The Tissue Level Of Organization
BIO 137: Anatomy & Physiology I
Tissues
• Tissues are a group of cells with a common
embryonic origin that function together to
carry out specialized activities.
– They include various types,
ranging from hard (bone)
to semisolid (fat) to
liquid (blood).
Intercellular Junctions
• Tissues are formed by
grouping cells together using a
variety of Intercellular
Junctions .
– Intracellular Junctions
connect adjacent cells
mechanically at the cell
membranes or through
cytoskeletal elements
within and between cells.
Intercellular Junctions
• Tight Junctions are
found where a leakproof
seal is needed between
cells.
– They keep materials from
leaking out of organs like
the stomach and bladder.
Intercellular Junctions
• Adherens Junctions make an adhesion belt (like
the belt on your pants) that keeps tissues from
separating as they stretch and contract.
• Cadherin is a
glycoprotein that forms
the belt-like “plaque”.
Intercellular Junctions
• Desmosomes act as “spot welds”. They also
use cadherin glycoprotein (plus intermediate
filaments) to hook into the cytoplasm.
Intercellular Junctions
• Hemidesmosomes are half-welds that join cells
to the basement membrane.
Intercellular Junctions
• Gap Junctions are
pores (connexons)
that allow small
substances like ions
to pass between
cells. If one of the
cells gets sick or dies,
these seal like a
hatch to prevent
damage to other
cells.
The 4 Basic Tissues
• Of all the cells in the body, they combine to
make only 4 basic tissue types:
– Epithelial tissues
– Connective tissues
– Muscular tissues
– Nervous tissues
Epithelial Characteristics
Cover body surfaces, form glands, line hollow organs,
body cavities and ducts.
• Tightly packed sheets of
cells w/ little intercellular
material
• All epithelia have a free
surface that faces an
opening and an attached
basal surface
– Basement membrane
• May possess cilia or
microvilli on free surface
• Avascular
• Readily divide
Epithelial Locations & Functions
• Epidermis
• Protection
• Covers ventral body
organs (serous
membranes)
• Absorption
• Lines body cavities
(parietal membranes)
• Excretion
• Lines exocrine glands
• Lines hollow organs
• Lines capillaries
• Secretion
• Filtration
• Diffusion
Classification of Epithelium
• Number of Layers
• Simple
• Stratified
• Pseudostratified
• Shape of Cells
• Squamous
• Cuboidal
• Columnar
Epithelium Classification
Epithelium Studied in BIO 137
• Simple Squamous ET (lung alveoli)
• Simple Cuboidal ET (thyroid gland)
• Simple Columnar ET (duodenum)
• Pseudostratified Columnar ET (trachea)
• Stratified Squamous ET (skin)
• Transitional ET (ureter)
• Glandular ET (not studied in lab)
Simple Squamous Epithelium
A
single layer of thin, flattened cells
• Locations:
–
–
–
–
*Lining air sacs (alveoli)
Lining capillaries
Kidney glomeruli
Lining vessels
• Functions:
– Diffusion (exchange of
gases, nutrients, wastes)
– Filtration
Simple Squamous Epithelium
(a) Simple squamous epithelium
Description: Single layer of
flattened cells with disc-shaped
central nuclei and sparse cytoplasm;
the simplest of the epithelia.
Function: Allows passage of
materials by diffusion and
filtration in sites where protection
is not important; secretes
lubricating substances in serosae.
Location: Kidney glomeruli; air
sacs of lungs; lining of heart,
blood vessels, and lymphatic
vessels; lining of ventral body
cavity (serosae).
Air sacs of
lung tissue
Nuclei of
squamous
epithelial
cells
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (400x).
Simple Cuboidal Epithelium
• A single layer of cube-shaped cells with large
prominent nuclei
• Locations:
– Lining kidney tubules
– Lining the ducts of
exocrine and endocrine glands
• Functions:
– Secretion (exocrine and endocrine glands)
– Secretion and Reabsorption (kidney tubules)
Simple Cuboidal Epithelium
(b) Simple cuboidal epithelium
Description: Single layer of
cubelike cells with large,
spherical central nuclei.
Simple
cuboidal
epithelial
cells
Function: Secretion and
absorption.
Location: Kidney tubules; ducts
and secretory portions of small
glands; ovary surface.
Basement
membrane
Connective
tissue
Photomicrograph: Simple cuboidal epithelium
in kidney tubules (400x).
Simple Columnar Epithelium
• A single layer of column like cells, with nuclei located near the
basement membrane
• Other structures of interest:
– Goblet cells - mucus
– Microvilli – increase surface area for absorption
– May be ciliated
• Location: Intestinal lining
(Villi), uterus
• Functions:
– Protection
– Absorption
– Secretion
Intestinal Villi: Simple Columnar
Epithelium
GOBLET CELL
Ciliated Pseudostratified Columnar Epithelium
• A single layer of elongated cells
– Nuclei dispersed throughout the cytoplasm (appears to
have layers)
• Other structures of interest:
– Cilia
– Goblet cells
• Location: Lining of trachea
• Functions:
– Secretion
– Protection
Ciliated Pseudostratified Columnar
Epithelium
GOBLET CELL
CILIA
Epithelium
• Stratified Squamous Epithelium has an apical
surface that is made up of squamous (flat) cells.
