Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Circulatory System

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Circulatory System

The circulatory system is responsible for transporting substances (gases, nutrients, waste products) throughout the body. It is fundamental in connecting all the bodily systems and ensuring they function correctly.

Why is there a need for a circulatory system?

Consider the two questions in this section.

Can multicellular organisms rely on diffusion alone for transport and exchange of substances?

The answer is a NO, right?

The main reason is that the large sizes of multicellular organisms result in a small surface area to volume ratio. Substances need to travel large distances to get inside designated cells, tissues and organs. The surface that substances enter proportionately reduces. This becomes too time-consuming if the only means of the exchange of substances is diffusion.

In short, the larger an object, the smaller the surface area to volume ratio, as highlighted in the diagram below:

This is why multicellular organisms require circulatory systems (or ‘internal pipes’) to transport substances from one site to another.

Animals have hearts, but plants do not. Why is this?

Animals and plants are both multicellular organisms and have their own ‘piping systems’ (i.e. vessels). However, animals have a high metabolic rate that is necessary for generating sufficient energy (ATP). Since animals cannot photosynthesise, they have the capacity for locomotion to obtain food which requires a lot of energy. Therefore, a biological pump (i.e. the heart) is essential for maximising the exchange of metabolic substances across cells.

What are the functions of circulatory systems?

Circulatory systems are well-organised transport systems with pumps to keep fluid moving through them. Their relevant functions can be summarised as follows:

  • Supplying respiring cells with nutrients such as glucose absorbed from small intestines

  • Maintaining a constant supply of oxygen from lungs to cells undergoing aerobic respiration

  • Getting rid of metabolic waste products such as carbon dioxide in respiring tissues and transporting it back to the lungs

Besides the importance of circulatory systems in respiration, they also transport substances made from one part of the body to another, such as hormones made in the pancreas to muscle cells.

What are the different components of the circulatory system?

There are four components of the circulatory system, whose names and functions are described below.

Table 1. The main components of the circulatory system and their function.

Lymph
Vessels
Heart

Medium for specialised cells (e.g. red blood cells, white blood cells) to carry out their function

Made of tissue fluid to regulate the osmotic pressure in the body

Facilitates the movement of blood to specific tissues in the body.

A hollow, muscular organ that pumps blood. Made of specialised muscle cells that contract involuntarily without rest.

Red blood cells play a role in the transport of oxygen and carbon dioxide.

Medium for specialised white blood cells (e.g. lymphocytes) to carry out their function

There are five different types of vessels (arteries, arterioles, capillaries, venules and veins)

Also contains plasma where solutes (e.g., glucose) are dissolved and transported.

What are the types of circulatory systems in multicellular organisms?

With a better understanding of the importance of circulatory systems, let’s go into more detail about the different types of circulatory systems out there. The examples focus on the types of circulatory systems in animals.

There are two main types of circulatory systems - the open circulatory system and the closed circulatory system. Below is a table to contrast their differences.

Table 2. Differences between open and closed circulatory systems.

Open circulatory system

Closed circulatory system

No gas exchange. Haemolymph only transports food and waste products.

The exchange of substances happens instead via the walls of the blood vessels. As closed circulatory systems facilitate gas exchange, oxygen-carrying pigment is often present.

Present in arthropods such as insects and most molluscs.

Present in echinoderms (e.g., starfish, sea urchins), cephalopod molluscs (e.g., squids), earthworms, and all vertebrates.

Blood’ (haemolymph) leaks out of vessels into the cavities surrounding cells under low pressure (haemocoel), then re-enters the heart via an open-ended vessel.

‘Leak free’ because blood is contained within tubes without coming into direct contact with cells, allows a continuous journey of blood out to the most distant parts of the body and back to the heart at high pressures.

Both snails and squids are from the same mollusc phylum; however, they have evolved different circulatory systems. A squid has a closed circulatory system that creates a high-pressure blood flow, so when the squid is injured you would see black ink gushing out. A snail has an open circulatory system where the blood flow is slower due to the lower hydrostatic pressure. If you pick up a snail, you will notice that it feels squishy (this is from the lower pressure).

What are the types of closed circulatory systems?

Given how closed circulatory systems facilitate efficient blood flow, these circulatory systems are crucial in organisms with higher oxygen demand. For example, in warm-blooded animals with high metabolic rates, closed circulatory systems satisfy the need to remove waste products rapidly.

