Chemistry and Physiology: Foundations for Anatomy & Physiology

Chemistry and Physiology

Introduction to Chemistry in Physiology

Chemistry forms the foundation for understanding physiological processes in the human body. Atoms, molecules, and chemical bonds are essential for the structure and function of cells, tissues, and organs.

Atoms: Basic Structural Units of Matter

Atomic Structure

• Atoms are the smallest units of matter that retain the properties of an element.

• Protons: Positively charged particles located in the nucleus; determine the atomic number and identity of the element.

• Neutrons: Neutral particles also found in the nucleus; contribute to atomic mass but not charge.

• Electrons: Negatively charged particles that orbit the nucleus in energy levels (shells).

• Protons and neutrons contribute to the atomic mass.

Atomic Number and Mass

• The atomic number equals the number of protons in an atom and is unique for each element.

• The number of neutrons can vary, resulting in different isotopes of an element.

• In a neutral atom, the number of electrons equals the number of protons.

• Example: Carbon has an atomic number of 6, so it has 6 protons and, in its most common form, 6 neutrons and 6 electrons.

Electron Arrangement and Energy Levels

• Electrons occupy specific energy levels or shells around the nucleus.

• The arrangement of electrons determines an atom's chemical properties and reactivity.

• Valence electrons are those in the outermost shell and are involved in chemical bonding.

Ions and the Periodic Table

Formation of Ions

• Ions are charged particles formed when atoms gain or lose electrons.

• Atoms that lose electrons become cations (positively charged).

• Atoms that gain electrons become anions (negatively charged).

• The periodic table can be used to predict the charges of ions formed by different elements.

Periodic Table and Ion Prediction

• Groups (columns) on the periodic table indicate the number of valence electrons and typical ionic charges.

• For example, Group 1 elements form +1 ions, Group 2 form +2 ions, Group 17 form -1 ions, etc.

Chemical Bonds

Ionic Bonds

Ionic bonds are formed when electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions that attract each other.

• Ionic bonds are generally weaker than covalent bonds in aqueous solutions because water can disrupt them by forming hydration spheres around ions.

• Example: Sodium chloride (NaCl) dissociates in water into Na+ and Cl- ions.

Covalent Bonds

Covalent bonds occur when atoms share valence electrons. These bonds can be nonpolar or polar depending on the equality of electron sharing.

• Nonpolar covalent bonds: Electrons are shared equally (e.g., H2, O2).

• Polar covalent bonds: Electrons are shared unequally, creating partial positive and negative poles (e.g., H2O).

• Oxygen, nitrogen, and phosphorus often form polar covalent bonds due to their high electronegativity.

Hydrogen Bonds

Hydrogen bonds are weak attractions between the slightly positive hydrogen atom of one polar molecule and the slightly negative atom of another polar molecule. They are crucial for the properties of water and the structure of biological molecules.

• Hydrogen bonds are responsible for water's surface tension and its role as a universal solvent.

• They also stabilize the structures of proteins and nucleic acids.

Hydrophilic vs. Hydrophobic Molecules

• Hydrophilic molecules are water-soluble because they can form hydration spheres (e.g., glucose, amino acids).

• Hydrophobic molecules are nonpolar and do not dissolve in water (e.g., lipids).

Acids, Bases, and pH

pH Scale

• The pH of a solution measures its hydrogen ion (H+) concentration.

• The pH scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Acids have a pH less than 7; bases have a pH greater than 7.

Acids and Bases

• Acids are proton donors; they release H+ ions in solution.

• Bases are proton acceptors; they decrease H+ concentration in solution.

Acid	Symbol	Base	Symbol
Hydrochloric acid	HCl	Sodium hydroxide	NaOH
Phosphoric acid	H3PO4	Potassium hydroxide	KOH
Nitric acid	HNO3	Calcium hydroxide	Ca(OH)2
Sulfuric acid	H2SO4	Ammonium hydroxide	NH4OH
Carbonic acid	H2CO3

Buffers and Blood pH

• Buffers are molecules that minimize changes in pH by binding or releasing H+ ions.

• The bicarbonate buffer system is crucial for maintaining blood pH:

$\mathrm{H_2O + CO_2 \leftrightarrow H_2CO_3 \leftrightarrow H^+ + HCO_3^-}$

• This reaction can shift to add or remove H+ as needed.

• Normal blood pH is 7.35–7.45; deviations can result in acidosis (pH < 7.35) or alkalosis (pH > 7.45).

Summary Table: Key Chemical Concepts in Physiology

Concept	Definition	Example
Atom	Smallest unit of an element	Carbon atom
Ion	Charged atom or molecule	Na+, Cl-
Ionic bond	Attraction between oppositely charged ions	NaCl
Covalent bond	Atoms share electrons	H2O
Hydrogen bond	Weak attraction between polar molecules	Between water molecules
Acid	Proton donor	HCl
Base	Proton acceptor	NaOH
Buffer	Minimizes pH changes	Bicarbonate system