Introduction to Anatomy and Physiology: Organization, Requirements for Life, and Anatomical Terminology

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Chapter 1: Introduction to Anatomy and Physiology

Form (Anatomy) Determines Function (Physiology)

This section introduces the foundational concepts of anatomy and physiology, emphasizing how the structure of body parts (anatomy) determines their function (physiology).

Anatomy: The study of the structure of body parts and their relationships to one another.
Physiology: The study of the function of body parts; how they work to carry out life-sustaining activities.

Subdivisions of Anatomy:

Gross anatomy	Microscopic anatomy
Regional	Cytology
Systemic	Histology
Surface

Histology is the study of body tissues.
Renal physiology examines the function of the kidneys.

Principle of Complementarity: Structure and function are inseparable; what a body part is capable of doing depends on its specific form.

The Body’s Organization: From Atoms to the Entire Organism

Levels of Structural Organization

The human body is organized in a hierarchy from the simplest to the most complex levels:

Chemical
Cellular
Tissue
Organ
Organ system
Organismal

Organ: A part of an organism that is typically self-contained and has a specific vital function.

The 11 Organ Systems of the Human Body

Each organ system has major organs and specific functions essential for survival.

Organ system	Major organs	Overall function(s)
Integumentary system	Hair, skin, nails	Forms external body covering and protects deeper tissues from injury
Skeletal system	Bones, joints	Protects and supports body organs; provides framework for muscles
Muscular system	Skeletal muscles	Maintains posture, produces heat
Nervous system	Brain, spinal cord, nerves	Fast-acting control system; responds to internal and external changes
Endocrine system	Thyroid gland, thymus, adrenal gland, pancreas, ovary, testis, pituitary gland	Secretes hormones that regulate processes such as growth, reproduction, and metabolism
Cardiovascular system	Heart, blood, blood vessels	Transports blood, oxygen, nutrients, and wastes
Lymphatic/Immune system	Red bone marrow, thymus, lymphatic vessels, thoracic duct, spleen, lymph nodes	Picks up fluid leaked from blood vessels and returns it to blood; disposes of debris; houses white blood cells
Respiratory system	Nasal cavity, pharynx, larynx, trachea, bronchi, lungs	Keeps blood supplied with oxygen and removes carbon dioxide
Digestive system	Oral cavity, esophagus, liver, stomach, small intestine, large intestine, rectum, anus	Breaks down food into absorbable units
Urinary system	Kidney, ureter, urinary bladder, urethra	Eliminates nitrogenous wastes; regulates water, electrolytes, and acid-base balance
Male and female reproductive system	Prostate, penis, testis, scrotum, ductus deferens, mammary glands, ovary, uterus, vagina, uterine tube	Production of offspring

Requirements for Life

Functional Characteristics Necessary to Maintain Life

Humans must perform several vital functions to sustain life. These include:

Term	Definition
Maintaining boundaries	Defining limits of a physical object that constrain distribution of elements to one side or the other
Movement	Motion of the entire body, or individual body parts, including organs, tissues, and cells
Responsiveness	Ability to respond to stimuli
Digestion	Breaking down of ingested foodstuffs to simple molecules that can be absorbed into the blood
Metabolism	All chemical reactions that occur within body cells
Excretion	Process of removing waste from the body
Reproduction	Process by which stimulated cells divide to create additional body mass
Growth	Increase in size of a body part or the organism as a whole

Survival needs include: nutrients, oxygen, water, normal body temperature, and appropriate atmospheric pressure.

Homeostasis and Feedback Mechanisms

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes. It is essential for normal body functioning and sustaining life.

Receptor: Monitors the environment and responds to stimuli.
Control center: Determines the set point, analyzes input, and coordinates an appropriate response.
Effector: Carries out the response to restore balance.

In a negative feedback mechanism, the response reduces or shuts off the original stimulus (e.g., regulation of body temperature, blood sugar levels, blood pressure). In a positive feedback mechanism, the response enhances the original stimulus (e.g., blood clotting, labor contractions).

Example	Negative or positive feedback mechanism?
Blood clotting	Positive
Body temperature	Negative
Labor contractions	Positive
Blood sugar levels	Negative
Blood pressure	Negative

Negative feedback mechanisms are more common because they counteract changes, helping maintain homeostasis.
Homeostatic imbalance can lead to disease; for example, declining efficiency of negative feedback with age can result in less stable internal conditions.

Anatomical Position and Terminology

Anatomical Position

The standard anatomical position is standing upright, facing forward, with feet flat on the ground, arms at the sides, and palms facing forward.

Directional Terms

Directional terms describe the locations of structures relative to other structures or locations in the body.

Directional Term	Definition	Example
Superior (cranial)	Toward the head or upper part of a structure or the body	The head is superior to the chin
Inferior (caudal)	Away from the head or toward the lower part of a structure or the body	The navel is inferior to the chin
Anterior (ventral)	Toward or at the front of the body; in front of	The breastbone is anterior to the spine
Posterior (dorsal)	Toward or at the back of the body; behind	The heart is posterior to the breastbone
Medial	Toward or at the midline of the body; on the inner side of	The heart is medial to the arm
Lateral	Away from the midline of the body; on the outer side of	The arms are lateral to the chest
Intermediate	Between a more medial and a more lateral structure	The collarbone is intermediate between the breastbone and shoulder
Proximal	Closer to the origin of the body part or the point of attachment	The elbow is proximal to the wrist
Distal	Farther from the origin of a body part or the point of attachment	The knee is distal to the thigh
Superficial (external)	Toward or at the body surface	The skin is superficial to the skeletal muscles
Deep (internal)	Away from the body surface; more internal	The lungs are deep to the skin

Regional Terms

Regional terms are used to designate specific areas within major body divisions. The anterior (ventral) and posterior (dorsal) views of the body are labeled with standard regional terms, such as:

Anterior/Ventral: Thorax, abdomen, umbilical, pubic, cervical, axillary, brachial, antebrachial, carpal, palmar, digital, femoral, patellar, crural, tarsal, hallux, etc.
Posterior/Dorsal: Back (dorsum), scapular, vertebral, lumbar, sacral, gluteal, perineal, popliteal, sural, calcaneal, plantar, etc.

These terms are essential for accurately describing locations and relationships of body parts in anatomy and physiology.