Puberty is the time in an individual’s life when they physically become sexually mature and able to have children. Generally speaking, it’s considered delayed if puberty hasn’t started for a female by age 13 and for a male by age 14.
The hypothalamic (HYpo-tha-lamb-ic)-pituitary-gonadal (Go-nad-al) axis is a system of hormonal signaling between the hypothalamus, pituitary gland, and gonads, the gonads are either the testes or the ovaries, and this will control sexual development and reproduction. Gonadotropin (Go-nad-ah-tro-pin) -releasing hormone is released into the hypophyseal (high-poth-ah-see-al) portal system, which is a network of capillaries connecting the hypothalamus to the hypophysis (high-pof-o-sis), or pituitary. When gonadotropin(Go-nad-ah-tro-pin) -releasing hormone reach the pituitary gland, it stimulates cells in the anterior pituitary, called gonadotrophs (Go-nad-a-trofs), to release gonadotropin hormones: luteinizing hormone and follicle-stimulating hormone which then enter the blood. These gonadotropin hormones then stimulate the gonads to produce sex specific hormones. These are estrogen and progesterone in females and testosterone is the major sex specific hormone in males.
Early on in male development, testosterone helps the external sex organs to differentiate into male genitals and causes the testes to descend from the abdomen into the scrotal sac. Beginning at puberty, the Leydig cells of the testes respond to the luteinizing hormone by converting more cholesterol into testosterone. In addition, the Sertoli cells of the testes respond to follicle-stimulating hormone by producing more sperm. The major sex specific hormones in women are estrogen and progesterone, and they are produced by the ovarian follicles that are scattered on the ovaries. Each ovarian follicle is made up of a ring of granulosa and theca cells surrounding a primary oocyte at its core. Beginning at puberty, theca cells respond to luteinizing hormone by producing androstenedione, an androgen. Then, the granulosa cells respond to follicle stimulating hormone by converting the androstenedione into estrogen and progesterone.
Waves of estrogen and progesterone regulate monthly changes to the ovary stroma to promote egg maturation and ovulation, and as well, it changes to the uterine wall lining as part of the menstrual cycle.
The increased production of sex hormones drives the development of primary and secondary sex characteristic that we see during puberty. Primary sex characteristics refers to the genitals, which are the organs directly involved in sexual reproduction. Secondary sex characteristics refers to any sex-specific physical characteristic that is not directly involved or necessary in sexual reproduction, like pubic hair and breasts, in females.
The Tanner scale, or Tanner stages, is a predictable set of steps that males and females go through as they develop primary and secondary sex characteristics and become sexually mature. The Tanner scale centers on two, independent criteria: the appearance of pubic hair in both sexes; and the increase in testicular volume and penile size and length in males, and breast development in females. There are five stages: In stage 1, the pre-pubertal stage, no pubic hair is present in either sex. Males have a small penis and testes. Females have a flat-chest. In stage 2, pubic hair appears and there’s a measurable enlargement of the testes; and breast buds appear. In stage 3, pubic hair becomes coarser; the penis begins to enlarge in both size and length; and breast mounds form. In stage 4, pubic hair begins to cover the pubic area; the penis begins to widen; and breast enlargement continues to form something called a “mound-on-mound” contour. In stage 5, pubic hair extends to the inner thigh; the penis and testes have enlarged to adult size; and the breast takes on an adult contour.
Puberty is delayed if progression through the Tanner scale hasn’t begun by the time 95% of an individual’s peers have begun to sexually mature. Generally, that means puberty has not started by age 13 in females and age 14 in males. Hypogonadism, or lower levels of sex hormones from low gonad activity, is central to a delay in puberty. As a result, sex characteristics are under-developed. Permanent infertility can occur if puberty never begins or fails to complete and sexual maturity is never reached.