Foundations of Human Anatomy & Physiology: Cells, Tissues, Organs, and Systems

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Introduction to Anatomy & Physiology

Overview of Key Disciplines

Anatomy and physiology are foundational sciences in medicine and biology, focusing on the structure and function of the human body. Several subfields help organize the study of the body at different levels.

Cytology: The study of individual cells, their structure, function, and pathology.
Histology: The study of tissues (groups of cells) and their microscopic structure.
Anatomy: The study of the bodily structure, including gross (macroscopic) and microscopic anatomy.
Pathological Anatomy: Study of structural changes in cells, tissues, and organs caused by disease.
Physiology: Study of bodily functions at the level of systems, organs, cells, and molecules.
Systemic Physiology: Study of the function of organ systems (e.g., cardiovascular, respiratory).
Surface Anatomy: Study of external features of the body (shapes, markings, visible contours).
Regional Anatomy: Study of specific regions of the body (e.g., head, neck, thorax).
Embryology: Study of organism development from fertilized egg (zygote) to birth.

Levels of Organization in the Human Body

The human body is organized from the simplest to the most complex levels:

Atoms
Molecules
Organelles
Cells
Tissues
Organs
Organ Systems
Organism

Organization can be described as: organism → systems → organs → tissues → cells.

Organ Systems, Major Organs, and Functions

Summary Table of Organ Systems

System	Major Organs	Main Functions
Integumentary	Skin, hair, nails, sweat glands	Protection, thermoregulation, sensation, barrier to infection/water loss
Skeletal	Bones, cartilage, ligaments	Support, protection, movement, mineral storage, hematopoiesis
Muscular	Skeletal muscles (and smooth & cardiac in others)	Movement, posture, heat generation
Nervous	Brain, spinal cord, peripheral nerves, sense organs	Controls body activities via nerve impulses; sensory input; processing
Endocrine	Pituitary, thyroid, adrenal, pancreas, gonads	Hormone secretion; regulation of metabolism, growth, reproduction
Cardiovascular	Heart, blood vessels	Transport of nutrients, gases, wastes
Lymphatic/Immune	Lymph nodes, lymph vessels, spleen, thymus, tonsils	Return of interstitial fluid to bloodstream; immune responses
Respiratory	Lungs, trachea, bronchi, pharynx, larynx, nasal cavity	Gas exchange (O2 in, CO2 out); helps with pH balance
Digestive	Mouth, esophagus, stomach, intestines, liver, pancreas, gallbladder	Breakdown of food; absorption of nutrients; elimination of wastes
Urinary (Excretory)	Kidneys, ureters, bladder, urethra	Removal of wastes; regulation of water & electrolyte balance; acid-base balance
Reproductive	Male: testes, penis; Female: ovaries, uterus, fallopian tubes, vagina	Reproduction; production of sex cells & hormones; nurturing offspring

Anatomical Position, Body Positions, and Directional Terms

Anatomical Position

The standard reference position for anatomical terminology is standing upright, facing forward, arms at sides, palms facing forward, feet together or slightly apart, toes pointing forward.

Supine position: Lying on the back, face upward.
Prone position: Lying face down, back upward.

Directional Terms

Term	Meaning
Cephalic/Cranial	Toward the head or superior end
Caudal	Toward the tail or inferior end
Anterior/Ventral	Front of the body
Posterior/Dorsal	Back of the body
Medial	Toward the midline of the body
Lateral	Away from the midline/toward the sides
Proximal	Closer to the point of attachment or to the trunk
Distal	Farther away from the point of attachment or from the trunk
Superficial	Closer to the surface of the body
Deep	More internal, away from the surface

Example: The wrist is distal to the elbow (the wrist is farther from the trunk than the elbow).

Body Cavities and Serous Membranes

Functions of Body Cavities

Protection of organs by cushioning and allowing movement.
Allowing changes in size and shape of internal organs (e.g., expansion of lungs).

Major Body Cavities

Dorsal cavity: Includes cranial cavity (brain) and vertebral/spinal cavity (spinal cord).
Ventral cavity: Includes thoracic cavity (lungs, heart, esophagus, trachea) and abdominopelvic cavity (stomach, liver, intestines, kidneys, bladder, reproductive organs).

