Characteristics and Organization of Living Things

Characteristics of Living Things

• Living things produce and consume energy, using it for various functions.
• Metabolism encompasses all chemical reactions that support life functions. Anabolism constructs large molecules from smaller ones, while catabolism breaks down complex molecules into simpler ones.
• Growth and repair mechanisms enable organisms to increase size and adapt to their environment, including maintaining specialized cell functions.
• Living organisms adapt by responding to and reacting to environmental changes. Homeostasis is the ability to maintain a stable internal environment.
• Reproduction creates new organisms through cell replication (cellular) or by creating offspring (organismal).

Levels of Organization in the Body

• Chemical level: atoms and molecules form the basis of cells.
• Cellular level: cells with unique functions form tissues.
• Tissue level: similar cells with a common function form tissues.
• Organ level: tissues combine to perform specific functions (e.g., heart, kidney).
• System level: multiple organs collaborate for a common purpose (e.g., digestive system).
• Organismal level: the sum total of all structural levels, working together to maintain life.

Cell Theory

• All living organisms are made up of one or more cells.
• Cells are the functional units of life, influencing the organism's overall function.
• Cells carry out metabolic activities necessary for life.
• Cells arise from pre-existing cells.
• Cells use hereditary information to create biomolecules and enable reproduction.

Cells are the Living Unit of Life

• Cells are the building blocks of tissues.
• Cells maintain homeostasis.
• Cells share common components: membrane, genetic material, and cytosolic fluid.
• Specialized human cells contain membrane-bound organelles, leading to compartmentalization and increased complexity.
• Gene expression drives specialization of cells.

Cell Differentiation

• Cells develop specific features and functions during differentiation.
• Cell differentiation is typically an irreversible process.
• Early cells are totipotent (stem cells), and as tissues and organs develop, these cells differentiate.
• Differentiated cells carry out specialized functions.

Tissues

• Tissues are groups of similar cells with common structure and function.
• There are four basic tissue types: Epithelial (covering), Connective (support), Muscle (movement), and Nervous (control).
• Different tissue combinations form organs with diverse structures and capabilities.

Integrating Tissues: Organs

• Organs are structures formed from two or more tissues working together to perform a specific function.
• All tissues within an organ work together to achieve the organ's function.

Intro to the Organ Systems

• Integumentary System: Skin, hair, nails, and glands, involved in protection, temperature regulation, and sensory functions.
• Nervous System: Brain, spinal cord, and nerves that detect external and internal signals to coordinate physiological responses.
• Musculoskeletal System: Bones, muscles, cartilage, tendons, and ligaments for movement, support, protection, and blood cell production.
• Respiratory System: Nasal passage, trachea, and lungs that regulate the intake of air and gas levels in the blood.
• Cardiovascular System: Heart, blood vessels, and blood for transporting materials throughout the body.
• Immune & Lymphatic systems: Lymphoid tissues, spleen, thymus, lymph nodes, and immune cells involved in defending against pathogens (disease-causing agents).
• Endocrine System: Hormone-secreting glands such as the thyroid, pituitary, adrenal, and parathyroid involved in coordinating growth, metabolism, and reproduction, as well as physiological homeostasis.
• Urinary System: Kidneys, ureters, urinary bladder, and urethra, responsible for purifying blood, regulating plasma volume, and excreting wastes.
• Digestive System: Mouth, salivary glands, esophagus, stomach, intestines, liver, and pancreas involved in food digestion and nutrient absorption.
• Reproductive System: Production of gametes (sex cells); maintenance, and reproduction.

Regional Anatomical Terms

• Regions are for describing locations of the human body.
• Axial region includes the head, neck, and trunk.
• Appendicular region includes the arms, legs, and associated girdles.
• Specific regions within the two major regions are described using directional terms.

The Body Cavities

• Cavities are enclosed spaces in the body.
• Posterior aspect (dorsal cavity): contains the cranial cavity (brain) and the vertebral canal (spinal cord).
• Ventral cavity: contains the thoracic cavity (heart, lungs, and associated structures), and the abdominopelvic cavity (digestive organs, reproductive organs, bladder, etc.). The diaphragm separates the thoracic cavity from the abdominopelvic cavity.
• Serous membranes line body cavities and reduce friction between organs.

Serosa

• Serosa are delicate membranes lining body cavities and covering organs, creating a fluid-filled space for friction reduction during organ movement.
• The membrane consists of two layers: parietal (lines the outer wall of the cavity) and visceral (covers the organ).
• The fluid in between these layers reduces friction.

The Thoracic Cavity

• The thoracic cavity is located in the chest and is surrounded by the ribs and muscles.
• Three compartments: pleural cavities (containing the lungs), pericardial cavity (containing the heart), and mediastinum (central compartment containing the trachea, esophagus, thymus, and other structures).
• Pleural cavities are two-layered serous membranes surrounding the lungs.
• Pericardial cavity surrounds the heart similarly.

The Abdominopelvic Cavity

• The abdominopelvic cavity is located below the diaphragm, divided into abdominal and pelvic components.
• The abdominal cavity contains most of the digestive organs (e.g., stomach, intestines, liver, spleen, kidneys).
• The pelvic cavity contains the reproductive organs and urinary bladder.
• The abdominal cavity is separated by the superior ridge of the hips.

Abdominopelvic Regions

• Anatomists use nine regions to describe locations within the abdominopelvic cavity. There is a set of prefixes that are used to describe these locations.
• There are also four quadrants used for similar purposes in clinical settings.

Directional Terms

• Directional terms describe the relative positions of structures in the body.
• Common directional terms include anterior/posterior, superior/inferior, medial/lateral, proximal/distal, superficial/deep.

Body Planes and Sections

• Body planes are imaginary flat surfaces that section the body into different parts for detailed anatomical views.
• Common planes include sagittal, midsagittal (medial), coronal, and transverse.

Homeostasis

• Homeostasis is the ability of the body to maintain stable internal conditions, despite environmental changes.
• Homeostasis maintains dynamic equilibrium.
• A body is in homeostasis when its needs are adequately met—and functions smoothly.

Homeostasis Mechanisms

• Variables are regulated substances or processes in the body.
• Stimuli are changes in these variables.
• Homeostatic regulatory systems include sensors (receptors), a control center (integrator), and effectors that respond to the stimulus.
• A set point defines the normal range for a particular variable in the body.

Negative v. Positive Feedback

• Negative feedback loops are common homeostatic mechanisms that maintain equilibrium by negating ongoing changes. A change in a variable triggers a response that counters the change, returning the variable to its normal range.
• In contrast, positive feedback loops amplify the stimulus change, rather than reversing it. Positive feedback is less common in homeostatic mechanisms but is vital in certain processes.