21.2: The Cardiac Cycle - Biology

21.2: The Cardiac Cycle - Biology

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The main purpose of the heart is to pump blood through the body; it does so in a repeating sequence called the cardiac cycle. The cardiac cycle is the coordination of the filling and emptying of the heart of blood by electrical signals that cause the heart muscles to contract and relax. In each cardiac cycle, the heart contracts (systole), pushing out the blood and pumping it through the body; this is followed by a relaxation phase (diastole), where the heart fills with blood, as illustrated in Figure 1. Closing of the semilunar valves produces a monosyllabic “dup” sound.

The pumping of the heart is a function of the cardiac muscle cells, or cardiomyocytes, that make up the heart muscle. Cardiomyocytes, shown in Figure 2, are distinctive muscle cells that are striated like skeletal muscle but pump rhythmically and involuntarily like smooth muscle; they are connected by intercalated disks exclusive to cardiac muscle. They are self-stimulated for a period of time and isolated cardiomyocytes will beat if given the correct balance of nutrients and electrolytes.

The autonomous beating of cardiac muscle cells is regulated by the heart’s internal pacemaker that uses electrical signals to time the beating of the heart. The electrical signals and mechanical actions, illustrated in Figure 3, are intimately intertwined. The internal pacemaker starts at the sinoatrial (SA) node, which is located near the wall of the right atrium. Electrical charges spontaneously pulse from the SA node causing the two atria to contract in unison. The pulse reaches a second node, called the atrioventricular (AV) node, between the right atrium and right ventricle where it pauses for approximately 0.1 second before spreading to the walls of the ventricles. From the AV node, the electrical impulse enters the bundle of His, then to the left and right bundle branches extending through the interventricular septum. Finally, the Purkinje fibers conduct the impulse from the apex of the heart up the ventricular myocardium, and then the ventricles contract. This pause allows the atria to empty completely into the ventricles before the ventricles pump out the blood. The electrical impulses in the heart produce electrical currents that flow through the body and can be measured on the skin using electrodes. This information can be observed as an electrocardiogram (ECG)—a recording of the electrical impulses of the cardiac muscle.

Visit this site to see the heart’s “pacemaker” in action

21.2 Barrier Defenses and the Innate Immune Response

The immune system can be divided into two overlapping mechanisms to destroy pathogens: the innate immune response, which is relatively rapid but nonspecific and thus not always effective, and the adaptive immune response, which is slower in its development during an initial infection with a pathogen, but is highly specific and effective at attacking a wide variety of pathogens (Figure 21.2.1).

Figure 21.2.1 – Cooperation between Innate and Adaptive Immune Responses: The innate immune system enhances adaptive immune responses so they can be more effective

Any discussion of the innate immune response usually begins with the physical barriers that prevent pathogens from entering the body, destroy them after they enter, or flush them out before they can establish themselves in the hospitable environment of the body’s soft tissues. Barrier defenses are part of the body’s most basic defense mechanisms. The barrier defenses are not a response to infections, but they are continuously working to protect against a broad range of pathogens.

The different modes of barrier defenses are associated with the external surfaces of the body, where pathogens may try to enter (Table 21.2). The primary barrier to the entrance of microorganisms into the body is the skin. Not only is the skin covered with a layer of dead, keratinized epithelium that is too dry for bacteria in which to grow, but as these cells are continuously sloughed off from the skin, they carry bacteria and other pathogens with them. Additionally, sweat and other skin secretions may lower pH, contain toxic lipids, and physically wash microbes away.

Barrier Defenses (Table 21.2)
Site Specific defense Protective aspect
Skin Epidermal surface Keratinized cells of surface, Langerhans cells
Skin (sweat/secretions) Sweat glands, sebaceous glands Low pH, washing action
Oral cavity Salivary glands Lysozyme
Stomach Gastrointestinal tract Low pH
Mucosal surfaces Mucosal epithelium Nonkeratinized epithelial cells
Normal flora (nonpathogenic bacteria) Mucosal tissues Prevent pathogens from growing on mucosal surfaces

Another barrier is the saliva in the mouth, which is rich in lysozyme—an enzyme that destroys bacteria by digesting their cell walls. The acidic environment of the stomach, which is fatal to many pathogens, is also a barrier. Additionally, the mucus layer of the gastrointestinal tract, respiratory tract, reproductive tract, eyes, ears, and nose traps both microbes and debris, and facilitates their removal. In the case of the upper respiratory tract, ciliated epithelial cells move potentially contaminated mucus upwards to the mouth, where it is then swallowed into the digestive tract, ending up in the harsh acidic environment of the stomach. Considering how often you breathe compared to how often you eat or perform other activities that expose you to pathogens, it is not surprising that multiple barrier mechanisms have evolved to work in concert to protect this vital area.

Chapter 21. The Circulatory System

Figure 21.1. Just as highway systems transport people and goods through a complex network, the circulatory system transports nutrients, gases, and wastes throughout the animal body. (credit: modification of work by Andrey Belenko)


Most animals are complex multicellular organisms that require a mechanism for transporting nutrients throughout their bodies and removing waste products. The circulatory system has evolved over time from simple diffusion through cells in the early evolution of animals to a complex network of blood vessels that reach all parts of the human body. This extensive network supplies the cells, tissues, and organs with oxygen and nutrients, and removes carbon dioxide and waste, which are byproducts of respiration.

At the core of the human circulatory system is the heart. The size of a clenched fist, the human heart is protected beneath the rib cage. Made of specialized and unique cardiac muscle, it pumps blood throughout the body and to the heart itself. Heart contractions are driven by intrinsic electrical impulses that the brain and endocrine hormones help to regulate. Understanding the heart’s basic anatomy and function is important to understanding the body’s circulatory and respiratory systems.

Gas exchange is one essential function of the circulatory system. A circulatory system is not needed in organisms with no specialized respiratory organs because oxygen and carbon dioxide diffuse directly between their body tissues and the external environment. However, in organisms that possess lungs and gills, oxygen must be transported from these specialized respiratory organs to the body tissues via a circulatory system. Therefore, circulatory systems have had to evolve to accommodate the great diversity of body sizes and body types present among animals.

