Chapter 7 The endocrine system

1. Chapter 7 The endocrine system The endocrine system, along with the nervous system, allows for communication between distant sites in the body. the endocrine system has three components : 1-endocrine glands that secrete chemical messengers into the bloodstream; 2-the chemical messengers themselves, called hormones; 3-and the target cells or organs that respond to the hormones.

2. Conditions of Disease or Injury Hypothyroidism Result from malfunction of the thyroid gland, the pituitary, or the hypothalamus. -If it results from thyroid gland malfunction, low TH (thyroxin hormone) levels are accompanied by high TSH( thyroid stimulating hormone) and high TRH (thyroid releasing hormone) because of the lack of negative feedback on the pituitary and hypothalamus by TH. -If hypothyroidism results from pituitary malfunction, low levels of TH are caused by low TSH. TRH from the hypothalamus is high because there is no negative feedback on its release by TSH or TH.

4. Hypothyroidism caused by hypothalamic malfunction results in low TH, low TSH, and low TRH. Causes of Hypothyroidism • - Hashimoto's disease, also called autoimmune thyroiditis, results from autoantibody destruction of thyroid gland tissue. • - Endemic goiter is hypothyroidism caused by a dietary deficiency of iodide. N.b., A goiter is an enlargement of the thyroid gland. • - Thyroid carcinoma may cause hypothyroidism or hyperthyroidism.

5. Clinical Manifestations • - Sluggishness and slow thinking, and slow movements. • - Decreased heart rate. • - Edema of the skin, especially under the eyes and in the ankles(myxedema) • - Intolerance to cold temperatures. • - Decreased metabolic rate, decreased caloric requirements, decreased appetite and nutrient absorption across the gut. • - Constipation Diagnostic Tools Measuring levels of TH (both T3 and T4), TSH, and TRH will allow diagnosis of the condition and localization of the problem .

6. Pediatric Consideration • Infants born without a thyroid gland or with defects in TH synthesis will develop congenital hypothyroidism, a disease sometimes referred to as cretinism. It is characterized by low TH, with high TSH and TRF. TH is necessary for all cells ,including cells of the central nervous system (CNS). Development of the CNS occurs in utero and for approximately 1 year after birth. Because an infant with congenital hypothyroidism was exposed to maternal TH in utero, it will be born neurologically intact. If TH is not replaced, severe mental retardation will result. With thyroxine replacement, CNS damage can be avoided.

7. Hyperthyroidism Hyperthyroidism is excessive levels of circulating TH. -Increased TH caused by malfunction of the thyroid gland is accompanied by decreased TSH and TRF, as a result of the negative feedback on their release by TH. -Hyperthyroidism caused by malfunction of the pituitary results in high TH and high TSH. TRF is low because of negative feedback from TH and TSH. -Hyperthyroidism caused by malfunction of the hypothalamus shows high TH accompanied by excess TSH and TRH.

8. Clinical Manifestations • - Increased heart rate. • - Increased muscle tone, tremors, irritability • - Increased basal metabolic rate and heat production, intolerance to heat, excess sweating. • - Weight loss, increased hunger. • - Exophthalmos (bulging of the eyes) may develop. • - Increased number of bowel movements. • - Goiter (usually). Diagnostic tools - Measuring levels of TH (both T3 and T4), TSH, and TRH will allow diagnosis of the condition and localization of the problem.

9. Adrenal Insufficiency Adrenal insufficiency is a decrease in the circulating level of the glucocorticoids. The mineralocorticoid aldosterone may also be reduced. Adrenal insufficiency may be caused by dysfunction of the adrenal gland, called primary adrenal insufficiency, or by dysfunction of the pituitary or hypothalamus. Both of these latter conditions cause secondary adrenal insufficiency.

10. Primary adrenal insufficiency is characterized by low levels of glucocorticoids, especially cortisol, accompanied by high ACTH( adreno corticotropic hormone) and high CRH( cortzone releasing hormone) because there is no negative feedback on their release. • If the cause of adrenal insufficiency is secondary to a pituitary dysfunction, low glucocorticoids will be accompanied by low ACTH and high CRH. In this case, adrenal androgens will also be low. If there is zero ACTH, aldosterone levels will be reduced. • If adrenal insufficiency is caused by a hypothalamus malfunction, the glucocorticoids, ACTH, and CRH will be low.

