Anterior Pituitary Hormones
Adrenocorticotrophic Hormone (ACTH)
Corticotrophic releasing hormone (CRH) from the hypothalamus instructs the corticotropic cells of the pituitary to produce ACTH. This hormone is released into the blood stream in spurts or pulses, travels through the blood and attaches to receptors on cells in the outer layer of the adrenal glands located on top of both kidneys. Following a circadian pattern, higher levels of ACTH are produced in the early hours of the morning and low levels at night.
In the Adrenal glands, ACTH causes the secretion of cortisol. It can also stimulate the production of hormones such as adrenaline. Cortisol is transported through the blood to attach to receptors on almost every body cell: organs, skin, & muscle. Cortisol manages blood pressure, blood sugar, inflammation, immunity, the metabolism of fats, proteins and carbohydrates, sleep cycle and stress response. The level of ACTH and cortisol is maintained by the feedback mechanism previously described.
Thyroid Stimulation Hormone (TSH)
Thryrotropin Releasing Hormone (TRH) from the hypothalamus stimulates the pituitary to make and secret thyroid stimulating hormone (TSH). Produced in a circadian fashion, TSH acts on the thyroid gland to make Thyroxine, or tetraiodothyronine (T4), and Triiodothyronine (T3). These hormones work together outside the thyroid where most T4 is converted to T3. T3 acts in body cells to regulate the rate of food conversion into energy (metabolic rate), heart and muscle function, digestion, bone health, and is important for brain development particularly in the developing fetus.
Growth Hormone (Somatotropin [GH])
Growth hormone releasing hormone from the hypothalamus stimulates the production and release of growth hormone from the somatotroph cells of the pituitary. As with other hormones, GH secretion is regulated by circadian cycles and feedback mechanisms. However, somatostatin released from the hypothalamus also stops GH production. GH is produced in very short pulses with higher production at night after the onset of slow wave sleep. It has a very short life and therefore it’s challenging to capture the highest levels in blood. However, each pulse stimulates the liver to produce insulin growth factor-1 (IGF-1) which is
more stable to measure over time. Therefore, IGF-1 is used as an indicator of growth hormone levels. Normal IG-1 levels also change with sex and age.
GH in children is needed for growth. However, growth plates fuse once adult height is achieved. Adults use growth hormone to help stabilize blood sugar levels, effectively use fats, maintain healthy bones and muscles, has an impact on memory, energy, mood, and sense of wellbeing. Stress, exercise, sleep, and low blood sugar levels stimulate the production of GH.
Luteinizing Hormone (LH)
Follicle Stimulating Hormone (FSH)
Gonadotropin-releasing hormone from the hypothalamus stimulates the pituitary to produce and secrete LH and FSH. Together FSH and LH are known as gonadotroph hormones. After secretion, they are transported in the blood and attach to receptors on cells in the ovaries in women and testes in men. In women they regulate the production of oestrogen and progesterone and the menstrual cycle. In men the Leydig cells of testes produce testosterone leading to sperm production.
Both hormones are necessary for sexual development, the development of sex features known as secondary sex characteristics specific to sex at birth and fertility. Production of both is controlled by a feedback mechanism.
Prolactin (Luteotropic hormone [LTH])
Prolactin production is controlled by Dopamine. Dopamine is a neurotransmitter or a chemical messenger that is delivered from the hypothalamus down the pituitary stalk (infundibulum) to the lactotroph cells of the pituitary. In contrast to other hormones, dopamine inhibits or stops the production of prolactin in the pituitary. Also, in contrast to other hormones, prolactin level is controlled by its own production. Higher levels of prolactin signal the hypothalamus to increase the release of dopamine, thereby decreasing the production of prolactin.
Prolactin’s primary function in females is to prepare mammary glands and respond to infant suckling by producing milk- quickly! In males, normal levels enhance sperm production.