1_Lecture 1. SUBJECT OF PHYSIOLOGY. STRUCT_ FUNCTIONAL ORGANIZATION_ANIMAL ORGANISM. HOMEOSTASIS_Prof_IvanPenchev

SUBJECT OF PHYSIOLOGY

Physiology is a biological discipline focused on studying living processes in healthy organisms and the mechanisms regulating these processes. It serves as a fundamental and pre-clinical component of medical education, including veterinary medicine. One term often associated with the regulation of these processes is homeostasis, which refers to maintaining a stable internal environment despite changes outside the organism.

INTRODUCTION TO PHYSIOLOGY

The introduction to physiology covers various aspects of the structural and functional organization of living organisms. The primary goal of physiology is to describe the interrelationship between an organism's structure and its functions. Understanding these relationships is crucial for grasping significant physiological processes, such as those regulating homeostasis.

STRUCTURAL ORGANIZATION OF LIVING ORGANISMS

Living organisms exhibit several levels of structural organization:

  1. Chemical Level: This is the most fundamental level, concerning atoms and molecules essential for life (e.g., carbon, hydrogen, oxygen).

  2. Cellular Level: Cells are the basic structural and functional units of life, composed of various molecules.

  3. Tissue Level: Tissues are groups of similar cells that perform a common function, classified into four main types: muscle, nervous, connective, and epithelial tissues.

  4. Organ Level: Organs consist of two or more types of tissues working cooperatively to carry out specific functions.

  5. Organ System Level: Organ systems are groups of organs that work together to perform complex functions essential for survival.

  6. Organism Level: This is the highest level of organization, representing a complete living entity.

HOMEOSTASIS

Homeostasis involves maintaining internal stability (e.g., body temperature, pH levels) amidst external changes. The term roots from Greek, where 'homeo' means 'unchanging' and 'stasis' means 'standing'. Homeostasis highlights the dynamic equilibrium of physiological functions, indicating that all organ systems contribute to maintaining stable internal conditions.

For instance, the human body maintains a temperature of around 37°C, regulated through various mechanisms involving the skin, kidneys, liver, and endocrine and nervous systems. Any deviation from homeostasis can lead to disease, highlighting its significance in physiology.

MECHANISMS OF REGULATION

Regulatory mechanisms in physiology ensure that the body's parameters remain within a normal range.

  • Negative Feedback: Most physiological processes are regulated via negative feedback, wherein the response reduces the effect of the initial stimulus, facilitating the restoration of homeostasis (e.g., regulation of blood glucose).

  • Positive Feedback: Less common in normal physiology, this involves amplifying responses to deviations. This can lead to critical processes like childbirth and blood clotting. However, if dysregulated, it can cause harmful conditions.

During regulation, a variety of signals (input signals) trigger responses. For instance, when blood glucose levels rise, pancreatic beta cells secrete insulin to reduce glucose concentrations.

ADAPTATION

Adaptation allows organisms to adjust to external changes, maintaining homeostasis through the nervous and endocrine systems. Hans Selye first described its mechanisms, but the body’s ability to adapt is limited—prolonged or intense changes can lead to diseases like hypertension, cardiovascular issues, and diabetes. Stress plays a key role, with some viewing mild stress as beneficial while others see it as harmful. Understanding adaptation is crucial in physiology, as it helps explain functional disorders and disease development.

REGULATORY SYSTEMS

The primary regulatory systems include:

  • Nervous System: Rapidly detects internal changes and coordinates quick responses.

  • Endocrine System: Regulates longer-term changes through hormone secretion and influences multiple target cells over longer distances.

Both systems work in concert; for example, sensations like stress lead to both quick nervous responses and longer-term hormonal adjustments to restore homeostasis.

Overall, understanding physiology equips veterinary and medical students with crucial knowledge of how health is maintained and how deviations can lead to diseases. This foundational knowledge enhances the ability to diagnose and treat patients, leading to a higher quality of care.