The Endocrine System Glands and Hormones By: Ashley Moran
Overview Second messenger system of the body Uses chemical messages (hormones) that are released into the blood Hormones control several major processes - Reproduction - Growth and development - Mobilization of body defenses - Maintenance of much of homeostasis - Regulation of metabolism
Overview Secretion of most hormones is regulated by a negative feedback system The number of receptors for a specific hormone can be altered to meet the body’s demand
Hormone Overview Hormones are produced by specialized cells Cells secrete hormones into extracellular fluids Blood transfers hormones to target sites These hormones regulate the activity of other cells
Chemical Classification of HormonesSteroid Hormones: Lipid soluble Diffuse through cell membranes Enter the nucleus Bind to a specific protein within the nucleus Bind to specific sites on the cell’s DNA Activate genes that result in synthesis of new proteins
Chemical Classification of HormonesNonsteroid Hormones: Hormone binds to a membrane receptor Hormone does not enter the cell Sets off a series of reactions that activates an enzyme Catalyzes a reaction that produces a second messenger molecule Oversees additional intracellular changes to promote a specific response
Negative Feedback System Negative feedback is the primary mechanism through which your endocrine system maintains homeostasis Secretion of a specific hormone s turned on or off by specific physiological changes (similar to a thermostat) EXAMPLE: plasma glucose levels and insulin response
Pineal Gland Small pine cone shaped gland that is part of the thalamus region of the brain. Glands secrete melatonin, a hormone that plays a role in regulating the bodys circadian rhythm.
Hypothalamus In brain just superior to pituitary Made of modified nervous tissue Secretes hormones that are stored in posterior pituitary Stimulates pituitary
Pituitary gland “Master gland” of body Located in the depression of sphenoid bone Produces many hormones that affect other glands: − Thyroid stimulating hormone − Somatotropin- growth hormone − Lutenizing (LH)- causes ovulation − ICSH- causes testes to secrete testosterone − Melanocyte stimulating- distribution of melanin in skin − ADH- antidiuretic hormone Secretion is controlled by the hypothalamus in the base of the brain
Thyroid Found at the base of the throat Consists of two lobes and a connecting isthmus Produces two hormones − Thyroid hormone − Calcitonin
Thyroid Hormone Within the colloid are the thyroid hormones − Thyroxine (T4) – secreted by thyroid follicles − Triiodothyronine (T3) – conversion of T4 at target tissues * When stimulated (by TSH or by cold), these are released into the circulatory system and ↑ the metabolic rate. “C” cells within the thyroid produce the hormone calcitonin.
Parathyroid Glands Tiny masses on the posterior of the thyroid Secrete parathyroid hormone: − Stimulates osterclasts to remove calcium from bone − Stimulates the kidneys and intestine to absorb more calcium − Raise calcium levels in the blood
Thymus Located on superior surface of the heart Thymosin – controls production and maturation of lymphocytes Reaches maximum size during puberty, then shrinks making elderly people more susceptible to disease
Adrenal Glands Located just above the kidneys Secretes many hormones Epinephrine Norepinephrine Many steroid hormones, inc estrogen and androgens. The Adrenal Medulla secretes the catecholamine hormones norepinephrine and epinephrine
Pancreas Located slightly behind the stomach Secretes insulin, a type of hormone that transports glucose into cells. It: − Promotes glycogenesis − Inhibits gluconeogensis Also secretes glucagon which increases glucose in bloodstream
Reproductive GlandsGonads and Ovaries: the endocrine glands associated with human reproduction, both have endocrine functions. Female ovaries produce eggs Male gonads produce sperm
Reproductive GlandsOvaries: Located in the abdominal cavity adjacent to the uterus. Under the control of LH and FSH from the anterior pituitary they manufacture estrogen and protesterone Estrogen and Progesterone have several functions, including sexual development and preparation of the uterus for implantation of the egg.Testes: Located in the scrotum Produce sperm for reproduction Manufacture testosterone - promotes male growth and masculinization Controlled by anterior pituitary hormones FSH and LH.
