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Medical Physiology 2 > Male Reproductive System > Flashcards

Male Reproductive System Flashcards

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USMLE® Step 1 flashcards
1
Q

What the male gonads are, where they are located and what they do.

A

Testes, gametogenesis

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2
Q

Male reproductive tract

A

Testis -> epididymis -> vas deferens -> seminal vesicles -> ejaculatory duct -> prostate gland -> bulbouretheral gland -> urethra (erectile tissue) -> glans penis

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3
Q

what a vasectomy is and be able to describe the physiological consequences of the procedure

A

cutting of the vas deferens to block spermatozoa from propelling

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4
Q

Male accessory glands

A

Prostate Gland, Seminal vesicles and Bulbourethral glands

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5
Q

why the male gonads are located in the scrotum and the consequences of cryptorchidism

A

The most effective rates of spermatogenesis occur at environmental temperatures of 3-5oC below core body temperature. This is of course why the testes are located in the scrotum (outside the pelvic cavity) and why the failure of testes to descend (known as cryptorchidism) results in greatly attenuated spermatogenesis.

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6
Q

Assuming spermatogenesis is 100% efficient, how many spermatozoa will result from a single primary spermatocyte?

A

4

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7
Q

Which of the following substances has a positive effect on the rate of spermatogenesis?

testosterone
follicle stimulating hormone
androgen binding protein

A

all

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8
Q

Which of the following is NOT an effect of follicle stimulating hormone (FSH)?

maturation of Sertoli cells
stimulation of inhibin secretion
stimulation of testosterone secretion
stimulation of spermatogenesis
stimulation of androgen binding protein secretion

A

stimulation of testosterone secretion

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9
Q

Which of the following would be observed in a male subject following a large intravenous injection of inhibin?

A

circulating levels of follicle stimulating hormone (FSH) would decrease

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10
Q

Which of the following blood test results would be most likely to come from a man with a tumour in the anterior pituitary which caused hypersecretion of luteinising hormone (LH)?

A

increased testosterone and decreased GnRH

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11
Q

shortest part of the urethra?

A

membraneous urethra

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12
Q

Which of the following is NOT a function of Sertoli cells?

secretion of testosterone

supply of nutrients to developing sperm cells

phagocytosis of cellular debris

secretion of seminiferous tubule fluid

regulation of spermatogenesis.

A

secretion of testosterone

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13
Q

The cells generated following three mitotic divisions of a single spermatogonium are known as?

A

primary spermatocytes

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14
Q

Spermatozoa swim from the lumen of the seminiferous tubles into the epididymis. True or false?

A

false

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15
Q

the order of structures through which spermatozoa move through the male reproductive tract

A

seminiferous tubules – epididymis – vas deferens – ejaculatory duct – prostatic urethra

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16
Q

The complete process by which primordial germ cells are transformed into spermatozoa is known as?

A

spermatogenesis

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17
Q

Which of the following would have a detrimental effect on the generation of an erection?

A

Increased sympathetic tone to the penile arterioles.

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18
Q

On which of the following cell types would you expect to find the highest concentration of receptors for luteinising hormone (LH)?

A

Leydig cells

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19
Q

The blood-testes barrier consists of specialised junctions between the endothelial cells of blood vessels supplying the testes. True or false?

A

false

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20
Q

Which of the following types of cells would you expect to find in the testes of a typical seven year old?

Spermatogonia
Sertoli cells
Spermatids

A

Spermatogonia
Sertoli cells

21
Q

The optimal temperature for spermatogenesis in humans is in the order of?

A

32 - 34 oC

22
Q

During spermiogenesis, which cytoplasmic organelle develops into the acrosome?

A

Golgi apparatus

23
Q

The major constituent of semen volume comes from which of the following structures?

A

seminal vesicles

24
Q

In which of the following structures would you expect to find spermatozoa and seminal fluid but NOT prostatic fluid?

A

ejaculatory duct

25
Q

Seminiferous tubules before puberty

A

fairly simple seminiferous tubules consisting of small numbers of germ cells (spermatogonia) arranged around the periphery of the tubules and positioned between supporting Sertoli cells which are attached to the basal surface of the tubule but project towards the lumen

26
Q

Seminiferous tubules beginning of puberty (11-14)

A
  • spermatogonia begin to divide and dramatically increase the number of cells at the base of the tubule
  • increasing numbers of these spermatogonia begin the sequence of events by which they are transformed into spermatozoa
27
Q

as spermatogonia transform into spermatozoa, the developing cells (positioned between the _____ _____) move away from the periphery of the seminiferous tubules towards the _____

