Foundations of Anatomy & Physiology: Structure, Function, Chemistry, and Homeostasis

Organization of Life

Structure-Function Relationship

The study of anatomy and physiology is rooted in understanding how the structure of biological components determines their function. This principle is foundational to the organization of living things.

• Anatomy: Study of the structure of cells, tissues, organs, and organisms.

• Physiology: Study of the function of cells, tissues, organs, and organisms.

• Structure dictates function: Evolution selects for favorable functions, which are determined by underlying structures.

• Examples:

  • Kangaroo rat – desert adaptation

  • Human – hand structure for tool use

  • Fish – gills for water respiration

Organization of Living Things

Living organisms are organized hierarchically, with each level contributing to the overall function and survival of the organism.

• Principles of matter/energy (Physics)

• Atoms and molecules (Chemistry)

• Organic molecules (Biochemistry)

• Cells (Cellular Biology)

• Tissues (Histology)

• Organs (Physiology/Anatomy)

• Organ/body systems (Physiology/Anatomy)

• Organism (Physiology/Anatomy)

Basic Functions of Organisms

Maintenance of Boundaries

Organisms must separate their internal environment from the external world to maintain homeostasis.

• Viruses: Protein coat surrounds DNA/RNA interior.

• Cells: Cell membrane (semipermeable, selective).

• Organism: Skin acts as a boundary.

Movement

Movement is essential for transporting materials and locomotion.

• Cells: Cilia and flagella (e.g., sperm).

Responsiveness

Responsiveness is the ability to sense and react to changes in the environment.

• Nervous system: Quick response to change.

• Endocrine system: Medium/longer changes.

Digestion

Digestion breaks down food into usable/absorbable forms.

• Digestive system: Breaks down and absorbs essential materials.

Metabolism

Metabolism encompasses all chemical reactions in cells and the body.

• Anabolism: Building larger molecules.

• Catabolism: Breaking down larger molecules.

• Regulated primarily by the endocrine system.

Cellular respiration: Breaking bonds of larger molecules for usable energy (ATP).

• Digestive system: Mainly carbohydrates and fats.

• Respiratory system: Oxygen and carbon dioxide exchange.

• Cardiovascular system: Distribution of nutrients and gases.

Equation:

$\text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water} + \text{ENERGY (stored in ATP)}$

Excretion

Excretion removes all types of waste from the body.

• Digestive system: Unused foodstuffs.

• Urinary system: Nitrogenous wastes (urea) and electrolytes (salt balance).

• Respiratory system: Carbon dioxide.

Reproduction

Reproduction creates new organisms of the same species.

• Cells: Process of cell division (mitosis).

• Sperm and egg: Sexual reproduction.

• Regulated by hormones (especially female).

Growth

Growth increases the size of cells, organs, or organisms.

• Number of cells can increase (mitosis).

• Size of cells can increase (fat cells).

Basic Biological Needs of Humans

Nutrients

Nutrients are molecules required for structure and energy.

• Carbohydrates: Primary energy source and structural component (glycogen, sugars).

• Lipids (fats): Insulation, energy, structure; major component of membranes (phospholipids); highest energy content by weight (calories).

• Proteins: Structure, enzymes, signaling; includes neuropeptides (enkephalins of nervous system).

• Vitamins: Act as cofactors for enzyme functioning.

• Minerals: Essential for signaling and structure (e.g., Na+, K+, Ca2+, Cl-, Fe in hemoglobin, bone – Ca2+, phosphate).

Oxygen

Oxygen is essential for maximum energy gain from food.

• Cellular respiration depends on oxygen.

• Nervous system uses 25% of all oxygen in humans.

Water

Water is essential for cellular reactions and transport.

Body Temperature

Most human enzymes work best at 37°C (98°F).

Atmospheric Pressure

Proper absorption of oxygen requires appropriate atmospheric pressure.

Homeostasis

Definition and Importance

Homeostasis is the maintenance of relatively constant internal conditions in response to internal and external changes. It is essential for survival and proper function.

• Dynamic process: Changing but relatively constant within limits.

• Maintains internal environment of the body despite external changes.

• Requires proper balance of oxygen, carbon dioxide, and other variables.

Examples of Homeostatic Mechanisms

• Proper nutrient levels in blood (e.g., insulin/glucagon for blood glucose).

• Proper heart rate and blood pressure (adrenaline response to stimuli).

• Removing wastes from the blood (kidneys for urea, lungs for carbon dioxide).

• Maintaining proper oxygen levels in blood (brain and respiratory system adjust breathing rate).

• Body posture and simple muscular reflexes (nervous and muscular systems).

General Characteristics of Homeostatic Control Mechanisms

• Nervous & Endocrine Systems are general controls.

• Basic organization:

  • Receptor: Monitors internal/external stimuli and sends info to control center via afferent path.

  • Control center: Analyzes info and compares to a "set point" for that variable.

  • Effector: Acts from the control center via efferent path to restore balance.

Negative Feedback Mechanisms

Negative feedback reduces the intensity of a stimulus, helping to maintain homeostasis.

• Example: Regulation of glucose levels in blood.

  • Person eats a candy bar (high sugar).

