Reproductive Physiology(medlearn) Flashcards
What are the two main functions of the Human Male Reproductive System
The human male reproductive system is (if compared to the female system) relatively simple. The two main functions are the provision of androgens (primarily testosterone) to initiate and sustain the necessary male phenotype, and the production of mature sperm.
Label the diagram
- Bladder 2.Pubic bone 3.Suspensory ligament of penis 4.Puboprostatic ligament 5.Perineal Membrane 6. External urethral sphincter 7. Penis(body)8.Corpus cavernosum 9.Glans Penis 10.Foreskin 11.Urethral opening 12. Scrotum 13. Testicles 14. Epididymis 15. Vas deferens 16. Anus 17. Cowpers gland 18. Prostate Gland 19.Ejaculatory Duct 20. Seminal Vesicle 21.Rectum 22. Sigmoid colon
Recall the details of the function of the testis
Contains seminiferous tubules (which produce sperm) and Leydig (interstitial) cells which produce testosterone (and some other androgens). Testosterone is released into the circulation, from where it can affect the whole body.
What is the function of the epididymis and describe the passage of sperm
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.
Describe the regulation of the male reproductive system
Figure 2.2 Summarises the main regulatory pathways within the adult human male reproductive system.
A complex interplay between hypothalamic, pituitary and gonadal factors is needed to control the normal production of human sperm.
In Figure 2.3 the processes needed for spermatogenesis are summarised, and include the change from diploid precursor cells to haploid gametes. The overall production of sperm from both testes is estimated to up to 200 million sperm per day.
Once the process of spermatogenesis starts (at puberty) it normally continues for the rest of adult life. The quality and quantity of sperm produced may decline with increasing age, but men are capable of fathering children at well over 70 years of age.
Describe the funtions of the key tissues of the female reproductive system
The ovary Parallel functions to the testes, in that they produces the gametes (oocytes) and the steroids needed for female reproductive function (progesterone and estrogens).
The Fallopian tube (oviduct) through which the oocyte reaches the uterus. Provides an appropriate environment to sustain either an oocyte or a conceptus (fertilised oocyte).
The uterus, in which the conceptus normally implants and is supported throughout pregnancy.
This schematic summarises the changes in follicular structure as they develop and increase in size, but also notes that follicles may not develop all the way to ovulation – atresia is common, as shown (Figure 2.5). The thecal cells of the developing follicles are responsible for the production of estrogens, and the granulosa-luteal cells produce estrogens and progesterone during the second half of the ovarian cycle.
Label the following image
Right Vertical:1.Uterine cavity 2.Body of the uterus 3.Internal Orifice 4.Endocervical Canal 5. Cervix 6. External orifice 7. Vagina
Left Vertical: 1. Fimbria 2. Hilus of ovary 3. Mesovarium 4. Ovary 5. Ovarian Ligament 6. Mesometrium 7. Endometrium 8. Myometrium 9. Mucosal folds
Horizontal: 1. Fundus of uterus 2. Uterine portion of the oviduct 3. Isthmus of the oviduct 4. Mesosalpinx 5. Ampulla of oviduct 6. Suspensory ligament
What is the problem with the frequency of the end-points for the ovarian and endometrial cycles
Both the ovarian and endometrial cycles have end-points that occur approximately once per month; this superficial similarity disguises some differences that need to be considered if the complexities of oocyte production are to be identified correctly.
GIve the details of the different durations of the human menstrual cycle
The human menstrual cycle lasts approximately 28 days, but this varies substantially between human females, and also in individuals. Most sources suggest a normal range between 21 – 35 days in adult females, but in younger teenagers (i.e shortly after menarche), the length may be up to 45 days. At the other end of the reproductive spectrum, when a woman is approaching the menopause, her menstrual cycle is likely to become irregular in length; shorter or longer, or perhaps skip a month or two before resuming.
Summarise the main events of the mentrual cycle
Summarise the regulation of hormones during the human menstrual cycle
Figure 2.7 Summarises the regulation of hormones during the human menstrual cycle, and the interactions between hypothalamus, pituitary and ovaries in this process. Note the change in regulation of the hypothalamic-pituitary axis, changing from negative feedback to positive feedback, to cause the LH surge and ovulation.
