Male Hypogonadism Flashcards
Where is testosterone secreted from?
- Testes
- Ovaries
- Adrenal glands
How much testosterone do males secrete daily and what proportion is secreted from the adrenal glands?
7mg daily
5% secreted from adrenal glands
What percentage of testosterone is free in the blood (not bound to protein)?
2%
How much testosterone is bound to albumin?
Approx 50%
How much testosterone is bound to SHBG?
44%
Do pre-pubertal boys and hypogonadal men have more or less SHBG than normal men?
More
Who has more SHBG between men and women
Women
What are the two anatomical regions of the testes?
Seminiferous tubules which synthesis inhibin B and AMH via Sertoli cells. It is also where sperm is produced.
Interstitium which contains Leydig cells that produce androgens and peritubular myoid cells (smooth muscle that surround the seminiferous tubules)
What does Inhibin B do?
Controls FSH via negative feedback
What does Anti-Mullerian Hormone do?
Prevents the development of the Mullerian ducts into the uterus (in male embryo), allowing for the development of the male reproductive system.
How is testosterone produced from cholesterol?
1) Cholesterol ——> Pregnenolone
2) Pregnenolone ———–> Progesterone or Dehydroepiandrosterone (DHEA)
Also, Progesterone ——> DHEA
3) Progesterone ——–> Testosterone
Also, DHEA ——–> Testosterone
What enzyme converts Testosterone into Dihydrotestosterone (DHT)?
5a-reductase
What enzyme converts Testosterone into Oestradiol?
Aromatase
How does the Hypothalamic-Pituitary-Testicular axis work?
1) Pulsatile release of GnRH leads to the secretion of LH and FSH (both are composed of two glycoprotein chains)
2) LH is involved in the release of testosterone
3) FSH is involved in spermatogenesis and Inhibin B secretion
How does testosterone act on target cells
Enters target cells and then gets converted into 5a-dihydrotestosterone before it binds to androgen receptors.
Alternatively, testosterone can get aromatised into oestrogens
What does testosterone do to lean body mass and fat mass?
Increases lean body mass
Decreases fat mass
What can male hypogonadism lead to?
Decrease in testosterone and sperm production
What are the two types of male hypogonadism?
Primary: Disease of the testes
Secondary: Disease if the hypothalamus or pituitary
What happens in primary hypogonadism?
Testosterone levels are low but FSH and LH levels are normal-high
What happens in secondary hypogonadism?
Testosterone levels are low but FSH and LH levels are normal-low
What are some causes of primary hypogonadism?
- Klinefelter syndrome (XXY)
- Cryptorchidism (when one/both testes fails to descend from abdomen into scrotum)
- Radiation
- Trauma
- Torsion (twisting of the spermatic cord)
What are some causes of secondary hypogonadism?
- Congenital GnRH deficiency
- Hyperprolactinaemia
- Opioids
- Anorexia
- Pituitary disorder
What are some signs/symptoms of hypogonadism?
- Eunuchoidism (incomplete sexual development, can lead to lower sex drive and less spontaneous erections)
- Gynecomastia
- Decrease in body hair
- Small/shrinking body hair
- Infertility
How do you examine for hypogonadism?
- Amount of body hair
- Breast exam for enlargement/tenderness
- Size and consistency of testicles
- Size of penis
- Arm span
What is investigated when investigating hypogonadism?
- Serum testosterone
- LH/FSH
- SHBG
- Semen analysis
- Pituitary function test
What scan can be done to investigate for hypogonadism?
MRI
What can lower SHBG levels?
- Obesity
- Nephrotic syndrome
- Hypothyroidism
- Glucocorticoids
What can increase SHBG levels?
- Ageing
- Hepatic cirrhosis
- Hyperthyroidism
- Oestrogens
- Anticonvulsants
- HIV
What can hypogonadism be treated with?
Testosterone
How can testosterone be given?
- Gel
- Injection
- Buccal
What is gynecomastia?
Benign proliferation of the glandular tissue of the male breast.
What are the two types of gynecomastia?
Unilateral and Bilateral
How is gynecomastia diagnosed?
On examination the mass of tissue will be at least 0.5cm in diameter
What causes gynecomastia?
An imbalance of androgens and oestrogens and it occurs to 60% of boys during puberty
What illnesses/diseases can cause gynecomastia?
- Cirrhosis
- Hyperthyroidism
- Testicular tumour
- Leydig cell dysfunction
- Hypogonadism