animal tissues1

7/28/2019 Animal Tissues1

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Notes in Zoology Archived by: N.R. Bautista

ANIMAL CELLS AND TISSUES

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. Inthe most commonly encountered animals, the mobile stage is the adult, although some animals(such as corals and sponges) have sessile (or nonmobile) adult phases and mobile juvenileforms. Both animal and plant evolutionary history show the development of multicellularity and themove 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 lessenwater loss, muscles that allowed them to move in search of food, brains and nervous systems forintegration of stimuli, and internal digestive systems.

Organs in animals are composed of a number of different tissue types. For example, the stomachshown in Figure 1, has epithelial tissue making linings and secreting gastric juices, connectivetissues

Figure 1. Cells and tissues that comprise the stomach. Image from Purves et al., Life: TheScience 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 thando vertebrate animals. Organs are composed of tissues, which are in turn composed of cells.


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Plants have three tissue types: ground, dermal, and vascular. Animals have four: epithelial,connective, muscle, and bone.

Epithelial Tissue

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 orstratified. Simple epithelium hasonly a single cell layer. Stratifiedepithelium has more than onelayer of cells. Pseudostratifiedepithelium is a single layer of cellsso shaped that they appear at firstglance to form two layers.

Figure 2. Cuboidal epithelium.Note the single layer of simplecuboidal epithelium lining eitherside of a tubule.

Figure 3. (Left) Epithelium liningthe intestine of a rat, as seen withSEM. This image is from

Figure 4. (Above right, in violet color) Columnar epithelial cells. Note: I have outlined one of thecolumnar epithelium cells.


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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. Multicellularglands 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 secretemucus or other materials from their skin, such as earthworms do.

Figure 5. (left) Glandular epithelium.

Connective Tissue

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 anon-cellular matrix. The matrix may be solid (as inbone), soft (as in loose connective tissue), or liquid (asin blood). Two types of connective tissue are LooseConnective Tissue (LCT) and Fibrous Connective Tissue(FCT). Fibroblasts (LCT) are separated by a collagenfiber-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. (Left) Adipose tissue, a type ofconnective tissue.

Adipose tissue, shown in Figure 6, hasenlarged fibroblasts storing fats and reducedintracellular matrix. Adipose tissue facilitatesenergy storage and insulation.

Fibrous Connective Tissue has many fibersof collagen closely packed together. FCT

occurs in tendons, which connect muscle tobone. Ligaments are also composed of FCTand connect bone to bone at a joint.

Cartilage and bone are "rigid" connectivetissues. Cartilage, shown in Figure 7, hasstructural proteins deposited in the matrix

between cells. Cartilage is the softer of the two "rigid" connective tissues. Cartilage forms theembryonic skeleton of vertebrates and the adult skeleton of sharks and rays. It also occurs in the


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human body in the ears, tip of the nose, and at joints such as the knee and between bones of thespinal column.

Figure 7.(Left) Cartilage, a type of"soft" connective tissue.

Bone, shown in Figure 8, hascalcium salts in the matrix, givingit greater rigidity and strength.Bone also serves as a reservoir(or sink) for calcium. Protein fibersprovide elasticity while mineralsprovide elasticity. Two types ofbone occur. Dense bone hasosteocytes (bone cells) located inlacunae connected by canaliculi.Lacunae are commonly referred toas 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. Note thehaversian canal and surroundedby osteocytes and a mineralizedmatrix. The second image (below)shows the structure andvascularization of bone.


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Blood is a connective tissue of cells separated by a liquid (plasma) matrix. Illustrations of bloodcells 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 dissolvedglucose, wastes, carbon dioxide and hormones, as well as regulating the water balance for theblood cells. Platelets are cell fragments that function in blood clotting.

Figure 9. Elements ofthe blood. Note thered blood cells and thesingle neutrophil.Erythrocytes as seemwith the SEM. Thebottom image is humanred blood cells,

p l a t e l e t s andT-l y m p h o c y t e(erythrocytes = red;

platelets = yellow; T-lymphocyte = light

green) (SEM x 9,900).

Muscle Tissue

Muscle tissue facilitatesmovement of theanimal by contractionof individual musclecells (referred to asmuscle fibers). Threetypes of muscle fibersoccur in animals (the

only taxonomickingdom to havemuscle cells):

* skeletal (striated)* smooth* cardiac

Muscle tissue andorganization is shownin Figure 10.


