Unit 21: Circulation & Respiration

Helpful web sites and diagrams:

Human heart structure
Heart pacemaker system
Heart pacemaker system
Blood cell types
Blood clotting cascade Don't get bogged down in "factors" details; note role of Ca.

All living organisms must acquire energy and nutrients from their environment. For plants and other autotrophs that source of energy is sunlight. Animals, fungi, and other heterotrophic organisms depend consuming complex food that comes directly or indirectly from autotrophs. Regardless of their source of energy and nutrients, as organisms get larger and more complex this task of delivering nutrients to their cells becomes increasingly difficult. In part, this challenge has been met by the evolution of circulatory systems that transport nutrients throughout the body of the organism and respiratory systems that bring oxygen into the body and remove CO₂. We study these two systems together because they are so closely related both in terms of their structure and  function as well as their evolutionary history.

 

Honors and AP students will study the circulatory and respiratory systems of animals in this unit. AP students will also study the analogous transport systems of higher plants in Unit 22.

 

Learning Objectives: Successful students will be able to ...

 

• outline the basic functions of the circulatory and respiratory systems and give specific examples of these functions.
• explain the differences between open and closed circulatory systems and describe specific examples of each.
• name the basic components of blood and describe the functions of each including the three major cell types.
• compare the basic structure and function of arteries, veins, capillaries, and lymphatic vessels.
• describe in detail the pathway of circulation and the structures of the heart in a typical fish, amphibian, reptile, mammal, and bird.
• explain the anatomical and functional relationships of the circulation pathways in these animals to their respiratory organs.
• outline the events of the cardiac cycle and their relationship to blood pressure, the ECG, and the intrinsic and extrinsic control of heart rate and stroke volume.
• describe the various respiratory structures found in insects, fish, amphibians, and terrestrial vertebrates.
• use Fick's Law of Diffusion to analyze the structure and function of respiratory surfaces.
• compare the mechanisms of respiration in mammals and birds and relate the differences to the behavior and energy needs of these two groups of vertebrates.
• describe the role of the nervous system in controlling respiration.

 

Lesson One: Circulatory and Respiratory Systems.

Go to the Clinton Community College web site and read the sections down through "Closed Circulatory Systems." Focus on the types of circulatory systems, their functions, and examples of animal types with open vs closed systems. There is a very nice diagram in this reading showing the relationship of the circulatory system to the other organ systems. This should give you a better idea of the many functions of the circulatory system.

Now go to the Human Circulatory System web site and read the introductory pages: Blood Vascular System, Types of Blood Vascular Systems, and Differences Between Open and Closed Circulatory System. Become familiar with the basic vocabulary describing the types of circulatory systems and their various structures. In particular, pay attention to the differences between open and closed systems and their anatomical and physiological characteristics.

Homework, Due . Go to Bill Tietjen's pages at Bellarmine University and use the information you will find there to answer the following questions and email them using your Fontbonne account.

 

1. Do all animals have a circulatory system? Explain why some animals might be able to do fine without one. Give two specific examples.
2. Scroll down to the block diagram of the "Two-Chambered Hearts." The top diagram is of an open circulatory system found in land snails and the bottom diagram is of a closed system such found in squids. The blue areas represent structures containing deoxygenated (low O₂ concentration) blood and the red areas are structures containing oxygenated blood. The yellow circles with the arrows are meant to indicate the blood pressure.  What is the single most significant anatomical difference between these two systems?
3. Compare the blood pressure as it circulates through the two systems. Where in the circulation pathway is the pressure similar and where is it markedly different?
4. Keep in mind that the capillaries are located in the organs (e.g. muscles, intestines, brain, etc). How do the pressure differences affect the flow of blood (and therefore oxygen and nutrients) into the cells of these organs?

 

 

Lesson Two: Blood and Oxygen Transport.

Animals that have a circulatory system have either blood (in closed systems) or hemolymph (in open systems). Hemolymph is simply the extracellular fluid that surrounds tissues and organs. This fluid is carried throughout the body by the blood vessels and then bathes the organs before reentering the blood vessels. Blood on the other hand, is contained within the blood vessels (for the most part) and is brought into close, but not direct, contain with the tissues and organs.

Go to the Kimball pages on blood and read the entire section. Understand the difference between plasma and blood. Be able to name, describe, and recognize the three major types of blood cells. There are many types of white blood cells; don't worry about distinguishing among these. Use diagram of the blood cell "family tree" to appreciate how the three types of blood cells and lymphocytes originate from stem cells and the platelets and red blood cells belong to a separate branch of the family from the white blood cells.

 

• Red blood cells: be able to describe their development, the general structure of hemoglobin (alpha, beta, heme group), and the general role of rbc's in oxygen/carbon dioxide transport. Be sure you can describe the role of temperature and pH in the affinity of hemoglobin and oxygen gas. Understand the role of bicarbonate ions in the transport of CO₂.
• White blood cells: Be able to compare these cells to rbc's (size, presence of nucleus, function). Be able to give specific examples of their role in the immune system (immunity, phagocytosis, etc.).
• Platelets: Compare these to the other types of blood cells (size, nucleus, etc.). Be able to give a general description of their function in blood clotting (more on this in an other lesson).

