Tissues
Honors Anatomy & Physiology
Chapter 4
Human Anatomy & Physiology
Tissues & Homeostasis
• 4 basic types of tissues in human body
contribute to homeostasis by providing
diverse functions including
• protection
• support
• communication among cells
• resistance to disease
• & many more
Definition
• a tissue is a group of similar cells that
usually have a common embryonic origin &
function together to carry out specialized
activities
Embryology of Tissues
1.
▫
2.
▫
3.
▫
4.
▫
Epithelial
from all 3 layers
Connective
mesoderm
Muscular
mesoderm
Nervous
ectoderm
Tissues
• their structure & properties are influenced
by factors such as:
▫ nature of the extracellular material
surrounding tissue cells
▫ type of connections between cells
Classification of Tissues
1. Epithelial
▫ covers body surfaces & lines hollow
organs, cavities, & ducts
▫ forms glands
2. Connective
3. Muscle
4. Nerve
Functions of Epithelial Tissues
• protection
• absorption
• filtration
• excretion
• secretion
• sensory reception
Epithelial Tissue
• 5 distinguishing characteristics
1. polarity
2. specialized contacts
3. supported by CT (connective tissue)
4. avascular but innervated
5. ability to regenerate
Polarity
• apical & basal surfaces
▫ differ in structure & function
• most apical surfaces contain
microvilli, or cilia
• basal surface has thin
supporting sheet called basal
lamina
▫ selective filter
▫ scaffolding for cells to migrate
along
Specialized Contacts
• epithelial cells form
continuous sheets
▫ not glandular
epithelium
▫ lateral cell surfaces
see desmosomes &
tight jcts (keeps
things from
diffusing between
cells)
Supported by CT
• all epithelial sheets
rest on CT
• reticular lamina:
just below basal
lamina
• basal lamina +
reticular lamina =
basement
membrane
Avascular / Innervated
• epithelium contains NO blood vessels
▫ nutrients, O2 diffuse from underlying CT
vessels
• has nerve fibers
Regeneration
• epithelial cells will reproduce rapidly
when neighboring cells damaged or
destroyed
▫ as long as necessary nutrients can get to
epithelium
Classification of Epithelia
• classified according to 2 characteristics:
1. # of layers
• single layer = simple
• multiple layers = stratified
• single layer that looks like multiple =
pseudostratified
2. cell shape
• squamous
• cuboidal
• columnar
Squamous Cells
• flattened, scalelike
• protect
Cuboidal Cells
• boxlike, cubes
• secretion, absorption
Columnar Cells
• tall, column shaped cells
• secretion
Simple Epithelium
1 layer of cells, often in sheets
functions:
filtration
secretion: production & release of
substances (sweat, mucus)
• absorption: intake of fluids or other
substances
•
•
•
•
Simple Squamous Epithelium
• cells flattened laterally
• surface view: tiled floor
• cross-section: fried egg
• thin, permeable  where rapid diffusion
important
▫ Lungs
▫ Kidneys
Endothelium
• simple squamous epithelium that lines
lymphatic and blood vessels and lines the
cardiac atria and ventricles
• capillaries consist only of 1 endothelial
cells thick (site of gas exchange)
Mesothelium
• epithelium found in serous membranes
▫ line ventral body cavities
▫ cover organs in ventral cavities
Simple Cuboidal Epithelium
• square cells with round, central nuclei in a
sheet
• secretion
• absorption
• forms walls of small ducts of glands &
kidney tubules
Simple Columnar Epithelium
• single layer, tall, closely packed cells
• absorption
• secretion
• line digestive tract where cells have 2
modifications:
1. dense microvilli on apical surface
2. glands that secret mucus (Goblet
cells)/intestinal juices
Pseudostratified Columnar Epithelium
• cells vary in height
• nuclei at variable heights
• ciliated or nonciliated
• all cells rest on BM (basement membrane)
but not all reach free surface
▫ short cells replace tall ones if damaged
Stratified Epithelium
• 2 or more cell layers
• cells are generated from below
• more durable than simple epithelium
• protection: major function
• type of stratified epithelium determined
by cell shape of top layer
Stratified Squamous Epithelium
• found in areas subjected to wear and tear
▫ upper layers rubbed away
▫ lower cells replace
• top cells are squamous
• as cells pushed up further from BM fewer
nutrients reach them  die  lipids from
atrophied cells add some water proofing
• keratinized/not keratinized
▫ keratin: tough protein
Stratified Squamous Epithelium
• upper layers
contain keratin:
tough, fibrous
protein that
protects underlying
tissues from heat,
microbes,
chemicals
• found: skin
• found: lining
mouth (buccal
mucosa) &
esophagus
• protect underlying
tissues from wear &
tear and from
invasion by
microbes
• Keratinized
• Nonkeratinized
