Chapter 1 Objectives

1. Define the following terms: anatomy, subdivisions of anatomy, subdivisions of microscopic anatomy, physiology, homeostasis, anatomical position, axial, appendicular.

2. Describe the following concepts: complementarity of structure and function, hierarchy of structural organization, functional characteristics of life, survival needs, control mechanisms (3 parts, positive and negative feedback).

3. Use anatomical terminology to describe the location of body structures.

4. Describe body planes and identify relationships to body structures.

5. Describe dorsal and ventral body cavities (thoracic, abdominopelvic) including the organs found in each. (also organs found in the 4 abdominopelvic quadrants)

6. Describe serous membranes: structure in terms of parietal and visceral layers.

 

CHAPTER 1

THE HUMAN BODY: AN ORIENTATION

Three essential concepts will form the basis of our study and will unify the various sections:

1. Complementarity of structure and function
2. Hierarchy of structural organization
3. Homeostasis

Definitions:

Anatomy: (Greek "to cut apart") - the study of the form, or structure of body parts and of how these parts relate to one another. Static image.

Physiology: the study of the functioning of the body's structural machinery - how the parts of the body work and carry out their life-sustaining activities. Dynamic processes.

Anatomy is a broad field with many subdivisions.

1. Gross anatomy: study of large body structures visible to the naked eye.

a. Regional anatomy: all structures in one part of the body are studied at the same time.
b. Systemic anatomy: various systems of the body are studied.

2. Microscopic anatomy: examination of body tissues using a microscope

a. Cytology: study of the cells of the body
b. Histology: study of the tissues of the body

3. Other subdivisions:

Embryology: developmental changes occurring before birth
Pathology: disease related changes
Molecular biology: subcellular level

Physiology is also subdivided into several specialized areas based on the functioning of specific organ systems (such as digestive, muscular, etc.) or a functional system (such as the immune system).

Essential Concepts

"Complementarity of structure and function" -- function always reflects structure. What a structure can do depends on its specific form.

"Hierarchy of Structural Organization" -- the human body incorporates many levels of structural complexity:

Levels of the Hierarchy:

Atoms: building blocks of matter
Molecules
: water, sugar, proteins -- groups of atoms
Organelles
: basic components of microscopic cells
Cells
: living structural and functional units of an organism
Tissues
: groups of similar cells having common structure and function. Four basic types.
Organ
: complex physiological processes become possible. Discrete structure composed of at least two tissue types; four tissue types more common.
Organ System
: organs that cooperate and work closely together to accomplish a common purpose.
Organism
: sum total of all levels of complexity working continuously and in unison.

"Homeostasis" - ability to maintain relatively stable internal conditions despite a changing external environment. Dynamic state of equilibrium, or balance. The body is said to be in homeostasis when its cellular needs are adequately met and functional activities are occurring smoothly. Virtually every organ system plays a role in maintaining the internal environment.

Maintenance of Life: Functional characteristics

1. Maintenance of boundaries: keeps the internal environment separate and distinct from the external environment. Cell membranes contain its contents while admitting needed substances and restricting the entry of unnecessary or harmful substances.

2. Movement: includes all activities promoted by the muscular system such as walking, running, movement of blood, food, urine rough the internal organs, etc.

3. Responsiveness: ability to sense change and respond to it.

4. Digestion: breakdown of ingested food into usable molecules.

5. Metabolism: all chemical reactions occurring within the cells. Depends on other systems and is regulated by the endocrine system.

6. Excretion: removal of unusable waste products.

7. Reproduction: formation of offspring.

8. Growth: increase in size.

 

Survival Needs:

The ultimate goal of nearly all body systems is to maintain life. Requires several factors acting together for its persistence.

1. Nutrients: chemical substances used for energy and cell building and maintenance. carbohydrates (CHO) - major energy fuel; proteins/fats - building cell structures; minerals/vitamins – assist in chemical reactions

2. Oxygen: absolutely essential. Chemical reactions that release energy from food are oxidative reactions and require oxygen. 20% of the air we breathe.

3. Water: 60-80%of body weight. Provides liquid environment for chemical reactions and fluid base for body secretions/excretions.

4. Body Temperature: must be maintained around 37oC (98.6oF). Decreased temp: physiological reactions slowed. Increased temp: chemical reactions proceed too rapidly, body proteins denature.

