Prostate Gland  

The Prostate – Mysterious Organ That Makes Love Potions

The prostate gland and seminal vesicles enrich the juice carried by the ductus deferens on the way to an important mission to ensure the survival of the human race.

The prostate is a part of the male anatomy. It surrounds the urethra, and lies immediately inferior to the urinary bladder. There is no analogous structure in female anatomy.

Structurally it is a chestnut-shaped bulb divided into concentric zones around the urethra.

Three Concentric Rings Surrounding the Urethra and a Cap

The art piece shows a transverse view of the prostate and reveals the basic structural framework of the prostate.  It consists of  three concentric rings which include the peripheral zone, the central zone and the transitional zone which surround the urethra (U -yellow).  The most anterior surface consists of a cap of  fibromuscular tissue (pink). The prostate gland can be viewed as The peripheral zone, accounts for 70% of the parenchyma, the central zone accounts for 25% of the parenchyma, and the transitional zone with the  fibromuscular zone (anterior layer) account for the remaining 5% of parenchyma. 

Parts of the Prostate in Sagittal View

The ART PIECE reveals the prostate in sagittal view. The peripheral zone (darkest maroon) is the largest portion and occupies the base, extending the entire length of the posterior wall to the apex. The central zone (medium red) lies inward of the peripheral zone and is that part through which the ejaculatory duct courses. The transitional zone (pearl white) surrounds the urethra, and the anterior fibromuscular layer (pink) runs from the base to the apex anteriorly. The ureter is overlaid in orange and the ejaculatory duct (yellow) empties into the widened portion of the urethra called the verumontanum

The prostate is comprised of approximately 30% glandular and 70% fibromuscular stromal elements.

Glandular and Stromal Elements of the Gland

The diagram reflects the basic histological makeup of the prostate in axial projection. It is composed of 30% glandular tissue (white) and 70% stromal tissue (pink). The glandular tissue is made up of branching tubuloalveolar glands and the stroma consists of smooth muscle, collagen, elastic tissue and fibrous tissue. The compound tubuloalveolar acini feed into a system of ductules and finally form 30-50 excretory ducts that enter into the prostatic urethra. In this diagram the two ejaculatory ducts are shown posterior to the prostatic urethra, and represent the confluence of the ducts of the seminal vesicles and the vasa deferentia. At a slightly more inferior level of the axial cut, they will enter the prostatic urethra at the verumontanum

The function of the prostate is to secrete a fluid which combines with the secretions of the seminal vesicles, to form part of semen.  It is a truly a secret concoction and contains half of the recipe for all mammalian life.

Love Potions Accumulate in the Prostatic Urethra Just Prior to the Opening of the Sluice Gates

The prostatic urethra serves as the mixing pot for the components of semen by acting as the receptacle of secretions from the prostate itself, the seminal vesicles and the vas deferentia. This artistic rendition shows the region of the verumontanum which is the site where the mixing pot stands receiving sperm from the testes via the vas deferentia (red), the secretions of the seminal vesicles (orange) and the secretions of the prostate gland white). The last component contributed by the bulbourethral glands (Cowpers’s glands – green) joins the secretions in the penile urethra to form semen.

Volume Ratios of the Components of Semen Concoction

The diagram reveals the components of semen.  The fluid from the seminal vesicles account for 65-70% of the volume, prostatic fluid, 25-30%, sperm 2-5%, and fluid from Cowper’s gland represents less than 1% of the volume. Each ejaculate contains between .1-10mls (1-2 teaspoons) with an average of 3.5mls (Owen)

Common diseases include:  Prostate cancer, prostatitis, BPH, prostatism, and less commonly abscess

Zonal Anatomy and Predilections For Carcinoma – Peripheral Zone

The diagram depicts the zonal morphology relevant to the locations where disease arises. The normal gland is seen in image (a). Image (b) shows BPH (benign prostatic hypertrophy) which is caused by hyperplasia and enlargement of the transitional zone (green). Image (c) shows carcinoma (bright lime green) arising from the peripheral zone which is the characteristic site of origin of this disease. Image (d) shows a combination of BPH in the transitional zone and carcinoma in the peripheral zone. This is a common combination of diseases in the elderly population.