Stratified Cuboidal Epithelium
• rare
• found in some ducts of larger glands
▫ mammary glands, some sweat glands
• 2 layers of cuboidal cells
Stratified Columnar Epithelium
• limited distribution in body
▫ male urethra
▫ some glandular ducts
▫ @junction between 2 other types of
epithelial cells
Glandular Epithelium
• gland: 1 or more cells that make & secrete
a product called a secretion
• secretions are aqueous solutions
▫ composition varies by gland
Secretion
• active process of gland releasing its
product (also called secretion)
2 Classes of Glands
1. Endocrine glands (ductless glands)
▫ internal secretion: cells exocytose 
extracellular space  capillaries  target
cells  prompts some response in cell
▫ hormones: messenger chemicals
2. Exocrine glands (glands with ducts)
▫ external secretion
▫ secrete product onto surfaces or into body
cavities
Types of Exocrine Glands
Unicellular
• Mucous cells & Goblet
cells
• sprinkled thru GI
tract, respiratory tract
Multicellular
• 2 parts:
1. Duct
2. Secretory cells
▫ surrounded by CT
forming fibrous
capsule  divides
it into lobes
Types of Multicellular Exocrine Glands
Unicellular
Multicellular
Connective Tissue
• most abundant & widely distributed of the
4 tissue types
• major functions:
1. binding & supporting
2. protecting
3. insulating
4. storing
5. transporting
Classification of CT
• CT proper
▫ fat
▫ fibrous tissue
• cartilage
• bone
• blood
Characteristics of CT
• common origin
▫ mesenchyme
• degrees of vascularity
▫ cartilage: avascular
▫ dense CT poorly vascularized
▫ other types richly vascularized
• extracellular matrix
▫ few cells/ lots extracellular matrix
3 Main Elements in CT
1. ground substance
2. fibers
3. cells
• 1 + 2 = extracellular matrix
• large variation in composition &
arrangement of the three  large
diversity of CTs each adapted to specific
function
Ground Substance
• fills space between cells
• contains fibers
• function: molecular sieve
• consists of
▫ water
▫ interstitial fluid
▫ cell adhesion proteins (glue)
CT Fibers
• provide support
• secreted by fibrocytes
• 3 types:
1. collagen
2. elastic fibers
3. reticular fibers
Collagen Fibers
• made of cross-linked protein collagen
▫ #1 protein in body
▫ very strong, high tensile strength
Elastic Fibers
• long, thin, branching fibers
• made of protein: elastin
• can be stretched  return to original
shape
• function: provide elasticity to tissues
• found in: cartilage, skin, lungs, blood
vessel walls
Reticular Fibers
• form delicate networks that surround
small blood vessels& support soft tissue
organs (liver, spleen)
• made of collagen derived protein
• also found in BM of epithelium, around
capillaries
CT Cells
• each class of CT has resident cell type:
▫ immature form –blast
▫ mature form - cyte
Loose CT
• 3 types:
1. Areolar
2. Adipose
3. Reticular
Areolar CT
• Functions:
▫ support & bind other tissues
▫ hold body fluids (reservoir of water & salts)
▫ store nutrients
• Cells: all CT cells
• Features: loose arrangement of fibers
• Found: subcutaneous tissue
Adipose Tissue
• Functions: store triglycerides, insulation,
protection
• Cells: adipocytes
• Features: scant matrix, closely packed
cells, rich blood supply
• Found: ass’c w/areolar CT, around heart,
kidneys, lymph nodes
Adipose Tissue
• 2 types:
1. White: most adipose tissue
2. Brown: abundant mitochondria
▫ use fat to generate heat (less ATP, more
heat)
▫ found on back of newborns: unable to
shiver if chilled
Reticular Connective Tissue
• Function: reticular fibers form internal
framework = stroma
• Cells: fibroblasts = reticulocytes
• Features: only fibers are reticular
• Found: lymph nodes, spleen, bone marrow
Dense CT
• 3 types:
1. Dense Regular
2. Dense Irregular
3. Elastic
Dense Regular CT
• Functions: resistance to tension
• Cells: fibroblasts
• Features: closely packed, parallel collagen
fibers (parallel to direction of pull);
appears white, flexible
• Found: tendons (muscle to bone) & most
ligaments (bone to bone)
Cartilage
• Function: withstands tension &
compression
• Cells: chondroblasts (lay down cartilage),
chondrocytes found in lacunae
• Features: qualities intermediate between
dense CT and bone, no nerve or blood
supply, surrounded by perichondrium
• Found: ends of long bones, see next slide
Types of Cartilage
1. Hyaline
2. Elastic
3. Fibrocartilage
Hyaline Cartilage
• Function: provides flexibility & support
• Cells: chondrocytes in lacunae
• Features: matrix appears glassy, most
abundant type of cartilage,
• Found: embryonic skeleton, tips of nose,
ends of long bones, connects ribs, to
sternum, trachea, epiphyseal plates
Elastic Cartilage
• Function: maintains shape, strength and
elasticity
