Reproductive Physiology - 20.02.2020

Question 1

What are the two main functions of the male reproductive system?

Answer 1

• provision of androgens (primarily testosterone) to initiate and sustain the necessary male phenotype
• production of mature sperm.

Question 2

Epididymis

Answer 2

• One within each scrotal sac.
• Sperm are released from the testis and stored here prior to ejaculation.
• At ejaculation sperm pass through the two Vas Deferens (which are contractile), and are mixed with fluid from the seminal vesicles.
• The fluid then leaves the ejaculatory duct, and passes into the urethra where it mixes with secretions from the prostate gland.

Question 3

REGULATORY hormones in the male reproductive system

Answer 3

Gonadotrophin releasing hormone (GnRH)
- Hypothalamus

Luteinising hormone (LH)
- Anterior pituitary

Follicle stimulating hormone (FSH)
- Anterior pituitary

Testosterone (T)
- Testis

(in the male the names of the hormones don’t make sense, they are used because they are the same hormones as in females)

Question 4

Spermatogenesis

Answer 4

Primordial germ cell

• Very rapid process
• sperm are produced in the millions every day

Question 5

male reproductive function summary

Answer 5

• Starts at puberty
• Functions continually
• Normally continues throughout the rest of life
• Sperm quantity and quality generally decreases gradually with increasing age (best sperm at age fo around 20s)
• LH stimulates testosterone production
• FSH and testosterone sustain Sertoli cell function
• Sertoli cells support spermatogenesis

Question 6

How much of male sperm is good quality?

Answer 6

• 4%
• sperm production is a very fast and imperfect process
• only 4% of the sperm is good quality
• but there is a large amount of sperm produced

Question 7

Female reproductive system summary

Answer 7

• Starts at puberty
• Functions cyclically
• Normally operates until ~45 years of age (usually complete by about 55)
• Egg quality generally decreases with increasing age -> e.g. chromosomal abnomalities
• FSH stimulates (some) development of ovarian follicles & 17b-estradiol synthesis
• LH stimulates progesterone production
• The steroids regulate uterine endometrium

Question 8

Hormonal axis in females at different parts of the cycle?

Answer 8

Early
- negative feedback by oestradiol

Mid
- positive feedback by oestradiol

Late
- negative feedback by progesterone

Question 9

Draw out the hormone changes throughout the female reproductive cycle

Answer 9

x (slide 11)

Question 10

What happens to the uterus in the menstrual cycle?

Answer 10

• early: 2-4 mm in thickness
• secretory phase: 7-16mm thickness
• endometrial lining changes throughout the cycle, increasing in thickness gradually in the first 2/3 of the cycle (then when it is thickest implantation should occur) and then the endometrium starts to break down over 3-4 days.
• this is under the control of steroids
• oestrogen drive the growth of endometrium
• then progesterone and oestrogen to cause thickening
• a decline in progesterone towards the end of the cycle is the signal for shedding of the uterine lining.
• control is ovarian -> endometrial

Question 11

Folliculogenesis

Answer 11

1. primordial follicle
2. primary follicle
3. growing follicle
4. antral follicle
5. ruptured follicle
6. corpus luteum
7. degenerating corpus luteum

• This process is longer than a month.
• in fact it actually lasts more than 2 complete cycles before the egg is ovulating
• a number of eggs are doing this at the same time and in both ovaries. One egg is chosen -> Graafian follicle
• usually left and right ovaries usually change every month genernally
• non-identical twins can be from the same or from the two different ovaries
• both first and second meiotic division are paused during follicle development.

Question 12

Oogenesis

Answer 12

Oogenesis:

• early stages occur in utero
• later stages occur when the girl reaches puberty

The gap between when the egg started developing and when it actually becomes and egg that can be fertilised has an effect on the quality - this is though to be a reason why the egg quality decreases with age.

• Ovulation = release of mature oocyte (egg) from the ovary
• Oocyte is 2n at this stage, in meiotic arrest (metaphase II)
• Enters the Fallopian tube
• Needs to be fertilised within 24 hours, as it degenerates after this

Question 13

What is ovulation?

Answer 13

• Ovulation = release of mature oocyte (egg) from the ovary (approximately day 14)
• at this stage the egg (oocyte) is still diploid in meiotic arrest (metaphase II)
• Enters the Fallopian tube
• Needs to be fertilised within 24 hours, as it degenerates after this

Question 14

Fertilisation

Answer 14

• malfunctioning sperm cannot swim very long/at all/very well -> malfunctioning sperm does not reach the egg
• sperm have to travel a long way, from the cervix, up the correct Fallopian tube etc.
• acrosome on sperm
• penetrates zona pellucida
• head of the sperm enters the ovum
• decondenses into a male pro-nucelus
• they do not form a diploid nucleus!!
• meiotic arrest in the female stops
• female cell becomes 1n now and gives rise to the second polar body
• formation of mitotic spindle and duplication ->2 chromosome clusters formed -> cell division
• 2 cell embryo stage, each cell has a nucleus.

