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Animal Physiology
Topic: Endocrine System
Badiozaman Sulaiman
BSc.(UKM), MSc.(USM) – Molecular Biology
Department of Zoology
Faculty of Resource Science & Technology
Universiti Malaysia Sarawak
This OpenCourseWare@UNIMAS and its related course materials are licensed under a Crea<ve Commons A>ribu<on-­‐NonCommercial-­‐ShareAlike 4.0 Interna<onal License. At the end of the unit, you should be able to: 1. Discuss the func7on of endocrine system. 2. Explain the process of hormone signaling and s7mula7on. 3. Compare the signaling process of lipid-­‐soluble hormones and water-­‐soluble hormones. 4. Describe the posi7ve and nega7ve feedback mechanisms. Endocrine system • Endocrine system is made up of ductless glands, which secretes chemical signal (hormone) into circula<on system. • It works in conjunc<on with the nervous system as a way of communica<on between different body parts. • The endocrine system sends hormone to ini<ate slow-­‐ and long-­‐term responses while nervous system sends nerve impulse to ini<ate fast-­‐ and short-­‐term responses. Hormone • Hormone is a chemical that carries regulatory message to target <ssues that have the complimentary receptor. • It is secreted into body’s fluid and transported to the whole body via circulatory system (i.e. blood stream or haemolymph). • It regulates physiological ac<vity through command and feedback mechanism. Example of major vertebrate glands and hormones Gland Hormone Target Ac7on Posterior pituitary An<diure<c hormone (ADH) Kidney, blood vessel Water reten<on Anterior pituitary Growth hormone (GH) Various organs Promote growth and metabolism Thyroid Calcitonin Bone Lower blood calcium level Parathyroid Parathyroid hormone (PTH) Bone, kidney, intes<ne Increase blood calcium level Adrenal Epinephrine Many organs Stress response Pancreas Insulin Liver, skeletal muscle, adipose <ssue Decrease blood glucose level Ovary Progesterone Uterus, mammary gland Menstrual cycle, pregnancy, sexual characteris<c Tes<s Testosterone Many organs Secondary sex characteris<c, sperm forma<on General process of hormonal signaling Endocrine gland produce and release hormone into extracellular fluid The hormone enters circulatory system and spreads throughout the body The hormone binds to specific receptor of the target <ssue The target <ssue ini<ates response and feedback signal The feedback signal alerts the gland to either stop or increase hormone produc<on Hormone s7mula7on • The release of hormone can be triggered by three types of s<mula<on: 1. Hormonal – when the release is ac<vated by other hormones. 2. Humoral – when the release is ac<vated by changes of certain ions in blood. 3. Neuronal – when the release is ac<vated by nerve impulse. Example of hormone s<mula<ons 1. Hormonal s<mula<on – e.g. pituitary gland release TSH to s<mulates thyroid gland and ACTH to s<mulates adrenal cortex. 2. Humoral s<mula<on – e.g. low Ca2+ in blood signals the parathyroid gland to release PTH. 3. Neuronal s<mula<on – e.g. sympathe<c preganglionic nerve signals the adrenal medulla to release epinephrine and norepinephrine Example of hormone s<mula<ons (con<nue) Hormonal Humoral Neuronal Types of hormones • In general, hormone can be divided into two types: – Lipid soluble (amines, polypep<des, glycoproteins). – Water soluble (steroids, eicosanoids). • The types of solubility determine their mode of ac<ons. Lipid-­‐soluble hormone • Able to diffuse across the plasma membrane and bind to receptor protein within the cytoplasm. • The resulted hormone-­‐receptor complex moves into nucleus and binds to DNA as transcrip7on factor. • Ac7vate gene expression and synthesis of new protein. Lipid-­‐soluble hormone (process) 1. Hormone diffuses into the cell. 2. It binds to a receptor protein in the cytoplasm. 3. The hormone-­‐receptor complex enters into the nucleus , binds to DNA and serves as transcrip<on factor. 4. mRNA is then translated into protein by ribosome. Lipid-­‐soluble hormone (anima7on) 1. Hormone diffuses into the cell. 2. It binds to a receptor protein in the cytoplasm. 3. The hormone-­‐receptor complex enters into the nucleus , binds to DNA and serves as transcrip<on factor. 4. mRNA is then translated into protein by ribosome. Water-­‐soluble hormone • Binds to receptor protein on the membrane surface and ini7ates signal transduc7on. • The signal is transmi>ed across the plasma membrane and triggered secondary messenger pathway inside the cytoplasm. • Ac7vates cellular response (enzyme ac<on, uptake or secre<on of molecules, etc). • The secondary messenger pathway also resulted in amplifica7on of the hormonal signal. Water-­‐soluble hormone (process) 1. Hormone binds to receptor protein on membrane surface. 2. The hormone-­‐receptor complex triggers secondary messenger pathway in cytoplasm. 3. Amplified cellular response is ac<vated. Water-­‐soluble hormone (anima7on) 1. Hormone binds to receptor protein on membrane surface. 2. The hormone-­‐receptor complex triggers secondary messenger pathway in cytoplasm. 3. Amplified cellular response is ac<vated. Feedback mechanism • Acer a hormone has been secreted, the resulted changes will become a feedback signal to the gland. • These feedback can be categorized as a Nega7ve-­‐
feedback if the signal reduces the hormone secre<on. • Or as Posi7ve-­‐feedback if the signal increases the hormonal secre<on. Feedback mechanism (con7nue) • Hormones that involve in homeostasis processes are under the influence of nega<ve feedback mechanism. • Certain processes such as labor contrac<on and milking are under the influence of posi<ve feedback mechanism. Nega7ve feedback – blood glucose 1. The increase of blood glucose level s<mulates pancreas to secretes insulin. 2. Insulin trigger conversions of glucose into glycogen in liver and uptakes of glucose by body <ssue. 3. The decrease of blood glucose level s<mulates pancreas to secretes glucagon. 4. Glucagon triggers the breakdown of glycogen into glucose in liver. Posi7ve feedback – labor contrac7on 1. Oxytocin s<mulate uterine contrac<ons and prostaglandin secre<ons in placenta. 2. Prostaglandin escalates uterine contrac<on. 3.Uterine contrac<on s<mulates pituitary to release more oxytocin. Further reading: Reece, Urry, Cain, Wasserman, Minorsky & Jackson. (2013). Campbell Biology (10th edi<on). Benjamin Cummings. Willmer, Stone & Johnston. (2005). Environmental Physiology of Animals (2nd edi<on). Blackwell Publishing.