1. Thyroid Stimulating Hormone (TSH or thyrotropin)

2. Follicle Stimulating Hormone (FSH, a gonadotropin)

3. Luteinizing Hormone (LH, a gonadotropin)

4. Adrenocorticotropic Hormone (ACTH, or corticotropin)

5. Growth Hormone (GH)

6. Prolactin (PRL)

1. TSH – target thyroid gland and stimulates secretion of thyroid hormone (TH).

2. FSH – targets follicles in the ovaries of females and stimulates growth of follicle and production of estrogen. In males it targets the testes and stimulates sperm cell production.

3. LH – targets follicle, triggers ovulation and increases secretion of progesterone. In males, it stimulates testosterone production.

4. ACTH – targets the adrenal cortex and causes the secretion of glucocorticoids.

5. GH - targets most bodily tissues and stimulates metabolism and growth of those tissues.

6. PRL - targets the breasts in females. Stimulates breast development and lactation.

Of the six anterior pituitary hormones, four directly stimulate other endocrine glands and are known as tropic hormones (TSH, ACTH, FSH, LH).

Targets and Functions of the Posterior Pituitary Hormones

1. ADH- antidiuretic hormone (vasopressin) – stimulates water reabsorption by kidneys.

2. Oxytocin – stimulates labor contractions during birth.

Hypothalamic-Pituitary (hypophysis) Regulation

• Controls many functions of several endocrine glands

• Produces releasing hormones that stimulate the production of trophic hormones by anterior pituitary

One of the most important features of the endocrine system is its regulation (control) by negative feedback. This means that the glands within the endocrine system that stimulate the release of a hormone (for example, the pituitary) from another gland (for example, the thyroid) are eventually shut off, in a sense, so that too much hormone is not produced and a hormone imbalance is avoided.

An example of negative feedback is the regulation of the blood calcium level. The parathyroid glands secrete parathyroid hormone, which regulates the blood calcium amount. If calcium decreases, the parathyroid glands sense the decrease and secrete more parathyroid hormone. The parathyroid hormone stimulates calcium release from the bones and increases the calcium uptake into the bloodstream from the collecting tubules in the kidneys. Conversely, if blood calcium increases too much, the parathyroid glands reduce parathyroid hormone production. Both responses are examples of negative feedback because in both cases the effects are negative (opposite) to the stimulus.

A small number of hormones are regulated by the positive feedback mechanism. This occurs when rising levels of a hormone cause another gland to release a hormone that is stimulating to the first.

An example of positive feedback can be found in childbirth. The hormone oxytocin stimulates and enhances labor contractions. As the baby moves toward the vagina (birth canal), pressure receptors within the cervix (muscular outlet of uterus) send messages to the brain to produce oxytocin. Oxytocin travels to the uterus through the bloodstream, stimulating the muscles in the uterine wall to contract stronger (increase of ideal normal value). The contractions intensify and increase until the baby is outside the birth canal. When the stimulus to the pressure receptors ends, oxytocin production stops and labor contractions cease.

Also, exogenous forms of hormones (drugs) can influence the normal feedback control of hormones production and release. 

Disorders of the Endocrine System

Pituitary

The most frequent cause of pituitary disorders is pituitary gland tumors. The pituitary gland is made of several cell types. Sometimes these cells grow too much or produce small growths.

These growths are called pituitary tumors, and they are fairly common in adults. These are not brain tumors and are not a form of cancer. In fact, cancerous tumors of this sort are extremely rare. Pituitary tumors, however, can interfere with the normal formation and release of hormones.

Two types of tumors exist - secretory and non-secretory.

Hypersecretion

Hyposecretion

Tumor mass effects

• GH levels (normal or elevated)
• Decreased birth length
• Decreased growth rate
• Normal intelligence
• Short stature
• Obesity with immature facial features
• Delay in skeletal maturation
• Delayed puberty

• Present in childhood or adult onset
• Increased cardiovascular mortality
• CV risk factors (central adiposity, insulin resistance and dyslipidemia-metabolic syndrome)

Gigantism

Acromegaly

Thyroid Disorders

The thyroid gland has two lobes connected by an isthmus (small connecting stalk) and is in the lower part of the neck just below the larynx. The thyroid gland is the biggest gland in the neck. The thyroid gland takes the shape of a butterfly with the two wings being represented by the left and right thyroid lobes which wrap around the trachea. Thyroid hormone has two major functions:  it increases metabolism and protein synthesis and it is necessary for growth and development in children.

