What Is the Hypothalamus?
The hypothalamus (pronounced hai-puh-tha-luh-muhs) is a gland in your brain that controls your hormone (endocrine) system. It's sort of like your body's thermostat; it receives signals from other organs in your endocrine system as well as other areas of your brain and sends signals (hormones) to a specific part of your brain called the pituitary gland. Your pituitary (pronounced puh-too-uh-teh-ree) gland is also called your "master gland" because it makes, stores, and releases hormones to all the organs in your endocrine system, including your thyroid, adrenal glands, kidneys, and reproductive organs, as well as your bones and muscles.
Your endocrine system controls many of the most important functions of your body, such as:
- Your ability to grow and repair your body
- Your salt and water balance
- Your body temperature
- Your heart rate and blood pressure
- How fast you breathe
- How hungry and thirsty you feel
- Your ability to digest your food
- When you feel sleepy
- Your mood
- Sexual arousal
- Your ability to produce milk if you're nursing
Thalamus vs. hypothalamus
The thalamus is an area in the middle of your brain. Your hypothalamus sits right underneath your thalamus. "Hypothalamus" is Greek for under (hypo) the thalamus (inner chamber). The thalamus takes in signals from your senses (except for your sense of smell) and sorts those signals to find what's important. It then sends the important signals to your cerebral cortex, which is the part of your brain that controls your higher-level processes, such as your ability to use language, remember past events, think about problems, and make decisions.
Your thalamus is important to your ability to learn and remember things, focus on what's important, stay awake and alert, regulate your emotions, and some other functions.
Where Is the Hypothalamus Located?
Your hypothalamus is in the lower middle part of your brain.
It's about the size of an almond and sits underneath your thalamus, attached to the top of your pituitary gland. Your hypothalamus and pituitary are right in the middle of your head if you trace a line from the bridge of your nose back into your skull. They're right above your brainstem, at the very base of your brain.
Like the thermostat in your house works to keep the temperature stable, your hypothalamus's job is to keep your body in a stable state called homeostasis. Homeostasis is your body's way of adapting to the changing conditions in the world around you to keep your body's internal balance. For instance, if it gets signals from your body that your temperature has dropped lower than about 98.6 F, it signals your pituitary gland that you need to warm up. Your pituitary gland sends signals to your heart, blood vessels, and skin to help you keep the heat you have, for instance, by shrinking your blood vessels so you lose less heat through your skin. If your body temperature rises above about 98.6 F, your hypothalamus sends signals to your pituitary that you need to cool down, which sends signals to your blood vessels to expand. And this process continues in what is called a feedback loop to keep things on an even balance.
Hypothalamus and pituitary gland
Your hypothalamus balances your body by making hormones that it sends to be stored in an area of your pituitary called the posterior pituitary. Or, it signals your pituitary to send hormones that it made or stored to the parts of your body that those hormones work on.
Your hypothalamus makes hormones that it sends to a part of your pituitary gland called the anterior (pronounced an-tee-ree-ur) pituitary. Anterior means at or near the front, so your anterior pituitary is the front of your pituitary. The anterior pituitary then releases hormones it has made or stored to various parts of your body, in response to the hormones from the hypothalamus.
The hormones your hypothalamus makes and their functions are as follows:
Thyrotropin-releasing hormone (TRH). TRH triggers your anterior pituitary to send thyroid-stimulating hormone (TSH) to your thyroid gland. TSH then makes your thyroid release the hormones thyroxine (T4) and triiodothyronine (T3). T4 and T3 help control how your cells use energy (calories) from the food you eat.
Corticotropin-releasing hormone (CRH), which makes your anterior pituitary send adrenocorticotropic hormone to your adrenal glands. Your adrenal glands then send out the stress hormone, cortisol, as well as other signals that help regulate how your body gets energy from your food and how your immune system responds to invaders.
Growth hormone-releasing hormone (GHRH), which triggers your anterior pituitary to send growth hormone (GH) to your long bones and big muscles so they grow.
Dopamine. This is known as the "feel-good" hormone. It makes you feel nice so that you are motivated to do the things that make you feel good. It affects your mood and motivation. Dopamine also signals your pituitary to stop sending prolactin to your breast tissue.
Somatostatin. This hormone tells your pituitary to stop sending out GH to your bones and muscles and TSH to your thyroid gland. It also tells your pancreas to stop releasing insulin and your small intestine to stop releasing cholecystokinin. In this way, somatostatin helps regulate your ability to grow and use the food you eat.
Gonadotropin-releasing hormone (GnRH), which tells your pituitary gland to make and send out follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH help your reproductive organs mature and keep functioning.
Your hypothalamus also makes two hormones that it sends to the back (posterior) of your pituitary. These two hormones are stored in your posterior pituitary until you need them. When you do, your hypothalamus sends another signal to release them into your blood. These two hormones are:
Oxytocin, which is involved in human emotional bonds, sexual arousal, trust, your ability to recognize other people, how your sleep cycle works, and your feelings of well-being. It also stimulates your uterus to contract when it's time to give birth and the ability to release milk (lactate) to an infant you are nursing.
Vasopressin (also known as antidiuretic hormone), which works on your kidneys to help you keep hydrated and control your blood pressure.
Other hormones made by the hypothalamus include orexin and ghrelin, which increase your appetite, and leptin, which decreases your appetite.
