Inorganic Compounds and Water: Foundations for Anatomy & Physiology

Inorganic Compounds in Biology

Overview of Inorganic Compounds

Inorganic compounds are essential to biological systems, even though living organisms are primarily composed of organic molecules. Inorganic compounds do not contain both carbon and hydrogen together. Key inorganic compounds relevant to Anatomy & Physiology include:

• Water

• Salt

• Acid

• Base

Each of these compounds consists of a cation (positively charged ion) and an anion (negatively charged ion). The chemical formula of an inorganic compound is written with the cation first, followed by the anion.

Water

Structure and Importance of Water

Water (H2O) is the most abundant inorganic compound in living organisms, making up 60-80% of living cells. Water can also be represented as HOH, with H+ as the cation and OH- as the anion. Water is referred to as a hydroxyl ion when considering its dissociation.

• High heat capacity: Water absorbs and retains heat, helping to stabilize temperature changes in biological systems.

• High heat of vaporization: Water requires significant energy to change from liquid to gas, which is important for cooling mechanisms such as sweating.

• Polar solvent properties: Water is a polar molecule, allowing it to dissolve many ionic and polar substances. This property is crucial for biochemical reactions.

• Reactivity: Water participates in chemical reactions, including hydrolysis and dehydration synthesis.

• Cushioning: Water provides protection to organs and tissues, such as the fluid surrounding a fetus in the uterus.

Example: Water surrounds and cushions the brain and spinal cord, protecting them from trauma.

Properties of Water

Key Physical and Chemical Properties

• Polarity: Water molecules have a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms, making water an excellent solvent for ionic compounds.

• Hydrogen bonding: The polarity of water allows for hydrogen bonds between molecules, contributing to its high heat capacity and surface tension.

Example: Water's polarity enables it to dissolve salts such as sodium chloride (NaCl).

Salts

Definition and Biological Role

Salts are ionic compounds formed by the reaction of an acid and a base. They consist of a cation other than H+ and an anion other than OH-. Salts dissociate in water to release ions, which are essential for various physiological processes.

• Electrolytes: Salts dissociate into ions that conduct electrical currents in solution, crucial for nerve impulse transmission and muscle contraction.

• Examples: Sodium chloride (NaCl), potassium chloride (KCl), calcium phosphate (Ca3(PO4)2).

Example: NaCl dissociates in water to form Na+ and Cl- ions.

Acids and Bases

Definitions and Functions

• Acid: A substance that releases H+ ions in solution. Example: Hydrochloric acid (HCl) in the stomach.

• Base: A substance that releases OH- ions or accepts H+ ions. Example: Sodium hydroxide (NaOH) in digestive juices.

Example: HCl dissociates in water to form H+ and Cl-; NaOH dissociates to form Na+ and OH-.

Neutralization

Acid-Base Reactions

Neutralization occurs when an acid reacts with a base to produce water and a salt. This is an important process in maintaining pH balance in biological systems.

• General reaction:

$\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$

Example:

$\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}$

In this reaction, hydrogen ions from the acid combine with hydroxide ions from the base to form water, while the remaining ions form a salt.

Dissociation of Ions and pH

Ionic Dissociation and pH Scale

When salts, acids, or bases dissolve in water, they dissociate into their respective ions. The concentration of hydrogen ions (H+) in solution determines the pH, which is a measure of acidity or alkalinity.

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

• Formula:

$\mathrm{pH} = -\log_{10}[\mathrm{H^+}]$

• Blood pH: Normal blood pH is 7.4, with acceptable limits from 7.35 to 7.45. Values outside this range can be harmful.

Example: Lemon juice has a pH of about 2, while household bleach has a pH of about 9.5.

Table: pH Values of Common Substances

Substance	pH Value
1 M Sodium hydroxide	14
Oven cleaner, lye	13.5
Household ammonia	10.5–11.5
Household bleach	9.5
Egg white	8
Blood	7.4
Milk	6.3–6.6
Black coffee	5
Wine	2.5–3.5
Lemon juice, gastric juice	2

Buffers

Role in pH Regulation

A buffer is a solution that resists changes in pH when small amounts of acid or base are added. Buffers are vital in maintaining stable pH in biological fluids, such as blood.

• Bicarbonate buffer system: The main buffer system in blood, helping to maintain pH within a narrow range.

Example: The kidneys and lungs work together to regulate blood pH by controlling the levels of bicarbonate and carbon dioxide.

Summary Table: Inorganic Compounds and Their Functions

Compound	Function	Example
Water	Solvent, temperature regulation, cushioning	Cerebrospinal fluid
Salt	Electrolyte balance, nerve conduction	NaCl
Acid	pH regulation, digestion	HCl in stomach
Base	pH regulation, neutralization	NaOH in digestive juices

Additional info: The notes have been expanded to include definitions, examples, and academic context for each compound, as well as the role of buffers and the pH scale in physiology.