Anatomy & Physiology Exam 1 Review: Homeostasis, Physiology, Cells, and Tissues

Homeostasis and Reflex Pathways

Reflex Pathway Steps

Reflex pathways are fundamental mechanisms by which the body maintains homeostasis in response to internal and external changes. The process involves several key steps:

• Stimulus: A change in the environment (e.g., temperature).

• Sensor: Detects the change (e.g., thermometer senses temperature).

• Input Signal: Signal sent from sensor to integrating center.

• Integrating Center: Processes the input and determines the response (e.g., control box programmed to respond).

• Output Signal: Signal sent from integrating center to target.

• Target: The effector that carries out the response (e.g., heater).

• Response: The action taken to restore homeostasis (e.g., water temperature increases).

Example: In a fish tank, a thermometer senses a drop in water temperature, sends a signal to a control box, which activates a heater to restore the temperature.

Consequences of Failed Homeostasis

Homeostasis is the maintenance of a stable internal environment. Failure to maintain homeostasis can lead to pathophysiology, illness, or death.

• External/Internal Change: Triggers loss of homeostasis.

• Compensation: The organism attempts to restore balance.

• Outcomes: If compensation fails, illness or disease occurs; if successful, wellness is maintained.

The Science of Physiology

Experimental Science and Hypothesis Testing

Physiology is an experimental science driven by hypotheses and the scientific method.

• Hypothesis: A logical guess about how an event takes place.

• Scientific Method: Involves developing and testing hypotheses through experiments.

• Variables: Independent variable (experimental manipulation) and dependent variable (measured outcome).

Example: "Cold temperatures cause birds to eat more." Independent variable: Temperature (27°C, 4°C, 0°C, -12°C). Dependent variable: Food intake amount.

Compartmentation: Cells and Tissues

Body Compartments

The body is organized into anatomical and functional compartments to separate biochemical processes.

• Anatomical Compartments: Body cavities (cranial, thoracic, abdominal, pelvic).

• Functional Compartments: Body fluid compartments (extracellular fluid, intracellular fluid).

Example: The extracellular fluid (ECF) is outside cells, while intracellular fluid (ICF) is inside cells. Blood plasma is a component of ECF.

Organs and Lumen

Some organs have lumens that are considered part of the external environment (e.g., digestive tract, blood vessels).

• Lumen: The interior space of a hollow organ.

• External Environment: The lumen of the digestive tract is technically outside the body.

Cell Membrane Structure and Function

Fluid Mosaic Model

The cell membrane is a dynamic structure composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Phospholipid Bilayer: Provides barrier and fluidity.

• Proteins: Integral and peripheral proteins serve as channels, carriers, receptors, and enzymes.

• Carbohydrates: Attached to proteins and lipids, involved in cell recognition.

Membrane Transport Mechanisms

Cells exchange substances with their environment through various transport mechanisms:

• Simple Diffusion: Passive movement of small, nonpolar molecules (e.g., O2, CO2) down their concentration gradient.

• Facilitated Diffusion: Passive transport of polar molecules via protein channels or carriers (e.g., glucose via GLUT transporters).

• Osmosis: Movement of water across a semi-permeable membrane.

• Active Transport: Movement of substances against their concentration gradient, requiring energy (ATP).

Fick's Law of Diffusion:

$J = -D \frac{dC}{dx}$ Where: J = rate of diffusion D = diffusion coefficient dC/dx = concentration gradient

Osmolarity and Tonicity

Osmolarity refers to the concentration of solute particles per liter of solution. Tonicity describes how a solution affects cell volume.

• Hypertonic Solution: Causes cells to shrink (water leaves the cell).

• Isotonic Solution: No net change in cell volume.

• Hypotonic Solution: Causes cells to swell (water enters the cell).

Cell Junctions and Tissue Types

Types of Cell Junctions

Cell junctions connect cells and facilitate communication and structural integrity.

Junction Type	Function	Example
Gap Junctions	Communication; allow chemical and electrical signals to pass directly between cells	Cardiac muscle
Tight Junctions	Prevent movement of material between cells	Intestinal epithelium
Desmosomes	Anchor cells to one another and to the extracellular matrix	Skin epithelium

Major Tissue Types

The human body is composed of four primary tissue types, each with distinct functions:

• Nervous Tissue: Internal communication (brain, spinal cord, nerves).

• Muscle Tissue: Contracts to cause movement (skeletal, cardiac, smooth muscle).

• Epithelial Tissue: Forms boundaries, protects, secretes, absorbs, filters (skin, lining of GI tract).

• Connective Tissue: Supports, protects, binds other tissues (bones, tendons, fat).

Additional info:

• Some content inferred from context and standard Anatomy & Physiology curriculum, such as the definition of Fick's Law and tissue functions.