LAB TOPIC 23
VertebrateAnatomy III:
The Excretory,Reproductive,and
Nervous Systems
Laboratory Objectives
After completingthis iab topic, you should be able to:
Identify and describethe function of all parts of the excretorysystem
of the fetal pig, noting differencesbetweenthe sexesand noting structures sharedwith the reproductive system.
2 . Identify and describethe functron of all parts of the reproductive sysiems of male and femalefetal pigs and trace the pathway of sperm and
eggfrom theiroriginout of the body.
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3 Descnbethe structureof a neuron.
4 . Describethe pathwayof a simplereflex,relatingthis to the structureof
the spinal cord.
Describethe struc[ureof a representative
sensoryreceptor,the eye.
6 . Discussthe role playedby the nervousand endocrinesystemsin integrating all vertebra[esystemsinto a functioning whole organism.
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Introduction
In Lab Topic22,VertebrateAnatomy II, you sawthat, functionally the excretory systemis closelyrelated to the circulatory and respiratorysystems.
Developmentally,however,the excretorysystemsharesmany embryonic
and some adult structureswith the reproductivesystem.ln the first two
exercisesof this lab topic, you will investigateform and functional relationshipsin the excretoryand reproductivesystems.ln the last exerciseof
this lab topic, you will study the nervoussystem,which keepsal1organsys[ems functioning appropriaLelyand in harmony
The action and interaction of organsystemsmust be preciselytimed to meet
specificneedswithin the animal. Two systemsin the body, the nervoussystem and the endocrinesystem,coordinatethe actinties of all organsystems.
The nervoussystemconsistsof a sensorycomponent,madeup of sensory
receptors that detectsuch stimuli aslight, sound,touch, and the concentration of oxygenin the blood, and sensory nerves, which carry the data
to the central nervous system. The central nervous systemconsistsof the
brain and spinal cord. Ir integratesinformation from all stimuli, externai
and internal, and, when appropriate,sendssignalsto the motor system.
The motor system carriesimpulsesalong motor nervesto effectors such
as glands,muscles,and other organs,bringing about the appropriate
response.The nervoussystemprovidesrapid, precise,and complexcontrol
of body activi.ties.
604
Lab Topic 23:Yertebrate Anatomy lll: The Excretory Reproductive,and Nervous Systems
The endocrinesystemconsistsof endocrineglands,which respond to stimuli by secretinghormonesinto the blood to be transportedto target tissues
in the body. The target tissuesthen bring about the response.You have
akeadyobservedseveralendocrine glands,including the thgnus, thyroid,
and pancreas.ln this lab topic, you will study additionalendocrineglands:
ovari.esand testes.Controi mediatedby hormonesin the endocrinesystem
is slower and lessprecisethan nervoussystemcontrol. The interactionof
the nervous and endocrine systemsbrings about the coordination of physiologicalprocessesand the maintenanceof intemal homeostasis, the steady
statecondition in thq vertebratebody
E X E R C I S E2 3 . T
The Excretory System
Materials
preservedfetalpig
instruments
dissecting
dissecting pan
disposable gloves
Introduction
Severaiimportant functions are performed by the vertebrateexcretorysystem, including osmoregulation, the control of tissuewater balance,and
the elimination of excesssaltsand :urea,a wasteproduct of the metabolism
of amino acids.In terrestrialanimals,including most mammals,water conservalion is an important function of the excretory system. Studying this
systemin the pig wrll revealthe organsand structuresinvolved in producing and eliminatingmetabolicwastewith minimal water loss.
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Wear disposablegloveswhen dissectingpreservedanimals.
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Procedure
1. Locatethe blood vesselsservingthe kidneys,exposedin the dissection
of the circulatory system.The arteriesbranch from the dorsal aortacaudal to the cranial mesenteric afiery. Blood enters the kidney through
the renal artery and exits through the renal vein. Identify thesevesselsand the kidneys lying deep to the parietal peritoneum lining the
abdominal cavity This membrane was observedand removed in Lab
Topic22, VertebrateAnatomy lI.
