Body Cavities and Anatomical Organization

Major Body Cavities

The human body contains several major cavities that house and protect internal organs. Understanding their locations and contents is fundamental in anatomy.

• Thoracic Cavity: Located above the diaphragm and within the rib cage. It contains the lungs, heart, and other structures.

• Abdominopelvic Cavity: Inferior to the diaphragm, this is the largest body cavity in the anterior plane. It contains digestive, urinary, and reproductive organs.

• Cranial Cavity: Houses the brain within the skull.

• Spinal (Vertebral) Cavity: Encloses the spinal cord.

Example: The heart is located within the thoracic cavity, specifically in the mediastinum.

Directional and Regional Terms

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

• Superior: Toward the head or upper part of a structure ("above").

• Inferior: Away from the head or toward the lower part of a structure ("below").

• Anterior (Ventral): Toward the front of the body.

• Posterior (Dorsal): Toward the back of the body.

• Medial: Toward the midline of the body.

• Contralateral: On opposite sides of the body (e.g., left and right elbows).

• Ipsilateral: On the same side of the body.

• Coccygeal Region: Refers to the area of the coccyx or tailbone at the base of the spine.

Example: The nose is superior to the mouth and medial to the eyes.

Skeletal System: Major Bones

Key Bones and Their Common Names

• Femur: Commonly called the thigh bone; it is the longest and strongest bone in the human body.

• Ilium, Ischium, Pubis: Bones of the pelvis.

Example: The femur articulates with the pelvis at the hip joint and with the tibia at the knee joint.

Homeostasis and Feedback Mechanisms

Definition and Control

Homeostasis is the maintenance of a stable internal environment within the body. It is primarily achieved through feedback loops.

• Feedback Loops: Mechanisms that detect changes and initiate responses to return the body to a set point.

• Negative Feedback: Most common; reverses a change to maintain balance (e.g., body temperature regulation).

• Positive Feedback: Enhances the original stimulus (e.g., blood clotting).

Example: Blood glucose regulation by insulin and glucagon is a negative feedback process.

Basic Chemistry for Anatomy & Physiology

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules. Their strength and type affect biological molecules' properties.

• Covalent Bond: Strong bond formed by sharing electrons.

• Ionic Bond: Formed by transfer of electrons; moderate strength.

• Hydrogen Bond: Weak bond between a hydrogen atom and an electronegative atom (e.g., oxygen, nitrogen).

• Van der Waals Force: Weakest interaction; temporary attractions between molecules.

Example: Hydrogen bonds stabilize the double helix structure of DNA.

Water Properties and Biological Phenomena

Water's cohesion and adhesion are responsible for several biological phenomena.

• Cohesion: Attraction between water molecules.

• Adhesion: Attraction between water molecules and other substances.

• Phenomena: Root pressure, capillary action, and guttation in plants.

Isotopes and Half-Life

An isotope is a variant of an element with a different number of neutrons. The half-life is the time required for half of the isotope to decay.

• After one half-life: 50% remains.

• After two half-lives: 25% remains.

Equation:

Where is the remaining amount, is the original amount, and is the number of half-lives.

Atomic Structure

• Mass Number: The sum of protons and neutrons in an atom; does not include electrons.

• Atomic Number: The number of protons in an atom.

Biomolecules and Cellular Processes

Carbohydrates

• All dietary carbohydrates are eventually converted to glucose, the primary energy source for cells.

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).

ATP Hydrolysis

Adenosine triphosphate (ATP) is the main energy currency of the cell. Hydrolysis of ATP involves breaking the bond between phosphate groups, releasing energy.

• Phosphate Group: The component whose bond is broken during ATP hydrolysis.

Equation:

Proteins and Protein Structure

• Peptide Bond: Covalent bond linking amino acids in a protein.

• Hydrogen Bonds: Play a significant role in maintaining the three-dimensional structure of proteins in aqueous environments.

• Disulfide Linkages: Covalent bonds that stabilize protein structure.

• Hydrophobic Interactions: Non-covalent interactions that help proteins fold properly.

Genetic Code and Nucleic Acids

• Nucleotides: The building blocks of the genetic code (DNA and RNA).

• Amino Acids: The building blocks of proteins, not the genetic code itself.

Enzyme Deficiencies and Genetic Diseases

• Lesch-Nyhan Syndrome: Caused by a mutation in the gene for hypoxanthine-guanine phosphoribosyltransferase (HGPRT), affecting purine metabolism.

Post-Translational Modifications

• Glycosylation: The addition of carbohydrate groups to proteins, typically occurs in the Golgi apparatus.

Ribosomes and Protein Synthesis

• Polysomes (Polyribosomes): Complexes of multiple ribosomes translating the same mRNA simultaneously, increasing the efficiency of protein synthesis.

Summary Table: Key Terms and Concepts