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Figure 10. Organization of muscle tissue.

Muscle fibers are multinucleated, with the nuclei located just under the plasma membrane. Mostof the cell is occupied by striated, thread-like myofibrils. Within each myofibril there are dense Z


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lines. A sarcomere (or muscle functional unit) extends from Z line to Z line. Each sarcomere hasthick and thin filaments. The thick filaments are made of myosin and occupy the center of eachsarcomere. Thin filaments are made of actin and anchor to the Z line.

Skeletal (striated) muscle fibers,shown in Figure 11, havealternating bands perpendicularto the long axis of the cell. Thesecells function in conjunction withthe skeletal system for voluntarymuscle movements. The bandsare areas of actin and myosindeposition in the cells.

Figure 11. Striated muscle cells.

Smooth muscle fibers, shown in Figure 12, lack the banding, although actin and myosin stilloccur. These cells function in involuntary movements and/or autonomic responses (such asbreathing, secretion, ejaculation, birth, and certain reflexes). Smooth muscle fibers are spindle


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shaped cells that form masses. These fibers are components of structures in the digestivesystem, reproductive tract, and blood vessels.

Figure 12.Smooth musclecells.

Cardiac muscle fibers are a type of striated muscle found only in the heart. The cell has abifurcated (or forked) shape, usually with the nucleus near the center of the cell. The cells areusually connected to each other by intercalated disks, as shown in Figure 13.

Figure 13. Cardiacmuscle cells. Note thedark band of theintercalated disk thatseparates two musclecells. The bottom imageis of a heart muscle cell(nucleus, mitochondria,actin-myosin) (TEMx15,400).


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Nervous Tissue

Nervous tissue, shown in Figure 14, functions in the integration of stimulus and control ofresponse to that stimulus. Nerve cells are called neurons. 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 oftensurround them.

Figure 14. (Left)Organization of a neutron.

The neuron is the functionalunit of the nervous system.Humans have about 100billion neurons in their brainalone! While variable in sizeand shape, all neurons havethree parts. Dendrites receiveinformation from another celland transmit the message to

the cell body. The cell bodycontains the nucleus,mitochondria and otherorganelles typical ofeukaryotic cells. The axonconducts messages awayfrom the cell body. Neuronsare shown in Figure 15.

Figure 15. Microphotograph of Neurons..


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Review Questions

1. Which of these is not an animal tissue? a) connective; b) xylem; c) epithelial; d) nervous

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 theperformance of the cell's role; d) none of these

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

4. Layered epithelial tissue is referred to as which of these? a) squamous; b) stratified; c)voluntary; d) pseudostratified

5. Which of these cell types covers the inside of the mouth? a) squamous epithelium; b)cartilage; c) blood; d) cuboidal epithelium

6. Protection of the body from infectious organisms is accomplished by which of these tissues?a) bone; b) muscle; c) nerve; d) blood

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

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

9. The storage of fat is accomplished by which of these cell types? a) adipose; b) squamousepithelium; c) cuboidal epithelium; d) stratified epithelium

10. Glands are composed of which of these tissue types? a) epithelium; b) connective; c)muscle; d) nervous

11. Hard parts of the body would be made of which of these cell/tissue types? a) blood; b) bone;

c) muscle; d) nerves

12. Bone acts as a reservoir for which of these elements? a) carbon; b) nitrogen; c) calcium; d)hydrogen

13. The major function of bone is ___. a) covering body surfaces; b) support; c) movement; d)integration of stimulus

14. New blood cells are formed in the ___. a) matrix; b) bone marrow; c) liver; d) adipose cells

15. The blood cells that transport oxygen within the body are the ___. a) macrophages; b)erythrocytes; c) platelets; d) leukocytes

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 isinvolved? a) cardiac; b) skeletal; c) smooth

18. Contraction of your heart is accomplished by which of these cell types? a) cardiac; b)skeletal; c) smooth

19. Contractions of the uterus during birth are accomplished by which of these cell types? a)cardiac; b) skeletal; c) smooth


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20. The junctions between nerve cells are known as ___. a) gap junctions; b) synapses; c) tightjunctions; d) villi

21. Transmission of the nerve message within the neuron is ___ in nature. a) chemical b)electrical

Answers:1. B; 2. B 3. C 4. D 5. A 6. D 7. B 8. C 9. A 10. A 11. B

12. C 13. B 14. B. 15. B 16. A 17. B 18. A 19. C 20. B 21. B

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