Similarly, there are two main types of closed circulatory systems. These include single and double circulatory systems. Below is a table that contrasts their differences:

Table 3. Single and double circulatory systems

Single circulatory system
Double circulatory system
Has only one circulatory route that involves two sets of capillaries:
  • First set - oxygen and carbon dioxide exchange.
  • Second set - exchange of substances between the blood and cells.
Has two different circulatory routes:
  • Systemic - carries oxygenated (oxygen-rich) blood to the body, then back to the heart after gas exchange.
  • Pulmonary - carries deoxygenated (oxygen-poor) blood to the lungs, then back to the heart upon oxygenation.
Blood travels once through the heart on one complete ‘circuit.’
Blood travels twice through the heart on one complete ‘circuit.’
Present in fish, echinoderms and earthworms where oxygen demand is low.
Present in warm-blooded animals (e.g., mammals and birds), also reptiles.

The structure of the human circulatory system

The human circulatory system is a closed double circulatory system consisting of both pulmonary and systemic circulation.

In pulmonary circulation, blood leaves the right ventricle via the pulmonary artery, enters the lung to get oxygenated, then is directed to the left atrium via the pulmonary vein. On the other hand, blood leaves the left ventricle to the rest of the body via the aorta, then returns to the right side of the heart in the vena cava in the systemic circulation.

What are the advantages of a double circulatory system?

There are two advantages of a double circulatory system:

  1. Ensures that there is no mixing of blood - not only allows respiring cells to receive as much oxygen as possible but blood flow can also be directed more precisely to the organs that need most oxygen and nutrients.

  2. Enables pressure differences - the systemic circulation has a higher pressure to receive oxygenated blood rapidly. The pulmonary circulation has a lower pressure to prevent damage to vessels and allow gas exchange.

Food for thought: I like to compare double circulatory systems to the water pipes in our homes, where there are separate pipes for clean and dirty water to prevent cross-contamination.

Circulatory System - Key takeaways

  • Multicellular organisms need circulatory systems due to their small surface area to volume ratios. Animals require hearts for maximal efficiency of the exchange of metabolic substances across cells.
  • The circulatory system plays a role in respiration and the transport of substances. It consists of four components - blood, lymph, vessels and heart.
  • Animals have either open or closed circulatory systems. There are two types of closed circulatory systems - closed single and double circulatory systems. Humans have closed double circulatory systems.
  • The advantages of closed circulatory systems include no mixing of blood and pressure differences enabled.

Frequently Asked Questions about Circulatory System

The circulatory system works by transporting nutrients, oxygen and waste products throughout the body with the help of the heart as a pump and blood vessels as routes of transportation.

The three types of circulatory systems include open, closed single and closed double circulatory systems.

Vessels, heart, blood and lymph.

The circulatory system has four main functions:

  • supplying respiring cells with nutrients such as glucose 
  • maintaining a constant supply of oxygen to cells undergoing aerobic respiration
  • getting rid of metabolic waste products
  • transporting hormones from the organ produced to the target site

The organs in the circulatory system include the heart, lungs, blood and lymphatic vessels.

Final Circulatory System Quiz

Question

The heart is made up of specialised muscle cells that contract voluntarily (True/ False)

Show answer

Answer

False - the heart is made up of specialised muscle cells that contract INVOLUNTARILY


Show question

Question

Multicellular organisms have a large surface area to volume ratio (True/ False)


Show answer

Answer

False - multicellular organisms have a SMALL surface area to volume ratio

Show question

Question

Fill in the blanks.

Multicellular organisms require circulatory systems due to their _____ surface area to volume ratio. Therefore they cannot rely on _____ alone like unicellular organisms (e.g. yeasts) for the exchange of substances. This is because their large _____ require substances to travel large ______ to enter. Subsequently, the surface for substances to enter proportionately______, ultimately becoming too _________if diffusion is the only means of exchanging substances .


Animals need a _____ because of their high metabolic rate necessary for generating sufficient energy (ATP). As animals are unable to ______ like plants, they have the capacity for _______ to obtain food. A biological pump is then essential for maximal _____ of the exchange of metabolic substances across cells.

Show answer

Answer

Multicellular organisms require circulatory systems due to their small surface area to volume ratio. Therefore they cannot rely on diffusion alone like unicellular organisms (e.g. yeasts) for the exchange of substances. This is because their large sizes/volumes require substances to travel large distances to enter. Subsequently, the surface for substances to enter proportionately reduces, ultimately becoming too time-consuming if diffusion is the only means of exchanging substances.


