The Endocrine System/Part II

Joe Pistack MS/ED

Thyroid Gland

• Largest of the endocrine glands.

• Situated on the front sides of the trachea.

• Butterfly-shaped, has two lobes connected by a tissue band called the isthmus.

Thyroid Gland• Thyroid gland contains two

types of cells:

• Follicular cells-located within the thyroid follicle. Secrete T3 and T4 (discussed later)

• Parafollicular cells-located between the follicles.

• Each type of cells secrete a particular hormone.

Thyroid Gland

• Composed of secretory units called follicles.

• Each follicle is filled with a clear, viscous substance called colloid.

• Follicular cells secrete two thyroid hormones:• (1) triiodothyronine (T3)• (2) tetraiodothyronine (T4 or thyroxine)

Thyroid Gland

• Functions of T3 and T4:

• Regulate all phases of metabolism and are necessary for the proper functioning of all other hormones.

• Thyroid hormones are necessary for the normal maturation of the nervous system and for normal growth and development.

Hypothyroidism

• Adult-results in a condition called Myxedema.

• Myxedema-slowed metabolic state.

• Skin becomes thick and puffy due to accumulation of a thick fluid under the skin.

Hypothyroidism

• Signs/Symptoms:• Slow heart rate• Sluggish peristalsis• Constipation• Low body temperature• Low energy• Loss of hair• Weight gain

Hypothyroidism• Cretinism-infant born

with no thyroid gland.• Fails to develop both

physically and mentally.• Child will be short and

stocky with abnormal skeletal development and severe mental retardation.

Hyperthyroidism

• Hyperthyroidism-caused by an excess of thyroid hormone.

• Metabolic state is “sped-up”.

• At risk for developing fast rhythm disorders of the heart.

Hyperthyroidism• Grave’s disease-common type of

hyperthyroidism.• Signs/Symptoms:• Increased heart rate• Increased peristalsis/diarrhea• Elevation in body temperature• Hyperactivity• Weight loss • Emotional swings

Hyperthyroidism

• Grave’s disease is also characterized by bulging eyes (exophthalmia).

• Bulging of eyes is caused by fat pads behind the eyeballs pushing the eyeballs forward in the eye socket.

Iodine• Synthesis of T3 and T4 requires iodine.

• Iodine in the body comes from dietary sources.

• Most of the iodine in the blood is pumped into the follicular cells of the thyroid hormones where it is used in the synthesis of thyroid hormones.

Iodine Deficiency• Iodine deficient state –T3 and T4 production

decreases because iodine is necessary for the synthesis of the thyroid hormones.

• With insufficient iodine, negative feedback is not possible.

• Persistent stimulation of the thyroid gland by TSH causes thyroid to enlarge.

Iodine Deficiency

• Enlarged Thyroid gland is called a goiter.

Diagnosis is usually made by ultrasound.

Calcitonin

• Calcitonin-secreted by the parafollicular cells of the thyroid gland.

• Calcitonin helps regulate blood levels of calcium.

Parathyroid Glands

• Four tiny glands that lie along the posterior surface of the thyroid gland.

• Secretes parathyroid hormone (PTH).

Parathyroid Glands• Low blood level of calcium stimulates the

release of PTH.

• PTH has three target organs:– Bone– Digestive tract– Kidneys

• Overall effect of PTH is to increase calcium levels.

Parathyroid Gland• Hypocalcemia-low calcium levels.

• Calcium deficiency results in continuous muscle contraction known as tetany.

• Contorts the wrist , can cause sustained contraction of the muscles of the larynx

(laryngospasm).

Hypercalcemia• Increased calcium level.

• PTH stimulates osteoclastic activity in the bones, moves calcium out of the bone causing hypocalcemia.

• Hypercalcemia depresses the nervous, cardiac and GI systems causing fatigue, bradycardia, anorexia and constipation.

Adrenal Glands

• small glands located above the kidneys.

• Consists of two regions:

• Inner medulla• Outer cortex

Adrenal Medulla

• Inner region of the adrenal gland, considered an extension of the sympathetic nervous system “fight or flight”.

• Catecholamines- Hormones that are secreted in emergency situations. They are:

– Epinephrin (adrenaline)– Norepinephrine

Adrenal Medulla• Catecholamines help the body respond to

stress by:• Elevating blood pressure.• Increasing heart rate.• Convert glycogen to glucose in the liver, more

glucose available to the cells.• Increases metabolic rate, making more energy.• Opens up the bronchial passages.

Adrenal Cortex• Outer region of the

adrenal gland.

• Secretes hormones called steroids.

• Three steroids-• Glucocorticoids• Mineralcorticoids• Sex hormones

Adrenal Cortex

• Adrenal cortical hormones are essential for life.