• Cells: chondrocytes in lacunae
• Features: very flexible
• Found: pinna, epiglottis
Bone: Osseous Tissue
• Function: support and protect, cavities
allow storage of fat and production of
blood cells
• Cells: osteoblasts, osteocytes, osteoclasts
• Features: hard but some flexibility, more
collagen than cartilage + inorganic
calcium salts
• Found: skeletal system
Bone
• 2 types:
1. Compact Bone
2. Spongy Bone
Compact Bone
• basic unit of compact bone is the osteon
(haversian system)
• has 4 parts:
1. Lamellae
▫
▫
concentric rings of extracellular material &
collagen
make bone hard & strong
2. Lacunae
3. Canaliculi
4. Central (haversian) canal)
Spongy Bone
• lacks osteons
• found only inside compact bone
• consists of columns of bone called
trabeculae
▫ spaces between trabeculae filled with red
bone marrow
Blood
• liquid CT made up of:
• Plasma
▫ liquid portion of blood (yellow)
▫ water, dissolved nutrients, wastes, plasma
proteins, hormones, gases, ions
• RBCs: transport O2
• WBCs: phagocytes, immune response,
allergic reactions
• Platelets: cell particles involved in blood
clotting
Muscle Tissue
• Function: movement, maintain posture,
generate heat
• Cells: muscle fibers containing actin and
myosin
• Features: contraction & relaxation
• Found: skeletal system, walls of vessels
and hollow organs, heart
Smooth Muscle
• Function: movement
• Cells: 1 central nucleus, fusiform cells
• Features: involuntary & not striated,
innervated by ANS,
• Found: walls of vessels & hollow organs,
between hair follicles and dermis
Cardiac Muscle
• Function: propel blood thru body
• Cells: branching with gap jcts =
intercalated discs
• Features: striated, involuntary (ANS)
• Found: only in wall of heart
Skeletal Muscle
• Function: move bones
• Cells: multinucleated (peripherally
located) muscle fibers
• Features: striated and voluntary
• Found: attached to bones or skin
Nervous Tissue
• Function: regulate and control body
functions
• Cells: neurons, neuroglial cells
• Features: neurons can generate and/or
respond to action potentials
• Found: nervous system
Membranes
• are flat sheets of pliable tissue that cover or
line a part of the body
• 2 types:
1. epithelial membrane:
▫
▫
epithelial layer + underlying CT
types: mucous membrane, serous
membrane, cutaneous membrane (skin)
2. synovial membrane:
▫
▫
+ CT but - epithelium
line joints
Mucosae (Mucous Membranes)
• Function: absorption and secretion
• Cells: stratified squamous epithelium or
simple columnar epithelium, lie over CT
layer = lamina propria
• Features: moist, most secrete mucus
• Found: line all body cavities that open to
outside body
Serosa (Serous Membranes)
• Function: lubrication
• Cells: simple squamous epithelium (called
mesothelium) on areolar CT
• Features: moist, squamous cells secrete
thin watery serous fluid, serosa named
according to organ: pleura, pericardium,
peritoneum
• Found: closed ventral cavities
Tissue Repair
• 3 phases:
1. Inflammation
2. Organization
3. Regeneration/Fibrosis
Inflammation
• nonspecific reaction
• injury causes tissue cells, macrophages, mast
cells  inflammatory chemicals  capillaries
dilate & become more permeable 
neutrophils, monocytes & plasma fluid
(clotting factors, abys) enter injured area 
form clot stops bleeding, holds wound
together, isolating injured area giving some
protection to infection scab forms
Inflammation
• Characterized by area of:
• redness (rubor)
• swelling
• +/- pain (dolor)
• warmth
Organization Phase of Tissue Repair
• begins during inflammatory pahse
• blood clot replaced by granulation tissue:a
friable, delicate tissue
▫ capillaries
▫ fibroblasts collagen, growth factors 
when phase complete become inactive or
apoptosis
▫ macrophages phagocytize injured cells/cell
debris, clot
Organization Phase of Tissue Repair
Regeneration & Fibrosis Phase
• fibrous tissue beneath scab matures 
epithelium regenerate until it resembles
surrounding skin
• +/- scar tissue
Injury Below Skin
• skin surface not breached
• usually involves infection (pimple, sore
throat)
▫ minor : heals by regeneration only
▫ more serious  clot formation possibly
scarring
Scar Tissue
• permanent fibrous patch
• if wound was extensive  replaced only with
scar tissue does not replace function of normal
tissue
• adhesions: scar tissue that forms around
irritated organs in abdominopelvic cavity or
w/in hollow organs
Healing in Different Tissues
• heal well: epithelium, areolar CT, dense irregular
CT, bone, blood forming tissue
• moderate capacity to heal: smooth muscle, dense
regular CT
• poor healing: skeletal muscle, cartilage
• NO healing: cardiac muscle, nerve tissue
• https://www.dnalc.org/resources/3d/cells
ignals.html