Homeostasis and Survival Needs

Survival Needs

Humans require several essential factors for survival, each of which must be maintained within appropriate limits to ensure health and function.

• Nutrients – Includes sugars (not table sugars), ions, and salts necessary for cellular processes.

• Oxygen – Required for cellular respiration and energy production.

• Water – Vital for chemical reactions, transport, and temperature regulation.

• Normal body temperature – Ensures optimal enzyme and metabolic activity.

• Appropriate atmospheric pressures – Necessary for effective gas exchange in the lungs.

Homeostasis

Homeostasis is the process of maintaining the body's internal environment in a relatively constant state, despite external changes. This includes regulation of temperature, blood pressure, glucose levels, and more.

• Homeostatic Imbalance – Any disturbance that disrupts the balance of the internal environment.

• Homeostasis is a ceaseless process of activities in response to stresses, aiming to maintain equilibrium.

Homeostatic Control Mechanisms

These mechanisms are generally self-regulating and maintain the homeostatic "steady state." They involve three main components:

• Receptor – Detects changes in the environment.

• Control Center – Processes information (often the brain).

• Effector – Carries out the response to restore balance.

Negative Feedback

Negative feedback mechanisms reduce the intensity of the original stimulus, helping to maintain stability.

• The output shuts off the original effect or reduces its intensity.

• A change in one direction results in feedback that causes a change or adjustment in the opposite direction.

• This is how most homeostatic control mechanisms function, similar to a thermostat.

Positive Feedback

Positive feedback mechanisms enhance the original stimulus, resulting in an accelerated response.

• Rare in life; examples include:

  • Blood clotting

  • Labor contractions

  • Orgasm

Basic Chemistry for Anatomy & Physiology

Energy

Energy is the capacity to do work or put matter into motion. It does not have mass or occupy space. The greater the work done, the more energy is used up.

Elements

All matter is composed of elements, which are substances that cannot be broken down into simpler substances by ordinary chemical methods.

• Four elements make up 96% of the human body:

  • Oxygen

  • Carbon

  • Hydrogen

  • Nitrogen

• The periodic table lists all known elements.

Atoms

Elements are made up of atoms, which are the smallest units of an element that retain its properties.

• Atoms are unique building blocks for each element.

• Atoms consist of a nucleus (protons and neutrons) and electrons orbiting the nucleus.

Molecules, Compounds, and Mixtures

Molecules and Compounds

• Molecule – General term for two or more atoms bonded together. Molecules with only one type of atom (e.g., O2, H2) are called elemental molecules.

• Compound – Specific molecule that has two or more different kinds of atoms bonded together (e.g., C6H12O6 = glucose).

Mixtures

Most matter exists as mixtures, which are two or more components physically intermixed. There are three basic types:

1. Solutions

   • Homogeneous mixtures; particles evenly distributed.

   • Solvent: Substance present in greatest amount (usually liquid, e.g., water).

   • Solute: Substance dissolved in solvent (e.g., glucose in blood plasma).

   • True solutions are usually transparent.

2. Colloids

   • Also known as emulsions; heterogeneous mixtures with particles not evenly distributed.

   • Can see large solute particles in solution, but they do not settle out.

   • Gives solution a cloudy or milky look.

3. Suspensions

   • Heterogeneous mixtures with large, visible solutes that do settle out.

   • Example: Mixture of water and sand.

   • Blood is considered a suspension because blood cells will settle out if left in a tube.

Chemical Bonds

Ionic Bonds

Ions are atoms that have gained or lost electrons and become charged. Oppositely charged ions attract each other to form ionic bonds.

• Number of protons does not equal number of electrons.

• Ionic bonds involve the transfer of valence shell electrons from one atom to another.

• One atom becomes an anion (negative charge), the other a cation (positive charge).

• Attraction of opposite charges results in an ionic bond.

Covalent Bonds

Covalent bonds are formed by the sharing of two or more valence shell electrons between atoms.

• Sharing of 2 electrons: single bond

• Sharing of 4 electrons: double bond

• Sharing of 6 electrons: triple bond

• Allows each atom to fill its valence shell at least part of the time.

• Two types: Polar and Nonpolar covalent bonds

Chemical Reactions

Overview

Chemical reactions occur when chemical bonds are formed, rearranged, or broken. These reactions can be written in symbolic forms called chemical equations.

• Reactants: Substances entering into reaction together

• Products: Resulting chemical end products

• Amounts of reactants and products are shown in balanced equations

Types of Chemical Reactions

1. Synthesis (combination) reactions: Atoms or molecules combine to form larger, more complex molecules.

   • Example equation:

2. Decomposition reactions: Breakdown of a molecule into smaller molecules or its constituent atoms (reverse of synthesis).

   • Example equation:

3. Exchange reactions: Also called displacement reactions, involve both synthesis and decomposition.

   • Bonds are both made and broken.

   • Example equations: and

Energy Flow in Chemical Reactions

All chemical reactions are either exergonic or endergonic:

• Exergonic reactions: Net release of energy (products have less potential energy than reactants; catabolic – breaking apart).

• Endergonic reactions: Net absorption of energy (products have more potential energy than reactants; anabolic – making bigger molecules).

Rate of Chemical Reactions

The speed of chemical reactions can be affected by several factors:

• Temperature: Increased temperature usually increases rate of reaction.

• Concentration/Pressure of Reactants: Increased concentration/pressure usually increases rate.

• Particle Size: Smaller particles usually increase rate.

• Catalysts: Increase the rate of reaction without being chemically changed or becoming part of the product. Enzymes are biological catalysts.

Summary Table: Types of Chemical Bonds

Summary Table: Types of Mixtures

Additional info: Some explanations and examples have been expanded for clarity and completeness.