Reproduction and defecation

In mammals and birds the external reproductive organs and waste removal organs see to be the same. Is this always the case with other animals such as insects etc… ? Are there any good reasons for it?

The cloaca, which is the common opening of the urinary, excretory, and reproductive systems, is present in birds as well as in non-avian reptiles (and thus presumably dinosaurs), amphibians, and monotremes (e.g., duck-billed platypus). To answer your first question, yes, this condition does seem to be universal for those groups mentioned above.

To answer your second question, evolutionary history is as good a reason as I can think of. The cloacal system has worked well enough for >350 million years (in the case of amphibians).

Reproduction and defecation - Biology

a School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, MRDC 1308, Atlanta, GA 30332-0405, USA
E-mail: [email protected]
Tel: +1 (404) 894-0573

b School of Biology, Georgia Institute of Technology, Atlanta, GA 30332, USA

c Division of Gastrointestinal Surgery, University of Alabama at Birmingham, Birmingham, AL 35294, USA


Animals discharge feces within a range of sizes and shapes. Such variation has long been used to track animals as well as to diagnose illnesses in both humans and animals. However, the physics by which feces are discharged remain poorly understood. In this combined experimental and theoretical study, we investigate the defecation of mammals from cats to elephants using the dimensions of large intestines and feces, videography at Zoo Atlanta, cone-on-plate rheological measurements of feces and mucus, and a mathematical model of defecation. The diameter of feces is comparable to that of the rectum, but the length is double that of the rectum, indicating that not only the rectum but also the colon is a storage facility for feces. Despite the length of rectum ranging from 4 to 40 cm, mammals from cats to elephants defecate within a nearly constant duration of 12 ± 7 seconds (N = 23). We rationalize this surprising trend by our mathematical model, which shows that feces slide along the large intestine by a layer of mucus, similar to a sled sliding down a chute. Larger animals have not only more feces but also thicker mucus layers, which facilitate their ejection. Our model accounts for the shorter and longer defecation times associated with diarrhea and constipation, respectively. This study may support clinicians use of non-invasive procedures such as defecation time in the diagnoses of ailments of the digestive system.

How Earth's oddest mammal got to be so bizarre

Credit: Unsplash/CC0 Public Domain

Often considered the world's oddest mammal, Australia's beaver-like, duck-billed platypus exhibits an array of bizarre characteristics: it lays eggs instead of giving birth to live babies, sweats milk, has venomous spurs and is even equipped with 10 sex chromosomes. Now, an international team of researchers led by University of Copenhagen has conducted a unique mapping of the platypus genome and found answers regarding the origins of a few of its stranger features.

It lays eggs, but nurses, it is toothless, has a venomous spur, has webbed feet, fur that glows and has 10 sex chromosomes. Ever since Europeans discovered the platypus in Australia during the late 1700's, the quirky, duck-billed, semi-aquatic creature has baffled scientific researchers.

Modern day researchers are still trying to understand how the platypus—often considered to be the world's oddest mammal—got to be so unique. Their understandings have now advanced, to a great degree. For the first time, an international team of researchers, led by University of Copenhagen biologists, has mapped a complete platypus genome. The study is published in the scientific journal, Nature.

"The complete genome has provided us with the answers to how a few of the platypus' bizarre features emerged. At the same time, decoding the genome for platypus is important for improving our understanding of how other mammals evolved—including us humans. It holds the key as to why we and other eutheria mammals evolved to become animals that give birth to live young instead of egg-laying animals," explains Professor Guojie Zhang of the Department of Biology.

The platypus belongs to an ancient group of mammals—monotremes—which existed millions of years prior to the emergence of any modern-day mammal.

"Indeed, the platypus belongs to the Mammalia class. But genetically, it is a mixture of mammals, birds and reptiles. It has preserved many of its ancestors' original features—which probably contribute to its success in adapting to the environment they live in," says Professor Zhang.

Lays eggs, sweats milk and has no teeth

One of the platypus' most unusual characteristics is that, while it lays eggs, it also has mammary glands used to feed its babies, not through nipples, but by milk—which is sweat from its body.

