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Structures & Functions of Organ Systems - Nervous, Skeletal, Endocrine, Cardiovascular, and Circulatory Systems

Updated on May 2, 2017

Structures and Functions of The Circulatory System

The Circulatory System is essentially the body’s road and highway system. There is constant travel within your body without your awareness (involuntary processes) and when things such as nutrients, hormones, oxygen, and waste need to get from one part of the body to another, they jump on a road within the circulatory system.

The Most important Traveler on these roads is Oxygenated blood. The Circulatory system transports oxygenated blood to all cells in the body using arteries, and then transports carbon dioxide and waste from those cells to the lungs to be expelled.

The Circulatory System

A network of blood vessels that transports oxygen, nutrients, and waste throughout the human body.

The Many "Roadways" of The Circulatory System

The circulatory system transports oxygen, nutrients and waste throughout the body by using a network of many different "Roadways" called Blood Vessels. These come in several shapes and sizes, and each has a specific purpose within the system.

The Aorta

This is like the highway. It’s the the main artery in the human body and connects to the heart in the left ventricle Oxygenated blood flows from the heart through the aorta and to the..


These are blood vessels that connect to the aorta, giving each part of the body a stop along the road, like exit signs. Arteries carry oxygenated blood from the aorta to the cells in the body. Every body part has its own artery (ie, the femoral artery.)


Arteries branch off into smaller tubes called Arterioles. To continue "metaphor-rizing" (yes, I made that word up) you can think of arterioles as the streets in a neighborhood or subdivision. Oxygenated blood flows from the artery through these more narrow structures to ultimately reach the capillary bed of the destination cell.


These are the tiniest part of the blood vessels, that connect arterioles to venules and facilitate the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between the blood and the tissues. Blood leaving the capillaries is now deoxygenated.

The Flow of Blood Through The Circulatory System


Branches of the veins that connect to the capillaries carry deoxygenated blood from the cell to the..


Blood vessels which carry deoxygenated blood to the lunges by connecting to the


The main vein in the body which connects to the lungs. Deoxygenated blood and waste from all parts of the body flow through here to the lungs to be excreted.

What Happens When Blood Reaches The Heart?

The Cardiovascular System

The Process by which blood flows through the heart and lungs to be re-oxygenated and eventually restart the circulatory process.

As we recall from the review of the Circulatory system, Arteries are blood vessels that transport oxygenated blood away from the heart to be distributed throughout the body, and veins transport deoxygenated blood back to the heart.

This begins The Cardiovascular System, which is essential in pumping oxygenated blood and nutrients to all parts of the body via the circulatory system.Because the these two organ systems are so closely related, and work together towards the same goal, the terms "Cardiovascular System" and "Circulatory System" are often used interchangeably.

For the purpose of this overview, we will separate the two, isolating our study of the Cardiovascular system to only the processes that take place within the heart and lungs, ending with oxygenated blood leaving the heart through the aorta to restart the circulatory system.

Blood's Journey Through the Heart

The above image shows the structures within the cardiovascular system and demonstrates the path of blood flow from through the heart and lungs (and heart again.)

This step in bloodflow is vital, because it is where deoxygenated blood from all parts of the body is re-oygenated,so it can return to the circulatory system and restart the process of delivering nutrients to the body's cells, maintaining the cycle.

Steps of the Cardiovascular System:

1. Deoxygenated blood leaving the body's cells via the circulatory system flows through the vena cava into the right atrium of the heart.

2. Blood is then pumped from the right atrium to the right ventricle

3. Deoxygenated blood flows from the right ventricle into the lungs through the Pulmonary Artery.

4. **Blood is oxygenated in the lungs**

5. Oxygenated Blood exits the lungs through the Pulmonary Vein and flows into the heart's Left Atrium

6. Blood flows from the Left Atrium to the Left Ventricle

7. Blood leaves the heart through the Aorta and begins the circulatory system.

Notice anything Strange...?

Remember when I told you that arteries carry only oxygenated blood, and that veins carry only deoxygenated blood?

Well...I lied.


As you can see, there is one (and ONLY one) exception to the vein/artery rule:

The Pulmonary Vein and Pulmonary Artery are the exact opposite.

The Pulmonary vein carries oxygenated blood (from the lungs to the heart), and the pulmonary artery carries deoxygenated blood (from the heart to the lungs.) Please to not let this confuse you! I pinky promise that for every other case throughout the circulatory system, the rule holds true: Veins = deoxygenated, Arteries: Oxygenated.

Moving on..

The Nervous System

A network of nerves and specialized cells called "neurons" that is responsible for carrying messages to and from the brain and spinal cord to various parts of the body.

Functions, Structures, and Processes of The Nervous System

The Nervous System is an essential Organ System found within all Humans and Animals. This system is responsible for carrying messages to and from the brain and spinal cord to various parts of the body.

This complex system of nerves and specialized cells can be considered the body's "electrical wiring." Without it, we would not be able to sense our environment or react to external stimuli, which could be very dangerous.

For example, the interaction between motor and sensory nerves within the Nervous System is the reason we know to pull our hand away from a flame or hot stove. The Nervous system carries the message: "This is painful" from the senses in this case, tactile/touch) to the brain, which tells our body to react (pull away) from the painful stimuli.

The Nervous System is divided into 2 parts: The Central Nervous System (CNS), comprised of the Brain and the Spinal cord, and The Peripheral Nervous system (PNS) which contains all the nerves that lie outside of the central nervous system (CNS).

The primary role of the PNS is to connect the CNS to the organs, limbs, and skin.This allows the brain and spinal cord to receive and send information to other areas of the body, which allows us to react to stimuli in our environment.

Cells in the Nervous system are called neurons, and bundles of neurons form nerves. These nerves extend from the central nervous system to the outermost areas of the body.The Nervous System receives stimuli from the outside world through sense organs, including the eyes, ears, nose, mouth, and skin through ganglion.

The Endocrine System

The Endocrine System is the collection of glands of that secrete chemical messengers called hormones directly into the circulatory system to regulate other parts of the body.

This system (along with the Nervous system) is one of the body’s 2 control systems, meaning it has the ability to communicate with and direct the processes of other body systems.

Hormones are chemical messengers that are secreted directly into blood or other surrounding fluids by the specialized endocrine glands listed below. Some hormones regulate growth, development, reproduction, and behavior. Other hormones regulate metabolism and help us react to external stimuli.

The Hypothalamus although technically a part of the nervous system, plays a large role in the endocrine system. It contains special cells called neurosecretory cells—neurons that secrete hormones and controlling the endocrine system through the pituitary gland.

Organs and Structures of The Endocrine System

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