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In erectile dysfunction, an individual is unable to develop or maintain an erection
during sex.
This disorder is also called impotence and like other sexual dysfunction, this condition
becomes more common with age.
Sex can be important within relationships, so erectile dysfunction often carries with
it emotional and psychological stigma.
In both males and females, sexual activity involves a sequence of events called the sexual
response cycle.
This cycle has four phases, excitement, plateau, orgasm, and resolution.
During the excitement phase, muscle tension, heart rate, and blood flow to the genitals
increases.
In males, this is called an erection.
When these reach the maximum level, it’s called the plateau phase.
Next, the accumulated sexual tension gets released during orgasm, causing ejaculation
in males.
Immediately after orgasm comes the resolution phase, where the body slowly returns to its
original, un-excited state.
Alright, let’s take a closer look at the penis which is made of three long cylindrical
bodies: the corpus spongiosum that surrounds the penile urethra, and the two corpora cavernosa
made of erectile tissue.
The corpora cavernosa are wrapped in a fibrous coat called the tunica albuginea, and each
corpus cavernosum is made up of blood-filled spaces called the cavernosal spaces.
These areas are lined with endothelial cells surrounded by smooth muscle.
Running down the centre of each corpus cavernosum is a large artery called the deep artery which
gives off smaller arteries that supply the cavernosal spaces.
Next, blood get drained from these spaces by small emissary veins, which drain into
the deep dorsal vein.
This vein then carries the blood back into the systemic circulation.
Now, the penis receives both somatic and autonomic innervation through the cavernous nerves,
which innervate both the corpus spongiosum, and the corpora cavernosa.
You can remember the functions of these fibers with the mnemonic “point and shoot.”
“Point” is erection and it’s caused by “P,” or parasympathetic fibers.
“Shoot” is ejaculation and the “S” is for sympathetic.
Now, an erection can happen in two ways, either by physical stimulation of the penis or genitals,
called reflex erection, or by becoming emotionally stimulated by a thought, called psychogenic
erection.
In both cases, the parasympathetic nerve fibers in the cavernosal spaces release acetylcholine
from their nerve endings.
The acetylcholine bind to muscarinic receptors on endothelial cells, which activates the
enzyme nitric oxide synthase.
Nitric oxide synthase converts the amino acid arginine into citrulline and nitric oxide.
The nitric oxide diffuses into the nearby smooth muscle cells, and activates guanylate
cyclase, which converts GTP molecules to cGMP.
This leads to a fall in intracellular calcium levels causing the smooth muscles to relax,
and allowing the cavernosal spaces to expand and fill with blood.
The corpora cavernosa grow in size, and compress the veins, making it harder for blood to leave.
With more blood coming in but very little blood leaving, the penis can maintain an erection.
Erectile dysfunction leads to an inability to develop and maintain a full erection.
Causes include psychological ones like stress, performance anxiety, and depression.
In addition, there are a number of physiologic causes as well.
The most common physiologic cause for erectile dysfunction is an inadequate blood supply
due to atherosclerosis and blood vessel damage from hypertension.
Atherosclerosis is caused by the buildup of atheromatous plaques that can harden the arteries
supplying the penis, which makes it difficult for them to dilate.
Hypertension causes wear and tear in the endothelial cells, and decrease their ability to produce
nitric oxide.
Another condition that can also damage the arteries is diabetes mellitus.
High glucose levels can cause hyaline arteriolosclerosis in the small arterioles in the penis.
This is where the arteriole walls develop hyaline deposits, which makes it harder for
them to dilate.
It also builds up in the capillaries causing the basement membrane to thicken which makes
it harder for oxygen to efficiently move from the vascular space to the tissues, causing
hypoxia and death of the smooth muscle cells.
This hypoxia also causes the parasympathetic nerve fibers to die off.
Damaged parasympathetic nerve fibers can’t release acetylcholine, so there’s less nitric
oxide synthase activation, and less nitric oxide is produced.
Also, conditions like stroke, multiple sclerosis, and back or pelvic trauma can directly damage
the nerves, leading to erectile dysfunction.
Next, endocrine dysfunctions that causes testosterone levels to fall, like hypogonadism, can cause
erectile dysfunction.
This happens because low testosterone levels are associated with lower levels of nitric
oxide synthase, which causes less nitric oxide to be produced, and less smooth muscle relaxation.
Since testosterone production decreases with age, it’s normal for erections to become
more difficult to achieve and maintain later in life.
Finally, many medications can cause erectile dysfunction as a side effect.
These include diuretics because they leave less fluid in your circulation, making it
difficult to achieve an erection, and medications like antidepressants and methadone, but those
mechanisms are not as well understood.
There is no specific test to diagnose erectile dysfunction, so the diagnosis largely relies
on the sexual experiences of the individual.
Careful questioning of psychological stressors as well as blood tests to check for testosterone
and glucose levels, a neurological assessment, and duplex ultrasound to evaluate blood flow
and atherosclerosis can be done to investigate the cause of erectile dysfunction.
Treatment of erectile dysfunction largely focuses on addressing the underlying cause.
In terms of medications, PDE-5 inhibitors, like sildenafil can be used.
These medications inhibit the PDE-5 enzyme in endothelial cells which normally breaks
down cGMP, leading to higher levels of cGMP.
That allows for more smooth muscle relaxation which facilitates an erection.
Sometimes, vacuum erection devices can be used.
These devices apply negative pressure around the penis which can help draw in blood to
achieve an erection.
Finally, surgical procedures like prosthetic implants can be embedded into the penis.
They does not cause erections but it could help keep the penis rigid.
All right, as a quick recap, erectile dysfunction is the inability to develop or maintain an
erection and it could have psychological or organic causes.
Organic causes can be due to cardiovascular disorders like hypertension, neurological
problems like those caused by diabetes, or hormonal dysfunction where testosterone levels
decrease.
Various medications, like diuretics can also cause erectile dysfunction as an side effect.
There’s no specific test to diagnose erectile dysfunction, so, diagnosis is typically geared
at detecting pre-existing causes.
Treatment includes PDE-5 inhibitors like sildenafil, vacuum erection devices, and surgery.