U1 : the human body

• Anatomy is the study of the structure and shape of the body and its parts
• Gross anatomy focuses on large structures that are easily observable
• Microscopic anatomy deals with structures that are too small to be seen with the naked eye, such as cells and tissues
• Physiology is the scientific discipline that deals with the processes or functions of living things
• Human physiology explains the specific characteristics and mechanisms of the human body
• Pathophysiology is the study of abnormalities in the physiologic functioning of living beings, resulting from the intersection of pathology and physiology
• The framework for pathophysiology includes etiology, pathogenesis, clinical manifestations, and treatment implications
• Homeostasis describes the body's ability to maintain relatively stable internal conditions despite changing external conditions
• Homeostatic control involves receptors that monitor changes, control centers that determine variable levels, and effectors that provide responses to stimuli
• Feedback mechanisms in homeostasis can be negative (shutting off or reducing the stimulus) or positive (increasing the disturbance)
• Cells are the structural and functional units of all living things, consisting of a nucleus, cytoplasm, and plasma membrane
• The nucleus contains genetic material (DNA), is the control center of the cell, and is necessary for cell reproduction
• The plasma membrane separates cell contents from the surrounding environment and is made up of phospholipids and globular protein molecules in a fluid mosaic model
• Cytoplasm is the major site of most activities carried out by the cell
• Extracellular fluid is a watery environment that contains glycoproteins, glycolipids, cholesterol, sugar groups, polar heads of phospholipid molecules, and a bimolecular lipid layer containing proteins with nonpolar tails of phospholipid molecules
• The structure of the plasma membrane includes channel proteins, filaments of the cytoskeleton, and a watery environment called cytoplasm
• Specialized cell types include:

  • Fibroblasts and erythrocytes that connect body parts
  • Epithelial cells that cover and line body organs
  • Skeletal, cardiac, and smooth muscle cells that move organs and body parts
  • Fat cells that store nutrients
  • White blood cells that fight disease
  • Nerve cells (Neurons) that gather information and control body functions
  • Oocytes (egg cells) and sperm for reproduction
• Fibroblasts secrete fibers and contain rough ER and Golgi apparatus but no organelles in the nucleus

  • Epithelial cells have intermediate filaments in the nucleus
  • Skeletal muscle cells have contractile filaments and multiple nuclei
  • Smooth muscle cells have a single nucleus
  • Fat cells contain a lipid droplet in the nucleus
  • White blood cells have lysosomes, macrophages, and pseudopods
  • Nerve cells have processes and rough ER
  • Sperm cells have a flagellum for movement
• During prophase:

  • Chromatin coils into chromosomes with identical strands called chromatids held together by a centromere
  • Centrioles direct the assembly of a mitotic spindle
  • The nuclear envelope and nucleoli break down
• In metaphase:

  • Chromosomes align in the center of the cell on the metaphase plate
  • A straight line of chromosomes is visible
• During anaphase:

  • Centromeres split
  • Chromatids move apart towards opposite ends of the cell
• In telophase:

  • Chromosomes uncoil to become chromatin
  • Spindles break down, nuclear envelope reforms around chromatin, and nucleoli appear in each daughter nucleus
• Cell physiology involves cells being able to metabolize, digest food, dispose of waste, reproduce, grow, move, and respond to stimuli
• Membrane transport involves solutions, which are homogeneous mixtures of two substances
• Solution is a homogeneous mixture of two or more components
• Solvent is the dissolving medium present in larger quantity, with water being the body's main solvent
• Solutes are components in smaller quantities within a solution
• Intracellular fluid includes nucleoplasm and cytosol, containing gases, nutrients, and salts dissolved in water
• Extracellular fluid (interstitial fluid) is the fluid on the exterior of the cell, containing various ingredients such as nutrients, hormones, neurotransmitters, salts, and waste products
• The plasma membrane is a selectively permeable barrier where some materials can pass through while others are excluded
• Two basic methods of transport:

  • Passive processes: substances are transported across the membrane without any input from the cell
  • Active processes: the cell provides the metabolic energy (ATP) to drive the transport process
• Passive transport methods include:

  • Diffusion
  • Simple diffusion
  • Osmosis
  • Facilitated diffusion
  • Filtration
• Active transport:

  • Aka "solute pumping"
  • Uses ATP to energize protein carriers (solute pumps)
  • Moves substances against the concentration gradient
  • For substances that are too large to pass through, lack special protein carriers, or may not dissolve in the fat core
  • Example: Sodium-potassium (Na⁺-K⁺) pump
• Filtration is the process where water and solutes are forced through a membrane by fluid or hydrostatic pressure, with pressure gradient pushing solute-containing fluid from higher to lower pressure areas
• Diffusion occurs from areas of higher concentration to lower concentration, affected by factors like difference in concentration, size of molecules, and temperature
• Types of passive transport:

  A. Simple diffusion: unassisted diffusion of solutes, especially lipid-soluble solutes

  B. Osmosis: diffusion of water through a selectively permeable membrane

  C. Facilitated diffusion: passage for certain needed substances that are lipid-insoluble, too large to pass through membrane pores, or charged; follows the laws of diffusion and uses a protein membrane channel or carrier
• Vesicular transport is used for substances that cannot be transported by active or passive transport, using ATP to fuse or separate membrane vesicles and the cell membrane

  • Exocytosis: actively secretes hormones, mucus, or ejects cellular wastes
  • Endocytosis: takes up extracellular substances by enclosing them in a vesicle, including phagocytosis, pinocytosis, and receptor-mediated endocytosis