus
*gonadal ridge forms at 3-5 weeks
*germ cells enter via the yolk sac at 6-8 weeks
*the Y chromosome has a sex-determining region (SRY) and the SRY gene product (testis-determining factor, TDF) is a DNA-binding protein that initiates male sex determination
*TDF → differentiation of seminiferous tubules
*Sertoli cells make AMH → Mullerian regression
*TDF → Leydig cells → testosterone → virilization of Wolffian ducts

Question 2

male gonadal descent

Answer 2

*testes are near the kidney at weeks 7-8, then start descending, facilitated by the gubernaculum (mesenchyme)
*testes are at the internal inguinal ring from weeks 10-15
*outpouching of peritoneum into scrotum (processus vaginalis)
*testis into inguinal canal at 20-28 weeks, then into scrotum at 7-8 months
*processus vaginalis usually closes at birth
*undescended testicle = cryptorchidism

Question 3

inguinal canal anatomy

Answer 3

*inguinal canal = spermatic cord + ilioinguinal nerve
*spermatic cord consists of: testicular artery, veins, vas deferens, lymphatics, and genital branch of genitofemoral nerve

Question 4

testes - overview

Answer 4

*the male gonads, responsible for:
1. spermatogenesis (production of sperm)
2. synthesis of various sex hormone, including testosterone
*2 testes are contained within the scrotum (a sac located underneath the penis, consisting of smooth muscle & skin)

Question 5

tunica albuginea - overview

Answer 5

*a thin layer of dense connective tissue that surrounds the testis
*on the posterior aspect of the testis, the tunica albuginea thickens considerably, forming the mediastinum testis, which contains the rete testis

Question 6

epididymis - overview

Answer 6

*a long, convoluted tube that lies posterior to the testis
*functions as the structure for sperm storage & maturation

Question 7

ductus deferens - overview

Answer 7

*a pair of long tubules that connect to the epididymis along with a pair of seminal vesicles to form the ejaculatory ducts
*one of the components of the spermatic cord (connects the testis to the abdominal inguinal ring)

Question 8

seminal vesicles - overview

Answer 8

*produce a secretion that contains various proteins, enzymes, and nutrients
*has an especially high concentration of fructose, which provides energy for sperm
*merge with the ductus deferens to form the ejaculatory ducts

Question 9

prostate gland - overview

Answer 9

*a walnut-sized exocrine gland wedged between the bladder and rectum
*produces an alkaline fluid that makes up 1/3 of seminal fluid
*the alkaline fluid helps neutralize the acidic environment of the vagina and prolongs the life of sperm
*within the prostate, the 2 ejaculatory ducts merge at the prostatic urethra, sharing a common passage for semen ejaculation

Question 10

prostate glands - 3 zones

Answer 10

1. peripheral zone = comprises 70% of total volume of prostate; most common site for prostate cancer
2. central zone = comprises 25% of prostate volume; surrounds the ejaculatory ducts
3. transitional zone = responsible for most symptoms of benign prostatic hyperplasia (enlarging of the transitional zone compresses the prostatic urethra)

Question 11

arterial supply to the testes

Answer 11

*testicles have a “redundant blood supply” because it has several sources of blood
1. testicular artery
2. cremasteric artery
3. vasal artery

Question 12

arterial supply to the testes: testicular artery

Answer 12

*aka internal spermatic or gonadal artery
*from the superior mesenteric artery (SMA)
*courses anterior to ureter and via inguinal canal into spermatic cord

Question 13

arterial supply to the testes: cremasteric artery

Answer 13

*from inferior epigastric artery
*travels with vas deferens before anastomosing to testicular artery within the testis

Question 14

arterial supply to the testes: vasal artery

Answer 14

*aka artery of the vas deferens
*branch of superior vesical artery
*occasional collaterals from inferior vesical artery

Question 15

venous drainage of the testes

Answer 15

*both testes initially drain separately into a network of tiny veins along the spermatic cord: the pampiniform plexus
*ipsilateral pampiniform plexus coalesces into one gonadal vein (one on each side - left and right)
*right-sided vein drains directly into inferior vena cava
*left-sided vein drains into the left renal vein prior to draining into IVC
*therefore - right-sided varicocele is much more rare than left-sided

Question 16

lymphatic drainage of testes

Answer 16

*follows embryology (via retroperitoneum / great vessels)
*right side goes to interaortocaval nodes, followed by precaval/preaortic
*left goes to para-aortic and preaortic nodes, followed by interaortocaval
*right sided much more likely to cross midline (important for cancer)
*scrotal lymphatics drain to inguinal nodes

Question 17

innervation of testes

Answer 17

*from aortic and renal plexus
*ureteral stone pain radiates toward the testes
*cross-communication such that unilateral pathology can create bilateral pain
*no innervation inside the testicle (i.e. ends at tunica albuginea - outer coating)