2. Dissectthe left kidney as follows. Leavingthe kidney in the body and
attachedto all blood vesselsand tubes,make a frontal sectionalong the
outer periphery dividing it into dorsaland ventralportions (Figure23.la
and Color Plate63). Observethe renal cortex, renal medulla, renal
pyramids, renal pelvis, and ureter.
Lab To
Renal
cortex
23: YertebrateAnatomy III: The Excret
Reproductive,and NervousS
Figure 23.1.
Structure of the kidney.
(a) The kidney consisrsof three major
regions:the cortex,the medulla,and
the pelvis. Renalpyramids make up
the medulla, and the pelvis is conrinuous with the urerer. (b) An enlarged
wedge of the kidney, including the
corticalregionoverone pyramid.
Nephrons consisting of Bowman's
capsule,a proximal convoluted
tubule; the loop of Henle, a distal
convolutedtubule; and a collecting
duct extendover the corticaland
meduilary regions.Wastecarried in
the collectingduct ultimately passes
into the pelvis and ureter.
Renal
pelvrs
Renal
medulla
Bowman's
capsule
LOOp Ot
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Collectingduct
b.
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Distal
convoluted
tubule
Proximal
convoluted
tubule
606
Lab Topic 23: VertebrateAnatomy III: The Excretory Reproductive,and Nervous Sysrems
Eachkidney is madeup of microscopictubules,blood vessels,and thousandsof nephrons (approximatelyI million in humans).A nephron
(not visiblein your dissections)consistsof Bowman'scapsule,a proximal convolutedtubule, the loop of Henle, a distal convolutedtubule,
and a collectingduct (Figure23.1b). (For detailsof nephron funcrion,
seeyour text.) Bowman'scapsule,proximal and distalconvolutedtubules,
and associated
blood vesselslie in the renalcortex.Loons of Henle and
collecting ducts extend into renalpyramids,which make up the renal
medulla.Both the ioop of Henle and the collecting duct play a role in
producing a concentratedurine, a significant adaptation for terrestrial
vertebrates.The hypertonicurine passesinto the collectingducts,which
ultimately empty into the renal pelvis,an expandedpoftion of the ureter
into the kidney
3. Using Figure23.2 asa reference,follow the ureterasit exirsthe kidney
at its medial border and turns to run caudally beside the dorsal aorta.
The ureter then entersthe urinary bladder. Also locatethe urererdraining the right kidney and traceit to the urinary bladder. In rhe fetal pig,
the urinary bladder is an elongatestructure lying between the two
umbilical arteries identified in Lab Topic 22, VerrebrareAnatomy II.
It narrows into the small allantoic stalk identified in the study of the
umbilical cord in Lab Topic 21, VertebrateAnatomy I.
Do not damagereproductiveorgansas you exposethe
structuresof the excretorysystem.
4. Pull on the umbilical cord, extendingthe urinary bladder,and locarea
single tube, the urethra, exiting the urinary bladder near the attachments of the ureters.At this stage,you will see only the end of the
urethra near the entranceof the ureters.In male pigs (seeFigure 23.2a),
the urethra leadsinto the penis. This will be visible only after you have
dissectedthe reproductivestructures.ln femalepigs (Figure 23.3a),
the urethrajoins the vagina, florminga chamber,the vaginal vestibule.
You will identify thesestructuresafter exposingthe reproductive
stmctures.
In male humans, the urethra is a tube in the penis. In femalehumans,
the urethra does not join the vagina but empties to the outside of the
body through a separateopening.The urethra becomesfunctional after
birth when the umbilical cord and allantoiswither and fall away Wasre
storedin the bladderpassesinto the urethra,where it is carriedto the
outsideof the body.
Results
Describethe pathwayof metabolicwastefrom the aortato the outsideof the
body in the fetal pig.
Lab Topic 23: VertebrateAnatomy III: The Excretory Reproductive,and Nervous Systems 607
Discussion
How doesthe eliminationof metabolicwastein the pig changeafterbirth?
