Endocrine System (Grade 10) PDF

Endocrine Glands Hormones Hormones are chemical messengers that regulate the physiological processes in living organisms. These act upon specific target cells/tissues and organs. Differences between Hormonal Control and Nervous Control Hormonal Control...

Endocrine Glands Hormones Hormones are chemical messengers that regulate the physiological processes in living organisms. These act upon specific target cells/tissues and organs. Differences between Hormonal Control and Nervous Control Hormonal Control Nervous Control Transmitted electro-chemically through nerve Transmitted chemically through blood fibres Transmitted slowly Transmitted rapidly Affects different organs Affects specific organs Is not affected by previous experience Is affected by previous experience Has both long lasting and short lasting Has short lasting effect effects Glands Exocrine glands – Glands that discharge their secretions into ducts Examples: salivary gland in buccal cavity, sebaceous gland in skin Endocrine gland– Glands that do not discharge their secretions into ducts, but directly into blood These are also called ductless glands. Examples: pituitary gland, thyroid gland, adrenal gland, etc. Human Endocrine System Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads are the organised endocrine glands in our body. In addition, GI tract, liver, kidney, heart also produce hormones. Adrenal gland It is divided into: Adrenal medulla – It secretes adrenaline (epinephrine) and noradrenaline (norepinephrine). These are collectively called as catecholamines. These hormones are also called emergency hormones. Adrenal cortex – It secretes hormone called corticoids. Corticoid such as glucocorticoid regulates carbohydrate metabolism. Example includes cortisol. Corticoid such as mineralocorticoid maintains the sodium potassium level in blood and tissue. Example includes aldosterone. Hyposecretion : Less secretion from adrenal cortex. Disease caused is called Addison's disease. Hypersecretion: Excess of secretion from adrenal cortex Disease caused is called Cushing's Syndrome. Pancreas The islets of Langerhans have two types of cells: α – cells – secrete glucagon 1. β – cells – secrete insulin Insufficient Secretion of Insulin Disease caused: Diabetes mellitus Over- Secretion of insulin Disease caused: Hypoglycemia  Hyperglycemia – Increased blood glucose level Glucagon is a hyperglycaemic hormone. Hypoglycaemia – Decreased blood glucose level Insulin is a hypoglycaemic hormone. Diabetes mellitus – Abnormal high glucose level in blood, which results in release of sugar in urine and formation of toxic ketone bodies Testis Leydig cells (Interstitial cells) – Secrete androgens, mainly testosterone Testosterone plays a role in spermatogenesis and development of male secondary sexual characters. Ovary It secretes two hormones. Estrogen – Secreted by Graafian follicle, it regulates the development of female secondary sexual characters. Progesterone – Secreted by corpus luteum, it acts on mammary glands and helps in milk secretion. Human endocrine system Hypothalamus: Contains neurosecretory cells that produce hormones Hormones regulate the synthesis and secretion of pituitary glands. Two types of hormones are released. Releasing hormones – Stimulate pituitary gland to release hormones Inhibiting hormones – Inhibit pituitary gland from releasing hormones Pineal gland  It secretes a hormone called melatonin. It also regulates the rhythm of body. Thyroid gland It secretes two hormones: Tetraiodothyronine or thyroxin (T4) Triiodothyronine (T3) Deficiency of iodine results into Hypothyroidism. The disease is known as goitre Creatinism Myxodema High level of iodine results into hyperthyroidism. Thyroid hormone plays a role in carbohydrate, fat, and protein metabolism in the body. It also secretes thyrocalcitonin, which lowers the calcium level in blood plasma. Parathyroid gland: It regulates calcium level in body. It increases the reabsorption of calcium ions by renal tubules and digested food. Pituitary gland (i). Adenohypophysis is further divided into two regions: Pars distalis (anterior pituitary): Growth hormone – It is involved in growth and development of the body. Low secretion of growth hormone results in dwarfism and acromegaly (extra  growth of bones in jaws, hands or feet) Prolactin – It helps in growth of mammary gland and milk formation. Thyroid stimulating hormone – It helps in secretion of thyroxine from thyroid glands. Adreno-corticotrophic hormone – It helps in secretion of glucocorticoid hormone from adrenal cortex. Gonadotrophic hormone – It includes the following. Luteinizing hormone – It helps in secretion of androgen from testis. It also induces ovulation from Graafian follicles. Follicle stimulating hormone – It maintains the growth and development of Graafian follicle. Pars intermedia: It secretes melanocyte-stimulating hormone (MSH), which maintains skin pigmentation. (ii). Neurohypophysis (posterior pituitary): – It contains pars nervosa region. Pars nervosa region secretes two hormones: Oxytocin – It helps in contraction of uterus and milk ejection. Vasopressin (Anti-diuretic hormone) – It stimulates reabsorption of water by distal convoluted tubules.Deficiency causes Diabetes Insipidus. Thymus This gland is degenerated with the age. Thymus produces a hormone called thymosins. Thymosins produce T-lymphocytes that protect the body against infectious agents. It provides cell-mediated immunity and also humoral immunity. Endocrine glands  Hormones are secreted by endocrine glands such as the pituitary gland, thyroid gland, adrenal gland, pancreas etc. Major endocrine glands in humans are Pituitary Hypothalamus Pineal Thyroid Thymus Pancreas Adrenal Testis in men /ovary in women A feedback mechanism (positive and negative) regulates the action of the hormones. Characteristics of hormones: Hormones act as chemical messengers. They are secreted by living cells/tissues or organs called glands. They are secreted in very small quantities by glands. They act upon specific cells, tissues, or organs called the target sites. They are generally slow in action, but have long lasting effects. They either accelerate or inhibit a reaction.