Human penis in the context of "Sexual intercourse"

Urology (from Greek οὖρον ouron "urine" and -λογία -logia "study of"), also known as genitourinary surgery, is the branch of medicine that focuses on surgical and medical diseases of the urinary system and the male reproductive organs. Organs under the domain of urology include the kidneys, adrenal glands, ureters, urinary bladder, urethra, and the male reproductive organs (testes, epididymides, vasa deferentia, seminal vesicles, prostate, and penis).

The urinary and reproductive tracts are closely linked, and disorders of one often affect the other. Thus a major spectrum of the conditions managed in urology exists under the domain of genitourinary disorders. Urology combines the management of medical (i.e., non-surgical) conditions, such as urinary-tract infections and benign prostatic hyperplasia, with the management of surgical conditions such as bladder or prostate cancer, kidney stones, congenital abnormalities, traumatic injury, and stress incontinence.

Oral sex, sometimes referred to as oral intercourse, is sexual activity involving the stimulation of the genitalia of a person by another person using the mouth (including the lips, tongue, or teeth). Cunnilingus is oral sex performed on the vulva while fellatio is oral sex performed on the penis. Anilingus, another form of oral sex, is oral stimulation of the anus.

Oral sex may be performed as foreplay to incite sexual arousal before other sexual activities (such as vaginal or anal intercourse), or as an erotic and physically intimate act in its own right. Like most forms of sexual activity, oral sex can pose a risk for contracting sexually transmitted infections (STIs). However, the transmission risk for oral sex, especially HIV transmission, is significantly lower than for vaginal or anal sex.

Anal sex or anal intercourse principally means the insertion and thrusting of the erect penis into a person's anus, or anus and rectum, for sexual pleasure. Other forms of anal sex include anal fingering, the use of sex toys, anilingus, and pegging. Although anal sex most commonly means penile–anal penetration, sources sometimes use anal intercourse to exclusively denote penile–anal penetration, and anal sex to denote any form of anal sexual activity, especially between pairings as opposed to anal masturbation.

While anal sex is commonly associated with male homosexuality, research shows that not all homosexual men engage in anal sex and that it is not uncommon in heterosexual relationships. Types of anal sex can also be part of lesbian sexual practices. People may experience pleasure from anal sex by stimulation of the anal nerve endings, and orgasm may be achieved through anal penetration – by indirect stimulation of the prostate in men, indirect stimulation of the clitoris or an area in the vagina (sometimes called the G-spot) in women, and other sensory nerves (especially the pudendal nerve). People may also find anal sex painful, sometimes extremely so, which may be due to psychological factors in some cases.

A man is an adult male human. Before adulthood, a male child or adolescent is referred to as a boy.

Like most other male mammals, a man's genome usually inherits an X chromosome from the mother and a Y chromosome from the father. Sex differentiation of the male fetus is governed by the SRY gene on the Y chromosome. During puberty, hormones which stimulate androgen production result in the development of secondary sexual characteristics that result in even more differences between the sexes. These include greater muscle mass, greater height, the growth of facial hair and a lower body fat composition. Male anatomy is distinguished from female anatomy by the male reproductive system, which includes the testicles, sperm ducts, prostate gland and epididymides, and penis. Secondary sex characteristics include a narrower pelvis and hips, and smaller breasts and nipples.

The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body, and within the pelvis.

The main male sex organs are the penis and the scrotum, which contains the testicles that produce semen and sperm, which, as part of sexual intercourse, fertilize an ovum in the female's body; the fertilized ovum (zygote) develops into a fetus, which is later born as an infant. The corresponding system in females is the female reproductive system.

Orgasm (from Greek ὀργασμός, orgasmos; "excitement, swelling"), sexual climax, or simply climax, is the sudden release of accumulated sexual excitement during the sexual response cycle, characterized by intense sexual pleasure resulting in rhythmic, involuntary muscular contractions in the pelvic region. Orgasms are controlled by the involuntary or autonomic nervous system and are experienced by both males and females; the body's response includes muscular spasms (in multiple areas), a general euphoric sensation, and, frequently, body movements and vocalizations. The period after orgasm (known as the resolution phase) is typically a relaxing experience due to the release of the neurohormones oxytocin and prolactin, as well as endorphins (or "endogenous morphine").

Human orgasms usually result from physical sexual stimulation of the penis in males (typically accompanied by ejaculation) and of the clitoris (and vagina) in females. Sexual stimulation can be by masturbation or with a sexual partner (penetrative sex, non-penetrative sex, or other sexual activity). Physical stimulation is not a requisite, as it is possible to reach orgasm through psychological means. Getting to orgasm may be difficult without a suitable psychological state. During sleep, a sex dream can trigger an orgasm and the release of sexual fluids (nocturnal emission).

Hard flaccid syndrome (HFS), also known as hard flaccid (HF), is a rare acquired dysautonomic condition characterized by a flaccid penis that remains in a firm, semi-rigid state in the absence of sexual arousal. Patients often describe their flaccid penis as firm to the touch, rubbery, shrunken, and retracted, frequently accompanied by pain, discomfort, and various other symptoms. While the condition is not fully understood, current research indicates that HFS results from excessive sympathetic nervous system activity in the smooth muscle tissue of the penis, triggered by a pathological activation of a proposed pelvic/pudendal-hypogastric reflex. Among other causes, injuries to the erect penis, blunt trauma to the pelvis or perineum, and damage to the cauda equina are thought to induce this reflex. Although unproven, axon sprouting in sympathetic ganglia following a peripheral nerve injury is a possible explanation for HFS. The majority of patients are in their 20s and 30s, with symptoms severely affecting their quality of life. Treatment typically involves a combination of alpha blockers and PDE5 inhibitors, although there is limited evidence supporting their efficacy. Due to the lack of comprehensive understanding and awareness within the scientific and medical communities, there is currently no definitive treatment for HFS.

Human sexual reproduction, to produce offspring, begins with fertilization. Successful reproduction typically involves sexual intercourse between a healthy, sexually mature and fertile male and female. During sexual intercourse, sperm cells are ejaculated into the vagina through the penis, resulting in fertilization of an ovum to form a zygote.

While normal cells contain 46 chromosomes (23 pairs), gamete cells contain only half that number, and it is when these two cells merge into one combined zygote cell that genetic recombination occurs. The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 38-week gestation period for the embryo (and eventually foetus) that is followed by childbirth.