Body Organization, Homeostasis, Basic Chemistry, and Terminology

Anatomical Position and Directional Terminology

• Standard Anatomical Position:

  • Upright stance with feet slightly apart, palms facing forward, and thumbs pointing outward.

  • Serves as the baseline reference for all anatomical directional terms.

  • Right and left always refer to the subject's sides, not the observer's.

• Directional Terms:

  • Anterior (or Ventral): Describes the front or toward the front of the body.

  • Posterior (or Dorsal): Describes the back or toward the back of the body.

  • Superior (or Cranial): Describes a position above or higher than another body part; toward the top of the head.

  • Inferior (or Caudal): Describes a position below or lower than another body part; near or toward the tail (in humans, the coccyx, which is the lowest part of the spinal column).

  • Examples: The nose is superior to the chin. The ears are posterior to the eyes.

• Lateral: Away from the midline of the body or on the outer side of the body.

• Medial: In or toward the midline of the body or on the inner side of the body.

• Proximal: Position in a limb that is nearer to the point of attachment to the trunk of the body.

• Distal: Position in a limb that is farther from the point of attachment to the trunk of the body.

• Superficial: Position closer to the surface of the body.

• Deep: Position farther from the surface of the body.

Anatomical Regional Terms

• Anterior Body Regions:

  • Cephalic (Head): Frontal (forehead), Orbital (eye region), Nasal (nose), Buccal (cheek), Oral (mouth), Mental (chin).

  • Cervical: Neck region.

  • Thoracic: Sternal (breastbone), Axillary (armpit), Mammary (breast).

  • Abdominal: Umbilical (navel).

  • Pelvic: Inguinal (groin).

  • Pubic: Genital region.

  • Upper Limb: Acromial (point of shoulder), Brachial (arm), Antecubital (front of elbow), Olecranal (back of elbow), Antebrachial (forearm), Carpal (wrist).

  • Manus (Hand): Metacarpal (back of hand), Palmar (palm), Pollex (thumb), Digital (fingers).

  • Lower Limb: Coxal (hip), Femoral (thigh), Patellar (front of knee), Popliteal (back of knee), Crural (leg), Sural (calf), Fibular or Peroneal (side of leg).

  • Pedal (Foot): Tarsal (ankle), Calcaneal (heel), Metatarsal (top of foot), Digital (toes), Plantar (sole), Hallux (great toe).

• Posterior Body Regions:

  • Cephalic: Otic (ear), Occipital (back of head).

  • Cervical: Neck region.

  • Back (Dorsal): Scapular (shoulder blade), Vertebral (spinal column), Lumbar (lower back), Sacral (area between hips), Gluteal (buttock), Perineal (region between anus and external genitalia).

Body Planes and Sections

• Body Planes: Flat surfaces along which the body or body structures may be cut for anatomical study.

  • Sagittal Plane: Cuts vertically into right and left portions.

  • Frontal (Coronal) Plane: Cuts vertically into front (anterior) and back (posterior) portions.

  • Transverse (Horizontal) Plane: Cuts horizontally into upper (superior) and lower (inferior) portions.

• Sections: Cuts made along a body plane, named after the plane along which they are cut:

  • Frontal / Coronal Section: Cut along the frontal plane.

  • Transverse / Cross Section: Cut along the transverse plane.

  • Midsagittal Section: Cut along the sagittal plane precisely at the midline.

  • Parasagittal Section: Cut along the sagittal plane off-center.

  • Oblique Sections: Cuts made at angles other than a right angle ($90^\circ$).

Body Cavities and Membranes

• Body Cavities: Internal spaces closed to the outside environment that house and protect internal organs.

  • Cavities provide varying degrees of protection to the organs inside.

  • Hernias: Occur when an organ protrudes through the wall of its designated cavity.

• Dorsal (Posterior) Body Cavity: Protects nervous system structures.

  • Cranial Cavity: Encloses the brain within the skull.

