Homeostasis & Body Fluid in Physiology

Homeostasis & Body Fluid

• Homeostasis is the maintenance of a relatively stable internal environment (ECF) within narrow limits despite continuous external and internal changes.
• The body is in a dynamic steady state, meaning constant adjustments are made to maintain stability.
• Homeostasis is crucial for the survival and function of all body cells.
• It maintains necessary conditions like nutrient levels, oxygen supply, waste removal, and temperature.
• Cells depend on homeostasis to maintain a suitable internal environment.
• Failure of homeostasis can lead to illness or death.

Learning Objectives

• Understand the importance of maintaining a constant internal environment in biological systems.
• Understand the components of the control system in our bodies.
• Learn about negative and positive feedback mechanisms.
• Identify different body fluid compartments and their compositions.
• Differentiate between osmolarity and tonicity.

Introduction to Physiology

• Physiology is the study of the functions of living things, especially how the human body works.
• There are two key approaches for explaining physiological events: analyzing the purpose of a body process and its underlying mechanisms.

Homeostasis - The Stabilizer

• It is a process that opposes initial changes, maintaining a controlled variable within a narrow range.
• It restores the variable to its set point.
• Homeostatic mechanisms involve sensors, integrating centers, and effectors that work together to respond to changes in the internal environment.
• Homeostasis is important for maintaining various critical physiological variables, such as temperature, blood glucose, and blood pressure.
• Its failure can lead to an uncontrolled overshoot of change.

Regulation of Body Functions

• Extrinsic/Systemic Controls:
  • Nervous system: Responsible for fast responses using electrical signals, controlling various bodily functions such as heart rate, and working in conjunction with the endocrine system.
  • Endocrine system: Controls slower responses using hormones in the bloodstream. Insulin and glucagon regulate blood sugar, for instance.
• Intrinsic/Local Controls: These controls occur at the tissue level, providing localized adjustments to changing environmental conditions. Blood vessel dilation during exercise is an example.

Control of Homeostasis

• A feedback system or feedback loop is a cycle of events that monitors and evaluates changes in body condition.
• Feedback systems comprise three key components:
  • Receptor/Sensor: Detects deviations from the set point.
  • Integrating Centre: Determines and initiates the appropriate response.
  • Effector: Produces a response to counter the deviation.

Negative Feedback System

• It's a process that opposes an initial change, maintaining a controlled variable within a certain range.
• It works to restore the variable to a set point.
• An example is the regulation of body temperature.
• The mechanism involves detecting the deviation, initiating a response to correct it, and ceasing the response once the set point is reached, stabilizing the internal condition.

Example of Negative Feedback System (Blood Glucose)

• Eating increases blood glucose.
• Pancreatic islets release insulin to increase cellular glucose uptake.
• Blood glucose levels drop.
• If blood glucose drops too low, the body reacts by releasing glucagon and cellular glucose secretion from the liver.

Positive Feedback System

• It enhances or amplifies an initial change, moving a variable further in the direction of the change.
• It's triggered by an initial stimulus, leading to a self-reinforcing cycle.
• An example of a positive feedback system is childbirth, lactation, and blood clotting.

Example of Positive Feedback System (Childbirth)

• Baby's head pushes against the cervix.
• This triggers uterine contractions that push the baby further.
• These contractions amplify until the birth is complete.

Distribution of Body Fluid/Water

• The human body is approximately 60% fluid.
• Females have a slightly lower percentage of body fluid compared to males because females have more adipose tissue (fat).
• Adiposity decreases the total body water (TBW).
• Age also affects the amount of body fluid, with older adults having less.
• Approximately 40% of body weight in an average person is fluid - including 40% Intracellular fluid and 20% Extracellular fluid.

Body Fluids Compartments

• Body fluids are distributed into two major compartments:
  • Intracellular fluid (ICF): Fluid inside cells.
  • Extracellular fluid (ECF): Fluid outside cells.
  • ECF consists of plasma (fluid portion of blood), interstitial fluid, small amounts of other fluids such as lymphatic fluid and cerebrospinal fluid.

Body Fluid Compartments Solute Concentration

• Solute concentration in body fluid compartments is measured in osmoles.
• Osmolarity: Solute concentration per liter of solution.
• Osmolality: Solute concentration per kilogram of water.
• Isosmotic solutions have the same solute concentration to the respective compartment.
• Hyperosmotic solutions have a higher solute concentration compared to the respective compartment.
• Hypoosmotic solutions have a lower solute concentration compared to the respective compartment.

Osmosis

• Osmosis is the movement of water across a semipermeable membrane, driven by differences in solute concentrations. Water moves away from the more dilute solution to the more concentrated solution.

Osmotic Pressure

• Osmotic pressure is the minimum pressure needed to prevent water movement across a semipermeable membrane.
• Important nonpenetrating solutes, impermeable to cell or membrane, create osmotic pressure.

Tonicity

• Tonicity describes the effect of the concentration of nonpenetrating solutes in a solution on cell volume. This impacts how the cell will change volume and shape.
• Isotonic: Maintaining the same concentration of nonpenetrating solutes inside and outside the cell, preventing water movement, and maintaining cell size.
• Hypotonic: Solution with a lower concentration of nonpenetrating solutes, causing water to move into the cell, potentially leading to swelling or lysis.
• Hypertonic: Solution with a higher concentration of nonpenetrating solutes, causing water to move out of the cell, potentially leading to shrinkage or crenation.

Regulation of Blood Osmolality

• Normal plasma osmolality ranges from 280 to 290 mOsm/L.
• Factors like dehydration can cause changes in blood volume and plasma osmolarity.
• Osmoreceptors in the hypothalamus detect these changes and initiate responses.
• The body regulates blood osmolarity primarily through water reabsorption and excretion in the kidneys, and adjusting thirst.

This quiz explores the concept of homeostasis and its vital role in maintaining a stable internal environment within the body. Understand the mechanisms involved, including feedback systems and the importance of body fluid compartments. Test your knowledge on how these processes are crucial for survival and overall health.