SPR L4 Male Reproductive Function Flashcards Preview

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Flashcards in SPR L4 Male Reproductive Function Deck (21):
1

Learning Outcomes

(for general perusal)

  • To elucidate the importance of Reproduction to the human
  • To describe and distinguish the processes of spermatogenesis, spermiogenesis spermiation, and sperm capacitation that underly the production of millions of male gametes per day.
  • To outline the secretions of the male accessory glands of reproduction
  • To delineate processes occurring in the male during sexual intercourse
  • To describe the hormonal function of the testes in  producing testosterone

2

Testes and Accessory Glands

What is the function of the testes?

Production of the male gametes (spermatozoa) and the male sex hormone testosterone.

Therefore, Endocrine AND Reproductive Functions

3

Testes and Accessory Glands

  1. Where do spermatogenesis and spermiogenesis take place?
  2. Where does testosterone production take place?

  1. in the convoluted seminiferous tubules
  2. in the interstitial cells of Leydig (in between these seminiferous, in between these seminiferous tubule coils)

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4

Testes and Accessory Glands

Where is the fluid median in which the spermatozoa may be transported (via epididymis and vas deferens) produced?

created by the accessory glands of the male reproductive tract: the seminal vesicles, the Prostate gland and the bulbourethral (Cowpers) glands.

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Testes and Accessory Glands

  1. Where do the testes develop in the foetus?
  2. How do they descend into the scrotum?
  3. What is Cryptorchidism?
    1. How is it treated?

  1. in the abdomen
  2. descend down the inguinal canal so at birth they lie within the scrotum
  3. undescended testes - occurs in 3% of full term and 30% of premature babies and can lead to infertility and increased risk of cancer
    1. It is often treated by surgery. 

6

Why are the testes located externally?

to facilitate the 2-3oC below core temperature that is necessary for spermatogenesis

7

Testes and Accessory Glands

  1. Ideally, what temperature should the testes be kept at?
  2. What helps to remove heat from the testes?
  3. What role does the Cremaster Muscle have in temperature regulation of the testes?
  4. Although far too unreliable, what have been proposed as potential male contraceptives, and should be avoided by males attempting to concieve?

  1. 32oC
  2. the anatomic arrangement of the spermatic arteries and paminiform plexus of the spermatic veins (running parallel but in opposite directions) - in a similar countercurrent exchange mechanism seen in the kidneys
  3.  acts to alter the distance that the scrotal sac hangs from the abdomen, conserving heat in cold conditions and allowing ventilation and cooling in warm conditions. 
  4. hot baths (35-45oC for half an hour per day) and insulated athletic supporters

8

Sperm Formation

Sperm formation takes place in 4 stages, outline them...

  1. Spermatogenesis
  2. Spermiogenesis
  3. Spermiation
  4. Capacitation

 

  1. involves the formation of haploid gametes from the diploid precursors (spermatogonium) found at the basal lamina of the seminiferous tubules.
  2. the gametes (spermatids) undergo structural changes to render them motile.
  3.  The spermatozoa are then released into the lumen of the seminiferous tubules.
  4. takes place between the epdidymis and the female genital tract is called capacitation and renders the spermatozoa capable of fertilising the female gamete.

9

Summarise the stages of sperm formation

  • Spermatogenesis - production of haploid gametes from diploid precursors
  • Spermiogenesis - The gametes (spermatids) change to become motile
  • Spermiation - release of spermatocytes into the lumen of the seminiferous tubules where they swim in seminiferous fluid
  • Capacitation - in epididymis and female genital tract.  Final step rendering spermatocytes capable of fertilising the ovum 

10

Spermatogenesis

  1. When does sperm production begin?
  2. From what do Spermatozoa develop from? How?
  3. Outline the events which follow

 

  1. at puberty and continues throughout the rest of adult life in the male.
  2. from progenitor cells next to the basement membrane: spermatogonia. These divide by mitosis with one of the resulting cells maturing to become spermatozoa and the other one left behind to form a permanent reserve.
  3. After this initial differentiation, the daughter cell  undergoes meiosis.  This involves 2 divisions.  Initially the genetic material in the cell duplicates, giving a primary spermatocyte with 2 copies of each of the 23 chromosome pairs (essentially giving the  primary spermatocyte 2n + 2n genes).  The gene pairs (homologous chromosomes) line up and exchange genetic material with one another (genetic recombination). These then split and cell division occurs (meiosis I) to form the secondary spermatocytes which are haploid cells, each chromosome now being unpaired (n + n in each cell).

