Human Anatomy and Physiology - I. V. Gayvoronsky 2011

The Human Body as a Single Entity. Basics of Cytology and Histology
Structural and Functional Organization of the Human Body

Humans occupy the highest place among vertebrates, belonging to the phylum Chordata; the subphylum Vertebrates, Vertebrata; and the Class Mammals, Mammalia, which are characterized by live birth and nourishing newborns with mother's milk. Within the class of mammals, humans belong to the Subclass Theria (viviparous mammals with a Placenta and Mammary Glands); the Order Primates; the suborder Anthropoids, Anthropoidea; the superfamily Hominoidea; the family of hominids, Hominidae; and the species Homo sapiens.

The Structure OF THE human body can be conventionally divided into the following Levels of Organization:

1) organismal (The Human Body as a unified whole);

2) systemic-organ (Organ Systems);

3) organ (Organs);

4) tissue (tissues);

5) cellular (Cells);

6) subcellular (Cell Organelles and corpuscular-fibrillar-membranous structures).

It should be noted that the presented Structural organization of the human body exhibits a clear hierarchy. The organismal, systemic-organ, and organ levels of body structure serve as anatomical Objects of Study, whereas the tissue, cellular, and subcellular levels are the subjects of histological, cytological, and ultrastructural research. It is logical to begin studying the structural ORGANIZATION OF THE human body with its most fundamental morphological level—THE CELLULAR LEVEL, whose basic building block is The Cell. The body of an adult human consists of a vast number of cells (approximately 10¹²–10¹⁴).