The SAC Syllabus - Andrology
Summary of Testicular Embryology
The Male Reproductive Hormonal Axis - the hypothalamo-pituitary-gonadal axis
Spermatogenesis - Testis, Epididymis & Ductus Deferens; meiosis & mitosis
Physiology of Erection and Ejaculation

• Spermatogenesis, sexual behaviour, erection and ejaculation and their endocrine control
• Age related changes in erections, ejaculation and fertility
• The effect of urological disease and its treatment on erections, ejaculation and fertility
• Causes of erectile dysfunction (ED)
• Investigations in ED and potential sources of error in interpretation
• Therapies in ED including surgical options such as prostheses
• Peyronie's disease
• Priapism - high and low flow; management
• Retrograde ejaculation; management
• Infertility - causes and investigation
• Varicocele - controversies regarding its role in infertility
• Role of scrotal exploration, vasography and biopsy
• Treatment of infertility including the various types of artificial conception techniques
• Vasectomy - counselling, techniques and results
• Vasectomy reversal - counselling, techniques and results

The Y chromosome is critical for normal male sexual determination because Yp has the SRY gene that induces testicular formation.

At 7/40, the cells in the primitive genital ridge differentiate into Leydig and Sertoli cells providing the endocrine and exocrine components of the gonad.

The Leydig cells, initially under the influence of chorionic gonadotrophin, produce testosterone. This leads to mesonephric duct differentiation (seminal vesicles, vasa deferentia, corpus and cauda epididymis). 5 alpha R (1) in the genital sinus leads to external virilisation.

MIF (Mullerian inhibitory factor) is produced by the Sertoli cells and helps to induce testicular descent (first phase) which is completed under the control of the GF nerve and CR-P (calcitonin related peptide).

Knowledge of this sexual endocrine axis is central to understanding the physiology of male sexual development and maintenance of normal function (Figure 1).

Gn RH is a decapeptide encoded for on chromosome 8p. It is released via neurosecretory neurons into the portal circulation in pulses every 70 to 90 minutes. T1/2 is 3 mins (not easily assayable as yet). The pulsatility is essential in having a stimulatory effect on LH/FSH release and the pulse frequency may have effects on LH/FSH ratios.

LH/FSH are made from the same cell type. They are glycoproteins weighing 28 and 33 kDa and have a T1/2 of 30 mins and 4 hours respectively. They share a common alpha subunit with TSH and hCG. Diurnal variations are only of significance in the pubertal period.

Prolactin may have an inhibitory effect on GnRH secretion and so alter the pulsatility (N.B. - oestradiol is 1000x more potent than testosterone in inhibiting LH/FSH).

Inhibin (2 types) is a glycoprotein which is produced by the Sertoli cells and selectively inhibits FSH secretion. Activins are produced from beta units of Inhibin. Other peptides and GFs are also important e.g. TGF beta.

Both FSH and testosterone are needed for normal quantitative and qualitative spermatogenesis but their role is unclear.

LH induces testosterone synthesis using C from cell stores or by inducing synthesis via the HMGCoA pathway. HDL C may also be used. Dependent on STAR (steroidogenic acute regulatory protein). Congenital loss leads to lipid adrenal hyperplasia.

Age related changes to the axis - LH/FSH rise from 6 years to puberty with LH being more pronounced and associated with the testosterone spurt. With old age, LH/FSH rise with a definite lowering of circulating testosterone and associated androgens even in health. This may be due to increased peripheral aromatisation and higher E levels producing significant negative feedback, even though there are low testosterone levels.

Hypogonadal patients can be hyper or hypogondotropic. Kallman's syndrome (associated with anosmia, colour blindness). PRL levels should be checked with an image and possibly a clomiphene test.

Spermatogenesis

This is a highly complicated process where primitive totipotent stem cells divide to renew themselves or produce germ cells destined to become haploid gametes via meiosis and, subsequently, highly specialised spermatozoa ideal for fertilisation of the egg in the female tract.

Specialised environment of the testis

Applied Anatomy

• 15 - 25 ml. Three coats - vaginalis, albuginea and vasculosa.
• Interstitium (25% volume) has Leydig cells (700million), mast cells, macrophages and support tissue.
• Seminferous tubules (STs) - 1000 all U-shaped with short straight segments (tubuli recti) which connect to testis. Ten ductuli efferentes lead from here to the epididymis.
• There are no somatic nerves but ANS nerves come from the renal plexus. The blood supply comes from 3 artries - int spermatic artery, deferential artery and cremasteric artery. The veins do not run with the arteries and may have a counter current system for heat exchange.

