1. ENDOCRINE SYSTEM

2.  Regulates metabolic activities in certain organs and tissues.  It acts by secretion of hormones which have slow and diffused effect.  These hormones are secreted directly to the blood stream to influence remote target organs  Regulates metabolic activities in certain organs and tissues.  It acts by secretion of hormones which have slow and diffused effect.  These hormones are secreted directly to the blood stream to influence remote target organs

3. Endocrine System Ductless Glands (thyroid) Clusters of Cells (Islets) Endocrine Cells (EE Cells)

4. STRUCTURESTRUCTURE  Connective Tissue Stroma: –Slender dense irregular collagenous connective tissue capsule, derived from the deep fascia of the neck. –Capsule sends septa which subdivide the gland into lobules. –Embedded within the capsule, on the posterior aspect, the parathyroid gland.  Connective Tissue Stroma: –Slender dense irregular collagenous connective tissue capsule, derived from the deep fascia of the neck. –Capsule sends septa which subdivide the gland into lobules. –Embedded within the capsule, on the posterior aspect, the parathyroid gland.

5. PARENCHYMAPARENCHYMA Composed of thyroid follicles which are formed of single layer of epithelial cells encircling a spherical space containing homogenous colloid. The epithelial cells vary from low cuboidal (in non active state) to columnar with microvilli (in active state). The follicular cells are joined by tight junctions near the lumen and by gap junctions along the lateral membranes. Composed of thyroid follicles which are formed of single layer of epithelial cells encircling a spherical space containing homogenous colloid. The epithelial cells vary from low cuboidal (in non active state) to columnar with microvilli (in active state). The follicular cells are joined by tight junctions near the lumen and by gap junctions along the lateral membranes.

6. The follicular cells have a rounded nuclei, basophilic cytoplasm, distended RER, lysosomes, rod-shaped mitochondria, supranuclear Golgi complex and numerous short microvilli extended into the colloid. Basal lamina and reticular fibers surround the epithelial follicular cells. Between follicles, there are network of blood vessels, unmyelinated sympathetic fibers The follicular cells have a rounded nuclei, basophilic cytoplasm, distended RER, lysosomes, rod-shaped mitochondria, supranuclear Golgi complex and numerous short microvilli extended into the colloid. Basal lamina and reticular fibers surround the epithelial follicular cells. Between follicles, there are network of blood vessels, unmyelinated sympathetic fibers

7. Parafollicular cells – Small cells that produce calcitonin. They are enclosed within the basal lamina of the follicular epithelium. They are not connected to the follicular lumen. – They lie in clusters or single. – They have rounded nuclei, moderate RER, elongated mitochondria, well-developed Golgi complex and small dense secretory granules. Parafollicular cells – Small cells that produce calcitonin. They are enclosed within the basal lamina of the follicular epithelium. They are not connected to the follicular lumen. – They lie in clusters or single. – They have rounded nuclei, moderate RER, elongated mitochondria, well-developed Golgi complex and small dense secretory granules.

8. Effects of T3 and T4 Increase of the cellular metabolism. Increase growth rate in young. Facilitate mental processes. Stimulate other endocrine activities. Stimulate carbohydrate metabolism..................................................... etc. Increase of the cellular metabolism. Increase growth rate in young. Facilitate mental processes. Stimulate other endocrine activities. Stimulate carbohydrate metabolism..................................................... etc.

9. Effects of Calcitonin Inhibits bone resorption by osteoclasts, so lowering the calcium concentration in blood. Its release from the parafollicular cells is stimulated by the high calcium level of the circulating blood. Inhibits bone resorption by osteoclasts, so lowering the calcium concentration in blood. Its release from the parafollicular cells is stimulated by the high calcium level of the circulating blood.

10. Hyperthyroidism (Graves’ disease) Hyperplasia of follicular cells and increase of the total size of the thyroid gland. Increase production of thyroid hormones. It causes loss of weight, increase heart rate, hypertension, muscle tremors, tiredness, nervousness, impotence in males and excessive menstrual bleeding in females. Hyperplasia of follicular cells and increase of the total size of the thyroid gland. Increase production of thyroid hormones. It causes loss of weight, increase heart rate, hypertension, muscle tremors, tiredness, nervousness, impotence in males and excessive menstrual bleeding in females.

11. GoitreGoitre Insufficient dietary intake of iodine will cause thyroid gland to enlarge. It is due to increase release of TSH from pituitary (as a response to low level of thyroid hormone of blood) which stimulate hypertrophy and proliferation of the follicular cells. Iodine intake will improve the condition. Insufficient dietary intake of iodine will cause thyroid gland to enlarge. It is due to increase release of TSH from pituitary (as a response to low level of thyroid hormone of blood) which stimulate hypertrophy and proliferation of the follicular cells. Iodine intake will improve the condition.

