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Endocrine & Reproductive Systems > L13 14 Male > Flashcards

L13 14 Male Flashcards

0
Q

Why are testis being located outside of body?

A
  • Because sperm production is only at its max when the temperature is not too high
  • By contracting muscles: Dartos and cremaster, to lift testis up closer to the core body = warmth
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1
Q

What is the function of testis?

A
  • To produce sperms and androgens
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2
Q

What are the processes have to go through before sperms are made?

A
  • Carry sperms up to urethra and combine the seminal fluid made by accessory glands to form semen
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3
Q

Where is the exact location which sperms are produced?

A
  • at seminiferous tubules and sperms then travel through the epididymis and reaches the tail of epididymis, where it is the junction with ductus deferens = travel up to urethra
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4
Q

What are the two main area in the testis?

A
  • seminiferous tubule and interstitial area
  • seminiferous tubule contains sertoli cells (acts as supporting cells and forms tight junction so have a continuous cytoplasm), gem cells. They are encircled by myoid cells
  • interstitial area contains leydig cells, lymph vessels and macrophages
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5
Q

What are the compartment of the testis?

A
  • 1) Vascular: blood vessels
  • 2) Interstitial: Leydig cells, macrophage
  • 3) Basal: Sertoli cells and gem cells below the level of the blood- testis barrier
  • 4) Adluminal: Sertoli cells and gem cells above the blood-testis barrier
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6
Q

What is the purpose of blood-testis barrier?

A
  • To maintain differences in fluid composition between fluid within tubule and outside tubule
  • Tubular fluid has a higher level of inositol and potassium; a lower level of Na and testerone
  • This can provide an optimal environment for sperm production, developing gem cells and it is the vehicle for sperm transport
  • Fluid is secreted and maintained by sertoli cells
  • also regulate passage of ions, selective flow of water steroids & carbs into the lumen

2) To protect developing sperms from autoimmune attack
- sperms do not develop until puberty so immune system would not be able to recognise them as ‘self’ materials. Otherwise, immune systems can make sperm antibodies against them

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7
Q

What are the 4 main classes of steroids produced by testis?

A
  • Progesterones, androgens, oestrogens and cortisosteroids

* first 3 are sex hormones

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8
Q

Testiculuar androgen synthesis

A
  • LH binds to the LEYDIG cell and triggers conversion of cholesterol into pregnenolone via the delta 5 pathway into androstenediol and then converted into testosterone
  • some testosterone would diffuse into blood but most are being converted into dihydrotestosterone in sertoli cells by enzyme ‘5 ALPHA REDUCTASE’. Then move into tubular fluid
  • dihydrotestosterone is more potent than testosterone so can have a longer acting effect on the body

*95% of testosterone comes from leydig cells but some can be from the peripheral blood

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9
Q

What are the functions of testosterone and dihydotestosterone (DHT) in male sex development?

A
  • Testosterone is responsible for Wolffian duct differentiation and later forms the epididymis, seminal vesicles and vas deferens
  • DHT is responsible for virilisation or external genitalia (ie the looking of penis)
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10
Q

What is the normal production level of testicular hormones?

A
  • testosterone: 3-10mg/day; androstenedione: 2.0 mg/day
    and Adrenal production of testosterone and peripheral conversion of androstenedione to 0.5 mg/day of testosterone
    -DHT= 70 microgram/day
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11
Q

What is the testicular oestrogen synthesis pathway?

A
  • LH binds to LEYDIG cell to initiate cholesterol converts into pregnelolone and then into androstenediol via the delta 5 pathway
  • Androstenediol is then converted into testosterone.
  • In sertoli cell, testosterone is converted into oestradiol 17 beta by using enzyme AROMATASE
  • some oestradiol 17 beta is released into blood an dlymph by leydig cell but mostly by sertoli cell!!
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12
Q

What is the function of oestrogen in male?

A
  • essential for male fertility and spermatogenesis
  • fluid reabsorption by proximal epididymis and efferent ductules so concentrate sperms
  • required for development and maturation of male tract
  • testis produces oestradiol 0.03mg/day
  • most oestradiol in men is from peripheral conversion of testosterone and androstenedione
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13
Q

How are androgens circulate in blood?

