Glands for Life!
The endocrine system is made up of glands that make hormones to help our (parents and kids) bodies function properly. Hormones are the body’s chemical messengers. Imagine making a phone call on your cell phone. The base stations that your cell phone connect to, act the same as your glands. In order for your cell phone to make a call, it needs to message the base station that it requires a voice call from your handset to another handset. These requests are send through the network as messages. Just like the cell network, hormones carry information and instructions from one set of cells to another, basically, a network of glands that secrete chemicals, like the cell phone network. Unlike the cell phone network infrastructure, the endocrine system is vaslty more complex, and many facets yet to be discovered. The endocrine system influences almost every cell, organ, and function of our and our fur kids’ bodies.
- The endocrine system is made up of a network of glands;
- These glands secrete hormones to regulate many bodily functions, including growth and metabolism;
- Endocrine diseases1 are common and usually occur when glands produce an incorrect number of hormones.
The endocrine system works to regulate certain internal processes. Endocrine should not be confused with exocrine. Exocrine glands, such as sweat and salivary glands, secrete externally and internally via ducts. Endocrine glands secrete hormones internally, using the bloodstream.
(Image source: Merck Veterinary Manual)
What Does the Endocrine System Do?
- Endocrine glands release hormones into the bloodstream. This lets the hormones travel to cells in other parts of the body;
- The endocrine hormones help control mood, growth and development, the way our organs work, metabolism, and reproduction;
The endocrine system regulates how much of each hormone is released. This can depend on levels of hormones already in the blood, or on levels of other substances in the blood, like calcium. Many things affect hormone levels, such as stress, infection, and changes in the balance of fluid and minerals in blood.
The endocrine system helps control the following processes and systems:
- Growth and development;
- Homeostasis (the internal balance of body systems);
- Metabolism (body energy levels);
- Response to stimuli (stress and / or injury).
Too much or too little of any hormone can harm the body.
What Are the Parts of the Endocrine System or Network?
While many parts of the body make hormones, the major glands that make up the endocrine system are the:
- Pineal Gland;
- Pituitary Gland;
These glands produce different types of hormones that evoke a specific response in other cells, tissues, and / or organs located throughout the body. The hormones reach these faraway targets using the blood stream. Like the nervous system, the endocrine system is one of your body’s main communicators. But instead of using nerves to transmit information, the endocrine system uses blood vessels to deliver hormones to cells.
Humeral versus Neural Control
- The nervous system uses physical structures for communication;
- The endocrine system uses body fluids to transport message.
Did you know: There are two types of endocrine glands. They are known as exclusive endocrine glands and partial endocrine glands.
- Exclusive endocrine glands – the glands which secrete only hormones are called ‘exclusive endocrine glands.’ They have no other function. Examples: Parathyroid gland, pineal gland, adrenal gland, pituitary gland, and thymus.
- Partial endocrine glands – these organs secrete hormones, and they perform other functions as well. Examples: Gonads (ovary in females, testis in males), pancreas, duodenal epithelium, gastric epithelium, kidneys, and placenta in pregnant women.
The pancreas is part of the endocrine system and the digestive system. That’s because it secretes hormones into the bloodstream and makes and secretes enzymes into the digestive tract.
Hypothalamus: The hypothalamus is in the lower central part of the brain. It links the endocrine system and nervous system. Nerve cells in the hypothalamus make chemicals that control the release of hormones secreted from the pituitary gland. The hypothalamus gathers information sensed by the brain (such as the surrounding temperature, light exposure, and feelings) and sends it to the pituitary. This information influences the hormones that the pituitary makes and releases.
Pituitary: The pituitary gland is at the base of the brain and is no bigger than a pea. Despite its small size, the pituitary is often called the “master gland.” The hormones it makes control many other endocrine glands. However, there is no consensus here – some belief the thyroid is the master gland.
