CoverModule 1.0. Homeostasis, Membranes, Electrophysiology and ANS1.1. Homeostasis1.1.1. Homeostasis Defined1.1.2. Homeostatic Control Systems1.1.3. Feedback Response Loop1.2. Cell Transport; Water & Solutes1.2.1. Fluid Compartments1.2.2. Osmosis1.2.3. Diffusion of Solutes1.2.4. Active Transport1.2.5. Bulk Transport1.3. Electrophysiology1.3.1. Ions and Cell Membranes1.3.2. Membrane Potentials1.3.3. Graded Potential1.3.4. Action Potentials1.3.5. Refractory Periods1.3.6. Propagation of an Action Potential1.4. The Synapse1.5. The Autonomic Nervous System1.5.1. Organization of the Nervous System1.5.2. Structural Organization of the ANS1.5.3. The SNS and the PNS1.5.4. The Enteric Nervous System1.5.5. Physiology of the ANS1.5.6. Neurotransmitters of the ANS1.5.7. Receptors of the ANS1.5.8. Actions of the Autonomic Nervous System1.5.9. Table of Actions for the SNS and PNS and Some Common DrugsModule 2.0. Skeletal Muscle and Special Senses2.1. Structural Organization of Skeletal Muscle2.2.1. Neuromuscular Junction, Excitation-Contraction Coupling2.2.2. Muscle Contractures and Cramps2.3. Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology2.3.1. Motor Units2.3.2. Factors that Influence the Force of Contraction2.3.2. Factors that Influence the Force of Muscle Contraction2.3.3. Energy Source for Muscle Contraction2.3.4. Skeletal Muscle Fiber Types2.3.5. Fatigue2.3.6. Muscle Pharmacology2.4. Smooth Muscle2.4.1. Smooth Muscle Contraction2.5. Control of Body Movement2.5.1. Voluntary Control of Muscle2.5.2. Reflexes2.6. Taste and Smell2.6.1. Taste2.6.2. The Sense of Smell2.7. Vision2.7.1. Structure of the Eye2.7.2. Focusing Light on the Retina2.7.3. Converting Light to Action Potentials2.7.4. The Retina2.7.5. Phototransduction2.7.6. Receptive Fields2.8. Hearing and Equilibrium2.8.1. The Nature of Sound2.8.2. The Hearing Apparatus2.8.3. Sound Vibrations to Action Potentials2.8.4. The Sense of Balance and EquilibriumModule 3.0. Cardiovascular System3.1. Structure of the Heart3.1.1. Chambers and Circulation3.2. Cardiac Cell Action Potentials3.2.1. Action Potentials in Cardiac Muscle Cells3.2.2. Action Potentials in Cardiac Autorhythmic cells3.2.3. Cellular Mechanisms of Inotropy and Chronotropy3.3. Electrophysiology of Heart Muscle3.3.1. Heart Conduction System3.3.2. Electrocardiogram (ECG)3.3.3. Abnormal ECG - Current of Injury3.4. The Cardiac Cycle3.4.1. Cardiac cycle3.4.2. Cardiac Measurements and Pressure Volume Loops3.5. Blood vessels and Blood Pressure3.5.1. Arteries and Veins3.5.2. Capillaries3.5.3. Blood Pressure Regulation and Shock3.5.4. Capillary Exchange3.5.5. Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation3.6. Blood3.6.1. Composition of Blood3.6.2. Hematopoeisis3.6.3. Breaking Down Red Blood Cells3.6.4. HemostasisModule 4.0. Urinary and Respiratory Systems4.1. Function and Structure of the Kidney4.1.1. Urinary System Function4.1.2. Functional Anatomy of the Urinary System4.1.3. The Nephron: Functional Unit of the Kidney4.1.4. The Renal Corpuscle: Bowman's Capsule4.2. Physiology of Urine Production4.2.1. Filtration4.2.2. Renal Clearance4.2.3. Tubular Reabsorption4.2.4. Urine Concentration and Dilution4.2.5. Hormonal Regulation of Urine Production4.3. Acid/Base Balance4.3.1. Buffers4.3.2. Acid/Base Disturbances4.4. The Respiratory System4.4.1. Respiratory System Structure and Function4.4.2. Respiratory Membrane4.4.3. Respiratory pressures and Inspriation/Expiration4.4.4. Alveoli and Surfactant4.4.5. Pneumothorax4.4.6. Pressure-Volume Loops and the Work of Breathing4.5. Gas Exchange and Transport4.5.1. Gas Laws4.5.2. Partial Pressure Gradients in the Lung4.5.3. Alveolar Gas Equation4.5.4. Oxygen and Carbon Dioxide Transport in the Blood4.5.5. Alveolar Ventilation4.5.6. Ventilation/Perfusion Ratio4.6. Chronic Bronchitis and Emphysema4.6.1. Respiratory Control by the Medulla Oblongata4.6.2. Chemicals that Regulate VentilationModule 5.0. Digestive, Endocrine and Reproductive Systems5.1. Functional Anatomy of the Digestive System5.1.1. Layers of the Digestive Tract5.1.2. Enteric Nervous System5.1.3. Organs of the Digestive System5.2. Digestion5.2.1. Carbohydrates5.2.2. Proteins5.2.3. Lipids5.2.4. Lipoproteins5.3. Regulation of Digestive Secretions5.4. Endocrine System5.4.1. Overview of the Endocrine System5.4.2. Hormone Receptors5.4.3. Hormones of the Body5.4.4. Other Hormones: Melatonin and Pheromones5.5. The Hypothalamus and Pituitary Gland5.5.1. Structure and Function of the Hypothalamus and Pituitary Gland5.5.2. The Posterior Pituitary5.5.3. The Anterior Pituitary5.5.4. Growth Hormone5.5.5. Prolactin5.5.6. Thyroid Hormones5.5.7. Adrenal Hormones5.6. Pancreas5.6.1. Insulin and Glucagon5.6.2. Diabetes Mellitus5.7. Reproductive System Anatomy5.7.1. Female Reproductive Anatomy5.7.2. Male Reproductive Anatomy5.7.3. Sexual Development at Puberty5.7.4. Male Reproductive Endocrine Axis5.7.5. Spermatogenesis5.7.6. Female Reproductive System: Oogenesis5.7.7. Ovulation and Fertilization5.7.8. The Ovarian Cycle5.7.9. The Uterine Cycle5.7.10. PregnancyAppendix A. GenderAppendix B. The Placebo EffectB.2.1. The Placebo EffectB.2.2. Examples of the Placebo EffectB.2.3. How do Placebos Work?B.2.4. Are Placebos Ethical?B.2.5. How do we validate actual effectiveness of placebosB.2.6. Tips for evaluating scientific evidenceB.2.7. What about Faith Healings