21.2: The Cardiac Cycle - Biology

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The heart beats rhythmically in a sequence called the Cardiac Cycle, a rapid coordination of contraction, systole, and relaxation, diastole. An electrical signal sent from the sinoatrial node, near the right atrial wall causes both atria to simultaneously contract and push blood into the ventricles.

When the pulse reaches the atrioventricular node between the right atrium and right ventricle, it pauses for approximately a 1/10th of a second which allows blood to completely empty from the atria.

The charge then spreads through the Bundle of His, down the intraventricular septum by way of the right and left bundle branches and then through the walls of the ventricles' Purkinje fibers inducing ventricular contraction and pumping blood out of the heart and into the pulmonary artery and aorta.

After the heart muscle relaxes, the atria fill with blood and the cycle is repeated.

22.7: The Cardiac Cycle

The heart beats rhythmically in a sequence called the cardiac cycle&mdasha rapid coordination of contraction (systole) and relaxation (diastole).

The Process

Electrical signals&mdashsent from the sinoatrial (SA) node in the right atrial wall to the atrioventricular (AV) node between the right atrium and right ventricle&mdashcause both atria to simultaneously contract. When the signal reaches the AV node, it pauses for approximately a tenth of a second, allowing the atria to contract and empty blood into the ventricles before they contract.

The electrical impulses are then conducted by the bundle of His and propagated to the left and right bundle branches. The signal is then conducted by Purkinje fibers in the ventricular walls, inducing ventricular contraction and pumping blood out of the heart.

During diastole (relaxation), the heart fills with blood, and the cycle is repeated.

Troiani, Diana, and Ermanno Manni. &ldquoThe Work by Giulio Ceradini in Explaining the Mechanism of Semilunar Cardiac Valve Function.&rdquo Advances in Physiology Education 35, no. 2 (June 1, 2011): 110&ndash13. [Source]

Ho, Ivan Shun. &ldquoVisualizing the Cardiac Cycle: A Useful Tool to Promote Student Understanding.&rdquo Journal of Microbiology & Biology Education : JMBE 12, no. 1 (May 19, 2011): 56&ndash58. [Source]

3.6 Cellular Differentiation

How does a complex organism such as a human develop from a single cell—a fertilized egg—into the vast array of cell types such as nerve cells, muscle cells, and epithelial cells that characterize the adult? Throughout development and adulthood, the process of cellular differentiation leads cells to assume their final morphology and physiology. Differentiation is the process by which unspecialized cells become specialized to carry out distinct functions.

A stem cell is an unspecialized cell that can divide without limit as needed and can, under specific conditions, differentiate into specialized cells. Stem cells are divided into several categories according to their potential to differentiate.

The first embryonic cells that arise from the division of the zygote are the ultimate stem cells these stems cells are described as totipotent because they have the potential to differentiate into any of the cells needed to enable an organism to grow and develop.

The embryonic cells that develop from totipotent stem cells and are precursors to the fundamental tissue layers of the embryo are classified as pluripotent. A pluripotent stem cell is one that has the potential to differentiate into any type of human tissue but cannot support the full development of an organism. These cells then become slightly more specialized, and are referred to as multipotent cells.

A multipotent stem cell has the potential to differentiate into different types of cells within a given cell lineage or small number of lineages, such as a red blood cell or white blood cell.

Finally, multipotent cells can become further specialized oligopotent cells. An oligopotent stem cell is limited to becoming one of a few different cell types. In contrast, a unipotent cell is fully specialized and can only reproduce to generate more of its own specific cell type.

Stem cells are unique in that they can also continually divide and regenerate new stem cells instead of further specializing. There are different stem cells present at different stages of a human’s life. They include the embryonic stem cells of the embryo, fetal stem cells of the fetus, and adult stem cells in the adult. One type of adult stem cell is the epithelial stem cell, which gives rise to the keratinocytes in the multiple layers of epithelial cells in the epidermis of skin. Adult bone marrow has three distinct types of stem cells: hematopoietic stem cells (which give rise to red blood cells, white blood cells, and platelets), endothelial stem cells (which give rise to the endothelial cell types that line blood and lymph vessels), and mesenchymal stem cells (which give rise to the different types of muscle cells).

The process of hematopoiesis involves the differentiation of multipotent cells into blood and immune cells. The multipotent hematopoietic stem cells give rise to many different cell types, including the cells of the immune system and red blood cells.


When a cell differentiates (becomes more specialized), it may undertake major changes in its size, shape, metabolic activity, and overall function. Since all cells in the body, beginning with the fertilized egg, contain the same DNA, how do the different cell types come to be so different? The answer is analogous to a movie script. The different actors in a movie all read from the same script, however, they are each only reading their own part of the script. Similarly, all cells contain the same full complement of DNA, but each type of cell only “reads” the portions of DNA that are relevant to its own function. In biology, this is referred to as the unique genetic expression of each cell.

In order for a cell to differentiate into its specialized form and function, it need only manipulate those genes (and thus those proteins) that will be expressed, and not those that will remain silent. The primary mechanism by which genes are turned “on” or “off” is through transcription factors.

While each body cell contains the organism’s entire genome, different cells regulate gene expression with the use of various transcription factors. Transcription factors are proteins that affect the binding of RNA polymerase to a particular gene on the DNA molecule.

Everyday Connection: Stem Cell Research

Stem cell research aims to find ways to use stem cells to regenerate and repair cellular damage. Over time, most adult cells undergo the wear and tear of aging and lose their ability to divide and repair themselves. Stem cells do not display a particular morphology or function. Adult stem cells, which exist as a small subset of cells in most tissues, keep dividing and can differentiate into a number of specialized cells generally formed by that tissue. These cells enable the body to renew and repair body tissues.

