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Lecture 3
Histology
Study of Tissues
Primary Tissue Classes
 Intro
 A tissues is a mass of similar cells and cell products that forms a discrete region
of an organ and performs a specific function
 A matrix is material that surrounds the cells, and is composed of fibrous
proteins and ground substance
o Tissue differences:
 Types and functions of the cells
 Characteristic of the matrix (extracellular material) that surrounds
the cells
 Relative amount of space occupied by cells versus matrix
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Epithelial Tissue
o Epithelium is a type of tissue composed of one or more layers of closely
adhering cells, either covering on organ surface or forming the secretory
tissue and ducts of a gland
 It’s found in the linings of organs, the lining of body cavities, and
forms the epidermis of the skin
 The extracellular material is so thin that there is no room for blood
vessels, so they rely on blood vessels in loose connective tissue for
nourishment
 Anchoring the epithelium to the connective tissue below is a layer
of tissue called the basement membrane
 Surfaces of epithelium that face the basement membrane
are basal surfaces
 Surfaces that face away from the basement membrane are
apical surfaces
 Types of Epithelium:
 Simple – having only a single layer of cells
 Simple squamous – single layer of flat, scale-like cells
o Found in air sacs of lungs, glomerular capsules of kidneys
o Allows rapid diffusion or transport through membranes
 Simple cuboidal – single layer of cube-shaped (though perhaps
rounded) cells
o Found in the liver, thyroid, many glands
o For absorption and secretion
 Simple columnar – single layer of cells that are taller than they
are wide – greater volume allows more absorption & secretion
o Found in lining of stomach, intestines, uterus
o Absorption, secretion of mucus
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o Simple ciliated columnar epithelium has cilia to move the
egg through the uterine tubes
 Pseudostratified columnar – Epithelium that has the appearance
of having multiple layers (stratified), but which actually has a
single layer of cells that are not all the same height
o Found in respiratory tract
o Secretes and propels mucus
 This tissue has cilia to move mucus and dust
 Stratified – having two or more layers of cells, with some cells
resting on others, rather than being in direct contact with the
basement membrane
 Stratified squamous – multiple layers of flat, scale-like cells
o Actually, not all of the cells in this tissue will necessarily
appear flattened. The tissue type is named for the flattened
cells that appear at the surface
o There are two kinds of stratified squamous epithelium, one
containing the protein keratin, and the other without
 Keratinized stratified squamous epithelium is found on
the skin surface and resists water loss and provides
resistance to skin penetration
o Found in the epidermis
o Resists abrasion, penetration, water loss
 Nonkeratinized stratified squamous epithelium provides a
surface that is abrasion resistant, but also moist and
slippery
o Found in the mouth, esophagus, vagina
o Resists abrasion and penetration by pathogens
 Stratified cuboidal – multiple layers of cube-shaped cells
o Found in sweat gland ducts, in ovaries and testes
o Contributes to sweat, secretes hormones, produces sperm
 Stratified columnar – multiple layers of cells that are taller than
they are wide
o Rare, found only in parts of the pharynx, anal canal, urethra
 Transitional epithelium – multiple layers of cells that were
once thought to represent a transitional stage between
squamous and columnar
o Found in the urinary bladder and part of the urethra
o Stretches to allow filling of urinary tract
Connective Tissue
o Functions:
 Binding of organs – tendons bind muscle to bone, ligaments bind
bone to bone, fat holds the kidneys in place, etc.
 Also support, protection, movement, storage, heat production,
transport
o Components:
o
Cells
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Fibroblasts – Large flat cells that appear tapered at the ends and
produce the fibers and ground substance that form the matrix of the
tissue
 Macrophages – Large phagocytic cells that engulf and destroy
bacteria, foreign matter, or dead and dying cells
 Leukocytes – White blood cells that react against bacteria, toxins,
and other foreign agents
 Mast cells – Cells found along blood vessels that secrete heparin or
histamine to inhibit blood clotting or increase blood flow
 Adipocytes – Fat cells
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Fibers
 Collagenous fibers – Tough, flexible fibers, made of collagen
 Reticular fibers – Thin collagen fibers coated with glycoprotein,
forming a spongelike network
 Elastic fibers – Fibers composed of a protein called elastin, which
has a coiled structure that allows it to stretch and recoil like a
rubber band
 Ground substance – Three classes of large molecules that form a
gel in connective tissue that slowes down the spread of bacteria
and other pathogens. They also bind tissue components together.
