Study guide: Body Fluids and Biomolecules

📋 Course Outline

1. Chemical Basis of Life
2. Blood Composition and Plasma
3. Blood Cells and Haematocrit
4. Electrolytes and Fluid Balance
5. Solutes and Osmotic Effects
6. Water Properties and Pressure
7. Pulmonary Surfactant
8. Carbohydrates and Proteins

📖 1. Chemical Basis of Life

📝 Essential Points

• More than 95% of a living organism is composed of oxygen, carbon, hydrogen, and nitrogen.

💡 Memory Hook

OCHN: oxygen, carbon, hydrogen, nitrogen

📖 2. Blood Composition and Plasma

🔑 Key Concepts & Definitions

• Blood: Composed of formed elements suspended in a liquid called plasma.

★ Must-know

• Plasma accounts for 55–60% of blood and contains water, inorganic salts, and proteins.

📌 Plasma is the fluid in which blood cells are suspended, whereas serum is the fluid remaining after blood has clotted and lacks platelets and fibrinogen.

Further detail

• Carbon dioxide is a waste product of cellular respiration and can stimulate respiration when arterial carbon dioxide levels rise.

💡 Memory Hook

Plasma carries suspended cells; serum remains after clotting

📖 3. Blood Cells and Haematocrit

🔑 Key Concepts & Definitions

• Haematocrit: Measures the volume of packed red blood cells relative to the volume of whole blood.

★ Must-know

📐 Formula — Haematocrit equals the height of red blood cells divided by the height of all blood components, multiplied by 100: $HCT = \frac{\text{height of RBC}}{\text{height of all blood components}}\times 100.$

Further detail

• The buffy coat accounts for less than 1% of blood and contains white blood cells and platelets.

📌 An increased haematocrit increases blood viscosity and can affect resistance in blood vessels.

💡 Memory Hook

Higher haematocrit → higher blood viscosity → altered vascular resistance

📖 4. Electrolytes and Fluid Balance

🔑 Key Concepts & Definitions

• Hypernatremia: A plasma or serum sodium ion level that is higher than usual.

★ Must-know

• Normal saline is a sterile, non-pyrogenic 0.9% sodium chloride solution used intravenously for fluid and electrolyte replenishment, volume expansion, and electrolyte replacement.

• The stated physiological roles include:

  • Calcium in nerve impulses, muscle contraction, blood clotting, and bone
  • Chloride as the major extracellular anion and contributor to water balance
  • Potassium as the major intracellular cation involved in nerve impulses

Further detail

• Because sodium attracts water, increased sodium can retain water and affect water balance, indirectly affecting blood pressure.

💡 Memory Hook

Na⁺ is mainly extracellular, whereas K⁺ is mainly intracellular

📖 5. Solutes and Osmotic Effects

🔑 Key Concepts & Definitions

• Solute: A substance that dissolves into a solution through a solvent.

★ Must-know

• Examples of non-electrolytes include:
  • Glucose
  • Lipids
  • Creatinine
  • Urea

📌 Effective osmoles affect osmotic pressure and can cross the membrane, whereas ineffective osmoles cannot affect osmotic pressure and can cross the membrane.

Further detail

• Examples of effective osmoles include sodium ions and glucose, while urea is an example of an ineffective osmole.

💡 Memory Hook

Electrolytes dissociate into ions; non-electrolytes do not

📖 6. Water Properties and Pressure

🔑 Key Concepts & Definitions

• Surface Tension: The observation that a liquid surface behaves as though tense because of cohesive forces between water molecules linked by hydrogen bonds.
• Manometer: A manometer measures pressure by means of a vertical column of fluid, such as in a mercury sphygmomanometer for arterial blood pressure or a saline manometer for central venous pressure.
• Meniscus: The curve in the upper surface of a liquid where the liquid touches the container surface.

💡 Memory Hook

Cohesion creates surface tension, while adhesion helps form the meniscus

📖 7. Pulmonary Surfactant

🔑 Key Concepts & Definitions

• Pulmonary Surfactant: A mixture of phospholipids and proteins produced by type 2 alveolar cells that reduces surface tension at the alveolar air–liquid interface.
• Neonatal Respiratory Distress Syndrome: A breathing disorder of premature newborns caused by absent or insufficient surfactant, which allows alveoli to collapse.

★ Must-know

• Surfactant lubricates alveoli, allowing them to expand without overstretching and become smaller without collapsing.

Further detail

• Neonatal respiratory distress syndrome is mostly seen before the 28th week, while surfactant production normally begins around 24–26 weeks of gestation and reaches mature levels around 34–35 weeks.

💡 Memory Hook

Insufficient surfactant → alveolar collapse → neonatal respiratory distress

📖 8. Carbohydrates and Proteins

★ Must-know

📌 Monosaccharides are single carbohydrate units, disaccharides contain two monosaccharides, and oligosaccharides contain more than one linked monosaccharide.

• Lactose intolerance results from insufficient lactase in the small-intestinal brush border, causing colonic bacteria to ferment lactose and produce gas and osmotic effects.

• The four levels of protein structure are:

  • Primary structure: amino acid chain
  • Secondary structure: alpha helix or pleated sheet
  • Tertiary structure: three-dimensional folding from R-group interactions
  • Quaternary structure: two or more polypeptide chains

• Examples of fibrous proteins include:

  • Keratin
  • Collagen
  • Elastin
  • Fibrinogen

Further detail

• Hydrolysis of glycogen during fasting releases glucose monomers into the blood and prevents blood glucose from falling to dangerously low levels.

• A disulfide bond forms between two sulfur atoms of cysteine, while a hydrophobic interaction occurs between two non-polar side chains.

💡 Memory Hook

Protein structure: primary → secondary → tertiary → quaternary

📊 Synthesis Tables

Blood Fluid Comparisons

Component	Composition or location	Key role
Plasma	Fluid containing blood cells; 55–60% of blood	Carries water, salts, and proteins
Serum	Fluid remaining after clotting; lacks platelets and fibrinogen	Post-clotting fluid
Buffy coat	Less than 1%; white blood cells and platelets	Cellular blood component
Erythrocytes	40–45% of blood	Measured by haematocrit