Human Tissue Histology Part 1 Organization of the
- Slides: 54
Human Tissue & Histology Part 1: Organization of the Human Body
Tissue n n Tissue: A group of similar cells (and cell products) that arise from the same region of the developing human embryo and work together to perform a specific task. Primary Germ Layers are the rapidly dividing cells of a zygote organized into 3 layers that form epithelial tissue: ¨ Endoderm: The innermost germ layer; develops into parts of the digestive and respiratory system. ¨ Mesoderm: The middle germ layer; develops into bone, muscle, and connective tissue. ¨ Ectoderm: The outermost germ layer; develops into epithelium and nervous tissue
Types of Tissue n Four basic types of tissue: ¨ Epithelial: Covers surfaces or lining tubes and hollow organs in the body, also forms glands ¨ Connective: Provides support, protection, and fills spaces. n Helps bind organs together; Stores energy reserves; Useful in providing immunity ¨ Muscular: When stimulated by nerve impulses, produces movement. ¨ Nervous: Neurons initiate nerve impulses. n Neuroglia provide support to neurons.
Epithelial Tissue n Epithelium: Cells tightly arranged in continuous sheets with little intracellular space. ¨ Form boundaries between the body’s organs or protects the body from the external environment ¨ High rate of cell division helps keep the tissue in constant repair n TWO primary categories: Covering & Lining Epithelium n Glandular Epithelium n
Covering & Lining Epithelium Forms the outer covering of skin and some organs n Forms the lining of blood vessels, ducts, and body cavities n Lines the interior of most of the body’s systems (respiratory, digestive, reproductive, etc. ) n Further subdivided by layer and cell type. n
Covering & Lining Epithelium: Layers n 3 Layers: ¨ Simple: A single layer of cells that functions in diffusion, osmosis, filtration, secretion, and absorption ¨ Stratified: Composed of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear. ¨ Pseudostratified: Contains a single layer of cells; not all cells reach the apical surface and are either ciliated or secrete mucous
Covering & Lining Epithelium: Cell Shapes n Cell Shapes: ¨ Squamous: Thin and tile-like ¨ Cuboidal: Cube shaped. ¨ Columnar: Column shaped ¨ Transitional: Change shape
Covering & Lining Epithelium in the Human Body n Simple Squamous Epithelium: Lines the heart and blood vessels (endothelium), air sacks of the lungs, and serous membranes (mesothelium)
Covering & Lining Epithelium in the Human Body n Simple Cuboidal Epithelium: Used primarily in secretion and absorption
Covering & Lining Epithelium in the Human Body n Simple Columnar Epithelium: Found in the lining of the gastrointestinal tract (nonciliated) and respiratory tract (ciliated)
Covering & Lining Epithelium in the Human Body n Stratified Squamous Epithelium: Lines wet surfaces like mouth, epiglottis and vagina (non-Keratinized); superficial skin layer (Keratinized), ureters, and urethra.
Covering & Lining Epithelium in the Human Body n Transitional Epithelium: Lines urinary bladder to permit distension
Glandular Epithelium n Glandular Epithelium: The primary function is sectretion. ¨ Gland: Any collection of cells that secrete substances either into the blood, onto the surface, or into the ducts. Two major categories: Endocrine and Exocrine
Endocrine Glands: Secrete hormones directly into the bloodstream to regulate body activities. n Examples: n ¨ Pituitary Gland ¨ Adrenal Gland ¨ Thyroid Gland
Exocrine Glands n n n Exocrine Glands: Secrete various materials such as mucous, saliva, and sweat into ducts that then empty onto the surface of a covering or lining epithelium. Two major categories: Unicellular (like goblet cells) or Multicellular (like sebaceous or oil glands) Means of Secretion: Merocrine Glands: Use exocytosis to secrete materials from cells and release secretions synthesized by ribosomes. Ex. Salivary pancreatic glands. ¨ Apocrine Glands: Accumulate secretions on the surface of the cell which are then “pinched off”. Ex. Mammary glands ¨ Holocrine Glands: Accumulate secretions in the cytosol until the entire cell ruptures to release it. Ex. Sebaceous glands on skin. ¨
Epithelial Membranes n Epithelial Membrane: Combination of an epithelial layer and an underlying connective tissue layer. 3 Main Types: ¨ Mucous Membranes (Mucosa): Lining of the body cavities that open to the outside of the body. n E. g. lining of the entire digestive, respiratory, and reproductive tracts. ¨ Serous Membranes (Serosa): Cover the organs & the cavities that contain them ¨ Cutaneuous Membranes: Skin! n Synovial Membranes: Lines the cavities of movable joints, secreting a fluid that lubricates the cartilage covering the bones at such joints.