Chambers and Circulation

The heart is composed of two pumps. The right side of the heart receives oxygen-poor blood, known as deoxygenated blood, from the systemic circulation and pumps the blood to the lungs where oxygen and carbon dioxide are exchanged. The left side receives oxygen-rich, known as oxygenated blood, from the lungs and pumps it to the rest of the body. These two circulations are referred to as the pulmonary circulation (to the lungs) and the systemic circulation (to the rest of the body), respectively.

Systemic and Pulmonary Circulation.
 Image created by BYU-Idaho student Tabitha Daughtery Spring 2014
Image created by BYU-Idaho student Nate Shoemaker Winter 2016
Aortic semilunar valves
Image by BYU-I Student Becky Torgerson – S18

Notice how coronary arteries receive blood during diastole.  During systole, the blood opens the semilunar valves and rushes through. Blood does not easily enter the coronary vessels easily during systole.

Heart Chambers  

Mammalian hearts have four chambers, two receiving chambers called atria and two pumping chambers called ventricles.  The right side of the heart is separated from the left side of the heart by a thick wall known as the septum. The right atrium receives oxygen-poor blood from the systemic circulation and the left atrium receives oxygen-rich blood from the pulmonary circulation. Blood from the right atrium enters the right ventricle, which then pumps the blood to the lungs. The right side of the heart is a low-pressure system and seldom produces pressures above 40 mmHg. Blood from the left atrium enters the left ventricle, which pumps the blood to the systemic circulation. Blood is pumped through the systemic circulation starting at the aorta, a major artery in the body. Branching immediately from the aorta are two smaller arteries called coronary arteries (See image above). These arteries supply the heart with oxygen-rich blood. The left side of the heart is a high-pressure system and routinely produces pressures of around 120 mmHg and during times of physical stress can generate pressures over 200 mmHg.