The mechanisms that induce a non-differentiated cell to become a specialized cell are poorly understood. In a laboratory setting, it is possible to induce stem cells to differentiate into specialized cells by changing the physical and chemical conditions of growth. Several sources of stem cells are used experimentally and are classified according to their origin and potential for differentiation. Human embryonic stem cells (hESCs) are extracted from embryos and are pluripotent. The adult stem cells that are present in many organs and differentiated tissues, such as bone marrow and skin, are multipotent, being limited in differentiation to the types of cells found in those tissues. The stem cells isolated from umbilical cord blood are also multipotent, as are cells from deciduous teeth (baby teeth). Researchers have recently developed induced pluripotent stem cells (iPSCs) from mouse and human adult stem cells. These cells are genetically reprogrammed multipotent adult cells that function like embryonic stem cells they are capable of generating cells characteristic of all three germ layers.

Because of their capacity to divide and differentiate into specialized cells, stem cells offer a potential treatment for diseases such as diabetes and heart disease (Figure 3.6.1). Cell-based therapy refers to treatment in which stem cells induced to differentiate in a growth dish are injected into a patient to repair damaged or destroyed cells or tissues. Many obstacles must be overcome for the application of cell-based therapy. Although embryonic stem cells have a nearly unlimited range of differentiation potential, they are seen as foreign by the patient’s immune system and may trigger rejection. Also, the destruction of embryos to isolate embryonic stem cells raises considerable ethical and legal questions.

Figure 3.6.1 – Stem Cells: The capacity of stem cells to differentiate into specialized cells make them potentially valuable in therapeutic applications designed to replace damaged cells of different body tissues.

In contrast, adult stem cells isolated from a patient are not seen as foreign by the body, but they have a limited range of differentiation. Some individuals bank the cord blood or deciduous teeth of their child, storing away those sources of stem cells for future use, should their child need it. Induced pluripotent stem cells are considered a promising advance in the field because using them avoids the legal, ethical, and immunological pitfalls of embryonic stem cells.

Chapter Review

One of the major areas of research in biology is of how cells specialize to assume their unique structures and functions, since all cells essentially originate from a single fertilized egg. Cell differentiation is the process of cells becoming specialized as their body develops. A stem cell is an unspecialized cell that can divide without limit as needed and can, under specific conditions, differentiate into specialized cells. Stem cells are divided into several categories according to their potential to differentiate. While all somatic cells contain the exact same genome, different cell types only express some of those genes at any given time. These differences in gene expression ultimately dictate a cell’s unique morphological and physiological characteristics. The primary mechanism that determines which genes will be expressed and which ones will not, is through the use of different transcription factor proteins, which bind to DNA and promote or hinder the transcription of different genes. Through the action of these transcription factors, cells specialize into one of hundreds of different cell types in the human body.

2.4 Inorganic Compounds Essential to Human Functioning

The concepts you have learned so far in this chapter govern all forms of matter, and would work as a foundation for geology as well as biology. This section of the chapter narrows the focus to the chemistry of human life that is, the compounds important for the body’s structure and function. In general, these compounds are either inorganic or organic.

  • An inorganic compound is a substance that does not contain both carbon and hydrogen. A great many inorganic compounds do contain hydrogen atoms, such as water (H2O) and the hydrochloric acid (HCl) produced by your stomach. In contrast, only a handful of inorganic compounds contain carbon atoms. Carbon dioxide (CO2) is one of the few examples.
  • An organic compound is a substance that contains both carbon and hydrogen. Organic compounds are synthesized via covalent bonds within living organisms, including the human body. Recall that carbon and hydrogen are the second and third most abundant elements in your body. You will soon discover how these two elements combine in the foods you eat, in the compounds that make up your body structure, and in the chemicals that fuel your functioning.

The following section examines the four groups of inorganic compounds essential to life: water, salts, acids, and bases. Organic compounds are covered later in the chapter.

As much as 70 percent of an adult’s body weight is water. This water is contained both within the cells and between the cells that make up tissues and organs. Its several roles make water indispensable to human functioning.

Water as a Lubricant and Cushion

Water is a major component of many of the body’s lubricating fluids. Just as oil lubricates the hinge on a door, water in synovial fluid lubricates the actions of body joints, and water in pleural fluid helps the lungs expand and recoil with breathing. Watery fluids help keep food flowing through the digestive tract, and ensure that the movement of adjacent abdominal organs is friction free.

Water also protects cells and organs from physical trauma, cushioning the brain within the skull, for example, and protecting the delicate nerve tissue of the eyes. Water cushions a developing fetus in the mother’s womb as well.

Water as a Heat Sink

A heat sink is a substance or object that absorbs and dissipates heat but does not experience a corresponding increase in temperature. In the body, water absorbs the heat generated by chemical reactions without greatly increasing in temperature. Moreover, when the environmental temperature soars, the water stored in the body helps keep the body cool. This cooling effect happens as warm blood from the body’s core flows to the blood vessels just under the skin and is transferred to the environment. At the same time, sweat glands release warm water in sweat. As the water evaporates into the air, it carries away heat, and then the cooler blood from the periphery circulates back to the body core.

Water as a Component of Liquid Mixtures

A mixture is a combination of two or more substances, each of which maintains its own chemical identity. In other words, the constituent substances are not chemically bonded into a new, larger chemical compound. The concept is easy to imagine if you think of powdery substances such as flour and sugar when you stir them together in a bowl, they obviously do not bond to form a new compound. The room air you breathe is a gaseous mixture, containing three discrete elements—nitrogen, oxygen, and argon—and one compound, carbon dioxide. There are three types of liquid mixtures, all of which contain water as a key component these are solutions, colloids, and suspensions.

For cells in the body to survive, they must be kept moist in a water-based liquid called a solution. In chemistry, a liquid solution consists of a solvent that dissolves a substance called a solute. An important characteristic of solutions is that they are homogeneous that is, the solute molecules are distributed evenly throughout the solution. If you were to stir a teaspoon of sugar into a glass of water, the sugar would dissolve into sugar molecules separated by water molecules. The ratio of sugar to water in the left side of the glass would be the same as the ratio of sugar to water in the right side of the glass. If you were to add more sugar, the ratio of sugar to water would change, but the distribution—provided you had stirred well—would still be even.

