15. Thyroid Hormones -The thyroid gland consists of 2 lobes located on the ventral surface of the trachea. -This gland produces two similar hormones synthesized from the amino acid tyrosine: triiodothyronine (T 3 ) and tetraiodothyronine (T 4 ). -These hormones are responsible for vertebrate development and maturation such as skeletal growth, mental development, and the metamorphosis of a tadpole into a frog. -Goiter occurs when there is an iodine deficiency.
16. Parathyroid Hormone and Calcitonin: Control of blood calcium levels -The amount of calcium ions in the blood is essential in regulating skeletal muscles. The usual calcium level is maintained at 10mg/100mL. -When blood calcium level falls, the parathyroid glands, embedded in the surface of the thyroid, secrete parathyroid hormone (PTH) to increase release and absorption of calcium ions. -A rise in blood calcium level promotes the thyroid gland to release calcitonin, which reduces the release and uptake of calcium ions. -PTH stimulates osteoclasts in the bone to release calcium into blood. -PTH also directly stimulates uptake of calcium in kidneys. -PTH indirectly allows kidneys to convert vitamin D into its active hormonal form, which stimulate uptake of calcium in the intestines.
17. Insulin and Glucagon: Control of Blood Glucose Levels -The pancreas is considered both an endocrine and exocrine gland with important functions in endocrine and digestive systems. -Endocrine cells called islets of Langerhans are scattered throughout the tissues of the pancreas. -Each islet contains populations of either alpha or beta cells. -When blood glucose level rises, beta cells release the hormone insulin, which stimulates all body cells to take up glucose from blood and slows glycogen breakdown in the liver. -As blood glucose level drops, alpha cells release the hormone glucagon signaling liver cells to increase glycogen hydrolysis, convert amino acids and glycerol into glucose, and release glucose into the blood. -Glucose is a major fuel for cellular respiration and a source of carbon skeletons for the synthesis of organic compounds. The recommended blood glucose level is set at about 90mg/100mL.
18. Adrenal Hormones: Response to Stress -The adrenal glands are adjacent to the kidneys and each adrenal gland are made of the adrenal cortex, or outer portion, and adrenal medulla, or the central portion. -The adrenal medulla releases hormones called catecholamines synthesized from tyrosine. Among the catecholamines are epinephrine and nonepinephrine, which are secreted due to short-term stress response. -The adrenal cortex synthesizes and releases a family of steroids called corticosteroids. Glucocorticoids and mineralocorticoids are released as a result of long-term stress response. -The adrenal medulla is stimulated by nerve signals while the adrenal cortex is stimulated by ACTH from the blood vessels.
19. Gonadal Sex Hormones -The gonads produce and secrete three major categories of steroid hormones: androgens, estrogens, and progestins. -Estrogens, such as estradiol, are responsible for the development and maintenance of the female reproductive system. -Androgens, especially testosterone, are synthesized by the testes and they stimulate the development and maintenance of the male reproductive system. -Progestins are involved in preparing and maintaining the uterus, which supports growth and development of an embryo. -Both of the gonadotropic hormones (FSH and LH) in males and females stimulate activities of the gonads and control the synthesis of steroid hormones.
20. Melatonin and Biorhythms -The pineal gland is a small mass of tissue near the center of the brain. -This gland makes and secretes melatonin, a modified amino acid. -Melatonin’s primary functions are related to the biological rhythms associated with reproduction. Thymus Gland -The thymus gland is an organ that lies underneath the top of the breast bone. -The thymus gland is an organ that lies underneath the top of the breast bone.
![Overview and Introduction ,[object Object],[object Object],[object Object],[object Object],[object Object],HORMONE](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)