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

• Ventral (Anterior) Body Cavity: Houses internal organs (viscera). Separated into upper and lower cavities by the diaphragm:

  • Thoracic Cavity: Superior compartment containing:

  • $2$ Pleural Cavities: Each surrounds one lung.

  • Mediastinum: Central region containing the esophagus, trachea, and the Pericardial Cavity (which surrounds the heart).

  • Abdominopelvic Cavity: Inferior compartment below the diaphragm containing:

  • Abdominal Cavity: Superior portion containing most digestive organs, spleen, etc.

  • Pelvic Cavity: Inferior portion containing reproductive organs, urinary bladder, and rectum.

Abdominopelvic Regions and Quadrants

• Nine Abdominopelvic Regions:

  • Right hypochondriac region | Epigastric region | Left hypochondriac region

  • Right lumbar region | Umbilical region | Left lumbar region

  • Right iliac region | Hypogastric region | Left iliac region

• Four Abdominopelvic Quadrants:

  • Right Upper Quadrant ($\text{RUQ}$)

  • Left Upper Quadrant ($\text{LUQ}$)

  • Right Lower Quadrant ($\text{RLQ}$)

  • Left Lower Quadrant ($\text{LLQ}$)

Ventral Body Membranes

• Serous Membranes (Serosa): Double-layered membranes in thoracic and abdominopelvic cavities with lubricating fluid to reduce friction.

  • Visceral Serosa: Covers outer organ surfaces (e.g., visceral pericardium, pleura, peritoneum).

  • Parietal Serosa: Lines internal cavity walls (e.g., parietal pericardium, pleura, peritoneum).

Basic Chemistry and Physiological Processes

• Chemical reactions drive all physiological functions (e.g., movement, digestion, nerve signaling) and guide medical treatments like rehydration therapy.

Matter and Energy

• Matter: Occupies space and has mass.

  • States: Solid (definite shape/volume), Liquid (changeable shape, definite volume), Gas (changeable shape

• Energy Conversions: Energy changes forms, but process is inefficient with heat loss.

Elements, Atoms, and Body Composition

• Elements: Fundamental substances indivisible by chemical means.

• Atoms: Smallest unit retaining an element's unique properties.

• Body Composition: Four major elements comprise $96\%$ of total body mass, led by Oxygen ($\text{O}$) at $65\%$.

Elements, Atoms, and Atomic Structure

• Elements: Fundamental substances that cannot be broken down into simpler substances by ordinary chemical methods.

• Atoms: The smallest particles of an element that retain the unique chemical and physical properties of that element.

• Chemical Composition of the Human Body:

  • Four Major Elements: Make up $96\%$ of total body mass:

  • Oxygen ($\text{O}$): $65\%$

  • Carbon ($\text{C}$): $18\%$

  • Hydrogen ($\text{H}$): $10\%$

  • Nitrogen ($\text{N}$): $3\%$

  • Lesser Elements: $9$ elements constitute $3.9\%$ of total body mass.

  • Trace Elements: $11$ elements constitute less than $0.01\%$ (<0.01\%$) of total body mass.\n\n\n\n- **Periodic Table**:\n - **Groups (Columns)**: Contain elements sharing similar physical and chemical properties.\n - **Periods (Rows)**: Contain elements that possess the same number of electron shells.\n- **Subatomic Particles**:\n - **Protons**: Carry a positive electrical charge ( +$), have a mass of$1\,\text{amu} (atomic mass unit), and reside inside the nucleus. The proton count varies across different elements.\n - **Neutrons**: Carry no electrical charge (0$), have a mass of$1\,\text{amu}, and reside inside the nucleus. Neutrons can vary in number among isotopes of the same element.\n - **Electrons**: Carry a negative electrical charge (-$-$), have virtually no weight ($0\,\text{amu}$), and orbit around the nucleus.

• Atomic Number: Number of protons in the nucleus; determines element identity and equals electron count in a neutral atom. Written as a subscript (e.g., ${}_3\text{Li}$).

