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Transcript
IB BIOLOGY ENDOCRINE SYSTEM The endocrine glands are also known as ductless glands. They secrete certain chemical substances which guide and control the various metabolic activities, the growth and differentiation of various systems and thereby bringing about a correct physiological balance between them. Such substances are also referred to as chemical co-ordinators. Differences between exocrine and endocrine glands. 1) Exocrine glands-: The secretion of these glands are carried away from them to the site of action by special ducts. For example The Salivary glands are exocrine gland . The saliva is carried from them to the mouth by a duct. The liver is also an exocrine gland as the bile manufactured is carried away by bile duct. 2) Endocrine glands:- The secretions of these glands are not carried away by any duct at all. Instead, they get mixed in the blood stream directly and are carried away to all the parts of the body via the blood. Pituitary and Adrenal glands are good examples . They manufacture hormones that are spread through the body by the blood. Characterisitics of hormones: 1. Hormones themselves do not create biochemical processes, but it modifies the existing metabolic processes and change the rate of action. 2. Hormones are secreted in response to specific stimuli. 3. hormones can be secreted independently of one another. 4. Hormones have a high degree of target specificity. 5. hormones are believed to be catalytic in their effects. The pituitary gland : It is the chief center of the endocrine system. It forms an important link between the nervous and endocrine system. It controls other endocrine glands. It is located at the base of the brain and connected by the hypothalamus to the brain. Hormones secreted by anterior lobe of the brain: 1. Growth hormone. 2. thyroid stimulating hormone (TSH) 3. Adrenocortico trophic hormone (ACTH) 4. Follicle stimulating Hormone (FSH) 5. Interstitial cell stimulating hormone or Luteinizing hormone (ICSH or LH) 6. Prolactin or Luteotrophic hormone Hormones secreted by the posterior lobe: 1. Antidiuretic hormone (ADH) or Vasopressin. 2. Oxytocin. Thyroid gland: It consists of pair of lobes which lie on either side of the larynx in the neck region. Functions of thyroid: 1. It stimulates the normal growth and development, particularly that of skeletal and nervous system. 2. It controls the rate of cellular oxidation and basic metabolic activities. Basal metabolic rate: It is defined as the amount of heat produced in the body in a given time in complete state of physical and mental rest at room temperature. Hypothyroidism can cause cretinism in children , myxedema in adult. Goitre is caused due to iodine deficiency. Hyperthyroidism causes Grave’s disease or Exophthalmic goiter. Adrenal gland : Adrenal cortex: Aldosterone – promote the resorption of sodium ions from the renal glomerular filtrate, and plays an important role in stress tolerance. Cortisone stimulates the production of glucose from non carbohydrate sources such as fats and aminoacids. Also acts as an anti-inflammatory agent. Adrenal medulla secretes adrenalin. Prepares you for emergency situations Testes – secrete male hormone testosterone. Ovaries secrete female hormones estrogen, progesterone. Islets of Langerhans: ) Alpha cells secrete- glucagons. Beta cells secrete –insulin Delta cells secrete –somatostatin (they work to reduce the rate at which food is absorbed from the contents of the intestine)