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Introduction

  • Tissue: a functional aggregation of cells and their intercellular materials that combine to perform common functions.
  • Organ: an anatomically discrete structure (e.g. heart, skin) with 1 or more functions.
  • Four tissues are considered basic or primary: epithelial, connective, muscular and nervous.
  • Many organs contain all 4 types of tissues e.g. skin (covering, packing, muscles, nerves)
  • Microvilli (singular: microvillus): microscopic cellular membrane protrusions that increase the surface area of cells,[1] and are involved in a wide variety of functions, including absorption,secretion, cellular adhesion, and mechanotransduction.
  • A cilium: an organelle in eukaryotes. Cilia are slender protuberances that project from the much larger cell body.[2] There are two types of cilia: motile cilia and non-motile, or primary cilia, which typically serve as sensory organelles.
  • The lamina propria: thin layer of loose connective tissue which lies beneath the epithelium and together with the epithelium constitutes the mucosa. The lamina propria contains capillaries and a central lacteal (lymph vessel) in the small intestine, as well as lymphoid tissue. Lamina propria also contains glands with the ducts opening on to the mucosal epithelium, that secrete mucus and serous secretions.
  • Stroma = supporting CT
  • Parenchyma = secreting tissue

Slide 1: Gall bladder (simple epithelium)

  • Gall bladder doesn’t make bile, it stores it
    • The liver makes bile
  • We see simple columnar epithelium
    • The nuclei are at the bottoms of the cells (near the basement membrane)
  • Pink stuff are collagen (part of the connective tissue)
  • Red area deep to the epidermis is smooth muscle
    • It contracts to squeeze out bile
  • The chicken-wire area is fat cells
  • Thick walled blood vessel is an artery
    • Surrounded by smooth muscle layer
    • Artery and muscle are wrapped in collagen layer (protective)
  • Nerves:
    • Think of a transverse section through a cable
    • Wavy-looking cells
    • Like a peanut
  • Red cells are the red blood cells.
  • The cells that look like “all nuclei” are leucocytes.
  • The dark collection of cells surrounding the hole are lymph aggregations.
    • Hole is a fold in epithelium (3D), surrounded by a cluster of leucocytes (lymphocytes in this case)
    • These lymphocytes are close to the lumen of the gallbladder
    • They are an army waiting, ready to kill antigens that may enter

Slide 2: Oesophagus (stratified epithelium)

  • Stratified squamous epithelium
  • No keratin
    • There is nothing rough for the oesophagus to come into contact with. All food is mixed with saliva.
  • Mucous glands make food slippery
    • Light staining centres = mucous
    • Mucous protects surface cells from abrasion
    • Leucocytes surround the mucous glands to prevent pathogens invading (army at the ready)
  • Layers (basic):
    • Epithelium
    • Lamina propria mucosae
    • Connective tissue
  • Close to the stomach, oesophageal muscle is smooth.
  • Close to the mouth, oesophageal muscle is skeletal.
  • Image A is a section of the human esophagus. Moderately magnified. The section is transverse and from near the middle of the gullet.
  1. Fibrous covering.
  2. Divided fibers of longitudinal muscular coat.
  3. Transverse muscular fibers.
  4. Submucous or areolar layer.
  5. Muscularis mucosae.
  6. Mucous membrane, with vessels and part of alymphoid nodule.
  7. Stratified epithelial lining.
  8. Mucous gland.
  9. Gland duct.
  10. Striated muscular fibers cut across.

Slide 3: Thick skin (e.g. palm or sole)

  • Keratinising stratified squamous epithelium
    • The keratinocytes are produced in the stratum basale (very mitotic layer—above: germinativum)
    • As they move up, they die at the stratum granulosum.
    • They then fall off and produce keratin
  • Keratin on the surface is produced by dead keratinocytes of the stratum corneum.
    • These cells and keratin fall off constantly and are replaced by mitotic cells in the dermis.
  • Ridging between the dermis (dermal papillae) and epidermis (epidermal pegs) to form fingerprints. Holds down the epidermis
  • Sweat ducts appear as adjacent ovals in the epidermis (spiralling duct that is cut straight)
  • At the base of the sweat ducts are the sweat glands.
  • Meissner’s corpuscle: sensory receptor (think of it like a spring)
    • Sensitive to light pressure. Quite superficial (below the stratum basale)
  • Pacinian corpuscle: sensory receptor (onion that squashes).
    • Sensitive to firm/heavy pressure. Very deep.
  • Pink material = collagen (structural protein)
  • Black lines in the dermis = elastic fibres (we have an elastic stain)
  • Link Structure to Function: skin has to stretch (e.g. obesity, pregnancy)
  • Can stretch beyond elastic potential, when they’ll snap (fail to obey Hooke’s law) → you get stretch marks (which are irreversible)
  • In between the fibres are spaces:
    • Some shrinkage
    • Also ground substance between fibres
    • Some injuries – oil substance comes out
      • Changes viscosity (slows down bacteria)
      • Haluronic acid, glycosaminoglycans: big molecules that bind to water and make it viscous like honey/jelly
      • Buys time so that your leucocytes can come defend
  • Fat is in the hypodermis (deep to the dermis)
  • Dermis’ collagen is anchored down here (holding on the palm of your hand)