A

Sertoli cells
lumen

28
Q

Mitosis

A

Spermatogonia -> mitotic division -> 2 daughter cells -> one stays at periphery (retains germ cell stocks) and 2nd undergoes a further 2 mitotic divisions -> 4 cells available to undergo subsequent development

29
Q

Meiosis

A

spermatogonia -> primary spermatocytes -> meiosis -> 2 secondary spermatocytes (remain couples by narrow cytoplasmic bridges) -> 2nd meiotic division -> 2 spermatids each (remain coupled) -> each primary spermatocyte gives rise tp 4 spermatids

30
Q

Spermiogenesis

A
  • spermatids metamorphose into the lean mean swimming machines required for effective fertilisation
  • the maturing spermatozoa remain associated with the Sertoli cells, but most of the action takes place towards the luminal surface
31
Q

key elements of spermiogenesis

A
  1. nuclear reorganisation: the centrally-located spermatid nucleus moves to non-luminal side and nucleus beings to elongate and chromatin becomes denser
  2. acrosome formation: formed at Golgi apparatus between migrating nucleus and plasma membrane - as spermiogenesis progresses, acrosome grows around the elongating nucleus and covers its anterior and lateral surfaces
  3. tail assembly: involves reorganisation of the remaining cytoplasm and plasma membrane in to a single long whip-like structure around a long microtubule core which arises from one spermatids centrioles -> arrangement of two microtubules surrounded by nine pairs of microtubles arranged equidistant from each other - movement of tail enabled by fromation of transient cross-bridges between the microtubules which cause them to slide relative to each other - powered by ATP generated by the large number of mitochondria found in the initial portion of the tail known as the midpiece
32
Q

functions of Sertoli cells in relation to spermatogenesis

A
  • formation of Blood-Testes Barrier
  • Supply of Nutrients to Developing Sperm Cells
  • Phagocytosis of Cellular Debris
  • Secretion of Seminiferous Tubule Fluid
  • Regulation of Spermatogenesis
33
Q

the structural basis of the blood-testes barrier and its functional significance

A
  • have specialised tight junctions between them which prevents the movement of blood-borne substances into the lumen of the ST
  • the developing spermatogonia are permitted to move past by remodelling of the barrier around them
33
Q

describe the changes in circulating hormone levels that are associated with puberty in males

A
  • spermatogenesis is initiated at puberty by increasing levels of GnRH (secreted by hypothalamus) -> stimulates secretion of LH & FSH (by anterior pituitary gland) - is subsequently regulated by the negative feedback control mediated by testosterone and inhibin
33
Q

what gonadotropins do and the important roles they play in spermatogenesis

A

LH:
- binds to specific receptors on Leydig Cells of the IS of testes -> stimulates their initial development and secretion of testosterone

FSH:
- acts on Sertoli Cells of the ST causing them to mature and (with secretion of testosterone) -> spermatogenesis
- also stimulates secretion of inhibin and androgen binding protein by the Sertoli cells

34
Q

Know where testosterone comes from and be able to describe its developmental and ongoing physiological roles

A
  • secreted by Leydig cells under influence of LH
  • responsible for the ‘masculinisation of the brain’, musculoskeletal growth, enlargement of the accessory organs, development of male secondary sex characteristics and the stimulation of spermatogenesis (together with FSH)
  • effects greatly enhanced by ABP - enhances the local concentration of testosterone and hence its stimulatory effect on spermatogenesis
  • Testosterone has a powerful inhibitory effect on the hypothalamus which results in a decline in GnRH and consequently a fall in circulating levels of both FSH and LH
  • if testosterone levels increase, the feedback loop will reduce LH levels and subsequently testosterone secretion
  • if testosterone levels start to drop, the inhibitory influence will decline and LH levels will rise to stimulate testosterone
35
Q

Be able to describe the functional significance of both inhibin and androgen binding protein.
Inhibin

A
  • inhibin inhibits the anterior pituitary gland, has inhibitory effect on spermatogenesis
  • androgen greatly enhances the local concentration of testosterone and hence its stimulatory effect on spermatogenesis
36
Q

Spermatogenesis is responsible for controlling the production of spermatozoa in numbers in the order of __________ sperm/gram testis/day for healthy 20 year old men. This figure declines progressively with age to approximately __________ sperm/gram/day in _____ year old men.