12. HypothyroidismHypothyroidism Fatigue, increase sleep, muscle weakness. Slow heart rate, decreased cardiac output and blood volume, mental sluggishness. Constipation, increase body weight, loss of hair. Intolerance to cold weather. Myxedema: non-pitting edema. In congenital absence of thyroid it causes cretinism: failure of growth, mental retardation. Fatigue, increase sleep, muscle weakness. Slow heart rate, decreased cardiac output and blood volume, mental sluggishness. Constipation, increase body weight, loss of hair. Intolerance to cold weather. Myxedema: non-pitting edema. In congenital absence of thyroid it causes cretinism: failure of growth, mental retardation.

13. STRUCTURESTRUCTURE  Connective Tissue Stroma: –Thin collagenous connective tissue capsule. –Capsule sends septa which subdivide the gland into incomplete lobules. –These septal trabeculae support the parenchymal cells and carries blood vessel, lymphatics and nerve fibers. –With age, the septa contain adipose cells.  Connective Tissue Stroma: –Thin collagenous connective tissue capsule. –Capsule sends septa which subdivide the gland into incomplete lobules. –These septal trabeculae support the parenchymal cells and carries blood vessel, lymphatics and nerve fibers. –With age, the septa contain adipose cells.

14. STRUCTURESTRUCTURE  Parenchymal cells: –Are formed of branching and anastomosing cords or clusters of cells. –The parenchyma of the parathyroid are formed of two types of cells: Chief (principal) cells and Oxyphil cells.  Parenchymal cells: –Are formed of branching and anastomosing cords or clusters of cells. –The parenchyma of the parathyroid are formed of two types of cells: Chief (principal) cells and Oxyphil cells.

15. Chief Cells The major functional parenchymal cells. Small in size (8 microns) Slightly acidophilic cytoplasm containing lipofuscin pigments and smaller dense secretory granules containing the parathormone. It also contains RER, Golgi complex and elongated mitochondria. Some cells have also glycogen granules but less parathormone granule (less active cells) The major functional parenchymal cells. Small in size (8 microns) Slightly acidophilic cytoplasm containing lipofuscin pigments and smaller dense secretory granules containing the parathormone. It also contains RER, Golgi complex and elongated mitochondria. Some cells have also glycogen granules but less parathormone granule (less active cells)

16. Oxyphil Cells Less in number. Larger than chief cells (more than 10 microns) Strongly acidophilic cytoplasm containing less secretory granules, less RER and Golgi complex and more mitochondria than the chief cells. Appears in single form or in small groups. It function is not known or it may be a stage of the chief cell development. Less in number. Larger than chief cells (more than 10 microns) Strongly acidophilic cytoplasm containing less secretory granules, less RER and Golgi complex and more mitochondria than the chief cells. Appears in single form or in small groups. It function is not known or it may be a stage of the chief cell development.

17. Function of the parathyroid The parathyroid hormone or the (parathormone) increases the blood level of calcium through: The parathyroid hormone or the (parathormone) increases the blood level of calcium through: 1.Activate osteoclasts to mobilize calcium from bone. 2.Promote absorption of calcium from the intestine. 3.Increase reabsorption of calcium by proximal convoluted tubules of kidney. The parathyroid hormone or the (parathormone) increases the blood level of calcium through: The parathyroid hormone or the (parathormone) increases the blood level of calcium through: 1.Activate osteoclasts to mobilize calcium from bone. 2.Promote absorption of calcium from the intestine. 3.Increase reabsorption of calcium by proximal convoluted tubules of kidney.

18. Primary hyperparathyroidism Due to tumor in the chief cells and leads to high blood calcium level, low phosphate, heart disturbance and kidney stones. Treated by surgical removal of the parathyroid tumor. Due to tumor in the chief cells and leads to high blood calcium level, low phosphate, heart disturbance and kidney stones. Treated by surgical removal of the parathyroid tumor. Secondary hyperparathyroidism Occurs secondary to decrease absorption of calcium from intestine due to Vit. D deficiency (in Rickets). So, the calcium level well be low in the blood. Occurs secondary to decrease absorption of calcium from intestine due to Vit. D deficiency (in Rickets). So, the calcium level well be low in the blood.

19. HypoparathyroidismHypoparathyroidism Decrease parathormone (as after thyroidectomy) leads to lower blood calcium. Leads to muscle cramps, tremors, mental confusion and memory loss, may be fatal convulsions. Decrease parathormone (as after thyroidectomy) leads to lower blood calcium. Leads to muscle cramps, tremors, mental confusion and memory loss, may be fatal convulsions.

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