Introduction to Physiology
In this chapter we will introduce the basics of anatomy and physiology.
"Anatomy is the foundation of the art of painting."
Leonardo da Vinci
Anatomy is the study of the structure of the body and its parts. It includes the study of the gross anatomy (major body structure, those are structures visible to the naked eye) and the microscopic anatomy (structure visible only with a light microscope).
Physiology is the study of the functioning of living organisms or their constituent tissues or cells (the body and its parts). It includes the study of how the body and its parts interact to maintain a state of balance or homeostasis and how the body responds to external changes.
Human body is the physical substance of the human organism, composed of living cells and extracellular materials and organized into tissues, organs, and systems. The levels of organization in the human body from the smallest to the largest are cells, tissues, organs, organ systems, and finally the entire organism.
In this chapter, we will discuss levels of organization in the human body. The major levels of organization in the body, from the simplest to the most complex are: atoms, molecules, organelles, cells, tissues, organs, organ systems, and the human organism. These principal systems are part of an intricate system, with varying levels of the organization. As presented by Liachovitzky (2023) these levels are:
The simplest level is the chemical level. The atom is the smallest amount of a chemical element. Atoms can combine to form molecules. About 96% of the human body is composed of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus (Geddes 2016).
Despite being incredibly small, an atom is composed of even smaller particles, such as protons, neutrons, and electrons.
The next level of organization is the cellular level. Atoms and molecules bind to form the building blocks of the body – cells. The body is made of many different cell types, each with a particular function. All human cells are made of a cell membrane (thin outer layer) that encloses a jelly-like cellular fluid containing tiny organ-like structures called organelles. The nucleus, which is the control center of the cell, is an organelle.
The next level is tissue level. A tissue is a group of similar cells that work together to perform a specific function. There are four main tissue types in humans: muscular, epithelial, nervous and connective tissue. These tissues are then organized into organs, which brings us to the next level:
organs. An organ is an identifiable structure of the body composed of two or more tissues types (for example, the stomach contains muscular tissue made of muscle cells, which allows it to change its shape, epithelial tissue which lines both the inner and outer surface of the stomach, nervous tissue which sends and receives signals to and from the stomach and the central nervous system, and connective tissue which binds everything together). Organs often perform a specific physiological function (for example, the stomach helps digest food).
"The human body is the most complex machine on Earth, with a myriad of intricate interconnected systems functioning together to sustain life."
Aristotle
The next level of organization is the organ system, also called the body system. An organ system is a group of organs that work together to perform a specific function (for example, the stomach, small and large intestines are all organs of the digestive system that work together to digest foodstuff, move nutrients into the blood and get rid of waste). The body has 11 main body systems, none of which work in isolation (for example, endocrine and nervous systems work together closely) (Roberts 2016). The most complex level of organization, the human organism (human body) is composed of many organ systems that work together to perform the functions of an independent individual.