During our own evolution, we humans lost all three so-called vitellogenin genes, each of which is important for the production of egg yolks. Chickens on the other hand, continue to have all three. The study demonstrates that platypuses still carry one of these three vitellogenin genes, despite having lost the other two roughly 130 million years ago. The platypus continues to lay eggs by virtue of this one remaining gene. This is probably because it is not as dependent on creating yolk proteins as birds and reptiles are, as platypuses produce milk for their young.

In all other mammals, vitellogenin genes have been replaced with casein genes, which are responsible for our ability to produce casein protein, a major component in mammalian milk. The new research demonstrates that the platypus carries casein genes as well, and that the composition of their milk is thereby quite similar to that of cows, humans and other mammals.

"It informs us that milk production in all extant mammal species has been developed through the same set of genes derived from a common ancestor which lived more than 170 million years ago—alongside the early dinosaurs in the Jurassic period," says Guojie Zhang.

Another trait that makes the platypus so unique is that, unlike the vast majority of mammals, it is toothless. Although this monotremes' nearest ancestors were toothed, the modern platypus is equipped with two horn plates that are used to mash food. The study reveals that the platypus lost its teeth roughly 120 million years ago, when four of the eight genes responsible for tooth development disappeared.

Only animal with 10 sex chromosomes

Yet another platypus oddity investigated by the researchers was how their sex is determined. Both humans and every other mammal on Earth have two sex chromosomes that determine sex—the X and Y chromosome system in which XX is female and XY is male. The monotremes, however, including our duck-billed friends from Down Under, have 10 sex chromosomes, with five Y and five X chromosomes.

Thanks to the near-complete chromosomal level genomes, researchers can now suggest that these 10 sex chromosomes in the ancestors of the monotremes were organized in a ring form which was later broken away into many small pieces of X and Y chromosomes. At the same time, the genome mapping reveals that the majority of monotreme sex chromosomes have more in common with chickens than with humans. But what it shows, is an evolutionary link between mammals and birds.

  • The platypus is endemic to eastern Australia and Tasmania. It is a protected species and classified by the IUCN as near-threatened.
  • Among the reasons why platypuses are considered mammals: they have mammary glands, grow hair and have three bones in their middle ears. Each trait helps to define a mammal.
  • The platypus belongs to the mammalian order monotreme, so named because monotremes use a singular opening for urination, defecation and sexual reproduction.
  • The animal is an excellent swimmer and spends much of its time hunting for insects and shellfish in rivers.
  • Its distinctive beak is filled with electrical sensors which are used to locate prey in muddy river beds.
  • The male platypus has a venomous spur behind each of its hind legs. The venom is poisonous enough to kill a dog and is deployed when males fight for territory.
  • Another 2020 study demonstrated that platypus fur is fluorescent. The animal's brown fur reflects a blue-green color when placed under UV light.

Paula Spaeth Anich et al. Biofluorescence in the platypus (Ornithorhynchus anatinus), Mammalia (2020). DOI: 10.1515/mammalia-2020-0027

