Biology 211 Anatomy & Physiology I Orientation to the Human Body

Throughout this course, we will focus on three "major concepts" which are central to the understanding of anatomy and physiology: a) Adaptation of anatomical structures to carry out specific physiological functions b) A "structural heirarchy" in both anatomy and physiology, from atoms to the entire organism. c) Homeostasis maintained by feedback mechanisms

First major concept: All complex animals share a number of basic physiological functions for which anatomical structures are specifically adapted, including: - Protection of internal body environment from external environment - Maintenance of stable internal environment - Responsiveness - Ingestion, digestion, elimination - Metabolism - Excretion - Reproduction Each function is divided among many systems and Each system has multiple functions

Second major concept: The structures and functions of all complex animals are based on a “structural heirarchy” These are interdependent. Abnormalilties at one level will affect all higher levels

Example #1: Your body consists of trillions of cells of at least 400 different types About a dozen types: Lymphocytes One type of lymphocyte: CD4 cell Suppose a virus attacks and destroys your CD4 cells, while all other cells (including all other lymphocytes) remain healthy.

Example #2: Your body consists of trillions of cells of at least 400 different types Four types found in pancreatic islets One type of islet cell: beta cell, which produces insulin Suppose your body attacks and destroys the beta cells, while all other cells (including other islet cells) remain healthy.

Example #3: Your body consists of trillions of cells of at least 400 different types One type of cell in nervous system: oligodendrocyte Oligodendrocytes: dozens of organelles One organelle: plasma membrane Plasma membrane: hundreds of types of molecules. One type of molecule: myelin Suppose your body attacks and damages the plasma membranes of oligodendrocytes so they can’t properly produce myelin, while all other organelles of these cells and all other cells remain healthy.

Third major concept: Homeostasis: A state of "dynamic (changing) equilibrium (balance)" in which the body's internal environment is maintained within narrow limits even when the external environment changes significantly. For example: You must maintain a steady internal body temperature of approximately 37oC even if the external temperature changes from -20oC to over 100oC. Homeostasis requires communication among many different organelles, cells, tissues, and organs

Homeostasis involves feedback mechanisms: Positive Feedback: When a small change occurs, the body responds by producing a greater change in the same direction. Allows rapid response and magnification Examples: Blood clotting Immunity Negative Feedback: When a small change occurs, the body responds by producing change in the opposite direction. Causes return to the original condition Examples: Body temperature Blood glucose concentration

Positive Feedback Blood Clotting The body responds to a small clot by forming an even larger clot

Negative Feedback: Temperature Regulation The body responds to an increase in temperature by decreasing the temperature, or The body responds to a decrease in temperature by increasing the temperature

Concentration of glucose in blood Negative Feedback: Concentration of glucose in blood The body responds to an increase in blood glucose by lowering its concentration, or Eating increases blood glucose. Blood glucose stimulates pancreatic islets to secrete insulin. Insulin stimulates muscle cells and liver cells to absorb glucose from blood. Absorption of glucose by liver & muscle lowers its concentration in blood. This returns blood glucose to original level

Concentration of glucose in blood Fasting lowers blood glucose. Blood glucose stimulates pancreatic islets to secrete glucagon. Glucagon stimulates muscle cells and liver cells to release glucose back into blood. Release of glucose by liver & muscle increases its concentration in blood. This returns blood glucose to original level Negative Feedback: Concentration of glucose in blood The body responds to an increase in blood glucose by lowering its concentration, or The body responds to a decrease in blood glucose by increasing its concentration

For example, in the blood: Negative feedback is the mechanism your body uses to keep literally thousands of things within “normal” limits (homeostasis). For example, in the blood: Arterial pH 7.35 - 7.43 Bicarbonate 21.3 - 28.5 mEq/L Sodium 136-151 mEq/L Calcium 4.6 - 5.2 mEq/L Oxygen 17.2 - 22 ml / 100 ml Urea 12 - 35 mg / 100 ml Amino acids 3.3 - 5.1 mg / 100 ml Protein 6.5 - 8 g / 100 ml Total lipids 350 - 850 mg / 100 ml Glucose 75 - 110 mg / 100 ml

Next: A few basic concepts of anatomy which we will use throughout this course 1) Planes or sections 2) Terms indicating relative positions 3) Regions of the body 4) Primary and secondary body cavities 5) Three-dimensional relationships

1) In discussing the organization of the human body and its parts, we often establish our "point of view" according to three planes or sections: Coronal or Frontal Plane Horizontal or Transverse Plane Sagittal Plane

How a structure appears depends on the plane in which you view it:

2) In discussing parts of the human body, we also use a number of terms of relative position: Superior (cranial): Toward head or upper part of structure Inferior (caudal): Toward sacrum or lower part of structure Anterior (ventral): Toward the front Posterior (dorsal): Toward the back Medial: Toward the midline of the body or of a structure Lateral: To side of midline of the body or of a structure Proximal: Closer to center or origin Distal: Away from center or origin Superficial: Toward the surface of the body or of a structure Deep: Toward the center of the body or of a structure

3) Various regions of body have specific names: Anterior

Various parts of body have specific names: Posterior

You should be able to identify the regions shown on these diagrams. For example: The region of the upper limb between the shoulder and elbow is the_________ region brachial carpal For example: The _________ region is immediately distal to the antebracheal region

4) Primary Body Cavities (Formed by folding of the embryo)

Secondary Body Cavities (Formed in place as organs develop) Examples: - Pericardial cavity around heart - Pleural cavities around lungs - Synovial cavities between bones - Nasal cavity - Oral cavity - Orbital cavities - External, Middle, and Inner ear cavities

5) Finally: Positional relationships are very important, so as we discuss the human body, get your brain to think three-dimensionally and focus on those relationships . . .