Question 15

After fertilisation

Answer 15

• Meosis of maternal chromosomes resumes, forming female pronucleus (23 chromatids), and 2nd polar body.
• Sperm chromosomes decondense to form male pronucleus (23 chromatids).
• Chromatids in both pronuclei are duplicated
• They align on the mitotic spindle, and are separated into 2 identical ‘daughter’ cells (1st cleavage division of the embryo).

Question 16

n-numbers from fertilisation to the two first cells

Answer 16

• at first a 1n male nucleus and a 2n female nucleus are in the cell
• female mitotic arrest stops, there is a division and the second polar body is formed
• now there is 1n female and 1n male
• duplication to 2n male and 2n female
• first mitotic division to 2n (m+f) and 2n (m+f) cells.

Question 17

When are the 2 polar bodies formed?

Answer 17

• the first one is formed in the process of folliculogenesis

- the second polar body is formed after fertilisation

Question 18

What are some important tissues in the female reproductive tract?

Answer 18

• Ovaries (hormone production)
• Fallopian tubes (appropriate environment to sustain the oocyte or conceptus is produced)
• Uterus (conceptus normally implants here)

Question 19

What are some important tissues in the male reproductive tract?

Answer 19

• testes (sperm and hormone production; is made of seminiferous tubules and leydig (=interstitial) cells)
• epididymis (sperm is stored here before ejaculation)
• vas deferens (sperm pass through the 2 vas deferens which are contractile)
• ejaculatory duct (formed by the union of the vas deferens with the duct of the seminal vesicle)
• fluid leaves the ejaculatory duct and passes through the urethra where it mixes with the secretions of the prostate gland)

Question 20

How many cells are generated in the testes and in the ovaries?

Answer 20

Ovaries:

• Contain ~6 million primordial follicles at ~20 weeks of development.
• By delivery of the infant, this has fallen to ~1 million per ovary.
• About 400 follicles will be ovulated during the reproductive life-time.

Testes

• Produce about 100 million sperm per day, from puberty onwards.
• The production of gametes is very different

Question 21

Folliculogenesis - when are the meiotic pauses?

Answer 21

• Meiosis I starts during embryonic development, but halts at the diplotene stage of prophase I (primary follicle);
• this persists until puberty when meiosis resumes as secondary follicles develop.
• Only a sub-population of follicles become secondary follicles, and these undergo another pause in meiosis at the metaphase stage of Meiosis II.
• Only fertilisation can cause the completion of meiosis in a human oocyte.

Question 22

What are the different meanings of ‘sex’?

Answer 22

• Biological sex: identifies gender (m or f); result of chromosomes, production of gametes.
• sexual reproduction: produces offspring that differ genetically from both parents
• sexual intercourse: required for sexual reproduction; sexual activity; sexual pleasure; human bonding.

Question 23

Penis function

Answer 23

Sexy thoughts -> brain (limbic system) -> spinal cord -> efferent and afferent connections to the penis
also there is a tactile stimulus to the penis

Question 24

Molecular changes during erection

Answer 24

• Initiated by: increased parasympathetic activity to smooth muscle of pudendal artery
• Increases the activity of Nitric Oxide Synthase (NOS), and hence nitric oxide (NO)
• NO increases production of cyclic GMP which induces dilatation of arterial smooth muscle.
• counteracts sympathetic-maintained myogenic tone
  increases blood flow in corpus cavernosum
  which compresses the dorsal vein, restricting the outflow of blood
• The urethra is protected from increased pressure by surrounding corpus spongiosum (less turgid)

Question 25

How does viagra work?

Answer 25

• Cyclic GMP is normally de-activated by a phosphodiesterase enzyme, and this will reverse the changes leading to penile erection.
• Viagra inhibits the phosphodiesterase, thus potentiating the effects of cyclic GMP.

Question 26

Which nerve is important in terms of erection?

Answer 26

Pudendal Nerve

Question 27

What are the different phases in the endometrial and the ovarian cycle?

Answer 27

• ovarian:
  follicular (14d)
  luteal (14d)
• endometrial:
  menstrual (5d)
  proliferative (9d)
  secretory (13d)

Question 28

What is the female erectile tissue?

Answer 28

• clitoris is the equivalent of the penis
• increases in size as a result of increased blood flow into the tissue
• mechanism is the same (release of NO)

Question 29

Detailes main events in fertilisation (medlearn)

Answer 29

• Deposition of sperm within female system following sexual intercourse.
• Sperm are deposited near cervix
• Cervical mucus is normally hostile to sperm
• This forms a physical barrier to sperm
• Cervical mucus changes at mid-cycle
• This change permits sperm to enter uterus
• Passage of sperm through uterus
• Passage of sperm into Fallopian tube
• Swim from there to Fallopian tube ampulla
• ~30 µm/sec average speed; 2 mm/min; 12 cm/hour
• Survival of the fittest (a few days)
• Capacitation – takes time within uterus
• Capacitation is essential preparation before the sperm meet the oocyte
• Meeting of egg with sperm
• Fusion of egg and one sperm (within 24 hours post ovulation)
• Acrosome reaction: penetration of Zona Pellucida (& Coronal cells)
• Calcium flux
• Resumption of meiosis, release of 2nd polar body
• Alignment of maternal and paternal chromosomes to generate zygote.
• Change in Zona Pellucida to prevent additional sperm fusing with zygote.
• Initiation of mitotic (cleavage) divisions in embryo.

