EEB202H1 Lecture Notes - Pseudobranch, Umbilical Vein, Pulmonary Circulation

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Lecture 18 (Feb. 16. 2011)
<Cardiovascular or circulatory components>
Vertebrates have a closed cardiovascular or circulatory system meaning that blood
passes through and rarely leaves a system of vessels or tubes. While the fluid
components of blood can leave the tubes, it is rare that actual components of blood
cells (called formed elements) ever leave the tubes. While we can get part of fluid
portion of the blood leaving the tubes, the blood cells under normal circumstances do
not contact the body cells, which lie in their own interstitial fluid.
There are 4 basic parts of CVS :
1) Muscular heart: receives blood at one end and pumps out on the other end
2) Arteries: system of tubes that carries blood AWAY from the heart
- A kind of blood (in terms of oxygenation level) in a vessel does not determine what
the vessel is. What determines the kind of a vessel is the DIRECTION of the blood.
3) Vein: vessels that bring blood TO the heart
4) Capillary networks: Joining arteries & veins.
- Quite small tubes (microscopic) but large enough to allow a single blood cell (RBC) to
pass through them
- This is where a real action of CVS occurs: in general, no cell is ever very far away from
the capillary network. We got millions of capillary networks in our body.
- Where gas exchange occurs (carrying O2 to cells)
From a capillary’s point of view, an artery is a vessel that brings blood to the capillary
and a vein is a vessel that carries blood away from the capillary. In a functional way, this
is just as same as using the heart as a reference view.
Portal vein: a vein that extends b/w 2 capillary systems
Takes blood from one capillary system and does not lead it directly to the heart,
the blood makes its way towards the heart but before doing so, the blood has to
pass through another capillary system
E.g. hepatic portal vein: drains blood from the capillaries of the gut (structures in
the abdominal cavity) and conducts it to the liver where it subdivides into capillary
networks within the substance of the liver.
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(Function of CVS)
1. A bulk transportation system (main function): moving things from place to place. i.e.
transport nutrients to the cells, taking up waste such as CO2)
2. Communication: coordinating the body’s activities accomplished by circulating
hormones throughout the body
3. Contribute to homeostasis: maintaining constant internal environment by helping to
maintaining a uniform interstitial fluid and by helping to maintain relatively constant
internal temperature
4. Involved in immune response: protect and repair tissue
(General pattern of CVS)
In fish: Blood that is low in O2 gets taken to the gills -> blood gets oxygenated & is sent
to the rest of the body -> goes through capillaries of body, return to vein, back to the
heart
- Every time blood goes through body once, it passes through the heart once.
In tetrapods: becomes more complex because the lungs do not reside where the gills
used to be. In this case, we have to get blood from the heart to the lungs, and send it
back to the heart and then send it throughout rest of our body. Therefore the blood has
to travel twice for every time (a single circuit) it goes around the body once
- Have 2 circulatory paths:
1) Pulmonary circulation: goes to the lungs
2) Systemic circulation: goes to the rest of the body (lungs are included)
(4 venous system - subdivision of veins)
1. Sub-intestinal vein/system: only the posterior portion becomes hepatic vein and
hepatic portal vein
2. Dorsal veins/ Cardinal veins: are functionally replaced by the vena cavae in higher
tetrapods
3. Abdominal veins
4. Pulmonary veins
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1. Sub-intestinal veins:
- first vessels to arise in the embryo
- Initially they are paired and extend along the ventral surface of the gut -> at later
stage of development, the 2 coalesce and form a single sub-intestinal vein
- The anterior or front part of the sub-intestinal vein or proximally the front half will
later form the heart and the ventral aorta
- The posterior part of the sub-intestinal vein forms the hepatic vein and the hepatic
portal vein. The way that this happens is that the liver is a ventral outgrowth of the
gut and as it develops it grows into and subdivides the posterior part of the sub-
intestinal (subdivides the posterior division of the sub-intestinal). The anterior part
of the subdivision becomes the hepatic vein and the posterior part becomes the
hepatic portal vein
- In tetrapods and begin with lungfish: the hepatic vein winds up being a tributary of
the inferior/posterior vena cavae. Dogfish do not have the posterior vena cavae so
the hepatic vein (called them sinuses) empty directly into the sinus venosus which
is the most posterior chamber of the heart. Therefore in dogfish, the hepatic vein
draining the liver goes from the liver straight to the heart. In lungfish & tetrapods,
goes from the liver to the posterior vena cavae.
2. Dorsal veins/Cardinals:
- In higher vertebrates (lungfish and above) becomes functionally replaced by the vena
cavae
- Look at Diagrams too
- In agnathan embryo: the anterior cardinals are the main vessels that collect blood
anterior to the heart and return it to the heart. The posterior cardinals are the main
vessels that receive blood from the kidneys & musculature from the tail (caudal vein) &
pass it forward, back into the heart. This system is almost same as in dogfish with
difference that dogfish & several other lower vertebrates develop a renal portal system
as well, that is the blood coming back from the tail, not bypass the kidney, but go to
kidney capillaries before going back to the heart
- In most tetrapods (except mammals), the main part of each anterior cardinal is a vessel
called “lateral head vein this starts off in the orbit and passes posteriorly along the
lateral surface of the outside braincase and then receives tributaries from the brain and
enters the common cardinal.
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Document Summary

Vertebrates have a closed cardiovascular or circulatory system meaning that blood passes through and rarely leaves a system of vessels or tubes. While the fluid components of blood can leave the tubes, it is rare that actual components of blood cells (called formed elements) ever leave the tubes. While we can get part of fluid portion of the blood leaving the tubes, the blood cells under normal circumstances do not contact the body cells, which lie in their own interstitial fluid. There are 4 basic parts of cvs : muscular heart: receives blood at one end and pumps out on the other end, arteries: system of tubes that carries blood away from the heart. A kind of blood (in terms of oxygenation level) in a vessel does not determine what the vessel is. What determines the kind of a vessel is the direction of the blood: vein: vessels that bring blood to the heart, capillary networks: joining arteries & veins.

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