Water is considered the “universal solvent” and it is believed that life cannot exist without water because of this. Water is certainly the most abundant solvent in the body essentially all of the body’s chemical reactions occur among compounds dissolved in water. Since water molecules are polar, with regions of positive and negative electrical charge, water readily dissolves ionic compounds and polar covalent compounds. Such compounds are referred to as hydrophilic, or “water-loving.” As mentioned above, sugar dissolves well in water. This is because sugar molecules contain regions of hydrogen-oxygen polar bonds, making it hydrophilic. Nonpolar molecules, which do not readily dissolve in water, are called hydrophobic, or “water-fearing.”

Concentrations of Solutes

Various mixtures of solutes and water are described in chemistry. The concentration of a given solute is the number of particles of that solute in a given space (oxygen makes up about 21 percent of atmospheric air). In the bloodstream of humans, glucose concentration is usually measured in milligram (mg) per deciliter (dL), and in a healthy adult averages about 100 mg/dL. Another method of measuring the concentration of a solute is by its molarilty—which is moles (M) of the molecules per liter (L). The mole of an element is its atomic weight, while a mole of a compound is the sum of the atomic weights of its components, called the molecular weight. An often-used example is calculating a mole of glucose, with the chemical formula C6H12O6. Using the periodic table, the atomic weight of carbon (C) is 12.011 grams (g), and there are six carbons in glucose, for a total atomic weight of 72.066 g. Doing the same calculations for hydrogen (H) and oxygen (O), the molecular weight equals 180.156g (the “gram molecular weight” of glucose). When water is added to make one liter of solution, you have one mole (1M) of glucose. This is particularly useful in chemistry because of the relationship of moles to “Avogadro’s number.” A mole of any solution has the same number of particles in it: 6.02 × 10 23 . Many substances in the bloodstream and other tissue of the body are measured in thousandths of a mole, or millimoles (mM).

A colloid is a mixture that is somewhat like a heavy solution. The solute particles consist of tiny clumps of molecules large enough to make the liquid mixture opaque (because the particles are large enough to scatter light). Familiar examples of colloids are milk and cream. In the thyroid glands, the thyroid hormone is stored as a thick protein mixture also called a colloid.

A suspension is a liquid mixture in which a heavier substance is suspended temporarily in a liquid, but over time, settles out. This separation of particles from a suspension is called sedimentation. An example of sedimentation occurs in the blood test that establishes sedimentation rate, or sed rate. The test measures how quickly red blood cells in a test tube settle out of the watery portion of blood (known as plasma) over a set period of time. Rapid sedimentation of blood cells does not normally happen in the healthy body, but aspects of certain diseases can cause blood cells to clump together, and these heavy clumps of blood cells settle to the bottom of the test tube more quickly than do normal blood cells.

The Role of Water in Chemical Reactions

Two types of chemical reactions involve the creation or the consumption of water: dehydration synthesis and hydrolysis.

  • In dehydration synthesis, one reactant gives up an atom of hydrogen and another reactant gives up a hydroxyl group (OH) in the synthesis of a new product. In the formation of their covalent bond, a molecule of water is released as a byproduct (Figure 2.4.1). This is also sometimes referred to as a condensation reaction.
  • In hydrolysis, a molecule of water disrupts a compound, breaking its bonds. The water is itself split into H and OH. One portion of the severed compound then bonds with the hydrogen atom, and the other portion bonds with the hydroxyl group.

These reactions are reversible, and play an important role in the chemistry of organic compounds (which will be discussed shortly).

Figure 2.4.1 – Dehydration Synthesis and Hydrolysis: Monomers, the basic units for building larger molecules, form polymers (two or more chemically-bonded monomers). (a) In dehydration synthesis, two monomers are covalently bonded in a reaction in which one gives up a hydroxyl group and the other a hydrogen atom. A molecule of water is released as a byproduct during dehydration reactions. (b) In hydrolysis, the covalent bond between two monomers is split by the addition of a hydrogen atom to one and a hydroxyl group to the other, which requires the contribution of one molecule of water.

Recall that salts are formed when ions form ionic bonds. In these reactions, one atom gives up one or more electrons, and thus becomes positively charged, whereas the other accepts one or more electrons and becomes negatively charged. You can now define a salt as a substance that, when dissolved in water, dissociates into ions other than H + or OH – . This fact is important in distinguishing salts from acids and bases, discussed next.

A typical salt, NaCl, dissociates completely in water (Figure 2.4.2). The positive and negative regions on the water molecule (the hydrogen and oxygen ends respectively) attract the negative chloride and positive sodium ions, pulling them away from each other. Again, whereas nonpolar and polar covalently bonded compounds break apart into molecules in solution, salts dissociate into ions. These ions are electrolytes they are capable of conducting an electrical current in solution. This property is critical to the function of ions in transmitting nerve impulses and prompting muscle contraction.

Figure 2.4.2 – Dissociation of Sodium Chloride in Water: Notice that the crystals of sodium chloride dissociate not into molecules of NaCl, but into Na + cations and Cl – anions, each completely surrounded by water molecules.

Many other salts are important in the body. For example, bile salts produced by the liver help break apart dietary fats, and calcium phosphate salts form the mineral portion of teeth and bones.

Acids and Bases

Acids and bases, like salts, dissociate in water into electrolytes. Acids and bases can very much change the properties of the solutions in which they are dissolved.

An acid is a substance that releases hydrogen ions (H + ) in solution (Figure 2.4.3a). Because an atom of hydrogen has just one proton and one electron, a positively charged hydrogen ion is simply a proton. This solitary proton is highly likely to participate in chemical reactions. Strong acids are compounds that release all of their H+ in solution that is, they ionize completely. Hydrochloric acid (HCl), which is released from cells in the lining of the stomach, is a strong acid because it releases all of its H + in the stomach’s watery environment. This strong acid aids in digestion and kills ingested microbes. Weak acids do not ionize completely that is, some of their hydrogen ions remain bonded within a compound in solution. An example of a weak acid is vinegar, or acetic acid it is called acetate after it gives up a proton.

Figure 2.4.3Acids and Bases: (a) In aqueous solution, an acid dissociates into hydrogen ions (H + ) and anions. Nearly every molecule of a strong acid dissociates, producing a high concentration of H + . (b) In aqueous solution, a base dissociates into hydroxyl ions (OH – ) and cations. Nearly every molecule of a strong base dissociates, producing a high concentration of OH – .