• Adrenal cortical hormones regulate:• Glucocorticoids sugar• Mineralcorticoids salt• Sex hormones sex

Adrenal Cortex• Glucocorticoids-convert amino acids into

glucose (gluconeogenesis).

• Maintain blood glucose levels between meals.

• Ensures steady supply of glucose for the brain and other cells.

• Chief glucocorticoid is cortisol.

Adrenal Cortex• Cortisol is secreted in greater amounts during

stress. (physiological stress, disease, physical injury, emotional stress).

• Has an anti-inflammatory effect.

• Ex. Cortisol-like drug-prednisone, used in treatment of arthritis or severe allergic response.

Adrenal Cortex• Mineralocorticoids:

• Aldosterone-chief mineralocorticoid.

• Plays a role in the regulation of blood volume and blood pressure and in the concentration of electrolytes.

• Called salt retaining hormone.

Adrenal Cortex

• Sex hormones:

• Secreted in small amounts.

• Female hormones-estrogens.

• Male hormones-androgens.

Adrenal Gland• Adrenal insufficiency is life threatening and

must be treated with steroids and replacement of fluids and electrolytes.

• Hypersecretion-excess of adrenal cortical hormones.

• Cushing’s syndrome-elevated blood levels of steroids, such as prednisone.

Adrenal Cortex• Cushing’s syndrome s/s:• Truncal obesity.• Rounded facial appearance (moon face).• Excess fat deposition between the shoulders

(buffalo hump).• Facial hair (hirsutism).• Thin skin that bruises easily.• Bone loss .• Muscle weakness.

Cushing’s Syndrome

Adrenal Gland• Hyposecretion-adrenal gland fails to secrete

adequate amounts of adrenal cortical hormones.

• Addison’s disease-adrenal insufficiency.

• s/s-generalized weakness, muscle atrophy, bronzing of the skin, severe loss of fluids and electrolytes.

Addison’s Disease

The Pancreas• Long slender organ that lies transversely

across the upper abdomen.

• Functions as an endocrine and exocrine gland.

• Secretes two hormones: insulin and glucagon.

• Islets of Langerhans-hormone-secreting cells of the pancreas.

The Pancreas

Pancreas

• Islets of Langerhans contain two types of cells:

• Alpha cells-secrete glucagon.

• Beta cells-secrete insulin.

• Both regulate blood sugar.

Pancreas• Insulin is released in response to increased

blood levels of glucose as occurs following a meal.

• Secretion of insulin decreases as blood levels of glucose decrease.

• Insulin has many target tissues, exerts widespread effects.

Insulin and Blood Glucose

• Insulin decreases blood glucose levels for two reasons:– Increases transport of glucose from the blood into

the cells.– Stimulates the cells to burn glucose as fuel.

• Insulin is the only hormone that lowers blood glucose.

Pancreas

• Hyperglycemia-excess glucose in the blood.• Signs/symptoms:• Glucosuria-glucose in the urine.• Polyuria-excretion of large volumes of urine.• Polydipsia-excessive thirst.• Polyphagia-excessive eating.• Acidosis-due to the rapid breakdown of fatty

acids.

Pancreas

• Hypoglycemia-low blood sugar.• Signs/symptoms:• Cool, clammy skin• Weakness• Pale• Lethargy• Headache• Shakiness

Gonads• Sex glands:

• Ovaries in female.• Testes in male.

• Ovaries secrete : estrogen and progesterone.– Females appear female because of estrogen

• Testes secrete : testosterone– Males appear male because of testosterone.

Thymus Gland

• Thymus gland-lies in the thoracic cavity behind the sternum.

• Larger in child than in an adult, becomes smaller as child hits puberty.

• Secretes the hormones called thymosins, play a role in immunity.

Thymus Gland

Pineal Gland

• Cone-shaped gland, located close to the thalamus in the brain.

• Called the body’s “biological clock” controlling many biorhythms.

• Secretes a hormone called melatonin.

Pineal Gland

• Plays a role in sexual maturation and the sleep-wake cycle.

• Melatonin secretion is lowest during the daylight hours and highest at night.

Pineal Gland

Prostaglandins• Hormones derived from a fatty acid called

arachidonic acid- a fatty acid found in the membranes of body cells

• Produced by many tissues.

• Chemical mediators of pain and inflammation, increase sensitivity of nerve endings to pain

• Aspirin and ibuprofin block synthesis of prostaglandins-useful in pain control.

As we Age• Alteration in the secretion of hormones.• Decrease in the levels of secretion of the

glands.• Decrease in the level of thyroid hormones and

decreased metabolic rate.• Decrease in the amount of growth hormone,

decrease in muscle mass and increase in storage of fat.

• Diminished circadian control.