11. Diseases of Adrenal Insufficiency • Primary adrenal insufficiency, called Addison's disease, occurs from destruction of the adrenal cortex. The disease is usually autoimmune, and may results from infections such as TB or tumors. Addison's disease is characterized by low glucocorticoid levels accompanied by high ACTH and high CRH. Total loss of the adrenal gland results in the loss of adrenal androgens and aldosterone as well. Aldosterone deficiency leads to increased loss of sodium in the urine, resulting in hyponatremia (decreased sodium in the blood), dehydration, and hypotension (water follows salt). Decreased potassium excretion in the urine will lead to hyperkalemia (increased potassium concentration in the blood).

12. Clinical Manifestations • - Depression, because cortisol levels influence mood and emotions. • - Fatigue, related to hypoglycemia, and decreased gluconeogenesis. • - Anorexia, vomiting, diarrhea, and nausea. • - Hyperpigmentation of the skin if ACTH levels are high (primary adrenal insufficiency) as ACTH has melanin-stimulating hormone like effects on the skin. • - Sparse body hair in women, if the adrenal cells producing androgens are destroyed . • - Inability to respond to stressful situations, perhaps leading to severe hypotension.

13. Glucocorticoid Excess Glucocorticoid excess refers to any condition in which there are very high levels of circulating glucocorticoids. The cause of glucocorticoid excess may be at the level of the adrenal gland or at the pituitary/hypothalamic level. If the cause is primary adrenal gland hypersecretion, (usually an adrenal tumor present). In this situation, low ACTH and low CRH levels will be present as a result of negative feedback. Adrenal androgen levels will be low because ACTH is low. Bronzing of the skin will not occur.

14. Diseases of Excess Glucocorticoids • - Cushing's syndrome refers to any condition of high glucocorticoids and includes glucocorticoid excess caused by therapeutic administration of corticosteroids. • - Cushing's disease refers to high glucocorticoids caused specifically by malfunction of the anterior pituitary resulting in excess ACTH. Clinical Manifestations • - Altered fat metabolism leading to fat pads on the back (buffalo hump), moon face, protruding abdomen with thin extremities, and stretch marks on breasts, thighs, and abdominal surface.

15. - Muscle weakness from protein breakdown. • - Hypertension as a result of increased catecholamine responsiveness. • - Weight gain resulting from strong appetite stimulation. • - Inhibition of immune and inflammatory reactions, leading to poor wound healing. • - Masculinization of women and children as a result of adrenal androgen stimulation if ACTH levels are high. • - Bronzing of the skin if ACTH levels are high.

16. Growth Hormone Deficiency(Pituitary Dwarfism) • Growth hormone deficiency is a decrease in circulating levels of GH. Most cells of the body will be affected. GH deficiency is usually clinically recognized only in children. Usually is caused by a pituitary adenoma . • Clinical Manifestations • - proportional short stature . • - Delayed onset of puberty Growth Hormone Excess • Growth hormone excess is the increase in circulating levels of GH usually caused by a GH-secreting tumor of the anterior pituitary.

17. Diseases of GH Excess • - Gigantism, a disease of excess longitudinal growth of the bones of the skeleton, is seen as a result of GH excess before puberty. • - Acromegaly, a disease of connective tissue proliferation, is seen in adults with GH excess. Because long bone growth has stopped in adults, GH excess cannot cause growth of the skeleton. It is associated with growth of the cartilage of the hands, feet, nose, jaw, chin, and facial bones. Clinical Manifestations • - Tall stature with gigantism. • - Thickening of the fingers, jaw, forehead, hands, and feet with acromegaly.

18. Gonadotropin Deficiency Gonadotropin deficiency is a decrease in circulating levels of FSH and LH. Clinical Manifestations • - Amenorrhea (lack of menstrual periods), vaginal, uterine, and breast atrophy in women. • - Testicular atrophy and reduction in beard growth in men.

19. Syndrome of Inappropriate Antidiuretic Hormone (ADH) (SIADH) is characterized by increased release of ADH from the posterior pituitary Clinical Manifestations • - Water retention and weight gain. • - Decreased urinary output. • - Nausea and vomiting worsening with the degree of water intoxication. Diagnostic Tools Blood tests measuring increased levels of ADH with low plasma sodium concentration ( hyponatremia) .

20. Diabetes Insipidus Diabetes insipidus is a disease of decreased ADH production. Clinical Manifestations - Large volumes of dilute urine. - Polydipsia (excessive thirst). Diagnostic Tools Blood tests measuring decreased levels of ADH with hypernatremia will allow diagnosis of the condition. Complications Severe dehydration may occur if large volumes of drinking water are unavailable.