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Illustration A shows a cross section of a sponge, which has a thin, vase-like body bathed both inside and out by fluid. Illustration B shows a bell-shaped jellyfish.
Simple animals consisting of a single cell layer such as the (a) sponge or only a few cell layers such as the (b) jellyfish do not have a circulatory system. Instead, gases, nutrients, and wastes are exchanged by diffusion.

For more complex organisms, diffusion is not efficient for cycling gases, nutrients, and waste effectively through the body; therefore, more complex circulatory systems evolved. Most arthropods and many mollusks have open circulatory systems. In an open system, an elongated beating heart pushes the hemolymph through the body and muscle contractions help to move fluids. The larger more complex crustaceans, including lobsters, have developed arterial-like vessels to push blood through their bodies, and the most active mollusks, such as squids, have evolved a closed circulatory system and are able to move rapidly to catch prey. Closed circulatory systems are a characteristic of vertebrates; however, there are significant differences in the structure of the heart and the circulation of blood between the different vertebrate groups due to adaptation during evolution and associated differences in anatomy. [link] illustrates the basic circulatory systems of some vertebrates: fish, amphibians, reptiles, and mammals.

Illustration A shows the circulatory system of fish, which have a two-chambered heart with one atrium and one ventricle. Blood in systemic circulation flows from the body into the atrium, then into the ventricle. Blood exiting the heart enters gill circulation, where gases are exchanged by gill capillaries. From the gills blood re-enters systemic circulation, where gases in the body are exchanged by body capillaries. Illustration B shows the circulatory system of amphibians, which have a three-chambered heart with two atriums and one ventricle. Blood in systemic circulation enters the heart, flows into the right atrium, then into the ventricle. Blood leaving the ventricle enters pulmonary and skin circulation. Capillaries in the lung and skin exchange gases, oxygenating the blood. From the lungs and skin blood re-enters the heart through the left atrium. Blood flows into the ventricle, where it mixes with blood from systemic circulation. Blood leaves the ventricle and enters systemic circulation. Illustration C shows the circulatory system of reptiles, which have a four-chambered heart. The right and left ventricle are separated by a septum, but there is no septum separating the right and left atrium, so there is some mixing of blood between these two chambers. Blood from systemic circulation enters the right atrium, then flows from the right ventricle and enters pulmonary circulation, where blood is oxygenated in the lungs. From the lungs blood travels back into the heart through the left atrium. Because the left and right atrium are not separated, some mixing of oxygenated and deoxygenated blood occurs. Blood is pumped into the left ventricle, then into the body. Illustration D shows the circulatory system of mammals, which have a four-chambered heart. Circulation is similar to that of reptiles, but the four chambers are completely separate from one another, which improves efficiency.
(a) Fish have the simplest circulatory systems of the vertebrates: blood flows unidirectionally from the two-chambered heart through the gills and then the rest of the body. (b) Amphibians have two circulatory routes: one for oxygenation of the blood through the lungs and skin, and the other to take oxygen to the rest of the body. The blood is pumped from a three-chambered heart with two atria and a single ventricle. (c) Reptiles also have two circulatory routes; however, blood is only oxygenated through the lungs. The heart is three chambered, but the ventricles are partially separated so some mixing of oxygenated and deoxygenated blood occurs except in crocodilians and birds. (d) Mammals and birds have the most efficient heart with four chambers that completely separate the oxygenated and deoxygenated blood; it pumps only oxygenated blood through the body and deoxygenated blood to the lungs.

As illustrated in [link] a Fish have a single circuit for blood flow and a two-chambered heart that has only a single atrium and a single ventricle. The atrium collects blood that has returned from the body and the ventricle pumps the blood to the gills where gas exchange occurs and the blood is re-oxygenated; this is called gill circulation    . The blood then continues through the rest of the body before arriving back at the atrium; this is called systemic circulation    . This unidirectional flow of blood produces a gradient of oxygenated to deoxygenated blood around the fish’s systemic circuit. The result is a limit in the amount of oxygen that can reach some of the organs and tissues of the body, reducing the overall metabolic capacity of fish.

In amphibians, reptiles, birds, and mammals, blood flow is directed in two circuits: one through the lungs and back to the heart, which is called pulmonary circulation    , and the other throughout the rest of the body and its organs including the brain (systemic circulation). In amphibians, gas exchange also occurs through the skin during pulmonary circulation and is referred to as pulmocutaneous circulation    .

