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In this lab we will be looking at the circulatory system in the
pleuroperitoneal cavity of the dogfish and mud puppy and in the abdominal
cavity of the mammal. This system basically consists of the arterial branches of
the dorsal aorta, the renal and hepatic portal systems and the venous system
leading from the body to the heart. In addition, we will look at the lymphatic
system. The lymphatic system evolved to get excess water back into the
circulatory system as water and ion exchange into tissues at the arterial end
of capillary beds is greater than the exchange into the capillaries at the
venous end.
The
arterial system in the dogfish is injected in red. Last week you looked at the
afferent arteries leading from the gills and the paired dorsal aorta and
internal carotids leading to the head. The coronary arteries leave the second and
third gill loops, then join, to take blood to the heart. The afferent arteries
join to form the dorsal aorta, which enters the pleuroperitoneal cavity. We
will look at the somatic branches first. Find the first paired branch, the subclavians, which arise just
anterior to the fourth afferent artery and serve the pectoral fins. The dorsal
aorta gives rise to many intersegmental arteries, which carry blood to
the segmented muscles and form renal arteries to the kidneys.
Posteriorly, the dorsal aorta gives rise to the paired iliac arteries leading to the pelvic
fins as the femoral arteries. The dorsal aorta continues in the tail as the caudal artery. The visceral
branches may be paired or unpaired. There are four major branches off of the
dorsal aorta. The first is the celiac artery, which departs above the liver to run in
the mesentery and go to several organs. The branches indicate the organs they
serve. The first branch is ovarian or testicular, then the gastrohepatic and
pancreaticomesenteric, the duodenal and anterior intestinal arteries. The next
artery leaving the dorsal aorta is near the spleen. The anterior mesenteric
artery goes
to the intestine and its valves. Just posterior to it is the gastrosplenic
artery to the spleen, stomach and dorsal lobe of the pancreas. A little ways
posterior to this branch is the posterior mesenteric artery leading to the rectal
gland.
The
portal systems transport blood from one organ to a different part of the same
organ or a different organ. The renal portal system takes the blood from
the caudal vein in the tail to the kidneys via the two renal portal veins. The
blood enters the kidneys on afferent renal veins, which connect, via
capillaries to efferent renal veins, which drain the kidneys into the posterior
cardinal sinuses.
The
hepatic portal system takes the blood from the abdominal viscera to the liver. In
the dogfish, this system is injected yellow. The liver can metabolize, detoxify
and store substances in the blood. Branches from the organs (gastric,
lienomesenteric, pancreaticomesenteric) veins come together to form the hepatic
portal vein,
which enters the liver and subdivides. From the liver, blood is drained via the
hepatic vein
to the sinus venosus.
Systemic
veins usually run close to the arteries and share the same name. These are
injected blue. Sometimes larger pools of venous blood are found in sinuses. We
have already examined the renal portal system. The posterior cardinal veins
drain into the posterior cardinal sinuses, which also connect with the genital
sinuses.
The posterior cardinal sinuses drain into the common cardinal veins and then
the sinus venosus of the heart. Posteriorly the femoral, iliac and cloacal
veins enter the lateral abdominal veins located in the lateral muscles of the
body wall. Intersegmental veins join in, as do the subclavian veins just before they all
enter the common cardinal veins and sinus venosus. The head is drained by
sinuses, which enter the anterior cardinal sinuses. The small jugular
veins
also enter the common cardinal sinuses, which lead to the sinus
venosus and
ventricle of
the heart.
In the dogfish, a number of sinusoids drain extra circulatory fluids into the veins, and appear to function like the lymph system of other vertebrates. A large spleen is also present.
Necturus Circulatory System
Just
after the junction of the two radices of the dorsal aorta, the two subclavian
arteries
branch off to serve the arms. Note the pulmonary artery runs the length of each
lung after leaving the junction of the second and third efferent arteries. The dorsal
aorta
gives off intersegmental arteries. Some of these supply the kidneys (renal
arteries),
gonads (genital
arteries),
and the hindlimbs (iliac and femoral arteries). The dorsal aorta continues to the
tail as the caudal artery. The ventral arteries coming off the dorsal
aorta are the single gastric artery taking blood to the stomach, which can be found
just posterior to the subclavians. Just posterior to the gastric artery is the
single, celiacomesenteric artery with branches to the organs (splenic,
hepatic, pancreaticoduodenal, mesenteric). Posteriorly, a number of mesenteric
arteries
go to the large and small intestines. Note that this system shows little change
from that of a dogfish, although the celiac and mesenteric arteries are joined.
