Biology, The Science of Life

The Circulatory System and Blood: Introduction

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Overview: This lecture consists of the instructor lecturing for 50 minutes in an authoritative fashion on the human circulatory system. A short video clip on the circulatory system will be presented at the end of the lecture to summarize the topic visually.There will be a tangent discussion on the popular television series “Dexter”. More specifically, various details of his job will be explained to demonstrate to the students that the study of blood does happen outside the classroom. A take-home crossword will be assigned at the end of class.

Materials: The teacher will need the class computer, projector, and screen to present the Power Point presentation for the majority of the duration of the class (the Power Point is made available to download above). The digital media object which are used as a teaching tool in this lesson will consist of a summary video (similar to lesson 01) and clips of the hit television show “Dexter”, as well as the Power Point presentation.The instructor may also use the white board to further emphasize the material when they feel the need to use it. Students will need paper, pen or pencil, or their laptops to take down notes. The Power Point presentation is made available therefore the students must focus their notes on what is not presented on the slides. 

Assessment: A take-home crossword will be distributed at the end of class for a total worth of 2% of the final grade. The crossword provides questions similar to the exam presented at the end of the 10 lectures therefore it is a great practice and review tool. Crosswords are chosen as the method of assessment for these authoritarian lectures because they turn a 50 min lecture into an interactive game. A lot of material is covered in lessons set-up like this one and a crossword is more amusing to complete than a simple questionnaire; it provides clues and to a certain level, a confirmation of your answer. It also covers the material in as much detail as any questionnaire. It is available for download at the top of the page.

Extra Notes: This lecture is an introduction to the circulatory system, therefore further details (i.e. detailed composition of blood) are covered at the next biology course level. The discussion on "Dexter" will not be material for the exam.


  • Closed Circulatory System (4 minutes)
  • Double Circulation (4 minutes)
  • Mammalian Circulation (10 minutes)
  • Blood (3 minutes)
  • The Heart (5 minutes)
  • Other Circulatory Systems (brief overview) (5 minutes)
  • Summary Video (3 minutes)
  • Science in Society (10 minutes)

Open the Power Point presentation and begin explaining the material. The white board may be used to further emphasize the material.

As you previously learned, small, non-polar molecules such as oxygen and carbon dioxide can move between cells and their immediate surroundings by diffusion. But diffusion is very slow for distances of more than a few millimeters, therefore how does each cell of an animal participate in exchange? Natural selection has resulted in two general solutions to this problem:
The first solution is a body size and shape that keep many or all cells in direct contact with the environment. Each cell can thus exchange materials directly with the surrounding medium (found in sponges and cnidarians). The second solution, found in all other animals, is a circulatory system that moves fluid between each cell’s immediate surroundings and the tissues where exchange with the environment occurs. Today we will focus on the mammalian circulatory system.

Closed Circulatory System
In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid. One or more hearts pump blood into large vessels that branch into smaller ones coursing through the organs. Materials are exchanged between the smallest vessels and the interstitial fluid bathing the cells.
The closed circulatory system of humans and other vertebrates is often called the cardiovascular system. Blood circulates to and from the heart through an amazingly extensive network of vessels. FYI: The total length of blood vessels in an average human adult is twice Earth’s circumference at the equator!
Arteries, veins, and capillaries are the three main types of blood vessels. Arteries carry blood away from the heart to organs throughout the body. Within organs, arteries branch into arterioles, small vessels that convey blood to the capillaries. Capillaries are microscopic vessels with very thin, porous walls. Networks of these vessels, called capillary beds, infiltrate each tissue. Across the thin walls of capillaries, chemicals, including gas, are exchanged by diffusion. At their “downstream” end, capillaries converge into veins, the vessels that carry blood back to the heart. Portal veins carry blood from capillaries in the digestive system to capillary beds in the liver.
The hearts of all vertebrates contain two or more muscular chambers. The chambers that receive blood entering the heart are called atria. The chambers responsible for pumping blood out of the heart are called ventricles.

Double Circulation
The circulatory systems of amphibians, reptiles, and mammals have two distinct circuits, an arrangement called double circulation. The pumps of the two circuits serve different tissues but are combined into a single organ, the heart.
One pump, the right side of the heart, delivers oxygen-poor blood to the capillary beds of the gas exchange tissues, where there is a net exchange of oxygen into the blood and carbon dioxide out. This part of the circulation is called a pulmonary circuit. After the oxygen-enriched blood leaves the gas exchange tissues, it enters the other pump, the left side of the heart. Contraction of the heart propels this blood to capillary beds in organs and tissues throughout the body. Following the exchange of oxygen and carbon dioxide, now oxygen-poor blood returns to the heart, completing the systemic circuit.

