Body Fluids Quiz

Body Fluids

• Extracellular Fluid (ECF) makes up 1/3 of total body water, and is the fluid environment cells live in.
• It comprises Plasma, found inside blood cells, and Interstitial Fluid, which surrounds cells.
• Intracellular Fluid (ICF) makes up 2/3 of total body water and is found within all body cells. It has high levels of potassium (K+) and lower levels of sodium (Na+).
• ICF has a negative charge due to the presence of proteins.
• The total body water content for a 70kg male is roughly 42 liters.
• This results in 28 liters of ICF and 14 liters of ECF.
• Plasma accounts for 3.5 liters of ECF and Interstitial Fluid accounts for 10.5 liters.

Balancing Internal and External Environments

• Cells exchange nutrients and wastes with their surroundings.
• The intracellular fluid is conditioned by the interstitial fluid.
• The interstitial fluid is conditioned by the plasma.
• The plasma is conditioned by the organ systems it passes through.
• The internal environment refers to the fluid surrounding cells (Extracellular Fluid).

Homeostasis

• Homeostasis refers to the maintenance of a relatively constant and stable internal environment (extracellular fluids).
• It is often regulated by negative feedback control.

Negative Feedback

• An initial change leads to a response that suppresses the initial change.
• For example, eating food increases glucose levels in the blood, the pancreas releases insulin to lower blood glucose levels.
• Negative feedback is used for frequent adjustments of conditions like body temperature blood pressure and glucose regulation.

Positive Feedback

• An initial change leads to a response that increases the initial change.
• It is short-lived and not required for continuous adjustments.
• Examples include: blood clotting, urination, LH increase before ovulation, Na+ inflow in the generation of nerve signals, and uterine contractions during childbirth.

Feed-Forward Control

• A response is made in anticipation of a change.
• The stimulus directly affects the control system before the action of feedback.
• This prepares the body for the change.
• Examples include shivering before diving into cold water and salivation in response to smelling food.

Human Cell

• The human body is multicellular, composed of different types of cells.
• An estimated 50-100 trillion cells are present in the human body.
• Differentiation is the process of cells becoming specialized.
• The unique functions of cells result in varied sizes and shapes.
• The cell membrane is selectively permeable.
• It allows lipid-soluble materials to cross, while lipid-insoluble (water-soluble) materials need channels.
• Cell membranes contain 40% protein, 55% lipid, and 3 % carbohydrates.

Cell Membrane

• Phospholipids are the major component of the cell membrane.
• They have a bilayer structure.
• The water-soluble heads form the surface, while the water-insoluble tails form the interior.
• It is permeable to lipid-soluble substances.

Movements Into and Out of the Cell

• Passive processes move substances down a concentration gradient, do not need ATP and include simple diffusion, facilitated diffusion, and osmosis.
• Active processes move substances against a concentration gradient, need energy, and include primary active transport and secondary active transport.

Simple Diffusion

• It is the movement of a substance from a region of higher concentration to a region of lower concentration.
• It doesn't require a carrier molecule or energy.
• It is affected by factors like the concentration gradient, temperature, membrane permeability, and surface area.

Facilitated Diffusion

• It is the movement of a substance from a region of higher concentration to a region of lower concentration.
• It requires a carrier or transporter molecule but does not require energy.
• Carrier or transporter molecules increase the rate of diffusion.
• It is specific and affected by saturation.

Osmosis

• It is the movement of water molecules from a region of higher water concentration to a region of lower water concentration across a selectively permeable membrane.
• It is driven by differences in water potential or osmotic pressure.
• It is crucial for maintaining cell volume and fluid balance.
• It is affected by the concentration of solutes on each side of the membrane.
• It relies on aquaporins (specific water channels) for efficient transport.

Active Transport

• It is the movement of a substance from a region of lower concentration to a region of higher concentration.
• It requires energy and a carrier protein.
• It maintains concentration gradients and is crucial for cellular functions.

Primary Active Transport

• It directly uses energy from ATP hydrolysis to move the substance against its concentration gradient.
• It involves carrier proteins that bind to the substance and undergo conformational changes to move it across the membrane.
• Examples include the Na+/K+ pump, Ca++ active transport, active transport of H+ in the stomach and kidneys, and the H+/K+ pump.