A

6.5 million
3.8 million
50-90

37
Q

The male sexual act is split up into three fairly well defined stages:

A

a. erection
b. emission
c. ejaculation

38
Q

Understand how engorgement of erectile tissue with blood is brought about in order to form an erection

A
  • erection enabled by the engorgement of three columns of penile erectile tissue with blood
  • arterioles that supply them are constricted under the influence of noradrenaline released from the post-ganglionic neurones of the sympathetic division of the autonomic nervous system
  • During sexual arousal changes in autonomic nervous system tone are brought about by a variety of psychogenic stimuli as well as a direct spinal reflex activated by mechanoreceptors in the penis
  • sympathetic tone to the arterioles is decreased and parasympathetic tone is increased and the penile arterioles dilate -> increase in blood flow into the penis and a concomitant relaxation of the smooth muscle of the penile erectile tissue to accommodate the blood
  • diameter and length of the penis increase
  • enhanced even further by decreased venous outflow
  • parasympathetic division of the autonomic nervous system also stimulates secretion of mucus from the bulbourethral glands
39
Q

Understand the role that nitric oxide and cGMP play in the formation of an erection

A
  • Acetylcholine released from the parasympathetic postganglionic neurones binds to muscarinic receptors on the endothelial cells that line the venous sinusoids of the erectile tissue -> triggers NO synthesis
  • NO is small molecule that is an intercellular messenger in a variety of physiological systems
  • The NO released by the endothelial cells readily diffuses into the adjacent smooth muscles of the erectile tissue and stimulates the intracellular enzyme guanylate cyclase to produce elevated levels of cyclic guanosine monophosphate (cGMP)
  • cGMP activates a complex intracellular-messenger cascade that causes relaxation of these smooth muscle cells and permits the erectile tissue to become engorged with blood
40
Q

Be able to explain why phosphodiesterase type-5 inhibitors can be used to treat erectile dysfunction

A

Of course it is desirable that erections are maintained for only the appropriate amount of time so these smooth muscle cells have an enzyme known as phosphodiesterase type-5 (PDE5) that breaks down the cGMP, inhibiting smooth muscle relaxation and enabling the penis to become flaccid again.

41
Q

processes involved in emission

A
  • involves the transfer of spermatozoa from the vas deferens and the various secretions of the accessory sex glands into the urethra
  • brought about by heightened tactile and psychogenic stimuli and are mediated by an increase in sympathetic activity to the smooth muscle lining the walls of the vas deferens, ejaculatory duct, prostate gland and seminal vesicles
  • causes spermatozoa, prostatic fluid, seminal fluid and mucus from the bulbourethral glands to mix (forming semen) in the urethra
42
Q

processes involved in ejaculation

A
  • The very rapid filling of the urethra during emission causes even further sensory outflow from the penis -> enhances the sympathetically mediated contraction of the smooth muscle of the male ductal system and stimulates the rhythmic contraction of a number of skeletal muscles at the base of the penis which further increases the pressure in the erectile tissue
  • net effect is the rapid expulsion of semen from the urethra which is accompanied by a feeling of intense gratification referred to as the orgasm
  • urethra closest to the bladder constricts to prevent back flow of semen into the bladder
  • ## volume of semen ejaculated is in the order of 2-6 mL with the average around 3 mL
43
Q

The major contribution of ejaculation is from ______ ______ followed by _______ ____ with the remaining volume consisting of the ____ secreted by the ___________ _______ and the _______ themselves.

A

seminal fluid
prostatic fluid
mucus
bulbourethral glands
spermatozoa

44
Q

secretions of seminal vesicles and the functional significance of it

A

major volume component of semen contributing around 65% of total volume and contains elements which play a very important role in fertilisation:
- fructose - main energy source for sperm
- prostaglandins -stimulation of the male ductal system during emission and ejaculation, stimulation of spermatozoa motility & stimulation of contraction of the female ductal system
- semenogelin - This fibrinogen-like protein is believed to be responsible for the coagulation of semen into a gel-like mass immediately following ejaculation. This “clot” is believed help the semen adhere to the wall of the vagina and thus retain the semen within the female reproductive tract

45
Q

secretions of prostate gland and the functional significance of it

A
  • Prostatic fluid contributes around 25% of the semen volume
  • highly alkaline fluid which helps to neutralise the very acid secretions of the vas deferens (due to metabolic waste products of spermatozoa) and the vagina
  • important because spermatozoa are most motile in environments with a pH around 6.0
  • Another important constituent of prostatic fluid is prostate specific antigen (PSA). PSA is a proteolytic enzyme that is believed to act on the semen clot produced by semenogelin and break it down and thus releasing the spermatozoa.
46
Q

secretions of bulbourethral glands and the functional significance of it

A
  • exocrine secretions flow along ducts that empty into the penile urethra
  • During sexual arousal, secrete a clear alkaline mucus that help neutralise the acidity caused by a residual urine present in the urethra as well as acting as a lubricant for intercourse and the flow of semen through the penile urethra during ejaculation
  • constitute approximately 5% of semen volume.

Medical Physiology 2 (6 decks)

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