BLOOD

• Types of tissue


  • Epithelial tissue
  • Connective tissue
  • Nervous tissue
  • Muscle tissue
• Differentiated by


  • Cellular elements
  • Extracellular matrix
• Blood


  Specialized connective tissue, due to its constituents
• Blood


  • Unlike other connective tissue, does not contain fibrous proteins but rather globular proteins
  • Globular proteins make blood liquid in nature, not gel-like/colloidal
• Functions of blood


  • Oxygen and nutrient transport
  • Transport of hormones and regulation of body processes
  • Hemostasis or forming blood clots
  • Immunity
  • Removal of waste products
  • Body temperature regulation
  • Maintaining osmotic balance
  • Maintaining acid-base balance
• Physical characteristics of blood

  • 5-6L of blood on average
  • Comprises 7-8% of body weight
  • pH: 7.35-7.45, slightly alkaline
  • Viscosity: about 5 times as viscous as water
  • Temperature: about 38°C
  • Color: Arterial blood - bright red, Venous blood - dark red, Capillary blood - mixture
• Formed elements of blood

  • Erythrocytes (44% of whole blood)
  • Buffy coat (<1% of whole blood)
  • Platelets
  • Leukocytes
• Erythrocytes


  Red blood cells, anucleate, contain hemoglobin, biconcave disk shape, 7-8 micrometers diameter, 2.5 micrometers thickness, 120 days lifespan, flexible to fit microvasculature
• Leukocyte types


  • Neutrophils
  • Lymphocytes
  • Monocytes
  • Eosinophils
  • Basophils
• Neutrophils


  • 3-5 lobed nucleus, faint/light pink cytoplasmic granules, 50-70% differential count, 1-4 days lifespan, kill and phagocytose bacteria
• Eosinophils


  • Bilobed nucleus, red/dark pink cytoplasmic granules, 1-4% differential count, 1-2 weeks lifespan, kill helminthic and other parasites, modulate local inflammation
• Basophils


  • Bilobed or S-shaped nucleus, dark blue/purple cytoplasmic granules, 0.5-1% differential count, several months lifespan, modulate inflammation, release histamine during allergy
• Lymphocytes


  • Rather spherical nucleus, no specific granules, 20-40% differential count, hours to many years lifespan, effector and regulatory cells for adaptive immunity
• Monocytes


  • Indented or C-shaped nucleus, no specific granules, 2-8% differential count, hours to years lifespan, precursors of macrophages and other mononuclear phagocytic cells
• Skeletal muscle


  Composed of large, elongated, multinucleated fibers that show strong, quick, voluntary contractions
• Cardiac muscle


  Composed of irregular branched cells bound together longitudinally by intercalated discs and shows strong, involuntary contractions
• Smooth muscle


  Composed of grouped, fusiform cells with weak, involuntary contractions, small amount of extracellular connective tissue
• Sarcoplasm


  The cytoplasm of muscle cells
• Skeletal muscle development


  1. Mesenchymal myoblasts fuse, forming myotubes with many nuclei

  2. Myotubes further differentiate to form striated muscle fibers
• Skeletal muscle fibers


  • Elongated nuclei found peripherally just under the sarcolemma
  • Small population of reserve progenitor cells called muscle satellite cells remains adjacent to most fibers
• Organization of a skeletal muscle

  • Epimysium (external sheath of dense connective tissue)
  • Perimysium (thin connective tissue layer surrounding each bundle of muscle fibers)
  • Endomysium (very thin, delicate layer of reticular fibers and scattered fibroblasts surrounding individual muscle fibers)
• Skeletal muscle fibers


  • Elongated nuclei found peripherally just under the sarcolemma
  • Small population of reserve progenitor cells called muscle satellite cells remains adjacent to most fibers
• Organization of a skeletal muscle

  1. Epimysium - external sheath of dense connective tissue surrounding the entire muscle

  2. Perimysium - thin connective tissue layer surrounding each bundle of muscle fibers (fascicle)

  3. Endomysium - very thin, delicate layer of reticular fibers and scattered fibroblasts surrounding individual muscle fibers
• Development of skeletal muscle

