Information

16.9: Reproductive System - Biology


Learning Objectives

  • Identify the structure and function of the reproductive system

In simple terms, reproduction is the process by which organisms create descendants. This miracle is a characteristic that all living things have in common and sets them apart from nonliving things. But even though the reproductive system is essential to keeping a species alive, it is not essential to keeping an individual alive.

In human reproduction, two kinds of sex cells or gametes are involved. Sperm, the male gamete, and a secondary oocyte (along with first polar body and corona radiata), the female gamete, must meet in the female reproductive system to create a new individual. For reproduction to occur, both the female and male reproductive systems are essential. It is a common misnomer to refer to a woman’s gametic cell as an egg or ovum, but this is impossible. A secondary oocyte must be fertilized by the male gamete before it becomes an “ovum” or “egg.”

While both the female and male reproductive systems are involved with producing, nourishing and transporting either the oocyte or sperm, they are different in shape and structure. The male has reproductive organs, or genitals, that are both inside and outside the pelvis, while the female has reproductive organs entirely within the pelvis.

The Male Reproductive System

The male reproductive system consists of the testes and a series of ducts and glands. Sperm are produced in the testes and are transported through the reproductive ducts. These ducts include the epididymis, vas deferens, ejaculatory duct and urethra. The reproductive glands produce secretions that become part of semen, the fluid that is ejaculated from the urethra. These glands include the seminal vesicles, prostate gland, and bulbourethral glands.

Table 1 describes the major components of the male reproductive system.

Table 1. Components of the Male Reproductive System
StructureLocation & DescriptionFunction
Bulbourethral glands (2)Pea sized organs posterior to the prostate on either side of the urethra.Secretion of gelatinous seminal fluid called pre-ejaculate. This fluid helps to lubricate the urethra for spermatozoa to pass through, and to help flush out any residual urine or foreign matter. (< 1% of semen)
EpididymisTightly coiled duct lying just outside each testis connecting efferent ducts to vas deferens.Storage and maturation of sperm.
PenisThree columns of erectile tissue: two corpora cavernosa and one corpus spongiosum. Urethra passes through penis.Male reproductive organ and also male organ of urination.
Prostate glandSurrounds the urethra just below the urinary bladder and can be felt during a rectal exam.Stores and secretes a clear, slightly alkaline fluid constituting up to one-third of the volume of semen. Raise vaginal pH.(25-30% of semen)
Seminal vesicles (2)Convoluted structure attached to vas deferens near the base of the urinary bladder.About 65-75% of the seminal fluid in humans originates from the seminal vesicles. Contain proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins. High fructose concentrations provide nutrient energy for the spermatozoa as they travel through the female reproductive system.
TestesInside scrotum, outside of body.Gonads that produce sperm and male sex hormones.Production of testosterone by cells of Leydig in the testicles.
UrethraConnects bladder to outside body, about 8 inches long.Tubular structure that receives urine from bladder and carries it to outside of the body. Also passage for sperm.
Vas deferensMuscular tubes connecting the left and right epididymis to the ejaculatory ducts to move sperm. Each tube is about 30 cm long.During ejaculation the smooth muscle in the vas deferens wall contracts, propelling sperm forward. Sperm are transferred from the vas deferens into the urethra, collecting fluids from accessory sex glands en route

The Female Reproductive System

Reproduction can be defined as the process by which an organism continues its species. As noted earlier, in the human reproductive process, two kinds of gametes are involved: the male gamete (sperm) and the female gamete (egg or ovum). These two gametes meet within the female’s uterine tubes located one on each side of the upper pelvic cavity, and begin to create a new individual. The female needs a male to fertilize her egg; she then carries offspring through pregnancy and childbirth.

Female Reproductive System

  • Produces eggs (ova)
  • Secretes sex hormones
  • Receives the male spermatazoa during
  • Protects and nourishes the fertilized egg until it is fully developed
  • Delivers fetus through birth canal
  • Provides nourishment to the baby through milk secreted by mammary glands in the breast

The major components of the female reproductive system are shown in Table 2.

