Digestive 
Blood
Cardiovascular
Dermatology
Genitourinary,
Hormones
Infections
Oncology and
Musculo-skeletal
Mental health and
Parasites
Respiratory
Senses
Various
All men may have trouble achieving an erection at some time in their lives, especially when they are tired, under stress or under the influence of alcohol, or are suffering from a serious illness.
The penis consists of two columns of erectile tissue called corpora cavernosa (they produce an erection) and a duct (urethra) through which urine flows. During erection, the erectile tissue is filled with blood, the penis enlarges and becomes rigid.
Erectile dysfunction can be organic (physical origin) or psychological. However, in many patients with erectile dysfunction of organic origin an added psychological component aggravates it.
