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Sexual Physiology

Sexual physiology and development begin in early childhood and represent a complex process of events that lead to the final development of sexual orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment and behavior. Sexual behavior and interactions include several changes that are quite different between males and females.

Last updated: 10 Aug, 2021

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Introduction

There are 3 ways to determine a person’s biologic sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria:

  • Genetic sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria: determined by presence of sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure (XX = female, XY = male)
  • Gonadal sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria: determined by presence of reproductive structures ( ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries: Anatomy in females, testes Testes Gonadal Hormones in males) 
  • Phenotypic sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria: Human gonads Gonads The gamete-producing glands, ovary or testis. Hormones: Overview and Types produce different hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types that determine external phenotype Phenotype The complete genetic complement contained in the DNA of a set of chromosomes in a human. The length of the human genome is about 3 billion base pairs. Basic Terms of Genetics.

Terms

Behaviors during sexual development

Appropriate:

  • During early childhood years:
    • Showing interest in exploring one’s own or other’s genitals
    • Undressing self or others
    • Masturbatory movements
    • Asking reproductive or sexual questions
    • Increased interest in sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria words or play
    • Masturbation is considered a normal behavior at all ages and occurs equally in both genders (it is pathological only when it interferes with normal functioning).
  • Exploring human sexuality is normal, especially during teenage years, with different- or same- sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria partners.

Abnormal:

  • Repeated insertion of objects into vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor: Anatomy or anus
  • Inappropriate sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria play (simulating genital–genital, oral–genital, or anal–genital sexual intercourse)
  • Use of force in sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria play
  • Age-inappropriate sexual knowledge

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Tanner Stages

The Tanner stages is a scale Scale Dermatologic Examination that measures physical/sexual development in children, adolescents, and adults. It involves genitalia in males, breast in females, and pubic hair in both.

Table: Tanner stages in females
Tanner 1 Tanner 2 Tanner 3 Tanner 4 Tanner 5
Age Prepubertal 8–11.5 years 11.5–13 years 12–15 years > 15 years
Pubic hair Villus hair only Sparse hair along the labia Coarse and curly hair covers the pubis. Adult hair that does not spread to the thigh Thigh The thigh is the region of the lower limb found between the hip and the knee joint. There is a single bone in the thigh called the femur, which is surrounded by large muscles grouped into 3 fascial compartments. Thigh: Anatomy Adult hair reaching the thigh Thigh The thigh is the region of the lower limb found between the hip and the knee joint. There is a single bone in the thigh called the femur, which is surrounded by large muscles grouped into 3 fascial compartments. Thigh: Anatomy
Breasts Breasts The breasts are found on the anterior thoracic wall and consist of mammary glands surrounded by connective tissue. The mammary glands are modified apocrine sweat glands that produce milk, which serves as nutrition for infants. Breasts are rudimentary and usually nonfunctioning in men. Breasts: Anatomy Elevation of papilla only Breast buds are palpable (1st sign of puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty in females) and areolae are enlarged. Breast tissue grows with no contour or separation. Breasts Breasts The breasts are found on the anterior thoracic wall and consist of mammary glands surrounded by connective tissue. The mammary glands are modified apocrine sweat glands that produce milk, which serves as nutrition for infants. Breasts are rudimentary and usually nonfunctioning in men. Breasts: Anatomy enlarge and areolae form secondary mound on the breast. Adult breast contours are present. Only the papilla is raised.
Other observations Adrenarche and ovarian growth Clitoral enlargement, labial pigmentation, growth of uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy Axillary hair, acne Menarche Menarche The first menstrual cycle marked by the initiation of menstruation. Menstrual Cycle and development of menses Menses The periodic shedding of the endometrium and associated menstrual bleeding in the menstrual cycle of humans and primates. Menstruation is due to the decline in circulating progesterone, and occurs at the late luteal phase when luteolysis of the corpus luteum takes place. Menstrual Cycle Adult genitalia
Table: Tanner stages in males
Tanner 1 Tanner 2 Tanner 3 Tanner 4 Tanner 5
Age Prepubertal 8–11.5 years 11.5–13 years 12–15 years > 15 years
Pubic hair Villus hair only Sparse hair at base of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy Coarse and curly hair appears over the pubis. Adult- quality Quality Activities and programs intended to assure or improve the quality of care in either a defined medical setting or a program. The concept includes the assessment or evaluation of the quality of care; identification of problems or shortcomings in the delivery of care; designing activities to overcome these deficiencies; and follow-up monitoring to ensure effectiveness of corrective steps. Quality Measurement and Improvement hair in the pubic area, sparing the thigh Thigh The thigh is the region of the lower limb found between the hip and the knee joint. There is a single bone in the thigh called the femur, which is surrounded by large muscles grouped into 3 fascial compartments. Thigh: Anatomy Adult- quality Quality Activities and programs intended to assure or improve the quality of care in either a defined medical setting or a program. The concept includes the assessment or evaluation of the quality of care; identification of problems or shortcomings in the delivery of care; designing activities to overcome these deficiencies; and follow-up monitoring to ensure effectiveness of corrective steps. Quality Measurement and Improvement hair in the pubic area, reaching the thigh Thigh The thigh is the region of the lower limb found between the hip and the knee joint. There is a single bone in the thigh called the femur, which is surrounded by large muscles grouped into 3 fascial compartments. Thigh: Anatomy
Genitalia
  • Testes Testes Gonadal Hormones < 2 cm
  • No growth of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy
  • Testes Testes Gonadal Hormones: 3.3–4 cm
  • Increase in length of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy
  • Testes Testes Gonadal Hormones: 4.1–4.5 cm
  • Growth of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy, darkening of the scrotum Scrotum A cutaneous pouch of skin containing the testicles and spermatic cords. Testicles: Anatomy
Other observations Adrenarche Decrease in body fat Gynecomastia Gynecomastia Gynecomastia is a benign proliferation of male breast glandular ductal tissue, usually bilateral, caused by increased estrogen activity, decreased testosterone activity, or medications. The condition is common and physiological in neonates, adolescent boys, and elderly men. Gynecomastia, breaking of voice, increased muscle mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast Axillary hair, voice change, acne Facial hair, increase in muscle mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast

