Unit 3-Anatomy

Histology

study of tissues

Tissues vary in structure and function due to: (3)

• The types of cells present

• The arrangement of layering of the cells as well as the cell junctions aka connections or attachments

• The composition of the extracellular material, aka extracellular matrix, around the cells

4 Major Groups of Tissues (Primary Tissue Types)

• Epithelial tissue

• Connective tissue

• Muscular tissue

• Nervous tissue

3 Primary Germ Layers

Ectoderm (outer)

Endoderm (inner)

Mesoderm (middle) e

Endoderm Layer

Digestive system, Liver, Pancreas, Lungs (inner)

Mesoderm Layer

Circulatory system, lungs (epithelial layers), skeletal system, muscular system

Ectoderm Layer

Hair, Nails, Skin, Nervous System

Cell junctions

contact points between the plasma membranes of tissue cells

Types of Cell Junctions (5)

Tight, Adhering, Desmosomes, Hemidesmosomes, Gap

Tight (occluding) junctions

Consist of weblike strands transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between cells. Lines organs of the digestive, cardiovascular, and urinary

Adherens junctions

contains a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. Helps cells resist separation during contractile. Smooth muscle of gut contracting as food moves through it

Desmosomes

Like adherens, prevents epithelial cells of the skin’s epidermis from separating under tension and cardiac muscle cells from pulling apart during contraction; also like adherens, contain plaque as well as the transmembrane glycoproteins (CAMs) called cadherins; main difference here is the attachment to different filaments

Hemidesmosomes

Resembled desmosomes but do not link adjacent cells (hemi = looks like half of a desmosome); contains transmembrane glycoproteins (CAMs) called integrins instead of cadherins and, though not shown, they are attached to a protein called laminin which makes up the basal lamina of the basement membrane (discussed shortly) à thus, they anchor epithelial cells all over the body to their basement membrane, not to each other

Gap (communicating) junctions

Made of membrane proteins (CAMs) called connexins which form fluid-filled tunnels called connexons that connect neighboring cells and allow ions and small molecules to diffuse from one cell to another, e.g., in the transfer of nutrients and wastes in bone and the spread of electrical signals called action potentials in muscle and neurons for communication and coordination and during development; unlike tight junctions where the membranes of cells are fused, there are only narrow inter-cellular gaps found here

Comparison between Epithelial and Connective Tissue

Epithelial tissue: many cells tightly packed together and little to no extracellular matrix; avascular

Connective tissue: few scattered cells surround by large amounts of extracellular matrix; vascular

Epithelial tissue always forms a surface layer exposed to:

• the outside of the body

• the space within a body cavity

• the lumen/passageway of internal hollow organs (inside of GI and respiratory tracts)

Epithelial Tissue Functionally

Protects, Secretes, absorbs and filters/exchanges as it excretes

Basement membrane

a thin extracellular layer that commonly consists of 2 layers, the basal lamina and reticular lamina

Basement membrane (functions)

anchors epithelial tissue to underlying connective tissue, forms a surface, restricts passage of larger toxic or infectious pathogens, participates in filtration

Pap Smear

Involves collection and microscopic examination of epithelial cells that have been scraped off the top/apical layer of a multi-layer (stratified) tissue with short healing time

Colposcopy

performed after an abnormal pap, uses a magnifying instrument to help the clinician get a closer look and allows for biopsy

Biopsy

the removal of a sample of living tissue for microscopic examination, helps to more definitively diagnose disorders

Epithelial Maintenance and Renewal due to: (5)

Disruptive enzymes from digestion, toxic chemicals in air and food, pathogens/microbes in air and food, mechanical abrasion from physical trauma, radiation

How are Epithealial Renewed?

Replaced through time via continual division of stem cells near the basal lamina

2 Major Types of Epithelial Tissues

Glandular Epithelia and Surface Epithelia

Glandular Epithelia

Consists of epithelial cells making up secreting portion of endocrine glands such as the thyroid and adrenal glands and of exocrine glands such as sweat and digestive glands

Surface Epithelia (Covering and Lining Epithelia)

Consists of continuous sheets of cells that form: the other covering of the skin (epidermis) and the inner lining facing the opening of body cavities as well as respiratory, digestive, and uro-genital tracts, of the blood, lymphatic vessels and of the ducts of exocrine glands

How is Surface Epithelia classified?