The thyroid gland produces three hormones:

• Thyroxine (T4)
• Triiodothyronine (T3)
• Calcitonin

T4 and T3 help oxygen get into cells, and make your thyroid the master gland of metabolism. The thyroid has the only cells in the body capable of absorbing iodine. The thyroid takes in iodine, obtained through food, iodized salt, or supplements, and combines it with the amino acid tyrosine. The thyroid then converts the iodine/tyrosine into the hormones T3 and T4. The "3" and the "4" refer to the number of iodine molecules in each thyroid hormone molecule. Once released by the thyroid, the T3 and T4 travel through the bloodstream. The purpose is to help cells convert oxygen and calories into energy.

The secretion of the thyroid hormone is regulated by the hypothalamic-pituitary-thyroid feed. The hypothalamus senses low circulating levels of thyroid hormone (T3 and T4) and responds by releasing thyrotropin-releasing hormone (TRH). The TRH stimulates the pituitary to produce thyroid-stimulating hormone (TSH). The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland.

Hypothyroidism:

CLINICAL MANIFESTATIONS

Hypothyroidism:

ETIOLOGY

Hypothyroidism:

PATHOGENESIS

Hyperthyroidism: 

ETIOLOGY

Hyperthyroidism:

PATHOGENESIS

Hyperthyroidism:

CLINICAL MANIFESTATIONS

Parathyroid Disorders

Parathyroid glands are small glands of the endocrine system which are located in the neck behind the thyroid. Parathormone is the parathyroid hormone. This hormone plays a key role in regulating and maintaining a balance of your body's levels of two minerals — calcium and phosphorus. Parathyroid glands control the calcium in our bodies--how much calcium is in our bones, and how much calcium is in our blood. Calcium is the most important element in our bodies (we use it to control many systems), so calcium is regulated very carefully. Parathyroid glands (we all have 4 of them) are normally the size of a grain of rice. Occasionally they can be as large as a pea and still be normal.

Serum calcium levels provide the feedback necessary to regulate parathyroid hormone (PTH) secretion. A decrease in serum calcium causes a release of PTH. An elevated serum calcium level leads to suppression of PTH secretion. Not under the control of the hypothalamic-pituitary system.

Hyperparathyroidism:

ETIOLOGY

Hyperparathyroidism:

PATHOGENSIS

Hyperparathyroidism:

CLINICAL MANIFESTATIONS

Hypoparathyroidism:

ETIOLOGY

Hypoparathyroidism:

PATHOGENESIS

Hypoparathyroidism:

CLINICAL MANIFESTATIONS

The manifestations of acute hypocalcemia include numbness, paresthesias of the distal extremities, muscle cramps, fatigue, anxiety and depression. Severe symptoms include carpopedal spasm, laryngospasm, and seizures. You will also neuromuscular irritability. This neuromuscular instability can also be displayed through the elicitation of the Chvostek's sign and Trousseau's sign.

Hypercalcemia, polyuria, dehydration, anorexia, nausea, vomiting, constipation, bradycardia, heart block, and cardiac arrest.