Question 30

Significance of granulosa and thecal cells for sex steroid production

Answer 30

Thecal cells:
- two layers (theca interna and externa)

LH binds to R on thecal cells. This causes androgen production. Aromatase in granulosa cells turn these androgens into 17-beta-oestradiol.
FSH binds to receptors on Granulosa cells and activates aromatase.

Question 31

Neuroendocrine control: what are the brain pathways associated with pleasure and what is their contribution to securing procreation, human bonding and parental behaviours?

Answer 31

a) Pathways for rewards and pleasure (mesolimbic dopaminergic pathway)
b) control of movements (nigrostriatal tract)
c) neuroendocrine pathways regulating fertility and parenting

• Activation of pleasure pathways therefore encourages intercourse, thus continuation of the human race.
• These brain functions complement those discussed earlier in this chapter, in which the role of the brain in controlling the production of gametes (hypothalamic-pituitary-gonadal axes) was considered.

Question 32

where fo the ovaries lie?

Answer 32

• located on either side of the uterus
• within the abdominal cavity in the pelvis
• each ovary is attached to the posterior wall nu the suspensory ligaments and to the uterine broad ligament bu the ovarian mesentery ( a wide fold of the peritoneum extending from the uterus to the wall of the pelvis on either side known as the mesovarium.

Question 33

where fo the ovaries lie?

Answer 33

• located on either side of the uterus
• within the abdominal cavity in the pelvis
• each ovary is attached to the posterior wall nu the suspensory ligaments and to the uterine broad ligament bu the ovarian mesentery ( a wide fold of the peritoneum extending from the uterus to the wall of the pelvis on either side known as the mesovarium.

Question 34

Recognise the mechanisms of fertilisation

Answer 34

• intercourse, ejaculation in vagina, sperm reaches fallopia tubes, sperm capacitation
• sperm binds to ZP3, penetrates zona pellucida
• cortical reaction, other sperm cannot enter now.
• By this stage, Meiosis II in the maternal chromosomes is completed, leading to the formation of polar body II, and the female pronucleus.
• The head of the sperm is undergoing decondensation, with the previously tightly packed paternal chromosomes forming a much looser structure.
• Both pronuclei are haploid at this stage of fertilisation.
• Both pronuclei are now visible;
• by this stage duplication of the DNA in both pronuclei has been duplicated, making 2n chromosomes of maternal and of paternal origin.
• next: mitotic division, giving 2 daughter cells, which must have the same chromosomal complement, so duplication is required at this stage.
• Maternal and paternal chromosomes mix for the first time, as the metaphase plate of the first cleavage division is formed.
• separation of male and female chromatids

note: the pronuclei do not fuse

Question 35

Recognise the mechanisms of fertilisation

Answer 35

• intercourse, ejaculation in vagina, sperm reaches fallopia tubes, sperm capacitation
• sperm binds to ZP3, penetrates zona pellucida
• cortical reaction, other sperm cannot enter now.
• By this stage, Meiosis II in the maternal chromosomes is completed, leading to the formation of polar body II, and the female pronucleus.
• The head of the sperm is undergoing decondensation, with the previously tightly packed paternal chromosomes forming a much looser structure.
• Both pronuclei are haploid at this stage of fertilisation.
• Both pronuclei are now visible;
• by this stage duplication of the DNA in both pronuclei has been duplicated, making 2n chromosomes of maternal and of paternal origin.
• next: mitotic division, giving 2 daughter cells, which must have the same chromosomal complement, so duplication is required at this stage.
• Maternal and paternal chromosomes mix for the first time, as the metaphase plate of the first cleavage division is formed.
• separation of male and female chromatids

note: the pronuclei do not fuse

Question 36

Draw a diagram of oogenesis

Answer 36

see notes

Question 37

Gametogenesis in human males and females

Answer 37

= the process in which cells undergo meiosis to form gametes

Males:

• primordial germ cell (2n)
• spermatogonium (2n)
• primary spermatocyte (2n) (next: meiotic division to form=>)
• secondary spermatocyte (1n) (next: meiotic division to form=>)
• spermatids (1n)
• mature sperm (1n)

Females:

• primordial germ cell (2n)
• oogonium (2n)
• primary oocyte (2n) => next is 1st meiotic division
• secondary oocyte + 1st polar body (1n) => next is 2nd meiotic division
• ovum + 2nd polar body (1n)