E X E R C I S E2 3 . 2
The Reproductive System
Materials
items from Exercise23.1
Introduction
Reproduction is perhaps the ultimate adaptive activity of all organisms.It
is the meansof transmitting geneticinformation from generationto generation. Lesscomplex animals may reproduce sexually or asexually,but in
general,vertebratesreproducesexuah Sexualreproduction promotes genetic
variation,which is important for speciesto adaptto changingenvironments.
For evolution to occur,heritablevariation must exist in populations.Although
mutation is the sourceof variation, sexualreproduction promotesnew and
diverse combinations of genetic information. Ultimately, all sexual reproduction involves the production of gametesand the bringing together of
gametesto enablefertilization to take place.
Lab Study A. Male Reproductive System
The male reproductivesystemconsistsof gonads,ducts, and glands.Testes,
the male gonads,produce sperrnand secretetestosteroneand other male sex
hormones. Sperm passfrom the testesinto the epididymis, where they
mature and are stored. When ejaculationtakesplace, sperrnpassfrom the
epididl'rnis through the ductus deferens-also called the vas deferens-to
the urethra. The urethra leadsto the penis, which carriesthe sperm to the
outside of the body. As sperm passthrough the male tract, secretionsfrom
the seminalvesicles,the prostategland, and the bulbourethralglandsareadded,
producing semen,a fluid containing sperm, fructose,amino acids,mucus,
and other substancesthat produce a favorableenvironment for sperm survival and motilinr
Vertebrate
uctive,and Nervous
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Diaphragm
Caudalvena cava
Renalcortex
Aorta
Renalpelvis
Renalartery
and vein
Renal
medulla
Ureter
Ductusdeferens
I n g u i n acla n a l
Urethra
Urinarybladder
Cut pelvic
girdle
Penis
Bulbourethral
gland
Umbilicalartery
Umbilicalvein
Epididymis
Umbilicalartery
ano vetn
Allantoicstalk
Scrotum
Preputial
orifice
Figure 23.2a.
Organs of the excretory and reproductive systems in the male fetal pig. The
ureters enter the urinary bladder between the umbilical arteries.The urethra
exitsthe urinary bladderand leadsto the penis.The penis leadsto the preputial
orifice. The testeslie in pouchesin the scrotum. Sperm are produced in the
testes,storedin the epididymison the testissurface,and passto the ductus
deferens,which leadsto the urethra.
Procedure
You will dissectthe reproductivesystemof only one sex.
However,you should observethe dissectionof a pig of the
oppositesex and be able to identifyand describevarious
structuresof both sexes.
Exposethe structuresof the male reproductive system(Figure 23.2a).
The penis is locatedin the flap of venrralbody wall caudalto the umbilical cord. To prevent damageto this structure,locateit beforeyou make
Lab Topic 23: VertebrateAnatomy III: The ExcretoryReproductive,and NervousSystems 609
Urlnarybladder
Ductusdeferens
gland
Prostate
Seminal
vesicle
an incision. Hold the flap between your fingers and feel for the cordlike penisjust below the skin. Once you locatethe penis,using scissors,begin at the urogenital opening, rhe preputial orifice (identified
in Lab Topic 2I, VertebrateAnaromyI), and make a longitudinalincision, extending caudally,just through the skin. Pushasidethe skin and
use the probe to locate and exposethe long penis from the orifice caudally until it turns dorsally to meer the urethra (seeFigure 23.2b).
Next, begin to exposethe testis,epididymis, and ductus deferens.To do
this, locate the ureters (identified in Exercise23.1) and observethe
right and left ductus deferentia (sing., deferens),which loop over rhe
ureters.Follow a ductus deferensoutward and caudallyto the inguinal
canal leading into the scrotum. Use scissorsto cut carefully along the
canal to exposethe testis lying in a membranoussac.Removethis sac
and identify the various structures.
a. Identify the testis, a bean-shapedgonad.The testesfirst developin
the abdominal cavity and descendbefore birth into the scrotal sacs.
b. Identify the epididymis, a convolutedduct that originatesat the cranial end of the testis,extendscaudallyalong one side,then tums and
continues cranially as the ductus deferens.
c. Identify the ductus deferens, a duct that leads away from the
epididymis back into the abdominal cavity,where ir loops over
the ureter and entersthe urethra. Also locate the ductus deferens
from the other testis.