As shown in [link] b , amphibians have a three-chambered heart that has two atria and one ventricle rather than the two-chambered heart of fish. The two atria (superior heart chambers) receive blood from the two different circuits (the lungs and the systems), and then there is some mixing of the blood in the heart’s ventricle    (inferior heart chamber), which reduces the efficiency of oxygenation. The advantage to this arrangement is that high pressure in the vessels pushes blood to the lungs and body. The mixing is mitigated by a ridge within the ventricle that diverts oxygen-rich blood through the systemic circulatory system and deoxygenated blood to the pulmocutaneous circuit. For this reason, amphibians are often described as having double circulation    .

Most reptiles also have a three-chambered heart similar to the amphibian heart that directs blood to the pulmonary and systemic circuits, as shown in [link] c . The ventricle is divided more effectively by a partial septum, which results in less mixing of oxygenated and deoxygenated blood. Some reptiles (alligators and crocodiles) are the most primitive animals to exhibit a four-chambered heart. Crocodilians have a unique circulatory mechanism where the heart shunts blood from the lungs toward the stomach and other organs during long periods of submergence, for instance, while the animal waits for prey or stays underwater waiting for prey to rot. One adaptation includes two main arteries that leave the same part of the heart: one takes blood to the lungs and the other provides an alternate route to the stomach and other parts of the body. Two other adaptations include a hole in the heart between the two ventricles, called the foramen of Panizza, which allows blood to move from one side of the heart to the other, and specialized connective tissue that slows the blood flow to the lungs. Together these adaptations have made crocodiles and alligators one of the most evolutionarily successful animal groups on earth.

In mammals and birds, the heart is also divided into four chambers: two atria and two ventricles, as illustrated in [link] d . The oxygenated blood is separated from the deoxygenated blood, which improves the efficiency of double circulation and is probably required for the warm-blooded lifestyle of mammals and birds. The four-chambered heart of birds and mammals evolved independently from a three-chambered heart. The independent evolution of the same or a similar biological trait is referred to as convergent evolution.

Section summary

In most animals, the circulatory system is used to transport blood through the body. Some primitive animals use diffusion for the exchange of water, nutrients, and gases. However, complex organisms use the circulatory system to carry gases, nutrients, and waste through the body. Circulatory systems may be open (mixed with the interstitial fluid) or closed (separated from the interstitial fluid). Closed circulatory systems are a characteristic of vertebrates; however, there are significant differences in the structure of the heart and the circulation of blood between the different vertebrate groups due to adaptions during evolution and associated differences in anatomy. Fish have a two-chambered heart with unidirectional circulation. Amphibians have a three-chambered heart, which has some mixing of the blood, and they have double circulation. Most non-avian reptiles have a three-chambered heart, but have little mixing of the blood; they have double circulation. Mammals and birds have a four-chambered heart with no mixing of the blood and double circulation.