Secondary Active Transport

• It uses the potential energy stored in an electrochemical gradient established by primary active transport.
• It couples the movement of one substance (e.g., Na+) down its electrochemical gradient with the movement of another substance (e.g., glucose) against its concentration gradient.
• Examples include glucose and amino acid co-transport and Na+/Ca++ counter-transport.

Membrane Resting Potential

• It is a constant potential difference across the resting cell membrane.
• The cell's ability to fire an action potential is dependent on maintaining a resting potential of approximately -70mV.
• Changes in resting potential influence basic neuronal signaling properties.

Membrane Potential

• The membrane potential is the difference in electrical potential across a cell membrane.
• It is influenced by:
  • The concentration gradients of ions (Na+, K+, Cl-, Ca++) across the membrane.
  • The permeability of the membrane to these ions.
  • The activity of ion pumps (e.g., the Na+/K+ pump).
• Resting potential is a specialized case when the membrane is not transmitting signals.
• The membrane potential is dynamic and changes in response to stimuli, like nerve impulses.
• It plays a crucial role in various cellular processes, including:
  • Nerve signal transmission.
  • Muscle contraction.
  • Hormone release.
  • Sensory perception.
  • Cellular communication.
  • Maintaining cell volume and shape.

Introduction

• The body is a complex structure with each organ serving a vital role
• The structure of each organ helps it perform its function
• For example, the chest cavity protects the heart and lungs, and changes shape to enable breathing

Levels of Organization

• The body is organized into levels of increasing complexity, from the chemical level to the organismic level
• Chemical level: involves atoms and molecules like Oxygen, Nitrogen, Carbon, Hydrogen, and molecules such as water, CO2, CHO, and proteins.
• Cellular level: comprises cells, the basic unit of life, responsible for performing the necessary functions of life.
• Tissue level: composed of similar cells with the same structure and specialized function working together, Examples include epithelial, connective, muscle, and nerve tissues.
• Organ level: made up of two or more tissues working together towards a common function, Examples of organs are the skin, femur, heart, kidney.
• System level: a group of related organs with a common function. For example, the digestive system.
• Organismic level: the whole human being, a complex organism made up of all the above levels.

Body Fluids

• The total body water of a healthy adult is 60% of their body weight
• Body water content decreases with age and is lower in females due to higher fat content.
• Water is the most suitable liquid for the body due to its specific heat, capillary action, solvent properties, and role in redox reactions.

Feedback Systems

• Feedback systems maintain homeostasis in the body.
• Negative feedback: a mechanism that reduces or reverses a change in the body to maintain equilibrium, for example blood glucose regulation.
• Positive feedback: a mechanism that amplifies an initial change, for example, blood clotting, LH increase before ovulation, and contraction of the uterus during childbirth.
• Feed-forward control: a mechanism that anticipates a change and prepares the body for it, for example, shivering before diving into cold water, or salivation when we smell food before eating.

The Human Cell

• The human body is multicellular and contains 50-100 trillion cells.
• Cells differentiate to specialize in various functions, contributing to the survival of the organism.

Cell Membrane Physiology

• Simple Diffusion: movement of non-polar, lipid-soluble molecules, small polar covalent bonds, and water across the cell membrane.
• Facilitated Diffusion: movement of lipid-insoluble, water-soluble substances across the membrane with the help of membrane proteins.
• Osmosis: movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration, it is important for functions at the cellular and tissue levels.

Osmotic Pressure and Solutions

• Osmotic pressure of a solution depends on the concentration of solutes.
• Hypotonic solution: the osmotic pressure of the solution is lower than the osmotic pressure of the cells (water enters the cells).
• Hypertonic solution: the osmotic pressure of the solution is higher than the osmotic pressure of the cells (water exits the cells).
• Isotonic solution: the osmotic pressure of the solution is equal to the osmotic pressure of the cells (water movement is balanced).

Example: Blood Volume Restoration

• Infusing isotonic NaCl solution is better than an isoosmotic solution of a penetrating solute (such as urea) because only isotonic NaCl solution can maintain blood volume at the proper level; urea would diffuse into the cells, leading to fluid accumulation and cellular swelling.