Arrangement of cells into layers and shapes of cells

Squamous (Surface Epithelia) - Shape

Thin and flat like tiles which reduces both surface area for absorption and cell volume needed for the organelles required for energy dependent transport processes. Function in filtration and rapid passage of substance via diffusion/osmosis; does not offer much protection unless present in multiple layers (stratified) as in skin then it provides the most protection

Cuboidal (Surface Epithelia) - Shape

Shaped like cubes (hexagons), cells are large enough for the functions of secretion and absorption (some have microvilli to increase absorptive capacity) but not so large that they can easily lose structural integrity, offering some protection especially if present in multiple layers

Columnar (Surface Epithelia) - Shape

Shaped like columns, these columnar cells are even larger providing a significant ability to function in secretion and absorption yet, as their tall shape can lead to loss of structural integrity, they provide some but less protection, especially as a single layer (some also have microvilli to increase absorptive capacity; others have cilia which move material/fluid across the cell surface)

Transtional/Urothelial (Surface Epithelial) - Shape

found within organs of the urinary system, transitions in shape from cubodial when the bladder and ureter/urethra collapses or relaxes after urine emptying to squamous as they stretch or distend during urine fillinf, which flattens the cells

Simple/Unilaminar (Surface Epithelia) - Arrangement

Single layer or cells that functions in diffusion/osmosis and filtration if squamous, as well as secretion (production and release of sweat or mucus) and absorption (recovering nutrients and fluid from the urinary tract)

Stratified (multilaminar) epithelium

Consists of 2 or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear; some may contain goblet cells in between that secrete mucus (if columnar)

Psedostratified (Surface Epithelia) - Arrangement

Appears to have multiple layer becase the cell nuclei lay at different levels and not all cells reach apical surface; some may contain goblet cells in between that secrete mucus; offers some protection but not as much as true stratified

2 Sub-Types of Glandular Epithelial Tissue

Exocrine and Endocrine glands

Endocrine glands

hormone secreations only: most are culticellular, some unicellulat; they ductless and secrete their secretion (hormone) into the interstitial fluid which end up in blood

Exocrine glands

secretions are oil (lipid), serous, mucous, and/or mixed serous + mucous (seromucous) based: most are multicellular, some unicellular; these used ducts to secrete their secretion onto surface of skin or into a body cavity or into lumen of hollow organs

Specialized epithelial cells

form glands that secretet substances into ducts and onto surfaces (exocrine) or into intestitial (tissue) fluid ending up in blod (endocrine)

Unicellular

Only exampe in the body are muchous or goblet cells that produe mucin which combines with water to form mucus

Multicellular glands

Most in body including mucouse/goblet glands, serous glands, lipid/oil glands, digestive glands, salivary glands, tear/lacrimal glands, sudoifererous/sweat glands, mammary galnds, cerumious/earwax glands

Only unicellular exocrine gland we have:

goblet (mucous) cell

Exocrine glands functional grouping

Apocrine, Holocrine, Merocrine

Merocrine

Most common in body e.g pancreatic and liver glands, saliva glands, tear glands, sweat glands, serous glands and goblet cells/glands

Apocrine

E.g earwax glands, milk glands, and sometimes goblet cells/glands

Holocrine

E.g sebaceous and meibomian oul glands in skin and eyelids (whole cell dies and becomes the secretory product)

Ground substance + Protein Fibers

Connective Tissues Extracellular Matrix/Material (ECM)

Properties of Connective tissue ground substance

• Clear and colorless unless theres an infection

• Conttains (and stores) water of the ECF with one or more of several protein and carbohydrates complexes suspended in it

• Absorbs compressive forces to help protect/support more delicate tissues while binding some cells together

• May plan an active role in how CT cells develop, migrate, proliferate and change shape as well as how they carry out their metabolic functions by regulating the local chemical environment

• Provides a medium for exchangee substances may be