Anatomy & Physiology: Practice Exam Study Notes – Body Regions, Ions, Hydrophobicity, pH, and Biomolecules

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Body Regions and Anatomical Terminology

The human body is divided into specific regions for anatomical reference. The anterior (front) aspect of the body includes several key regions:

Cranial: Refers to the head or skull region.
Popliteal: The area behind the knee (posterior, not anterior).
Sternal: The region overlying the sternum (breastbone) in the center of the chest.
Calcaneal: The heel of the foot (posterior, not anterior).

Example: The sternal region is located on the anterior (front) side of the body, while the popliteal and calcaneal regions are posterior.

Body Fluids and Electrolytes

Body fluids are divided into intracellular and extracellular compartments. The extracellular fluid (ECF) contains several important ions:

Sodium (Na+): The most abundant cation in ECF; crucial for nerve impulse transmission and fluid balance.
Calcium (Ca2+): Important for muscle contraction, blood clotting, and signaling; present in lower concentrations than sodium.
Chloride (Cl-): The major anion in ECF; helps maintain osmotic balance and electrical neutrality.
Potassium (K+): The major intracellular cation; present in lower concentrations in ECF.

Example: Sodium and chloride are found in higher concentrations in the extracellular fluid compared to potassium.

Hydrophobic and Hydrophilic Substances

Hydrophobic substances are those that do not dissolve in water. This property is important in cell membrane structure and function.

Water: Hydrophilic (water-loving), dissolves many substances.
Na+ (Sodium ion): Hydrophilic, dissolves in water.
Glucose: Hydrophilic, dissolves in water.
Lipid: Hydrophobic, does not dissolve in water; forms the core of biological membranes.

Example: Lipids such as fats and oils are hydrophobic and aggregate in aqueous environments.

Acid-Base Balance and Blood pH

The pH of blood is a measure of its hydrogen ion concentration. Normal blood pH is tightly regulated between 7.35 and 7.45.

Acidosis: A condition where blood pH falls below 7.35, indicating excess hydrogen ions (H+).
Severe acidosis: Can impair cellular function, enzyme activity, and oxygen delivery.
Diabetic coma: Often associated with ketoacidosis, where the body produces excess acidic ketone bodies.

Equation:

Example: In diabetic ketoacidosis, blood pH may drop below 7.0, leading to life-threatening complications.

Additional info: Acidosis affects the function of hemoglobin and can depress the central nervous system, leading to coma or death if untreated.

Homeostasis and Control Systems

Homeostasis is the maintenance of a stable internal environment. Negative feedback mechanisms counteract changes to restore balance.

Components: Sensor (detects change), control center (processes information), effector (carries out response).
Example: If body temperature rises, sensors in the skin and brain detect the change, the hypothalamus (control center) activates sweat glands (effectors) to cool the body.

Additional info: Negative feedback loops are essential for regulating variables such as blood glucose, pH, and electrolyte balance.

Oxygen and Solubility

Oxygen is a nonpolar molecule but is slightly soluble in water due to its small size and ability to form weak interactions.

Bonds: Oxygen forms covalent bonds within the O2 molecule; does not form hydrogen bonds with water.
Solubility: Limited in water; transported in blood mainly bound to hemoglobin.

Example: Only a small fraction of oxygen is dissolved in plasma; most is carried by red blood cells.

Proteins: Structure and Function

Proteins are the most versatile biomolecules, performing a wide range of functions in the body.

Example: Insulin is a protein hormone that regulates blood glucose levels.