Endocrine system

Over the course of our lifetimes, our bodies undergo a series of extraordinary metamorphoses: we grow, experience puberty, and many of us reproduce. Behind the scenes, the endocrine system works constantly to orchestrate these changes.

Alongside growth and sexual maturity, this system regulates everything from your sleep to the rhythm of your beating heart, exerting its influence over each and every one of your cells.

The endocrine system relies on interactions between three features to do its job: glands, hormones and trillions of cell receptors.

Firstly, there are several hormone-producing glands: three in your brain, and seven in the rest of your body. Each is surrounded by a network of blood vessels, from which they extract ingredients to manufacture dozens of hormones. Those hormones are then pumped out in tiny amounts, usually into the bloodstream.

From there, each hormones needs to locate a set of target cells in order to bring about a specific change. To find its targets, it's helped along by receptors, which are special proteins inside or on the cell's surface. Those receptors recognise specific hormones as they waft by and bind to them.

When this happens, that hormone-receptor combination triggers a range of effects that either increase or decrease specific processes inside the cell to change the way that cell behaves.

By exposing millions of cells at a time to hormones in carefully-regulated quantities, the endocrine system drives large-scale changes across the body.

Take, for instance, the thyroid and the two hormones it produces, triiodothyronine and thyroxine. These hormones travel to most of the body's cells, where they influence how quickly those cells use energy and how rapidly they work. In turn, that regulates everything from breathing rate to heartbeat, body temperature, and digestion.

Hormones also have some of their most visible—and familiar—effects during puberty. In men, puberty begins when the testes begin secreting testosterone. That triggers the gradual development of the sexual organs, makes facial hair sprout, and causes the voice to deepen and height to increase.

In women, estrogen secreted from the ovaries signals the start of adulthood. It helps the body develop, makes the hips widen, and thickens the womb's lining, preparing the body for menstruation or pregnancy.

An enduring misconception around the endocrine system is that there are exclusively male and female hormones. In fact, men and women have estrogen and testosterone, just in different amounts.

Both hormones play a role in pregnancy, as well, alongside more than 10 other hormones that ensure the growth of the fetus, enable birth, and help the mother feed her child.

Such periods of hormonal change are also associated with fluctuations in mood. That's because hormones can influence the production of certain chemicals in the brain, like serotonin.

When chemical levels shift, they may cause changes in mood, as well. But that's not to say that hormones have unlimited power over us.

They're frequently viewed as the main drivers of our behaviour, making us slaves to their effects, especially during puberty. But research shows that our behaviour is collectively shaped by a variety of influences, including the brain and its neurotransmitters, our hormones, and various social factors.

The primary function of the endocrine system is to regulate bodily processes, not control us. Sometimes disease, stress, and even diet can disrupt that regulatory function, however, altering the quantity of hormones that glands secrete or changing the way that cells respond.

Diabetes is one of the most common hormonal disorders, occurring when the pancreas secrets too little insulin, a hormone that managed blood sugar levels. And hypo- and hyperthyroidism occur when the thyroid gland makes too little or too much thyroid hormone.

When there's too little thyroid hormone, that results in a slowed heart rate, fatigue and depression, and when there's too much thyroid hormone, weight loss, sleeplessness, and irritability.

But most of the time, the endocrine system manages to keep our bodies in a state of balance. And through its constant regulation, it drives the changes that ultimately help us become who we are.

An interactive three-dimensional model of the pancreas and duodenum, a part of the small intestine. Parts of the pancreas, duodenum and surrounding tissue are annotated with descriptions.

1. Pancreas: The pancreas is an organ located in the abdomen. It plays an essential role in converting the food we eat into fuel for the body's cells. The pancreas has two main functions: an exocrine function that helps in digestion and an endocrine function that regulates blood sugar.
2. Duodenum: The duodenum is the first part of the small intestine. It is located between the stomach and the middle part of the small intestine, or jejunum. After foods mix with stomach acid, they move to the duodenum, where they mix with bile from the gallbladder and digestive juices from the pancreas.
3. Pancreatic duct: The pancreatic duct, or duct of Wirsung (also, the major pancreatic duct due to the existence of an accessory pancreatic duct), is a duct joining the pancreas to the common bile duct to supply pancreatic juice provided from the exocrine pancreas, which aids in digestion.
4. Common bile duct: The common bile duct is a small, tube-like structure formed where the common hepatic duct and the cystic duct join. Its physiological role is to carry bile from the gallbladder and empty it into the upper part of the small intestine (the duodenum). The common bile duct is part of the biliary system.
5. Portal vein: The portal vein or hepatic portal vein is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents.
6. Abdominal aorta: The abdominal aorta is a continuation of the descending thoracic aorta. It supplies all of the abdominal organs, and its terminal branches go on to supply the pelvis and lower limbs. It also supplies the undersurface of the diaphragm and parts of the abdominal wall.
7. Merging of pancreatic duct and common bile duct

• DeMasi, K. (Barkandji), Shen, D. (Ngarrindjeri), Richards-Satour, P. (Adnyamathanha & Barngarla), Renehan, C. (Central Arrernte), Morey, K. (Anmatyerr & Eastern Arrernte), Glover, K. (Mein:tnk & Wotjobaluk), Leane, C. (Dharug), Woods-Hampton, K. (Anmatijerre), Garay, L. (Anangu), Baker, E. (Adnyamathanha & Barngarla), Nielson, R. (Kalkadoon), & Brown, K. (2025). An Aboriginal women-led approach to design a maternal and child health model when cardiometabolic complications are experienced in pregnancy in South Australia. Medical Journal of Australia, 223(6), 312–319. https://doi.org/10.5694/mja2.70033