A base is a substance that releases hydroxyl ions (OH – ) in solution, or one that accepts H+ already present in solution (see Figure 2.4.3b). The hydroxyl ions (also known as hydroxide ions) or other basic substances combine with H + present to form a water molecule, thereby removing H+ and reducing the solution’s acidity. Strong bases release most or all of their hydroxyl ions weak bases release only some hydroxyl ions or absorb only a few H + . Food mixed with hydrochloric acid from the stomach would burn the small intestine (the next portion of the digestive tract after the stomach), if it were not for the release of bicarbonate (HCO3 – ), a weak base that attracts H + . Bicarbonate accepts some of the H+ protons, thereby reducing the acidity of the solution.

The Concept of pH

The relative acidity or alkalinity of a solution can be indicated by its pH. A solution’s pH is the negative, base-10 logarithm of the hydrogen ion (H + ) concentration of the solution. As an example, a pH 4 solution has an H + concentration that is ten times greater than that of a pH 5 solution. That is, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5. The concept of pH will begin to make more sense when you study the pH scale, as shown in Figure 2.4.4. The scale consists of a series of increments ranging from 0 to 14. A solution with a pH of 7 is considered neutral—neither acidic nor basic. Pure water has a pH of 7. The lower the number below 7, the more acidic the solution, or the greater the concentration of H + . The concentration of hydrogen ions at each pH value is 10 times different than the next pH. For instance, a pH value of 4 corresponds to a proton concentration of 10 –4 M, or 0.0001M, while a pH value of 5 corresponds to a proton concentration of 10 –5 M, or 0.00001M. The higher the number above 7, the more basic (alkaline) the solution, or the lower the concentration of H + . Human urine, for example, is ten times more acidic than pure water, and HCl is 10,000,000 times more acidic than water.

Figure 2.4.4 The pH Scale

The pH of human blood normally ranges from 7.35 to 7.45, although it is typically identified as pH 7.4. At this slightly basic pH, blood can reduce the acidity resulting from the carbon dioxide (CO2) constantly being released into the bloodstream by the trillions of cells in the body. Homeostatic mechanisms (along with exhaling CO2 while breathing) normally keep the pH of blood within this narrow range. This is critical, because fluctuations—either too acidic or too alkaline—can lead to life-threatening disorders.

All cells of the body depend on homeostatic regulation of acid–base balance at a pH of approximately 7.4. The body therefore has several mechanisms for this regulation, involving breathing, the excretion of chemicals in urine, and the internal release of chemicals collectively called buffers into body fluids. A buffer is a solution of a weak acid and its conjugate base. A buffer can neutralize small amounts of acids or bases in body fluids. For example, if there is even a slight decrease below 7.35 in the pH of a bodily fluid, the buffer in the fluid—in this case, acting as a weak base—will bind the excess hydrogen ions. In contrast, if pH rises above 7.45, the buffer will act as a weak acid and contribute hydrogen ions.

Homeostatic Imbalances

The excessive acidity of acids and bases, of the blood, and other body fluids is known as acidosis. Common causes of acidosis are situations and disorders that reduce the effectiveness of breathing, especially the person’s ability to exhale fully, which causes a buildup of CO2 (and H + ) in the bloodstream. Acidosis can also be caused by metabolic problems that reduce the level or function of buffers that act as bases, or that promote the production of acids. For instance, with severe diarrhea, too much bicarbonate can be lost from the body, allowing acids to build up in body fluids. In people with poorly managed diabetes (ineffective regulation of blood sugar), acids called ketones are produced as a form of body fuel. These can build up in the blood, causing a serious condition called diabetic ketoacidosis. Kidney failure, liver failure, heart failure, cancer, and other disorders also can prompt metabolic acidosis.

In contrast, alkalosis is a condition in which the blood and other body fluids are too alkaline (basic). As with acidosis, respiratory disorders are a major cause however, in respiratory alkalosis, carbon dioxide levels fall too low. Lung disease, aspirin overdose, shock, and ordinary anxiety can cause respiratory alkalosis, which reduces the normal concentration of H + .

Metabolic alkalosis often results from prolonged, severe vomiting, which causes a loss of hydrogen and chloride ions (as components of HCl). Medications can also prompt alkalosis. These include diuretics that cause the body to lose potassium ions, as well as antacids when taken in excessive amounts, for instance by someone with persistent heartburn or an ulcer.

Chapter Review

Inorganic compounds essential to human functioning include water, salts, acids, and bases. These compounds are inorganic that is, they do not contain both hydrogen and carbon. Water is a lubricant and cushion, a heat sink, a component of liquid mixtures, a byproduct of dehydration synthesis reactions, and a reactant in hydrolysis reactions. Salts are compounds that, when dissolved in water, dissociate into ions other than H + or OH – . In contrast, acids release H + in solution, making it more acidic. Bases accept H + , thereby making the solution more alkaline (caustic).

Anatomy & Physiology

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Anatomy & Physiology Study Guide of 368 Table of Contents Chapter 1: Basic A a omical Terminology . 12 1.1 Superficial Anatomy . 13 1.2 Sectional Anatomy. 15 1.3 Chapter One Review . 18 Chapter 2: General Organization of the Body. 19 2.1 Hierarchy of Organization. 19 2.2 General Breakdown of Organ Systems . 20 2.3 Maintenance of the Internal Environment. 21 2.4 Chapter Two Review . 23 2.5 Chapter Two Practice Exam . 24 Chapter 3: Cellular Level of Organization. 25 3.1 Cell Structure. 25 3.2 Material Transport. 26 3.3 Cell Life Cycle. 31 3.4 Chapter Three Review . 32 3.5 Chapter Three Practice Exam . 35 Chapter 4: The Tissue Level of Organization. 36 4.1 Epithelial Tissue. 36 4.2 Connective Tissue. 39 4.3 Muscle Tissue . 41 4.4 Neural Tissue. 43 4.5 Tissue Repair . 43 4.6 Chapter Four Review. 44 4.7 Chapter Four Practice Exam. 48 Chapter 5: The Chemical Level of Organization . 49 5.1 Atoms. 49 5.2 Chemical Bonding. 50 5.3 Types of Chemical Reactions. 52 5.4 Electrolytes and Body Fluids . 52 5.5 Carbohydrates. 53 5.6 Lipids . 54 5.7 Proteins. 54 ©2018 Achieve Page 3

