Fisiología | Clase 1 | Introducción a la Fisiología, Homeostasis y Mecanismos de Regulación.

Introduction to Physiology

Overview of the Course

• The course begins with a focus on basic concepts and general principles of physiology, making future topics easier to understand.

Definition of Physiology

• The term "physiology" is derived from Greek roots: "physis" meaning nature and "logos" meaning study or knowledge. It refers to the science that studies the functioning of living beings, specifically human physiology in this course.

Understanding Homeostasis

Key Concept: Homeostasis

• Homeostasis is defined as the dynamic equilibrium of the internal environment, derived from Greek roots meaning equal (homeo) and stability (stasis). This concept is crucial for understanding physiological regulation.

Dynamic Equilibrium vs. Fixed Values

• Unlike fixed values, homeostasis involves maintaining stable conditions through dynamic processes within the body, ensuring it remains balanced despite external changes.

Internal Environment and Its Regulation

Internal Medium: Extracellular Fluid

• The internal medium referred to in homeostasis is extracellular fluid (ECF), which bathes all cells in the body, similar to how water surrounds fish or air envelops us. Understanding ECF's variations is essential for studying cellular function.

Impact on Cellular Functioning

• Physiological studies focus on how changes in extracellular fluid affect cell function, emphasizing its importance for overall health and stability within organisms.

Regulatory Processes in Homeostasis

Dynamic Regulation Mechanism

• Homeostatic regulation requires understanding key concepts such as regulated variables (e.g., blood glucose levels, temperature) that must be maintained within specific reference ranges for optimal functioning.

Reference Values for Key Variables

• Examples include:

• Blood glucose should be between 70–100 mg/dL.

• Body temperature should range from 36.5–37.5 °C.

• pH levels should remain between 7.35–7.45 (with a narrower range of 7.37–7.42).

Sensors and Integration Centers

Role of Sensors

• Sensors continuously monitor regulated variables to ensure they remain within reference values; examples include thermoreceptors and chemoreceptors that detect various bodily conditions like temperature and chemical composition respectively.

Integration Center Functions

• The hypothalamus serves as a primary integration center that compares sensor data against reference values and determines necessary actions to maintain homeostasis by sending signals to effectors throughout the body.

Effectors' Role in Maintaining Homeostasis

Action by Effectors

• Effectors are components that enact changes based on signals received from integration centers; they can include organs like the liver releasing insulin or adjusting blood vessel diameter through vasodilation or vasoconstriction as needed to restore balance in regulated variables.

Continuous Adjustment Process

• This process exemplifies a constant cycle where regulated variables fluctuate around their reference values, illustrating how homeostasis operates dynamically rather than statically over time while maintaining equilibrium within biological systems.( t =479 s)

Homeostasis and Feedback Mechanisms in Physiology

Regulation of Body Temperature

• The regulated variable is temperature, which must be maintained between 36.5 to 37.5 degrees Celsius, with this information stored in the hypothalamus.

• Thermoreceptors continuously monitor body temperature; if it drops significantly (hypothermia), the hypothalamus sends signals to effectors to increase temperature.

• Muscles contract (shivering) and blood vessels constrict to conserve heat when body temperature decreases.

• Conversely, if body temperature rises above 37.5 degrees during intense exercise, the hypothalamus signals effectors to lower it.

• This involves vasodilation of skin blood vessels and activation of sweat glands for evaporative cooling.

Dynamic Equilibrium and Homeostasis

• The process maintains a dynamic equilibrium within internal conditions through continuous adjustments based on feedback mechanisms.

• Understanding how regulated variables maintain homeostasis is crucial in physiology.

Feedback Mechanisms: Negative vs Positive

Negative Feedback

• Negative feedback is the most common mechanism where an increase in a variable leads to responses that decrease it, and vice versa.

• Examples include sweating to reduce elevated body temperature or insulin release to lower high blood glucose levels.

• If blood glucose drops too low, glucagon prompts the liver to release glucose back into circulation, demonstrating negative feedback's role in maintaining balance.

Positive Feedback

• Positive feedback amplifies changes rather than counteracting them; it's less common but essential for certain physiological processes.

• An example is childbirth: pressure from the fetus against the cervix stimulates oxytocin release, leading to stronger uterine contractions until delivery occurs.

Understanding Positive Feedback Mechanisms in Physiology

Coagulation Process

• The coagulation process is initiated when blood exits a small cut and contacts collagen in connective tissue, activating the coagulation cascade.

• This cascade leads to the formation of a clot, which continues to activate more clotting factors until the wound is completely sealed.

Action Potential in Nerve Fibers

• The action potential in nerve fibers involves voltage-sensitive sodium channels that generate electrical charges, leading to further channel openings.

• This propagation of action potentials along an axon occurs continuously until it reaches the end of the axon, demonstrating positive feedback.

Anticipatory Responses

• Anticipatory or forward feeding processes occur before a stimulus fully manifests; they prepare the body for potential challenges.

• A classic example is the activation of the sympathetic nervous system due to fear or stress, preparing for fight-or-flight responses.

Physiological Changes During Stress

• Activation of the sympathetic nervous system increases muscle blood flow, heart rate, blood pressure, and glucose release in response to perceived threats.

• These physiological changes ensure that resources are available for immediate physical action if necessary.

The Importance of Homeostasis and Disease

Role of Negative Feedback

• Negative feedback mechanisms are crucial for maintaining homeostasis; they counteract deviations from set points within physiological systems.

Consequences of Homeostatic Imbalance

• Loss of homeostasis can lead to disease; various factors can disrupt this balance and result in health issues.

Examples of Homeostatic Disruption

• Disruptions may arise from sudden changes in regulated variables or failures in effectors or sensors responsible for maintaining balance.

Understanding Fever and Its Effects

Shivering Response

• Shivering during fever is a muscular activity that generates heat, raising body temperature as part of a physiological response.

Hypothalamic Regulation

• In fever conditions, the hypothalamus misinterprets temperature signals and raises its reference point above normal levels (36.5 - 37.5 degrees Celsius).

Medication Impact on Fever

• Medications like paracetamol work by resetting hypothalamic reference points back to normal levels, helping regulate body temperature effectively.

Integrating Knowledge in Physiology

Understanding Through Reasoning

• Mastery of physiology requires understanding concepts rather than rote memorization; integration of knowledge about bodily functions is essential for grasping complex interactions.