 

Homework, Due . Go to the Interactive Oxyhemoglobin Dissociation Curve site. This web page demonstrates the relationship between the amount of oxygen available in the lungs (partial pressure of oxygen gas) and the amount of oxygen bound to the hemoglobin molecules in the red blood cells. Read the first four section listed in the "Contents" to become familiar with the terms, factors that influence the affinity of hemoglobin for oxygen, and how to interpret the dissociation graph. Once you have done that, go to the interactive tool and use it to answer the following questions. Email your answers using your Fontbonne account.

Notice that you can manipulate a variety of factors including body temperature, pH, CO₂ and O₂ partial pressures. The default values are for a "normal adult." Click on reset before entering new numbers.

 

1. Start with temperature. Normal body temperature is 37 C. Give your patient a fever of 39 C and then 41 C. What happens to the dissociation curve? Pay particular attention to the P50 since this is a standard measure of O₂ affinity. Does a fever make it harder or easier to deliver oxygenated blood to tissue? Explain your answers.
2. If you hold your breath, CO₂ builds up in your blood and lowers the pH. What happens to the P50 as pH drops? Do some research and explain the function of the aortic and carotid bodies in relationship to blood pH. How do these structures insure that you cannot hold your breath for more than a minute or two? Explain your answers. PS: Partial pressures can be measured in mm Hg (millimeters of mercury) or in KPa (kilopascals). You can use either unit with this program, just be sure you have set the correct unit to match your numbers.
3. Climb Mount Everest. Do some research and find the partial pressure of O₂ at the summit. Use this number as a rough estimate of PaO₂ (pressure of O₂ in the lungs, not the external atmosphere). How does the dissociation curve show why it is so difficult to survive at high altitudes without additional oxygen? Again, watch your units. Suggest why people and other animals living at high altitudes can cope with this problem and why some athletes "blood dope" to enhance their performance.

 

Lesson Three: Comparative Heart Anatomy.

Go to Kimball and read the sections dealing with the heart structure/function of a variety of vertebrate animals. Pay particular attention to the flow of blood into the ventricles and how oxygenated blood from the lungs or gills is separated (or not) from the systemic deoxygenated blood returning from the organ systems (muscles, liver, intestines, brain, etc.).

Return to Bill Tietjen's page and scroll down to the diagrams of the circulatory systems of a typical fish, lungfish, and mammal and bird. Again, the blue blood vessels carry deoxygenated blood and the red vessels carry oxygenated blood. Study the diagram of the fish circulatory system and notice the relationship of the two chambered heart to the gills. The strongest pumping chamber of the heart (ventricle) functions to move blood through the narrow capillaries of the gills where it picks up oxygen and then move the blood to the organs of the body. The other chamber (atrium) receives deoxygenated blood from the body and pumps it into the ventricle.

Compare this very simple circular movement to the system in lungfish. Lungfish are remarkable fish that have lungs in addition to gills. They are found in Africa, South America, and Australia. They often hibernate in dried up ponds by borrowing deep into the mud. Look closely at the diagram. What does the addition of lungs do to the structure of the heart. Consider which of the two atria (right or left) corresponds to the single atrium of the more typical fish. In the typical fish, the ventricle pumps deoxygenated blood to the gills. How does this pattern change in the lungfish?

Finally, scroll down to the diagram of the mammal/bird heart. Here you see a four chambered/two separate pump style heart. Think about how this arrangement is much more efficient at delivering highly oxygenated blood to the organs of the body compared to the lungfish (and amphibians). Below this diagram is a more realistic diagram of a human heart with an outline of blood flow through the heart/organs (systemic) and lungs (pulmonary). You need to know this flow pattern.

Homework, Due . Answer the following questions and email the results using your Fontbonne account.

 

1. Lungfish were used as examples of how our ancient fish ancestors could have evolved into terrestrial tetrapods. Do a little research and find what features lungfish have in addition to lungs to justify this hypothesis.
2. If you were a drop of blood sitting in the left atrium, list the structures you would travel through (including lungs and systemic organs) that you would pass through (or by in the case of the valves) before you returned to the left atrium.
3. It is not too much of an exaggeration to say that mammals have two hearts working in parallel. Describe the general organization and flow of blood in mammalian circulation that justifies this description. How are the "two" hearts interdependent on one another?
4. What is the "septum" of a vertebrate heart? Describe its function and how this function varies in amphibians, lizards, and mammals. Why don't most fish have a septum in their heart?

African lungfish from Fish Index.

 

 

 

 

 

 

 

 

Lesson Four: Control of the Cardiac Cycle.

One of the characteristics of cardiac muscle tissue is the ability to contract rhythmically without external stimulation. For most vertebrates this intrinsic contractile activity is insufficient to meet the circulatory needs of the animal. The cycle of contraction in the human heart is regulated by a complex set of intrinsic and extrinsic mechanisms.