– The other layers have different
shapes, but the name is based
on the apical layer.
– The many layers are ideal for
protection against
strong friction
forces.
Transitional Epithelium
• Multilayered cells that change shape due to
changes in pressure in the tissue
• Locations:
– Lining of Urinary bladder
– Lining of Ureter
• Function:
– Distensibility
TRANSITIONAL ET: URETER ~LOW POWER~
TRANSITIONAL ET
SMOOTH MUSCLE
Copyright 2006 Dr. Mary Cat Flath
Epithelium
• Although epithelia are found throughout the
body, certain ones are associated with specific
body locations.
Connective Tissue
• Includes bones, adipose, blood, cartilage and
other connective tissues
• Functions: support, framework for
attachment, hematopoiesis, energy stores,
protection
Connective Tissue
• Connective Tissues are the most abundant
and widely distributed tissues in the body
• Sparse cells separated by
intercellular material called
matrix
• Can usually divide
Connective Tissues
• Collagen is the main protein of C.T. and the most
abundant protein in the body, making up about
25% of total protein content.
• Connective tissue is usually
highly vascular and supplied
with many nerves.
– The exception is cartilage and
tendon - both have little or no
blood supply and no nerves.
Connective Tissue Matrix
• Found between cells, secreted by immature blast
cells
• 2 components of matrix
– Protein Fibers – 3 types of fibers
• Secreted by fibroblasts
• Fiber types vary among CT
– Ground substance – fluid, semi-fluid, gelatinous or
calcified
• Material in CT that provides a media for movement of
nutrients and gases & binds CT components together
Connective Tissue Fibers
• Collagen
– Give a tissue High tensile
strength and resists pulling
– Found in ligaments and tendons
• Elastic Fibers
– Composed of elastin protein
– Give a tissue Elasticity
– Fibers are easily stretched and
reformed
– Found in Vocal cords, external
ear and air passages
• Reticular Fibers
– Composed of collagen fibers
called reticulin
– Found in basement membrane,
also support capillaries and
nerve fibers
Cell Types Found in CT
• Fibroblasts
– Most abundant, produce
fibers of matrix
• White Blood Cells
– Macrophages phagocytosis
– Mast Cells - Release heparin
and histamine for Tissue
repair and healing
• Chondrocytes - cartilages
• Osteocytes – bone
Connective Tissue Classification
• Embryonic connective tissue
– Mesenchyme
– Mucous connective tissue
• Mature connective tissue
– Loose connective tissue
– Dense connective tissue
– Cartilage
– Bone
– Liquid
Embryonic Connective Tissues
• There are 2 Embryonic Connective Tissues:
– Mesenchyme gives rise to all other connective tissues.
– Mucous C.T. (Wharton's Jelly) is a gelatinous substance
within the umbilical cord and is a rich source of stem cells.
CT Studied in Bio 137
•
•
•
•
•
•
•
Loose Areolar CT
Adipose Tissue
Dense Regular CT (White fibrous CT)
Hyaline Cartilage
Elastic Cartilage
Blood
Bone
Loose Areolar Connective Tissue
• The most widely distributed in the body.
• Contains several types of cells and all three
fiber types.
• Location: papillary layer of dermis,
Component of basement membrane,
Between muscles, between other tissues
• Functions:
– Diffusion & Cushioning
– Binds skin to underlying tissues
Loose Areolar Connective Tissue
Loose Areolar Connective Tissue
(a) Connective tissue proper: loose connective tissue, areolar
Photomicrograph: Areolar connective tissue,
a soft packaging tissue of the body (400x).
Adipose Tissue
• Cells: Adipocytes filled with fat globules
• Locations:
– Subcutaneous layer
– Around organs and joints
• Functions:
–
–
–
–
Energy Store
Protection
Cushion
Insulation
Adipose Tissue
Mature Connective Tissues
• Dense Connective Tissues
– Dense Irregular Connective Tissue consists
predominantly of fibroblasts and collagen fibers
randomly arranged.
• It provides strength when forces are pulling from many
different directions.
– Dense regular
– Elastic
Dense Regular Connective Tissue
• Matrix of tightly packed collagen fibers with
few fibroblasts
• Lacks a direct blood supply
• Locations:
– Tendons Ligaments
• Functions:
– Attachment/ High tensile strength
Dense Regular Connective Tissue
Cartilage
• Rigid connective tissue with a poor direct
blood supply
• Abundant collagen and/or elastic fibers in gellike ground substance
• Primary cell is chondrocyte
• Do not divide often
• Classified by type of matrix
Hyaline Cartilage
• Most abundant type of cartilage in the body
• Locations:
– Wall of trachea and larynx
– Nose
– Embryonic Skeleton
– Costal cartilages
– Ends of long bones
• Function: Support and protection
Hyaline Cartilage
Fibrocartilage
• Thick bundles of collagen fibers
• A very strong, tough cartilage.