A
  • They bind to binding proteins, e.g. mostly sex hormone binding proteins. Most are bind to sex hormone binding proteins so can be transported to different parts of body.
  • total levels of testosterone in blood is 3-11 ng/ml and there is a rapid removal by liver so short half life
  • If not bound, would be metabolised by liver
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14
Q

Recap of production of DHT/ oestradiol 17beta into testosterone

A
  • only 5-10% of testosterone is converted into DHT by enzyme 5-alpha-reducatse. DHT acts on prostate and skin, eg. beard growth
  • majority 90% of testosterone is inactivated by liver and kidneys
  • 0.% of testosterone is converted into osetradiol 17 beta by enzyme aromatase. Oestradiol acts on brain and bone (=resorption)
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15
Q

What are the functions of testosterone?

A
  • At puberty: induce growth and development of male reproductive tract and secondary sex characteristics (BUT maintained by DHT) + growth and fusion of long bones
  • At adults: spermatogenesis, libido and normal sexual function, maintains muscle mass and bone, maintain accessory sex glands and regulate secretion of gonadotrophins
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16
Q

How does the hypothalamo-pituitary-testicular axis regulate level of LH?

A
  • GnRH stimulates anterior pituitary to release LH and LH stimulates leydig cells in testis to produce testosterone and oestradiol 17beta. Testosterone in turn acts on the negative feedback mechanism to inhibit further release of GnRH and hence LH
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17
Q

What are the factors that can affect level of LH and testosterone?

A
  • Gonadectomy
  • Androgen administration
  • Diurnal rhythm
  • illness or stress
  • too much sexual activity
  • age
  • endocrine disorder
  • hypogonadism can be induced by taking exogenous steroids so more present in the periphery. A negative feedback loop is formed to reduce level of GnRH produced by hypothalamus
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18
Q

What is androgen insensitivity syndrome?

A
  • the cause is unknown
  • the chromosome would appear as male (XY) but no presence of male genitalia because the individual is insensitive to androgen in blood
  • could be partial (dependent on level of sensitivity) or complete
19
Q

How does the hypothalamo-pituitary testicular axis regulate FSH level?

A
  • similar to LH where GnRH stimulates the production of FSH and LH in anterior pituitary and there is a negative feedback mechanism by oestradiol and inhibin with presence of testosterone
20
Q

Why is FSH crucial for male?

A
  • Testosterone and FSH are both required for spermatogenesis
21
Q

What are the main stages of sperm production?

A

1) spermatogenesis:
- mitotic proliferation, meiotic division (forming hiploid gamates), spermiogenesis

2) spermiation

22
Q

What is the process of spermatogenesis?

A
  • by type A dark spermatogonia (the main stem cell in seminiferous tubule) form spermatozoa
  • 3 stages:
    1) mitotic proliferation produces reservoir of identical cells = spermatogonia proliferate, forming primary spermatocytes
    2) meiotic division produces haploid gametes ( primary spermatocytes form spermatids)
    3) spermiogenesis or cytoplasmic remodelling produces specialised germ cells (spermatids -> spermatozoa)
23
Q

Where does spermatogenesis occur? And what is the cell layer?

A
  • In the seminiferous tubule epithelium
  • cell layer: spermatogonia (light and dark) at the bottom -> primary and secondary spermatocytes -> spermatids -> spermatozoa (at the top)
24
Q

Where can you find the mature sperms in the seminiferous epithelium?

A
  • above the blood-testis barrier

- The spermatogonia moves the cells up the barrier once became mature

25
Q

When do the ‘sperms’ become haploid cells?

A
  • when secondary spermatocytes undergo meiosis division and form spermatids
  • spermatids are still immature
26
Q

Why is there a mosaic arrangement in germ cell development?

A
  • Because there are different stages of production of sperm at each cross section so there can be a continuous production of sperms
27
Q

How long does it take for the whole process of sperm production?

A
  • 64 days
  • it is a long process so the epithelium will contain 4 successive batches of cells progressing through spermatogenesis at any one time
28
Q

How often do the type A spermatogonia initiate a new wave of spermatogenesis?

A
  • every 16 days
29
Q

What is cell associations in sperm production?

A
  • it is where the progression of the 4 successive batches is highly organised so each patch of epithelium is recognised by a particular cell associations
30
Q

What occurs in spermiogenesis?

A
  • (formation of spermatids into spermatoza)
  • The formation of acrosome (enzymes in the head of sperm), flagellum(for movement) and midpiece(contains lots of mitochondria for sperm to swim)
  • There is a loss of excess cytoplasm
  • Within this stage, the sperm starts to elongate,
31
Q

What are the key roles of sertoli cells?