Methods for Studying Mite Reproduction

There are two methods for studying mite reproduction. One method is simply to survey, uncapping worker or drone cells in colonies and determining the percentage of mites that reproduced (fertility), or the number of offspring (fecundity) of mites. This method gives information about what is happening under natural conditions, but the information one gets is limited because nothing is controlled or manipulated. Another method is to perform manipulations, either on the mites or on the host, then artificially introduce mites into the cells and wait 9-10 days to determine fertility and fecundity. The frames can be reintroduced into a colony (which risks removal by bees due to hygienic behavior), or incubated in a laboratory. The basic steps for this process are as follows. 1). Harvest mites either from brood cells or from phoretic hosts in a colony with a high number of mites. We now routinely harvest mites using the sugar dusting method,, and then clean the sugar off them using a moistened brush. 2). Obtain brood cells that are recently capped (within 6 hours). This should be from a colony with no mites, so that you do not have natural invasion into the cells that you are trying to introduce mites to– if you have two mites in one cell, you do not know which one is the introduced one. Mites will not reproduce if introduced into cells that have been capped for more than 14 hours. Ideally, the cells should be capped within the last six hours. Scientists often use a piece of transparency to map the brood marking those that are being capped (with holes on the cap), waiting for six hours, coming back and marking again. Those cells that had a hole the first time, but were totally capped after, are the cells that you need. Make sure to mark the two holes (from fixing the transparency on the frame) on the wooden frame with Sharpies also, because bees may seal the small holes with wax, and you lose the reference. 3). Open the cell slightly using a fine scalpel, an insect pin, or a pair of fine forceps, and introduce a mite carefully into the small slit using a horse hair or a fine brush. 4). Push the wax capping back, and seal it with melted beeswax with a brush. 5). Keep the frame upright at all times, and the relative humidity at 50%, and at a temperature of 32-35 °C. 6). Check the frame daily for signs of wax moth larvae, because they can destroy the data do not put the frame flat on a surface, but keep it upright during this process. 7). Finally, on day nine (mite transfer day designated as day one), one can uncap the cells and count and record how many males, daughter mites (mature, deutonymphs and protonymphs) are there.


Understanding the relationship between the environmental conditions and life-history traits (such as growth, reproduction, and size at specific life stages) is important for understanding the population dynamics of a species and for constructing adaptable, relevant, and efficient conservation measures. For the endangered loggerhead turtle, characterizing effects of environmental conditions on the life-history traits is complicated by this species’ longevity, global distribution, and migratory way of life. Two significant environmental factors – temperature and available food – often account for most of observed intra-population variability in growth and reproduction rates, suggesting that those two factors determine the biological responses of an individual. Adopting this hypothesis, we simulate a range of the two environmental factors to quantify effects of changes in temperature and food availability on an individual's physiology (energy investment into processes such as growth, maturation, and reproduction) and the resulting life-history traits. To represent an individual, we use a previously developed mechanistic dynamic energy budget (DEB) model for loggerhead turtles. DEB models rely on one of the empirically best validated general ecological theories, which captures rules of energy acquisition and utilization. We found that the ultimate size (length and mass) is primarily affected by food availability, whereas growth and maturation are primarily affected by temperature whilst also showing positive correlation with available food. Reproduction increases with both food availability and temperature because food availability determines energy investment into egg production, and temperature affects the rate of related processes (such as vitellogenesis). Length at puberty varies between simulated scenarios by only a small proportion, suggesting that inter-individual variability plays a larger role for length at puberty than the environmental factors do.

Changes in Kit Fox Defecation Patterns During the Reproductive Season: Implications for Noninvasive Surveys

Abstract: Noninvasive survey methods based on analyzing DNA extracted from feces can be useful for carnivores that are difficult to study by other methods. Changes in fecal deposition patterns associated with reproduction in kit foxes (Vulpes macrotis) might affect results of such surveys. We used a trained dog to collect fresh scats on 2-km transects in the home ranges of 11 radiocollared female kit foxes in January, February, and March 2008 and determined sex of the individual that deposited the scats by amplifying the zinc finger protein gene. Female foxes give birth in mid-February to mid-March. We found a similar number of scats each month. In January, the sex ratio of the scats was not different from the expected 1:1. However, in February there were almost 2 male scats for every female scat and in March there were >8 male scats for every female scat. Comparing March to January, there were more male scats on all 11 transects and fewer female scats on 10 of 11 transects. Around the time pups are born, both sexes appear to show changes in fecal deposition patterns that make it easier to find male scats and harder to find female scats. Effects of these changes on survey results will vary depending on the purpose and design of the survey. Surveys to determine distribution and relative abundance would probably not be negatively affected by these changes. However, if surveys to estimate abundance are conducted during the reproductive season, they could result in an underestimate of population size unless the increased heterogeneity in scat detectability is taken into account.

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In this randomized trial, we compared functional outcomes following conservative colorectal surgery and segmental resection in deep endometriosis responsible for large infiltrations of the rectum. Although previous case-series and comparative observational studies suggested better functional outcomes following conservative surgery, our present trial does not show a statistically significant superiority of conservative surgery for mid-term functional digestive and urinary outcomes in this specific population of women with large involvement of the rectum.