Diagnostic evaluation is initially via rectal examination and the evaluation of a blood test called the PSA – prostate specific antigen.  Common modalities used for imaging the prostate include:  Ultrasound, MRI, CT scan

Normal Zonal Anatomy – MRI T2 Weighted

The patient is a 60 year old man. His MRI was performed with a transrectal coil and the image shows the T2 weighted sequence in the axial projection (a,b). The scan shown demonstrates the normal zonal anatomy of the prostate. The outer peripheral zone  (maroon, pz) is often canoe shaped in the axial projection.  The central zone (dark pink, cz) accounts for 25% of the parenchyma. The transitional zone (light green), and the fibromuscular zone (light pink, fmz) account for 5% of the volume of the gland

Normal Size Prostate 26 Year Old Male

The CT scan is from a 26 year old male with a normal prostate seen in the axial plane (a,b) and in the sagittal planes (c,d). The bladder (yelow) is distended. Note the shape of the gland in the transverse planer is heart shaped and in the sagittal plane almost rectangular when normal in size. The internal sphincter surrounds the top of the urethra at the base of the bladder and the urethra extends through the prostate as the prostatic urethra and into the penile urethra.

Advantages and Disadvantages of Ultrasound

The series of US and CT scans are from a 50 year old man with an elevated PSA Image a is an ultrasound performed in the transverse plane, and show a minimally prominent nodular prostate. Image b shows the needle tip (teal blue arrow) in the left peripheral zone. Image c is a CT scan in the  transverse projection of the prostate and shows a nodular anterior surface while image d shows an almost 3cms external iliac node. The biopsy was positive for prostate carcinoma.

Whereas ultrasound is able to characterize the lesion and provide guidance for biopsy, it is unable to consistently visualise lymph nodes and hence CT is necessary for staging.  The combination of the two modalities is required.  PET CT is even more helpful.

Treatments Medical treatment includes the use of hormonal agents, antibiotics, and chemo therapy although in severe disease surgery and radiation are commonly employed.

The prostate is most easily conceptualised in the transverse plane by 3 concentric rings surrounding the urethra and topped off by an anterior cap

Histology

The prostate is comprised of approximately 30% glandular and 70% fibromuscular stromal elements.

Glandular and Stromal Elements

The diagram reflects the basic histological makeup of the prostate in axial projection. It is composed of 30% glandular tissue (white) and 70% stromal tissue (pink). The glandular tissue is made up of branching tubuloalveolar glands and the stroma consists of smooth muscle, collagen, elastic tissue and fibrous tissue. The compound tubuloalveolar acini feed into a system of ductules and finally form 30-50 excretory ducts that enter into the prostatic urethra. In this diagram the two ejaculatory ducts are shown posterior to the prostatic urethra, and represent the confluence of the ducts of the seminal vesicles and the vasa deferentia. At a slightly more inferior level of the axial cut, they will enter the prostatic urethra at the verumontanum

Size

The prostate is smaller than one would expect.  It has been compared to a small kiwi fruit, small plum, an almond and a chestnut.  In fact after a small experiment involving the purchase of these fine fruits and nuts it was found that the chestnut was closest in size in all dimensions.

Size of the Prostate

The diagram depicts the variety of structures that have been compared to the size of the prostate. After a shopping spree to Russo’s in Newton Massachusetts and some significant research into the true sizes of the fruits and nuts that have been compared to the prostate, it was found that the chestnut (e) is closest to the size of the prostate. The kiwi (b) and plum (c) were far larger and A-P dimensions particularly excessively large. The walnut (d) was close but A-P dimension too large, the plum tomato (f) too round, and the almond (g) too thin in the A-P dimension.

Shape

In the A-P projection it is cone shaped and almost heart shape with the apex directed inferiorly while the base is in contact with the bladder superiorly.

The Shape of the Prostate and The Shape of the Chestnut 

The diagram depicts the chestnut and correlative artistic renderings in the A-P (a,b), transverse (c,d) and sagittal projections (e,f). The rounded anterior and lateral borders and flattened posterior border fit perfectly with the shape of the chestnut.  In the frontal projection the prostate is also heart shaped.

Position

Frontal View of the Prostate – Central Position between the Bladder and the Penis

The diagram reflects the basic anatomy of the chestnut shaped prostate lying in the deep pelvis between the bladder above and the urogenital diaphragm below and surrounded by the obturator internus and levator ani muscles and the inferior aspect of the ischium and pubic bones. The prostatic urethra runs through the prostate and connects the bladder with the penile urethra.

