08/19 Lecture Anatomy & Physiology: Foundational Concepts, Body Organization, and Cellular Structure

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Anatomical Position and Directional Terms

Anatomical Position

The anatomical position is the standard reference for the body, used in all medical fields. In this position, the body is erect, feet are slightly apart, palms face forward, and the thumbs point away from the body. This position is the standard for viewing a patient, regardless of how they are actually lying. It is always from the patient’s perspective.

Importance: Provides a consistent frame of reference for anatomical terminology and medical procedures.
Application: Used to describe the location of injuries, pathologies, or surgical sites.

Directional Terms

Directional terms are used to describe the location of one body part in relation to another. Mastery of these terms is crucial for anatomical accuracy.

Superior (Cranial): Toward the head or upper part of a structure; above. (e.g., The head is superior to the trunk.)
Inferior (Caudal): Away from the head or toward the lower part of a structure; below. (e.g., The trunk is inferior to the head.)
Anterior (Ventral): Toward or at the front of the body. (e.g., The sternum is anterior to the heart.)
Posterior (Dorsal): Toward or at the back of the body. (e.g., The spinal column is posterior to the kidneys.)
Medial: Toward the midline of the body. (e.g., The heart is medial to the lungs.)
Lateral: Away from the midline of the body. (e.g., The right lung is lateral to the heart.)
Intermediate: Between a more medial and a more lateral structure. (e.g., The heart is intermediate to the lungs.)
Proximal: Closer to the origin of a body part or the point of attachment of a limb to the body trunk. Used for arms and legs. (e.g., The elbow is proximal to the wrist.)
Distal: Farther from the origin of a body part or the point of attachment of a limb to the body trunk. Used for arms and legs. (e.g., The fingers are distal to the elbow.)
Superficial: Toward or at the body surface. (e.g., Veins are superficial to arteries.)
Deep: Away from the body surface; more internal. (e.g., Arteries are deep to veins; muscles are deep to the skin.)

Examples: The antebrachial region refers to the forearm (radius and ulna area). The anterior knee (patellar) and posterior knee (popliteal) have different names.

Body Planes and Sections

Body planes are imaginary surfaces along which the body or its structures can be cut to create sections. Understanding these planes is crucial for interpreting medical images like MRIs.

Sagittal Plane: A vertical plane that divides the body into right and left portions. A midsagittal or median plane is directly down the middle. A parasagittal plane is off the midline.
Frontal (Coronal) Plane: A vertical plane that divides the body into anterior (front) and posterior (back) portions.
Transverse (Horizontal) Plane: A horizontal plane that divides the body into superior (upper) and inferior (lower) portions, producing a cross-section (CS).

Examples: The appearance of an organ, like a kidney, looks very different depending on the plane it was sectioned in. A coronal section of a kidney might show its classic bean shape, while a transverse section would appear as a circle.

Body Cavities and Membranes

Body Cavities

The body contains two major cavities that house and protect the internal organs, also known as viscera.

Dorsal Body Cavity: Located posteriorly, it protects the central nervous system. It is subdivided into the Cranial Cavity (enclosing the brain) and the Vertebral Cavity (enclosing the spinal cord).
Ventral Body Cavity: The larger, anterior cavity housing the viscera. It is separated by the diaphragm into two main parts:
- Thoracic Cavity: Contains the heart (in the pericardial cavity), lungs (in the pleural cavities), and mediastinum (central compartment).
- Abdominopelvic Cavity: Contains digestive organs, spleen, kidneys (abdominal cavity), and bladder, reproductive organs, rectum (pelvic cavity).

Additional info: The testes in males develop from the same embryonic tissue as ovaries in females and descend into the scrotum just before birth. If testosterone is not present, the same tissue develops into ovaries.

Serous Membranes

Serous membranes are thin membranes associated with organs within the ventral body cavity to create serous fluid, which allows organs to slide and reduces friction. They consist of two continuous layers: an outer parietal layer lining the cavity wall and an inner visceral layer covering the organ’s surface. The space between these layers is the serous cavity, containing serous fluid.

Parietal layer: Lines the cavity wall (e.g., parietal pericardium, parietal pleura, parietal peritoneum).
Visceral layer: Covers the surface of the organ (e.g., visceral pericardium, visceral pleura, visceral peritoneum).
Serous cavity: The potential space between the two layers, filled with lubricating serous fluid.
Examples: Include the pericardium (heart), pleura (lungs), and peritoneum (abdominal organs).
There are no serous membranes associated with the pelvic cavity.