Our study presents some limitations. The presumption of a 40% difference favourable to conservative surgery in terms of postoperative functional outcomes resulted in a lack of power to demonstrate the difference for the primary endpoint. The differences between the frequencies of functional symptoms composing the primary endpoint, as well as the values of GIQLI, KESS and SF36 scores in the two arms suggest that the functional outcomes of the two surgical approaches are close. As regards immediate complications, we found a higher risk of rectal stenosis after segmental resection requiring additional endoscopic or surgical procedures.

The inclusion of only large infiltrations of the rectum does not allow the extrapolation of conclusions to small nodules of <20 mm in length. However, we chose to include only large nodules due to the presumption that many surgeons would consider segmental resection to be an overtreatment in small rectal nodules.

There was an over-representation of patients enroled in the first centre (Rouen) due to the presence of the primary investigator and author of the protocol (H.R.). Despite harmonization meetings and exchanges between investigators, patient enrolment in the two associated centres was still inferior to that of the primary centre. This unbalanced enrolment of patients may raise questions about the external validation of the study. However, the homogeneity of results between the three centres could not be tested, because of the lack of statistical power and allocation of the five patients enroled in Paris and Lille to the same arm. As all surgeons were experienced in the management of rectal endometriosis, it is less likely that unbalanced enrolment of patients significantly impacted the outcomes.

The unblinded design of the trial was specifically required by the ethics committee. No patient had an a priori preference for one or other procedure, thus it was less likely that their answers were impacted by their allocation to either of the two arms. It was unlikely that surgeons influenced patients’ answers to the questionnaires or the primary endpoint.

Our trial also has several strengths. The allocation was randomized, which allowed comparison between two arms with similar characteristics, which were managed by only experienced gynaecologic surgeons and general surgeons. The patients were carefully followed-up and assessed, allowing for accurate results. Only two conversions were observed in the conservative surgery arm, meaning that 96.7% of patients enroled in the trial received the allocated procedure. Four different conservative procedures were employed to treat patients allocated to the conservative surgery arm, however, we estimated that they would each have a comparable impact on functional outcomes, because all four procedures allowed for systematic preservation of the mesorectum, with only limited variations of the length of rectum and the volume of rectal reservoir. Last but not least, the trial focussed on a question of major interest in the dynamic topic of the management of deep endometriosis.

Exhaustive assessment of digestive function using standardized questionnaires showed that complete removal of large deep endometriosis infiltrating the rectum does not guarantee relief from digestive complaints ( Kupelian and Cutner, 2016 Riiskjaer et al., 2016). We had presumed that on average half of all patients managed by segmental resection would report significant abnormal postoperative bowel function, and we were not mistaken. Conversely, our hypothesis that conservative surgery would result in much better functional outcomes was not confirmed. Our presumption was based on a small number of retrospective case-series which reported data on postoperative functional outcomes. However, these retrospective studies may have compared patients with more severe disease managed by colorectal resection and patients with smaller digestive nodules managed by shaving. This unbalanced distribution may have pointed to better postoperative outcomes in patients managed conservatively.

Removal of deep rectal nodules by shaving or disc excision does preserve the mesorectum, rectal vascularization and nerves, as the procedure exclusively concerns the anterior rectal wall and does not modify the overall length of the rectum. However, this did not have a major positive impact on postoperative rectal function, when compared to colorectal resection. Several explanations might be considered. Deep endometriosis infiltrating the rectum may also involve uterosacral ligaments, vagina, parametrium, inferior hypogastric plexus and splanchnic nerves. Complete resection of large endometriosis lesions may induce postoperative dysfunction of vegetative nerves ( Possover, 2011 Bonneau et al., 2013 Roman et al., 2013b Darwish and Roman, 2017 de Resende et al., 2017). Despite the employment of nerve-sparing techniques ( Ceccaroni et al., 2012), it is obvious that inferior hypogastric plexus and splanchnic nerves may be injured by either the disease or the surgeon, resulting in various concerns with bowel and bladder function ( Darwish and Roman, 2017). Furthermore, recent studies have shown that patients with colorectal endometriosis may preoperatively present with rectal or bladder dysfunction ( Mabrouk et al., 2012), i.e. anal and urethral sphincter hypertonia, and these troubles may be irreversible and not restored by removal of nodules.