Seminiferous Tubules (ST) - where the first two phases of spermatogenesis occur. Support cells include the Sertoli and basal cells. They are surrounded by adventitia, myoid cells and an inner fibrous layer rich in collagen. There is significant cell to cell interaction.

Sertoli cell - highly specialised cell with irregular nucleus, low mitotic index, connections to germ cells and tight junctions between adjacent cells to produce the testis-blood barrier. Polarised with cytoplasmic projections abutting on germinal cells at various stages of division within the basal and adluminal compartments. It produces several peptides e.g. the ABP. FSH and T dependent and P-Mod-S from peritubular cells. The spermatocytes move to the adluminal area in the extended meiotic prophase involving leptotene, zygotene and pachytene.

The role of the BTB is unclear - possibly immunogenic or gives stability for meiosis.

Complex cellular interactions exist. The germinal epithelium gives rise to 120 x 106 spermatozoa daily. The phases include proliferation, meiosis including reduction division to haploid spermatids and spermiogenesis to the mature gamete.

Thirteen germ types have been seen by LM. From the least to the most differentiated these are:

• dark type A spermatogonia (Ad)
• pale type A (Ap)
• type B (B)
• preleptotene primary spermatocytes (R)
• leptotene primary (L)
• zygotene primary (Z)
• pachytene primary (P)
• secondary (II) and Sa
• b1
• b2
• c
• d1 and d2 spermatids

Ap spermatogonia divide at 16 day intervals to give B which are committed to form spermatocytes. There is a 40% degeneration rate from hereon. The entire process takes 74 days in humans. Viewed from a single point in the ST, 6 cellular associations or stages occur in a predictable fashion. The complete series of segments representing the stages is a wave of the seminferous epithelium. Genes critical for the process have been identified on the Y chromosome (AZF zone and DAZ gene). Age reduces the number of cells in the STs and in the interstitium.

Role of the Epididymis and Ductus deferens

Passage through the epididymis is essential for complete maturation of the spermatozoa to allow capacitation and acrosome reactions in the female tract. Epididymal function is androgen dependent.

There are 3 regions - the caput, corpus and cauda. There are highly complex histological divisions and contractile cells with sympathetic innervation.

The epithelial cells are divided into 2 types - principal and basal cells (macrophages). There is also a blood epididymal barrier. Functions include - transport (1 to 11 days), storage and maturation of the spermatozoa. Motility improves as the sperm pass through the complex (from high amplitude, low frequency to low amplitude, high frequency). Important constituents of epididymal fluid include glcerylphosporylcholine, carnitine and sialic acid. Several proteins have also been identified e.g. forward motility protein.

Spermatozoa

They are 60 microns long and composed of an acrosomal cap, a head with condensed chromatin, a powerhouse of mitochondria and the 9+2 flagellum or axoneme. They also include ZP3 protein binders.

Historically, Aristotle thought erections were induced by air!

Applied anatomy of the penis

The tunica albuginea is essential for penile flexibilty, rigidity and tissue strength. The corpora have a bilayered structure with outer longitudinal and inner circular elastic fibres interposed with collagen. The inner layer has intracavernosal pillars that act as struts. The tunica is deficient between 5 and 7 o'clock where there is a potential weakness (cf - erosion of prosthesis).Emissary veins have a short route between the two layers.

The corpora have an incomplete septum between them and the proximal crura are separate. The cavernosa have smooth muscle trabeculae and interconnecting sinusoids. The nerves and helicine arteries are closely related to the smooth muscle. At rest, the blood in the sinusoids is venous.

The spongiosum and glans have larger sinusoids and weaker support from connective tissue.

Arterial supply - internal pudendal from the internal iliac artery. Branches may come from the external iliac artery, obturator, inferior vesical and femoral arteries.

The internal pudendal artery is the common penile artery and it divides into the dorsal, bulbourethral and cavernous arteries. The dorsal artery is responsible for tumescence of the glans and the bulbourethral artery for the spongiosum.

The cavernous artery enters at the hilum of the penis. Distally, it gives several helicine branches. These become taut during erection.

