ANIMAL CELLS AND TISSUES

ANIMAL CELLS AND TISSUESby Michael J. Farabee, Ph.D., Estrella Mountain Community

College, updated 12/06

Organization of the Animal Body | Animals are multicellular heterotrophs whose cells

lack cell walls. At some point during their lives, all

animals are capable of movement, although not all animals

have muscles they use for this. In the most commonly

encountered animals, the mobile stage is the adult,

although some animals (such as corals and sponges) have

sessile (or non-mobile) adult phases and mobile juvenile

forms. Both animal and plant evolutionary history show

the development of multi-cellularity and the move from

water to land (as well as a secondary adaptation back to

water, for example dolphins, whales, duckweed, and

elodea).

Animals developed external or internal skeletons to

provide support, skin to prevent or lessen water loss,

muscles that allowed them to move in search of food,

brains and nervous systems for integration of stimuli,

and internal digestive systems.

Organs in animals are composed of a number of different

tissue types. For example, the stomach shown in Figure 1,

has epithelial tissue making linings and secreting

gastric juices, connective tissues

Figure 1. Cells and tissues that comprise the

stomach. Image from Purves et al., Life: The Science of

Biology, 4th Edition, by Sinauer Associates

(www.sinauer.com) and WH Freeman (www.whfreeman.com), used

with permission.

Plants are simpler organisms than animals, having three

organ systems and fewer organs than do vertebrate

animals. Organs are composed of tissues, which are in

turn composed of cells. Plants have three tissue types:

ground, dermal, and vascular. Animals have four:

epithelial, connective, muscle, and bone.

Epithelial Tissue | Back to Top

Epithelial tissue covers body surfaces and lines body

cavities. Functions include lining, protecting, and

forming glands. Three types of epithelium occur:

Squamous epithelium is flattened cells.

Cuboidal epithelium is cube-shaped cells.

Columnar epithelium consists of elongated cells.

Any epithelium can be simple or stratified. Simple

epithelium has only a single cell layer. Stratified

epithelium has more than one layer of cells. Pseudo

stratified epithelium is a single layer of cells so

shaped that they appear at first glance to form two

layers.

Figure 2. Cuboidal epithelium. The image is cropped

from Loyola University's LUMEN site

athttp://www.meddean.luc.edu/lumen/MedEd/Histo/Hist

oImages/hl1-04.jpg. Note the single layer of simple

cuboidal epithelium lining either side of a tubule.

Figure 3. Epithelium lining the intestine of a

rat, as seen with SEM. This image is from

http://130.102.208.100/FMRes/FMPro?-

db=images.fp3&key=32816&-img, used by permission

of Nanoworld.

Figure 4. Columnar epithelial

cells. The above image is cropped

and modified from Loyola

University's LUMEN site

athttp://www.meddean.luc.edu/lumen

/MedEd/Histo/HistoImages/hl1-

12.jpg. Note: I have outlined one

of the columnar epithelium cells.

Functions of epithelial cells include:

movement materials in, out, or around the body.

protection of the internal environment against the

external environment.

Secretion of a product.

Glands can be single epithelial cells, such as the goblet

cells that line the intestine. Multicellular glands

include the endocrine glands. Many animals have their

skin composed of epithelium. Vertebrates have keratin in

their skin cells to reduce water loss. Many other animals

secrete mucus or other materials from their skin, such as

earthworms do.

Figure 5. Glandular epithelium.

The image is from Loyola


at http://www.meddean.luc.edu/lum

en/MedEd/Histo/HistoImages/hl1-

24.jpg).

Connective Tissue | Back to Top

Connective tissue serves many purposes in the body:

binding

supporting

protecting

forming blood

storing fats

filling space

Connective cells are separated from one another by a non-

cellular matrix. The matrix may be solid (as in bone),

soft (as in loose connective tissue), or liquid (as in

blood). Two types of connective tissue are Loose

Connective Tissue (LCT) and Fibrous Connective Tissue

(FCT). Fibroblasts (LCT) are separated by a collagen

fiber-containing matrix. Collagen fibers provide

elasticity and flexibility. LCT occurs beneath epithelium

in skin and many internal organs, such as lungs, arteries

and the urinary bladder. This tissue type also forms a

protective layer over muscle, nerves, and blood vessels.