The
renal portal system is more primitive than that of the dogfish in that the
embryonic connection of the posterior cardinal veins to the sinus venosus is
not lost anterior to the kidney. The blood from the tail and hindlimbs is taken
to the kidneys via the renal portal veins, which run on the lateral edge of the
kidneys.
The
hepatic portal system is not injected in the mud puppy and will be difficult to find. Venous blood enters the liver from
branches that drain the tail and hindlimbs (abdominal vein), intestine
(mesenteric vein), gastrosplenic vein and pancreaticoduodenal vein. The major
change that has taken place is that now some of the blood from the hindlimbs,
cloaca, bladder and body wall enters the hepatic portal system via the ventral
abdominal vein. This vein is homologous to the lateral abdominal veins of the
shark, which now forms a single vein and lays midventrally.
The
lungs have pulmonary veins along their length, which unite anteriorly to
form a single vessel entering the left atrium of the heart. A new, single vein,
the posterior vena cava, drains the posterior region of the body. This is
partly made up from the embryonic paired posterior cardinal veins and the right
hepatic vein. It runs up the midline between the kidneys, receiving the renal
veins,
then the ovarian or testicular veins, hepatic veins at the liver and
anterior to the septum splits into two hepatic sinuses, which join the common
cardinal veins.
Since the posterior cardinal veins persist in the mud puppy, some blood from the
kidneys (subcardinal veins) and the body wall (intersegmental veins) is drained
to the common cardinals via these vessels. The common cardinal veins also receive
blood from the anterior of the body. The internal and external jugular veins drain into the subclavians from the arms and they
enter the common cardinal veins. The common cardinal veins, after collecting
blood from the posterior cardinal veins, and posterior vena cava, enters the sinus
venosus
and right atrium of the heart.
In
amphibians, there is a well-developed lymphatic system in the subcutaneous area
to return fluids to the blood. The lymph flows in channels and is moved by pulsating
lymph hearts with valves to eliminate backflow. The spleen and thymus gland are lymphoid masses.
Mammal
Circulatory
System
Follow the dorsal aorta into the abdominal cavity. Note the small intercostal arteries and other intersegmental arteries which form the adrenolumbar arteries (to the adrenals), renal arteries (to kidneys), spermatic or ovarian arteries (to gonads), lumbar and iliolumbar arteries to back muscles, and iliac and femoral arteries to the limbs. The first unpaired artery, which goes ventrally to the organs, is the celiac artery. This artery has many branches, gastric, splenic, hepatic, gastroduodenal are the major ones. The branch to the pancreas joins with the pancreatic branch of the next visceral branch forming a loop. The anterior mesenteric artery lies just posterior to the celiac artery and has branches to the pancreaticoduodenal area (forming the loop), colic and intestinal areas. The posterior mesenteric artery is smaller. It branches to the colon and rectum and then joins with the loop from the anterior mesenteric artery. Note again that this system is similar to that of the dogfish.
The
renal portal system does not exist in mammals.
The
hepatic portal system is not injected in your specimen. It drains the viscera
from the mesenteric veins, gastrosplenic vein, coronary vein,
pancreaticoduodenal vein and their branches. They all enter the hepatic
portal vein, which
leads to the liver. Note that the blood from the hindlimbs no longer flows into
this system.
Venous
blood from the hindlimbs flows via the femoral and iliac veins to the single
median postcava (posterior vena cava). The caudal vein joins the left common iliac
vein. Blood also enters from the iliolumbar and lumbar veins, the right spermatic
or ovarian vein and the renal veins. The left spermatic or ovarian vein drains
via the left renal vein as does the left adrenolumbar and phrenic veins (to
diaphragm). Those on the right side enter separately. Near the diaphragm, the
hepatic veins and superior phrenic veins enter the postcava, which then
penetrates the diaphragm and enters the right atrium of the heart. In the head
region, blood is drained via the external and internal jugular veins. The
subclavian veins from the forelimbs join and together they descend as the
innominate (branchiocephalic) veins, joining to form the precava (anterior
vena cava). This
vessel enters the right atrium of the heart.
Thin
walled, permeable vessels are located throughout the body. Fingerlike
capillaries called lacteals project into the villi of the small intestine
for fat absorption. These molecules are then transported to the blood. Excess
lymphatic fluid is returned to the venous system by a thoracic duct, which
opens near the left subclavian vein. Lymph nodes, which filter and
destroy viruses and bacteria, are found in the neck, intestinal and groin
areas, smaller ones are scattered throughout the system. These nodes also house
lymphocytes for immune responses.
The thymus gland produces lymphocytes. Tonsils act like lymph nodes,
eliminating possible foreign invaders. The spleen is engaged in immune response,
produces leukocytes, can make erythrocytes and destroy old ones, and is a
reservoir of blood platelets.
Updated
by Sandra Millen, December, 2003