Heart Valves (See Images above)

To ensure that the blood moves efficiently through the heart, two sets of one-way valves prevent the blood from flowing backward. The atrioventricular (AV) valves are located between the atria and the ventricles. Between the right atrium and right ventricle is the right AV or tricuspid valve and between the left atrium and left ventricle is the left AV, the bicuspid or the mitral valve. The names bi- and tricuspid are derived from the number of cusps or flaps that make up the valve. A closer look at these valves reveals that they are supported by small tendon-like attachments called chordae tendineae, which attach the edges of the valves to small nipple-like projections of muscle called papillary muscles. This arrangement prevents the valves from pushing back into the atria when the ventricles contract, a condition known as prolapse of the valve.

The semilunar valves are located between the ventricles and the large arteries that receive blood from them. Between the right ventricle and the pulmonary trunk is the pulmonary semilunar valve or simply pulmonary valve, and between the left ventricle and the aorta is the aortic semilunar valve or aortic valve. The structure of these valves is different from the AV valves. Each valve is composed of three pocket-like structures. When blood from the large arteries moves back toward the ventricles, these valves balloon out like small parachutes. Their three cusps come together preventing blood from moving backward.

Heart Murmurs

Heart murmurs can be caused by improperly functioning heart valves. There are two basic types of problems that can occur. The valve may become stiff and not open properly. This is referred to as valvular stenosis. The stenotic valve creates turbulent flow as the blood passes through which creates a sound or murmur that can be detected with a stethoscope (The art of listening to body sounds via a stethoscope is called auscultation). Conversely, the valve may not close properly and blood will backflow through the valve. This is referred to as valvular regurgitation. Again, the backflow of blood creates turbulent flow, generating a detectable murmur. Not all murmurs are due to valve disease. It is not uncommon to detect murmurs in young, thin individuals or during times of greatly increased blood flow as would occur during strenuous physical activity. These murmurs are considered normal and do not pose a risk to the individuals. Valvular disease, on the other hand, increases the workload on the heart and if severe and not treated can lead to heart failure. Historically, it was a fine art to detect the type of valvular abnormality based on the sound and timing of the murmur. Modern technology, such as cardiac ultrasonography, has made it much easier to determine the nature of the valvular disease and determine the proper course of treatment.

Cardiac muscle cells are much smaller than skeletal muscle cells and they are branched. In addition, cardiac muscle cells are connected end-to-end by special structures called intercalated discs (in-ter’kă-lā-ted). Located on the intercalated discs are different types of cell junctions that are part of keeping communication open between the cells. These are desmosomes, and gap junctions.

Cell Junctions.
 Author: John W. Kimball. Site: License: CC BY 3.0

Desmosomes tightly connect the cells together. Recall that skeletal muscle attaches to bone via tendons so that when it contracts, it pulls on the bones generating movement. Cardiac muscle cells, on the other hand, do not connect to anything except other cardiac muscle cells. When cardiac muscle contracts, the desmosomes all pull against each other causing the diameter of the chambers to decrease, which generates the pressure necessary to pump the blood.

The intercalated disks also contain gap junctions which allow communication between the connected cells. This allows movement of cytoplasm, including ions, between the cells, effectively lowering the resistance, and more importantly, this allows action potentials to spread from one cell to the next. The gap junctions along with the intricate branching of the muscle cells allow an electrical signal to spread from cell-to-cell resulting in contraction of the entire heart. Hence, even though there are millions of cells in each chamber, functionally they act as a single cell. This arrangement is referred to as a functional syncytium (syn = together; cyt = cell).

Other differences between cardiac and skeletal muscle include the following:

Cardiac Sarcomere
Author: Richard E. Klabunde. Site: LicenseCC BY-NC-SA 4.0. Permission kindly granted by the author in February of 2017 for use.

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