Homeostasis and Feedback Mechanisms

Definition and Components

Homeostasis refers to the maintenance of a stable internal environment in an organism, despite external changes. It is essential for proper physiological function.

• Sensor (Receptor): Detects changes in the environment (e.g., skin thermoreceptors for temperature).

• Control Center: Processes information and determines the response (e.g., hypothalamus in the brain).

• Effector: Carries out the response (e.g., muscles shivering to generate heat).

Memory tip: S-C-E: Sensor → Control → Effector.

Feedback Loops

• Negative Feedback: The most common type; opposes the initial change to maintain balance. Examples: Temperature regulation, blood glucose control.

• Positive Feedback: Amplifies the initial change. Examples: Childbirth contractions, blood clotting.

Set Point: The target value for a physiological variable (e.g., body temperature ≈ 37°C).

Examples and Applications

• Negative Feedback Example: Body temperature regulation—if temperature rises, mechanisms activate to cool the body.

• Positive Feedback Example: During childbirth, contractions intensify until delivery.

Atoms, Ions, and Isotopes

Atomic Structure

• Atom: The smallest unit of matter, composed of protons, neutrons, and electrons.

• Atomic Number (Z): Number of protons in the nucleus; defines the element.

• Atomic Mass: Sum of protons and neutrons.

• Atomic Weight: Weighted average of all isotopes of an element.

Ions

• Cation: Positively charged ion (more protons than electrons).

• Anion: Negatively charged ion (more electrons than protons).

Example: Na+ is a cation; Cl- is an anion.

Isotopes and Radioactivity

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Radioisotopes: Unstable isotopes that emit radiation as they decay.

• Half-life: Time required for half of a radioactive sample to decay.

Chemical Bonds and Molecules

Types of Bonds

• Ionic Bonds: Transfer of electrons from one atom to another (e.g., NaCl).

• Covalent Bonds: Sharing of electron pairs between atoms (e.g., H2O).

• Polar Covalent Bonds: Unequal sharing of electrons, leading to partial charges (e.g., H2O).

Molecules and Compounds

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: Substance formed from two or more different elements (e.g., CO2).

Polyatomic Ions

• Examples: NH4+, OH-, HCO3-, NO3-, SO42-, PO43-

Acids, Bases, and pH

Definitions

• Acid: Substance that donates H+ ions in solution.

• Base: Substance that accepts H+ ions or donates OH- ions.

• pH Scale: Measures the concentration of H+ ions; ranges from 0 (acidic) to 14 (basic).

Formula:

• Neutral: pH = 7

• Acidic: pH < 7

• Basic: pH > 7

Buffers: Substances that minimize changes in pH by accepting or donating H+ ions.

Cell Structure and Function

Cell Membrane and Organelles

• Cell Membrane: Phospholipid bilayer with hydrophilic heads (outward) and hydrophobic tails (inward); controls entry and exit of substances.

• Microvilli: Increase surface area for absorption.

• Centrioles: Involved in cell division.

• Cilia: Move fluids across cell surfaces.

• Flagella: Enable movement (e.g., sperm cells).

• Ribosomes: Synthesize proteins.

• Rough Endoplasmic Reticulum (Rough ER): Studded with ribosomes; synthesizes proteins.

• Smooth Endoplasmic Reticulum (Smooth ER): Synthesizes lipids, detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and ships proteins and lipids.

• Lysosomes: Contain enzymes to digest bacteria and waste.

• Peroxisomes: Break down toxins (e.g., H2O2).

• Mitochondria: Produce ATP (energy) via cellular respiration.

• Nucleus: Control center; stores DNA.

• Nuclear Envelope: Double membrane surrounding the nucleus.

• Nucleolus: Produces rRNA and ribosome subunits.

Genetic Information Flow

• Transcription: DNA is copied into mRNA.

• Translation: mRNA is used to synthesize proteins.

Summary: DNA → mRNA (transcription) → Protein (translation)

Cellular Fluids

• Extracellular Fluid (ECF): Fluid outside cells.

• Intracellular Fluid (ICF): Fluid inside cells (cytosol).

Cytoskeleton

• Function: Provides structural support, maintains cell shape, and assists in movement.

Organelle Functions Table

Case Study Example

• Lysosome Failure: If lysosomes fail, waste accumulates in cells, potentially leading to diseases such as rheumatoid arthritis.

Additional info: Some content was inferred and expanded for clarity, including standard definitions and examples of chemical and cellular concepts.