Overview of Anatomy and Physiology: Structural Organization and Characteristics of Living Organisms

Introduction to Anatomy and Physiology

Defining Anatomy and Physiology

Anatomy and physiology are foundational sciences in understanding the human body. Human Anatomy is the study of the structure or form of the human body, while Human Physiology focuses on the body's functions. The Principle of Complementarity states that structure (anatomy) determines function (physiology), and function reflects structure.

• Anatomy: Examines the physical structures of the body.

• Physiology: Investigates how those structures work and interact.

• Principle of Complementarity: The form of a structure is closely related to its function.

• Example: The thin walls of alveoli in the lungs facilitate gas exchange.

Characteristics of Living Organisms

Essential Properties of Life

All living organisms share several distinct properties that define life:

• Cellular Composition: Cells are the smallest units of life and the basic building blocks of all organisms.

• Metabolism: The sum of all chemical processes in the body.

  • Anabolism: Building up complex molecules from simpler ones.

  • Catabolism: Breaking down complex molecules into simpler ones.

• Growth: Increase in size and/or number of cells.

• Excretion: Removal of waste products generated by metabolic processes.

• Responsiveness (Irritability): Ability to sense and react to environmental stimuli.

• Movement: Motion of the organism or its individual cells.

• Reproduction: Production of new cells for growth, repair, or offspring.

• Example: Muscle cells contract to produce movement; nerve cells respond to stimuli.

Levels of Structural Organization and Body Systems

Hierarchical Organization of the Human Body

The human body is organized into progressively larger and more complex levels:

• Chemical Level: Atoms and molecules form the basis of all matter.

• Cellular Level: Molecules combine to form cells, the basic units of life.

• Tissue Level: Groups of similar cells and extracellular matrix perform common functions.

• Organ Level: Two or more tissue types form organs with specialized tasks.

• Organ System Level: Multiple organs work together to perform broad functions.

  • The human body has 11 organ systems.

• Organism Level: All organ systems function together to form the complete human organism.

Six Structural Levels of Organization

The six levels are: chemical, cellular, tissue, organ, organ system, and organism.

The 11 Organ Systems of the Human Body

Each organ system has specific functions essential for survival:

Organ System	Main Functions
Integumentary	Protects body, regulates temperature, provides sensory information
Skeletal	Supports body, protects organs, stores minerals, forms blood cells
Muscular	Produces movement, generates heat
Nervous	Controls responses, processes information
Endocrine	Regulates body functions via hormones
Cardiovascular	Transports nutrients, gases, and wastes
Lymphatic	Returns fluid to blood, defends against pathogens
Respiratory	Delivers oxygen, removes carbon dioxide
Digestive	Processes food, absorbs nutrients, eliminates waste
Urinary	Removes waste, regulates water and electrolytes
Reproductive	Produces offspring, sexual function

Types of Anatomy and Physiology

Approaches to Studying Anatomy

• Systemic Anatomy: Study of individual organ systems.

• Regional Anatomy: Study of body regions (e.g., head, neck).

• Surface Anatomy: Study of external body markings.

• Gross Anatomy: Study of structures visible to the naked eye.

• Microscopic Anatomy: Study of cells (Cytology) and tissues (Histology) using a microscope.

Subfields of Physiology

• Classified by organ or organ system (e.g., neurophysiology, cardiovascular physiology).

• Can also be studied at chemical, cellular, and tissue levels.

• Example: Cardiovascular physiology examines heart and blood vessel function.

Core Principles – Set of basic concepts of anatomy and physiology, related to maintaining the body’s internal environment (homeostasis)

•Feedback Loops

•Relationship of Structure and Function

•Gradients

•Cell-Cell Communication

•Homeostasis – The condition in which the body maintains a relatively stable internal environment

–Variables – Parameters in the internal environment, such as temperature, blood sugar, blood pressure, acidity and many others, that are controlled to stay close to a particular normal value = normal range

–Homeostatic Imbalances – Disturbances in homeostasis can lead to disease or death if uncorrected

Feedback Loops – A change in a regulated variable causes effects that feed back and in turn affect that same variable

•Negative Feedback Loops – Oppose the initial change

–Example: Used to bring a change in body temperature back to normal range

•Positive Feedback Loops – Reinforce the initial change

–Example: Used to further increase force of labor contractions (until baby is born)

Negative Feedback Loops – Promote stability

•Each variable has a Set Point that includes a Normal Range around that set point

Steps of a Negative Feedback Loop

1.Stimulus – A regulated variable that is outside the normal range

2.Receptor – Cellular structure that senses the stimulus; sends information to control center, usually via nervous or endocrine systems

3.Control Center – Determines whether a response is needed and signals effector

4.Effector – Cells or organ that will react

5.Response – Return of variable to the normal range

Positive Feedback Loops – Less common than negative feedback loops; Amplify the response to a stimulus

•Will eventually shut off in response to an external stimulus or some outside event that is not part of the positive feedback loop

•Examples:

–Blood clotting

–Labor contractions

•Childbirth begins when a woman goes into labor, which occurs by a positive feedback loop

•Baby’s head stretches the cervix (stimulus); Data from nerves in the cervix (receptors) are sent to the brain (control center); Uterus (effector) produces hormone oxytocin which stimulates uterine contractions (response); This continues and is amplified until the baby is born, which stops the feedback loop

•Pitocin is a synthetic version of oxytocin that is used when labor needs to be artificially started, or induced

•Misconception 1: Negative feedback is bad for the body; Positive feedback is good

–Under normal circumstances, both types of feedback loops promote homeostasis

•Misconception 2: Maintaining homeostasis means the body’s internal environment is static or unchanging

–Maintenance of normal ranges does not mean the internal environment is unchanging; Changes are normal and are occurring constantly

•Misconception 3: Regulatory mechanisms and feedback loops are either “on” or “off,” like a switch

–The internal environment is dynamic so feedback loops always exhibit some degree of activity

•Misconception 4: Any physiological variable can be controlled

–Variables can only be controlled through feedback loops if receptors exist to detect changes in the set point within a working feedback system

Principle of Complementarity of Structure and Function

•The form of a structure is such that it best suits its function; Applies to all levels of organization. The relationship between structure and function

Gradients are present any time more of something exists in one area than another and the two areas are connected

•Gradients drive many of our physiological processes

•Cells communicate with each other to maintain homeostasis

•Forms of communication:

–Electrical

Chemical