    Meiosis II occurs after this (upon sexual intercourse), the final division with each cell (spermatid) containing the haploid number of chromosomes unduplicated (n).  These spermatids must undergo further maturation to become fully motile spermatozoa (spermiogenesis, spermiation and capacitation).

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11

Outline the events in Spermatogenesis

  • Spermatozoa develop from progenitor cells next to the basement membrane called spermatogonia
  • These divide by mitosis with one of the resulting cells maturing to become spermatozoa and the other one left behind to form a permanent reserve.
  • After this initial differentiation, the daughter cell  undergoes meiosis (2 divisions) 
  • Initially the genetic material in the cell duplicates, giving a primary spermatocyte with 2 copies of each of the 23 chromosome pairs (essentially giving the  primary spermatocyte 2n + 2n genes).
  • The gene pairs (homologous chromosomes) line up and exchange genetic material with one another (genetic recombination).
  • These then split and cell division occurs (meiosis I) to form the secondary spermatocytes which are haploid cells, each chromosome now being unpaired (n + n in each cell). 
  • Meiosis II occurs after this, the final division with each cell (spermatid) containing the haploid number of chromosomes unduplicated (n). 

These spermatids must undergo further maturation to become fully motile spermatozoa (spermiogenesis, spermiation and capacitation)

 

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12

Spermiogenesis

The cells resulting from spermatogenesis have the correct genetic material but need to differentiate into the motile gametes 

  1. Where does this occur?
  2. What is the role of this type of cell?
  3. What forms a blood-testicle barrier?
  4. What is the final function of this cell?

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  1. within the folds of the Sertoli cell
  2. nourishes the developing sperm cells, phagocytoses old or defunct cells, and protects the sperm from blood-borne toxins.
  3. tight-junctions between the Sertoli cell and the basement membrane - any substance has to pass through it to get to the sperm. Steroids penetrate it, and proteins may pass the other way
  4. to secrete the sperm into the lumen (spermiation) along with the seminiferous tubule fluid (a fluid high in K+, androgens, estrogens, inositol and glutamic acids).

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13

The mature spermatozoon is a highly differentiated cell

  1. What does the head contain?
  2. What does the middle piece contain?
  3. What is the microtubular core formed from?
  4. When is the spermatozoon considered fully mature?
  5. Where do the sperm undergo capacitation?
  6. Where are all centroles inherited from?

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  1. the genetic material and an enzymatic cap called the acrosome.
  2. The middle piece contains the centrioles (essential in cell division and are the progenitors of all centrioles in foetal cells) and many mitochondria which are necessary to provide energy for the tail (flagellum) which makes the sperm motile by rotating in a corkscrew fashion.
  3. formed from the centrioles
  4. when it is exposed to the environment of the female. 
  5. In the uterus - becoming more motile, and capable of enzymatically penetrating the ovum with the acrosomal cap.
  6. All centrioles come from the father

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14

Hormonal Control

  1. What are the chief aims of the hormonal control in male reproductive function?
  2. What mechanism of hormonal control features?
  3. Where is gonadotropin releasing hormone (GRH) released from, and how often?
  4. What is it carried in?
  5. What does it stimulate the release of in the Anterior Pituitary?
  6. Where do these hormones act?
  7. What exerts feedback control?

  1. maintaining a turnover of spermatozoon production and ensuring an appropriate level of testosterone to maintain spermatogenesis and the secondary sexual characteristics of the male.
  2. Hypothalamo/Anterior Pituitary/End organ axis of endocrine control
  3. the hypothalamus, daily. This keeps the processes of gametogenesis and testosterone formation “ticking over”.

  4. Follicle Stimulating Hormone (FSH) and Luetenising Hormone (LH). 

  5. carried to target cells in the testes.  Leutenising hormone exerts its effects on the interstitial cells of Leydig and causes them to release testosterone, while Follicle Stimulating Hormone (FSH) promotes spermatogenesis by acting (along with locally produced testosterone) on the Sertoli cells.

  6. testosterone, directly on LH production in the anterior pituitary and GnRH production in the hypothalamus, and by the hormone Inhibin on FSH production in the anterior pituitary.

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15

Hormonal Control

Where do the following hormones released from the Ant Pit act?

