S4 L1 Puberty and the HPG axis Flashcards
Key terms:
- Adrenarche
- Gonadarche
- Thelarche
- Pubarche
- Menarche
Puberty:
- What is this?
- When are primary sexual characteristics established?
- Are the sequence of the events the same in everyone (even if started at different ages)?
- F and M start first?
- Primary and secondary sexual characteristics?
- Adrenarche - Maturation and increased activity of the adrenal glands prior to puberty.
- Gonadarche - activation of reproductive glands by the pituitary hormones FSH and LH
- Thelarche - The onset of breast development occurring near the beginning of puberty in girls.
- Pubarche – onset of the growth of pubic hair
- Menarche - The onset of menstruation at puberty
Timing of puberty
- What affects this? (list and explain some of the different factors)
- What stands the same in everyone?
- How does weight loss/very low BMI affect puberty in girls?
– In girls, critical weight 47 kg
– Significantly, weight loss = reproductive cycles cease
– Body weight important factor: nutrition
– Hormones such as Leptins may be involved in signalling – driving the
onset of reproductive function IF body environment is suitable…..
– Interestingly, puberty does not begin in adolescents who are deficient
in leptin.
Sexual Maturity Ratings (SMR)
- What scale is it measured on?
- How does this scale work?
- What is it based on in females?
- What is it based on in males?
- Tanner developed a scale in 1962 that divides the Sexual Maturity. Ratings into 5 classes
- Based on pubic hair and breasts in females and
- Pubic hair and genitalia in males
- The first visible sign of puberty in males is testicular enlargement, while in females it is breast development.
Female secondary sexual characteristics:
- When each ‘thing’ begins, including breast, pubic hair, growth spurt, menarche…
Male secondary sexual characteristics:
- When each ‘thing’ begins, including genital development, pubic hair, growth spurt…
Female:
1. 8-13 years; starts with
• Breast bud (thelarche)
• Pubic hair growth (T)
2. Leads to (adrenarche)
• Growth spurt
• Onset of menstrual
3. Menstrual cycles begin (menarche)
• Pubic hair adult
• Breasts adult
Male:
1. 9-14 years starts with;
• Genital development
2. Progresses to…
• Pubic hair growth
• Spermatogenesis
3. Completed by
• Growth spurt
• Genitalia adult
• Pubic hair adult
Accelerated somatic growth (i.e. growth spurt):
- When does this occur in each sex?
- Depends on?
- Ends when…
Summary - Puberty in male and female
- Range in puberty?
- Early maturation - what tends to be the phycological effect of this on F and M?
- Late maturation - what tends to be the phycological effect of this on F and M?
What other key ‘axis’ is switched on in puberty?
Reminder pic - of the different exocrine glands
- The normal range in pubertal development is very broad (it may not be always the same range across texts!)
- Early maturation is a positive experience for boys but may be negative for girls
- Late maturation is usually more difficult for boys than for girls
- Adolescents compare themselves to their peers and internalise the reaction of others to their changing bodies
Puberty: Pubertry is also the point in which the HPG axis is switched on
HPG axis:
- What is this axis and all the hormones involved
- What hormone initates puberty?
- Onset of puberty assocaited with rises in…
•Puberty initiated by the brain (H) - This hormone, needs to be in a large quantity to get over the activation threshold I.e. prepubertal, GnRH is at levels too level to trigger this cascade of effects, it is released by the hypothalamus
• Onset of puberty associate with steady
rise in FSH & LH secretion
GnRH
- Responsible for… and other hormones it causes the release of…
- Where does it’s production occur?
- What does it regulate?
- Initially at pubertry, how is GnRH released? Pattern of it’s release
- Which gene is responsible for it?
- Explain the reason for the pattern of release of the GnRH? why?
Responsible for maintaining the menstrual cycle in the female thr • oughout their reproductive life. Secretion of gonadotropin-releasing hormone(GnRH) by the hypothalamus stimulates the anterior pituitary gland gonadotrophs to secrete two gonadotropic hormones:
• follicle-stimulating hormone (FSH)
• luteinizing hormone (LH)
Production of GnRH occurs in the neurons of the hypothalamus and causes the
downstream production of sex hormones by the gonads.
This hormone ultimately regulates puberty onset, sexual development, and ovulatory cycles in females.
Initially, at puberty, GnRH is released in low-frequency pulses during the night, but after the maturation of synaptic connections, it matches the adult pattern. (In males, the GnRH pulses occur after 2 hours, while in a female, it changes according to the phases of the menstrual cycle)
GnRH -1 gene:
–primarily responsible for mammalian GnRH (there are other vertebrate variants of this gene)
–The GnRH-1 gene is expressed in the pituitary
What makes up the pituitary gland, other name for the two parts of the pituitary gland?
Hormones secreted in each ‘part’ of the pituitary gland?
A major organ of the endocrine system, the anterior pituitary (also called the adenohypophysis or pars anterior) is the glandular, anterior lobe that together with the posterior lobe (posterior pituitary, or the neurohypophysis) makes up the pituitary gland (hypophysis).
LH and FSH:
- In young children, what are the levels like of these hormones? What does this mean for development?
- When does the amplitude of these pulses of these hormones increase?
- What do these hormones do (related to gonads)?
- In males, explain three major hormone levels? (during day and night)
- In females, explain three major hormone levels? (during day and night)
- In young children, LH and FSH levels are insufficient to initiate gonadal function
- Between 9-12 yrs., blood levels of LH, FSH increase
- Amplitude of pulses increases, especially during sleep
- High levels of LH, FSH initiate gonadal development
On the whole, is this system positive or negative feedback?
In this HPG axis, where could dysregulation occur?
Negative feedback
- *MALE - ANDORGEN PRODUCTION**
- LH stimulates ____ cells, to produce ____ from ___
- Effect of which things, on production of this androgen?
- Role of FSH in males
- Role of LH in males
- LH stimulates Leydig cells in testis
- Leydig cells: Cholesterol —-> testosterone
- Produce Steroid hormone (from cholesterol) Testosterone
•There is an effect of :
–Circadian rhythm
–Highest early morning
–Effects of environmental stimuli
–Both driven by brain
Histology of the testes:
- Main sperm producing cells… what are they like histologically?
- Role of them…
- In between these cells, what is there?
Seminiferous tubule cells:
- 2 cell types in the complex epithelium…
- Go into more detail about s____ cell and its roles
Summary slide showing:
- HPG
- Sertoli cells and leydig cells
- The hormones both of these cells produce
- *FEMALE SYSTEM
- ** Role of FSH
- Role of LH
Female
- Histology of theca cells and granulosa cells (answer in pic this side of FC)
- Interactions between ovarian cells types (and their hormones)
How oestrogen and progesterone affect GnRH?
- Moderate levels of oestrogen… affect on GnRH?
- High levels of oestrogen… affect on GnRH?
How oestrogen and progesterone affect FSH and LH?
How Inhibin affects FSH
Role of leptin in triggering start of puberty
Central precocious puberty
- Definition
- Cause
- Diagnosis through…
- Sex hormones
Peripheral precocious puberty
- Definition
- Cause
- Diagnosis through…
- Sex hormones
Delayed onset of puberty
- Definition
- Causes (3 main)
