Biology of Sex Quiz 2 (Males)

Sex

Biological and physiological characteristics (gametes, chromosomes, hormonal profiles, internal and external sex organs).

Gender

A social construct: the behaviors, roles, expectations, and activities a society assigns as masculine or feminine.

Primary sex characteristics

The gonads (ovaries and testes) and associated structures.

Secondary sex characteristics

Overall appearance, such as external genitalia, body hair, and mammary glands.

Legal sex

The official designation of sex, heavily influenced by morphological sex at birth but also by chromosomal and gonadal sex.

Sexual identity

The psychological self-perception of being male, female, or other.

Gender role

The behaviors and attitudes considered appropriate for each sex within a specific culture.

Sexual orientation

Erotic attraction to members of the same species. Types include homosexual (same sex), heterosexual (opposite sex), bisexual (both), and asexual (neither).

Gender identity

A person's deep internal sense of being female, male, both, in between, or neither.

Gender expression

The external way a person expresses gender (clothing, hair, mannerisms, activities, social roles).

Gender perception

How others interpret a person's gender expression.

Gender diverse

Describes people whose gender behaviors, appearances, or identities differ from those culturally assigned to their birth sex.

Transgender

A person whose gender identity does not match their assigned sex.

Cisgender

A person whose gender identity and expression are consistent with the norms for the sex they were assigned at birth.

Agender

A person who does not identify as having a particular gender.

Affirmed gender

A person's gender identity as communicated to and validated by others as authentic.

Gender dysphoria

Distress from the incongruence between one's experienced gender and assigned gender (the DSM-5 diagnosis).

Gender identity disorder

The older DSM-IV diagnosis, replaced by gender dysphoria. It is no longer appropriate to use.

Chromosomal sex

Sex as determined by the sex chromosomes received at fertilization (males XY, females XX in mammals).

Y chromosome

A much smaller chromosome than the X, with fewer than 100 of its original genes. Without it, an individual develops as female (the default pathway).

SRY (sex-determining region of the Y)

The Y-chromosome gene that encodes testis-determining factor.

Testis-determining factor

Directs the embryonic gonads to become testes, which then secrete testosterone and MIS.

Müllerian inhibiting substance (MIS)

Causes regression of the Müllerian ducts, suppressing female ductal structures (uterus, Fallopian tubes).

Testosterone (in development)

Promotes male ductal structures (vas deferens), sex glands (prostate), and external genitalia.

Gonadal sex

Sex as determined by possessing ovaries or testes.

Gametic sex

Sex as determined by producing ova (females) or sperm (males). For some biologists this is the definition of biological sex.

Hormonal sex

Sex as determined by concentrations of androgens versus estrogens. Males tend to have more androgens and females more estrogens.

Morphological sex

Sex as determined by body form, including primary characteristics (present at birth) and secondary characteristics (appear at puberty).

Behavioral sex

Sex as determined by male-typical or female-typical behaviors. It is culturally influenced and determined by both genes and hormones.

Complete androgen insensitivity syndrome (CAIS)

XY individuals with no functional androgen receptors. They have testes but develop a female phenotype and are sterile.

Partial androgen insensitivity syndrome (PAIS)

Partial sensitivity to androgens.

Klinefelter syndrome (47,XXY)

Males with an extra X chromosome. Features include reduced fertility, smaller testicles, and gynecomastia. It is the most common sex chromosome disorder in males (about 1 in 500).

Turner syndrome (XO)

Females with a single X chromosome (monosomy). Features include non-working ovaries, a webbed neck, and heart defects (about 1 in 2,000 female births).

Barr body

An inactivated X chromosome. Turner (XO) females have none, while Klinefelter (XXY) males and normal XX females have one.

X-linked trait

A trait carried on the X chromosome, such as red-green color blindness. Males have only one X, so there is no redundancy.

Hormone

A chemical messenger secreted into the blood or extracellular fluid that can reach virtually every cell.

Endocrine system

Glands that secrete hormones into the blood. It broadcasts to essentially all cells.

Target cell

A cell that responds to a hormone because it has the specific receptor for it.

Receptor

A specific binding site that mediates a hormone's cellular actions. Receptors have high specificity, high affinity, and low capacity.

Membrane receptors

Receptors for protein hormones, located on the cell surface.

Intracellular receptors

Receptors for steroid hormones, located inside the cell.

Autocrine

Secretions that affect the secreting cell itself.

Paracrine

Secretions that affect neighboring cells.

Endocrine (mediation)

Chemicals made in one location that affect cells elsewhere in the body.

Ectocrine (exocrine)

Chemical cues released into the environment. Pheromones act within a species and kairomones act among species.

Intracrine

Substances that regulate intracellular events.

Hypothalamus

Brain region that controls hormone secretion.

Anterior pituitary

Secretes hormones that regulate the thyroid, adrenal cortex, and gonads, as well as growth.

HPG axis (hypothalamic-pituitary-gonadal axis)

The cascade linking hypothalamus, anterior pituitary, and gonad. Each step magnifies the signal, so small brain signals can have large effects.

GnRH (gonadotropin-releasing hormone)

Released by the hypothalamus. It stimulates the anterior pituitary to release LH and FSH.

LH (luteinizing hormone)

Released by the anterior pituitary. It acts on Leydig cells to promote testosterone production.

FSH (follicle-stimulating hormone)

Released by the anterior pituitary. It acts on the testis (Sertoli cells) to support sperm production.

Negative feedback

A product inhibits further secretion by the gland that led to its production. Testosterone inhibits the hypothalamus and pituitary through both short and long loops.