A
  • spermiation
  • provide physical and metabolic support for developing spermatozoa
  • form the blood-testis barrier to protect sperms from immune attack
  • secrete anti-lymphocytic factors
  • resorb leftovers from spermiogenesis
  • secrete and maintain ion composition of serminiferous tubular fluid
  • secrete INHIBIN
  • make androgen binding proteins
  • involved in steroid conversion ( from testosterone into DHT)
  • under FSH regulation (from puberty)
  • secret ANTI- MULLERIAN HORMONE during embryonic development= essential for male sex differentiation
32
Q

What are the accessory structures found in testis?

A
  • epididymis, accessory glands and vas deferens
33
Q

What functions are carried out in the epididymis?

A
  • Sperms are being concentrated at the head of epididymis with the presence of oestrogen (by reabsorbing the fluid)
  • Maturation of sperms take place here by passing sperms through the epididymis from head to tail (sperms in testis are immature): loss of cytoplasmic drop; stabilisation of cell membrane; increased energy reserve
  • Sperms are stored in the tail of epididymis (10 to the power of 9 sperm/ml)
  • sperm movement through testis ducts and epididymis is passive
  • sperm can survive in epididymis for about 10 days and then the non-ejaculated sperms are reabsorbed ( or lost in urine)
  • Being protected by blood-epididymal barrier and it is highly androgen and oestrogen dependent
34
Q

What are the male accessory glands?

A
  • seminal vesicles, prostate glands and bulbourethral glands
  • seminal vesicles and prostrate glands produce seminal fluid; whie bulbourethral glands produce pre-ejaculate fluids

(pre-ejaculate fluids is to flush urine out before the ejaculate comes round)
*seminal fluid is more alkaline

35
Q

What is the function of semen?

A
  • Normal ejaculate volume 2-5ml with sperms contributing 1%; while seminal plasma constitutes of 99%
  • its function is to act as a transport vehicle, buffering and nutrient supply
36
Q

What is oligospermia?

A

-low sperm count, ie <20 million per ml

37
Q

What is asthenospermia?

A
  • low sperm motility, ie around 60% of sperm must be alive
38
Q

What is teratospermia?

A
  • abnormal sperm morphology, i.e. has to contain more than 4% normal looking sperms
39
Q

What is hypospermia?

A
  • low semen volume <2ml
40
Q

What are the causes of male infertility?

A
  • obstructive azospermia (no sperms in ejaculate)
  • varicocele
  • presence of antibodies to sperms
  • pathological damages of seminiferous epithelium, ie radiation
  • Klinefelters syndrome (XXY)
  • ejaculatory malfunction
  • high scrotal temp
  • disorders of seminal plasma
  • drugs, eg cannabis
41
Q

What are the problems associated with sperm transport?

A
  • blockage of the excurrent ducts that prevent sperm from mixing with the seminal fluid
  • infections: eg. STDS, can block the epididymis or vas deferens, preventing sperms from mixing with seminal fluids
  • cogential absence of vas deferens
  • vasectomy
42
Q

What are the major reasons in erectile dysfunction?

A
  • failure to initiate, failure to fill and failure to store blood volume
  • could also by psychogenic factors, alcoholism, endocrine factors, trauma…
43
Q

What are the main treatments for erectile dysfunction?

A
  • intracorporal injection, ie prostaglandin E, papavarine but can cause priapism
  • Viagra (sildenafil citrate) or tadalafil ( <- that last longer ) Works by inhibiting phosphodiesterase type 5 enzyme that normally breaks down cyclic guanosine monophosphate, cGMP. cGMP is an intracellular messenger causing increase nitrate oxide and vasodilation
  • vasodilation can aid the relaxation of arterial bed= more blood travels to penis
44
Q

What are the common prostate disorders?

A
  • Prostatitis: inflammation of prostate gland
  • Benign prostatic hyperplasia: uniform, smooth enlargement of gland
  • prostatic cancer: craggy appearance
45
Q

What is the normal semen?

A
  • volume has to be 2-4ml; with 20 X 10to the power of 6 or more sperms per millilitre
  • > 50% has to exhibit progressive motility
  • > 30% has to have normal morphology

Endocrine & Reproductive Systems (11 decks)

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