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Histology - PowerPoint PPT Presentation

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Histology. The study of….webs?. http://meded.ucsd.edu/hist-img-bank/chapter_1/Slide_2_kidney/index.htm. Histo- Greek for ‘web’ Tissue-groups of similar cells ‘webbed’ together. http://www.tutorvista.com/content/science/science-i/tissues/animal-tissues.php. Epithelial.

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The study of….webs?





  • Protects outer body and lines inner organs

  • Sheets/tubes of tightly-packed cells

  • Polarity- has a top (apical) and a bottom (basal)

    • Apical- surface that can be exposed to air or fluid

      • Sometimes has cilia (hair-like growth)

        • Moves material over cell surface

      • Or microvilli (finger-like projections)

        • Increases surface area for absorption

    • Basal attaches to a connective tissue


Classification by layers-

  • Single-layered: simple

  • Multi-layered: stratified

  • Pseudostratified epithelium- appear multilayered because of differing cell lengths but it is only simple epithelium

Thickly cornified stratified squamous epithelium. The cells in the bright red layer and in the pale layers above it are completely flattened and dead, and have lost their nuclei.


Simple columnar epithelium with very regular line-up of nuclei



Key functions

  • Protection

    • Protects more vunerable structures in the body

  • Barrier

    • Prevents foreign objects from entering the body

  • Sensation

    • Sensory nerve endings in epithelial tissue connect with outside stimuli

  • Secretion

    • Can be specialized to secrete enzymes, hormones, and fluids

Connective tissue
Connective Tissue

  • It is the frame-work and support for organs, stores fat, transports substances, protects against disease, repairs tissue damage.

  • Classified by the extracellular matrix- what they lay in.

  • Collagen- fibrous protein

    • Gives the tissue the strength it needs

  • Connective tissue is made up of a mix of collagen, elastic, and reticular fibers


Primary types of connective tissue

  • Dense regular connective tissue: in tendons used as bundles of collagenous fibers to attach muscle to bone. In ligaments as elastic fibers from bone to bone, surrounding a joint, and anchoring organs.

  • Dense irregular connective tissue: fibers twist and weave to form thick tissue that withstands stress from any direction. Makes up inner skin layer called the dermis and the outer capsule of organs like the kidney and the spleen.

  • Reticular tissue: thin, branching fibers made of collagenous fibers. It is a filter found in the spleen, lymph nodes, and bone marrow.


  • Areolar (loose) tissue: almost everywhere in the body, it binds structures together and fills space. Made of collagenous protein fibers (wavy ribbons), elastic fibers (cylindrical threads), and amorphous ground substance (semisolid gel).



  • Adipose tissue: made from fat cells. Forms padding for internal organs, reduces heat loss, and stores energy in fat molecules (triglycerides). Have a ring-like structure bc fat molecules fill cells forcing the nuclei against the cell membranes. Has an intracellular matrix, not extracellular.


  • Bone (osseous) tissue: repeating patterns called Haversian systems. The Haversian canal (center of each system) contains blood vessels, lymph vessels, and nerves. It is surrounded by thin membranes called lamellae.

  • Blood: extracellular matrix is plasma. Erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets) are suspended in it.



  • Cartilage: firm, flexible tissue made of collagen and elastic fibers with no blood vessels or nerve cells. Contains openings called lacunae that enclose mature cells (chondrocytes). There are 3 types:

    • Hyaline- foundation for embryonic skeleton, forms the rib cartilages, makes nose cartilage, and covers articulating surfaces of bones

    • Fibrocartilage- thick, compact collagen fibers. Its sponge-like structure makes it a good shock-absorber. Found in intervertebral discs and symphysis pubis (front of pelvis).

    • Elastic cartilage- more tightly packed lacunae and chondrocytes beween parallel elastic fibers than hyaline. Makes the ear lobe and other structures with specific form. It tends to ‘bounce back’ into its original

Muscle tissue
Muscle Tissue

  • Made of fibers called myocytes

    • Cytoplasm in the fiber is called sarcoplasm

      • In the cytoplasm is myofibrils

        • They contain the protein filaments actin and myosin

          • These filaments slide past each other during muscle contractions to shorten the fiber.

  • There are 3 types



  • Smooth muscle tissue- contracts without conscious control. Made of spindle-shaped fibers with large, central nuclei. Found in internal organ walls. It is not striated.

  • Cardiac muscle tissue- known as myocardium. Branching fibers with a central nucleus and alternating light and dark striations make it. Intercalated discs are the dark structures between fibers. Controlled by the autonomic nervous system.

