Introduction to Human Anatomy & Physiology

Anatomy: Study of Structure

Anatomy is the branch of biology concerned with the study of the structures of the human body. It is divided into several subfields based on the scale and method of observation:

• Macroscopic anatomy (gross anatomy): Examines larger structures visible to the naked eye, such as organs and organ systems.

• Microscopic anatomy: Focuses on structures that require magnification, such as cells and tissues.

  • Cytology: The study of cells.

  • Histology: The study of tissues.

Approaches to Anatomical Study

There are several approaches to studying anatomy, each providing unique perspectives:

• Surface anatomy: Study of external features and landmarks.

• Systemic anatomy: Study of body systems (e.g., cardiovascular, skeletal).

• Regional anatomy: Study of specific regions of the body (e.g., head, thorax).

• Developmental anatomy: Study of structural changes throughout the lifespan.

Learning anatomy involves mastering terminology, observation, manipulation, palpation (feeling organs), and auscultation (listening to organ sounds).

Physiology: Study of Function

Physiology investigates the functions and mechanisms of the human body, often at the cellular and molecular levels. Understanding physiology requires knowledge of physics and chemistry, as many processes involve chemical reactions and physical principles.

• Most physiological studies are organized by organ systems.

• Form and function are closely related; for example, thin lung tissues allow rapid gas exchange, while thicker tissues would impede this process.

Levels of Organization in the Human Body

Chemical Level

The chemical level is the most basic level of organization, involving atoms and molecules:

• Atom: The smallest unit of an element. Common biological elements include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P).

• Molecule: Two or more atoms chemically bonded together.

• Compound: A molecule containing atoms of different elements.

• Small inorganic molecules: Examples include O2, CO2, H2O, and NaCl.

• Ion: An atom or molecule that has gained or lost electrons (e.g., H+, K+, Na+, Cl-, Ca2+, Mg2+, PO43-, HCO3-).

Major Classes of Organic Compounds

• Carbohydrates: Include monosaccharides (e.g., glucose, fructose), disaccharides (e.g., sucrose), and polysaccharides (e.g., glycogen).

• Lipids: Composed of fatty acids; form triglycerides, phospholipids, and steroids (e.g., cholesterol).

• Proteins: Made of amino acids linked by peptide bonds; structural proteins (keratin, collagen) and functional proteins (enzymes).

• Nucleic acids: Formed by nucleotides; include DNA and RNA.

Cellular Level

The cell is the smallest functioning unit of a living organism. All organisms are composed of one or more cells (unicellular or multicellular). Key features include:

• Cells share basic chemical composition and use energy.

• Cells arise from preexisting cells and contain DNA, which is replicated and passed on during cell division.

• Human (animal) cells are eukaryotic: they have a nucleus and membrane-bound organelles (e.g., mitochondria for energy production, ribosomes for protein synthesis).

Tissue and Organ Levels

Tissue Level

A tissue is a group of similar or related cells working together to perform a common function. Tissues also include nonliving material outside the cells, known as the extracellular matrix (ECM).

• Four main tissue types in the human body: Epithelial, Connective, Muscle, Nervous.

Organ Level

An organ is a distinct structure with a recognizable shape, composed of two or more tissue types that enable more complex functions.

• Example: The esophagus is an organ composed of multiple tissue types, allowing it to transport food from the mouth to the stomach.

Additional info: Organs are integrated into organ systems, which perform broad physiological functions essential for life.