• Mass Number: Sum of protons and neutrons ($\text{Mass Number} = \text{Protons} + \text{Neutrons}$); varies by isotope. Written as a superscript (e.g., ${}^7\text{Li}$).

• Atomic Symbol: 1–2 letter shorthand for an element (e.g., $\text{N}$, $\text{O}$, or Latin-derived $\text{Na}$).

• Periodic Table Context:

  • Groups (Columns): Contain elements with similar physical and chemical properties.

  • Periods (Rows): Contain elements that possess the exact same number of electron shells.

Isotopes and Radioisotopes

• Isotopes: Structural variations of an element that have the same atomic number (same number of protons) but different mass numbers due to differing numbers of neutrons.

  • Example: Hydrogen isotopes include Protium (${}^1\text{H}$), which contains $1$ proton and $0$ neutrons, and Deuterium (${}^2\text{H}$), which contains $1$ proton and $1$ neutron.

• Radioisotopes: Unstable isotopes that spontaneously decay to attain stability, emitting detectable radioactivity and potentially transforming into different elements.

• Applications and Safety:

  • Identical chemical behavior to stable isotopes enables their use in clinical diagnosis, biological research, and targeted tumor therapy.

  • All nuclear radiation can damage living tissue, causing cellular mutations or cancer (e.g., radon gas from uranium decay).

• Applications and Safety:

  • Radioisotopes share the same basic chemistry as their stable isotopic counterparts, allowing them to be absorbed and processed by the body in identical ways, making them valuable in clinical research and diagnosis.

  • Targeted radioactivity can be used clinically to destroy localized malignant tumours.

  • All nuclear radiation is damaging to living biological tissues and can induce cellular mutation or cancer. For example, radon gas produced during the natural decay of uranium is a significant cause of lung cancer.

Molecules and Compounds

• Molecules: Smallest particle retaining a substance's properties, formed when two or more atoms combine chemically (e.g., $\text{H}_2$, $\text{O}_2$).

• Compounds: Molecules containing two or more different types of atoms (e.g., $\text{C}_6\text{H}_{12}\text{O}_6$). All compounds are molecules, but not all molecules are compounds.

• Compounds: Specific molecules formed when two or more different kinds of atoms chemically bond together (e.g., $\text{C}_6\text{H}_{12}\text{O}_6$).

  • All compounds are molecules, but not all molecules are compounds.

Questions & Discussion

• Question 1: The most abundant elements in the foods and beverages consumed are oxygen, carbon, hydrogen, and nitrogen. Why might having these elements in consumables be useful?

  • Answer: These four elements ($\text{O}$, $\text{C}$, $\text{H}$, $\text{N}$) comprise $96\%$ of total human body mass. Ingesting them in foods and beverages provides the vital structural raw materials required to synthesize cellular components, build biological macromolecules (proteins, carbohydrates, lipids, nucleic acids), perform tissue repair, and support biochemical metabolic pathways that generate cellular energy ($\text{ATP}$).

• Question 2: A patient comes in with a screwdriver driven into their right lung. Which body cavities are penetrated by the screwdriver?

  • Answer: The screwdriver penetrates the ventral body cavity, specifically entering the thoracic cavity, and further penetrating the right pleural cavity that surrounds the right lung.

• Question 3: Oxygen, whose atomic number is eight, has three stable isotopes: ${}^{16}\text{O}$, ${}^{17}\text{O}$, and ${}^{18}\text{O}$. Explain what each has in terms of the number of protons, electrons, and neutrons.

  • Answer:

  • Because the atomic number of oxygen is $8$, all neutral oxygen isotopes contain $8$ protons and $8$ electrons.

  • ${}^{16}\text{O}$: Contains $8$ protons, $8$ electrons, and $16 - 8 = 8$ neutrons.

  • ${}^{17}\text{O}$: Contains $8$ protons, $8$ electrons, and $17 - 8 = 9$ neutrons.

  • ${}^{18}\text{O}$: Contains $8$ protons, $8$ electrons, and $18 - 8 = 10$ neutrons.