Puberty - Hormonal Changes - Physical Changes - TeachMePhysiology (2024)

Physical Changes

Puberty in Females

Thelarche

The first sign of puberty in girls is the beginning of breast development (thelarche). This typically occurs at around age 9-10. Breast budsappear as small mounds with the breast and papilla elevated. Tanner staging is used to assess breast size/development with stages I-V (shown below).

The breasts consist of lobulated glandular tissue embedded in adipose tissue, separated by fibrous connective tissue. Following the clearance of placental oestrogens after birth, the breasts are in a dormant stage until puberty. In this dormant stage there are only lactiferous ducts with no alveoli.

At puberty the increase in ovarian oestrogens causes the development of the lactiferous duct system as the ducts grow in branches with the ends forming the lobular alveoli (small, spheroidal masses). Mediated by progesterone, these lobules will increase in number through puberty.

The breasts continue to increase in size following menarche due to increased fat deposition. Throughout the menstrual cycle, oestrogen and progesterone affect the breast size and composition.

By M•Komorniczak -talk-, polish wikipedist. Illustration by : Michał Komorniczak This file has been released into the Creative Commons 3.0. Attribution-ShareAlike (CC BY-SA 3.0) If you use on your website or in your publication my images (either original or modified), you are requested to give me details: Michał Komorniczak (Poland) or Michal Komorniczak (Poland). For more information, write to my e-mail address: [emailprotected] [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Fig 1 – Tanner staging in females

Pubarche

The second sign of puberty in girls is typically the growth of hair in the pubic area. The hair initially appears sparse, light and straight; however, throughout the course of puberty it becomes coarser, thicker and darker.

Approximately 2 years after pubarche, hair begins to grow in the axillary area as well. In both sexes, hair growth is a secondary sexual characteristic mediated by testosterone.

Menarche

Menarche is thefirst menstrual period and marks the beginning of the menstrual cycles. It normally occurs around 1.5-3 years after thelarche and is due to the increase in FSH and LH.

The menarche process typically occurs at ~12.8 years (+/- 1.2 years) for Caucasian girls and 4-8 months later for African-American girls. More information can be found in our menstrual cyclearticle.

Puberty inMales

Genital Changes

The first sign of puberty in boys is the increase intesticular size. The increased LH stimulates testosterone synthesis by Leydig cells and the increased FSH stimulates sperm production by Sertoli cells. Spermatogenic tissue (Leydig cells and Sertoli cells) makes up the majority of the increasing testicular tissue. The progression of testicle size can be measured bytanner stagingfrom stage I to stage V.

As the testicles increase in size the scrotal skin also grows and becomes thinner, darker in colour and starts to hang down from the body. It also starts to become spotted with hair follicles (these appear as little lumps.)

Approximately a year after the testicles begin to grow, boys can experience their first ejaculation because the testicles are now producing sperm as well as testosterone. The first ejaculation marks the theoretical capability of procreation.However, on average fertility is reached one year after first ejaculation.

The growth of the penis follows the testicular enlargement. The penis first grows in length. Then the width of the penis increases as the breadth of the shaft increases. Theglans penis and corpus cavernosum also enlarge.

Pubarche

Another pubertal sign in boys is the growth of pubic hair at the base of the penis (pubarche). This often occurs alongside testicular growth. Pubic hairs will initially be light coloured, straight and thin; however, as puberty progresses they become darker, curlier, thicker and more widely distributed. Approximately 2 years following pubarche, hair also begins to grow on the legs, arms, axillae, chest and face.

By M•Komorniczak -talk-, polish wikipedist. Illustration by : Michał Komorniczak This file has been released into the Creative Commons 3.0. Attribution-ShareAlike (CC BY-SA 3.0) If you use on your website or in your publication my images (either original or modified), you are requested to give me details: Michał Komorniczak (Poland) or Michal Komorniczak (Poland). For more information, write to my e-mail address: [emailprotected] [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Fig 2 – Tanner staging in males

Growth Spurt (Males and Females)

The pubertal growth spurt is the product of a complex interaction between the gonadal sex steroids (oestradiol/testosterone), GH and insulin-like growth factor 1 (IGF-1). GH levels will rise in puberty due to the increase in sex steroids (testosterone which has been converted to oestradiol) and their positive effect on the pulsatile release of GH from the anterior pituitary gland.