Animals need a heart because of the high metabolic rate necessary for generating sufficient energy (ATP). As animals are unable to photosynthesise like plants, they have the capacity for locomotion to obtain food. A biological pump is then essential for maximal efficiency of the exchange of metabolic substances across cells.


Show question

Question

Double circulatory systems are found in organisms where oxygen demand is low (True/ False)

Show answer

Answer

False - single circulatory systems are found in organisms where oxygen demand is low

Show question

Question

Venules are a type of blood vessel (True/ False)


Show answer

Answer

True

Show question

Question

The circulatory system produces hormones such as insulin (True/ False)


Show answer

Answer

False - insulin is produced in the pancreas, the circulatory system TRANSPORTS insulin to target cells

Show question

Question

Outline the four different functions of circulatory systems.

Show answer

Answer

  • supply respiring cells with nutrients such as glucose (e.g. from small intestines to respiring tissues)
  • maintain a constant supply of oxygen to cells undergoing aerobic respiration (e.g., from lungs to respiring tissues)
  • rid metabolic waste products (e.g., carbon dioxide in respiring tissues back to the lungs)
  • transporting substances made from one part of the body to another (e.g., hormones such as insulin made in the pancreas to muscle cells)

Show question

Question

The blood pressure in the systemic circulation is higher than in the pulmonary circulation (True/ False)


Show answer

Answer

True

Show question

Question

Oxygenated and deoxygenated blood are mixed together to allow cells to receive as much oxygen as possible (True/ False)


Show answer

Answer

False - oxygenated and deoxygenated blood are separated to allow cells to receive as much oxygen as possible

Show question

Question

Fill in the blanks.

A single circulatory system has only ____ circulatory route that involves _____ sets of capillaries. The first set of capillaries facilitate the exchange of gases  _____ and ______,  whereas the second set is where the exchange of substances between the ______ and ______ occurs. Blood is said to travel _______ through the heart on one complete circuit. The single circulatory system is common in organisms where _____ ______ is ____, such as fish, echinoderms and earthworms.


On the other hand, a double circulatory system has ____circulatory routes. The ____ route carries ____ blood to the body, then _______ back to the heart after cellular gas exchange. Whereas the ______ route carries _______ blood to the lungs and back to the _____ upon oxygenation. Blood is said to travel _____ through the heart on one complete circuit. The double circulatory system is found in all _____- blooded animals and also _____.

Show answer

Answer

A single circulatory system has only one circulatory route that involves two sets of capillaries. The first set of capillaries facilitate the exchange of the gases oxygen and carbon dioxide,  whereas the second set is where the exchange of substances between the blood and cells occurs. Blood is said to travel once through the heart on one complete circuit. The single circulatory system is common in organisms where oxygen demand is low, such as fish, echinoderms and earthworms.


On the other hand, a double circulatory system has two circulatory routes. The systemic route carries oxygenated blood to the body, then deoxygenated blood back to the heart after cellular gas exchange. Whereas the pulmonary route carries deoxygenated blood to the lungs and back to the heart upon oxygenation. Blood is said to travel twice through the heart on one complete circuit. The double circulatory system is found in all warm-blooded animals and also reptiles.

Show question

Question

The circulatory system moves ammonia produced via deamination in the liver to the kidneys (True/ False)

Show answer

Answer

True


Show question

Question

The heart as a biological pump is crucial for maximal efficiency of the exchange of metabolic substances across cells (True/ False)


Show answer

Answer

True

Show question

Question

Describe the two main advantages of a double circulatory system.

Show answer

Answer

  • Ensures no mixing of blood allows cells to receive as much oxygen as possible and directs blood flow more precisely to the organs that need the most oxygen and nutrients.
  • Enables pressure differences - the systemic circulation has a higher pressure to receive oxygenated blood rapidly. The pulmonary circulation has a lower pressure to prevent damage to vessels and allow gas exchange.

Show question

Question

In single circulatory systems, blood travels once through the heart on one complete circuit (True/ False)

Show answer

Answer

True


Show question

Question

Lymphocytes are found in the blood (True/ False)


Show answer

Answer

False - lymphocytes are found in the lymph

Show question

Question

The diagram of the heart on paper usually has the left side of the heart on the right-hand side and the right side of the heart on the left-hand side. (True/ False)


Show answer

Answer

True

Show question

Question

How is the heart adapted to prevent over-distending with blood?


