Levels of Organization in the Human Body

Levels of Organization in the Human Body

• Human bodies, like all living things, have a hierarchical structure.
• Basic units are atoms.
• Atoms combine to form molecules.
• Molecules combine to form cells, considered the first level of life.
• Similar cells working together create tissues.

Human Cells

• Human cells are eukaryotic and heterotrophic (taking in external nutrients).
• They have a nucleus enclosing genetic material, unlike prokaryotes.
• Essential cell functions include nutrition, interaction, and reproduction.

Cellular Organelles

• Ribosomes: Protein production sites, non-membrane bound particles.
• Mitochondria: Oval shaped, site of cellular respiration and energy production.
• Endoplasmic Reticulum (ER): Network of membranous sacs and channels, rough (with ribosomes) and smooth types.
• Golgi Apparatus: Flattened sacs (cisternae) responsible for processing and packaging molecules.
• Vesicles: Small membranous sacs transporting and storing materials within the cell.

Cell Differentiation and Disease

• Cells follow a growth, division, and death cycle.
• Cancer: Uncontrolled cell proliferation, forming a tumor.
• Tumors can be benign (slow growth, confined) or malignant (cancer, invasive).
• Many factors contribute to cancer development.
• Prevention and early detection are crucial.

Tissue Types

• Muscle tissue: Composed of elongated cells (myocytes) with contractile proteins.
• Skeletal muscle: Striated, elongated cylindrical cells (multi-nucleated), voluntary movement (attached to bones).
• Cardiac muscle: Striated, branched cells (one or two nuclei), involuntary heart contractions.
• Smooth muscle: Non-striated, single-nucleated cells, involuntary movements (internal organs, blood vessels).
• Epithelial tissue: Layers of closely packed cells, covering surfaces and lining cavities.
  • Two types: lining and glandular.
• Nervous tissue: Conducts nerve signals, composed of neurons and glial cells.
  • Microglia: Protects against infections, removes damaged cells.
  • Oligodendrocytes: Forms a protective sheath around neuron extensions.
  • Neurons: Highly specialized cells, can't divide.
  • Astrocytes: Nourish neurons via blood capillaries.
• Connective tissue: Supports, connects and separates tissue.
  • Loose connective tissue: Abundant matrix, fills spaces between organs
  • Adipose tissue: Scarce matrix, fat-storing cells for insulation, energy reserves.
  • Blood tissue: Liquid matrix (plasma), transports substances.
  • Cartilaginous tissue: Flexible matrix with fibers, supports the developing skeleton.
  • Bone tissue: Hard solid mineralized matrix (calcium and phosphorus), provides structural support.

Function of Nutrition

• Nutrition provides materials for structure and energy for vital processes.
• Respiratory system: Gathers oxygen and releases carbon dioxide.
• Urinary system: Eliminates cellular waste products.
• Digestive system: Extracts nutrients and removes indigestible materials,.

Health and Illness

• Health: State of complete physical, mental, and social well-being, not just absence of disease (WHO definition).
• Three dimensions: social, physical, and mental health. Factors impacting well-being include societal structures like peace, education, housing, and equitable resources.
• Health-determining factors:
  • Biological: Genetics and physiology.
  • Lifestyle: Personal behaviours (diet, exercise).
  • Environment: Natural elements (climate), artificial factors (pollution), and socioeconomic aspects.
  • Health system: Quality and access to healthcare resources.
• Disease: Disruption to body structure or function.
• Etiology: The study of disease causes.

Types of Diseases

• Infectious (due to pathogens): caused by microorganisms like prions, viruses, bacteria, fungi, or parasites.
• Non-infectious:
  • Genetic: Gene mutations, e.g., Down Syndrome.
  • Tumor/Neoplastic: Abnormal cell growth, e.g., cancer.
  • Immune : Disorder of the immune system, e.g., allergies.
  • Mental disorders: Disturbances in thoughts, emotions, or behaviours, e.g., anxiety.
  • Degenerative: Progressive tissue/organ degradation, e.g., Alzheimer's.
  • Nutritional and behavioural: Poor nutrition, eating disorders.
  • Accidents: Injuries, burns, poisonings.
  • Environmental Exposure: E.g., asbestosis.

Pathogens, Reservoirs & Sources

• Pathogens: Microorganisms causing disease.
• Reservoir: Natural habitat of a pathogen.
• Source: Where a pathogen is acquired by the host.

Host, Endemic & Epidemic

• Host: An organism (animal, plant) harboring a pathogen.
• Endemic: Regular disease presence within a geographic area.
• Epidemic: Sudden spread of a disease within a geographic area.
• Pandemic: An epidemic spreading across multiple countries or continents.

Immunity

• Immunity: Body's defense system against harmful agents.
• Innate immunity: First and second lines of defense.
• Primary barriers: Prevent entry (skin, mucous membranes).
• Secondary barriers: Fight invaders (inflammation, phagocytes).
• Acquired immunity: Body adapts and improves defenses over time, remembering pathogens.