Table 2. Components of the Male Reproductive System
StructureLocation & DescriptionFunction
Ovaries (2)Ovoid structures on either side of the uterus in the pelvic cavityPrimary sex organs of female; contain ovarian follicles that contain the oocytes. Oocytes are released during the ovulation stage of the menstrual cycle.
Fallopian Tubes (2)Extend from lateral ares of uterus to near the ovariesTransport oocyte to uterus after fertilization and are the sites where fertilization by sperm actually occurs
UterusPear shaped structure divided into the fundus and the cervixSite of fetal development during gestation
VaginaLocated between rectum and urethra; smooth muscle lined with an epithelial mucous membranePath for menstrual blood and tissue to leave the body, as well as the fetus during childbirth. Produces a variety of secretions for lubrication and receives secretions that facilitate fertilization.
VulvaExternally located: labia majora and minora, mons pubis, clithoris, vestibule, greater and lesser vestibular glandsSexual function: heavily innervated and provide pleasure when properly stimulated.
PerineumArea between vagina and anusHelps form the muscular floor of pelvis; can be torn during vaginal childbirth
Mammary glandsSuperficial to pectoral musclesProvide nourishment to the baby through milk secretions

Comparing Male and Female Reproductive Systems

Similarities

The reproductive systems of the male and female have some basic similarities and some specialized differences. They are the same in that most of the reproductive organs of both sexes develop from similar embryonic tissue, meaning they are homologous. Both systems have gonads that produce (sperm and egg or ovum) and sex organs. And both systems experience maturation of their reproductive organs, which become functional during puberty as a result of the gonads secreting sex hormones.

Table 3.
IndifferentMaleFemale
GonadTestisOvary
Müllerian ductAppendix testisFallopian tubes
Müllerian ductProstatic utricleUterus, proximal vagina
Wolffian ductRete testisRete ovarii
Mesonephric tubulesEfferent ductsEpoophoron
Wolffian ductEpididymisGartner’s duct
Wolffian ductVas deferens
Wolffian ductSeminal vesicle
Wolffian ductProstateSkene’s glands
Urogenital sinusBladder, urethraBladder, urethra, distal vagina
Urogenital sinusBulbourethral glandBartholin’s gland
Genital swellingScrotumLabia majora
Urogenital foldsDistal urethraLabia minora
Genital tuberclePenisClitoris
PrepuceForeskinClitoral hood
Bulb of penisVestibular bulbs
Glans penisClitoral glans
Crus of penisClitoral crura

Differences

The differences between the female and male reproductive systems are based on the functions of each individual’s role in the reproduction cycle. A male who is healthy, and sexually mature, continuously produces sperm. The development of women’s “eggs” are arrested during fetal development. This means she is born with a predetermined number of oocytes and cannot produce new ones.

At about 5 months gestation, the ovaries contain approximately six to seven million oogonia, which initiate meiosis. The oogonia produce primary oocytes that are arrested in prophase I of meiosis from the time of birth until puberty. After puberty, during each menstrual cycle, one or several oocytes resume meiosis and undergo their first meiotic division during ovulation. This results in the production of a secondary oocyte and one polar body. The meiotic division is arrested in metaphase II. Fertilization triggers completion of the second meiotic division and the result is one ovum and an additional polar body.

The ovaries of a newborn baby girl contain about one million oocytes. This number declines to 400,000 to 500,000 by the time puberty is reached. On average, 500-1000 oocytes are ovulated during a woman’s reproductive lifetime. When a young woman reaches puberty around age 10 to 13, a promary oocyte is discharged from one of the ovaries every 28 days. This continues until the woman reaches menopause, usually around the age of 50 years. Occytes are present at birth, and age as a woman ages.

Learning Objectives

Watch the first three videos in this playlist for a review of the reproductive system:

A YouTube element has been excluded from this version of the text. You can view it online here: pb.libretexts.org/fob1/?p=478


Lifestyle and fertility: the influence of stress and quality of life on male fertility

Male infertility is a widespread condition among couples. In about 50% of cases, couple infertility is attributable to the male partner, mainly due to a failure in spermatogenesis. In recent times, the crucial role that modifiable lifestyle factors play in the development of infertility have generated a growing interest in this field of study, i.e. aging, psychological stress, nutrition, physical activity, caffeine, high scrotal temperature, hot water, mobile telephone use. Several studies have investigated associations between semen quality and the presence of lifestyle stressors i.e. occupational, life events (war, earthquake, etc.) or couple infertility overall, these studies provide evidence that semen quality is impaired by psychological stress. In this review, we will discuss the impact of quality of life (modifiable lifestyle factors) and psychological stress on male fertility. In addition, the role that increased scrotal temperature along with inappropriate nutritional and physical exercise attitudes exert on male fertility will be presented.