Questions & Answers

what are cluster A disease?
Saee Reply
because psychology is a natural science as well as a science. it's a interdisciplinary subject
Kamakshi Reply
yes absolutely we cabt out Psychology completely into science dur to its various measuring aspects
utkarsh
cannot* put*
utkarsh
Assess the relationship between heredity and environment in human development
Newman Reply
जिवन कक्षा विकासाच्या एकूण किती अवस्था आहेत
Digambar Reply
what happened Digambar?
sakshi
?
Reina
Is here anybody exactly awared about the medicine used for the schizophrenia?
Fazil
plz can i know if io psychology in demand ou it's better to continu in human resourses management?
Reina
there are many drugs used to alleviate the symptoms, but none are used for curing the disorder itself.
Rupert
Researchers believe that one important function of sleep is to facilitate learning and memory. How does knowing this help you in your college studies? What changes could you make to your study and sleep habits to maximize your mastery of the material covered in class?
whitecat Reply
Well, for starters, both are entirely different aspect for consideration. As a college student, having an adequate amount of sleep is relatively rare especially on instances where we are totally forced to stay all night (whether for studying or doing academic works).
Rupert
benefits of physcology
Irfan Reply
who define first physcology
Irfan
who define first physcology
Irfan
I think it was either Henry James Or William James are the father of psychology.
James
I haven't read the flash cards and memorized them sense 2015.
James
so iv forgotten some info and some has never left me . I'm very passionate about psychology.
James
I study medical psychology
John
the history of psychology usually traces back to ancient chinese practices. but modern times acknowledge Wilhelm Wundt as the first person to establish a school.of thought in psychology.
Rupert
huh
ANGELICA
is it wrong?
Rupert
please can i know what is the difference about io psychology and human resources managment and which is more in demand ?
Reina Reply
What is psychology
Tayyeba Reply
someone who can observe or understand a person's reactions.
Leanne
It is the scientific study of behavior and mental processes
Enos
Sarah is a 30 year old white female. Her occupation is part time chef. She is recently been divorced and has custody of her three children. She has extreme changes in her mood that began to appear in her 20’s but she never went to see a doctor about them. When family tries to talk to her about her u
Ere Reply
listen very carefully for red flags on both sides
Leanne
what does historical racism mean
Unasumming Reply
Means that racism was present in a group of peoples race in there past and maybe even now. Example is the Native Americans and African Americans also Asian people. Anyone of not caucasian resent. So people who are mixed races also experience rascism.
James
racism meaning I would believe is a negative impact on other separate cultures, causing some serious concerns to the human race.
Leanne
How do counsel someone that is kinda depressed, lonely and stuffs but the person is pushing you away with by saying stuffs you don't like? Your age mate
Ajayi Reply
let them figure themselves out met them come to you and listen more than speak
Jascelyn
don't take anything too personal someone who is depressed has more feelings other than being sad. I have been through it we dont alwaya mean the things we say. just give time and space but be there when they are ready.
Deanna
the person should be first dealt with very patience and understanding.......... person's trust should be won first to treat that kind of state if counsel is the priority..... don't rush small steps will lead to get successful results....... after the patient start trusting you conversate with them.
Amisha
OK..... Thank you very much It makes me look desperate for the person's attention Thanks tho
Ajayi
just let them know even if they aren't ready to tall right now, you will be here for them whenever they are.
Deanna
we need to wait till the stage comes when he/ she is ready at mental level to participate as he is the subject and the core of the part of that particular conscelling session
aaqib
A.Are they saying it in general manner or B.they are saying it cz they know something about you personally If it is A. then remember it's a part of counseling...even if you don't agree with their views..it is theirs.. so don't take it personally
PREETI
if it is B. tell them .. we are here to talk about them not you Also remember people takes time with things.. so it does get difficult at times.. but in counseling it's about them not you. And if it affecting you much .. see why is there .. and try to objective about it OR refer them to someone
PREETI
allow them time to always become comfortable by listening to all sorts of thoughts they all sound scattered but if you ,just let it go until their ready to ask for advice ,my thoughts of counciling would go for a few more sessions of them venting until they've had enough to feel they want geedback
Leanne
what is the trait in the given example?
Maya Reply
what's the given example?
SamieMike
my fat cock
Andrea
o.o u seem like u need to read this txt
SamieMike
learning to understand psychological effects of one's mind thoughts
Leanne
A trait is a distinguishing feature of a person's character, either behavioral or physical.   "Your Fat Cock", would be an example of a physical trait. Andrea, at what age did symptoms of your IED first occur Andrea? I'd say my, "This big dick!", outbursts are Circa 2009. & STILL GOING STRONG!
Ashley
mental state and behavior
Mufakir Reply
Feared ,lethargic, self isolated...
Leanne
because psychology basic is observation asa well as science, so people might skeptical about these two but if we look into it people might notice that it's different because psychology is study about mind and science is study about many thing around us and it's not study about mind clearly.
Karona Reply
empirical method is the method of observation on object rather than do experiment .
Karona
ology is the study of theory .
Karona
psyche means soul as well as butterfly.
Karona
psychology is the the study of mind and behavior
Karona
this is where I'm a little sceptical. we learning psychology based on books. but we ourselves r also human. when we to encounter a real life situation how well can we act accordingly
Aileen
im curious more of myself then others
Aileen
psychology is the scientific study of mind and behavior. scientific mean it's based on observation and experiments. yeah we can observe behavior easily but can't read mind directly that's why we do observe behavior and apply test and therapies to study mind basically we behave according to our mind
Faiza
educates a humans thoughts to expand and explore more of how far a mind will go if allowed
Leanne
wilhelm wundt studied psychology for the purpose of
Rufai Reply
i dont know, all inknow is that he pioneered the practice of introspective and his school of thought aims to study behavior as structured elements
Rupert
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Source:  OpenStax, Bmcc 103 - concepts of biology. OpenStax CNX. Aug 06, 2015 Download for free at https://legacy.cnx.org/content/col11855/1.2
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