Slide 4: Lymph node (silver stain)

Background

  • A lymph node is a small ball-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels.
  • Lymph nodes are garrisons of B, T, and other immune cells. They are important in the proper functioning of the immune system.
  • Lymph nodes also have clinical significance. They become inflamed or enlarged in various conditions, which may range from trivial, such as a throat infection, to life-threatening such as cancers. In the latter, the condition of lymph nodes is so significant that it is used for cancer staging, which decides the treatment to be employed, and for determining the prognosis.
  • Lymph nodes can also be diagnosed by biopsy whenever they are inflamed. Certain diseases affect lymph nodes with characteristic consistency and location.

Histology

  • Lymph nodes are little beads (pea sized)
    • In armpit, groin, etc [these ones are submandibular lymph nodes]
    • Connected to lymph vessels; form a chain
    • Dead cells etc. go through the lymph notes, and leucocytes aggregate there to deal with it (causes swelling; lymphadenitis)
  • Black lines = reticular fibres in the connective tissue
    • Made by fibroblasts (make collagen, fibrin, reticular fibres)
    • Reticular fibres form a framework.
    • Can’t see reticular fibres in H&E (need silver stain)
  • The stroma (reticular CT) provide a framework for the parenchyma (leucocytes) to reside in
  • A lot of lymphocytes (purplish)
    • Darker around the edges, lighter in the middle (as more leucocytes live on the edges of the lymph node)

Lymph node is encapsulated in collagen (pink jacket)

Slide 5: Trachea (hyaline cartilage)

  • No vessels or nerves are within the cartilage (purple bit)
  • Perichondrium = the layer of CT around the cartilage (in this case, around the trachea)
  • Lumen = hole (airway)
  • The dark purple cartilage is supposed to go all the way around
  • Dark lines on cartilage are folds in the slide (artefacts)
  • Cartilage is a good choice for the trachea (windpipe) because it is halfway between bone (too brittle) and muscle (too soft)

Slide 6: Decalcified rib

Background

  • Serratus anterior lives on top of the ribs.
  • Muscles between the ribs = intercostals
  • Bone is a type of CT.
  • Took out the calcium from the rib so that it can be cut with the microtome
  • Bone contains many blood vessels and nerves (sensitive)
  • Ligaments and tendons hook up to the periosteum, outer layer of compact bone

Histology

  • Bone marrow lies inside of the bone. There are also blood vessels inside the bone.
    • Marrow: big white areas = adipose (fat) cells
  • Big space around the blood vessel = artefact due to shrinkage.
  • Pink stuff = capillaries – to take red blood cells and white blood cells out of marrow (marrow is the birth place of rbc and wbc)
  • There are holes in the bone for blood vessels
  • The big cell in the bone marrow is a megakaryocyte (makes platelets)
  • Lamellae = concentric rings around
  • Haversian system/osteon: fundamental functional unit of much compact bone
    • Concentric rings (lamellae) of bone surrounding it (like a tree trunk)
    • Central hole = haversian canal contains the bone's nerve and blood supplies.
    • Boundary of an osteon = cement line
    • Interstitial lamellae = remnants of osteons between existing osteons
    • circumferential lamellae = Near the surface of the compact bone where lamellae are arranged parallel to the surface.
  • Osteoblasts line the inner periosteum and inner endosteum. They function to produce bone matrix.
    • Once they’re enveloped in their own matrix they develop into osteocytes, each living within its own small space, or lacuna.
    • Osteocytes make contact with the cytoplasmic processes of their counterparts via a network of small canals, or canaliculi. This network facilitates the exchange of nutrients and metabolic waste.
  • Collagen fibers in a particular lamella run parallel to each other but the orientation of collagen fibers within other lamellae is oblique. The collagen fiber density is lowest at the seams between lamellae, accounting for the distinctive microscopic appearance of a transverse section of osteons.