Figure 6. Adipose tissue, a type of

connective tissue. The image is cropped

from Loyola University's LUMEN page

athttp://www.meddean.luc.edu/lumen/MedE

d/Histo/HistoImages/hl2-11.jpg.

Adipose tissue, shown in Figure 6, has enlarged

fibroblasts storing fats and reduced intracellular

matrix. Adipose tissue facilitates energy storage and

insulation.

Fibrous Connective Tissue has many fibers of collagen

closely packed together. FCT occurs in tendons, which

connect muscle to bone.Ligaments are also composed of FCT

and connect bone to bone at a joint.

Cartilage and bone are "rigid" connective tissues.

Cartilage, shown in Figure 7, has structural proteins

deposited in the matrix between cells. Cartilage is the

softer of the two "rigid" connective tissues. Cartilage

forms the embryonic skeleton of vertebrates and the adult

skeleton of sharks and rays. It also occurs in the human

body in the ears, tip of the nose, and at joints such as

the knee and between bones of the spinal column.

Figure 7. Cartilage, a type of

"soft" connective tissue. The

image is cropped from Loyola

University's LUMEN page

athttp://www.meddean.luc.edu/lume

n/MedEd/Histo/HistoImages/hl4A-

36.jpg.

Bone, shown in Figure 8, has calcium salts in the matrix,

giving it greater rigidity and strength. Bone also serves

as a reservoir (or sink) for calcium. Protein fibers

provide elasticity while minerals provide elasticity. Two

types of bone occur. Dense bone has osteocytes (bone

cells) located in lacunae connected by canaliculi.

Lacunae are commonly referred to as Haversian

canals. Spongy bone occurs at the ends of bones and has

bony bars and plates separated by irregular spaces. The

solid portions of spongy bone pick up stress.

Figure 8. Bone. The first image of bone is cropped from

Loyola University's LUMEN page

athttp://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages

/hl4A-40.jpg. Note the haversian canal and surrounded by

osteocytes and a mineralized matrix. The second image

shows the structure and vascularization of bone. Image

from Purves et al., Life: The Science of Biology, 4th

Edition, by Sinauer Associates (www.sinauer.com) and WH

Freeman (www.whfreeman.com), used with permission.

Blood is a connective tissue of cells separated by a

liquid (plasma) matrix. Illustrations of blood cells are

shown in Figure 9. Two types of cells occur. Red blood

cells (erythrocytes) carry oxygen. White blood cells

(leukocytes) function in the immune system. Plasma

transports dissolved glucose, wastes, carbon dioxide and

hormones, as well as regulating the water balance for the

blood cells. Plateletsare cell fragments that function in

blood clotting.

Figure 9. Elements of the blood. The left image below is

cropped from Loyola University's LUMEN site


/hl2B-51.jpg. Note the red blood cells and the single

neutrophil. The right image below is cropped from Loyola


at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImage

s/hl2B-64.jpg. Erythrocytes as seem with the SEM. The

bottom image is human red blood cells, platelets and T-

lymphocyte (erythrocytes = red; platelets = yellow; T-

lymphocyte = light green) (SEM x 9,900). This image is

copyright Dennis Kunkel at www.DennisKunkel.com, used with

permission.

Muscle Tissue | Back to Top

Muscle tissue facilitates movement of the animal by

contraction of individual muscle cells (referred to

as muscle fibers). Three types of muscle fibers occur in

animals (the only taxonomic kingdom to have muscle

cells):

skeletal (striated)

smooth

cardiac

Muscle tissue and organization is shown in Figure 10.

Figure 10. Organization of muscle tissue. Images from

Purves et al., Life: The Science of Biology, 4th Edition,

by Sinauer Associates (www.sinauer.com) and WH Freeman

(www.whfreeman.com), used with permission.

