Sexual Physiology

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 Genetic sex Sex Determination: determined by presence of sex chromosomes Sex chromosomes The homologous chromosomes that are dissimilar in the heterogametic sex. There are the X chromosome, the Y chromosome, and the w, z chromosomes (in animals in which the female is the heterogametic sex (the silkworm moth bombyx mori, for example)). In such cases the w chromosome is the female-determining and the male is zz. Basic Terms of Genetics (XX = female, XY = male)
Gonadal sex Gonadal sex Sex Determination: 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 Phenotypic sex Sex Determination: 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

Gender Gender Gender Dysphoria identity:
- Represents individual’s inner sense of maleness or femaleness
- Usually established by age 3
Gender Gender Gender Dysphoria role or behavior:
- Represents behaviors exhibited by or expected from an individual
- Can be congruent or incongruent with individual’s gender Gender Gender Dysphoria identity
Sexual orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment:
- Individual’s pattern of physical and emotional arousal
- An individual assessment of one’s sexual orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment is termed sexual identity.
- Examples:
  - Homosexuality: attraction to those with same gender Gender Gender Dysphoria identity
  - Heterosexuality: attraction to those with opposite gender Gender Gender Dysphoria identity
  - Bisexuality: attraction to either gender Gender Gender Dysphoria identity
  - Asexuality: attraction to neither gender Gender Gender Dysphoria identity
- Coming out: defined as individual acknowledging their sexual orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment
Gender Gender Gender Dysphoria dysphoria:
- Emotional discomfort arising from misalignment between gender Gender Gender Dysphoria identity and sexual identity
- Seen in boys more frequently than in girls

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 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

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 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 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: 2.5–3.2 cm Thinning and reddening of the scrotum Scrotum A cutaneous pouch of skin containing the testicles and spermatic cords. Testicles: 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	Testes Testes Gonadal Hormones > 4.5 cm Adult genital size
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

Girls tanner stage — Tanner scale, also called sexual maturity rating (SMR) showing the different stages of breast and pubic hair development in girls
Image by Lecturio.

Tanner staging in boys — Tanner scale, also called sexual maturity rating (SMR) showing the different stages of breast and pubic hair development in girls
Image by Lecturio.

Sexual Response Cycle

Sexual dysfunctions (in males or females) arise from problems involving any stage of the sexual response cycle.

**Table: Stages of the sexual response cycle**
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 Anatomy (External & Internal), pulse, and BP)
Orgasm	Vaginal and uterine contractions	Tightening of the scrotal sac Secretion Secretion Coagulation Studies of a few drops of seminal fluid Ejaculation	Facial grimacing Release 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 mucosal 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 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 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. 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. 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 use disorder.

References

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.
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.
Forcier, M. (2020). Adolescent sexuality. UpToDate. Retrieved June 22, 2021, from https://www.uptodate.com/contents/adolescent-sexuality

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Introduction

Terms

Behaviors during sexual development

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Tanner Stages

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Sexual Response Cycle

Normal Sexual Changes with Aging

Clinical Relevance

References

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