Serous Membranes

Pleura: Covers the lungs (visceral & parietal pleura).
Pericardium: Covers the heart.
Peritoneum: Covers abdominal organs.

Example: The serous membrane covering the intestines is called the visceral peritoneum.

Regions and Planes of the Body

Major Regions

Brachial: upper arm
Antebrachial: forearm
Femoral: thigh
Gluteal: buttocks
Sural: calf
Crural: shank (front of leg)
Pedal: foot

Abdominopelvic Regions (9 regions)

Right hypochondriac
Epigastric
Left hypochondriac
Right lumbar
Umbilical
Left lumbar
Right iliac (inguinal)
Hypogastric (pubic)
Left iliac (inguinal)

Abdominal Quadrants (4 quadrants)

Right upper quadrant (RUQ)
Left upper quadrant (LUQ)
Right lower quadrant (RLQ)
Left lower quadrant (LLQ)

Body Planes

Mid-sagittal/median: Exactly in the midline, dividing into equal right & left halves.
Parasagittal: Parallel to sagittal but not at midline – unequal halves.
Frontal/coronal plane: Divides body into anterior (front) and posterior (back) portions.
Transverse/horizontal/axial plane: Divides body into superior (upper) and inferior (lower) parts.

Homeostasis, Feedback Mechanisms, and Regulation

Homeostasis

Homeostasis is the maintenance of relatively stable internal conditions (temperature, pH, fluids, electrolytes, etc.) despite changes in external environment.

Feedback Mechanisms

Positive feedback: Response enhances or amplifies the original stimulus (e.g., oxytocin during childbirth).
Negative feedback: Response counteracts the stimulus, maintaining stability (e.g., temperature regulation, blood glucose regulation).

Regulatory Components

Receptor (sensor): Detects a change (stimulus).
Control center (integrating center): Processes information and sets response.
Effector: Organ or cell that carries out the response.

Failure of homeostatic regulation leads to disease, dysfunction, or death.

Imaging Techniques & Clinical Terms

Imaging Techniques

X-rays
MRI (Magnetic Resonance Imaging)
CT scan (Computed Tomography)
Ultrasound
PET scans

Suffix -itis (Inflammation)

Pericarditis: Inflammation of the pericardium (membrane around the heart).
Pleurisy/Pleuritis: Inflammation of the pleura (membrane around the lungs).
Peritonitis: Inflammation of the peritoneum (membrane lining abdominal cavity).
Mediastinitis: Inflammation of the mediastinum (central compartment of thorax).

Cell Structure and Function

Basic Cell Facts

The cell is the basic structural and functional unit of the human body.
The smallest living unit within the human body is the cell.
The study of cells is called cytology.

Cellular Components

Cytoplasm: Fluid medium inside the cell.
Cytosol: Watery component of the cytoplasm.
Extracellular fluid (ECF): Watery medium that surrounds a cell; also called interstitial fluid.
Principal cations in body fluids: Sodium (Na+) and Potassium (K+).
Higher concentration of proteins is found in the intracellular fluid (ICF).
Extracellular fluid is considered a transport medium, not for protein storage.

Cell Membrane

Other names: Plasma membrane, plasmalemma.
The term "cell wall" is not used in human cells (used in plants, fungi, bacteria).
Functions:
- Physical isolation (barrier)
- Regulation of exchange (selective permeability)

Classification of Organelles

Membranous organelles:
- Nucleus
- Mitochondria
- Endoplasmic reticulum (RER & SER)
- Golgi apparatus
- Lysosomes
- Peroxisomes
Non-membranous organelles:
- Ribosomes
- Cytoskeleton
- Centrioles
- Microvilli
- Cilia
- Flagella

Functions of Key Organelles

Mitochondria: ATP production (powerhouse of the cell)
Ribosomes: Protein synthesis
Rough Endoplasmic Reticulum (RER): Synthesizes and modifies proteins
Smooth Endoplasmic Reticulum (SER): Synthesizes lipids, detoxifies drugs

Key Equations and Concepts

Homeostasis equation:

Summary Table: Anatomical Terms & Body Positions

Term	Definition
Supine	Lying on back, face upward
Prone	Lying face down, back upward
Medial	Toward midline
Lateral	Away from midline
Proximal	Closer to trunk/attachment
Distal	Farther from trunk/attachment

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the functions of organ systems and organelles, and the summary tables for anatomical terms.