Modern Australian

You need more than just testes to make a penis

  • Written by Mark Green, Merck Serono Senior Lecturer in Reproductive Biology, University of Melbourne

In prenatal ultrasounds or at delivery, many new parents look between their baby’s legs: the presence of a penis is taken as a strong sign that it’s a boy.

For humans and other animals, development of a penis was thought to be driven by “male hormones” (androgens) produced entirely by the testes of the male fetus as it grows in the uterus.

However, a new paper released today indicates this might not be the case. Instead, some of the masculinising hormones that drive penis development may come from other sources in the developing fetus. These include the liver, the adrenals (small glands found on the kidneys) and placenta.

For the first time, this work comprehensively looks at the possible sites of hormone production outside the testes and their role in regulating masculinisation – the process of gaining typical male characteristics. This helps us see how we develop as embryos, and might feed into a bigger picture of why disorders of penis development are increasing.

Read more: Our relationship with dick pics: it's complicated

Testosterone is not enough

The penis develops from an embryonic structure called the genital tubercle or GT.

The GT is present in both males and females, and develops into either a clitoris or penis, depending on its exposure to hormones secreted by the developing gonads (ovaries or testes).

In females, the developing ovaries do not produce early hormones and the GT becomes feminised, forming a clitoris.

In males, the developing testes produce testosterone. This circulates in the developing fetus and causes masculinisation of target tissues and induces penis development from the GT.

Testosterone itself is a relatively weak hormone. It is converted in the penis to another hormone called dihydrotestosterone (DHT), which has a much more potent masculinising effect.

It is the local conversion of testosterone to DHT within the tissue that is important for penis development and other changes.

There are several ways in which the fetus can make DHT. The most simple is via conversion from testicular testosterone (the so-called “canonical” pathway). However, DHT can also be produced via other steroid hormone pathways active in many tissues, which is explored further in this new paper.

Read more: What makes you a man or a woman? Geneticist Jenny Graves explains

Common birth defects

Understanding the pathways that control penis development is important. Disorders affecting penis development are among the most common birth defects seen in humans, with hypospadias (a disorder affecting development of the urethra) currently affecting around 1 in every 115 live males born in Australia, and rates are on the rise.

You need more than just testes to make a penis The urethra, the hole through which urine passes out of the body, is found in a range of different locations in the disorder known as hypospadias from www.shutterstock.com

In fact, the incidence of hypospadias has doubled over the past 40 years. Such a rapid increase in incidence has been attributed to environmental factors, with endocrine disrupting chemicals (EDCs) being proposed as a major cause. EDCs are man-made chemicals used in many industries – for example, in the production of plastics, cosmetics, flame retardants and pesticides. They can interfere with hormone and metabolic systems in our bodies.

Of the 1,484 EDCs currently identified, a large number are known to negatively affect male reproductive development.

Many studies have identified how EDCs negatively affect organs, such as the liver and adrenals, leading to diseases and disorders which damage the health of these organs and disturb male development.

Backdoor pathway

By measuring hormones from blood samples and tissues during the second trimester of human fetal development, this new research helps us understand the pathways driving the production of DHT, and masculinisation of the penis.

It suggests that in addition to the canonical pathway (testosterone from the testis converted to DHT in the GT and driving penis development), male steroids are synthesised by other organs, such as the placenta, liver and adrenal gland via a process called the “backdoor” pathway to contribute to masculinisation. Notably, the backdoor pathway was first discovered through research conducted here in Australia on marsupials.

The findings of this research suggest that EDCs might have effects in non-reproductive tissues, including the adrenals and liver, and then cause male reproductive diseases such as hypospadias.

Also, it indicates that placental defects, such as intrauterine growth restriction that results in babies being born small, might contribute to male reproductive diseases in humans.

Further research is now required to follow-up on these interesting findings to explore possible new causal pathways of disorders that begin during pregnancy.

Authors: Mark Green, Merck Serono Senior Lecturer in Reproductive Biology, University of Melbourne

Read more http://theconversation.com/you-need-more-than-just-testes-to-make-a-penis-111625

NEWS

VIDEO: Michelle Grattan on the next sitting week

University of Canberra Vice-Chancellor Professor Deep Saini discusses the week in politics with Michelle Grattan – one with a reduced pace, despite the 24 hour news cycle. They talk about...

Ministers fiddle while buildings crack and burn

The Building Ministers’ Forum (BMF) met yesterday yet again to discuss implementing the February 2018 Shergold-Weir Report they commissioned in mid-2017. The BMF is responsible for overseeing the Australian...

Why is nursing home food so bad? Some spend just $6.08 per person a day – that's lower than prison

If residents are given poor quality foods that don't meet their needs or preferences, they're less likely to eat it. ShutterstockThe Royal Commission into Aged Care Quality and Safety this...

What's not to like? Instagram's trial to hide the number of 'likes' could save users' self-esteem

Not enough likes? Not a nice feeling.Shutterstock.comInstagram is running a social media experiment in Australia and elsewhere to see what happens when it hides the number of likes on photos...

The waterwheel plant is a carnivorous, underwater snap-trap

The whaterwheel plant can snap up its prey in milliseconds.The ConversationSign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.Billabongs in...

What's the next 'giant leap' for humankind in space? We asked 3 space experts

Today, we're asking two astrophysicists and a planetary scientist: what's the likelihood we'll be living on Mars or the Moon in future?Pixabay/WikiImages, CC BYYou’ve probably heard that this week marks...

It's a new era for Australia's whistleblowers – in the private sector

Whistleblowing will always take some type of toll, but it need not be career suicide.www.shutterstock.comAs strange as it might sound, whistleblowers in Australia have reason to rejoice – so long...

what is leptospirosis and how can it harm us and our pets?

When a game of fetch can harm: leptospirosis can be transmitted to dogs (and humans) from stagnant water contaminated with rat urine.from www.shutterstock.comRecently reported cases of the often fatal bacterial...

Domestic abuse or genuine relationship? Our welfare system can't tell

Financial abuse can be misinterpreted as 'sharing finances', which can indicate a relationship in the criteria of the couple rule. ShutterstockIn Australia’s social security laws, the “couple rule” is used...

How our obsession with performance is changing our sense of self

How well we do – at work or on the sports field – influences how we see ourselves.from www.shutterstock.com, CC BY-NDWe live in a society obsessed with performance. For both...

Not one but two Aussie dishes were used to get the TV signals back from the Apollo 11 moonwalk

US astronaut Neil Armstrong on the Moon during the Apollo 11 mission.NASAThe role Australia played in relaying the first television images of astronaut Neil Armstrong’s historic walk on the Moon...

One-third of all preschool centres could be without a trained teacher in four years, if we do nothing

Currently, half of all early childhood teachers have a bachelor degree, with a further one-third still working towards one. from shutterstock.comOne-third of all preschools may lack a qualified teacher in...

Popular articles from Modern Australian

Deliveroo announces reusable packaging partnership with Returnr in world-first schemeDIY Home Remodelling Ideas That Adds ValueA place where design and functionality come togetherChoosing the Most Efficient and Effective HeatersGo on vacation without letting yourself goStaying Vibrant in Your Golden Years - 6 Tips to Stay HealthyHow to know when it is time to search for family law specialists in Sydney An All-in-one Guide to Buying Women’s Glasses5 advantages of getting an internship through PGP Australia5 Factors That Make All the Difference in Your Bathroom RemodelRelax on the beachIs A Multi-Room Audio System Right For My Home?Male power and food7 Tips for Preparing To Drive Across The Nullarbor