8. Male Physio Flashcards
Does the presence of chromosomes determine gonads?
Not entirely.
Initially, sexual differentiation is driven by what?
- Genetic sex is dirven by XX/XY chromosomes.
What is the process of sexual differentiation?
Describe using genetic sex, gonadal sex and phenotypic sex.
- Genetic sex is determined by XX or XY (SRY gene) chromomes.
- First 5 weeks of gestation: gonads are bipotential (not M/F)
- 6-7 weeks: testes develop in genetic M
- 9 weeks: ovaries develop in genetic F
- Normally, genetic sex determines gonadal sex (presence of male/female gonads (testes/ovaries))
- XY -> Testes are made up of sertoli cells and leydig cells -> male genital tract and external genitalia (phenotypic sex)
- Sertoli cells make AMH
- Leydig cells make testosteone.
- XX -> ovaries -> do not make AMH or testosterone -> female genital tract and external genitalia (phenotypic sex).
- XY -> Testes are made up of sertoli cells and leydig cells -> male genital tract and external genitalia (phenotypic sex)
Do the gonads appear in males of females first?
Appear in males slightly earlier.
What is phenotypic sex and what is it deteremined by?
- Physical characteristics of the internal genital tract and external genitalia.
- Phenotypic sex is determined by the homrones secreted from goands.
Male internal genital tract includes what?
1. prostate
2. seminal vesicles
3. vas deferens
4. epididymis
Female internal genital tract includes what?
1. Fallopian tubes
2. Uterus
3. Upper 1/3 of the vag
External genitalia in M/F.
- M: scrotum and penis
- F: clit, labia majora/minora, lower 2/3 of vagina.
How does gonadotropin (FSH/LH) secretion change over the lifetime?
Fetus:
Childhood:
Puberty:
Reproductive years:
Senescence:
- Secretion of FSH/LH begins at gestational week 10/12. Levels are low until puberty, with more FSH being secreted.
- Puberty and adult reproductive years: At puberty, secretion of GnRH, FSH and LH increases and becomes pulsatile and we begin to secrete more LH than FSH. During adulthood reproductive years, women begin periods and see cycles of FSH/LH release. Men have a steady secretion of FSH and LH.
- Senescence: Gonadatropic secretion increases in M/F, with FSH being secreted more than LH. In F, there is a sharp increase because menopause causes lack of negative FB.
What initiates puberty?
- Pulsatile secretion of GnRH, causing FSH and LH to be secreted pulsitile as well. This will then cause the secretion of [gonadal steriod hormones, testosterone and estradiol].
- -> cause secondary sex characteristics to appear
- What happens if GnRH analogue is administered in intermittent pulses to replicate normal pulsatile secretion?
- What about if a long-acting (non-pulsitile) GnRH anaglogue is given?
1. Puberty is initiated and reproductive function is established.
2. No puberty.
What can affect when puberty begins?
- CNS: melatonin, secreted from the pineal gland, is highest during childhood and decreases as we become adults. It inhibits GnRH release
- Stress or calories deprivation in girls
What happens to puberty if we remove pineal gland?
Puberty begins early.
Describe the functions of the testes and scrotum.
- Testes: spermatogenesis and secrete testosterone.
- Scrotum: keeps testes at. a lower temperature so spermatogenesis can occur.
Fx of the epididymis.
Main location for maturation and storage of sperm.
Function of vas deferens, seminal vesicles and prostate gland.
- Vas deferens is secretes a fluid rich in citrate and fructose and stores sperm in the ampulla.
- Seminal vesicles will then secrete a fluid rich in citrate, fructose, prostaglandins and fibrinogen giving it nutrients!
- Prostate gland will then secrete a alkaline milky soln that. is rich in citrate, Ca2+ and enzymes during emission to neutralize.
How does sperm leave the testes?
- Sperm leave the testes -> epididymis, the main location for the maturation and storage of sperm. They can stay in the epididymis for several months.
- During sexual arousal, contractions of the smooth muscle around the ducts pushes sperm through the epididymis.
- At ejaculation, sperm -> vas deferens -> ejaculatory duct..
- Ampulla of the vas deferens -> another storage area for sperm and secretes a fluid rich in citrate and fructose, which nourishes the ejaculated sperm.