Figure 23.2b.
Enlarged dorsal view of male
excretoryand reproductivestructures
in the fetal pig. Seminalvesicles1ie
near the junction of the urethra and
ductus deferens.Bulbourethral glands
lie on either side of the urethra.
610
t-aUTopic 23: VertebrateAnatomy III: The Excretory Reproductive,and Nervous Systems
a
+.
Turn your attention again to the areawhere the penis turns dorsally to
meet the urethra. Push the penis to one side and probe through the
muscle between the legs to locate the pubic sl.rnphysis,the portion of
the pelvic girdle that fusesin a posirion ventral to severalof the reproductive structuresand the rectum. Beingcarefulnot to go toodeepor to
cut thepenis,use hear,yscissorsto cut the pubic symphysisfrom posterior to anterior beginning at the bend in the penis. Pressthe hind limbs
apan and trim the endsof the symphysis.Use the probe to removeconnectivetissue,and exposethe urethra, which continuesanteriorly from
the bend of the penis. The urethra continuesinto the urinary bladder
lying betweenthe umbilical arteries.Identify the two largebulbourethral
glands lying on either side of the urethra anrerior to irs junction wirh
the penis (seeFigure23.2b).
Pull on the umbilical cord, reflectingthe urethra, and locatea pair of
glands,the seminal vesicles, that lie on the dorsal surfaceof the urethra near the junction of the ductus deferensand the urethra. The
prostate gland liesbetweenthe lobesof the seminalvesicles,but because
of its immaturesiageof development,it is difficult ro identifu
At this time, completethe study of the branchesof the dorsal
aorta (Exercise22.4,Lab Study A). ldentify the umbilical
arteries and the external iliac arteriesto the legs and their
branches,the femoral and deep femoral arteries,Also
identify the deep femoral, femoral, and common iliac veins,
which drain the legs and empty into the caudalvena cava.
5. After you concludethe study of the malepig, find someonewith a female
pig, and demonstratethe systemsto each other.
6. Placeyour pig in its plasticbag,make surerhe labelsarelegible,add preservative,securethe bag, and storeit.
Results
In Table23.1,list the organsand ducts through which sperm passfrom
their origin to the outside of the body Describewhat takes place in each
organ or duct, and note glandular secretionswhen appropriate.Referto
your text if needed.
Discussion
1. Vasectomyis the most common form of human male sterilizationused
for birth control. Describethis orocess.
2. What structuresidentified are common to both reproductiveand excretory systems?
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Lab To
Id
Table 23.1
Pathwayof Sperm
d
Organ/Duct
23: VertebrateAnatomy III: The Excretory,Re roductive, and Nervous
Activity and Glandular Secretion
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3. The testesdevelop inside the abdominal car,rtyand descendthrougt
the inguinal canal into the scrotum before birth. Explain the signifi.unc" of the external sclotum and externaltestesin mammals.Referto
your text if needed.
Lab Study B. Female Reproductive System
The femalereproductivesystemconsistsof the ovaries(femalegonads),
short uterine tubes (also calledJallopiantubes,or oviducts),the uterus, the
vagina,and the vaginalvestibule.The vaginalvestibuleis presentin the pig
bui not in the human. In the pig, the utems consistsof a uterine body and
two uterine horns in which embryonic pigs develop.ln the human female,
the uterusdoesnot haveuterinehorns but consistsof a dome-shapedportion, the fundus, which protrudesabovethe entlanceof the fallopian tubes,
and an enlargedmain portion, the body of the uterus, where embryos
develop.
