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The Endocrine System/Part II

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1 The Endocrine System/Part II
Joe Pistack MS/ED

2 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.

3 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.

4 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)

5 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. T3 and T4 have similar functions but T3 is the more potent of the two.

6 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.

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

8 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. Early diagnosis and and prompt treatment with thyroid hormone will prevent further developmantal delay.

9 Hyperthyroidism Hyperthyroidism-caused by an excess of thyroid hormone. Metabolic state is “sped-up”. At risk for developing fast rhythm disorders of the heart.

10 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

11 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. If the bulging is severe , it may be difficult for the patient to close eyelids over cornea. The exposed cornea may then dry out, ulcerate, and scar, leading to loss of vision.

12 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.

13 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. With insufficient iodine, thyroid hormones cannot be made in quantities great enough to shut off the secretion of TSH through negative feedback.

14 Iodine Deficiency Enlarged Thyroid gland is called a goiter.
Diagnosis is usually made by ultrasound.

15 Calcitonin Calcitonin-secreted by the parafollicular cells of the thyroid gland. Calcitonin helps regulate blood levels of calcium.

16 Parathyroid Glands Four tiny glands that lie along the posterior surface of the thyroid gland. Secretes parathyroid hormone (PTH).

17 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.

18 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).

19 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.

20 Adrenal Glands small glands located above the kidneys.
Consists of two regions: Inner medulla Outer cortex

21 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

22 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.

23 Adrenal Cortex Outer region of the adrenal gland.
Secretes hormones called steroids. Three steroids- Glucocorticoids Mineralcorticoids Sex hormones

24 Adrenal Cortex Adrenal cortical hormones are essential for life.
Adrenal cortical hormones regulate: Glucocorticoids sugar Mineralcorticoids salt Sex hormones sex

25 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.

26 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.

27 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.

28 Adrenal Cortex Sex hormones: Secreted in small amounts.
Female hormones-estrogens. Male hormones-androgens.

29 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.

30 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.

31 Cushing’s Syndrome

32 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.

33 Addison’s Disease

34 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.

35 The Pancreas

36 Pancreas Islets of Langerhans contain two types of cells:
Alpha cells-secrete glucagon. Beta cells-secrete insulin. Both regulate blood sugar.

37 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.

38 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.

39 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.

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

41 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.

42 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.

43 Thymus Gland

44 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.

45 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.

46 Pineal Gland

47 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.

48 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.


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