Anatomy & Physiology Study Guide of 368 5.8 DNA and RNA. 56 5.9 ATP. 57 5.10 Chapter Five Review. 58 5.11 Chapter Five Practice Exam . 61 Chapter 6: The Integumentary System . 62 6.1 The Cutaneous Membrane . 63 6.2 Accessory Structures. 66 6.3 Integumentary Injury and Repair . 69 6.4 Burns and Grafts . 70 6.5 Aging . 70 6.6 Chapter Six Review . 71 6.7 Chapter Six Practice Exam . 74 Chapter 7: Bone and Osseous Tissue . 75 7.1 Bone Classification . 75 7.2 Bone Structure . 76 7.3 Bone Composition . 76 7.4 Bone Types . 78 7.5 Bone Parts. 78 7.6 Bone Formation and Growth . 78 7.7 Fractures . 81 7.8 Aging . 81 7.9 Chapter Seven Review . 82 7.10 Chapter Seven Practice Exam. 84 Chapter 8: The Skeletal System. 85 8.1 Axial Skeleton. 85 8.2 Appendicular Skeleton . 89 8.3 Chapter Eight Review. 93 8.4 Chapter Eight Practice Exam. 96 Chapter 9: Joints and Articulations. 97 9.1 Classification of Joints. 97 9.2 Movement of Joints . 99 9.3 Types of Synovial Joints . 100 9.4 Intervertebral Discs . 101 9.5 Intervertebral Ligaments . 101 ©2018 Achieve Page 4

Anatomy & Physiology Study Guide of 368 9.6 Chapter Nine Review. 102 9.7 Chapter Nine Practice Exam. 104 Chapter 10: Muscle Tissue . 105 10.1 Skeletal Muscle. 105 10.2 Cardiac Muscle Tissue Structural Characteristics . 111 10.3 Smooth Muscle Tissue. 111 10.4 Chapter Ten Review. 113 10.5 Chapter Ten Practice Exam. 116 Chapter 11: The Muscular System . 118 11.1 Muscle Classification. 118 11.2 Levers. 119 11.3 Origins and Insertions. 119 11.4 Accessory Muscles . 119 11.5 Skeletal Muscle Names. 119 11.6 Aging. 120 11.7 Chapter Eleven Review. 121 11.8 Chapter Eleven Practice Exam. 123 Chapter 12: Structural Divisions of The Nervous System: Brain and Cranial Nerves . 124 12.1 Brain Regions and Landmarks. 125 12.2 Embryology of the Brain . 126 12.3 Ventricles of the Brain. 126 12.4 Protection and Support of the Brain . 127 12.5 The Blood Supply to the Brain. 128 12.6 The Cerebrum. 129 12.7 The Basal Nuclei . 129 12.8 Motor and Sensory Areas of the Cortex . 130 12.9 Association Areas. 130 12.10 Integrative Centers . 131 12.11 Brain Functions . 131 12.12 The Limbic System. 135 12.13 The Electroencephalogram (EEG) . 135 12.14 Cranial Nerves. 136 12.15 Chapter Twelve Review . 138 12.16 Chapter Twelve Practice Exam . 142 ©2018 Achieve Page 5

Anatomy & Physiology Study Guide of 368 Chapter 13: Neural Tissue. 143 13.1 Divisions of the Nervous System Structural . 143 13.2 Neurons. 144 13.3 Structure . 144 13.4 Structural Classification . 145 13.5 Functional Classification . 146 13.6 Neuroglia . 147 13.7 Transmembrane Potential . 148 13.8 Action Potential . 151 13.9 Synapses . 153 13.10 Neurotransmitters . 154 13.11 Neuromodulators . 154 13.12 Postsynaptic Potentials. 155 13.13 Chapter Thirteen Review . 155 13.14 Chapter Thirteen Practice Exam . 160 Chapter 14: Spinal Cord and Spinal Nerves . 161 14.1 Gross Anatomy of the Spinal Cord . 161 14.2 Spinal Meninges. 163 14.3 Gray and White Matter. 164 14.4 Anatomy of Spinal Nerves . 164 14.5 Neuronal Pools . 165 14.6 Reflexes . 166 14.7 Reinforcement and Inhibition. 168 14.8 Chapter Fourteen Review. 169 14.9 Chapter Fourteen Practice Exam. 172 Chapter 15: Functional Divisions of the Nervous System: Somatic and Autonomic Nervous System . 173 15.1 The Somatic Nervous System. 173 15.2 Levels of Processing and Motor Control. 174 15.3 The Autonomic Nervous System. 175 15.4 Higher Order Functions. 176 15.5 Aging. 178 15.6 Chapter Fifteen Review . 179 15.7 Chapter Fifteen Practice Exam . 183 Chapter 16: Senses . 184 ©2018 Achieve Page 6

Anatomy & Physiology Study Guide of 368 16.1 Sensory Receptors . 184 16.2 General Sensory Receptors . 186 16.3 Somatic Sensory Pathways . 187 16.4 Visceral Sensory Pathways . 188 16.5 Olfaction. 188 16.6 Gustation. 189 16.7 Sight . 189 16.8 Hearing and Balance . 196 16.9 Chapter Sixteen Review. 200 16.10 Chapter Sixteen Practice Exam. 205 Chapter 17: The Endocrine System . 206 17.1 Hormones. 206 17.2 Pituitary Gland . 209 17.3 Thyroid Gland. 211 17.4 Parathyroid Glands. 211 17.5 Suprarenal Glands. 211 17.6 The Pineal Gland. 213 17.7 Pancreas. 213 17.8 Secondary Endocrine Organs. 214 17.9 Cell Response to Hormones . 215 17.10 Role of Hormones in Growth . 215 17.11 The Alarm Phase. 216 17.12 The Effects of Hormones on Behavior . 216 17.13 Aging and Hormone Production. 216 17.14 Chapter Seventeen Review. 217 17.15 Chapter Seventeen Practice Exam. 221 Chapter 18: Blood . 222 18.1 Blood . 222 18.2 Characteristics of Blood. 222 18.3 Blood Composition . 222 18.4 Red Blood Cells. 224 18.5 White Blood Cells . 227 18.6 Platelets. 230 18.7 Hemostasis. 230 ©2018 Achieve Page 7