Conclusion

The decline of male fertility, particularly associated with advancing age, incorrect lifestyles and environmental factors plays an important role on natality, and its consequences on the future on human population makes this an important public health issue in this century. Thus, modification of lifestyle through a structured program of educational, environmental, nutritional/physical exercise and psychological support, combined with the use of nutraceutical antioxidants can prevent infertility and therefore, may help couples to obtain better quality of life and improved possibility to conceive spontaneously or optimize their chances of conception.


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Tuesday, March 15

8:00 AM&ndash9:20 AM

Daily Plenary Session&mdashInflammation and Neurodegenerative Disease


    Lecturer: Stephen Skaper, University of Padua, Padua, Italy.

    Lecturer: Alan I. Faden, University of Maryland School of Medicine, Baltimore, MD.

9:30 AM&ndash12:15 PM

Symposium Sessions

  • Drug-Induced Taste Change in Clinical Practice and Preclinical Safety Evaluation
  • Genotypic and Intrinsic Risk Factors That Increase Susceptibility to Inhaled Pollutants
  • Systems Understanding of the Impact of the Nrf2 Pathway on Chemical Toxicity and Cell Fate &diams
  • Unknown, Unknowns: Exploring the Unidentified Fraction of Complex Mixtures

Workshop Sessions

  • Bioactivity-Based Margin of Exposure Safety Assessment: The Next Stop along the Road to 21st Century Safety Assessments &spades
  • Maternal Exposure to Nanoparticles&mdashHow Does It Affect the Fetus? Status, Mechanisms, and Future Directions ♞
  • Multi-Omics in Predictive Toxicology: Development and Application in Environmental Monitoring Programs &diams
  • Scientific and Regulatory Advances in Safety Evaluation of Heavy Metals in Food &spades &clubs

Platform Sessions

9:30 AM&ndash12:45 PM

Poster Sessions

  • Alternative Models: Fish, Worms, and More &diams &spades
  • Carcinogenesis I
  • Carcinogenesis II
  • Chemical and Biological Weapons &hearts
  • Developmental Basis of Adult Disease ♞
  • Endocrine Toxiciology
  • Inflammation in Disease
  • Inflammation: Methods and Mechanisms
  • Liver&mdashMechanisms &diams
  • Liver&mdashModels
  • Risk Assessment 1
  • Stem Cell Biology and Toxicology
  • Toxic Inhalants Research

12:30 PM&ndash1:20 PM

Leading Edge in Basic Science Award Lecture

1:15 PM&ndash4:30 PM

Poster Sessions

  • 3D Cell and Organ-on-a-Chip Models &diams &spades
  • Alternative Models for Ocular and Skin Toxicity
  • Biological Modeling
  • Clinical and Translational Toxicology
  • Food Safety/Nutrition 1 &hearts
  • Gene Regulation and Signal Transduction &diams
  • Medical Devices
  • Neurotoxicology&mdashDopaminergic Systems and Toxicants ♜
  • Neurotoxicology&mdashManganese Neurotoxicity ♜ &clubs
  • Neurotoxicology&mdashNeurodegenerative Diseases ♜
  • Neurotoxicology&mdashPesticide Neurotoxicity ♜
  • Non-Pharmaceutical Safety Assessment &spades
  • Oxidative Injury and Redox Biology &diams
  • Particulate Matter Toxicology
  • Receptors

2:00 PM&ndash4:45 PM

Symposium Sessions

  • New Mechanistic Insights into How the Immune System Drives Hepatic Adverse Drug Reactions
  • Reciprocal Synergism: New Insights into Thyroid Hormone Action in Brain Development and Neurodevelopmental Toxicity ♜ ♞
  • The Role of Gene SLC30A10 on Manganese Homeostasis and Functional Outcomes: Implications for Homeostasis and Neurotoxic ♜ &clubs
  • Using Multi- and Transgenerational Effects of Environmental Exposures in Diverse Animal Models for Assessment of Human Health Risks ♞

Workshop Sessions

  • Cannabis in the Courtroom ♜
  • Read-Across: Building Scientific Confidence in the Development and Evaluation of Read-Across for Regulatory Purposes Using Tox21 Approaches &diams &spades
  • Safety Assessment of Topically Exposed Cosmetic Ingredients: Lessons Learned &spades

Platform Sessions


Conclusions

We have presented comprehensive evidence supporting the hypothesis that individual selection among selfers and outcrossers can drive the transition from dioecy to androdioecy, or to effective monoecy, when there is limited outcrossing in novel environments. Experimental transitions to selfing were due to reproductive assurance, notwithstanding selection of standing genetic diversity, the existence of a cost of males, and the potential for density dependent selection among selfing or outcrossing demes (as we did not model it). Our experiments further suggest that adaptation of dioecious populations, to the environment where outcrossing was once limiting to them, may reduce the opportunity for reproductive assurance that selfers can provide and, as a consequence, the probability of successful transitions to selfing.