5. Atmospheric Pressure: required for exchange of gases in the lungs.

 

Control Mechanisms:

Communications within the body are essential for homeostasis. Accomplished chiefly by the nervous and endocrine systems. All homeostatic control mechanisms have at least three interdependent components:

1. Control Center - determines the set point, analyzes input and determines the appropriate response.

2. Receptor - monitors the environment, sends information or input to the control center (afferent pathway)

3. Effector - provides the means by which the control center can cause a response to a stimulus (efferent pathway)

The result of the response then "feeds back" to influence the stimulus, either depressing it (negative feedback) or enhancing it (positive feedback). Most homeostatic control mechanisms are negative feedback mechanisms. The output of the system feeds back and decreases the input into the system. The net effect is to decrease the original stimulus or reduce its effects.

example: blood glucose regulation (insulin/glucagon)

All negative feedback mechanisms have the same goal -- prevention of sudden severe changes within the body.

In positive feedback mechanisms the response enhances the original stimulus and the output is accelerated. The change that occurs proceeds in the same direction as the initial disturbance, causing the further deviation from the original set point.

Positive feedback mechanisms usually control episodic/infrequent events that do not require continuous adjustments. Rarely used to promote moment to moment well being.

examples: coagulation labor contractions (oxytocin)

 

ANATOMICAL TERMINOLOGY

BODY ORIENTATION AND DIRECTION:

Note: These terms are dependent on an assumption of the anatomical position.

1. Superior/Inferior: Placement of a body structure along the long axis of the body. Divides the body into upper and lower

2. Anterior/Posterior: The most anterior structures or surfaces are those that are most forward (face, chest, abdomen). Posterior structures or surfaces are those toward the backside of the body.

3. Medial/Lateral: Toward the midline/away from the midline.

4. Cephalad/Caudal: Toward the head/toward the tail. Used interchangeably with superior and inferior.

5. Dorsal/Ventral: Backside/belly side. Used interchangeably with anterior and posterior.

6. Proximal/Distal: Nearer the truck or attachment end/farther from the trunk or point of attachment. Used primarily to locate various areas of the body limbs.

7. Superficial/Deep: Toward or at the body surface/away from the body surface or more internal. Used to locate body organs in terms of their relative closeness to the body surface.

Terminology of Anatomy

Universally accepted terminology that allows body structures to be located and identified.

1. Anatomical position and Directional terms: essential to have an initial reference point and indications of direction.

anatomical position - body is erect with feet together and palms facing forward with the thumbs pointing away from the body.

direction - "right and left" refer to those sides of the person or cadaver being viewed.

2. Regional Terms: the most fundamental divisions of the body are its axial and appendicular parts.

axial - makes up the main axis of the body. Consists of the head, neck, and trunk

appendicular - consists of the appendages or limbs

3. Body Planes and Sections: involves dissection in which the body or its organs are cut along an imaginary line, called a plane. The most frequently used planes are:

sagittal - runs longitudinally. Divides the body or organ into right and left portions.

midsagittal (median plane) - exactly midline and the parts are symmetrical or equal.

parasagittal - all other sagittal planes

a midsagittal plane

frontal - runs longitudinally, but the body or organs are divided into anterior and posterior.

a frontal plane (also called a coronal plane)

transverse - runs horizontally across and at a right angle to the long axis of the body or organ and divides it into superior and inferior parts.

a transverse plane

4. Body Cavities and Membranes: there are two major closed body cavities within the axial portion of the body:

Dorsal Body Cavity -Located nearer to the dorsal or posterior surface of the body. Subdivided into cranial and vertebral or spinal. They are continuous with one another. They house vital and very fragile organs – brain and spinal cord.

Ventral Body Cavity-More anterior and larger. Two major subdivisions: thoracic and abdominopelvic.

The thoracic is surrounded by the ribs and muscles of the chest and is subdivided: lateral pleural cavities each containing a lung. and medial mediastinum which contains the heart and remaining thoracic organs (esophagus, trachea etc.)

Abdominopelvic cavity: Divided into the abdominal cavity which contains the stomach, intestines, spleen, liver, and other organs and the pelvic cavity which contains the bladder, some reproductive organs, and the rectum.

Serous Membranes -- the walls of the ventral body cavity and the outer surfaces of the organs are covered with a thin, double layered membrane – serosa or serous membranes.

Part of the membrane lining the cavity walls - parietal serosa -folds on itself to form the visceral serosa which covers the organs in the cavity.

Parietal - "parie"- means wall
Visceral - "viscus"- means an organ in a body cavity

The serous layers are separated by a thin lubricating fluid -serous fluid. It allows the organs to slide easily across the cavity walls and one another without friction.

Serous membranes: named for the cavity and organs with which they are associated: 1. parietal pericardium - lines pericardial (heart) cavity 2. visceral pericardium - covers the heart 3. parietal pleura - lines thoracic wall in the pleural cavity 4. visceral pleura - covers the lungs

Inflammation of serous membranes, accompanied by a deficit of lubricating fluid results in excruciating pain as organs stick together. "pleurisy"

5. Abdominopelvic Quadrants: right upper, right lower, left upper, right lower