Go to the Kimball pages for a very brief introduction to become familiar with the basic terminology and important structures in the heart (the "pacemakers") and the nerves that influence  heart rate. No go back to Tietjen's page and find the corresponding diagrams of the human heart showing the details of the pacemaker system. Below this diagram is a simple animation showing the flow of electrical stimulation in the pacemaker system throughout the heart. You need to know these structures and the flow of stimulation starting from the sinoatrial node to the four chambers of the heart (the interventricular bundle is often called the Bundle of His). Keep in mind that although the tissue of the pacemaker system functions as if it were nervous tissue, it is actually modified cardiac muscle tissue. This page provides a good outline of the major events of the pacemakers during the cardiac cycle. And these pages from the Texas Heart Institute have a very good summary of this material.

Homework, Due . Read the instructions and email your answers using your Fontbonne account.

When muscle cells contract (really when any cell contracts) they generate an electrical potential that can be measured. This property of cells has been widely used to monitory the activity of the heart using the electrocardiogram (ECG or EKG). Deviations from the normal pattern can be used to diagnose potential heart diseases or congenital defects. Go to Get Body Smart to view this animation of a normal ECG. Be sure you understand what cardiac activity corresponds to the various waves of the ECG, P, Q, R, S, T. This is another nice animation of an ECG although it has little explanatory text with it. It is most helpful when you run the animation step by step rather than continuously.

Now visit the Six Second ECG Simulator. This site shows various ECG patterns including a normal ECG (sinus rhythm) and several abnormal ECGs.

 

1. How do you recognized a sinus arrhythmia and what do the changes in the ECG represent in terms of the function of the pacemaker system and heart chambers?
2. Same question for atrial fibrillation.
3. Same question of sinus arrest.
4. In addition to the intrinsic pacemakers, cardiac activity is influenced by several nerves. Name them and describe their effect on the heart.

 

Lesson Five: Gills, Lungs, and Gas Exchange.

There's not much point of circulating blood throughout the body if it does not have access to some form of respiratory organ where the blood tissue can take up oxygen and release toxic gases such as carbon dioxide. Animals have a wide variety of respiratory structures; we will focus on the gills of fish and the lungs of mammals and birds. Go to these Kimball pages to study the organization of the respiratory organs in insects, fish, amphibians, reptiles, birds, and mammals. Note that the tracheal system of insects is not found in many other arthropods; spiders have something called book lungs and aquatic insects and crustaceans have gills on various parts of their body. Appreciate the limitations of the gill system in fish in terms of its ability to deliver high oxygen pressure in both the lungs and the systemic organs. Consider how the addition of more chambers of the heart address this problem in tetrapods. Although the basic organization of the respiratory systems in amphibians, reptiles, birds, and mammals is the same, each group has its unique features (e.g. air sacs in birds, diaphragm in mammals). Understand these differences and their functions.

Now return to Tietjen's pages and scroll down to near the bottom and find the diagrams of blood/water flow through the gill arches of fish. Find the diagrams labeled "countercurrent" and "concurrent." What is the directional relationship between blood flow and water flow in these two alternative arrangements? Carefully study the diagrams showing the percent oxygen saturation in the external water vs the blood moving through the gills. Be sure you understand why the countercurrent arrangement is found in fish. Countercurrent flow systems are found in many other situations including your kidneys and the flippers of arctic mammals such as seals. Further down on this page are good diagrams of the human and bird respiratory systems. Go to the Online Biology text and the BiologyGuide for another review of this material and some excellent diagrams.

Finally use the Online Biology text to study the structures of the human respiratory system. Be sure you can identify the various structures. Be sure to understand the relationship between the capillaries of the circulatory system and the alveoli of the lungs. Use the diagrams and text to understand the structures involved in the exchange of oxygen and carbon dioxide in the alveoli. Pay particular attention to the role of diffusion, the partial pressures of O₂ and CO₂, hemoglobin, and bicarbonate and chloride ions.

Homework, Due . Follow the instructions below and email your answers using your Fontbonne account.

The rate of diffusion of gas (e.g. O₂ or CO₂) across a membrane can be approximated by Fick's Law which states that the rate of diffusion is directly proportional to the surface area (of the alveoli in the lungs) and the difference in  concentrations of the diffusing gas (partial pressure of oxygen or carbon dioxide, pO₂ or pCO₂) and inversely proportional to the distance the gas must travel (the thickness of the capillary and alveolar cell membranes). Describe how the following elements of gas exchange in the alveoli can be related to Fick's Law.

 

1. The binding of oxygen to hemoglobin as the oxygen diffuses into the red blood cells.
2. The countercurrent flow of water and blood in the gills of fish.
3. The one way movement of gases in birds because of the presence of air sacs in addition to the lungs.
4. The binding of CO₂ with H₂O to form bicarbonate ions in the red blood cells as CO₂ moves from the cells of organs into the capillaries.
5. The large number of alveoli in the lungs.

Basking Shark at the Houston Museum of Natural History.