Our findings were obtained in highly contrived conditions. Can they help explain transitions to selfing within the Caenorhabditis clade, Out of the 38 Caenorhabditis species that have been discovered so far, three have probably evolved androdioecy from ancestors that had a dioecious reproduction system [64],[65],[91]. Extant Caenorhabditis species inhabit sparse and ephemeral habitats [92],[93], and a metapopulation structure with variable density dynamics is the norm [93],[94]. Instead of individual selection, transitions to androdioecy in natural Caenorhabditis may have resulted from a correlated response to density dependent selection among demes for dispersal to and/or colonization of novel habitats where outcrossing was not necessarily limited [36],[37],[39]. The lack of a cost of meiosis in Caenorhabditis, since hermaphrodites do not outcross each other, and the existence of a cost of males in outcrossing lineages would then make certain that the first selfing colonizers would outcompete outcrossers reaching the same habitat at a later time, see for example [22] for an empirical example.

Particularly in C. elegans, the assumed dispersal life history stage, the dauer, is a stage from which more males than hermaphrodites survive and reach reproductive maturity [58]. Adult males are also more vagile than adult hermaphrodites [95], and several evolution experiments have shown that they can be maintained at intermediate frequencies under a variety of novel environments [55],[58]-[63], some of which with varying density dynamics. These observations suggest that selection among demes for dispersal and/or colonization of novel habitats, not before experienced by the ancestral dioecious populations, would favour males over hermaphrodites and, as a correlated response, outcrossing over selfing. Although it remains to be shown whether, in general, dioecious males likewise survive the dauer stage better and are more vagile than dioecious females, but see [75], selection among demes is not necessary for the transition from dioecy to androdioecy in Caenorhabditis. It is sufficient to speculate that in some of the novel environments the ancestral dioecious populations were challenged with restricted outcrossing.

In plants, most of the known transitions from outcrossing to selfing occurred from self-incompatible hermaphrodites that were able to cross-fertilize each other [3],[6],[26]. In this situation, a mutant self-compatible hermaphrodite that provided reproductive assurance when pollination agents were a limiting factor, and could outcross with other hermaphrodites, should have been favoured over a female-sterile hermaphrodite (pollen-only) [17],[27],[68]. In these transitions it remains uncertain whether the cost of meiosis, cost of pollen production, selection among selfers and outcrossers or density dependent selection can explain them. Yet, it appears that successful transitions rely on the short-term selective advantage of selfing over outcrossing, thus presumably on individual selection and reproductive assurance [15],[19]-[21]. Since in a few model plants, sex determination mutants can be obtained, and emasculation assays readily done, it would be valuable to perform evolution experiments similar in design to ours to disentangle the relative role of all the relevant processes that can explain transitions to selfing see for example [96] for experimental evolution under different reproduction systems using Arabidopsis thaliana.

In a small number of plants and animals, known transitions from outcrossing to selfing were similar to those of Caenorhabditis, from dioecy to androdioecy [68],[97],[98]. In these rare species, empirical evidence on population density dynamics and on the genetics of sex determination is scarce but individual selection could have been important for transitions to selfing. In the particular case of animals, their populations inhabit apparently homogeneous (aquatic) environments and spawn in large numbers, both circumstances that would be conducive to a lesser role for density dependent selection among demes. Also in common with Caenorhabditis, the derived self-compatible hermaphrodites of these androdioecious animals are biased in their allocation of reproductive resources towards the female function, a condition that may reflect the limited mutational options that were available to the dioecious ancestor for the evolution of self-compatibility [97],[99],[100].

