Anatomy & Physiology: Homeostasis, Biochemistry, and Cellular Basics

Homeostasis, Being Alive, and the Rules of Physiology

Anatomy and Physiology: Definitions and Scope

• Anatomy: The study of the structure of body parts and their relation to each other.

• Physiology: The study of how body parts work and interact with each other to sustain life.

Types of Anatomy

• Gross (Macroscopic) Anatomy:

  • Regional: Study by specific regions of the body.

  • Systemic: Study by organ systems.

  • Surface: Study of external features.

• Microscopic Anatomy:

  • Cytology: Study of cells.

  • Histology: Study of tissues.

Structure and Function Relationship

• Physiological roles are often determined by anatomical structure.

• Structure and function are complementary: function can often be inferred from structure.

Levels of Organization

• Cell: Smallest unit of life.

• Tissue: Groups of similar cells with common function.

• Organ: Discrete structure, at least 2 tissue types (most are made of all 4).

• Organ System: Organs collaborating to achieve a common purpose.

• Organism: The whole living package.

What Does It Take to Be Alive?

• Organized with boundaries (at organism and cellular level).

• Movement.

• Transformation of energy.

• Responsiveness to changes in the environment.

• Growth and changing over time.

• Reproduction.

• Homeostasis.

What Do Humans Need to Be Alive?

• Macronutrients:

  • Carbohydrates: Major source of energy.

  • Proteins: Some energy, but mainly for building cellular machinery and structures.

  • Lipids (fats): Energy storage, cell membranes.

  • Nucleic acids: Genetic material.

• Minerals/Vitamins: Essential for metabolic and chemical reactions.

• Oxygen: Required for metabolic and chemical reactions.

• Water: Most abundant chemical in the body, creates a watery environment for chemical reactions.

• Normal Body Temperature: 37°C (98.6°F); necessary for proper metabolic reactions.

• Normal Atmospheric Pressure: Required for proper gas exchange in the lungs.

Humans Are Alive: Boundaries

• Plasma Membrane: Helps with germ defense, maintains gradients, separates processes.

• Skin: Protects against chemicals, physical damage, UV rays, germs, etc.

Movement

• Movement of the body (conscious and unconscious).

• Movement of substances (e.g., blood, food, urine).

Responsiveness and Excitability

• Ability to sense changes in the environment (stimuli) and respond to them.

• Example: Reflex withdrawal from a hot stove.

Digestion and Metabolism

• Digestion: Breakdown of ingested food into simple molecules for absorption.

• Metabolism:

  • Catabolism: Breakdown of molecules.

  • Anabolism: Synthesis of molecules.

  • ATP: Adenosine Triphosphate, the fundamental unit of biological energy.

Excretion

• Removal of waste products from metabolism and digestion.

• Major excreta:

  • Urea: Byproduct of protein breakdown.

  • Carbon dioxide: Byproduct of cellular respiration.

  • Feces: Indigestible food residues.

Reproduction and Growth

• Reproduction:

  • Cellular: Cell division (mitosis).

  • Organismal: Production of offspring (sexual reproduction in humans).

• Growth:

  • Increase in size of a body part or the organism as a whole.

  • Some parts of the body can regenerate; most energy is dedicated to maintenance in adults.

Homeostasis & Biochemistry Basics

Homeostasis: Definition and Mechanisms

• Homeostasis: Maintenance of a relatively stable range of internal conditions despite continuous environmental changes.

• Dynamic, not static; requires energy.

• Law of Mass Balance: In a steady state, the total amount of a substance in the body must equal the amount it loses.

Homeostatic Control Systems

• Three main components:

  • Receptor: Detects change.

  • Control Center: Processes information and determines response.

  • Effector: Carries out the response.

• Variable: The factor being regulated.

• Set Point: The ideal value or range for a variable.

Types of Feedback

• Negative Feedback:

  • Most common; variable changes in the opposite direction to the initial change.

  • Example: Body temperature regulation.

• Positive Feedback:

  • Uncommon and powerful; variable changes in the same direction as the initial change.

  • Not good for managing frequent events.

  • Example: Childbirth (uterine contractions and oxytocin release).

• Feedforward:

  • Anticipatory response.

  • Example: Salivation in anticipation of food.

Homeostatic Imbalance

• Control systems become less efficient with age.

• Negative feedback mechanisms may become overwhelmed, leading to disease.

• Example: Heart failure due to decreased blood volume output and increased load on the heart.