A rise in GH causes a rise in the anabolic hormone IGF-1, which causes somatic growth via its metabolic actions (e.g. increases trabecular bone growth.)

Following the peak of the growth spurt in males, the larynx and vocal cords (voicebox) enlarge, and the boy’s voice may ‘crack’ occasionally as it deepens in pitch.

Clinical Relevance –Precocious Puberty

We define precocious puberty is as the appearance of secondary sexual characteristics before the age of 8 in girls or before the age of 9 in boys. There are a variety of causes/types:

  • Iatrogenicthis occurs as a result of exposure to exogenous oestrogens, e.g. via creams or lotions etc.
  • True/completedue to early maturation of the HPG axis resulting in high levels of GnRH, FSH and LH. This may be due to CNS lesions near or in the posterior hypothalamus, CNS neoplasms, harmatomas, primary hypothyroidism.
  • Incompletedue to increased levels of oestrogens in girls and androgens in boys that are independent of GnRH.

Precocious puberty may either be isosexual (early sexual development consistent with the genetic and gonadal sex of the child) or contrasexual (early sexual development associated with feminisation of a male or virilisation of a female).

Clinical Relevance – Delayed/Absent Puberty

We define delayed or absent puberty as the absence of secondary sexual characteristics by the age of 13 in girls or 16 in boys. There are various causes:

  • Hypogondaotropic hypogonadismthis is due to a disorder of either the hypothalamus or the pituitary gland. The disorder results in a deficiency in GnRH, LH or FSH.
  • Hypergonadotropic hypogonadismthis is due to a disorder of the gonads (ovaries or testicles.) The disorder results in absent or reduced gonadal steroid secretion which results in high circulating levels of LH and FSH as there is minimal negative feedback from the gonadal steroids on the pituitary gland.
  • Clinicians may see multiple conditions associated with delayed puberty. Be careful to watch out for these in exams:
    • Turner’s Syndrome (45 XO)
    • Klinefelter’s Syndrome (47 XXY)
    • Androgen Insensitivity Syndrome
    • Kallmann Syndrome
  • When investigating infertility, consider other conditions that are not congenital.

Doctors can treat severe delayed/absent puberty with carefully controlled hormonal replacement therapy.

As an enthusiast in the field of human development and endocrinology, I'm well-versed in the intricacies of puberty and its physiological changes in both males and females. My knowledge draws from various studies and scientific sources that delve deep into the hormonal, anatomical, and psychological transformations occurring during this crucial phase of life.

The onset of puberty in females begins with thelarche, the budding of breasts, stimulated by ovarian estrogen. These breast buds gradually evolve through Tanner stages, reflecting the maturation of breast tissue and ductal development. This process involves the proliferation of lobules and alveoli, facilitated by progesterone. Concurrently, pubarche, the growth of pubic hair, and later axillary hair, are mediated by testosterone.

Menarche, the first menstrual period, marks the start of the menstrual cycle, typically occurring after thelarche by around 1.5-3 years. The hormonal surge of FSH and LH triggers this milestone, usually around 12.8 years for Caucasian girls.

In males, puberty commences with an increase in testicular size, driven by elevated LH and FSH levels. This kickstarts testosterone synthesis and sperm production. Pubarche in boys follows, characterized by the growth of pubic hair and later hair growth in other areas like the chest, face, and limbs, also under the influence of testosterone.

The pubertal growth spurt in both genders results from a synergy between sex steroids, growth hormone (GH), and insulin-like growth factor 1 (IGF-1). This complex interplay leads to somatic growth, bone development, and, notably in males, the enlargement of the larynx and vocal cords.

Understanding clinical implications is crucial. Precocious puberty, marked by early onset of secondary sexual characteristics, and delayed or absent puberty, indicating the absence of expected developments by certain ages, can arise due to various factors affecting the hypothalamus, pituitary gland, gonads, or hormonal feedback mechanisms.

Conditions like Turner's syndrome, Klinefelter's syndrome, and others can be associated with delayed puberty. Treatment, in severe cases, might involve carefully managed hormonal replacement therapy.

This period of physical and hormonal changes is a critical phase in human development, influenced by a delicate interplay of hormones and physiological processes. Understanding these intricacies helps address concerns related to growth, development, and overall health during adolescence.

Puberty - Hormonal Changes - Physical Changes - TeachMePhysiology (2024)

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