Introduction to Human Physiology PDF

Introduction to Human Physiology In some variables, there may be multiple regulatory mechanisms. Feedforward regulation, another type of regulatory process often used in conjunction with feedback systems, anticipates changes in regulated variables, such as internal body temperature and...

Introduction to Human Physiology In some variables, there may be multiple regulatory mechanisms. Feedforward regulation, another type of regulatory process often used in conjunction with feedback systems, anticipates changes in regulated variables, such as internal body temperature and energy availability. This process improves the efficiency of the body's homeostatic responses and minimizes fluctuations in the levels of the variables being regulated. Examples are: 1. The detection of colder external temperatures by skin sensors provides input to higher brain centers to increase metabolic production of heat before any change in body temperature has occurred. 2. The cephalic phase of digestion, where the smell of food can stimulate the production of saliva, cause the churning of the stomach, as well as acid production, all in anticipation of the arrival of food. Learning can also contribute to this feedforward phenomenon. We learn the consequences of particular behaviors, and the body, over time, will anticipate the perturbations to homeostasis by initiating actions before the activity begins. A familiar example is the increase in heart rate experienced by athletes before a game or an event is about to begin. Homeostatic control systems include reflexes, which are stimulus-response sequences that respond to changes in a homeostatic variable, often without conscious input from the individual. These types of reflexes are termed involuntary, premeditated or built-in responses. Examples include withdrawing a hand from a hot object or blinking as an object approaches the eyes. While many reflexes appear stereotypical and automatic, they are often the result of learning and practice. Reflexes that involve complex actions are referred to as learned or acquired reflexes. A common example is driving a car, where most drivers can perform the intricate actions required to operate a vehicle—sometimes while engaging in other activities, such as talking on the phone. These driving actions, particularly with a manual transmission, become reflexive through practice. Introduction to Human Physiology The pathway mediating a reflex action is called a reflex arc. Afferent and efferent pathways in temperature homeostasis. Stimulus: A change in the environment initiates the reflex. Receptor: Detects and transduces the stimulus into a signal. Afferent Pathway: Carries the signal from the receptor to the integrating center. Integrating Center: Compares the input signal to a set point. It processes and generates an output signal to initiate the response. Efferent Pathway: Transmits the output signal from the integrating center to the effector. This pathway can involve neural or hormonal signals. Effector: Executes the appropriate response, such as a muscle contracting or a gland releasing a hormone. Response: The action performed by the effector, which typically restores homeostasis or mitigates the stimulus Importantly, reflexes do not exclusively involve nervous pathways. Hormones can serve as efferent/afferent pathways instead of nerves and may work in conjunction with neural pathways. For example, if an endocrine gland functions as the integrating center, a hormone may be released as the efferent signal. Regardless, afferent and efferent pathways must always differ from each other. While both pathways can involve neurons or hormones, they operate as one-way communication systems.Additionally, local homeostatic responses can occur, involving similar principles but on a localized scale rather than system-wide. * Local Homeostatic Responses These responses are initiated by a change in the internal or external environment, including an alteration in cell activity, with the net effect of countering the stimulus. Like a reflex, a local response is the result of a sequence of events triggered by a stimulus. Unlike a reflex, however, a local response generates the entire sequence of events within the vicinity of the stimulus. For example, active hyperemia is a reaction of the vascular smooth muscle to changes in factors associated with increased cellular metabolism found in the extracellular fluid. Increases in factors such as carbon dioxide, hydrogen ion concentration, adenosine, potassium, eicosanoids,