Muscle fibers are multinucleated, with the nuclei located

just under the plasma membrane. Most of the cell is

occupied by striated, thread-like myofibrils. Within each

myofibril there are dense Z lines. A sarcomere (or muscle

functional unit) extends from Z line to Z line. Each

sarcomere has thick and thin filaments. The thick

filaments are made of myosin and occupy the center of

each sarcomere. Thin filaments are made of actin and

anchor to the Z line.

Skeletal (striated) muscle fibers, shown in Figure 11,

have alternating bands perpendicular to the long axis of

the cell. These cells function in conjunction with

the skeletal system for voluntary muscle movements. The

bands are areas of actin and myosin deposition in the

cells.

Figure 11. Striated muscle cells. The left image of

striated muscle fibers is cropped from Loyola University's

LUMEN site


/hl3A-45.jpg. The right image

is fromhttp://130.102.208.100/FMRes/FMPro?-

db=images.fp3&key=32948&-img.

Smooth muscle fibers, shown in Figure 12, lack the

banding, although actin and myosin still occur. These

cells function in involuntary movements

and/or autonomic responses (such as breathing, secretion,

ejaculation, birth, and certain reflexes). Smooth muscle

fibers are spindle shaped cells that form masses. These

fibers are components of structures in the digestive

system, reproductive tract, and blood vessels.

Figure 12. Smooth muscle cells. The image of smooth muscle

cells is cropped from Loyola University's LUMEN site


/hl3A-42.jpg.

Cardiac muscle fibers are a type of striated muscle found

only in the heart. The cell has a bifurcated (or forked)

shape, usually with the nucleus near the center of the

cell. The cells are usually connected to each other by

intercalated disks, as shown in Figure 13.

Figure 13. Cardiac muscle cells. The top image of cardiac

muscle cells is cropped from Loyola University's LUMEN

site


/hl3A-48.jpg. Note the dark band of the intercalated disk

that separates two muscle cells. The bottom image is of a

heart muscle cell (nucleus, mitochondria, actin-myosin)

(TEM x15,400). This image is copyright Dennis Kunkel

at www.DennisKunkel.com, used with permission.

Nervous Tissue | Back to Top

Nervous tissue, shown in Figure 14, functions in the

integration of stimulus and control of response to that

stimulus. Nerve cells are calledneurons. Each neuron has

a cell body, an axon, and many dendrites. Nervous tissue

is composed of two main cell types: neurons and glial

cells. Neurons transmit nerve messages. Glial cells are

in direct contact with neurons and often surround them.

Figure 14. Organization of a neutron. Image from Purves et

al., Life: The Science of Biology, 4th Edition, by Sinauer

Associates (www.sinauer.com) and WH Freeman

(www.whfreeman.com), used with permission.

The neuron is the functional unit of the nervous system.

Humans have about 100 billion neurons in their brain

alone! While variable in size and shape, all neurons have

three parts. Dendrites receive information from another

cell and transmit the message to the cell body. The cell

body contains the nucleus, mitochondria and other

organelles typical of eukaryotic cells. The axon conducts

messages away from the cell body. Neurons are shown in

Figure 15.

Figure 15. Neurons. The left image of large multipolar

neuron (center of image) is cropped from Loyola



/hl3-03.jpg. The right image shows Pyramidal Neurons from

the Central Nervous System (SEM x3,960). This image is

copyright Dennis Kunkel at www.DennisKunkel.com, used with

permission.

Learning Objectives | Back to Top

Be able to list the major functions of each of the

four major animal tissue types.

Distinguish between simple and stratified epithelial

tissue.

Compare and contrast the different types of

connective tissues: loose, dense, fibrous, cartilage,

bone, blood, adipose. Be able to list the function of

each type.

Know the three types of muscle and be able to

differentiate them visually and according to their

functions.

Be able to diagram a typical neuron and its three

areas: dendrite, axon, and cell body.

Know the characteristics of the various types of

animal tissues. Learn the types of cells that compose

each tissue type and be able to give some examples of

organs that contain significant amounts of each

tissue type.

Detail the functions carried out by epithelial tissue

and state the general location of each type.

Be able to discuss the meaning of the term gland,

cite three examples of glands, and state the

extracellular products secreted by each.

Describe the basic features of connective tissue, and

explain how the cells of this tissue type enable

connective tissue to carry out its various tasks.

