[BIO] Chapter 13 - Hormone

© Hee Xin Wei (Copyrighted) Topic 1 3: Hormone

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 5% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions •tested twice in section B in the past 5 years •one of the three chapters under umbrella topic of Co-ordination and Response in Humans •linked to nervous system and homeostasis

hormone insulin and glucagon diabetes Key Concept

hormone •Hormone is a chemical substance, produced by endocrine gland and secreted directly to blood •It is transported by blood to target organ to exert its effect •After they have performed their functions, they are destroyed by the liver. There are 2 types of glands 1.Exocrine glands are glands that secrete their products via ducts eg sweat glands and salivary glands 2.Endocrine glands are glands that secrete their products directly into the bloodstream (our focus) •Some glands are both exocrine and endocrine, eg pancreas, which secretes pancreatic juice via the pancreatic duct, and also secretes the hormone insulin and glucagon from the islets of Langerhans directly into the bloodstream. •Other examples of endocrine glands that secrete hormone is as below: •Pituitary gland secretes antidiuretic hormone (ADH) •Hypothalamus regulates the secretion of some pituitary hormones. •Adrenal gland secretes adrenaline. •Pancreas islets of Langerhans secrete insulin and glucagon. •Testis (in males) secretes testosterone. •Ovary (in females) secretes oestrogen and progesterone.

blood glucose regulation insulin and glucagon 1.When blood glucose level increases beyond the norm, more insulin is released by islets of Langerhans in pancreas to the bloodstream 2.Blood transport insulin to the effector cells which are muscles cells and liver cells 3.Insulin decreases blood glucose concentration by: •Stimulating body cells to increase glucose uptake by increasing permeability of plasma membranes to glucose •Stimulating the liver and muscle cells to store glucose in the form of glycogen •Decreasing glycogen breakdown in the liver •Decreasing the conversion of fatty acids and amino acids to glucose in the liver 1.When blood glucose level falls below the norm, more glucagon is released by islets of Langerhans in pancreas to the bloodstream 2.Blood transports glucagon to the effector cells which are liver cells 3.Glucagon increases blood glucose concentration by stimulating liver cells to: •Convert stored glycogen in liver to glucose •Convert amino acids and fatty acids to glucose •Convert lactic acid into glucose normal blood glucose level

diabetes mellitus •Diabetes mellitus is a condition in which the body does not produce sufficient insulin or does not respond to insulin. •The excess glucose cannot be converted to glycogen and cannot be completely reabsorbed in the kidneys and are excreted in the urine. There are 2 types of diabetes 1.Type 1 diabetes or early onset diabetes