Immediate Neighbors of the Prostate

The CT scan reflects a normal prostate seen in the sagittal plane. The bladder is distended. Note the position of the prostate posterior to the pubic symphysis and anterior to the rectum (r =black bubble) covered posteriorly by Denonvilliers fascia. Superiorly it supports the bladder base and inferiorly it is supported by the perineal membrane.  (genitourinary diaphragm) The bladder is overlaid in yellow and the urethra is the channel overlaid in orange.

Character

Normal prostatic tissue feels rubbery, smooth, and symmetrical.

Blood Supply

The primary blood supply of the prostate comes from the prostatic artery which is a branch of the inferior vesical artery. Some accessory vessels to the prostate are supplied from the middle hemorrhoidal (rectal) and internal pudendal arteries.

Blood Supply from the Anterior Branch of the Internal Iliac Artery

The diagram shows the blood supply to the prostate coming off a branch of the anterior division of the anterior division of the internal iliac artery.

Venous Drainage

The venous drainage of the prostate is via the prostatic plexus.  The plexus surrounds the prostate like a net and joins the venous drainage of the penis (deep dorsal vein) in Santorini’s plexus.  The periprostatic plexus consists of the anterior plexus called Santorini’s plexus that lies behind the pubic symphysis in the retropubic space of Retzius and the para-prostatic plexus called the pudendal plexus (vesicoprostatic plexus) which drains both the inferior aspect of the bladder as well as the prostate. The usual drainage of the prostate is via the internal pudendal vein which drains into the anterior branch of the internal iliac vein.  The plexus however does collateralize with the external pudendal vein which drains into the external iliac system, and the vertebral venous system or Batson’s plexus, which is the valveless system that drains the spinal cord and vertebral column. The intervertebral veins and the epidural venous plexus, collateralize at all levels of the spinal canal and vertebral bodies and also drains into the azygos system. Thus venous drainage goes three ways; internal iliac, external iliac, and azygos via the collateral systems of Santorini’s plexus, vesicoprostatic plexus and Batson’s plexus

Venous Drainage of the Prostate

The diagram reflects the venous drainage of the prostate which is in common with the venous drainage of the penis and bladder. The dorsal vein of the penis divides into two forms a plexus anterior to the bladder called the preprostatic plexus of Santorini. This plexus collateralizes with the pudendal (para-prostatic ) plexus that lies on the lateral aspects of the prostate . The veins finally drain into the anterior branches of the internal iliac venous system via the internal pudendal vein.

Lymphatic Supply

Lymphatic drainage from the prostate is via the internal iliac, sacral, vesical, and external iliac nodes.

Lymphatic Drainage

The lymphatic drainage from the prostate is accommodated by the external iliac nodes, internal iliac nodes which will both drain to the common and para-aortic systems.

Nerve Supply

The autonomic nervous system helps to control the function of the prostate gland.  The parasympathetic division of the autonomic nervous system regulates erection, whereas ejaculation is triggered by sympathetic impulses. (Ventura)   The hypogastric nerve (sympathetic) join the pelvic splanchnic nerves (parasympathetic S2-S4) to form the pelvic plexus.

The Sympathetic Innervation by the Inferior Hypogastric Plexus with Contribution from L1 and L2

The diagram reveals the sympathetic nervous system of the body and in this instance attention is drawn to the innervation of the prostate by the inferior hypogastric plexus, with contributions of L1 and L2

Aging

At birth the prostatic acini are lined with squamous epithelia.  Stimulation of further development of the gland is dependent on maternal steroids, namely estrogens. As the levels of these hormones decrease, an involutional phase ensues during the first 5 months. Large transient surges of serum androgen, estrogen, and progesterone normally occur very early in postnatal life. This is usually between 2 to 3 months of age. At this time, levels may reach upward of 60 times normal prepubertal levels, approaching adult serum testosterone levels.  The prostate increases rapidly in size at puberty. During the fifth decade, it starts to show the effects of aging either resulting in atrophy but more commonly hyperplasia.

 

Getting Older and Bigger – The Story of the Prostate

The artistic rendition is of the normal prostate enlarging with time most commonly due to hyperplasia of the transitional zone. The diagram shows the normal cone shaped gland in maroon in the center with the ductus deferens (yellow) and seminal vesicles. The normal prostate is about the size of a kiwi fruit usually weighs between 20-30gms and has a maximum transverse diameter of 4cms, but can double in size

Then I grew old… and bigger and then
“The eternal battle of the streams: initially both robust,
eventually, both to rust.

Like basketball in reverse,
first shoots, then dribbles.” (Hyde)