Lesson 1 Chapter 1 – Homeostasis

Lesson 1 Chapter 1 – Homeostasis Unit 1 Study Guide 1 Physiology: the study of the functioning of the body's structural machinery - how the parts of the body work and carry out their life-sustaining activities. Dynamic processes. Levels of the Hierarchy: Atoms: building blocks of matter Molecules: water, sugar, proteins -- groups of atoms Organelles: basic components of microscopic cells Cells: living structural and functional units of an organism Tissues: groups of similar cells having common structure and function. Four basic types. Organ: complex physiological processes become possible. Discrete structure composed of at least two tissue types; four tissue types more common. Organ System: organs that cooperate and work closely together to accomplish a common purpose. Organism: sum total of all levels of complexity working continuously and in unison. Homeostasis Ability to maintain relatively stable internal conditions despite a changing external environment. Dynamic state of equilibrium, or balance. The body is said to be in homeostasis when its cellular needs are adequately met and functional activities are occurring smoothly. Virtually every organ system plays a role in maintaining the internal environment. Normal function of each cell depends on the maintenance of its fluid environment: - ICF (Intracellular fluid) ECF (Extracellular fluid) Feedback System Is any circular situation in which information about the status of something is continually reported to a central control system. • Negative feedback • Positive feedback • Feed forward Lesson 1 Chapter 1 – Homeostasis 2 Negative feedback system In negative feedback the system is always on, generating a product. Once a certain level of product is attained, or an inhibitor enters the system, this stimulus is observed by receptors that then transmit a signal from the control centre back to the control centre notifying its effectors to shut the system down. The system then shuts down until the stimulus is removed and the receptors stop transmitting a signal to the control centre. Negative feedback controls the rate of a process to avoid accumulation of a product, this is essential for homeostasis. Feedforward System A feedforward system reacts to changes within its environment, typically to maintain some form of equilibrium. The information is sent ahead of time to prepare a part of a control system. The effector system is activated before any change has taken place, by anticipating change the environment is in a prolonged state of readiness. Positive Feedback System Positive feedback occurs when the rate of a process increases as the concentration of the product increases. The rate of a process will continuously increase as long as substrate is available and the product is not used by some other process. Ultimately positive feedback results in an explosive growth and can only be stopped when a limit is reached (e.g. contractions in childbirth). Homeostatic control To maintain homeostasis, communication within the body is essential. The image above is an example of how a homeostatic control system works. Here is a brief explanation. 1. Stimulus- produces a change to a variable (the factor being regulated). 2. Receptor- detects the change. The receptor monitors the environment and responds to change (stimuli). 3. Input- information travels along the (afferent) pathway to the control center. The control center determines the appropriate response and course of action. 4. Output- information sent from the control center travels down the (efferent) pathway to the effector. 5. Response- a response from the effector balances out the original stimulus to maintain homeostasis. Think of it as an extremely complex balancing act. Here’s a few more definitions you may want to know. Afferent pathways - carry nerve impulses into the central nervous system. For instance, if you felt scorching heat on your hand, the message would travel through afferent pathways to your central nervous system. Efferent pathways - carry nerve impulses away from the central nervous system to effectors (muscles, glands). Lesson 1 Chapter 1 – Homeostasis 3 The feeling of heat would travel through an afferent pathway to the central nervous system. It would then interact with the effector and travel down the efferent pathway, eventually making the person remove their hand from the scorching heat. Homeostasis is maintained by 2 control mechanisms • Intrinsic control (internal environment) • extrinsic control by the nervous and endocrine system