o Fibrous connective tissue
 Loose connective tissue – Much space is occupied by ground
substance
 Areolar tissue – has fibers that run in random directions and
has highly variable appearance
 It surrounds blood vessels and nerves, allowing
passage through other tissues
 Provides space for immune defense, and provides
nutrients and waste removal for overlying epithelia
 Reticular tissue – has a mesh-like appearance and forms the
structural framework of the lymph nodes, spleen, thymus,
and bone marrow
 Adipose tissue – tissue in which adipocytes are the
dominant cell type
 It stores energy and provides cushioning
 Dense connective tissue – Fibers take up more space than cells or
ground substance
 Dense regular connective tissue
 Has fibers that are closely packed and the fibers run
parallel to the direction of force (such as in
ligaments and tendons)
 Binds muscle to bone and bone to bone
 Dense irregular connective tissue
 Has thick bundles of collagen which run in random
directions
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It binds skin to muscle and withstands stress
in unpredictable directions
o Cartilage – supportive connective tissue with a flexible rubbery matrix
 Hyaline Cartilage – Found in the trachea and over the ends of
bones at movable joints
 It holds the airway open and eases joint movement
 Elastic Cartilage – Fount in the external ear and nose
 It provides flexible, elastic support
 Fibrocartilage – Fount in the pubic symphysis and between the
bones of the vertebral column
 It withstands compression and absorbs shock
o Bone
 Spongy bone is bone tissue that fills the heads of the long bones.
 It is made up of many long delicate slivers that give it a
spongy appearance
 Compact bone is bone tissue that forms the surface of skeleton.
 It is more dense calcified tissue, with no spaces visible to
the naked eye
o Blood
 Plasma is the ground substance part of the blood (the liquid part)
 Formed elements are cells and cell fragments that carry oxygen,
fight infection, or help to form clots if an injury occurs
Nervous and Muscular Tissue
o Nervous Tissue is tissue specialized for rapid communication by means of
electrical and chemical signals
 Neurons are specialized cells that detect stimuli and transmit
information rapidly to other cells
 Soma – cell body that houses the nucleus and other
organelles
 Dendrites – processes extending from the cell body that
receive signals from other cells
 Axons – processes (1 for each neuron) that send outgoing
signals from the soma
 Glial cells – cells that support and assist the neurons
o Muscular Tissue is tissue that is specialized to contract when stimulated
(thus exerting physical force on other tissues)
 Skeletal muscle –
 Long cylindrical cells, with visible striations and multiple
nuclei per cell
 Muscles attached to bones, but also muscles controlling
voluntary sphincters
 Used for body movements, breathing, speech, and other
voluntary control
 Cardiac muscle
 Short branched cells connected by intercalated discs and
having only one nucleus per cell
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 Found in the heart
 Used for pumping blood (involuntary)
 Smooth muscle
 Short fusiform (spindle-shaped) cells, each with one
nucleus and no striations
 Found as sheets of tissue in the walls of internal organs, or
as part of sphincters of the urethra and anus
 Used for movement of food through the GI tract or urine
through the urinary system, etc. that are involuntarily
controlled
Glands and Membranes
o Glands are organs or cells that secrete substances for use in the body or for
elimination from the body
 Cells vs organs
 Single-celled glands – goblet cells are shaped somewhat
like a wineglass, and are found in the epithelia of many
mucous membranes
 Multicellular glands – include all other glands in which
multiple cells work together to produce secretions
 Exocrine glands are glands that convey their secretions through
ducts to the surface of the body or to the lumen (cavity) of another
organ
 Endocrine glands secrete their products directly into the
bloodstream for transport to target cells
 Types of secretions
 Serous glands produce relatively thin, watery fluids, such
as perspiration, milk, or tears
 Mucous glands produce a glycoprotein called mucin, which
absorbs water to form mucus (note the different spelling)
 Mixed glands contain both serous and mucous cells and
produce a mixture of the two types of secretions
 Cytogenic glands release whole cells (sperm or egg cells)
 Methods of secretion
 Merocrine glands release their secretions by exocytosis
(only the secretion is released from the gland)
 Holocrine glands accumulate products within the cell and
then the entire cell disintegrates, so that the substance released
is a mixture of product and cell fragments
 Apocrine glands were named when it was believed that bits
of apical cytoplasm broke away from the cell surface.
Technically this isn’t true, but there are differences between
these glands and merocrine glands.
o Membranes
 Cutaneous membranes – skin
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Statified squamous epithelium resting on a layer of
connective tissue
Mucous membranes – membranes that line passageways leading
the the exterior
 Digestive, respiratory, and reproductive tracts
Serous membranes – membranes that produce watery serous fluid
 Line the insides of some body cavities and form a smooth
surface on the outer surface of some viscera
Endothelium – Simple squamous epithelium that lines the lumens
of the blood vessels, heart, and lymphatic vessels
Synovial membranes – Membranes made of connective tissue that
span the gap from bone to bone and secrete slippery synovial fluid
into the joint
Tissue Growth and Repair
o Growth
 Hyperplasia – growth through cell multiplication
 Hypertrophy- enlargement of existing cells
o Repair
 Regeneration - Replacement of cells by the same type of cells
 Fibrosis – Replacment of damaged tissue with scar tissue,
composed mainly of collagen