The rectum is not the unique localization of deep endometriosis. Hence, the majority of patients had associated vaginal resection, some of them with hysterectomy. Some patients had separate resection of the sigmoid, left or transverse colon, caecum or bladder, along with surgery of the rectum (Table II). Although these additional procedures, sometimes in multiple sites, could have impacted functional outcomes, they could not be cancelled or postponed. However, as the study was randomized no difference was expected between the two arms with respect to the number of sites involved. In addition, the analysis was carried out according to the intention to treat principle, thus multiple procedures were not expected to impact the comparison between the two arms.

Previous studies have revealed a higher risk of rectovaginal fistula and leakage in women managed by colorectal resection when compared to those receiving shaving ( Roman et al., 2017b). However, our study was not powered for this relatively rare outcome, which varied from 3 to 12% depending on the characteristics of patients enroled in several series of patients managed for bowel endometriosis. Conversely, bowel stenosis was more frequent in patients enroled in the segmental resection arm, as it is more likely to occur after circular colorectal anastomosis ( Maytham et al., 2010) than after semicircular disc excision or shaving.

Although the rate of postoperative complications may appear high, our trial only included women with low colorectal localizations and frequent association of vaginal infiltrations. Among patients with digestive tract endometriosis, those presenting with infiltration of the rectum are probably exposed to a higher risk of postoperative complications, as well as postoperative digestive and urinary dysfunction. The rate of stenosis of colorectal anastomosis was unexpectedly high however, this complication may be overlooked in patients in whom postoperative constipation was either not taken into account or explored. Other authors have reported high rates of bowel stenosis after surgery for colorectal endometriosis, which suggests that this complication could be linked to the inflammatory status of the pelvis ( Maytham et al., 2010). As regards dysuria, we recorded this symptom both before and after surgery. Although nine patients (15%) required intermittent self-catheterization after surgery, only one of them had to continue over 24 postoperative months, suggesting that immediate postoperative bladder atony may progressively improve ( Dousset et al., 2010).

Cumulative pregnancy rates at 24 months post surgery were comparable between the two arms and with data reported in the literature. Furthermore, two-thirds of postoperative conceptions were spontaneous. Consequently, our results suggest that surgery for colorectal endometriosis may be safely offered to young women with severe endometriosis and pregnancy intention.

Our present study did not reveal any endometriosis recurrence during the 24 months following the surgery, however, it was not powered for this outcome, which requires more than 2 years of follow-up. An ancillary study on the recurrence rate of conservative versus radical rectal surgery with postoperative follow-up extended to 10 years is already ongoing. This ancillary study has been approved by the local Internal Review Board.

In conclusion, we were unable to demonstrate that conservative surgery for the management of deep rectal endometriosis improves digestive and urinary functional outcomes, when compared to radical colorectal resection. However, colorectal resection is responsible for a higher rate of bowel stenosis requiring complementary procedures under general anaesthesia. Patients should be informed that there is a risk of abnormal bowel movements in 40% of cases regardless of surgical management. The findings of our trial may be the support for sample size estimations for further randomized trials and may be included in future meta-analyses focusing on functional outcomes after colorectal surgery for endometriosis.

Chapter 22. Osmotic Regulation and Excretion

Figure 22.1. Just as humans recycle what we can and dump the remains into landfills, our bodies use and recycle what they can and excrete the remaining waste products. Our bodies’ complex systems have developed ways to treat waste and maintain a balanced internal environment. (credit: modification of work by Redwin Law)


The daily intake recommendation for human water consumption is eight to ten glasses of water. In order to achieve a healthy balance, the human body should excrete the eight to ten glasses of water every day. This occurs via the processes of urination, defecation, sweating and, to a small extent, respiration. The organs and tissues of the human body are soaked in fluids that are maintained at constant temperature, pH, and solute concentration, all crucial elements of homeostasis. The solutes in body fluids are mainly mineral salts and sugars, and osmotic regulation is the process by which the mineral salts and water are kept in balance. Osmotic homeostasis is maintained despite the influence of external factors like temperature, diet, and weather conditions.

