It is inability to either achieve or maintain a sustained erection sufficient enough for a penetrative intercourse.
How does normal erection occur?
Erection is a very dynamic and multistep process. The sexual desire is caused by normal level of testosterone and prolactin hormones in blood. Low level of testosterone and high level of prolactin can decrease sexual desire.
When one gets sexually excited by stimuli which can be visual, touch, sound some biochemical changes happen in brain which indicate to the brain that the individual is sexually excited. If the brain is disturbed because of any reason, it rejects the stimulus and erection will not be achieved. This can happen if the individual is under stress, depressed, anxious due to prior failures to achieve erection or if individual is mourning.
If the state of mind is sound, then it assesses the situation, if the situation is conducive for sex then the brain send signal to backbone through a network of nerves that can be considered akin to electrical wires. From the back, the signal is taken to penis through cavernosal nerves. If there is a back problem like slipped disc, these nerves may get compressed and may affect erection. Once the signal reaches the penis, the amino acid Argenine (this can be considered analogous to coal) is burned to produce chemical called nitric oxide (think of this as fire that is being produced by burning coal). Once the concentration of nitric oxide increases in penis it causes some changes in blood flow to penis.
There are 2 types of tubes in penis carrying blood in and out of penis. Under influence of nitric oxide, the tubes carrying blood into penis open up and more blood flows into the penis.
At same time the tubes carrying blood out of penis compresses. There is more inflow and less outflow of blood, leading to penile engorgement, a process called erection.
There are 5 stages of erection:
Stage 1:Penile blood flow increases and it leads to enlargement of penis. However it is not rigid.
Stage 2:There is pooling of blood in penis leading to mild rigidity. It will be difficult to penetrate the vagina if it is not well lubricated. However, if the vaginal is well lubricated one will be able to penetrate the penis in by supporting and directing it using ones hand.
Stage3: In this stage all the tubes carrying blood out of penis get completely occluded. The penis becomes hard and doesn’t buckle. Weather the vagina is lubricated or not, one will be able to penetrate in this stage.
Stage4:This happens at time of orgasm. The penis fills to its maximum capacity. There is no inflow of outflow of blood in this stage. The penis is hardest in this stage.
Stage5: After orgasm, all the changes get reversed and penis becomes flaccid again. It will remain flaccid for a variable time period called refractory period. In this period it is impossible to gain erection again.