Examples: Inflammation of the pericardium, the serous sac around the heart, is called pericarditis.

Abdominopelvic Quadrants

A clinical method used to locate abdominopelvic organs by dividing the cavity into four quadrants with two perpendicular lines intersecting at the umbilicus (navel).

The four quadrants are the Right Upper Quadrant (RUQ), Left Upper Quadrant (LUQ), Right Lower Quadrant (RLQ), and Left Lower Quadrant (LLQ).
This system helps medical personnel describe the location of pain, tumors, or other abnormalities.

Examples: Pain in the right lower quadrant (RLQ) is a typical indicator of appendicitis. Pain in the right upper quadrant (RUQ) can be a sign of gallbladder problems.

Cell Theory and Cellular Structure

The Cell Theory

The cell theory, primarily developed in the 1800s by Schleiden and Schwann, is a foundational principle of biology.

The cell is the basic structural and functional unit of life.
All organisms are composed of one or more cells.
All cells arise from pre-existing cells, which disproved the earlier concept of spontaneous generation.

Additional info: The theory was formulated by botanist Schleiden and zoologist Schwann after observing various plant and animal tissues. The third tenet, that all cells arise from pre-existing cells, was a later addition, illustrated by experiments like those involving meat in jars.

Body Fluids

Blood plasma: The liquid component of blood.
Cerebrospinal fluid: Fluid found within and surrounding the brain and spinal cord.
Cellular secretions: Substances released by cells, such as saliva and pancreatic juice.

The Plasma Membrane

The plasma membrane is the selectively permeable outer boundary of the cell, separating the intracellular environment from the extracellular environment. Its structure is described by the fluid mosaic model.

Physical Barrier: It encloses the cell and separates its contents.
Selective Permeability: It regulates the passage of substances into and out of the cell.
Cell Recognition: The glycocalyx on the surface acts as a biological marker, allowing the immune system to distinguish self from non-self.
Communication: It contains receptors that bind to specific molecules, initiating cellular responses.

Explanation: The membrane is a phospholipid bilayer with hydrophilic (water-loving) heads facing the aqueous environments inside and outside the cell, and hydrophobic (water-repelling) tails facing inward. This structure makes it permeable to lipid-soluble substances but not to most water-soluble substances. Cholesterol is embedded within the membrane of animal cells to modulate its fluidity. Membrane proteins are embedded within or attached to the bilayer and perform various functions like transport and signaling. The glycocalyx, formed by carbohydrate chains on the outer surface, is crucial for cell-to-cell recognition.

Cell Junctions

Cell junctions are points of contact between the plasma membranes of adjacent cells, ensuring the integrity and communication of tissues.

Tight junctions: Form a seal between adjacent cells, such as the skin, preventing them from tearing apart.
Desmosomes: Anchoring junctions that provide mechanical strength to tissues.
Gap junctions: Communicating junctions that provide a direct channel for chemical and electrical communication between adjacent cells. They are formed by protein channels that allow ions and small molecules to pass directly from one cell to the next. This is essential for rapid, coordinated activity in tissues like the heart muscle, ensuring that all cells contract in unison.

Abdominopelvic Quadrants Table

The following table summarizes the four abdominopelvic quadrants and their clinical significance:

Quadrant	Abbreviation	Major Organs	Clinical Relevance
Right Upper Quadrant	RUQ	Liver, Gallbladder, Right Kidney, Portions of Colon	Gallbladder disease, liver pathology
Left Upper Quadrant	LUQ	Stomach, Spleen, Left Kidney, Pancreas, Portions of Colon	Gastric ulcers, splenic injury
Right Lower Quadrant	RLQ	Appendix, Right Ovary, Right Ureter, Portions of Small Intestine	Appendicitis, ovarian cysts
Left Lower Quadrant	LLQ	Left Ovary, Left Ureter, Portions of Small Intestine and Colon	Diverticulitis, ovarian cysts

Key Formulas and Concepts

Surface Area to Volume Ratio: Important for understanding cell size and efficiency of nutrient/waste exchange. Formula:

Summary

Understanding anatomical position and directional terms is foundational for all of anatomy and physiology.
Body planes and sections are essential for interpreting medical images and understanding organ structure.
Body cavities and serous membranes protect and compartmentalize internal organs.
The cell theory underpins all of biology, emphasizing the centrality of the cell.
The plasma membrane and cell junctions are critical for cellular function, communication, and tissue integrity.