Foundations of Physiology: Core Concepts, Biomolecules, and Homeostasis

Chapter 1: Introduction to Physiology

1.1 What is Physiology?

Physiology is the study of how the body works, including its structure, function, and the mechanisms that keep it alive. It explores how anatomy, biochemistry, and physics integrate to maintain life.

• Emergent Properties: The whole is greater than the sum of its parts. For example, cells working together form tissues with new properties.

• Systems Integration: Different organ systems work together to maintain homeostasis and support life.

• Levels of Organization: Atoms → Molecules → Cells → Tissues → Organs → Organ Systems → Organism → Population → Ecosystem → Biosphere.

Example: The cardiovascular system transports oxygen, nutrients, and waste, integrating with respiratory and renal systems.

1.2 Teleological vs. Mechanistic Explanations

Physiological processes can be explained in two ways:

• Teleological: Explains the "why" (purpose) of a process.

• Mechanistic: Explains the "how" (mechanism) of a process.

Example: Teleological: "Why do we breathe? To supply oxygen to tissues." Mechanistic: "How do we breathe? By contraction of the diaphragm and intercostal muscles."

1.3 Fundamental Concepts in Biology

Physiology is grounded in several core biological principles:

• Structure and Function: Structure determines function at all levels.

• Energy: Energy is required for all biological processes.

• Information Flow: Genetic and cellular information is stored, transmitted, and used within and between cells.

• Homeostasis: The body maintains a stable internal environment.

• Evolution: Explains the adaptation of physiological processes.

Concept: Subdivision and Integration

Physiology integrates function across all levels of organization, from molecules to the whole organism.

Atoms, Molecules, and Cells

• Atoms: Basic units of matter.

• Molecules: Collections of atoms; in living organisms, molecules form cells.

• Cells: Basic unit of life; composed of biomolecules (lipids, proteins, carbohydrates, nucleic acids).

Cellular Organization

• Membrane: Separates cell from environment; composed of lipids and proteins.

• Cytoplasm: Contains organelles and cytosol.

• Nucleus: Stores genetic information.

Tissues and Organs

• Tissues: Connective, muscle, epithelial, nervous.

• Organs: Structures composed of multiple tissue types (e.g., pancreas, heart).

1.4 Homeostasis

Homeostasis is the maintenance of a relatively stable internal environment, essential for life. It involves dynamic processes that keep physiological variables within a normal range.

• Key Variables: Blood glucose, gases (O2, CO2), ions (Na+, K+, Ca2+), pH, temperature, blood pressure, volume, osmolarity.

• Pathophysiology: Disease states often result from loss of homeostasis (e.g., diabetes, cancer, autoimmune diseases).

Example: Blood glucose regulation involves the endocrine and digestive systems to maintain energy balance.

Compartmentalization

Body fluids are divided into compartments (intracellular, extracellular, interstitial, plasma) separated by membranes.

Mass Balance

What enters the body must be balanced by what leaves. This is crucial for maintaining homeostasis.

1.5 Control Systems and Feedback

Physiological control systems regulate variables to maintain homeostasis.

• Local Control: Restricted to a tissue or area (e.g., paracrine signaling).

• Reflex Control: Involves nervous and/or endocrine systems, often affecting distant sites.

Feedback Loops

• Negative Feedback: Counteracts change to restore homeostasis (e.g., temperature regulation).

• Positive Feedback: Reinforces change until a process is complete (e.g., childbirth contractions).

• Feedforward Control: Anticipates change and initiates response (e.g., salivation before eating).

Control System Components

• Sensor: Detects change.

• Integrating Center: Processes information and initiates response.

• Effector: Carries out response.

1.6 The Big Picture

Physiology involves both short-term variation and long-term stability. Multiple systems overlap to maintain variables such as blood glucose.

• Systems Involved: Digestive, circulatory, endocrine, nervous.

Chapter 2: Biomolecules and Chemical Principles

2.1 Biomolecules: Structure and Function

Biomolecules are organic molecules essential for life, including carbohydrates, proteins, lipids, and nucleic acids.

Biomolecule	Building Block	Function
Carbohydrate	Monosaccharide (simple sugars)	Structure, energy source, cell recognition
Protein	Amino acids	Structural support, enzymes, transport, signaling
Lipids	No single building block	Energy storage, membrane structure, insulation
Nucleic acids	Nucleotides	Genetic information storage and transmission

Lipids

• Nonpolar, insoluble in water.

• Triglycerides: Glycerol + 3 fatty acids; main energy storage in fat tissue.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; form cell membranes.

• Saturated vs. Unsaturated: Saturated = no double bonds; unsaturated = one or more double bonds.

• Steroids: Lipid-related molecules with four fused rings (e.g., cholesterol).

Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides linked (e.g., sucrose).

• Polysaccharides: Long chains for energy storage (e.g., glycogen).

• Oligosaccharides: Short chains, important for cell recognition.

Proteins

• Amino acids: 20 different types; sequence determines protein structure.

• Peptide bonds: Link amino acids.

• Levels of Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets (hydrogen bonds).

  • Tertiary: 3D shape (R group interactions).

  • Quaternary: Multiple polypeptides (e.g., hemoglobin).

Nucleic Acids

• Nucleotides: Phosphate group, sugar (ribose or deoxyribose), nitrogenous base.

• Bases: Purines (adenine, guanine), pyrimidines (cytosine, thymine, uracil).

• DNA: Double helix, stores genetic information.

• RNA: Single strand, involved in protein synthesis.

• ATP: Nucleotide that carries energy.

2.2 Chemical Bonds and Molecular Interactions

Atoms form bonds to achieve stability, creating molecules essential for life.

• Covalent Bonds: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bonds: Electrons transferred; forms ions (cations and anions).

• Hydrogen Bonds: Weak attraction between polar molecules (important in protein and DNA structure).

• Van der Waals Forces: Weak, transient electrical attractions.

Bond Influence on Molecular Shape and Function

• Molecular shape determines function (e.g., enzyme specificity, receptor binding).

• Attraction and repulsion between molecules affect folding and interactions.

2.3 Solutions and Solubility

• Solution: Homogeneous mixture of solute dissolved in solvent.

• Solvent: Substance that dissolves other substances (water is the most common in biology).

• Solute: Substance dissolved in the solvent.

• Solubility: Measure of how well a substance dissolves in a solvent.

• Hydrophilic: Water-loving, dissolves easily in water (polar or charged).

• Hydrophobic: Water-fearing, does not dissolve in water (nonpolar).

• Amphipathic: Molecules with both hydrophilic and hydrophobic regions (e.g., phospholipids).

Key Equations and Concepts

• Mass Balance: $\text{Input} = \text{Output}$

• Osmolarity: $\text{Osmolarity} = \frac{\text{Number of osmoles of solute}}{\text{Liter of solution}}$

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the integration of systems and the importance of molecular interactions in physiology.