Basic Chemistry and Biochemistry for Physiology

Common Elements in the Human Body

• Oxygen (O): 65% of mass; essential for aerobic metabolism.

• Carbon (C): 18.5% of mass; backbone of organic molecules, forms 4 covalent bonds.

• Hydrogen (H): 9.5% of mass; found in all organic molecules, important in acid-base chemistry.

• Nitrogen (N): 3.3% of mass; important in proteins and nucleic acids.

Ions

• An ion is an atom with an unequal number of protons and electrons, giving it a charge.

• Cation: Positively charged ion (e.g., Na+).

• Anion: Negatively charged ion (e.g., Cl-).

Common Essential Ions

Ion	Main Function
Calcium (Ca2+)	Bone, teeth, muscle contraction, neurotransmitter release
Phosphorus (P)	Bones, teeth, nucleic acids, phospholipids, ATP
Potassium (K+)	Main cation in intracellular fluids
Sodium (Na+)	Main cation in extracellular fluids
Chlorine (Cl-)	Main anion in extracellular fluids
Magnesium (Mg2+)	Cofactor for many enzymes
Iodine (I)	Thyroid hormone synthesis
Iron (Fe)	Oxygen transport, enzyme cofactor

Major Organic Compounds

• Carbohydrates

• Lipids (fats)

• Proteins

• Nucleic acids

Elements, Molecules, Compounds, and Mixtures

• Element: Pure substance of one type of atom.

• Molecule: Two or more atoms bonded together.

• Compound: Two or more different kinds of atoms bonded together.

• Mixtures:

  • Solutions: Homogeneous mixtures (e.g., mineral water).

  • Colloids: Heterogeneous, particles do not settle out (e.g., jello).

  • Suspensions: Heterogeneous, particles settle out (e.g., blood).

Chemical Reactions: Vocabulary

• Chemical reaction: When chemical bonds are formed, rearranged, or broken.

• Reactants: Substances entering a reaction.

• Products: Substances resulting from a reaction.

• Synthesis: Combining to form something larger or more complex.

  • General equation: $A + B \rightarrow AB$

• Decomposition: Breaking down into smaller units.

  • General equation: $AB \rightarrow A + B$

• Exchange: Combination of synthesis and decomposition.

  • General equation: $AB + C \rightarrow AC + B$

Reversibility of Chemical Reactions

• All chemical reactions are technically reversible, but many biological reactions are not practically reversible due to high energy requirements or removal of products.

Factors Affecting Rate of Chemical Reactions

• Temperature: Higher temperature increases reaction rate.

• Reactant concentration: Higher concentration increases frequency of collisions.

• Particle size: Smaller particles increase reaction rate.

• Catalysts/Enzymes: Lower activation energy, increase reaction rate, not consumed in the reaction.

Enzyme Function and Specificity

• Enzymes are highly specific, usually acting on a single substrate.

• They lower the activation energy required for reactions.

• Enzyme-substrate complex formation is key to their function.

Water and Its Importance in Physiology

Properties of Water

• High heat capacity: Absorbs and releases heat with little temperature change.

• High heat of vaporization: Evaporation requires a lot of energy.

• Polar solvent: Dissolves ionic substances, forms hydration shells.

• Reactivity: Involved in hydrolysis and dehydration reactions.

• Cushioning: Protects organs from physical trauma.

Water as a Polar Molecule

• Oxygen exerts strong pulls on electrons of other elements.

• Hydrogen easily gives up its single electron.

• Water forms hydrogen bonds, important for structure and function of biomolecules.

Acids, Bases, and pH

• pH: Measure of hydrogen ion concentration ($[H^+]$) in a solution.

• Acid: Releases $H^+$ (pH < 7).

• Base: Accepts $H^+$ (pH > 7).

• Buffers: Resist abrupt changes in pH; bicarbonate buffer system is important in blood.

Cellular Basics and Transfer of Biological Information

Benefits of Being Multicellular

• Division of labor (specialization of cells).

• Increased life span (single cells can die but organism persists).

• Complexity and adaptability.

Cell Diversity

• Estimated 400 unique cell types in the human body.

• Cells need each other to survive; different cells have different anatomy and physiology.

Summary Table: Major Elements and Their Functions

Element	Body Mass (%)	Main Functions
Oxygen	65	Component of water, needed for aerobic metabolism
Carbon	18.5	Backbone of all organic molecules
Hydrogen	9.5	Component of water and most organic molecules
Nitrogen	3.3	Component of proteins and nucleic acids

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.