  1. Mesenchymal cells (myoblasts) align and fuse to form longer, multinucleated tubes called myotubes

  2. Myotubes synthesize proteins to make up myofilaments and develop cross-striations

  3. Part of myoblast population remains as muscle satellite cells on external surface of muscle fibers
• Skeletal muscle fibers


  • Show cross striations of alternating light (I bands) and dark (A bands) bands
  • Repetitive functional subunit is the sarcomere, extending from Z disc to Z disc and about 2.5 μm long in resting muscle
• Cardiac muscle


  • Fibers are striated but consist of individual cylindrical cells, each with one or two central nuclei
  • Linked by adherent and gap junctions at prominent intercalated discs
  • Sarcomeres organized and function similarly to skeletal muscle
  • Contraction is intrinsic, regulated by autonomic nerves
• Smooth muscle


  • Fibers are elongated, tapering, and nonstriated cells
  • Thin and thick filaments do not form sarcomeres, no striations present
  • Thin actin filaments attach to α-actinin in dense bodies throughout sarcoplasm and near sarcolemma
  • Sarcoplasmic reticulum less well-organized, no transverse tubule system
  • Troponin lacking, proteins controlling sliding filaments include myosin light-chain kinase and calmodulin
• Comparison of skeletal, cardiac, and smooth muscle

  • Fibers
  • Cell/Fiber shape and size
  • Striations
  • Location of nuclei
  • T tubules
  • Sarcoplasmic reticulum
  • Special structural features
  • Control of contraction
  • Connective tissue organization
  • Major locations
  • Key function
  • Efferent innervation
  • Contractions
  • Cell response to increased load
  • Capacity for regeneration
• Neuron


  • Cell body (perikaryon) with large, euchromatic nucleus and well-developed nucleolus
  • Perikaryon contains basophilic Nissl substances (free polysomes and RER)
  • Numerous short dendrites extending from perikaryon to receive input
  • Long axon covered by myelin sheath, ending in many small branches (telodendria) forming synapses
• Structural classes of neurons

  • Multipolar
  • Bipolar
  • Unipolar or pseudounipolar
  • Anaxonic
• Neuroglial cell types


  • Oligodendrocyte
  • Astrocyte
  • Microglia
  • Ependymal cell
  • Radial glia
  • Schwann cell
• Neurons


  • Most neurons, including all motor neurons and CNS interneurons, are multipolar
  • Bipolar neurons include sensory neurons of the retina, olfactory mucosa, and inner ear
  • All other sensory neurons are unipolar or pseudounipolar
  • Anaxonic neurons of the CNS lack true axons and do not produce action potentials, but regulate local electrical changes of adjacent neurons
• Purkinje neuron


  Large neuron in the cerebellum with many dendrites emerging from its cell body and forming branches, with short projecting dendritic spines spaced closely along their length, each of which is a site of a synapse with another neuron
• Glial Cell Types


  • Oligodendrocyte
  • Schwann Cell (Neurolemmocyte)
  • Astrocyte
  • Satellite cells (of ganglia)
  • Ependymal cell
  • Microglia
• Oligodendrocyte


  Originates from the neural tube, located in the CNS, main functions are myelin production and electrical insulation
• Schwann Cell (Neurolemmocyte)


  Originates from the neural crest, located in peripheral nerves, main functions are myelin production and electrical insulation
• Astrocyte


  Originates from the neural tube, located in the CNS, main functions are structural and metabolic support of neurons, blood-brain barrier, and repair processes
• Satellite cells (of ganglia)

  Originate from the neural crest, located in peripheral ganglia, main functions are structural and metabolic support for neuronal cell bodies
• Ependymal cell


  Originates from the neural tube, lines the ventricles and central canal of the CNS, main function is to aid production and movement of cerebrospinal fluid
• Microglia


  Originates from bone marrow (monocytes), located in the CNS, main functions are defense and immune-related activities