Positive feedback

A product stimulates further secretion by the gland that led to its production.

Inhibin

Hormone from Sertoli cells that provides negative feedback.

Steroid hormone

A hormone derived from cholesterol (progesterone, androgens, estrogens, cortisol, aldosterone).

Androgens

The "male" sex steroids (testosterone, DHT, androstenedione). They mediate spermatogenesis, sexual and aggressive behavior, and male primary and secondary sex characteristics.

Estrogens

The "female" sex steroids (e.g., estradiol). In males they organize the brain.

Aromatase

Enzyme that converts testosterone to estradiol. It can be active in the gonads and target tissue, and during development estradiol organizes the male hypothalamus.

DHT (dihydrotestosterone)

A more potent androgen than testosterone, made by 5α-reductase. It is used by the prostate and external genitalia, especially during development (e.g., testis descent), and elevated levels are associated with male hair loss.

5a-reductase

Enzyme that converts testosterone to DHT.

Finasteride (Propecia)

Hair-loss drug that blocks 5α-reductase. Pregnant women should not handle it because it could disrupt DHT-dependent development in a male fetus. It can also cause fertility issues in some men.

Testes (testis)

The male gonads. They produce sperm and secrete hormones.

Scrotum

Supporting structure for the testes. Normal sperm production requires a temperature 2-3 °C below core body temperature.

Raphe

The external median ridge of the scrotum.

Scrotal septum

Internally divides the scrotum into two sacs, each with one testis.

Dartos muscle

Muscle in the scrotum wall. It contracts or relaxes to regulate testis temperature.

Cremaster muscle

Muscle associated with each testis. It contracts or relaxes to regulate testis temperature.

Seminiferous tubules

Coiled tubules in the testis where spermatogenesis occurs.

Spermatogenic cells

Sperm-forming cells.

Spermatogonia

Diploid stem cells that arise from primordial germ cells and give rise to sperm.

Primary spermatocyte

Diploid (2n) cell that duplicates its DNA and begins meiosis.

Secondary spermatocyte

Haploid (n) cell produced at the end of meiosis I.

Spermatid

Haploid cell produced at the end of meiosis II. Four are made per primary spermatocyte, linked by cytoplasmic bridges.

Spermatogenesis

The whole process of sperm production, taking 65-75 days.

Spermiogenesis

Transformation of spherical spermatids into elongated sperm (acrosome and flagellum form, mitochondria multiply).

Spermiation

Release of sperm from their connections to Sertoli cells. The sperm are not yet able to swim.

Sertoli cells

Support cells of the seminiferous tubules. They nourish developing sperm, form the blood-testis barrier, secrete inhibin, and regulate the effects of testosterone and FSH.

Blood-testis barrier

Tight junctions between Sertoli cells that prevent an immune response against sperm surface antigens.

Leydig (interstitial) cells

Cells between the seminiferous tubules, acted on by LH. They are the primary site of testosterone production.

Sperm (structure)

Head (nucleus with 23 chromosomes plus the acrosome) and tail (neck, middle piece, principal piece, end piece).

Acrosome

Vesicle in the sperm head filled with enzymes that penetrate the oocyte.

Middle piece

Part of the sperm tail containing mitochondria.

Epididymis

Tightly coiled duct where sperm mature, gaining motility and the ability to fertilize. It can store sperm for months.

Ductus (vas) deferens

Conveys sperm during sexual arousal by peristaltic contractions. It can also store sperm for months.

Rete testis, efferent ducts

Ducts of the testis that carry sperm from the seminiferous tubules to the epididymis.

Seminal vesicles

Accessory glands supplying about 60% of semen volume. Their secretion is alkaline and contains fructose, prostaglandins, and clotting proteins.

Prostate

Accessory gland supplying about 25% of semen volume. Its secretion is milky and slightly acidic, with citric acid, proteolytic enzymes, and seminalplasmin (an antibiotic).

Cowper's glands

Secrete alkaline fluid that neutralizes urine acids in the urethra, plus mucus that lubricates the penis.

Semen

Mixture of sperm and seminal fluid, about 2.5-5 mL with 50-150 million sperm/mL and a pH of 7.2-7.7. It coagulates after ejaculation.

Penis

Contains the urethra and erectile tissue (corpora cavernosa and corpus spongiosum). Its parts are the glans, prepuce (foreskin), and root.

Erection

Parasympathetic fibers trigger local nitric oxide (NO) production. NO relaxes arteriole smooth muscle so blood floods the penis.

Seasonal gonad cycling

Most seasonally breeding animals shrink and regrow their gonads yearly, with volume changing over 100-fold. Most of the growth is in Sertoli cells.

Testis size and mating strategy

Monogamous species have small testes and less sperm, while polygynous species have large testes and more sperm.

Testosterone

A steroid androgen produced primarily in the gonads. It stimulates development of male sex characteristics and needs functional receptors to work.

Testosterone benefits

Mediates reproductive and territorial behaviors and is responsible for many sexually selected traits.

Testosterone costs

Mortality, cancer, cuckoldry, reduced paternal care, and disease.

Behavior and T (two-way relationship)

Testosterone affects behavior, and behavior affects testosterone. T rises with territorial aggression and mating opportunities, which supports further aggression and mating.

Challenge response

Song sparrows increase LH and T when their territory is invaded. Human examples include World Cup fans (winners' T rose, losers' fell) and home-team players having higher pregame T.

Energetic cost of aggression

T-implanted lizards were more active but foraged less and died sooner. Food supplementation improved their survival.