Endocrinology of Puberty I Flashcards
What is an endocrine cell?
> What triggers the function of an endocrine cell?
- A cell that secretes hormones > Stimuli e.g. chemical
Amine hormones: (T3, T4, adrenaline, noradrenaline, dopamine, serotonin, 5-HT 5-hydroxytryptoamine)
1- How are they made? Where are they stored?
2- What do they act as?
3- What do they bind to?
1- Enzyme modifications on amino acids: Tryptophan + Tyrosine > Vesicles
2- Neurotransmitters in synapses within NS or endocrine mediators (hormones) in body
3-
- Cell surface receptors mainly GPCR
- T3/4 bind to Intracellular receptors
- 5-HTbinds to Ionotropic receptors
Protein: Follicle-stimulating hormone (FSH), Mullerian inhibiting hormone (MIH) + Peptide hormones: (GnRH, insulin)
1- How are they made?
2- Where are they stored?
3- What do they bind to?
4- Hydrophobic/ Hydrophillic?
1- Gene expression
2- Stored in intracellular secretory granules and released via exocytosis upon stimulation by a secretagogue
3- Specific cell surface receptors (GPCR or tyrosine kinase)
4- Hydrophilic, so mostly unbound in serum (except IGG1/2)
Glycoprotein hormone family:
1- Which proteins are members of the glycoprotein hormone family? What is the same and different between thes?
2- What do they bind to? Which of them bind to the same receptor? Why is this relevant?
3- Where are they produced
1- FSH/hCG/LH
> Same alpha chain code by same single gene on ch6
> Different beta chain
2- LH/ hCG > hCG is produced during early pregnancy to maintain activity of the LH
Steroid hormones: (Mineralocorticoids, glucocorticoids, sex steroids)
1- Where are they produced? What are they derived from?
2- Give 2 examples demonstrating peripheral conversion of steroids?
3- What do they bind to, what is significant about this?
4- How are they stored?
5- hydrophilic/hydrophobic?
1- Adrenal glands (expect oestrogen), gonads, and placenta. > Cholesterol
2- (e.g.weak adrenal androgens to testosterone by liver, adipocytes, skin or aromatization of testosterone to oestrogen in the brain)
3- Structurally related… activate the same receptors but have a different potency.
4- Not stored, synthesised when needed, by increasing activity of enzymes
5- Hydrophobic > diffuse freely across membrane whilst bound to plasma proteins e.g. albumin, androgen binding protein
How can endocrine activity be controlled via :
1- Hormone level/activity (4)
2- Receptor factors (4)
1-
- Amount of hormone produced/ secreted
- Affinity of hormone for receptor and half life in plasma (potency)
- Rate of hormone clearance
- Available transport proteins in plasma
2-
- alter activity of receptor
- alter signalling of receptor e.g. antagonists
- amount of receptors available for binding
- desensitisation of receptors upon high levels of agonist
1- How does hierarchal level of control regulate endocrine activity in reproductive physiology?
2- What happens under specific circumstances?
> Hypothalumus- pituitary gonad axis used as an example..
1- Initiated by signals from the cerebral cortex
> Negative feedback regulates this herarchic endocrine system
> Long loop (feedback from androgens to hypothalamus) and short loop (from androgens and oestrogens to anterior pituitary) feedback
2- Positive feedback can drive the axis for short period of time e.g. pre -ovulatory LH surge
1- What are primary sexual characteristics?
2- Name female and male primary characteristics:
- Gonads
- Internal genitalia
- External genitalia
1- Sexual characteristics developed during embryological and foetal developments.
2-
What determines the primary sexual characteristics in MALES?
> Sex determining region on the Y chromosome (SRY) gene initiates the differentiation of cells in the gonadal primordia ridge to become pre-Sertoli cells, which starts the development program to form testis
How do ovaries develop?
Is ovarian endocrine activity essential for the development of female primary sexual features?
> Absence of SRY
NO
How do we develop Ovaries and Testes?
- Migration of Primordial germ cells 4-6 weeks to Bipotential Gonadal primordia ridge allowing the tissue cells to express the SRY gene if they do have it > Testes
How is male internal genitalia developed?
What happens if there is a failing in testosterone and MIH hormone production?
- Paramesonephric duct is going to be maintained and further developed into female internal genitalia.
- Mesonephric duct will Degenrate as there Is no testosterone.
How is male and female external genitalia developed?
Progenitor cells must contain the right number of X chromosomes. What does oocyte growth and spermatogenesis require?
- Oocyte growth > 2 X chromosomes
- Spermatogenesis > 1 X chromosome
Testes develop in upper lumbar. How do they defend to scrotum?
Mention what happens at 15 AND 35 weeks
- Lengthening & regression of suspensory ligament (cranial) accompanied by shortening of gubernaculum (Caudal)
- Regulated via MIH + Testosterone + Insl3
- 15: testes in close proximity to inguinal canal
- 35 weeks: testes have reached scrotum
1- Compare when the growth spurt happens in males/ females
2- Final skeletal proportions results from balance between…
1- 2 years earlier in females
2-
> ↑ rate of longitudinal bone growth by sex steroids & GH/IGF-1 axis
> ↑ rate of epiphyseal growth plates closure by HIGH estrogens (derived from testosterone in testis and adipose)
Puberty is not just physical changes there are also psychological and behavioural changes.
What are the effects of testosterone on behaviour?
- Non primates > Castration = loss of male sexual behaviour
- Primates , more complex
>
- In humans Testosterone important for development of sexual behaviour ALONSIDE other factors e.g. social interactions, learning + biological
– Non-linear… more testosterone does not mean more sexual behaviour.
5-alpha reductase makes dihydrotestosterone from testosterone.
What are the effects of testosterone vs by dihydrotestosterone?
- Activation of Sertoli cells + initiation of spermatogenesis underpins some of the testicular growth and increase in scrotum volume
1- What initiates the process of spermatogenesis?
(Spermatozoan from Pro- spermatogonium)
2- What is the blood-testis barrier?
1- Start of puberty initiates spermatogenesis and it takes a few years for the male to become fully fertile. - Occurs within the seminiferous tubules
2- Develops during puberty
- Tight junctions around Sertoli cells
- Maintains intratubular fluid composition & protects spermatids from the immune system
Describe the production of spermatozoan.
> Spermatocytogenesis :
Pro-spermatogonium → spermatids
> Spermiogenesis
Spermatids → spermatozoa
*NOTE: During mitosis & meiosis, cytokinesis is incomplete – primary spermatocytes derived from a single spermatogonium are linked via cytoplasmic bridges
What is spermiogenesis? (5)
- Cytoplasmic and further maturation of genetic remodelling leading to distinctive morphology.
> Compact DNA in head
> Absence of cytosol
> Head topped by acrosome
> Mid piece : mitochondria
> Tail
1- What is the spatial organisation of spermatogenesis?
1- Sperm production (and thus fertility) is constant
> A single tubule produces spermatozoan all the time, but these develop from different segments within the tubule (spermatogenic wave)
> Sequential arrangement of different stages of germ cell development, forming a wave-like pattern
