The Endocrine System

• The pituitary, or hypophysis, is a small gland about the size of a cherry. It is located in a saddlelike depression of the sphenoid bone just posterior to the point where the optic nerves cross. It is surrounded by bone except where it connects with the hypothalamus of the brain by a stalk called the infundibulum

• The hormones produced in the anterior pituitary are not released until chemical messengers called releasing hormones arrive from the hypothalamus. These releasing hormones travel to the anterior pituitary by way of a special type of circulatory pathway called a portal system. By this circulatory “detour,” some of the blood that leaves the hypothalamus travels to capillaries in the anterior pituitary before returning to the heart. As the blood circulates through the capillaries, it delivers the hormones that stimulate the release of anterior pituitary secretions.

The “Master Gland”

• Regulates and controls activities of all other endocrine glands!

• Located at the midpoint of the skull, roughly behind the eyes and very close to the major arteries & veins carrying blood to and from the vein (WHY??)

• Made up of 3 sections: Anterior, Intermediate and Posterior Lobes

Anterior Lobe

• The front part of the pituitary gland• Hormones produced regulate metabolic activities of cells

and stimulate other endocrine glands

Produces 6 different hormones:1. Growth hormone (HGH)2. Thyroid-Stimulating Hormone (TSH)3. Adrenocorticotropic Hormone (ACTH)4. Follicle-Stimulating Hormone (FSH)5. Luteinizing Hormone (LH)6. Prolactin (PRL)

• Growth Hormone: also known as somatotropin or somatropin, is a peptide hormone that stimulates growth, cell reproduction and regeneration

• Thyroid-Stimulating Hormone: (also known as TSH or thyrotropin) is a hormone that stimulates the thyroid gland to produce thyroxine , and then triiodothyronine which stimulates the metabolism of almost every tissue in the body

• Adrenocorticotropic Hormone (ACTH): also known as corticotropin, is often produced in response to biological stress. Its principal effects are increased production and release of corticosteroids

• ACTH is also related to the circadian rhythm in many organisms

• Follicle-Stimulating Hormone: FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and luteinizing hormone (LH) act synergistically in reproduction. Specifically, an increase in FSH secretion by the anterior pituitary causes ovulation.

• Luteinizing Hormone (LH): also known as lutropin. In females, an acute rise of LH ("LH surge") triggers ovulation and development of the corpus luteum. In males, it stimulates Leydig cell production of testosterone. It acts synergistically with FSH.

• Prolactin(PRL): stimulates the mammary glands to produce milk (lactation), counteracts the effects of dopamine, linked to production of testosterone and estrogen

The Thyroid Gland

• Produces hormones that regulate metabolism, body heat and growth

• Located on the front of the neck, just below the larynx

• Consists of 2 lobes, 1 on either side of the trachea

• Produces Thyroxine which regulates the way cells release energy to create other substances such as protein

Thyroid Hormone - Thyroxine

• Overproduction: hyperthyroidism causes tiredness, anxiety, weight loss, diarrhea and intolerance to heat

• Underproduction: hypothyroidism causes tiredness, dry skin, hair loss, weight gain, constipation and hypersensitivity to cold

Parathyroid Glands

• Found on the lobes of the thyroid gland

• Produces Parathyroid Hormone which regulates the body’s calcium and phosphorus balance

Adrenal Glands

Consist of 2 parts: 1. Adrenal cortex (outer)2. Adrenal medulla

(inner)

Adrenal Cortex

• Absolutely essential for life• Produces Aldosterone which inhibits the

amount of sodium excreted in urine (a key part of regulating blood pressure and blood volume)

• Also produces Hydrocortisone, Corticosterone and Androgen which play a role in metabolizing fats, proteins and carbohydrates, as well as inhibiting inflammation of tissues

Adrenal Medulla

• Secretes the hormone Epinephrine (adrenalin – the ‘fight or flight’ hormone) and Norepinephrine

• Epinephrine increases heart rate, BP and respiration and suppresses digestion (WHY??)

• Norepinephrine (noradrenalin) increases heart rate, blood flow to the brain and skeletal muscle, triggers the release of glucose from energy stores

The Pancreas

• Part of both the endocrine and digestive systems

• Located behind the stomach, attached to the small intestine by a duct that transports its digestive juices to the intestine

• The Pancreas is the site of the Islets of Langerhans; endocrine cells within the pancreas that secrete 2 hormones essential for maintaining blood sugar levels:

• Insulin –stimulates the liver to remove glucose from the blood and convert it into glycogen for storage, thus lowering blood sugar levels

• Glucagon – stimulates the liver to convert glycogen into glucose and release it into the blood for use in the body’s cells, thus increasing blood sugar levels

The Gonads

• Ovaries in females and Testes in males• Hormones released by these glands are

responsible for spermatogenesis and ovulation and the development and maintenance of secondary sex characteristics such as muscle & bone mass, body and facial hair

• Controlled by the Pituitary Gland

Ishihara Test

• The Ishihara Color Test is an example of a color perception test for red-green color deficiencies.

• The test consists of a number of colored plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in color and size. Within the pattern are dots which form a number or shape clearly visible to those with normal color vision, and invisible, or difficult to see, to those with a red-green color vision defect, or the other way around.