List three of the functions of blood.

List two functions of bone and/or cartilage.

Distinguish among skeletal, cardiac, and smooth

muscle tissues in terms of location, structure, and

function.

Muscle tissues contain specialized cells that can

contract.

Neurons are organized as lines of communicaiton.

Terms | Back to Top

Adipose

tissueactin axon blood bone

Cardiac

muscleCartilag

e

Columnar

epithelium

Connective

tissue

Cuboidal

epitheliumdendrite

s

endocrin

e glands

Epitheli

al

tissue

erythrocyt

es

Fibroblast

s

Fibrous

Connective

Tissue

(FCT)

Glial

cellskeratin

leukocyt

es

Ligaments Loose

Connective

mucus Muscle

tissue

myofibri

ls

Tissue

(LCT)

myosinNervous

tissueneurons plasma

Platelet

s

sarcomer

e

Simple

epitheli

um

Skeletal

(striated)

muscle

Smooth

muscle

Squamous

epithelium

Stratifi

ed

epitheli

um

tendons

Review Questions | Back to Top

1.Which of these is not an animal tissue? a)

connective; b) xylem; c) epithelial; d) nervous ans

is b

2.Tissues are made of _______. a) groups of cells that

perform a different set of functions; b) collections

of cells that perform similar or related functions;

c) subellular structures that aid in the performance

of the cell's role; d) none of these ans is b

3.Which of these is NOT a function of epithelial

tissue? a) covering surfaces; b) secretion; c)

support of the body; d) lining internal exchange

areas ans is c

4.Layered epithelial tissue is referred to as which of

these? a) squamous; b) stratified; c) voluntary; d)

pseudostratified ans is d

5.Which of these cell types covers the inside of the

mouth? a) squamous epithelium; b) cartilage; c)

blood; d) cuboidal epithelium ANS is a

6.Protection of the body from infectious organisms is

accomplished by which of these tissues? a) bone; b)

muscle; c) nerve; d) blood ANS is d

7.Linking of bone to bone in a skeletal system is

accomplished by which of these tissues? a)

epithelial; b) connective; c) muscle; d) nervous ANS

is b

8.Cells that line the tubules in the kidney make up

which of these tissues? a) adipose; b) squamous

epithelium; c) cuboidal epithelium; d) stratified

epithelium ANS is c

9.The storage of fat is accomplished by which of these

cell types? a) adipose; b) squamous epithelium; c)

cuboidal epithelium; d) stratified epithelium ANS is

a

10. Glands are composed of which of these tissue

types? a) epithelium; b) connective; c) muscle; d)

nervous ANS is a

11. Hard parts of the body would be made of which of

these cell/tissue types? a) blood; b) bone; c)

muscle; d) nerves ANS is b

12. Bone acts as a reservoir for which of these

elements? a) carbon; b) nitrogen; c) calcium; d)

hydrogen ANS is c

13. The major function of bone is ___. a) covering

body surfaces; b) support; c) movement; d)

integration of stimulus ANS is b

14. New blood cells are formed in the ___. a)

matrix; b) bone marrow; c) liver; d) adipose cells

AMS is b

15. The blood cells that transport oxygen within the

body are the ___. a) macrophages; b) erythrocytes; c)

platelets; d) leukocytes ANS is b

16. The liquid part of the blood is ___. a) plasma;

b) adipose; c) cartilage; d) platelets ANS is a

17. When you move your arm to use your computer

mouse, which of these muscle cell types is involved?

a) cardiac; b) skeletal; c) smooth ANS is b

18. Contraction of your heart is accomplished by

which of these cell types? a) cardiac; b) skeletal;

c) smooth ANS is a

19. Contractions of the uterus during birth are

accomplished by which of these cell types? a)

cardiac; b) skeletal; c) smooth ANS is c

20. The junctions between nerve cells are known as

___. a) gap junctions; b) synapses; c) tight

junctions; d) villi ANS is b

21. Transmission of the nerve message within the

neuron is ___ in nature. a) chemical b) electrical

ANS is b

ANIMAL CELLS AND TISSUES

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