Sexual Response Cycle

Sexual dysfunctions (in males or females) arise from problems involving any stage of the sexual response cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation.

Table: Stages of the sexual response cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation
Stage Changes in females Changes in males Changes in both
Desire
  • Motivation or interest in sexual activity
  • Expressed by sexual fantasies
Excitement/arousal
  • Begins with either fantasy or physical contact
  • Vaginal lubrication
  • Clitoral erection Erection The state of the penis when the erectile tissue becomes filled or swollen (tumid) with blood and causes the penis to become rigid and elevated. It is a complex process involving central nervous system; peripheral nervous systems; hormones; smooth muscles; and vascular functions. Penis: Anatomy
  • Labial swelling Swelling Inflammation
  • Elevation of the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy in the pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy (tenting)
  • Begins with either fantasy or physical contact
  • Erection Erection The state of the penis when the erectile tissue becomes filled or swollen (tumid) with blood and causes the penis to become rigid and elevated. It is a complex process involving central nervous system; peripheral nervous systems; hormones; smooth muscles; and vascular functions. Penis: Anatomy and testicular enlargement
  • Flushing
  • Nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast erection Erection The state of the penis when the erectile tissue becomes filled or swollen (tumid) with blood and causes the penis to become rigid and elevated. It is a complex process involving central nervous system; peripheral nervous systems; hormones; smooth muscles; and vascular functions. Penis: Anatomy
  • Hemodynamic changes (increased respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy, pulse, and BP)
Orgasm Vaginal and uterine contractions
  • Facial grimacing
  • Release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of tension
  • Slight clouding of consciousness
  • Involuntary anal sphincter contractions
  • Acute increase in BP and pulse
Resolution Women experience little or no refractory period. Men have a refractory period lasting minutes to hours during which they cannot re-experience orgasm.
  • Muscles relax.
  • Cardiovascular state returns to baseline.
  • Sexual organs return to normal baseline.

Normal Sexual Changes with Aging

Healthy sexual behavior and desire persist into elderly adulthood.

