Define ACTH and Its Functions
Hormones are steroidal substances that are secreted from different organs. These biochemical substances are developed to control and manage various biological functions. Most human hormones are secreted by the pituitary gland present in the lower portion of the human brain. It is also called the master gland that controls the functions of other organs. One such hormone produced by the pituitary gland is adrenocorticotropic hormone (ACTH). In this section, we will study the ACTH function elaborately and the disorders caused by its abnormal levels.
What is ACTH Hormone?
Adrenocorticotropic Hormone (ACTH) is a steroidal substance that acts as a hormone. It is produced in the anterior section of the pituitary gland located under the human brain. This hormone is commonly called adrenocorticotrophin, arginine vasopressin, corticotropin, or serum adrenocorticotropic hormone.
This hormone is required for the functioning of the adrenal glands. As you can easily understand by its name, the prime ACTH hormone function is to maintain the vital functions of this pair of glands. These glands are responsible for the production and secretion of cortisol or stress hormones. These hormones are produced in the cortex region of these glands.
How ACTH is Synthesized?
The first stage is the production and release of the Corticotrophin-releasing hormone. This hormone acts as the precursor of the synthesis and release of ACTH. ACTH, after synthesis and release, reaches the bloodstream to reach the adrenal glands. These glands are present on the top of both kidneys. The cortisols are then synthesized in the cortex of these glands. These hormones then reach the hypothalamus of our brain to signal and stop the synthesis of ACTH.
Now that we have understood the answer for what is ACTH hormone, we need to go deeper into the synthesis and control of the ACTH level in our body. It is obvious that the hormone travels through the bloodstream and reaches the adrenal glands for action. It has been observed that the level of this hormone is the highest when you wake up in the morning. Eventually, it reduces throughout the day and is the lowest before you go to sleep. The level is controlled but three crucial organs of our body. They are the hypothalamus, adrenal glands, and pituitary gland.
We have learned that the level of this hormone is controlled by the cortisol or stress hormones present in the bloodstream. We also know that the lowest level of ACTH occurs during the night time when we are about to hit the bed. This proves that working relentlessly and taking stress release cortisol in the bloodstream. These stress hormones then reach the hypothalamus telling it to shut down the production. The ACTH hormone levels then significantly fall over the day in due course of time and action. This rhythmic synthesis and reduction of the ACTH hormone level during the daytime are called the diurnal or circadian rhythm.
Functions of ACTH Hormone
The list of ACTH functions is given below:
Resorption of bones
Protein catabolism
Anabolic effects of this hormone can be seen on bones and muscles
Proper stimulation and beginning of spermatogenesis
Proper metabolism of glucose, lipolysis, hyperglycemia, androgens, and immuno-suppression.
What Happens When the ACTH Level Drops?
When the ACTH hormone levels drop significantly, it can cause anomalies that are related to the functioning of the adrenal glands. It can happen due to hypopituitarism or the low functioning of the master gland. Cushing’s syndrome can also increase the level of cortisol that affects the synthesis of ACTH causing such issues.
What Happens When the ACTH Hormone Levels Increase?
The ATH level can significantly increase due to hyperpituitarism, Cushing’s disease, adrenal insufficiency (low cortisol levels), adrenal hyperplasia in the congenital condition, etc. Due to the increased ACTH level, it can cause Addison’s disease.
What are the ACTH Hormone Disorders?
When there is an improper level of ACTH in the bloodstream, it can indicate the presence of an anomaly in the physiology of the brain, the adrenal glands, etc. It can happen due to tumours present in the pituitary gland, Cushing’s disease, adrenal insufficiencies such as Addison’s disease, or congenital adrenal hyperplasia.
Conclusion
The definition of this hormone depicts the ACTH hormone function that is crucial for the proper functioning and development of the human body. It indicates the adrenal glands develop and promotes their functions. Indirectly, the functions of the adrenal glands are controlled by this hormone. The hormones produced in these glands are aldosterone, cortisol, noradrenaline, and adrenaline. These hormones function to control metabolism, blood sugar levels, water-slat balance, blood pressure, pregnancy, puberty, sexual characteristics development, balancing the sex hormones, etc.
FAQs on Adrenocorticotropic Hormone (ACTH)
1. What is Adrenocorticotropic Hormone (ACTH) and which gland produces it?
Adrenocorticotropic Hormone, or ACTH, is a crucial polypeptide hormone produced and secreted by the anterior pituitary gland, which is located at the base of the brain. Its primary role is to regulate the production and release of another vital hormone, cortisol, from the adrenal glands.
2. What are the main functions of ACTH in the body?
The main functions of ACTH are directly related to the adrenal glands. Its key roles include:
- Stimulating the adrenal cortex to secrete glucocorticoids, primarily cortisol, which helps regulate metabolism, blood pressure, and the immune response.
- Influencing the secretion of mineralocorticoids like aldosterone, which is essential for maintaining blood pressure and water-salt balance.
- Supporting the production of androgens (sex hormones) from the adrenal cortex.
3. How does the body control the level of ACTH in the bloodstream?
The body controls ACTH levels through a sophisticated negative feedback system known as the Hypothalamic-Pituitary-Adrenal (HPA) axis. The hypothalamus releases Corticotropin-Releasing Hormone (CRH), which signals the pituitary gland to secrete ACTH. ACTH then travels to the adrenal glands and stimulates cortisol release. As cortisol levels in the blood rise, they signal both the hypothalamus and pituitary gland to decrease their production of CRH and ACTH, thus maintaining a balanced hormonal state.
4. What are the common signs and symptoms associated with high ACTH levels?
High levels of ACTH lead to excessive cortisol production, which can cause symptoms characteristic of Cushing's disease. These symptoms often include:
- Weight gain, especially in the upper back, face (moon face), and abdomen.
- High blood pressure (hypertension).
- High blood sugar (hyperglycemia).
- Thinning skin that bruises easily.
- Muscle weakness and fatigue.
5. What happens to the body if ACTH levels are too low?
Low levels of ACTH result in insufficient cortisol production, a condition known as secondary adrenal insufficiency. This can lead to a range of symptoms, including chronic fatigue, muscle weakness, unexplained weight loss, low blood pressure (hypotension), and decreased appetite. It signifies a disruption in the signaling from the pituitary gland to the adrenal glands.
6. Why is the release of ACTH crucial during times of stress?
During times of physical or emotional stress, the hypothalamus increases the release of CRH, which in turn boosts ACTH secretion. This surge in ACTH stimulates the adrenal glands to produce more cortisol. Cortisol acts as the body's primary stress hormone, preparing it for a 'fight-or-flight' response by increasing blood sugar for energy, suppressing non-essential functions, and modulating the immune system. This mechanism is vital for short-term survival and adaptation to stressful situations.
7. How does ACTH relate to specific medical conditions like Cushing's syndrome and Addison's disease?
ACTH levels are a key diagnostic marker for differentiating between adrenal disorders. In Cushing's syndrome, if the cause is a pituitary tumour (Cushing's disease), ACTH levels will be high, leading to excess cortisol. Conversely, in Addison's disease, the adrenal glands are damaged and cannot produce enough cortisol. The pituitary gland tries to compensate by producing very high levels of ACTH, but the adrenal glands fail to respond.
8. Does the level of ACTH change throughout the day?
Yes, ACTH secretion follows a diurnal rhythm, meaning its levels fluctuate predictably over a 24-hour cycle. Levels are typically highest in the early morning (around 6-8 AM) to help wake the body and prepare it for the day's activities. They gradually decline throughout the day, reaching their lowest point around midnight, which aligns with the body's sleep and repair cycle.