Slide 7: Skeletal, smooth and cardiac muscle

Skeletal muscle

  • Found in biceps, triceps, hamstrings, quads
  • On the periphery of the skeleton
  • Striated (stripes across muscle cell = striations). These represent protein filaments. They are bands of actin and myosin.
  • Multinucleated, lots of cells on the edges.
  • In between muscle cells are tiny bits of collagen (gristle… wrappings around steak).
  • Lots of blood vessels.

Smooth muscle

  • Associated with visceral organs – stomach, uterus, urinary bladder.
  • Lives in sheets.
  • Not striated.
  • Single nucleus, usually in the centre. Long, cigar-shaped nuclei. Compressed cells.

Cardiac muscle

  • Is branched.
  • Nucleus in the middle of the cell.
  • Has striations.
  • Darker blue lines called intercalated discs.
  • Intercalated discs are tight junctions (cause all your muscles to contract as 1 unit, which is needed in the heart – much more important that they are all working together than in skeletal muscle). It interdigitates the cells so that nervous impulses are spread to all cells.

Slide 7: Tongue – circumvillate papillae

Background

  • Top of the tongue: circumvallate papillae
  • Inside the groove down the side of the papilla are taste buds.
  • Saliva dissolves food, takes it into groove where taste bud can detect flavours
  • Highly enervated for taste reception.
  • Dark purple blobs: mucous glands
  • Skeletal muscle in all different directions so that the tongue can move in all directions.

Histology

  • Top of tongue = stratified squamous epithelium
  • Thin-wall blood vessel = vein
  • Dots = fibroblast nuclei
  • Purple patches = glands
    • Some are dark, some are pale.
    • Mucous secreting (white plaque on tongue = mucous… more of it in smokers)
  • Red material = serous gland.
  • Material of the gland is pushed through the duct into the little cleft near the papilla.
  • Lymphoid aggregation occurs at the base of the cleft on the tongue
    • Army standing ready
  • Taste buds are on the papilla
    • “Hairs” stick out of the taste buds, which have nerve endings.
    • Food mixes with mucous and water/saliva.
    • Gustatory area in the brain deals with taste.
    • Point of taste = defence against invading microbes (e.g. off milk: gastroenteritis)
  • There are some little nerves amongst muscle (e.g. contracting muscle in tongue)

Slide 8: Peripheral nerve

Background

  • Could be ulnar, sciatic, femoral nerve etc
  • We have both a cross sectional (transverse) and a longitudinal section (think of a cable)
  • Nerves live in bundles with blood vessels
    • Neurovascular bundle (nerves and blood vessels hang out together)
  • They are also associated with fat, which insulates them and keeps them warm.
  • Bundle of nerves = fascicle.
    • Collagen wrapping around the nerves (connective tissue wrappings)
    • Muscles are also wrapped
  • Three levels of CT wrapping for nerves:
    • Wrapping around single nerve = endoneurium
    • Wrapping around nerve bundle = perineurium
    • Wrapping around all of them = epineurium.

Histology

  • Cross-section: inside nerve = circle with a pink dot in the middle. The pink dot is the axon.
  • Longitudinal: banana-shaped cell is a Schwann cell
    • Myelin-producing.
    • Myelin increases conduction speed.
  • Myelinated nerves = touch (e.g. touching the desk
  • Unmyelinated nerves = pain (e.g. touching a hot plate)
  • Dendrites = receivers
  • Axons = conductors.
  • Dark purple lines in longitudinal slide are axons
  • The fishbone/herringbone shape off the axon is called the “Schmidt-Lanterman cleft”
    • Results from the Schwann cell wrapping around the axon (ellipsoid spiral cleft)
    • In the peripheral nervous system (PNS) axons can be either myelinated or unmyelinated.
    • Myelination means that the axon is insulated by surrounding layers of fatty membrane (myelin) produced by Schwann cells.
    • These layers are continuous (like rolling up rope), but, due to the way they are formed, they often include small amounts of Schwann cell cytoplasm not displaced to the periphery during Schwann cell formation of the myelin.
    • These are the so called Schmidt-Lanterman cleft (a.k.a. Schmidt-Lanterman incisures,clefts of Schmidt-Lanterman, segments of Lanterman, medullary segments), which subdivide the myelinated axon into irregular portions.
    • They are histological evidence of the small amount of cytoplasm that remains in the inner layer of the myelin sheath created by Schwann cells wrapping tightly around a nerve.
  • Axons appear as cooked spaghetti, as they run out of the field of view and back again.
  • Pink stuff = collagen (endoneurium wrapping of fibres).