  • Skeletal, striated, muscle tissue- it attaches to the skeleton and is used throughout the central nervous system for movement. Fibers are cylindrical with several nuclei in each cell.

Nerve tissue
Nerve Tissue

  • Neurons are the only type of nerve tissue

  • It generates and conducts electrical signals throughout the body

  • Sense receptors receive a stimulus which then sends electrical impulses through finger-like cytoplasmic projections called dendrites.

  • It moves through the body through axons.




Skin, hair, nails, and glands



What does it mean?

  • Integere (Latin)- “to cover”

  • Dermato and cutis (Greek and Latin)- “skin”

  • Epi- (Greek)- “upon” or “above”


Why do we need it? overview

  • Largest organ

  • Retains moisture

  • Sensory receptors for:

    • pain,

    • Heat

    • Touch

  • Excretes salts

  • Excretes small amounts of waste

  • Stores blood

  • Regulates body temp.


  • 2 main parts

    • Epidermis and dermis

  • Under the dermis is the hypodermis (supericial fascia- subcutaneous tissue)

    • It acts a foundation not truly part of the skin




  • Surface skin

    • 1st line of defense against infection

    • Contains no blood vessels

    • Layers and layers of epithelial cells



  • Melanocytes

    • ¼ of stratum basale is made of these

    • Synthesize a pale yellow to black pigment called melanin

    • Cytocrine secretion- melanin is secreted into keratinocytes

  • Melanin- skin color and protection against uv rays

  • Keratinocytes

    • majority of stratum basale

    • Primary epithelial cell of skin


More about the epidermis

  • Carotene- in stratum corneum and fatty layers beneath the skin

    • Produces yellowish hue common with Asian ancestry

  • Hemoglobin- cause for pinkish color of Caucasian skin

    • Less melanin, more hemoglobin

  • Albinos- no melanin in skin at all

  • Ridges and grooves- increase friction to grasp other objects

    • Ex. Loops and whorls (fingerprints, palm prints, footprints)


The Dermis

  • Also known as the corium

  • Thicker and more fibrous than the dermis

  • 2 layers

  • Fibrolasts- connective tissue develops

  • Macrophages- engulf wastes and foreign microorganisms

  • Adipose tissue

  • Thinnest over eyelids and male sex organs

  • Thicker on back than stomach

  • Thickest on palms of hands and soles of feet


Papillary Layer

  • Top (outer) layer

  • Soft

  • Elastic, reticular fibers that enter the epidermis

    • Brings blood and nerve endings closer

  • Papillae are finger-like projections- loops of capillaries to increase the surface area of dermis and anchor epidermis

  • Meissner’s corpuscles- nerve endings sensitive to soft touch.

    • In some papillae


Reticular Layer

  • Rete- net (Latin)

  • Dense, irregular connective tissue

    • Interlacing bundles of collagenous and elastic fibers

      • Strong resistant layer

      • Gives skin strength, extensibility, ad elasticity

  • Oil glands (seaceous glands), sweat glands, fat cells, and larger blood vessels are in this layer



  • Follicles embedded in the epidermis and extend to the dermis angle hair growth (curly or straight).

  • Follicle bases are expanded (called bulbs) reach nerve endings

  • Epithelial cells in the bulb divide to create the hair shaft

  • Hair pigment: melanin

    • Gives hair its color

    • Gray and white hair grow when melanin levels decrease and air pockets form

  • sebaceous gland- sebum is produced (cholesterol, fats, and other substances)

    • Keeps hair soft, pliable, and waterproof


  • Hair has 3 layers

    • Medulla

      • Central core

      • Cells contain eleidin separated by air spaces

      • Fine hair- minimal/ nonexistent

    • Cortex

      • Major part of hair shaft

        • Several layers

        • Flattened cells

      • Elongated pigment-bearing cells in dark hair

      • Air pockets in white hair

    • Cuticle

      • Single layer, overlapping cells with free end pointing up

      • Strengthens and compacts the inner layers

      • Split ends

        • Abrasion wears away the end of the shaft, exposes the medulla and cortex to create the horrid split end



Sweat? Gross…or is it?

  • 2 types of sweat glands (sudoriferous)

    • Coiled tubules in the dermis

    • Eccrine glands-all over body

      • Watery (99%), salty secretion known as sweat

      • Passes through the epidermis to skin’s surface and opens to a sweat pore

      • Controlled by the sympathetic nervous system

    • Apocrine sweat glands

      • Under the armpits and groin area, associated with hair follicles

      • Same components as eccrine and is odorless

        • Bacteria breaks down apocrine sweat’s fatty acids and proteins

          • Creates the odor accompanying post exercise