Show answer

Answer

It is surrounded by an inelastic pericardial membrane.

Show question

Question

Explain the need for two sides of the heart.


Show answer

Answer

Each side of the heart is composed of separate pumps lying side by side. The left side receives oxygenated blood from the lungs and pumps it to the body and the right side receives deoxygenated blood from the body and pumps it to the lungs. Blood has to pass through the lungs first to be oxygenated before passing through the rest of the body. As there is a large drop in blood pressure after passing through the lungs, the heart needs to pump this blood to increase its pressure for it to pass through the rest of the body. Hence, the heart is split into two separate pumps lying side by side instead of one pump.


Show question

Question

Name the two veins that connect to the heart and outline their roles.


Show answer

Answer

  • Vena cava – brings deoxygenated blood from both the lower and upper body 
  • Pulmonary vein – brings oxygenated blood from the left and right lungs 

Show question

Question

Name the two arteries that connect to the heart and outline their roles.


Show answer

Answer

  • Aorta – large and arching, also branches into several smaller arteries to transport oxygenated blood up to the head and the rest of the lower body
  • Pulmonary artery – branches into two to transport deoxygenated blood into the left and right lungs

Show question

Question

Describe how the heart obtains its own blood supply.


Show answer

Answer

The heart obtains its own blood supply by having specialised arteries that branch from the aorta called coronary arteries. These arteries supply oxygenated blood to cardiac muscles to facilitate their necessary contraction and relaxation.

Show question

Question

Name the structure of the heart that stops blood of the left and right sides of the heart from mixing together.


Show answer

Answer

Septum

Show question

Question

Fill in the blanks

The upper chambers that are smaller in size are the ____ (singular _____). They are connected to the veins, with the _____ ______ connected to the vena cava and whereas the _____ _____  connected to the pulmonary vein. 

Show answer

Answer

The upper chambers that are smaller in size are the atria (singular atrium). The atria are connected to the veins, with the right atrium connected to the vena cava and whereas the left atrium connected to the pulmonary vein. 


Show question

Question

 Explain why the atria have thin walls.


Show answer

Answer

The atria have thin walls as they only pump blood into the ventricles that are small structures, whose lower pressure of pumping prevents the ventricles from bursting.

Show question

Question

Fill in the blanks

The lower chambers that are larger in size are the ______. The ventricles are connected to the _______, with the ____ ________ connected to the pulmonary artery whereas the ____ ______ is connected to the aorta.

Show answer

Answer

The lower chambers that are larger in size are the ventricles. The ventricles are connected to the arteries, with the right ventricle connected to the pulmonary artery whereas the left ventricle is connected to the aorta.

Show question

Question

Explain why the walls of the left ventricles are thicker than the right ventricles.


Show answer

Answer

The walls of the left ventricles are thicker than the right ventricles because the blood is pumped from the left ventricles to the extremities. This blood also needs to overcome the elastic recoil of arteries. As for the thinner walls of the right ventricles, the lungs that receive blood from the right ventricles not only are closer to the heart and are smaller than the rest of the body, but the capillaries of the lungs are extremely delicate.

Show question

Question

Valves serve to prevent backflow of blood. Valves in the arteries that connect to the heart are called semilunar valves. As for atrioventricular valves between the atria and ventricles, the right side of the heart has bicuspid valves whereas the left side of the heart has tricuspid valves. (True/ False)


Show answer

Answer

False - the right side of the heart has tricuspid valves whereas the left side of the heart has bicuspid valves

Show question

Question

Outline the role of tendinous cords found connected to atrioventricular valves.

Show answer

Answer

To prevent pressure from the heart from turning the valves inside out when the ventricles contract.

Show question

Question

Name the process given to the coordination of the different components of the heart in the organ’s series of contractions and relaxations.


Show answer

Answer

The cardiac cycle


Show question

Question

Outline the four roles of the heart.


Show answer

Answer

  • Pumping oxygenated blood to the other body parts.
  • Pumping hormones and other vital substances to different parts of the body.
  • Receiving deoxygenated blood and carrying metabolic waste products from the body and pumping it to the lungs for oxygenation.
  • Maintaining blood pressure

Show question

60%

of the users don't pass the Circulatory System quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.