The pituitary gland makes many hormones, such as:
- growth hormone, which stimulates the growth of bone and other body tissues and plays a role in the body’s handling of nutrients and minerals;
- prolactin, which activates milk production in women who are breastfeeding;
- thyrotropin, which stimulates the thyroid gland to make thyroid hormones;
- corticotropin, which stimulates the adrenal gland to make certain hormones;
- antidiuretic hormone, which helps control body water balance through its effect on the kidneys;
- oxytocin, which triggers the contractions of the uterus that happen during labour.
The pituitary also secretes endorphins, chemicals that act on the nervous system and reduce feelings of pain. The pituitary also secretes hormones that signal the reproductive organs to make sex hormones. The pituitary gland also controls ovulation and the menstrual cycle in women.
Thyroid: The thyroid is in the front part of the lower neck. It’s shaped like a bow tie or butterfly. It makes the thyroid hormones thyroxine and triiodothyronine. These hormones control the rate at which cells burn fuels from food to make energy. The more thyroid hormone there is in the bloodstream, the faster chemical reactions happen in the body.
Thyroid hormones are important because they help kids’ and teens’ bones grow and develop, and they also play a role in the development of the brain and nervous system.
Parathyroids: Attached to the thyroid are four tiny glands that work together called the parathyroids. They release parathyroid hormone, which controls the level of calcium in the blood with the help of calcitonin, which the thyroid makes.
Adrenal Glands: These two triangular adrenal glands sit on top of each kidney. The adrenal glands have two parts, each of which makes a set of hormones and has a different function:
- The outer part is the adrenal cortex. It makes hormones called corticosteroids that help control salt and water balance in the body, the body’s response to stress, metabolism, the immune system, and sexual development and function.
- The inner part is the adrenal medulla. It makes catecholamines, such as epinephrine. Also called adrenaline, epinephrine increases blood pressure and heart rate when the body is under stress.
Pineal: The pineal body, also called the pineal gland, is in the middle of the brain. It secretes melatonin, a hormone that may help regulate when you sleep at night and when you wake in the morning.
Reproductive Glands: The gonads are the main source of sex hormones. Most people don’t realize it, but both guys and girls have gonads. In guys the male gonads, or testes, are in the scrotum. They secrete hormones called androgens, the most important of which is testosterone. These hormones tell a guy’s body when it’s time to make the changes associated with puberty, like penis and height growth, deepening voice, and growth in facial and pubic hair. Working with hormones from the pituitary gland, testosterone also tells a guy’s body when it’s time to make sperm in the testes.
A girl’s gonads, the ovaries, are in her pelvis. They make eggs and secrete the female hormones estrogen and progesterone. Estrogen is involved when a girl starts puberty. During puberty, a girl will have breast growth, start to accumulate body fat around the hips and thighs, and have a growth spurt. Estrogen and progesterone are also involved in the regulation of a girl’s menstrual cycle. These hormones also play a role in pregnancy.
Pancreas: The pancreas makes insulin and glucagon, which are hormones that control the level of glucose, or sugar, in the blood. Insulin helps keep the body supplied with stores of energy. The body uses this stored energy for exercise and activity, and it also helps organs work as they should.
Diseases of the Endocrine System
Hormone levels that are too high or too low indicate a problem with the endocrine system2. Hormone diseases also occur if your body does not respond to hormones in the appropriate ways. The same behaviour applies to our fur kids. Stress, infection and changes in the blood’s fluid and electrolyte balance can also influence hormone levels3.
Diabetes occurs due to a lack of insulin. This lack of insulin can be absolute (meaning none is produced) or relative (meaning not enough is produced). When there is a lack of insulin, the blood sugar surges because glucose (food for the cell) cannot get into the cell without its carrier, insulin. Both dogs and cats can get diabetes, though dogs generally get insulin-dependent diabetes while cats generally get non-insulin dependent diabetes (usually associated with obesity). Clinical signs include increased water intake, increased urination, increased appetite, and weight loss.
