🫀Anatomy and Physiology II Unit 13 – Cellular & Molecular Organ System Basics

Key Concepts and Terminology

• Cells are the fundamental units of life that make up all living organisms
• Tissues consist of groups of cells with similar structure and function working together
• Organs are composed of multiple tissue types organized to perform specific functions
• Organ systems are groups of organs that work together to carry out complex functions in the body
• Homeostasis maintains stable internal conditions necessary for proper functioning of cells, tissues, and organs
• Negative feedback loops help maintain homeostasis by counteracting changes in the body's internal environment
  • Involves receptors, control centers, and effectors to detect and respond to deviations from set points (body temperature)
• Positive feedback loops amplify changes in the body and are less common than negative feedback loops (blood clotting)

Cell Structure and Function

• Cells are enclosed by a plasma membrane that regulates the movement of substances in and out of the cell
• Organelles are specialized structures within cells that perform specific functions
  • Nucleus contains genetic material (DNA) and controls cellular activities
  • Mitochondria generate energy (ATP) through cellular respiration
  • Endoplasmic reticulum synthesizes and transports proteins and lipids
  • Golgi apparatus modifies, packages, and distributes proteins and lipids
  • Lysosomes break down and recycle cellular waste and foreign materials
• Cytoskeleton provides structural support and enables cell movement
  • Composed of microfilaments, intermediate filaments, and microtubules
• Extracellular matrix surrounds and supports cells, providing structural and biochemical cues

Tissue Types and Organization

• Epithelial tissue covers body surfaces, lines cavities, and forms glands
  • Classified by cell shape (squamous, cuboidal, columnar) and number of layers (simple, stratified)
  • Functions include protection, absorption, secretion, and filtration
• Connective tissue supports and connects other tissues
  • Includes loose connective tissue (adipose), dense connective tissue (tendons, ligaments), and specialized connective tissue (cartilage, bone, blood)
• Muscle tissue enables movement and generates force
  • Three types: skeletal, smooth, and cardiac muscle
• Nervous tissue transmits electrical signals and processes information
  • Composed of neurons and glial cells

Major Organ Systems Overview

• Integumentary system protects the body and regulates temperature (skin, hair, nails)
• Skeletal system provides support, protection, and enables movement (bones, cartilage, ligaments)
• Muscular system generates force and movement (skeletal, smooth, and cardiac muscle)
• Nervous system processes information and coordinates body functions (brain, spinal cord, nerves)
• Endocrine system regulates body processes through hormones (glands, hormones)
• Cardiovascular system transports oxygen, nutrients, and waste products (heart, blood vessels, blood)
• Lymphatic system maintains fluid balance and defends against pathogens (lymph vessels, lymph nodes, lymphoid organs)
• Respiratory system exchanges gases between the body and the environment (lungs, airways)

Cellular Communication and Signaling

• Cells communicate through chemical messengers, such as hormones, neurotransmitters, and cytokines
• Receptors on cell surfaces or within cells bind to specific signaling molecules, initiating intracellular signaling cascades
• Signal transduction pathways relay information from the receptor to target molecules within the cell
  • Involves second messengers (cyclic AMP, calcium ions) and protein kinases that amplify and propagate the signal
• Cellular responses to signals include changes in gene expression, protein activity, and cell behavior (growth, division, differentiation)
• Paracrine signaling occurs between nearby cells through local diffusion of signaling molecules
• Endocrine signaling involves hormones secreted into the bloodstream, acting on distant target cells
• Synaptic signaling occurs between neurons or between neurons and target cells through neurotransmitters

Homeostasis and Feedback Mechanisms

• Homeostasis is the maintenance of stable internal conditions in the face of external changes
• Negative feedback loops are the primary mechanism for maintaining homeostasis
  • Deviations from the set point are detected by receptors, triggering a response to counteract the change
  • Examples include regulation of body temperature, blood glucose levels, and blood pressure
• Positive feedback loops amplify changes in the body and are less common
  • Examples include blood clotting, uterine contractions during childbirth, and the release of oxytocin during breastfeeding
• Feedback mechanisms involve communication between different organ systems to coordinate responses
• Disruptions in homeostasis can lead to disease states and impaired organ function

Molecular Basis of Organ Function

• Genes encode proteins that carry out cellular functions and determine tissue and organ properties
• Gene expression is regulated by transcription factors, hormones, and other signaling molecules
• Mutations in genes can lead to altered protein function and disease states
• Epigenetic modifications (DNA methylation, histone modifications) influence gene expression without changing the DNA sequence
• Proteins, such as enzymes, receptors, and structural proteins, are essential for organ function
  • Enzymes catalyze biochemical reactions, enabling metabolic processes
  • Receptors bind to signaling molecules and initiate cellular responses
  • Structural proteins provide mechanical support and enable tissue-specific functions (collagen, elastin)
• Cellular metabolism, including glycolysis, citric acid cycle, and oxidative phosphorylation, generates energy (ATP) for organ function

Clinical Applications and Relevance

• Understanding cellular and molecular mechanisms is essential for diagnosing and treating diseases
• Genetic disorders result from mutations in specific genes, leading to altered protein function and organ dysfunction (sickle cell anemia, cystic fibrosis)
• Cancer arises from uncontrolled cell division and growth, often due to mutations in genes regulating the cell cycle (tumor suppressors, oncogenes)
• Targeted therapies aim to correct or compensate for specific molecular defects in diseases
  • Gene therapy introduces functional copies of genes to replace defective ones
  • Enzyme replacement therapy provides missing or deficient enzymes in genetic disorders (Gaucher disease)
• Stem cell therapies exploit the ability of stem cells to differentiate into various cell types, potentially regenerating damaged tissues and organs
• Personalized medicine tailors treatments based on an individual's genetic profile and molecular characteristics of their disease
• Molecular diagnostics use biomarkers and genetic tests to detect and monitor diseases (PCR, DNA sequencing)