Connective Tissue n Connective Tissue: Supports, strengthens, and binds together the other tissues. ¨ Primary site of stored energy (adipose tissue) and immune response ¨ Provides the body its main transport system (blood) ¨ Often has a rich blood supply (with some exceptions) and generally consists of few cells scattered throughout an intercellular matrix or protein fibers and a ground substance which binds the cell together.
Connective Tissue Connective tissue arises from embryonic cells whose name ends in –blast and –cyte n BLAST cells have a high capacty for cell division and are responsible for making the matrix n Once the matrix is formed, the blast cells mature into CYTE cells designed to maintain the matrix. n
6 Types of Connective Tissue n 6 Types of Connective Tissue: ¨ Fibroblasts ¨ Macrophages ¨ Plasma Cells ¨ Mast Cells ¨ Adipocytes ¨ White Blood Cells
6 Categories of Mature Connective Tissue 1. Loose Connective Tissue: Most common type found in the human body. Composed of areolar, adipose, and reticular tissues. Many cells present and fibers loosely intertwined. 1. 2. 3. Areolar: Forms subcutaneous layer that attaches skin to underlying tissues. Adipose: Stores triglycerides (fat). Provides insulation and a source of energy reserves. Reticular: Forms the supporting framework of the liver, lymph nodes, and spleen and binds smooth muscle cells together.
6 Categories of Mature Connective Tissue 2. Dense Connective Tissue: Has thicker fibers and fewer cells than loose tissue. Due to toughness and pliability, forms tendons and ligaments, providing strong points of attachment. Subdivided into 3 kinds: 1. 2. 3. Dense Regular Connective Tissue: Tissue is tough, silvery -white and pliable – forms ligaments and tendons; contains regularly arranged bundles of collagen fibers Dense Irregular Connective Tissue: Occurs where forces pull from multiple directions; forms pericardium around the heart; heart valves and the dermis of skin; contains closely collagen fibers, irregularly arranged. Elastic Connective Tissue: Easily resumes normal shape after being stretched – makes up lung tissue and walls of elastic arteries; contains branching elastic fibers.
6 Categories of Mature Connective Tissue 3. Cartilage: Made up of tightly packed collagen and elastic fibers in a rubbery substance known as chondroitin sulfate. Provides support for ears, nose, and trachea, intervertebral disks; makes up the embryonic skeleton. 3 Types of Cartilage: 1. 2. 3. Hyaline Cartilage: Most abundant and weakest type in human body; provides smooth surface for movement at joints; located at articular cartilage & epiphyseal plates. Fibrocartilage: Exists at kneecaps and the discs between the vertebrae to provide support & connectivity; strongest type. Elastic Cartilage: Gives shape and support; found in epiglottis and external ear; provides strength and elasticity.
n n Hyaline Fibrocartilage n Elastic
6 Categories of Mature Connective Tissue 4. Bone Tissue: Known as osseous tissue; composed primarily of collagen and calcium phosphate (provides durability); divides into two categories: 1. Compact Bone: Composed of osteons 2. Spongy Bone: Lacks osteons
n Compact Bone n Spongy Bone
6 Categories of Mature Connective Tissue 5. Blood Tissue: Liquid matrix is blood plasma with formed elements suspended in it.
6 Categories of Mature Connective Tissue 6. Lymph: Extracellular fluid flowing in lymphatic vessels. Serves a variety of functions.