Leutenising Hormone

Follicle Stimulating Hormone

Leutenising hormone interstitial cells of Leydig, causes them to release testosterone

Follicle Stimulating Hormone - promotes spermatogenesis by acting (along with locally produced testosterone) on the Sertoli cells

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16

Testosterone Function

  1. What is testosterone?
  2. What are it's functions in males?
  3. What does it do in utero and prenatally?
  4. What is it's role in the young and mature adult?
  5. What type of hormone is it?
  6. What are it's behavioural effects?

  1. the dominant male sex steroid.
  2. amongst other essential functions in males, a local source of testosterone is necessary for spermatogenesis to proceed (it also carries out some functions in females). 
  3. gives the male phenotype in utero, and causes the pre natal structural changes that result in male external genitalia. 
  4. It develops and maintains the male reproductive system, is responsible for the changes seen in secondary sexual characteristics at puberty.  Promotes the adolescent sexual growth spurt & fusion of epiphyses.
  5. It is an anabolic hormone, promoting muscle deposition and increased metabolic rate.
  6. characteristic effects on male libido and agression.

17

Sexual Intercourse

  1. What must occur to make fertilisation possible?
  2. What does this involve?

  1. the motile male gametes must be deposited in the female genital tract whereupon they can make their way to the ovum. 
  2. penile erection enabling penetration of the vagina.  Ejaculation of semen then follows, leaving sperm near the opening of the cervical canal (the only route of access to the uterus and fallopian tubes where fertilisation of the egg will take place)

18

Erection

  1. When does erection happen?
  2. What may it be initiated by?
  3. What does the erection reflex involve?
  4. What may explain some phychological instances of erectile failure?
  5. What pathway is thought to be essential to erection?
    1. How is this pathway used?

  1. when dilation of the penile arterioles fills the erectile tissue of the penis (the paired corpus cavernosa and the corpus spongiosum) with blood, giving it sufficient turgor and rigidity.
  2. Erotic cognitive stimuli - strongly reinforced by stimulation of sensory receptors on the glans and anterior penis. Further reinforced when the veins draining the penis are compressed. 
  3. activation of parasympathetic dilator nerves and inactivation of sympathetic constrictor nerves. 
  4. The necessity of application of parasympathetic tone and withdrawal of sympathetic tone may
  5. The NO vasodilator pathway
    1. drugs that increase production of NO and its related vasodilators (cyclic GMP) are used in the treatment of erectile dysfunction, and, at this stage, have become household names.(e.g. Viagra)

19

Ejaculation

  1. What are the two phases?
  2. What occurs in the first phase?
  3. What occurs in the second phase?
  4. How much semen is released?
  5. How many sperm does each ml of semen contain?

  1. Emission and Expulsion
  2. a sympathetic reflex stimulates nerves in the smooth muscle walls of the epididymus, vas deferens and accessory glands (seminal vesicles and prostate), causing sperm and secretions of the accessory glands to be mixed together to form semen which is deposited in the urethra.
  3. relies on reflex contractions of skeletal muscle around the base of the penis (mainly the bulbocavernosus muscle), which expel the semen with great force into the vagina. 
  4. About 3.5mls 
  5. between 20 and 100 million sperm.

20

Semen

  1. What is the semen composed of?
    1. 60%
    2. 25%
    3. The remainder
  2. What is secreted that may be used clinically as a marker for prostate cancer?

  1. Composition of Semen
    1. fluid from the seminal vesicle: fluid rich in fructose to nourish the sperm, prostaglandins and agents which promote clotting of semen.
    2. from the prostate gland containing citrate and proteases which help break down clotted semen.
    3. mucoid secretion of the bulbourethral gland (pre ejaculate) which helps lubricate the urethra and clear away urine before ejaculation (also can carry sperm from previous expulsions - reason for failure of withdrawal as a contraceptive)
  2. Prostate specific antigen (PSA) The remaining fluid is the mucoid secretion of the bulbourethral gland (pre ejaculate) which helps lubricate the urethra and clear away urine before ejaculation

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21

Summing Up

(for general perusal)

  • Millions of male motile male gametes per day are created in the seminiferous tubule in a process that involves 4 stages; spermatogenesis, spermiogenesis, spermiation and sperm capacitation
  • This process is under the control of hormones from the hypothalamo/pituitary/gonadal axis and relies on locally produced testosterone, which exerts other effects.
  • Sexual intercourse deposits male gametes in close proximity with female ones and relies on a complex interplay between psychologic and physiologic factors

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