Ask students if they have any questions up to this point. The question period should be no more than 2-3 minutes.

Mammalian Circulation
Now let’s examine the overall organization of the mammalian cardiovascular system.
1) Contraction of the right ventricle pumps blood to the lungs via 2) the pulmonary arteries. As the blood flows through 3) capillary beds in the left and right lungs, it loads oxygen and unloads carbon dioxide. Oxygen-rich blood returns from the lungs via the pulmonary veins to 4) the left atrium of the heart. Next, the oxygen-rich blood flows into 5) the left ventricle, which pumps the oxygen-rich flood out to the body tissues through the systemic circuit. Blood leaves the left ventricle via 6) the aorta, which conveys blood to arteries leading throughout the body. The first branches of the aorta are coronary arteries, which supply blood to the heart. Then branches lead to 7) capillary beds in the head and arms. The aorta then descends into the abdomen, supplying oxygen-rich blood to arteries leading to 8) capillary beds in the abdominal organs and legs. Within the capillaries, there is net diffusion. Oxygen-poor blood from the head, neck, and forelimbs is channeled into a large vein, 9) the superior vena cava. Another large vein, 10) the inferior vena cava, drains blood from the trunk and hind limbs. The two venae cavae empty their blood into 11) the right atrium, from which the oxygen-poor blood flows into the right ventricle.

Ask students if they have any questions regarding the pathway of blood. The question period should be held between 2-3 minutes.

Blood composition and function:
Vertebrate blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma. Dissolved in the plasma are ions and proteins that function in osmotic regulation, transport, and defense. Plasma is composed of inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes. Suspended in blood plasma are two classes of cells: red blood cells, which transport oxygen, and white blood cells, which function in defense. Blood also contains platelets, fragments of cells that are involved in the clotting process.

The Heart:
The human heart is about the size of a fist. The contraction phase of the heart is called the systole, and the relaxation phase is called the diastole. Four valves in the heart prevent backflow and keep blood moving in the correct direction. An Atrioventricular valve lies between each atrium and ventricle. Semilunar valves are located at the two exits of the heart: where the aorta leaves and the left ventricle.

Other Circulatory Systems:
Briefly explain the following:
  • Gastrovascular Systems: animals that lack a distinct circulatory system (found in hydras).
  • Open Circulatory system: the circulatory fluid, called hemolymph, is also the interstitial fluid (found in arthropods).
  • Single Circulation: The blood passes through the heart once in each complete circuit (found in bony fishes and sharks).
  • Different hearts: Amphibians (3-chambered heart); Reptiles (3-chambered heart).
Close the Power Point presentation.

Show summary video below. Note: Any information from the video that was NOT covered in class will NOT be exam material.

Switch gears to the "science in society" aspect of the course.

Science in Society:
Provide a brief introduction of the show and the clips.
“Dexter” is a psychological thriller television series which is simply genius! It is centered on Dexter Morgan who is a day-time forensic bloodstain pattern analyst and a night-time serial killer. So what does this have to do with Biology class? If you find an interest in studying blood in class, it is possible to study blood outside of class! Show the videos in order from left to right, one after the other. Emphasize that if anyone is uncomfortable watching blood videos or witnessing dead bodies, they may leave the room.
Provide a brief explanation of Dexter's job in our society.

Bloodstain pattern analysis (BPA) is a specialty in the field of forensic science. This job demonstrates how the applications of modern science have brought forensics to a higher level. New technologies, especially advances in DNA analysis are available for detectives and criminologists to use in solving crimes.The science of bloodstain pattern analysis applies scientific knowledge from other fields to solve practical problems. Bloodstain pattern analysis draws on the scientific disciplines of biology, chemistry, physics, and mathematics. Here are some of the following things a bloodstain pattern analyst may be able to determine conclusively and state as fact:
  • Movement and direction of persons or objects while they were shedding blood.
  • Position of persons or objects during bloodshed.
  • Movement of persons or objects after bloodshed.
  • The mechanism or object used to create a specific pattern.
  • The direction a stain was traveling when it was deposited.
  • The area of origin of an impact pattern.
  • The minimum number of impacts during an incident.
  • The sequence of events.

Hand out the crosswords and if there is time remaining at the end of class, allow the students to begin working on it in small groups.