Lecture.1 Body fluids

Introduction to Human Physiology

  • Title: Introduction to Human Physiology

  • Presenter: Dr. Adel Hussein, Professor of Medical Physiology, Faculty of Medicine-Minia University.

Learning Objectives

  • At the end of the lecture, students should be able to:

    1. Understand the building up of the human body from cells to systems.

    2. Describe the composition of the human body.

    3. Discuss body fluid compartments (intracellular and extracellular).

    4. Discuss disorders of body water (dehydration and overhydration).

Overview of Human Physiology

  • Human physiology is the science that studies the functions of the human body under various internal and external environmental conditions to maintain life.

Human Body Organization

  • Cell: Smallest basic structural unit of the human body.

  • Tissue: Group of cells arranged side by side, having the same shape, structure, and function.

  • Organ: Composed of more than one tissue and performs a specific function (e.g., heart pumps blood).

  • System: Comprises multiple organs that perform complementary functions, determining the characteristic role of that system in life.

Basic Living Units of the Body

  • The basic living unit is the cell, with various examples:

    • Skin cells

    • Cells of the alimentary tract

    • Striated muscle cells

    • Nerve cells

    • Red blood cells

    • Sperm and egg cells

Systems of the Body

  • Endocrine System

  • Digestive System

  • Nervous System

  • Excretory System

  • Cardiovascular System

  • Reproductive System

  • Respiratory System

  • Musculoskeletal System

Composition of the Human Body

  • Chemically: The human body is composed of 60% water and 40% solids:

    • Organic: Protein (18%) and fat (15%).

    • Inorganic: Minerals (7%).

Body Fluids

  • Total Body Water: Approximately 60% of total body weight.

  • Intracellular Fluid (ICF): Constitutes about 2/3 of total body water (40% of body weight).

  • Extracellular Fluid (ECF): Constitutes about 1/3 of total body water (20% of body weight), divided into:

    • Intravascular Fluid (Plasma): 1/4 of ECF volume.

    • Extravascular Fluid: 3/4 of ECF volume, including interstitial fluid and transcellular fluids (e.g., cerebrospinal fluid).

Body Fluid Distribution

  • Breakdown of body fluid distribution in relation to total body weight:

    • Intracellular Fluid (ICF): 40% (solid content).

    • Extracellular Fluid (ECF): 20%, with interstitial fluid (15%) and plasma (5%).

  • Fluid movement occurs due to hydrostatic and osmotic pressure.

Calculation of Total Body Water

  • Example: Total Body Water in a 40-year-old male weighing 70 kg:

    • Total Body Water = 60/100 * 70 = 42 liters.

    • Intracellular volume = 42 X ⅔ = 28L.

    • Extracellular volume = 42 X ⅓ = 14L.

Composition of ECF vs. ICF

  • Extracellular Fluid (ECF):

    • Main cation: Na+ (142 mEq/L)

    • Main anion: Cl-

    • pH: About 7.4

  • Intracellular Fluid (ICF):

    • Main cation: K+ (140 mEq/L)

    • Main anion: HPO4 & proteins.

    • pH: About 7 due to low HCO3.

Functions of Body Water

  1. Medium for chemical and enzymatic reactions.

  2. Facilitates physical processes (e.g., diffusion and filtration).

  3. Acts as an ionizing medium to regulate pH and osmolarity.

  4. Regulates body temperature.

  5. Serves as a lubricant in joints.

  6. Acts as a refractive medium in the eye.

  7. Provides mechanical protection (cerebrospinal fluid).

  8. Medium for gas exchange (O2 & CO2) in lungs and tissues.

Regulation of Water Balance

  • Input = Output: To maintain constant fluid levels, the amount of water gain must equal loss.

  • Water Gain: 2300 ml from intake and food.

  • Water Loss: 2300 ml through urine, feces, sweat, and insensible loss.

Disorders of Water Balance

  • Dehydration: Negative water balance due to loss exceeding gain, caused by sweating, vomiting, diarrhea, or water deprivation. Mild dehydration can occur with a loss of just 1.5% of body water.

  • Overhydration: Positive water balance due to excessive gain, can result from excessive ADH secretion or drinking excessive water without salt.

Manifestations of Dehydration

  • Cold, pale skin; dry, wrinkled skin; sunken eyes; loss of body weight; increased thirst; hypotension; fatigue; oliguria/impaired renal function; irritability; and can lead to coma or death.

Correction of Dehydration

  • Body Role: In response to hypovolemia, ADH release increases, stimulating thirst and promoting retention of water.

  • Treatment: Oral or IV fluids (isotonic saline, glucose solutions).

Vulnerability to Dehydration

  • Infants and children are more susceptible due to higher ECF/ICF ratios and less renal water retention.

Manifestations of Overhydration

  • Generalized edema; increased blood pressure; nausea and vomiting; decreased plasma osmolarity; convulsions leading to coma and death due to cerebral edema.

Correction of Overhydration

  • Body Role: In response to hypervolemia, ADH secretion decreases, reducing water retention.

  • Treatment: Hypertonic saline IV and diuretics (e.g., Lasix) to increase urine output.

Sample Questions

  1. Which cation is most abundant in extracellular fluid?

  2. What is the normal amount of extracellular fluid in an adult male?

  3. Enumerate three manifestations of dehydration.