Hypothalamus Dysfunction Causes
Hypothalamus dysfunction is when your hypothalamus is damaged and doesn't work the way it should. This can happen for a few reasons, including:
- Congenital (present at birth) conditions from abnormal growth of your brain or hypothalamus that happens while you develop in your mom's uterus
- Genetic disorders, such as Prader-Willi syndrome or Kallmann syndrome
- Traumatic brain injury
- Brain tumors
- Brain surgery, radiation, or chemotherapy to treat brain tumors
- Brain aneurysms (abnormal bulging in the wall of blood vessels in your brain)
- Brain infections
- Inflammatory diseases that involve your brain, such as multiple sclerosis or neurosarcoidosis
- Disorders that happen when your immune system reacts to a cancer you have
The hypothalamus is also affected by nutrition and exercise. If your body doesn’t have enough energy, it goes into a stress state and makes cortisol, which can dampen activity in your hypothalamus and lead to problems. The stress response can be caused by eating disorders (such as bulimia or anorexia nervosa) that lead to:
- Emotional stress
- Too much exercise
- Not eating enough calories
- Low weight
High stress, drugs such as cocaine, and eating lots of saturated fats which cause inflammation may also lead to hypothalamic dysfunction.
Disorders that can be caused by hypothalamus dysfunction include:
Hypothalamic obesity. Injury to the hypothalamus can disrupt the balance between how hungry you feel and how many calories you burn. Injury to the hypothalamus may be due to a brain tumor on your hypothalamus or surgery to remove it. Injury may also be due to tumors on the pituitary gland, traumatic brain injury, infections, inflammation, radiation, or brain hemorrhage (bleeding). People who have hypothalamic obesity gain a lot of weight, usually immediately after the injury. Some people may also:
- Feel extremely hungry all the time, even when they've just eaten a meal
- Have trouble sleeping at night and feel sleepy during the day
- Have trouble regulating their body temperature
- Have trouble adjusting their heart rate and blood pressure based on what their body needs
- Have visual impairments, including blindness
- Have early or delayed puberty
- Have pituitary hormone deficiencies
Functional hypothalamic amenorrhea (also called secondary amenorrhea). For people assigned female at birth (AFAB), this condition is when you stop having a period for more than 3 months if you have regular periods or more than 6 months if you have irregular periods. The most common cause of this condition is hypothalamic dysfunction.
When your body doesn’t have enough energy from food or you are using too much energy from exercise, it can lower the GnRH levels released from your hypothalamus. Lower GnRH levels can ultimately shut down the hypothalamus feedback loop, which means you'll have low amounts of hormones that make you ovulate. If you don't ovulate, then you don't get a period and cannot get pregnant.
Central diabetes insipidus. This type of diabetes is a rare autoimmune disorder where your immune system damages your hypothalamus. Parts of your hypothalamus release a hormone called antidiuretic hormone, or vasopressin, which helps your kidneys filter water and keep you hydrated.
Damage to the hypothalamus leads to a lack of antidiuretic hormone and causes frequent peeing and thirst.
Kallman syndrome. Hypothalamus dysfunction can lead to absent or delayed puberty and no sense of smell, as in Kallman syndrome. This is a genetic condition that causes problems with the hypothalamus. It means you won't have enough hormones for sexual development. Symptoms can include:
- No periods
- Undescended testicles
- Small penis
- No or small breasts
- Kidney problems
- Hearing problems
- Cleft lip
- Cleft palate
Prader-Willi syndrome. This genetic condition is caused by a hypothalamus that doesn’t work properly. This can cause:
- Intellectual disabilities
- Poor growth
- An irresistible urge to eat
- Small genitals
- Behavioral problems
Syndrome of inappropriate antidiuretic hormone (SIADH). SIADH causes high antidiuretic hormone levels and low electrolytes. It's usually caused by stroke, infection, or cancer that damages the hypothalamus. Too much of this hormone can cause low sodium levels and lead to:
- Throwing up
- Trouble thinking
Hypothalamus Disorders Tests
Your doctor will ask you about your personal medical history and may order blood and urine tests based on your symptoms. The blood and urine tests check for different hormones, electrolytes, and autoimmune proteins and often include:
- Serum cortisol
- Serum estrogen
- Hormones from your pituitary, such as adrenocorticotropic hormone, GH, TSH, LH, FSH, and prolactin
- Thyroid hormones
- Sodium levels
- Solute levels in your blood and urine
Your doctor may also order tests for:
- Brain imaging, such as MRI or CT
- Visual field changes
- Genetic changes
- Autoimmune proteins in your blood
Hypothalamus Disorders Treatment
Most hypothalamus disorders are treatable, but the treatment depends on the cause and your signs and symptoms.
Treatments can include:
- Surgery or radiation for tumors
- Hormone medication for hormone problems such as hypothyroidism
- Sex hormone replacement for delayed puberty
- Appetite suppressing medications for overeating problems
- Dietary plans
- Obesity medications such as metformin
If you have other health problems, such as an eating disorder, high stress, or behavioral problems, your doctor might suggest therapy for your mental health or lifestyle counseling for stress and fitness.
Hypothalamus Disorders Complications
Hormone deficiencies can cause complications, such as:
- Heart problems
- High cholesterol
- Low blood pressure
- Electrolyte changes
- Short stature
- Infertility or trouble getting and keeping an erection
- Trouble during labor and breastfeeding
- Low sex drive
In addition, people with brain tumors may experience high blood pressure inside their head, seizures, and blindness or visual field defects.
Your hypothalamus is a gland in your brain that acts like your body's thermostat. It takes in signals from organs in your hormone (endocrine) system and other areas of your brain and sends hormones to your pituitary gland. Your pituitary gland makes, stores, and releases hormones to the organs in your endocrine system, including your thyroid, adrenal glands, kidneys, and reproductive organs, as well as your bones and muscles. Hypothalamus dysfunction can happen because of congenital or genetic conditions, brain injuries, or infections. This can cause several disorders that affect your appetite, sleep patterns, blood pressure and heart rate, body temperature, and libido.