  • Blood glucose rises rapidly.

  • Receptors sense increase in blood sugar.

  • Control center reduces blood sugar via insulin release.

  • Insulin causes cells to absorb glucose and store it as glycogen.

  • Glucose levels return to normal (0.9 mg/ml blood).

Positive Feedback Mechanisms

Positive feedback increases the intensity of a condition, often leading to a cascade effect.

• Example: Labor contractions during birth.

  • Baby rotates, causing pressure on cervix.

  • Receptors sense increased muscle tension.

  • Control center calls for release of oxytocin, causing muscles to contract.

  • Increased tension causes more oxytocin release.

  • Process continues until baby is delivered and stimulus is removed.

Matter and Energy

Matter

Matter is the fundamental building block of nature, composed of elements.

• Elements: Basic units of matter.

Energy

Energy is the capacity to do work (put matter into motion).

• Potential energy: Stored energy (e.g., water behind a dam, chemical bonds in glucose).

• Kinetic energy: Energy in motion (e.g., muscle work).

Forms of Energy

• Chemical energy: Energy in chemical bonds (e.g., ATP).

• Electrical energy: Movement of charged particles.

• Mechanical energy: Direct movement (e.g., muscle contraction).

• Electromagnetic energy: Energy traveling in waves (light, X-rays).

First Law of Thermodynamics

Energy can change from one form to another, but cannot be created or destroyed.

Equation:

$\text{Total Energy in} = \text{Total Energy Out}$

• Example: Food used to move body, digest, think, etc. Chemical energy (food/glucose) → physiology (80%) + heat (20%)

Atoms, Elements, and the Periodic Table

Atomic Structure

Atoms are composed of protons, neutrons, and electrons.

• Proton: +1 charge

• Neutron: 0 charge

• Electron: -1 charge

Atomic number = number of protons; atomic mass = protons + neutrons.

Organization of the Periodic Table

• Each element has a unique number of protons (atomic number).

• Isotopes: Same element, different number of neutrons.

Isotope	# Protons	# Neutrons	Atomic Mass
Carbon-12 (99%)	6	6	12
Carbon-13 (0.9%)	6	7	13
Carbon-14 (0.1%)	6	8	14

Electron Shells and Chemical Bonds

Electron shells are organized around the nucleus and determine chemical bonding.

• Ionic bond: One atom donates electron(s) to another (e.g., NaCl).

• Covalent bond: Two atoms share one or more electrons (e.g., CH4, CO2, NH3).

• Polar molecule: Unequal electron sharing (e.g., H2O).

• Non-polar molecule: Equal electron sharing (e.g., CH4).

Elements in the Human Body

Element	Function
Calcium (Ca)	Bones, teeth, muscle and nerve action, blood clotting
Phosphorus (P)	Bones and teeth, DNA, RNA, ATP
Sodium (Na)	Osmotic balance, cell voltage, muscle and nerve action
Potassium (K)	Osmotic balance, cell voltage, muscle and nerve action
Chlorine (Cl)	Osmotic balance, cell voltage, muscle and nerve action
Iron (Fe)	Hemoglobin and many enzymes
Magnesium (Mg)	Cofactor for many enzymes
Zinc (Zn)	Cofactor for many enzymes
Copper (Cu)	Cofactor for many enzymes
Selenium (Se)	Cofactor for many enzymes
Cobalt (Co)	Cofactor for many enzymes and vitamin B12
Molybdenum (Mo)	Cofactor for many enzymes
Iodine (I)	Required for normal thyroid function
Fluorine (F)	Teeth and bones

Chemical Reactions

Patterns of Chemical Reactions

• Chemical Equation: Number of atoms of each element is the same for reactants and products.

  • Example: $C_6H_{12}O_6 + 6O_2 \rightarrow 6H_2O + 6CO_2$

• Synthesis: Small molecules form larger molecules.

  • Example: Amino acids form proteins; sugars form polysaccharides.

  • $A + B \rightarrow AB$ (anabolic process)

• Decomposition: Larger molecules broken down into smaller molecules.

  • Example: Glycogen breaks down to glucose.

  • $AB \rightarrow A + B$ (catabolic process)

• Displacement: One part is exchanged.

  • $AB + C \rightarrow AC + B$

  • Example: $\text{glucose} + \text{adenosine-P-P (ATP)} \rightarrow \text{glucose-P} + \text{adenosine-P-P (ADP)}$

Exergonic vs. Endergonic Reactions

• Exergonic: Energy is released during the reaction.

  • $A + B \rightarrow C + D + \text{ENERGY}$

  • Example: $\text{glucose} + \text{oxygen} \rightarrow \text{water} + \text{carbon dioxide} + \text{ENERGY}$ (trapped by ATP)

• Endergonic: Energy is required for the reaction to proceed.

Summary

In anatomy and physiology, understanding the relationship between structure and function, the organization of living things, the basic needs and functions of organisms, and the chemical principles underlying biological processes is essential. Homeostasis is a central concept, maintained by feedback mechanisms and control systems. The study of matter, energy, atoms, and chemical reactions provides the foundation for understanding how the body works at the molecular and cellular levels.