• Locations:
– Intervertebral spaces
– Knee joints
• Support
Elastic Cartilage
• Chondrocytes surrounded by matrix filled
with elastic fibers
• Locations:
– Auricle or Pinna of External Ear
– Epiglottis
• Function:
– Flexibility with maintenance of shape
Elastic Cartilage
(g) Cartilage: elastic
Note the presence
of elastic fibers
Photomicrograph: Elastic cartilage from
the human ear pinna; forms the flexible
skeleton of the ear (640x).
Blood
• The only liquid connective tissue
• Blood cells (Erythrocytes, leukocytes, and
thrombocytes) in a liquid matrix of plasma
• Location:
– Heart and blood vessels
• Function:
– Transport of gases,
nutrients and wastes
Compact Bone
• Osteocytes surrounded by a solid matrix of
calcium phosphate and collagen
• Location: skeleton
• Functions:
– Support
– Protection
– Movement
– Hematopoiesis
– Calcium (mineral) Store
Figure 4.9i: Connective tissues (continued), pp. 137-138.
(i) Others: bone (osseous tissue)
Description: Hard, calcified matrix
containing many collagen fibers;
osteocytes lie in lacunae. Very well
vascularized
Function: Bone supports and protects
(by enclosing); provides levers for the
muscles to act on; stores calcium and
other minerals and fat; marrow inside
bones is the site for blood cell
formation (hematopoiesis).
Location: Bones
Central
canal
Lacunae
Lamella
Photomicrograph: Cross-sectional view
of bone (70x).
Summary of Mature Connective Tissues
Muscle Tissues
• Long, thin fibers that shorten and contract to
allow movement
• Three types:
– Skeletal muscle
– Smooth muscle
– Cardiac muscle
• Will be studied in greater detail during the
muscular and cardiovascular systems
Muscle Tissue
Nervous Tissue
• Neurons (nerve cells) with multiple
extensions surrounded by neuroglial cells
• Locations:
– Brain and spinal cord (CNS)
– Nerves (PNS)
• No reproduction of cells
• Function:
– Integration and coordination of all body parts
Nervous Tissue
Epithelial Membranes
• A layer of epithelium that lies over a layer of
connective tissue
• Three types of epithelial membranes:
– Serous Membranes
– Mucous Membranes
– Cutaneous Membranes
Serous Membranes
• Thoracic and Abdominopelvic Membranes
– Line the walls of body cavities and fold back to cover
the organs
– Secrete serous fluid for lubrication
• Visceral layer – covers an organ
• Parietal layer – lines a cavity or body wall
Serous Membranes
• Thoracic Membranes: Lungs
– Visceral Pleura
– Parietal Pleura
• Thoracic Membranes: Heart
– Visceral Pericardium
– Parietal Pericardium
• Abdominopelvic Membranes
– Visceral Peritoneum
– Parietal Peritoneum
Mucous Membranes
• Mucous membranes line interior body
surfaces open to the outside
– Digestive tract lining
– Respiratory Tract
– Reproductive Tract
• Functions:
– Protection
– Lubrication
Cutaneous Membrane
• Location: Skin
• Function:
– Protection
• Will be studied further in Chapter 5
Glandular Epithelium
• Composed of cells specialized that produce &
secrete substances into ducts or body fluids
• Usually simple cuboidal or simple columnar ET
• Function: Secretion
• Include exocrine and endocrine glands
Exocrine Glands
• Exocrine glands secrete substances through ducts to
the surface of the skin or into the lumen of a hollow
organ.
• Secretions of the exocrine gland include mucus,
sweat, oil, earwax, saliva, and digestive enzymes.
Exocrine Glands
• Merocrine secretion is the most common
manner of secretion.
– The gland releases its product by exocytosis and no
part of the gland is lost or damaged .
– Salivary gland
Exocrine Glands
• Apocrine glands “bud” their secretions off
through the plasma membrane, producing
membrane-bound vesicles in the lumen of the
gland.
– The end of the cell breaks off by “decapitation”,
leaving a milky, viscous odorless fluid.
– Mammary gland
Exocrine Glands
• Holocrine secretions are produced by rupture
of the plasma membrane, releasing the entire
cellular contents into the lumen and killing the
cell (cells are replaced by rapid division of stem
cells.)
– Sebaceous gland
Aging and Tissues
• Tissue heals faster in young adults.
• Surgery of a fetus normally leaves no scars.
• Young tissues have a better nutritional state,
blood supply, and higher metabolic rate.
• Extracellular components also change with
age.
• Changes in the body’s use of glucose,
collagen, and elastic fibers contribute to the
aging process.