UNIT1.pdf

Homeostasis 1  Homeostasis Definition : Maintenance of the relative stability of the physical and chemical aspects of the internal environment within a range compatible with cellular function. Maintaining a constant internal environment with all tha...

Homeostasis 1  Homeostasis Definition : Maintenance of the relative stability of the physical and chemical aspects of the internal environment within a range compatible with cellular function. Maintaining a constant internal environment with all that the cells need to survive (O2, glucose, minerals, ions, and waste removal) is necessary for individual cells. The processes by which the body regulates its internal environment are referred to as homeostasis. Components : 1) sensor 2) afferent pathway 3) integration center or comparator 4) efferent pathway 5) effector organ(s) Physiological control systems are the nervous system, endocrine system, and immune system through feedback mechanisms. 2 3  Extrinsic homeostatic systems Nervous System The nervous system maintains homeostasis by controlling and regulating the other parts of the body. – A deviation from a normal set point acts as a stimulus to a receptor, which sends nerve impulses to a regulating center in the brain. The brain directs an effector to act in such a way that an adaptive response takes place. The nervous system has two major portions: the central nervous system and the peripheral nervous system. 4 Classification of Nervous System 5  Regulating centers are located in the central nervous system, consisting of the brain and spinal cord. – The hypothalamus is a portion of the brain particularly concerned with homeostasis; it influences the action of the medulla oblongata, a lower part of the brain, the autonomic nervous system, and the pituitary gland. The peripheral nervous system consists of the spinal nerves. The autonomic nervous system is a part of peripheral nervous system and contains motor neurons that control internal organs. It has two divisions, the sympathetic and parasympathetic systems. 6 7  Endocrine System The endocrine system consists of glands which secrete special compounds called hormones into the bloodstream. Each hormone has an effect on one or more target tissues. In this way the endocrine system regulates the metabolism and development of most body cells and body systems. For e.g. the endocrine system has sex hormones that can activate sebaceous glands, development of mammary glands, alter dermal blood flow, and release lipids from adipocytes etc. besides governing reproduction. 8 Endocrine System 9  In the muscular system, hormones adjust muscle metabolism, energy production, and growth. In the nervous system, hormones affect neural metabolism, regulate fluid/electrolyte balance and help with reproductive hormones that influence CNS (central nervous system), development and behaviors. In the cardiovascular system, hormones regulate heart rate and blood pressure. Hormones also have anti-inflammatory effects and control the lymphatic system. 10  Negative feedback : a control system that causes the value of a physiological measurement to change in the direction opposite to the initial deviation from set point. 11  Positive feedback : a control system that causes the value of a physiological measurement to change in the same direction as the initial deviation from set point. 12