Fundamental Structures and Functions of the Human Body

Posted on Feb 3, 2026 in Biology

Joints and Articulations

A joint, also known as an articulation, is the point where two or more bones meet. Joints allow for movement, flexibility, and support within the skeletal system.

Classification of Joints

Joints are classified into three main types based on their structure and function:

  1. Fibrous Joints (Synarthroses): Immovable or slightly movable joints connected by fibrous tissue. Examples include sutures in the skull.
  2. Cartilaginous Joints (Amphiarthroses): Slightly movable joints connected by cartilage. Examples include intervertebral discs and the symphysis pubis.
  3. Synovial Joints (Diarthroses): Freely movable joints with a fluid-filled space between bones. Examples include:
    • Ball-and-socket joints (shoulder, hip)
    • Hinge joints (elbow, knee)
    • Pivot joints (neck)
    • Condyloid joints (wrist)
    • Saddle joints (thumb)

Types of Tissues

There are four primary types of tissues in the human body:

  1. Epithelial Tissue: Forms the lining of organs, glands, and body surfaces. Functions include protection, absorption, and secretion.
  2. Connective Tissue: Supports and connects other tissues and organs. Examples include bone, cartilage, fat, and blood.
  3. Muscle Tissue: Responsible for movement and contraction. Types include skeletal, smooth, and cardiac muscle.
  4. Nervous Tissue: Specialized for communication and transmission of nerve impulses. Comprises neurons and glial cells.

These tissues work together to maintain overall health and function.

Sensory Organs: Eye and Ear

Eye Anatomy

  1. Cornea: Transparent outer layer.
  2. Iris: Colored part controlling light entry.
  3. Pupil: Opening regulating light.
  4. Lens: Focuses light on the retina.
  5. Retina: Converts light to electrical signals.
  6. Optic Nerve: Transmits signals to the brain.

Eye Physiology

  1. Vision: Light enters through the cornea, pupil, and lens, focusing on the retina.
  2. Refraction: The bending of light rays.
  3. Accommodation: The lens adjusts focus.

Ear Anatomy

  1. Outer Ear: Includes the pinna (which collects sound) and the ear canal.
  2. Middle Ear: Includes the eardrum and ossicles (which transmit sound vibrations).
  3. Inner Ear: Includes the cochlea (for hearing) and the vestibular system (for balance).
  4. Auditory Nerve: Transmits sound signals to the brain.

Ear Physiology

  1. Hearing: Sound waves enter through the outer ear, causing eardrum vibrations.
  2. Sound Transmission: Ossicles transmit vibrations to the cochlea.
  3. Balance: The vestibular system maintains equilibrium.

Blood Coagulation and Hemostasis

Blood coagulation is the process by which blood changes from a liquid to a gel-like state, forming a clot. This process prevents excessive bleeding when a blood vessel is injured.

The Coagulation Pathway Steps

The coagulation pathway involves a series of complex steps, including:

  1. Vascular Spasm: Blood vessel constriction.
  2. Platelet Plug Formation: Platelets aggregate to form a temporary plug.
  3. Coagulation Cascade: A series of enzymatic reactions leading to stable clot formation.

Coagulation Factors

There are 13 coagulation factors, each playing a specific role:

  1. Factor I (Fibrinogen)
  2. Factor II (Prothrombin)
  3. Factor III (Tissue Factor)

These factors work together to form a stable blood clot.

Coagulation Pathways

  1. Intrinsic Pathway: Activated by damage inside the vascular system.
  2. Extrinsic Pathway: Activated by external trauma.

Cardiovascular System: Heart Structure and Function

Heart Anatomy

The heart consists of:

  1. Right Atrium: Upper chamber receiving deoxygenated blood.
  2. Right Ventricle: Lower chamber pumping blood to the lungs.
  3. Left Atrium: Upper chamber receiving oxygenated blood.
  4. Left Ventricle: Lower chamber pumping blood to the body.
  5. Septum: Wall separating the right and left sides.
  6. Valves: Ensure one-way blood flow (tricuspid, pulmonary, mitral, aortic).

ECG (Electrocardiogram)

An ECG measures the heart’s electrical activity, showing:

  1. P Wave: Atrial depolarization.
  2. QRS Complex: Ventricular depolarization.
  3. T Wave: Ventricular repolarization.

ECG helps diagnose heart conditions, such as arrhythmias and ischemia.

Heart Function

The heart pumps blood throughout the body, supplying oxygen and nutrients. The heart’s structure and function work together to maintain cardiovascular health.

Integumentary System: Skin Anatomy and Functions

Skin Anatomy: Layers

The skin consists of several layers:

  1. Epidermis: Outermost layer, providing barrier protection.
  2. Dermis: Middle layer, containing blood vessels, nerve endings, and hair follicles.
  3. Hypodermis (Subcutaneous Tissue): Innermost layer, attaching skin to underlying muscles and bones.

Skin Structures

  1. Sweat Glands: Regulate body temperature.
  2. Sebaceous Glands: Produce sebum, moisturizing the skin.
  3. Hair Follicles: Produce hair.
  4. Nerve Endings: Detect sensations (touch, pain, temperature).

Skin Functions

  1. Protection: Barrier against external factors (pathogens, UV radiation).
  2. Regulation: Body temperature regulation through sweating.
  3. Sensation: Detection of sensations.
  4. Excretion: Removal of waste products through sweating.

The skin plays a vital role in maintaining overall health and function.

The Lymphatic System

The lymphatic system is a network of organs and tissues that help defend the body against infection and disease.

