Male Reproductive Anatomy and Physiology
MALE REPRODUCTIVE SYSTEM
Vas Deferens / Ductus Deferens
Male Reproductive System
The male reproductive system consists of many parts, each with a specific task to perform.
Each part of the system can go wrong and cause problems for it’s owner – sometimes physical and sometimes psychological.
The Male Reproductive System consists of:
See Anatomy Gallery: Male Anatomy
The pituitary gland is a penny sized gland, in your brain, which is linked to the hypothalamus. Together, they form the control centre of all activity, as well as your reproductive system.
The hypothalamus signals the pituitary to release – or not release – certain hormones at outposts around your body.
These are called ‘releasing factors’, and all three reproductive signals consist of a single protein – LH-RH – luteinising hormone releasing hormone.
The pituitary gland is divided into a front and rear lobe or section.
The front lobe is joined to the hypothalamus by blood vessels and forms 70% of the pituitary gland. This section controls reproduction.
The rear lobe is linked to the hypothalamus by nerve cells. It regulates salt and water.
When the front lobe receives LH-RH messages from the hypothalamus, it secretes several hormones, known as gonadotrophins (gonad: testicle; trophic: nourishment).
The two responsible for regulating sperm production in men are:
FSH (follicle stimulating hormone); and
LH (luteinising hormone).
The hypothalamus is linked by blood vessels and nerve cells to your pituitary gland. It is located in your brain and sits between your eyes and above the roof of your mouth. It controls everything essential for life – e.g. thirst, hunger, body temperature.
It’s a pathway for electrical messages, en route to the rest of your body. Just how it converts these electrical messages into action is an exciting but little-understood aspect of biological science.
The gonads/testicles are two egg-shaped organs, which lie outside the male body and are cushioned in the scrotum.
By lying outside the body, they maintain a slightly cooler temperature – i.e.,. 34.8 deg C instead of 37 deg C – than the rest of the body so as not to ‘cook’ and destroy the sperm.
When cold, the scrotum contracts and ‘shrugs up’ to hug the body for warmth.
When warm, the scrotum relaxes to allow the testicles to hang away from the body and remain cooler.
Millions of nerve fibres run through the scrotum, making it so sensitive to pain, that men always try to protect their testicles.
A hard blow to the testicles could damage sperm production and result in infertility.
Their size and weight varies, depending on your overall size and weight.
Testes size can be measured, and sperm count tested. They are small before puberty, after which they grow.
Normal adult testes are approx 2 inches / 4.5cms long by 1.5 inches /3cms wide, with a volume of 25mls. See Testicular Measurement.
Immature testicles, due to a chromosomal abnormality or severe illness can result in infertility and small testicles.
Each testicle is filled with thousands of wrinkled threads up to a metre long. These are called seminiferous tubules and are where new sperm are born.
Three or four tubules twist together to form a lobule.
Thousands of lobules roll together and pack into each testicle.
Under the influence of hormones, tiny cells in the tubules start to produce sperm.
The epididymis a palpable ‘lump’ at the upper back of each testicle and is also known as the sperm holding tank. Here, sperm live for 12 days while learning to swim, before they pass along the vas deferens.
Each epididymis consists of a long, hollow length of tissue.
Unwound, they are about 12 – 15 feet long.
Wound up; they are about a ½ inch (12mm) long.
Vas Deferens / Ductus Deferens
The Vas Deferens (also called Ductus Deferens) are two long heavy tubes, located on either side of the pelvic cavity, which contain mature live sperm. Surrounded by arteries and veins, they make up the spermatic cord.
They pass through the scrotum and enter the body through the inguinal canals, before running alongside the bladder, over the ureters and down into the prostate gland. Here they empty into the ejaculatory ducts and finally into the urethra (urine passage).
Mature sperm are pulsated along the vas, towards the ampulla or pocket.
They remain here until they are ejaculated.
This is why, after vasectomy, there can still be live sperm in the ejaculate for up to 12 weeks.
The seminal vesicles are two pouches, adjacent to the upper ends of the vas deferens.
They secrete more than half the fluid ejaculated.
This is an acidic fluid which, by itself, would kill sperm.
The prostate is a multi-lobed gland at the upper part of, and surrounding, the urethra. The vas, the ejaculatory ducts and the urethra join together inside it.
It’s a walnut-sized organ that secretes chemicals which liquefy semen.
This richly alkaline fluid balances the ejaculate, in order to subdue the acid in the vagina.
Prostate fluid contains citric acid, acid phosphatase, several proteolytic enzymes – such as prostate-specific antigen (PSA), pepsinogen, lysozyme, amylase and hyaluronidase, which liquify the coagulated semen.
Secretions from the prostate gland enter the prostatic urethra through prostatic ducts.
They make up approx 25% of semen, help sperm motility and viability.
The prostate grows during puberty until age 30.
From 30-45 years of age, it is stable.
After 45 further growth may occur.
These pea-sized organs – also known as ‘bulbourethral glands’ – lie underneath the prostate, on either side of the urethra and have ducts which open into it.
During arousal, they pave the way for ejaculation by secreting an alkaline substance which protects sperm by neutralising acids in the urethra. They also secrete mucus which lubricates the tip of the penis and the urethral lining. This decreases the number of sperm damaged during ejaculation.
The urethra is a shared passage which passes through the prostate gland, the urogenital diaphragm and the penis.
The reproductive system passes semen through it.
The urinary system passes urine out of the body along it.
The urethra is about 8 inches / 20 cm long and consists of 3 parts.
The prostatic urethra is between 1 and 2 inches / 2 and 3 cm long.
The membranous urethra is 1/2 inch / 1 cm long.
The spongy (penile) urethra is 6-8 inches / 15-20 cm long ending at the spongy external urethral orifice or meatus.
Cylindrical in shape, the penis contains the urethra. Therefore, the penis provides the passageway for excretion of urine – and for the ejaculation of semen.
The body of the penis consists of three sections:
The corpus cavernosa penis.
The corpus spongiosum penis.
All three are enclosed in erectile tissue, permeated by blood supply.
The far (distal) end of the corpus spongiosum is a slightly enlarged, acorn-shaped area, called the glans penis.
The weight of the penis is supported by two ligaments called fundiform ligaments. These come from the suspensory ligament, which arises from the symphysis pubis or pubic bone region.
Erection is a parasympathetic reflex – ie. unconscious and involuntary.
When sexually stimulated, the arteries supplying the penis dilate. Large quantities of blood enter the blood sinuses.
Before ejaculation, semen is propelled into the penile section of the urethra by peristaltic contractions of the ductus deferens, seminal vesicles, ejaculatory ducts and the prostate gland.
When the arteries constrict at ejaculation, pressure on the veins is relieved and the penis returns to its flaccid state.
© Sexplained Ltd 2015