Introduction to Physiology and Homeostasis

What is Physiology?

• Physiology is the study of the vital functions of living organisms and their components.
• The human body is a complex system with many components, including organs, cells, and molecules.
• Physiology examines how each component works, how they interact with each other, and ultimately how they contribute to the overall function of the organism

Maintaining Homeostasis

• Homeostasis is the state of maintaining a stable internal environment.
• It is essential for the survival of cells and tissues, and ultimately, the organism.
• The body can resist changes to a certain extent, but prolonged deviation from homeostasis can lead to disease.

The Cell - The Basic Unit of Life

• The cell is the fundamental building block of all living organisms.
• It consists of cytoplasm, which is a gelatinous fluid that contains various organelles with specific functions.
• Some organelles like the nucleus, endoplasmic reticulum, and Golgi apparatus are typically singular, while others like mitochondria, chloroplasts, peroxisomes, and lysosomes can be numerous.

Structure of the Cell Membrane

• All cells are enclosed by a plasma membrane.
• The plasma membrane is semi-permeable, meaning it allows some substances to pass through while blocking others.
• Its selective permeability is maintained by ion channels, transport proteins, and other components.
• The membrane plays a crucial role in maintaining unique compositions of the intracellular fluid (ICF) and extracellular fluid (ECF).

Membrane Lipids

• Phospholipids are the major component of the cell membrane.
• Cholesterol molecules are also present in the phospholipid bilayer.
• The phospholipid bilayer acts as a barrier around the cell and controls the movement of substances between the ICF and the ECF.
• The fluidity of the membrane, which is influenced by the movement of phospholipids and cholesterol, allows cells to change shape.

Membrane Proteins

• Membrane proteins have various functions, including:
  • Ion channels: Facilitate the movement of ions across the membrane along their concentration gradients. (Downhill Transport)
  • Carriers: Bind and transport molecules across the membrane along their concentration gradients. (Downhill Transport)
  • Pumps: Use energy (ATP) to move molecules across the membrane against their concentration gradients. (Uphill Transport)
  • Receptors: Bind to signaling molecules like neurotransmitters and hormones, triggering changes in cellular functions. (Signal Transduction)
  • Enzymes: Catalyze specific biochemical reactions within the cell.
  • Cell adhesion molecules (CAM): Help cells adhere to each other, forming intercellular junctions.

Membrane Carbohydrates

• Membrane carbohydrates are located on the outer surface of the cell membrane.
• They are composed of glycoproteins and glycolipids.
• Membrane carbohydrates function as:
  • Receptors for certain hormones.
  • Cell recognition markers, allowing cells to identify and interact with each other.
  • Antigens, such as blood group markers.

Homeostasis and Its Regulation

• The internal environment of the body, the extracellular fluid (ECF), must be maintained within a narrow range of conditions for proper cell function.
• These conditions include:
  • pH: 7.4
  • Blood volume: 5 liters
  • Blood pressure: 120/80 mmHg
  • Temperature: 37°C
  • Partial pressure of oxygen (PO2): 100 mmHg in arterial blood
  • Partial pressure of carbon dioxide (PCO2): 40 mmHg in arterial blood
  • Concentration of water, electrolytes, nutrients, and waste products.

Body Systems Contributing to Homeostasis

• Multiple body systems work together to maintain homeostasis.
• These systems include:
  • Circulatory system: Transports nutrients, oxygen, carbon dioxide, waste products, and electrolytes throughout the body.
  • Respiratory system: Takes in oxygen and releases carbon dioxide, regulating blood gas levels.
  • Digestive system: Digests and absorbs nutrients.
  • Nervous system: Controls rapid, short-term responses to changes in the internal and external environments.
  • Endocrine system: Secretes hormones that regulate long-term processes like growth, reproduction, and metabolism.
  • Musculoskeletal system: Supports and moves the body, contributing to posture and stability.
  • Immune system: Defends against infections and foreign invaders.
  • Skin: Acts as a barrier to prevent entry of foreign substances and plays a role in vitamin D activation.
  • Urinary system: Excreates waste products, excess water, electrolytes, and hydrogen ions, maintaining fluid balance.

Homeostatic Control Systems

• Feedback mechanisms regulate homeostasis:
  • Feedback: refers to responses made after a change has been detected.
  • Receptor (sensor): Detects changes in the controlled variable.
  • Control center: Compares the current value of the variable to the set point and sends corrective instructions.
  • Effector: Receives commands from the control center and carries out the response to restore the variable to its set point.

Types of Feedback Mechanisms

• Negative Feedback: Primarily used in the body to oppose an initial change and promote stability.
  • Examples:
    • Regulating blood pressure
    • Maintaining body temperature
    • Regulating blood glucose levels
    • Regulating blood gas levels.
• Positive Feedback: Amplifies an initial change, pushing the variable further away from the set point, often used for specific short-term processes:
  • Examples:
    • Childbirth: Stretch receptors in the uterus trigger the release of oxytocin, which intensifies uterine contractions.
    • Blood clotting: Activated platelets trigger further platelet activation, accelerating the clotting process.
    • Stress response: Stress hormones can amplify the stress response itself, leading to a positive feedback loop.

Feedforward Control

• Feedforward control anticipates changes in a regulated variable and responds ahead of time:
  • Examples:
    • Increased saliva secretion at the sight, smell, or thought of food.
    • Increased respiration before exercise.
    • Shivering before entering cold water.
    • Increased insulin secretion in the digestive tract to prevent excessive blood glucose rise after a meal.

This quiz explores the fundamental concepts of physiology, focusing on the vital functions of living organisms and the importance of homeostasis in maintaining a stable internal environment. It will also delve into the cellular structure and the roles of different organelles within the cell. Test your understanding of these essential biological principles.