This condition occurs in middle aged to older cats. While it is possible for a dog to develop hyperthyroidism, it is rare. Hyperthyroidism occurs when there is an increased production of thyroid hormone, which leads to a high metabolic state. Hyperthyroidism in cats is usually due to benign proliferation of the thyroid gland, while in dogs, neoplasia (cancer) is usually to blame. Due to an increased metabolic state, affected animals will lose weight despite a voracious appetite.
The condition occurs in older dogs and very rarely in cats. Hypothyroidism refers to the condition when there is a decreased amount of thyroid hormone. The majority of canine cases are due to a benign destruction of thyroid cells. As you might imagine, too little thyroid hormone would lead to a decreased metabolic state, so unlike pets with hyperthyroidism, these dogs typically gain weight despite a steady diet. Skin conditions may also occur. Once diagnosed, dogs can be treated by supplementing their thyroid hormones daily.
Hyperadrenocorticism (Cushing’s disease)
Cushing’s disease occurs in dogs (and rarely cats) when the adrenal glands produce too much of a hormone called glucocorticoid. Glucocorticoid is an important hormone that helps the body deal with stress, but excess glucocorticoid can cause illness.The condition most frequently occurs because a pituitary tumour tells the adrenal gland to make excess hormone, but in about 10% of cases, an adrenal tumour is to blame. Clinical signs include increased thirst, increased urination, increased appetite, pot-bellied appearance, hair loss, and panting.
Hypoadrenocorticism (Addison’s disease)
Addison’s disease occurs in dogs (and rarely cats) when the adrenal glands do not produce enough glucocorticoids, mineralocorticoids, or both. These hormones are key in dealing with day to day stress as well as balancing important electrolytes.Clinical signs can be intermittent and include vomiting and diarrhoea, weakness, slow heart rate, and collapse. Diagnosis can be a little bit tricky, but once diagnosed, your pet will be treated with hormone supplements. Particular care should be taken during stressful situation, such as boarding.
Nutrients play a major role in providing nutrition to each organ and gland to efficiently fulfil their function. Without nutritional balance, our body is inefficient to manufacture energy needed for metabolism. When treating pets with endocrine disease, most veterinarians concentrate on medical or surgical treatments that can be used to manage or cure the disease. Dietary issues are frequently ignored or not properly addressed. However, nutritional support can play an integral role in the successful management of endocrine diseases. Furthermore, because most pets with endocrine disease are senior or geriatric, they may also have concurrent health conditions that warrant dietary intervention.
Articles and Videos
We only list a select view for your further perusal. However, as you would have noticed, many diseases of the endocrine system apply, and depending on the specific topic, you would need to further research topic specific.
- Nutritional endocrine disorders (Journal);
- The Endocrine System of Animals (MSD Manual);
- Anatomy and Physiology of Animals/Endocrine System (WikiBooks);
- Mechanisms that Lead to Disease of the Endocrine System in Animals (Journals) (PDF);
- The Endocrine Glands in the Dog: From the Cell to Hormone (SemanticSholar) (PDF);
- Interrelationship of Nutrition and Endocrinology (AmericanJournal);
Endocrinology – Overview
Dr. Becker and Dr. Dodds Discuss Thyroid Disease in Pets
Dr. Becker & Dr. Dodds Discuss Thyroid Disease in Pets (Part 2)
References and Research
- 1.Kooistra HS, Galac S, Buijtels JJCWM, Meij BP. Endocrine Diseases in Animals. Horm Res Paediatr. 2009:144-147. doi:10.1159/000178059
- 2.Rijnberk A, Kooistra H, Mol J. Endocrine diseases in dogs and cats: similarities and differences with endocrine diseases in humans. Growth Horm IGF Res. 2003;13 Suppl A:S158-64. doi:10.1016/s1096-6374(03)00076-5
- 3.Beatrice L, Boretti FS, Sieber-Ruckstuhl NS, et al. Concurrent endocrine neoplasias in dogs and cats: a retrospective study (2004–2014). Veterinary Record. January 2018:323-323. doi:10.1136/vr.104199