Main Organs of the Lymphatic System

  1. Lymph Nodes: Filter lymph fluid and trap pathogens.
  2. Spleen: Filters blood and stores lymphocytes.
  3. Thymus: Develops and matures immune cells (T cells).
  4. Tonsils: Trap pathogens and activate the immune response.
  5. Adenoids: Similar to tonsils, located in the nasal cavity.
  6. Peyer’s Patches: Lymphoid tissue in the small intestine.
  7. Appendix: Thought to play a role in the development of the gut microbiome.

Lymphatic System Functions

  1. Immune Response: Helps defend against infection and disease.
  2. Fluid Balance: Returns excess fluid from tissues to the bloodstream.
  3. Waste Removal: Removes waste and toxins from the body.

The lymphatic system plays a crucial role in maintaining overall health and function.

Cellular Structures

Mitochondria Structure

  1. Outer Membrane: Protective layer.
  2. Inner Membrane: Folded into cristae for energy production.
  3. Mitochondrial Matrix: Contains DNA and enzymes for energy generation.

Ribosome Structure

  1. Large Subunit: Helps form peptide bonds.
  2. Small Subunit: Reads mRNA instructions for protein synthesis.

Cardiac Rhythms: Bradycardia and Tachycardia

Bradycardia

Bradycardia is a heart condition where the heart rate is slower than normal, typically less than 60 beats per minute. This can lead to symptoms such as:

  • Fatigue
  • Dizziness
  • Shortness of breath

Tachycardia

Tachycardia is a heart condition where the heart rate is faster than normal, typically more than 100 beats per minute. This can lead to symptoms such as:

  • Rapid heartbeat
  • Palpitations
  • Shortness of breath
  • Chest pain

Bone Cells: Osteoblasts and Osteoclasts

Osteoblasts

Osteoblasts are bone-forming cells responsible for:

  1. Bone growth and development.
  2. Bone repair and remodeling.
  3. Mineralization of bone tissue.

Osteoclasts

Osteoclasts are bone-resorbing cells responsible for:

  1. Breaking down and resorbing bone tissue.
  2. Regulating bone remodeling and calcium levels.

The balance between osteoblasts and osteoclasts is crucial for maintaining bone health and density.

Foundational Concepts: Anatomy and Physiology

Anatomy

Anatomy is the study of the structure and organization of living organisms, including:

  1. Gross Anatomy: Study of visible structures (organs, tissues).
  2. Microscopic Anatomy: Study of tiny structures (cells, tissues).

Physiology

Physiology is the study of the functions and processes that occur within living organisms, including:

  1. Organ Systems: Study of systems (nervous, circulatory, etc.).
  2. Cellular Physiology: Study of cellular functions.

Anatomy and physiology are closely related, as understanding structure is essential to understanding function.

Planes of the Body

  1. Sagittal Plane: Divides the body into left and right sides.
  2. Midsagittal (Median) Plane: A specific sagittal plane that divides the body into equal left and right halves.
  3. Coronal (Frontal) Plane: Divides the body into front (anterior) and back (posterior) sections.

These planes help describe the location and orientation of structures in the body.

Skeletal Structure: The Long Bone

A long bone is a type of bone that is longer than it is wide. Characteristics include:

  1. Diaphysis (Shaft): The long, cylindrical part of the bone.
  2. Epiphysis (Ends): The rounded ends of the bone, covered with articular cartilage.
  3. Metaphysis: The region between the diaphysis and epiphysis.

Examples of Long Bones

  1. Femur (thigh bone)
  2. Humerus (upper arm bone)
  3. Tibia and fibula (lower leg bones)
  4. Radius and ulna (forearm bones)

Long bones provide support, structure, and facilitate movement in the body.

Cardiac Performance Metrics

The Cardiac Cycle

The cardiac cycle is the sequence of events that occurs in the heart with each heartbeat. It includes:

  1. Diastole: Relaxation phase, where the heart fills with blood.
  2. Atrial Systole: Atria contract, pumping blood into ventricles.
  3. Ventricular Systole: Ventricles contract, pumping blood out of the heart.

Cardiac Output (CO)

Cardiac output (CO) is the volume of blood the heart pumps per minute. It is calculated as:

CO = Heart Rate (HR) x Stroke Volume (SV)

Cardiac output is essential for delivering oxygen and nutrients to the body’s tissues.

Homeostasis

Homeostasis is the ability of the body to maintain a stable internal environment despite changes in external conditions. It involves regulating factors such as:

  • Temperature
  • pH
  • Blood sugar levels
  • Blood pressure

Cell Division: Mitosis and Meiosis

Mitosis

Mitosis is a type of cell division that results in two daughter cells with the same number of chromosomes as the parent cell. It is essential for:

  • Growth
  • Repair
  • Replacement of cells

Meiosis

Meiosis is a type of cell division that occurs in reproductive cells, resulting in four daughter cells with half the number of chromosomes as the parent cell. It is essential for:

  • Sexual reproduction
  • Genetic diversity

Both mitosis and meiosis are crucial for the development and function of living organisms.

Blood Composition

Blood is a liquid tissue that consists of:

  1. Plasma: The liquid portion, making up about 55% of blood. Components include:
    • Water
    • Proteins (e.g., albumin, globulins)
    • Nutrients (e.g., glucose, amino acids)
    • Waste products (e.g., urea)
    • Hormones
    • Gases (e.g., oxygen, carbon dioxide)
  2. Formed Elements: Cellular components, making up about 45% of blood. These include:
    • Red Blood Cells (Erythrocytes): Carry oxygen.
    • White Blood Cells (Leukocytes): Part of the immune system.
    • Platelets (Thrombocytes): Involved in blood clotting.