Question 18

sertoli cells

Answer 18

*form blood-testis barrier via tight junctions (creates a vasal and adlumenal compartment)
*stimulated by FSH
*predominant cell prior to puberty, but do not divide in the reproductive period
*support spermatozoa, phagocytize residual cytoplasm
*produce inhibin (negative feedback on FSH), androgen-binding protein, and AMH (Anti-Mullerian hormone)

Question 19

Leydig cells

Answer 19

*produce testosterone in response to LH
*LH stimulates Leydig cells (both start with L)

Question 20

spermatogenesis - overview

Answer 20

*spermatogenesis: the process of producing sperm cells (spermatids)

1. type A spermatogonia (eternal stem cells) produce type B spermatogonia
2. type B spermatogonia form primary spermatocytes via MITOSIS
3. primary spermatocytes form 2 secondary spermatocytes via MIOSIS 1
4. secondary spermatocytes form 2 spermatids via MIOSIS 2

Question 21

spermiogenesis - overview

Answer 21

*spermiogenesis: the process of MATURING spermatids (made via spermatogenesis) into spermatozoa

1. formation of acrosome from Golgi complex (contains enzymes to digest zona pellucida of oocyte)
2. condensation/elongation of the nucleus
3. development of flagellum from centrioles (similar to cilium)
4. shedding of cytoplasm

Question 22

formation of the ejaculatory duct

Answer 22

*ductus deferens travels behind the bladder and a dilated portion (ampulla) joins the duct of the ipsilateral seminal vesicle to create the ejaculatory duct
*the duct travels through the prostate and opens in the prostatic urethra

Question 23

seminal vesicles

Answer 23

*responsible for most of semen volume
*contains fructose, prostaglandins, and fibrinogen
*not designed to store sperm

Question 24

prostate

Answer 24

*alkaline secretions
*role as trigger for ejaculation, sperm activation, and capacitation
*contains 4% of body’s zinc, which causes citrate accumulation (buffer vs. acidic vagina) and stabilizes sperm DNA chromatin
*prostate specific antigen (PSA) is a serine protease that liquifies semen

Question 25

male bulbourethral glands (Cowper’s glands)

Answer 25

*located immediately distal to the prostatic urethra at the base of the penis
*secrete a clear fluid that helps lubricate the distal urethra and neutralizes its acidic pH, preparing for the passage of sperm during ejaculation (alkaline mucus)
*secretes PRIOR TO ejaculation (pre-ejaculate; does not contribute to the final volume of seminal fluid)

Question 26

passage of sperm during ejaculation: SEVEN UP

Answer 26

S - seminiferous tubules
E - epididymis
V - vas (ductus) deferens
E - ejaculatory ducts
N - (nothing)

U - urethra
P - penis

Question 27

breakdown of contributions from various glands to semen

Answer 27

1. testes - contribute ~200-500 million spermatozoa; about 2.5% of the composition of semen
2. seminal vesicles - contribute amino acids, citrate, FRUCTOSE, PROSTAGLANDINS, etc; accounts for about 65-75% of the composition of semen
3. prostate - contributes acid phosphates, PSA, citric acid, etc; accounts for about 25-30% of the composition of semen
4. bulbourethral glands - contribute galactose, mucus, etc; accounts for <1% of semen composition

Question 28

what is the main energy source of sperm cells

Answer 28

*fructose (contributed to semen by the seminal vesicles)

Question 29

role of prostaglandins in semen

Answer 29

*involved in suppressing an immune response by the female against the foreign semen
*contributed to semen by the seminal vesicles

Question 30

male sexual response

Answer 30

*four phases:
1. excitement
2. plateau
3. orgasm
4. resolution
*plus a refractory period

Question 31

nervous system control of: erection

Answer 31

*via parasympathetic input via pelvic nerve
*“Point” is parasympathetic

Question 32

nervous system control of: emission

Answer 32

*emission: release of sperm & accessory gland fluids into the pelvic urethra
*involves T12-L2 spinal segments
*first event is bladder neck contraction and then fluid deposition into proximal bulbar urethra
*“Shoot” is sympathetic

Question 33

nervous system control of: expulsion/ejaculation

Answer 33

*stimulated by seminal deposition (S2-4 nerves) and pudendal nerve causes rhythmic contractions of pelvic flood
*“Score”; visceral and somatic nerves (pudendal nerves)

Question 34

erectile function

Answer 34

*involves hormonal, psychological, neuronal, and vascular input
*tumescence (erection) involves smooth muscle relaxation
*detumescence involves smooth muscle contraction (pushing the blood back out)
*nonadrenergic noncholinergic neurons release nitric oxide (NO)
*NO increases cGMP, lowers intracellular calcium, myosin detaches from actin, and you get smooth muscle relaxation (vasodilation) and increased flow [pro-erectile]
*erectile response can be via local stimulation (i.e. paraplegic patients can still get erections and ejaculate)