The frequency of transitions to selfing is ultimately a function of mutation rates and of the genetic architecture of sex determination. In the dioecious C. remanei, at least two mutational steps are required to turn a wild-type female into a self-compatible and fertile protandrous hermaphrodite: one to repress oogenesis and initiate spermatogenesis, and another one to stop spermatogenesis, resume oogenesis and allow fertilization [29],[30]. In addition, partially to complete recessive alleles at several loci may have determined autonomous selfing in the ancestral dioecious Caenorhabditis[31], a situation that likely would have reduced the probability of the establishment of hermaphrodites, especially if populations during transitions were small or highly structured [101]. In spite of the genetic architecture of selfing, however, as shown here, once these mutants escape genetic drift and became established in the resident population [70], their fate due to selection would be contingent upon whether the ancestral dioecious population was already adapted to the environment where outcrossing was once limiting to them. The opportunity for reproductive assurance may, therefore, be circumscribed to very short evolutionary periods, which, together with limited and probably complex mutational options determining self-compatibility, can help explain why transitions from dioecy to androdioecy are the rarest of transitions to selfing in nature.


Structure of the reproductive system and hectocotylus in males of lesser flying squid Todaropsis eblanae (Cephalopoda: Ommastrephidae)

This paper introduces new data on Todaropsis eblanae morphology, morphometry and functional aspects of the male reproductive system and hectocotylus. Spermatophores differ in specimens from the Atlantic Ocean (average length, 18.28 ± 1.45 mm, 15.63 ± 0.8% of mantle length weight, 2.0–12.0 mg) and the Indian Ocean (average length, 24.8 ± 2.85 mm, 16.9 ± 2.1% of mantle length weight, 35.0–39.6 mg) (t = 3.14 p < 0.01 for absolute sizes and t = 0.711 p > 001 for relative sizes). An additional important distinctive trait is the form of connection of the cement body with the ejaculatory tube. In recent years, T. eblanae has been regularly caught in the Barents Sea, meaning its range has extended to subarctic waters. The morphology and morphometry of the spermatophoric complex of organs did not vary in investigated parts of its range. Hectocotylus patterns and some important spermatophore traits distinguish Todaropsis from other Ommastrephidae.


Conclusion

In conclusion, our worldwide data analysis demonstrates increasing utilization of ART, SET, and of frozen-thawed embryos. Substantial differences in live birth rates exist among various regions of the world. Since ART practices affect different patient populations in varying ways, further research is needed to better define individual practices in different patient populations. Concomitantly, the profession should strive to achieve worldwide consensus as to what metric(s) define(s) outcome success in association with ART.


Gene Expression and Transcriptome Analysis

Transcriptome analysis experiments enable researchers to characterize transcriptional activity (coding and non-coding), focus on a subset of relevant target genes and transcripts, or profile thousands of genes at once to create a global picture of cell function. Gene expression analysis studies can provide a snapshot of actively expressed genes and transcripts under various conditions.

Next-generation sequencing (NGS) capabilities have shifted the scope of transcriptomics from the interrogation of a few genes at a time to the profiling of genome-wide gene expression levels in a single experiment. Find out how NGS-based RNA sequencing (RNA-Seq) compares to other common gene expression and transcript profiling methods, gene expression microarrays and qRT-PCR. Learn how to analyze gene expression and identify novel transcripts using RNA-Seq.

Benefits of Gene Expression Profiling with RNA-Seq

Explore the advantages of NGS for analysis of gene expression, gene regulation, and methylation.


Trends in Population Sex Ratios May be Explained by Changes in the Frequencies of Polymorphic Alleles of a Sex Ratio Gene

A test for heritability of the sex ratio in human genealogical data is reported here, with the finding that there is significant heritability of the parental sex ratio by male, but not female offspring. A population genetic model was used to examine the hypothesis that this is the result of an autosomal gene with polymorphic alleles, which affects the sex ratio of offspring through the male reproductive system. The model simulations show that an equilibrium sex ratio may be maintained by frequency dependent selection acting on the heritable variation provided by the gene. It is also shown that increased mortality of pre-reproductive males causes an increase in male births in following generations, which explains why increases in the sex ratio have been seen after wars, also why higher infant and juvenile mortality of males may be the cause of the male-bias typically seen in the human primary sex ratio. It is concluded that various trends seen in population sex ratios are the result of changes in the relative frequencies of the polymorphic alleles of the proposed gene. It is argued that this occurs by common inheritance and that parental resource expenditure per sex of offspring is not a factor in the heritability of sex ratio variation.

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Watch the video: Welcome to the reproductive system. Reproductive system physiology. NCLEX-RN. Khan Academy (January 2022).