Explain how tissue structure changes during the menstrual cycle
Figure 2.8(image below)Shows the changes in tissue structures during the normal human menstrual cycle. Changes in endometrial thickness during the cycle are shown, as are the roles of estrogen (proliferative or follicular phase) and of progesterone in combination with estrogen (secretory or luteal phase). Note the terminology used: a focus on endometrial or uterine function will employ proliferative and secretory, as these describe endometrial function; for an ovarian emphasis, the terms would be follicular and luteal, as these summarise the state of the dominant ovarian follicle in the cycle.
Describe the hormonal changes during the human menstrual cycle
The key changes in the four main hormones are summarised, showing the time-frames of the changes. Note that the basal body temperature rises slightly (about 0.5°C) around the time of ovulation.
Give the details of what happens in folliculogenesis in the human ovary
Figure 2.10. Folliculogenesis in the human ovary. Note that the first meiotic division is completed during the formation of the Secondary follicle, linked to the LH surge. Meiosis II follows immediately after this, but pauses in metaphase II as shown.
Two important points need to be noted from this figure. Firstly, that the time taken for a primordial follicle to develop into a secondary (mature) oocyte is more than one month, so Figure 2.10 does NOT reflect ovarian function fully. This also applies to Figures 2.5 and 2.9, which imply a relatively rapid change from a primordial follicle to a ‘growing follicle’.
The reality is the human ovaries contain multiple follicles at all stages of development (stages 1-4 in Figure 2.10) at any time, with one dominant follicle entering the later stages to form a secondary (Graafian) follicle. The ovaries usually alternate the release of the follicle, so each ovary has approximately 56 days (2 Months) between the release of one secondary follicle, and the release of the next one. In addition, the human ovaries contain about 2 million primordial follicles at the time of birth, and only about 400 of them will be released at ovulation during a reproductive lifetime; 12 per year for 30-35 years on average.
The second point is that meiosis during human oogenesis is an intermittent process. Both the first meiotic division and the second meiotic division are paused during follicle development.
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.
Describe the numbers of follicles and sperms that females and males produce respectively
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.
Discuss the role of sex
Sexual Reproduction and Fertilisation
From an evolutionary perspective, the most important role of sex is to ensure that fertilisation of a mature oocyte by a mature sperm takes place, this being the necessary first step in continuing the human race.
Our understanding of these topics is now much more complex, with many more nuanced and important aspects, which will also be considered in this topic.
The term ‘sex’ and its related definitions is pertinent to three different aspects of relevance to sexual reproduction.
Sexual reproduction
Produces offspring that differ genetically from both parents.
This is the key definition for Chapter 2.4, and is the primary focus of the material.
Sexual intercourse
Required for sexual reproduction
Sexual activity
Sexual pleasure
Human bonding
Given that sexual intercourse is (normally) required for human reproduction, this is an important part of this topic. The ‘normally’ is included to acknowledge that during the last 30 years, the development of Assisted Reproduction or In Vitro Fertilisation, and linked technologies, there are complex topics which are linked to reproduction
Explain the changes that occur during an erection
Penis function
In addition to the complex pathways linked to reproduction outlined in Figure 2.11, it is clear that the regulation of penile erection is also partly under the control of the brain, via the spinal cord and efferent nervous system. This is not the complete picture, as tactile stimulus of the penis can activate the afferent system (pudendal nerve) as shown, involving a more direct interaction between the spinal cord and penis.
The changes during erection
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)
Explain how viagra works
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.
Explain the significance of the clitoris
The female equivalent of the penis is the clitoris
The clitoris, like the penis, increases in size as a result of an increased blood flow into the tissue
The mechanism is the same (i.e. release of NO)
Describe the process and main events of Fertilisation
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.
Give the details of the main events of fertilisation(work out difference with prvious card )
Fusion of the sperm with the egg is a complex process, requiring interaction with the zona pellucida so that the latter is digested by the enzymes released during sperm capacitation
The earliest changes in the oocyte following fertilisation are summarised in Figures 2.13 and 2.14. The cortical reaction is initiated, leading to hardening of the zona pellucida and the exclusion of other sperm. Note that the other sperm included in Figure 2.13, and the cumulus cells, will still be present at the stage shown in Figure 2.14, although they play no further role in the process.
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.
(in line with figure 2.15)Both pronuclei are now visible; note that by this stage duplication of the DNA in both pronuclei has been duplicated, making 2n chromosomes of maternal and of paternal origin. The next stage is development is a 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.
(in line with figure 2.16)Separation of the male (blue) and female (red) chromatids can be seen; each cell should receive one paternal copy and one maternal copy of each chromosome, so the 2 cells shown in (F) have an identical chromosomal complement.