Adrenal Glands

The adrenal glands work interactively with the hypothalamus and pituitary gland in the following process:

• the hypothalamus produces corticotropin-releasing hormones, which stimulate the pituitary gland.
• the pituitary gland, in turn, produces corticotropin hormones, which stimulate the adrenal glands to produce corticosteroid hormones.
• the glucocorticoids and the adrenal androgens is controlled by the ACTH secreted by the anterior pituitary gland

the outer portion of the adrenal gland, secretes hormones that have an effect on the body's metabolism, on chemicals in the blood, and on certain body characteristics. The adrenal cortex secretes corticosteroids and other hormones directly into the bloodstream. The hormones produced by the adrenal cortex include:

• Glucocorticoids (corticosteroid hormones)- regulated by the negative feedback mechanism of the hypothalamic-pituitary-adrenal system (HPA). 
• hydrocortisone hormone - this hormone, also known as cortisol, controls the body's use of fats, proteins, and carbohydrates.
• corticosterone - this hormone, together with hydrocortisone hormones, suppresses inflammatory reactions in the body and also affects the immune system.
• Mineralocorticoids (aldosterone hormone) - this hormone inhibits the level of sodium excreted into the urine, maintaining blood volume and blood pressure. Regulates potassium and sodium levels and water balance. Regulated by the renin-angiotension mechanism and blood levels of potassium.
• Adrenal Androgens (androgen hormones) - these hormones have minimal effect on the development of male characteristics.

the inner part of the adrenal gland, is not essential to life, but helps a person in coping with physical and emotional stress. The adrenal medulla secretes the following hormones:

• epinephrine (also called adrenaline) - this hormone increases the heart rate and force of heart contractions, facilitates blood flow to the muscles and brain, causes relaxation of smooth muscles, helps with conversion of glycogen to glucose in the liver, and other activities.
• norepinephrine (also called noradrenaline) - this hormone has little effect on smooth muscle, metabolic processes, and cardiac output, but has strong vasoconstrictive effects, thus increasing blood pressure.

Addison disease:

ETIOLOGY

Addison disease:

PATHOGENESIS

Addison disease:

CLINICAL MANIFESTATIONS

Cushing Syndrome:

ETIOLOGY

Cushing Syndrome:

PATHOGENESIS

When too much cortisol is produced in the adrenal glands, or an excess is taken in treating other diseases, significant changes occur in all of the tissues and organs of the body. All of these effects together are called Cushing Syndrome.

Spontaneous overproduction of cortisol in the adrenals is divided into two groups - those due to an excess of ACTH and those that are independent of ACTH.

Cushing Syndrome:

CLINICAL MANIFESTATIONS

Pheochromocytoma:

Pheochromocytoma:

PATHOGENSIS

Pheochromocytoma:

CLINICAL MANIFESTATIONS

Diabetes Mellitus (DM), Types 1 and 2:

ETIOLOGY

Type 1: Characterized by an absolute insulin deficiency caused by pancreatic cell failure; two forms include immune-mediated and idiopathic DM.

Type 2: Characterized by a relative insulin deficiency caused by decreased tissue sensitivity and responsiveness to insulin; risk factors include aging, sedentary lifestyle, obesity, and genetic predisposition.

Diabetes Mellitus (DM), Types 1 and 2:

PATHOGENESIS

Type 1: bCells of the pancreas are destroyed, resulting in loss of insulin production.

Immune mediated: Associated with certain HLA genetic makeup; may be autoimmune; viral infection or exposure to a toxic agent may be a responsible environmental influence.

Idiopathic: Associated with b-cell destruction without autoimmune markers.

Type 2: Relative insulin deficiency is caused by decreased tissue sensitivity and responsiveness to insulin; a decreased number of insulin receptors or abnormal translocation of glucose transporters is suspected; as the disease progresses, insulin production may become impaired.

Diabetes Mellitus (DM), Types 1 and 2:

CLINICAL MANIFESTATIONS

Diagnosed if any of the following occur more than once: random blood glucose level ³200 mg/dl with classic signs and symptoms; fasting blood glucose level >126 mg/dl ´ 2, or blood glucose level >200 mg/dl 2 hours after a 75 g oral glucose load is given.

Classic signs and symptoms include polyuria, polydipsia, polyphagia, and weight loss (less severe in type 2). Type 1 is more prone to development of ketoacidosis; type 2 is more prone to development of hyperglycemic hyperosmolar nonketotic syndrome (HHNS).

Chronic complications of DM are primarily caused by vascular and neuropathic dysfunction; complications include coronary artery disease, stroke, peripheral vascular disease, retinopathy, nephropathy, and neuropathy.