Disorders and Illnesses of the Endocrine System Endocrine illnesses can mostly be divided into 3 groups: − Gland hyposecretion − Gland hypersecretion − Abnormal growth Some examples of these include − Hypothyroidism (hyposecretion) − Polycystic ovary syndrome (hypersecretion) − Goiter (growth)
Hypothyroidism The most common cause of hypothyroidism is inflammation of the thyroid gland, which damages the glands cells. Signs and symptoms: − A physical examination may reveal a smaller than normal thyroid gland, although sometimes the gland is normal size or even enlarged (goiter). The examination may also reveal: − Brittle nails/ hair, pale or dry skin, swelling of the arms and legs − A chest x-ray may show an enlarged heart. Laboratory tests to determine thyroid function include: − TSH test and T4 test Lab tests may also reveal: − Anemia on a complete blood count (CBC) − Increased cholesterol levels − Increased liver enzymes − Increased prolactin − Low sodium
Hypothyroidism Treatment − The purpose of treatment is to replace the thyroid hormone that is lacking. Levothyroxine is the most commonly used medication. Doctors will prescribe the lowest dose possible that effectively relieves symptoms and brings your TSH level to a normal range. If the patient has heart disease or you are older, his/her doctor may start with a very small dose. − Lifelong therapy is required unless the patient has a condition called transient viral thyroiditis. − The patient must continue taking his/her medication even when the symptoms go away. When starting medication, his/her doctor may check hormone levels every 2 - 3 months. After that, thyroid hormone levels should be monitored at least every year.
Polycystic ovary syndrome One of the most common female endocrine disorders affecting 5% to 10% of women of reproductive age (12-45 years old) It is a complex, heterogeneous disorder of uncertain etiology, but there is strong evidence that it can to a large degree be classified as a genetic disease The principal features are: − Anovulation- resulting in irregular menstruation, − Amenorrhea- ovulation-related infertility − Polycystic Ovaries- excessive amounts or effects of androgenic (masculinizing) hormones, resulting in acne, hirsutism and insulin resistance, often associated with obesity, Type 2 diabetes, and high cholesterol levels. The symptoms and severity of the syndrome vary greatly among affected women
Polycystic ovary syndrome Diagnosing PCOS − History taking, specifically for menstrual pattern, obesity, hirsutism, and the absence of breast development − Gynecologic ultrasonography − Laparoscopic examination may reveal a thickened, smooth, pearl-white outer surface of the ovary − Various lab tests such as lipid profile, fasting glucose tolerance test, and serum levels of androgens Treatment − Diet and exorcise is the best treatment because it helps to stabilize and regulate the bodys hormones − Medications such as Metformin can help with insulin resistance, birth control pills can regulate menstrual cycles, Clomid for infertility, etc.
Non-toxic Goiter Enlargement of the thyroid that is not associated with overproduction of thyroid hormone or malignancy. The thyroid can become very large so that it can easily be seen as a mass in the neck. There are a number of factors that may cause the thyroid gland to become enlarged: − A diet deficient in iodine can cause a goiter, but this is rarely the cause because of the readily available iodine in our diets. − A more common cause of goiter in America is an increase in thyroid stimulating hormone (TSH) in response to a defect in normal hormone synthesis within the thyroid gland. Diagnosis of goiter: − Thyroidal radioactive iodine uptake − Thyroid scan − Laboratory tests such as measurement of serum free thyroxine (free T4) or free T4 index and total triiodothyronine
Non-toxic Goiter Treatment (depending on cause) − In iodine-deficient areas, iodine supplementation of salt; oral or IM administration of iodized oil yearly; and iodination of water, crops, or animal fodder eliminates iodine-deficiency goiter. Goitrogens being ingested should be stopped. − In other instances, suppression of the hypothalamic- pituitary axis with thyroid hormone blocks TSH production (and hence stimulation of the thyroid). Full TSH- suppressive doses of l-thyroxine are useful in younger patients. l-Thyroxine is contraindicated in older patients with nontoxic nodular goiter, because these goiters rarely shrink and may harbor areas of autonomy so that l- thyroxine therapy can result in hyperthyroidism. − Large goiters occasionally require surgery or 131I to shrink the gland enough to prevent interference with respiration or swallowing or to correct cosmetic problems.