Procedure
1. To study the femalereproductivesysrem(Figure 23.3a),use scissors
and make a median longitudinal incision, curting through the skin posterior to the umbilical cord. Push asideskin and musclesand probe in
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612
Lab Topic 23:YertebrateAnatomy III: The Excretory Reproductive,and Nervous Systems
the midline to locatethe pubic symphysis,the portion of the pelvic girdle that fusesin a position ventral to many of the femalereproductive
structuresand the rectum. Being careful not to go too deep, use hear,y
scissorsto cut through the musclesand the syrnphysis.Pressapart the
hind limbs and trim away the cut ends of the symphysis.
2 . Beginobservationsby locating the ovaries in the abdominal cavityjust
caudal to the kidneys (Figure 23.3a). They are a pair of small, beanshapedorgans,one caudalto eachkidney. (When the testesof the male
first develop, they are located in approximately the sameposition in
the abdominal cavity as the ovaries;however,the testeslater descend,
becoming supported in the scrotal sacs.)A small convoluted tube, the
uterine tube, can be observedat the border of the ovary.
3 . The reproductivestructuresform a long, continuous tract. Follow a
uterine tube from one ovary into the associatedhorn of the uterus.
Left and right horns join to form the body of the uterus. The body of
ta
Diaphragm
Caudalvena cava
Aorta
Ovary
Uterine
tube
Urinarybladder
Horn of the uterus
Umbilical
arrery
Body of theuterus
Umbilical
vein
Vagina
Urethra
Cut pelvicgirdle
Umbilical
vetn
Vaginalvestibule
a.
Urogenital
opening
Allantoic
stalk
Figure 23.3a.
Organs of the excretory and reproductive systems in the female fetal pig.
The ureters enter the urinary bladder. The urethra exits the urinary bladder and
joins the vagina, forming the vaginal vestibule.
te Anatomy lll: The Excretory,Reproductive,and Nervous Systems
the uterus lies dorsal to the urethra. Push the urethra asideand use the
probe to separatethe urethra from the uterus.Notice that the urethra
and the reproductivestructuresmeet.
4. The body of the uterusleadsinto the cervix of the uterus,which leads
into the vagina. To conclusivelyidentify theseregions,you must open
the uterus.Without disturbing thejunction of the urethraand the reproductive structures,use scissorsto make a longitudinal,lateralincision
in the reproductivestructuresand push back the sides,exposingthe
interior. Your dissectionshould resembleFigure23.3b. Now you should
be able to identify all parts of the uterus,the vagina,and the opening
of the urethra into the reproductivetract. Identily the cervix, easilyidentified by the presenceof internal ridges.The vagina,which joins the
cervix, doesnot have theseridges.The vaginajoins the urethra to form
a common chamber,the vaginal vestibule, leadingto the outside of
the body The outer opening is the urogenital opening, ventral to the
anus (identifiedin Lab Topic 21, VertebrateAnatomy I).
r.Y^e At this time, completethe study of the branchesof the dorsal
r
arteries and the external iliac arteriesto the legs and their
branches,the femoral and deep femoral arteries.Also
identify the deep femoral, femoral, and common iliac veins,
which drain the legs and empty into the caudalvenacava.
Body
Cervix
Figure 23.3b.
Enlarged view of the female reproductive system in a fetal pig. The
cervix and vagina have been opened to
show the ridges in the cervix, which
are absentin the vagina.The vaginal
vestibule is the common chamber
formed by the confluence of the
vagina and the urethra.
6L4
Lab Topi.c23: VertebrateAnatomy III: The Excretory Reproductlve,and Nervous Systems
5. After you conclude your study of the femalepig, find someonewith a
male pig, and demonstratethe systemsto each other.
6. Placeyour pig in its plasticbag,make sureyour labelsarelegible,add
preservative,securethe bag, and storeit.
Results
Describethe pathway of an egg from the ovary to the outside of the body
in a fetalpig, naming regionsof organswhen appropriate.