Anatomy & Physiology Study Guide of 368 18.8 Chapter Eighteen Review. 233 18.9 Chapter Eighteen Practice Exam. 236 Chapter 19: The Heart. 237 19.1 An Introduction to the Cardiovascular System. 237 19.2 The Pericardium. 237 19.3 Superficial Anatomy of the Heart . 237 19.4 Internal Anatomy and Organization. 240 19.5 The Blood Supply to the Heart. 243 19.6 Cardiac Physiology . 244 19.7 The Electrocardiogram . 246 19.8 The Action Potential in Cardiac Muscle Cells . 246 19.9 Cardiac Cycle. 247 19.10 Heart Sounds . 248 19.11 Hormones . 250 19.12 Chapter Nineteen Review . 251 19.13 Chapter Nineteen Practice Exam . 254 Chapter 20: Blood Vessels and Circulation . 255 20.1 Blood Vessels . 255 20.2 Arteries. 257 20.3 Capillaries. 258 20.4 Vasomotion. 259 20.5 Veins . 261 20.6 Venous Valves. 261 20.7 The Distribution of Blood . 261 20.8 Blood Pressure . 262 20.9 Autoregulation, Neural Mechanisms, and Endocrine Responses. 266 20.10 Vascular Supply to Special Regions . 267 20.11 Systemic Arteries. 269 20.12 Systemic Veins . 272 20.13 The Hepatic Portal System . 273 20.14 Placental Blood Supply. 274 20.15 Fetal Circulation in the Heart and Great Vessels. 274 20.16 Aging . 274 20.17 Chapter Twenty Review . 275 ©2018 Achieve Page 8

Anatomy & Physiology Study Guide of 368 20.18 Chapter Twenty Practice Exam . 279 Chapter 21: The Lymphatic System. 280 21.1 Anatomy. 280 21.2 Lymphatic Vessels . 280 21.3 Lymphocytes. 281 21.4 Lymphocyte Production. 281 21.5 Lymphoid Tissues . 281 21.6 Lymph Flow. 282 21.7 The Lymphatic System and Body Defenses. 284 21.8 Properties of Immunity . 287 21.9 Hormones of the Immune System. 289 21.10 Immune Disorders . 290 21.11 Aging . 290 21.12 Chapter Twenty-One Review. 290 21.13 Chapter Twenty-One Practice Exam. 295 Chapter 22: Respiratory System. 296 22.1 Functions of the Respiratory System. 296 22.2 Organization of the Respiratory System. 297 22.3 Upper Respiratory System . 297 22.4 Lower Respiratory System. 299 22.5 Respiration . 302 22.6 The Gas Laws . 306 22.7 The Respiratory Centers of the Brain . 307 22.8 Aging. 308 22.9 Chapter Twenty-Two Review . 308 22.10 Chapter Twenty-Two Practice Exam. 313 Chapter 23: The Digestive System . 314 23.1 Functions of the Digestive System . 314 23.2 The Digestive Organs and the Peritoneum. 314 23.3 The Movement of Digestive Materials. 315 23.4 Control of Digestive Functions . 316 23.5 The Oral Cavity. 316 23.6 The Pharynx . 318 23.7 The Esophagus . 318 ©2018 Achieve Page 9

Anatomy & Physiology Study Guide of 368 23.8 Stomach. 320 23.9 The Small Intestine. 321 23.10 Large Intestines. 321 23.11 The Rectum . 322 23.12 Secondary Digestive Organs . 322 23.13 Digestion . 323 23.14 Nutrition. 324 23.15 Aging . 324 23.16 Chapter Twenty-Three Review. 325 23.17 Chapter Twenty-Three Practice Exam. 330 Chapter 24: The Urinary System . 331 24.1 The Kidneys. 331 24.2 Internal Structure of Kidneys. 332 24.3 Tubular Transport Factors. 334 24.4 Transport of Specific Substances. 334 24.5 Diuresis . 335 24.6 Hormonal Involvement. 335 24.7 Aging. 336 24.8 Chapter Twenty-Four Review. 336 24.9 Chapter Twenty-Four Practice Exam. 337 Chapter 25: The Reproductive System. 338 25.1 Male Reproductive System. 338 25.2 Spermatogenesis . 340 25.3 The Male Reproductive Tract. 341 25.4 Hormones and Male Reproductive Function. 343 25.5 Female Reproductive System. 344 25.6 The Uterus. 346 25.7 Hormones and the Female Reproductive Cycle. 348 25.8 Sexual Function. 349 25.9 Aging. 350 25.10 Chapter Twenty-Five Review . 350 25.11 Chapter Twenty-Five Practice Exam . 353 Chapter 26: Development and Inheritance . 354 26.1 Prenatal . 354 ©2018 Achieve Page 10

21.2: The Cardiac Cycle - Biology

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Biology is the scientific study of life. And all living organisms share a few key characteristics. The biological world has a highly organized, and complex structure.

From molecules inside each cell to the organ systems that make up an organism's body. Organisms can reproduce to create offspring, and their inherited genetic material provide special instructions for growth and development. They can also react to the environment, for example, in a desert, by burrowing during the day to keep cool.

All of these internal and external processes are highly regulated. For instance, the cardiovascular system controls blood and heat flow in the ears of a desert hare, and is powered by chemical energy from food that is transformed into kinetic energy to perform work, like running away from predators. This combination of environmental interactions and genetics allows populations to adapt to their changing environments and evolve, as is the case with long ears and slim bodies in response to the desert heat. And short ears and large bodies to acclimate to the Arctic cold.

1.1: What is Biology?


Biology is the natural science that focuses on the study of life and living organisms, including their structure, function, development, interactions, evolution, distribution, and taxonomy. The scope of the field is extensive and is divided into several specialized disciplines, such as anatomy, physiology, ethology, genetics, and many more.

