Foundations of Anatomy & Physiology: Homeostasis, Chemistry, Cells, and Membranes

Homeostasis & Introduction to Metabolism

Levels of Biological Organization

Biological systems are organized hierarchically, from atoms and molecules up to cells, tissues, organs, organ systems, and the organism as a whole.

• Atoms & Molecules: The basic chemical units of life.

• Cells: The smallest living units, capable of independent function.

• Tissues: Groups of similar cells performing a common function.

• Organs: Structures composed of multiple tissue types.

• Organ Systems: Groups of organs working together for a specific function.

Example: The digestive system includes organs such as the stomach and intestines, which work together to process food.

Homeostasis

Homeostasis refers to the maintenance of a stable internal environment despite changes in external conditions.

• Negative Feedback: A process that counteracts changes, bringing the system back to its set point. Example: Regulation of body temperature.

• Positive Feedback: A process that amplifies changes, moving the system further from its set point. Example: Blood clotting.

Metabolism

Metabolism encompasses all chemical reactions occurring in the body, including those that build up (anabolism) and break down (catabolism) molecules.

• Anabolism: Synthesis of complex molecules from simpler ones.

• Catabolism: Breakdown of complex molecules into simpler ones.

Thermodynamics – Energy Use in Cells

• Exergonic Reactions: Release energy (e.g., ATP → ADP + P).

• Endergonic Reactions: Require energy input.

• Activation Energy: The energy required to initiate a chemical reaction.

Example: Cellular respiration is an exergonic process that releases energy for cellular activities.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Specificity: Each enzyme acts on a specific substrate.

• Regulation: Enzyme activity can be regulated by inhibitors, activators, and environmental conditions.

Example: Amylase catalyzes the breakdown of starch into sugars.

Chapter 2: Chemistry Review

Atomic Structure

Atoms consist of protons, neutrons, and electrons. The arrangement of electrons determines chemical reactivity.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Sum of protons and neutrons.

• Isotopes: Atoms with the same number of protons but different numbers of neutrons.

Chemical Bonds

Chemical bonds form between atoms to create molecules.

• Ionic Bonds: Transfer of electrons between atoms.

• Covalent Bonds: Sharing of electrons between atoms.

• Hydrogen Bonds: Weak attractions between polar molecules.

Example: Water molecules are held together by hydrogen bonds.

Properties of Water

• Polarity: Water is a polar molecule, allowing it to dissolve many substances.

• High Specific Heat: Water resists changes in temperature, helping maintain homeostasis.

Chapter 3: Biological Macromolecules

Types of Macromolecules

Biological macromolecules are large molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Provide energy and structural support.

• Lipids: Store energy, form cell membranes, and act as signaling molecules.

• Proteins: Perform a wide range of functions, including catalysis, transport, and structural support.

• Nucleic Acids: Store and transmit genetic information (DNA and RNA).

Monomers and Polymers

• Monomers: Small building blocks (e.g., amino acids, monosaccharides).

• Polymers: Large molecules made by joining monomers (e.g., proteins, polysaccharides).

Example: Glucose (monomer) forms starch (polymer).

Functions of Macromolecules

• Carbohydrates: Energy source, cell recognition.

• Lipids: Membrane structure, energy storage.

• Proteins: Enzymes, transport, signaling.

• Nucleic Acids: Genetic information storage and transfer.

Chapter 4: Cells

Cellular Organelles and Their Functions

Cells contain specialized structures called organelles, each with distinct functions.

• Nucleus: Contains genetic material and controls cell activities.

• Mitochondria: Site of ATP production through cellular respiration.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digest cellular waste and foreign material.

• Other Organelles: Peroxisomes, cytoskeleton, etc.

Example: Muscle cells contain many mitochondria to meet high energy demands.

Chapter 5: Membranes

Structure and Function of Cell Membranes

Cell membranes are composed of a phospholipid bilayer with embedded proteins, providing selective permeability and protection.

• Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails face inward.

• Membrane Proteins: Facilitate transport, signaling, and cell recognition.

Transport Across Membranes

Cells use various mechanisms to move substances across membranes.

Form of Transport	Passive Transport	Active Transport
Diffusion	X
Facilitated	X
Simple	X
Endocytosis/Exocytosis		X
Osmosis	X
Receptor-Mediated		X

Passive Transport: Movement of substances down their concentration gradient without energy input (e.g., diffusion, osmosis).

Active Transport: Movement of substances against their concentration gradient, requiring energy (e.g., sodium-potassium pump).

Osmolarity and Osmosis

Osmolarity refers to the concentration of solute particles in a solution. Osmosis is the movement of water across a semipermeable membrane from low to high solute concentration.

• Isotonic Solution: No net movement of water.

• Hypertonic Solution: Water moves out of the cell; cell shrinks.

• Hypotonic Solution: Water moves into the cell; cell swells.

Example: Red blood cells placed in a hypotonic solution will swell and may burst.

Membrane Permeability

Membrane permeability determines which substances can cross the membrane. Factors include size, polarity, and presence of transport proteins.

• Small, nonpolar molecules: Easily cross the membrane.

• Large or charged molecules: Require transport proteins.

Bulk Transport

Bulk transport involves the movement of large particles or volumes of fluid via vesicles.

• Endocytosis: Uptake of materials into the cell.

• Exocytosis: Release of materials from the cell.

Example: White blood cells engulf bacteria via endocytosis.

Physiological Relevance

Understanding membrane transport is essential for explaining physiological processes such as nerve impulse transmission, nutrient absorption, and fluid balance.

• Application: Use knowledge of osmosis and transport to predict cell behavior in different environments.

Additional info: Academic context and definitions have been expanded for clarity and completeness.