Blood: Internal Transport System and Composition

Blood – Internal Transport System

Overview of Blood Functions

Blood is the life-sustaining transport vehicle of the cardiovascular system, responsible for delivering essential substances and removing wastes from the body.

• Transport Functions:

  • Delivering O2 and nutrients to body cells

  • Transporting metabolic wastes to lungs and kidneys for elimination

  • Transporting hormones from endocrine organs to target organs

• Regulation Functions:

  • Maintaining body temperature by absorbing and distributing heat

  • Maintaining normal pH using buffers; alkaline reserve of bicarbonate

  • Maintaining adequate fluid volume in circulatory system

• Protection Functions:

  • Preventing blood loss (plasma proteins and platelets initiate clot formation)

  • Preventing infection (agents of immunity carried in blood: antibodies, complement proteins, white blood cells)

Composition of Blood

Blood as a Connective Tissue

Blood is the only fluid tissue in the body and is classified as a connective tissue. Its matrix is a nonliving fluid called plasma, and the cells are living blood cells called formed elements.

• A spun tube of blood yields three layers:

  • Erythrocytes (red blood cells) on bottom (~45% of whole blood)

  • Buffy coat (leukocytes and platelets) in the middle (<1%)

  • Plasma on top (~55%)

• Hematocrit: Percent of blood volume that is RBCs

  • Normal values: Males: 47% ± 5%; Females: 42% ± 5%

Visual Representation

The process of blood separation by centrifugation shows the distinct layers: plasma, buffy coat, and erythrocytes.

Physical Characteristics and Volume

Blood Color and pH

Blood color varies with oxygen content:

• High O2 levels: bright red

• Low O2 levels: dark red

Blood pH ranges from 7.35–7.45 and makes up about 8% of body weight.

• Average blood volume:

  • Males: 5–6 L

  • Females: 4–5 L

Blood pH Levels

• Death: <7.0

• Acidosis: 7.0–7.35

• Normal pH: 7.35–7.45

• Alkalosis: >7.45

Blood Plasma

Composition and Functions

Blood plasma is the straw-colored, sticky fluid portion of blood. It is composed of water, proteins, and dissolved solutes.

• 90% water: dissolves and suspends solutes, absorbs heat

• Solutes include:

  • Electrolytes (most abundant by number): sodium, potassium, calcium, magnesium, chloride, phosphate, sulfate, bicarbonate

  • Plasma proteins (8% by weight):

    • Albumin (60%): produced by liver, main contributor to osmotic pressure

    • Globulins (36%): transport proteins and antibodies

    • Fibrinogen (4%): forms fibrin threads of blood clot

  • Other solutes: nutrients, respiratory gases, hormones, nonprotein nitrogenous substances

Table: Composition of Plasma

Constituent	Description and Importance
Nonprotein nitrogenous substances	By-products of cellular metabolism (urea, uric acid, creatinine, ammonium salts)
Nutrients (organic)	Materials absorbed from digestive tract and transported for use throughout body (glucose, amino acids, fatty acids, vitamins)
Respiratory gases	Oxygen and carbon dioxide; oxygen mostly bound to hemoglobin in RBCs, carbon dioxide dissolved as bicarbonate or bound to hemoglobin
Hormones	Steroid and thyroid hormones carried by plasma proteins

Plasma Proteins

• Albumin: Maintains osmotic pressure and pH

• Globulins: Transport proteins and antibodies

• Fibrinogen: Forms blood clots

Clinical Importance

• Plasma proteins are essential for maintaining blood volume, pressure, and immune defense.

• Abnormal plasma protein levels can indicate liver or kidney disorders.

Additional info: Plasma also contains clotting factors, enzymes, and waste products, all crucial for homeostasis and diagnostic testing.