Pharmacotherapy exists to facilitate sexual behavior:

  • Sildenafil Sildenafil A phosphodiesterase type-5 inhibitor; vasodilator agent and urological agent that is used in the treatment of erectile dysfunction and primary pulmonary hypertension. Phosphodiesterase Inhibitors: to assist erection Erection The state of the penis when the erectile tissue becomes filled or swollen (tumid) with blood and causes the penis to become rigid and elevated. It is a complex process involving central nervous system; peripheral nervous systems; hormones; smooth muscles; and vascular functions. Penis: Anatomy in men
  • Hormonal creams/pills: to counteract vaginal atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation in women
Table: Sexual changes with aging
Changes in females Changes in males Changes in both
  • Vaginal dryness and thinning (due to decrease in estrogen Estrogen Compounds that interact with estrogen receptors in target tissues to bring about the effects similar to those of estradiol. Estrogens stimulate the female reproductive organs, and the development of secondary female sex characteristics. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. Ovaries: Anatomy)
  • Decreased sensitivity Sensitivity Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Blotting Techniques in sexual organs ( nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast, clitoral, vulva Vulva The vulva is the external genitalia of the female and includes the mons pubis, labia majora, labia minora, clitoris, vestibule, vestibular bulb, and greater vestibular glands. Vagina, Vulva, and Pelvic Floor: Anatomy)
  • Slower erection Erection The state of the penis when the erectile tissue becomes filled or swollen (tumid) with blood and causes the penis to become rigid and elevated. It is a complex process involving central nervous system; peripheral nervous systems; hormones; smooth muscles; and vascular functions. Penis: Anatomy
  • Weaker erection Erection The state of the penis when the erectile tissue becomes filled or swollen (tumid) with blood and causes the penis to become rigid and elevated. It is a complex process involving central nervous system; peripheral nervous systems; hormones; smooth muscles; and vascular functions. Penis: Anatomy
  • Decrease in intensity of ejaculation
  • Longer refractory period
  • More stimulation needed
Normal or slight decrease in the desire for sexual interest and activity

Clinical Relevance

  • Gender Gender Gender Dysphoria dysphoria: also known as gender Gender Gender Dysphoria identity disorder. Individuals with gender Gender Gender Dysphoria dysphoria have difficulties reconciling the incongruence between their expressed gender Gender Gender Dysphoria and assigned gender Gender Gender Dysphoria (continuous inner conflict between gender Gender Gender Dysphoria identity and sexual identity). The 1st signs of cross- gender Gender Gender Dysphoria behaviors begin around age 3, the time when gender Gender Gender Dysphoria identity is established.
  • Female sexual dysfunction Female sexual dysfunction Female sexual dysfunction represents a variety of disorders in any part of the sexual response cycle, including desire disorders, arousal disorders, orgasmic disorders, and pain disorders. The condition may result from stresses and interpersonal conflicts as well as physical illness or medication/substance use. Female Sexual Dysfunction: disorder in any part of the female sexual response cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation. This group of disorders includes desire disorders, arousal disorders, orgasmic disorders, and pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways disorders. The dysfunction might result from stresses and interpersonal conflicts, as well as from physical illness or medication/substance use. These disorders cause significant distress to the patient.
  • Male sexual dysfunction Male sexual dysfunction Male sexual dysfunction is any disorder that interferes with the male sexual response cycle and includes desire disorders, erectile disorders, and ejaculatory disorders. Sexual dysfunction has a varied etiology and may be due to psychological causes, endocrine diseases, neurogenic dysfunction, chronic medical illness, or medication/substance abuse. Male Sexual Dysfunction: disorder in any part of the male sexual response cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation. This group of disorders includes desire disorders, arousal disorders, and orgasmic disorders. The dysfunction may be caused by psychological disorders, endocrine diseases, neurogenic dysfunction, chronic medical illness, or medication/substance abuse.

References

  1. Blitzstein S., Kaufman M., Ganti L. (2016). Sexual dysfunctions and paraphilic disorders. Chapter 16 of First Aid for the Psychiatry Clerkship, 4th ed. McGraw-Hill Education/Medical, p. 172.
  2. Sadock, B. J., Sadock, V. A., & Ruiz, P. (2014). Human sexuality and sexual dysfunctions. Chapter 17 of Kaplan and Sadock’s Synopsis of Psychiatry: Behavioral Sciences/Clinical Psychiatry, 11th ed. Philadelphia: Lippincott Williams and Wilkins, pp. 564–574.
  3. Forcier, M. (2020). Adolescent sexuality. UpToDate. Retrieved June 22, 2021, from https://www.uptodate.com/contents/adolescent-sexuality

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