Venous drainage - From the sinusoids, the blood passes to the subtunical venular plexus before exiting as emissary veins.

From skin - superficial veins combine at the root to pass into the saphenous veins. From the penis, the veins drain into the deep dorsal, circumflex laterally and ventrally to the periurethral veins.

Haemodynamics and the mechanism of erection

In the flaccid state, the cavernosal smooth muscle is tonically contracted by the sympathetic discharge, allowing only nutritional supplies. Stimulation (either psychogenic, reflexogenic or in REMS) triggers release of neural transmitters from the nerves. Relaxation ensues. This leads to sinusoidal filling, compression of the subtunical venules, emissary veins, a rise in intracavernous pressure to 100mmHg (full erection) and finally ischiocavernosus contraction leading to rigid erection.

Seven phases have been described in animal experiments:
0 = flaccid, 1 = latent, 2 = tumescence,3 = full erection, 4 = rigid erection, 5 = initial detumescence, 6 = slow detumescence and 7 = fast detumescence.

Neuroanatomy and physiology

ANS and SNS - erections and detumescence/sensory and contraction of the bulbo and ischiocavernosus muscles.

ANS - The sympathetic pathway is from the T10 to L2 segments. Nerves travel to the inferior mesenteric and superior hypogastric plexuses and thence to the pelvic plexus. The parasympathetic pathway is from the S234 segments via the interomediolateral columns to the pelvic plexus and then down the cavernous nerves.

Psychogenic erection in sacral injured patients is via the medial preoptic axis and through the sympathetic pathways. Here reflexogenic erections are abolished.

Somatic pathways - sensory receptors for pain, heat, etc. A delta and C fibres move to the pudendal nerve from the dorsal nerve which is a mixed nerve.

Onuf's nucleus in the S234 segments is the somatomotor nucleus allowing the innervation of the muscles. The ischioC is essential for rigid erection whereas the bulboC is essential for ejaculation.

Supraspinal pathways - medial preoptic axis and paraventricular areas of the hypothalamus are crucial for sex drive and erection. Dopamine and adrenergic nerves may promote whilst serotonin may inhibit these areas.

Neurotransmitters - peripheral:
Flaccidity - Adrenergic fibres via alpha 1 a, b and c receptors and presynaptic alpha 1b. Endothelin may also be involved. Erection - acetylcholine - nicotinic receptors at the ganglia and M2 and 3 receptors at the smooth muscle.
NANC (non-adrenergic, non-cholinergic) nerves - nitric oxide release which induces cyclic guanylate monophosphate/PKG and then relaxation. Nitric oxide is made from L Arginine by nitric oxide synthsis. Nitric oxide is highly labile - other neurotransitters such as VIP (vasoactive intestinal peptide) may also induce synthesis of nitric oxide.

During erection, the smooth muscle cells must relax in a synchronised way. This is done by tight junctions between adjacent cells allowing 2nd messenger passage between cells (Christ 1997).

Central neurotransimitters - DA, Nadr, Serotonin. DA (apomorphine activity via D1 and 2 Rs).

Molecular mechanisms of smooth muscle contraction and relaxation - calcium related. Free levels rise from 120 nM to 700nM causing calmodulin-4-Ca complexes to bind to myosin light chain kinase. The light chain is then phosphorylated and a contraction cycle initiated. Signal transduction pathways act to switch on second messengers e.g. cAMP, cGMP, IP3 and DAG. These all activate Ca fluxes to produce cellular responses via ionic channels or sequesteration. PDEs degrade the cyclic 2nd messengers - especially type 5 in the cavernosal tissue.

Ejaculation and emission

This requires sufficient stimulation. Orgasm is dependent on intact pudendal nerves through which the cavernosus muscles can be stimulated.

Three phases are associated with ejaculation which include emission of fluid into the urethra (sympathetic), closure of the bladder neck sphincter and finally closure of the distal sphincter and rhythmic evacuation of the urethra.

Control is probably in the hypothalamus.

Most of the ejaculate is composed of seminal vesicle effluent or is from the prostate (65% and 30% respectively). The seminal vescicle fluid has fructose, PGs and coagulates. The prostate supplies citric acid, P and Zn.

Christ GJ (1997) Integrative erectile biology. Int J Imp Res. 9: 69- 84.