14.5 Mammal Sex

Mammals fall into three reproductive categories: monotremes, marsupials, and placental mammals. We will focus on one type of placental mammal (humans) for most of the remainder of this chapter, but the reproduction of monotremes and marsupials is interesting and worthy of mention.

Monotremes are clearly mammals because they have fur and they nurse their young with milk. However, monotremes are distinct from other mammals because they lay eggs. The only extant (or, not extinct) monotremes are platypuses and echidnas. Similar to that of other mammals, monotreme fertilization is internal. However, the genitals of monotremes differ from those of other mammals in that the females have a cloaca for urination, defecation, and copulation. Echidna males have a penis with four heads, two of which are active at a time. The males do not urinate from the penis, instead they have a cloaca similar to that of the female. Platypuses have two-headed penises, however the left penis is more developed. Female platypuses have two ovaries, but only the left one functions. In echidnas the eggs are incubated in a specialized pouch, while platypuses curl up around the eggs to incubate them. And like other mammals, all monotreme babies nurse to obtain nutrients from the mother, but they do so by lapping at specialized pores on the mother that secrete milk.

Figure 14.5 Platypuses

Marsupials are mammals that include opossum, kangaroos, koalas, wombats, and wallabies. Marsupials have internal fertilization that involves a bifurcated (split) penisin males, and two vaginas and two uteri in females. These animals give birth to very undeveloped young. The newborn animals make their way to a pouch in the mother. In the pouch they nurse for several weeks or months as they develop further, and become less dependent on the mother.

Placental mammals (including humans) have internal gestation, in which the offspring develops further than in marsupials, and nutrient exchange between mother and fetus relies on a well-developed placenta. The placenta is an organ formed during embryonic development. The placenta allows for nutrient and waste exchange between the mother and the developing offspring. While marsupial mammals also have placentas, the structure in the placental mammals is much larger to allow these animals to develop further internally. Like monotremes and marsupials, after birth, infant placental mammals obtain nourishment by nursing.

Effects of Aging on the Female Reproductive System

Around menopause, changes in the genital organs occur rapidly. Menstrual cycles stop, and the ovaries stop producing estrogen . After menopause, the tissues of the labia minora (which surround the opening of the vagina and urethra), clitoris, vagina, and urethra thin (atrophy). This thinning can result in chronic irritation, dryness, and a discharge from the vagina. Vaginal infections are more likely to develop. Also after menopause, the uterus, fallopian tubes, and ovaries become smaller.

With aging, there is a decrease in the amount of muscle and connective tissue, including that in muscles, ligaments, and other tissues that support the bladder, uterus, vagina, and rectum. As a result, the affected organs may sag or drop down (prolapse), sometimes causing a feeling of pelvic pressure or fullness, difficulty urinating, loss of control of urination or bowel movements (incontinence), or pain during sexual intercourse. Women who have had many children are more likely to have such problems.

Did You Know.

Some women enjoy sexual intercourse more after menopause.

Because there is less estrogen to stimulate milk ducts, the breasts decrease in size. The connective tissue that supports the breasts also decreases, leading to sagging and contributing to changes in shape. Fibrous tissue in the breasts is replaced with fat, making the breasts less firm.

For most women, age-related changes in reproductive organs do not interfere with sexual activity or sexual pleasure after menopause. Some women enjoy sexual activity more after menopause, possibly because they are no longer concerned about becoming pregnant. In addition, after menopause, the ovaries and adrenal glands continue to produce male sex hormones. Male sex hormones help maintain the sex drive, slow the loss of muscle tissue, and contribute to an overall sense of well-being.

Watch the video: How Your Urinary System Works? - The Dr. Binocs Show. Best Learning Videos For Kids. Peekaboo Kidz (January 2022).