- The seminal vesicles secrete a fluid rich in fructose, citrate, prostaglandins, and fibrinogen. As the vas deferens empties its sperm into the ejaculatory duct, each seminal vesicle contributes its secretions, which also provides nutrients for ejaculated sperm.
- Prostate gland then adds its own secretion of ejaculate: basic milky aqeuous rich soln in citrate, calcium and enzymes.
How do the prostaglandins in seminal fluid help with fertilization?
- React with cervical mucus and make it less thicc so sperm can penetrate.
- Cause backward, reverse peristaltic contraction in female reproductive tract to help sperm go to ovaries
What makes up the adult testis?
- Seminiferous tubules (80%), which have epithelium lined by sertoli cells and germ cells, such as spermatogonia and spermatocytes.
- Leydig cells (20%) intersitial cells between tubules that make and secrete testosterone when LH acts on them.
80% of adult testis is made up of seminiferous tubules (80%), which have epithelium lined by sertoli cells and germ cells, such as spermatogonia and spermatocytes.
What are spermatogonia and spermatocytes?
- Spermatogonia: immature germ cells located at the periphery of tubule
- Spermatozoa: mature germ cells located near the lumen of the tubule
Sertoli cells have 3 important functions that support spermatogenesis. What are they?
- Provide nutrients for differentiating sperm.
- From tight junctions with each other, creating the blood testes barrier.
- Secretes aqeuous fluid into the lumen of the seminiferous tubules which helps transport sperm -> tubules -> epidiymis.
What is the importance of the blood-testes barrier?
- A barreir between. testes and bloodstream that allows good things, like testosterone, to cross but not bad things that could damage developing sperm.
The TESTES make several male sex hormones (androgens), such as:
1. Testosterone (most adbundant)
2. DHT
3. Androgestenedione
Where is much of the testosterone we have eventually converted to DHT?
Target tissue.
Testosterone is made and secreted by our Leydig cells of the testes.
How does steriod synthesis result in testosterone and not other things?
- Testes do not have 21B-hydroxylase or 11B-hydroxylase, thus, no glucocorticoids or mineralcorticoids are made.
- They have 17B-hydroxysteroid DH, which converts androstendione -> T.
How do we concentrate testosterone in the lumen of the seminiferous tubules?
It is bound to ABP (androgen-binding protein).
Is testosterone the active hormone is all andronergic target tissue?
- No. In some tissue, it is DHT (prostate gland, external genitalia of male fetus, skin and liver).
- T-> DHT via 5-alpha reductase.
How does testoerone travel in blood?
Most bound to plasma proteins, such as sex-hormone binding globulin (SHBG) and albumin.
What are the main steroidogenic cells in the testis?
Leydig cells
Leydig cells make T. How?
- Make cholesterol de novo or get some from blood using LDL/HDL receptors
- Store cholesterol as cholesterol esters.
- Hormone-sensitive lipase frees up cholesterol from cholesterol esters to make androgens.
- Transferred within mitochondrial membrane via steriodogenic acute regulatory protein (StAR).
- Converted to prenenolone.
Do males make estrogen?
Yes, they make small amounts.
In the fluid in the seminiferous tubules, amount is actually high and we have more in other tissue, such as liver (80%)
What is the importance in males making estrogen?
- Potential role in spermatogenesis (bc sperm cells have at least 1 estrogen receptor).
Where is estrogen in males made?
Sertoli cells; it is a product made when T -> estradiol via aromatase.
What pathway what cholesterol go through to become pregnenolone?
1. Mitochondrial pathway: Cytochrome P450 removes side chain from cholesterol at carbon 20.
THIS IS THE RATE-LIMITING STEP.
Leydig cells are the main endocrine cell of the testis, making T.
Does it make alot of DHT and estradoil-17B?
It makes limited amounts. More is made peripherally.
After Leydig cells make T, where does it go?
- Goes into seminiferous tubules, bound to ABP.
- Peripheral circulation, bound to SHBG and albumin.
Cholesterol -> Prenenolone.
What is the enzyme and what regulates the enzyme action?
Cholesterol desmolase (P450scc), which is regulated by LH.
LH will increase synthesis of P450scc and increase affinity for cholesterol.
When does testosterone production begin?
7-8 weeks into gestation.