All living things share a few key traits: cellular organization, heritable genetic material and the ability to adapt/evolve, metabolism to regulate energy needs, the ability to interact with the environment, maintain homeostasis, reproduce, and the ability to grow and change.

The Complexity of Life

Despite its complexity, life is organized and structured. The cell theory in biology states that all living organisms are composed of one or more cells. The cell is the basic unit of life, and all cells arise from previously existing cells. Even single-celled organisms, such as bacteria, have structures that allow them to carry out essential functions, such as interacting with the environment and carry out chemical reactions that maintain life, or metabolism. In multicellular organisms, cells work together to form tissues, organs, organ systems, and finally, entire organisms. This hierarchical organization can extend further into populations, communities, ecosystems, and the biosphere.

Genetics and Adaptation

An organism&rsquos genetic material, the biological &ldquoblueprints&rdquo encoded in their DNA, is passed down to their offspring. Over the course of several generations, the genetic material is shaped by the biotic (living) and abiotic (non-living) environment. This process is called adaptation. Offspring of well-adapted parents have a high likelihood to survive in conditions that are similar to those that their parents lived in.

The process in which inherited traits increase survival and reproduction is called natural selection. Natural selection is the central mechanism of evolution. For example, some kangaroo rats live in hot and dry areas with little rainfall. To avoid the blistering heat and conserve water, they burrow into the soil where it is cooler and lower their metabolic rate to slow down evaporation. In this way, the kangaroo rat&rsquos genetics&mdashencoding this behavior and passed down through generations&mdashenables the animal to survive in such extreme environmental conditions.

Environmental Interactions

Organisms must also be able to successfully interact with their environment. This includes being able to navigate the world around them in search of resources or potential mates but also includes regulating their internal environments. Homeostasis is the ability of an organism to keep steady internal conditions. For example, humans maintain constant body temperature. If they get cold, they shiver if they are too hot, they start to sweat. Living things also maintain metabolism&mdashthe chemical processes that regulate energy needs. For instance, plants convert sunlight into sugar and store chemical energy in adenosine triphosphate.

Building Upwards from Basic Tenets

While &ldquoWhat is biology?&rdquo and &ldquoWhat is life&rdquo may seem like basic questions, they are important to understand and are prerequisites to asking more complicated questions. For example, without understanding the basic tenets of life&mdashsuch as how cells divide and replicate&mdashit would be difficult to investigate what causes cancer. This knowledge also allows scientist to develop the required tools and methods to study biological processes.

Forterre, Patrick. &ldquoDefining Life: The Virus Viewpoint.&rdquo Origins of Life and Evolution of the Biosphere 40, no. 2 (April 2010): 151&ndash60. [Source]

3.0 Introduction

Figure 3.0 – Fluorescence-stained Cell Undergoing Mitosis: A lung cell from a newt, commonly studied for its similarity to human lung cells, is stained with fluorescent dyes. The green stain reveals mitotic spindles, red is the cell membrane and part of the cytoplasm, and the structures that appear light blue are chromosomes. This cell is in anaphase of mitosis. (credit: “Mortadelo2005”/Wikimedia Commons)

Chapter Objectives

After studying this chapter, you will be able to:

  • Describe the structure and function of the cell membrane, including its regulation of materials into and out of the cell
  • Describe the functions of the various cytoplasmic organelles
  • List the morphological and physiological characteristics of some representative cell types in the human body
  • Explain the structure and contents of the nucleus, as well as the process of DNA replication
  • Explain the process by which a cell builds proteins using the DNA code
  • List the stages of the cell cycle in order, including the steps of cell division in somatic cells
  • Discuss how a cell differentiates and becomes more specialized

You developed from a single fertilized egg cell into the complex organism that you see when you look in a mirror, containing trillions of cells. During this developmental process, early, unspecialized cells become specialized in their structure and function (this is known as differentiation). These different cell types join to form specialized tissues that work in concert to perform all of the functions necessary for the living organism. Cellular and developmental biologists study how the continued division of a single cell leads to such complexity and differentiation.

Consider the difference between a structural cell in the skin and a nerve cell. A structural skin cell may be shaped like a flat plate (squamous) and live only for a short time before it is shed and replaced. Packed tightly into rows and sheets, the squamous skin cells provide a protective barrier for the cells and tissues that lie beneath. A nerve cell, on the other hand, may be shaped something like a star, sending out long processes up to a meter in length and may live for the entire lifetime of the organism. With their long winding appendages, nerve cells can communicate with one another and with other types of body cells and send rapid signals that inform the organism about its environment and allow it to interact with that environment. These differences illustrate one very important theme that is consistent at all organizational levels of biology: the form of a structure is optimally suited to perform particular functions assigned to that structure. Keep this theme in mind as you tour the inside of a cell and are introduced to the various types of cells in the body.

A primary responsibility of each cell is to contribute to homeostasis. Homeostasis is a term used in biology that refers to a dynamic state of balance within parameters that are compatible with life. For example, living cells require a water-based environment to survive in, and there are various physical (anatomical) and physiological mechanisms that keep all of the trillions of living cells in the human body moist. This is one aspect of homeostasis. When a particular parameter, such as blood pressure or blood oxygen content, moves far enough out of homeostasis (generally becoming too high or too low), illness or disease—and sometimes death—inevitably results.

The concept of a cell started with microscopic observations of dead cork tissue by scientist Robert Hooke in 1665. Without realizing their function or importance, Hooke coined the term “cell” based on the resemblance of the small subdivisions in the cork to the rooms that monks inhabited, called cells. About ten years later, Antonie van Leeuwenhoek became the first person to observe living and moving cells under a microscope. In the century that followed, the theory that cells represented the basic unit of life would develop. These tiny fluid-filled sacs house components responsible for the thousands of biochemical reactions necessary for an organism to grow and survive. In this chapter, you will learn about the major components and functions of cells and discover some of the different types of cells in the human body.

Watch the video: Cardiac cycle, stages, physiology, Diastole and systole in the cardiac cycle. (May 2022).