Muscle Tissue n Muscle Tissue: Consists of muscle fibers that use ATP to generate movement & heat. 3 classifications: Skeletal Muscle Tissue: Striated tissue attaches to bones of the skeleton, usually by tendons, & is used to produce movement & heat. Under voluntary control. ¨ Cardiac Muscle Tissue: Forms most of the heart wall & tissue; responsible for pumping blood; under involuntary control. ¨ n ¨ Cardiac muscle cells are branched & attach to each other by thick circles of plasma membrane known as intercalculated discs Smooth Muscle Tissue: Spindle-shaped fibers; under involuntary control; found along the hallow internal structures, mainly blood vessels, intestines, stomach, uterus, airways, etc. Primarily responsible for moving materials through these structures.
n n Skeletal n Smooth Cardiac
Nervous Tissue n Nervous Tissue: Senses stimuli & converts them into nerve impulses or signals to different parts of the human body. Two kinds of nerve cells: ¨ Neuron ¨ Neuroglia
Neuron n n Neuron: AKA Nerve cell; responsible for converting stimuli into impulses. Impulses travel only one direction along the cell. Made up of 3 Major Parts: Cell Body: Contains the nucleus and organelles ¨ Dendrites: Multiple branched tapering projections that receive impulses from other cells and move up toward the cell body. ¨ Axon: Single, cylindrical projection that carries the signals away from the cell body and to the next neuron or other tissue. ¨ n Nerve impulse always moves from the receiving dendrite, through the cell body, and out the axon to the axon terminals, synapse, and the next dendrite.
Neuroglia: AKA Glia. Comprise about half of the central nervous system & serve a variety of important roles. n More on these later! n
Cell Junctions: Places where cells anchor to one another to form seals; some form channels that allow molecules & ions to pass from cell to cell. n 5 Primary Types of Cell Junctions: n ¨ Adherens Junctions ¨ Desmonomes ¨ Gap Junctions ¨ Hemidesmosomes ¨ Tight Junction
Adherens Junctions n Adherens Junctions: Contain proteins on the inside of the cell membrane called plaque. ¨ Provides a strong attachment between adjacent cells by means of cadherins (glycoproteins which bind together to anchor cells next to each other).
Desmosomes n Desmosomes: Like adherens junctions, they provide a means of holding two cells tightly together ¨ Use keratin filaments ¨ Found in the epidermis (outer layer of the skin) & between cardiac muscle cells
Gap Junctions n Gap Junctions: Create intercellular channels that permit passage of small molecules & ions from one cell to another. ¨ Essential for the spread of nerve & muscle impulses ¨ In cardiac muscle & smooth muscle of the GI tract as well as some synapses in the brain
Hemidesmosomes n Hemidesmosomes: Resemble desmosomes, though their primary responsibility is to anchor other cells to the basement membrane (the extracellular layer between epithelium & connective tissue).
Tight Junctions n Tight Junctions: Strands of proteins that fuse cell membranes together, thus controlling the passage of molecules & ions through the space in between cells. ¨ Found in the lungs & tissues lining the stomach, intestines, and urinary bladder.
Tissue Repair n Tissue Repair: The process by which damaged, worn, or dead cells are replaced. The rate & capacity for repairing damaged cells varies with the kind of tissue. ¨ Epithelial Tissue: Undergoes lots of wear & tear and often has a high capacity for self-repair. n Stem Cells: Immature, undifferentiated cells that can divide to replace damaged cells. Sometimes mature, undifferentiated cells can divide to do the same. ¨ Connective Tissue: Capacity for renewal depends a large part on the blood supply. Bone, for example, renews cells easily, whereas cartilage does not. ¨ Muscle & Nervous Tissue: Have poor capacity for repair, mainly due t the lack of stem cells available.
Tissue Repair n Two primary types of tissue repair: ¨ Regeneration: Injured tissue is replaced through cell division of the same type of cells (known as parenchyma). ¨ Fibrosis: Fibroblasts synthesize collagen & other materials to form scar tissue. n If damage is extensive, both processes take place to create a growing connective tissue called granulation tissue which forms the stroma (framework) for new cells to move in & protects against bacteria.
Ailments That Prompt Tissue Repair n Cellulitis: A bacterial infection of the skin & underlying tissues.
Ailments That Prompt Tissue Repair n Abscesses: Inflamed infection of tissues as a result of pus accumulation.
Ailments That Prompt Tissue Repair n Ulcers: Open sores that result when inflamed tissue sloughs off from the surface of an organ.
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