Lab Study C. The PregnantPig Uterus
On demonstrationis an isolatedpregnantpig uterus, which should include
uterine horns and the body of the uterus. Ovariesand uterine tubesmay be
attached.Fetalpigs arelocatedin the uterine horns. Eachfetalpig is attached
to the mother pig by meansof the placenta,a structureconsistingof tissue
from the inner lining of the uterus (maternaltissue)and the chorionic vesicle (embryonic tissue).Thesetissuesare convoluted, creatinginterdigitating folds that increasethe surfaceswhere the exchangeof nutrienis, oxygen,
and wastestakesplace betweenmother and fetus.
Procedure
1. Observethe uteruswrth one uterine horn partially opened(Figure23.4).
Somefetal pigs should be visible.
2. If it is not aheadydissected,usingscissors,carefu\ cut into the chorionic
vesicle, a saclikestructuresurrounding each fetal pig. Note that the
chorionic vesicleis composedof two fusedmembranes,the outer chorion
and the inner allantois. Blood vesselsare visible lpng within the thin
allantois.In Lab Topic 21, VertebrateAnatomy I, you identified the
allantoicstalk, a small tube in the umbilical cord extendingbetweenthe
fetalpigs urinarybladder and the allantois.Speculateabout the function
of the allantois.The blood vesselsarebranchesof which vessels?
3. Observethe amnion, a very thin, fluid-filled sacaround the fetus.What
function do you think this membraneperforms?
4. Open the amnion and seethe umbilical cord attachingeachfetusto the
fetalmembranes.
Lab Topic 23: VertebrateAnatomy III: The Excretory Reproductive,and Nervous Systems 6f 5
Chorionic
vesicle
Allantois
Chorion
Foldsin
uterinewall
Umbilicalcord
Fetus
(chorionic
vesicleopened;
amnionremoved)
Results
Beginningwith those membranesclosestto the fetal pig, iist in order a1i
embryonicand maternalmembranesand tissuesassociated
with the fetalpig.
Discussion
1. Describe differences in the arrangement of the vagina and urethra in
fetal pig and human.
2. Tuballigation is a common form of human femalesterilization.Describe
this orocess.
Figure 23.4.
Section ofuterine horn from an
adult pig with two fetuses. Two
saclike structures.an amnion and a
chorionic vesicle,surround the fetus
on the left. The chorionic vesicle
around the other fetus has been
opened and the amnion removed.
622
Lab Topic 23: VertebrateAnat-omyIII: The ExcretoryReproductive,and NervousSystems
astigmatism:
cataracts:
2. Which of the aboveimpairments is (are)most likely to occur as a result
of aging?
Applying Your l(nowledge
L
lndividuals with high blood pressureareoften placedon a salt-restricted
diet. Explain the relationship between the amount of salt in the blood
and kidney function, urine volume, and blood pressure.Referto your
text if necessary.
2. Define homeostais.Describedisordersor diseasesthat may result when
homeostasisis disrupted owrng to problemsin the respiratory digestive,
circulatory,or excretorysystem.
3. A person who has lost a limb may experiencephantom pain, feeling
pain in the part of the body that is gone.Suggestan explanationfor this
pnenomenon.
Lab To
23: VertebrateAnatom
Reproductive,and Nervous
4. Both the eye and a camerafocus an image using a lens, but the mechanismsdiffer. How does the eye lens focus light on the retina?How is
this different in a camera?
5. As humans age, rhe lens loses its erasticity How would this affect
its
ability ro focus light on rhe retina?
occasionallyin a human male,one or both testesdo not descendrnto
the scrotal sacsbeforebirth but remain in the body cavity (a condition
known ascryptorchidism).
what functionalabnormalitier.ouldresultfrom
this condition?
References
Fawcett,D. w, and w Bloom.ATextboohoflltstolog,llth ed. philadelphia,
PA:SaundersCollegePublishing,1986.
Marieb, E. N. HumanAnatomyandphysiologt,4thed. Menlo park,
CA:
Benjamin/Cummings,1998.
Rust,T. G. AGuidetoBiologyLab. sanAnronio,TX:southwest Educational
Enterprises,1983.
)
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