Anatomy Drill & Practice: This site covers the human body, the chemical, cellular, and tissue levels of organization, the integumentary system, skeletal system, muscular system, nervous system, cardiovascular system, respiratory system, digestive system, excretory system, and reproductive system.
This site not only includes images of and information on the above listed systems, but it also includes interactive drills and practice questions for students. NOTE: Flash required for the quizzes/practice questions.
BioDigital Systems: Availble for free (individual) or for a fee (groups/businesses), this interactive system will first require you to sign in via your Facebook or Google account to gain access. Once inside the system, you can zoom and rotate your virtual skeleton. Eleven systems in total are able to view and examine. Note: this site allows you to repeatedly quiz yourself on all eleven systems that are covered within the site.
The AK Lectures are a series of lectures from a (external) educational platform designed to "promote collaboration between our users and help spread knowledge to every part of the world."
These lectures vary in length, and will open in a new window when you click on the provided link.
Introduction to the Human Respiratory System: The human respiratory system consists of specialized structures whose function is to take in oxygen from the surrounding environment and expel carbon dioxide from the body. The primary organ involved in this process is the lung and each individual contains a right and a left lung. The right lung consists of three lobes and two fissures while the slightly smaller left lung contains two lobes and one fissure. The lungs are found in the thoracic cavity of our body (chest region). Air passes into the nose and through the nasal cavity until it gets into the pharynx. From the pharynx, it travels into the larynx. The opening of the larynx contains a cartilaginous flap called the epiglottis that can close to prevent food from moving into the air passageway. From the larynx, the air moves into the trachea (commonly known as the wind pipe), which connects to the left and right bronchi. The bronchi in each lung split into tiny airways called bronchioles. These bronchioles terminate at balloon-like structures called alveoli. Below the lungs is a skeletal muscle called the diaphragm, which is involved in breathing. The lungs are actually fitted inside a double-layered serous membrane that protects and lubricates the lungs. This serous membrane is called the pleura - the outer membrane of the pleura is called the parietal pleura and the inner membrane of the pleura is called the visceral pleura. Between these two pleurae is the intrapleural space (also known as the pleural cavity) that contains a special fluid that lubricates the lungs and decreases the friction the lungs feel every time they contract and expand.
Respiration in the Lungs: The primary function of the lungs is to undergo the process of breathing (also known as ventilation or respiration). Respiration brings in oxygen into our body and expels carbon dioxide from our body. But how exactly does the process of respiration actually takes place? Respiration can be broken down into two stages - inhalation and exhalation. Inhalation occurs because of the action of the diaphragm and external intercoastal muscles. The contraction of these muscles expands the volume of the thoracic cavity, thereby expanding the volume inside the intrapleural space. By Boyle's law, we know that an increase in volume under constant temperature will decrease the pressure. This drop in pressure creates a pressure difference between the lungs (which has the same pressure as the outside environment because they are open to the atmosphere) and the intrapleural space. This pressure differential (also known as a negative pressure difference) causes the movement of air down its pressure gradient, from the outside to the inside of the lungs and this process is called inhalation. Exhalation occurs when the external intercoastal muscles and the diaphragm relax, decreasing the volume inside the intrapleural space and thereby increasing the pressure. When the muscles are fully relaxed, the pressure inside the pleural cavity will exceed the intrapulmonary pressure (pressure inside the lungs) and air will rush out of the lungs and to the surrounding environment as a result of this pressure gradient. Inhalation is an active process because it requires using energy but exhalation is not an active process because muscle relaxation does not require ATP.
Protective Capabilities of the Lungs: Every single time we take a breath, we take in some amount of harmful agents that can cause damage to the lungs and the rest of the body. For instance, we constantly breathe in pollutants, contaminants, dust particles, allergens, bacterial cells, viruses and other dangerous things. Since the lungs create a direct boundary between the outside world and our internal environment, the lungs need a way to keep these harmful substances away. Luckily, there are six important ways by which the lungs can protect themselves. This includes (1) mucous membrane secreted by goblet cells (2) cilia of cells found on the lining(3) tiny hairs within the nostrils (4) alveolar macrophages (5) airway constriction due to smooth muscle and (6) coughing.
Alveolar Structure and Gas Exchange: Bronchioles, the tiny air passageways found within the lungs, terminate at specialized structures called alveolar sacs. Each sac consists of many tiny balloon-like structures called alveoli and these alveoli are responsible for carrying out the process of gas exchange. Pulmonary arteries bring deoxygenated blood filled with carbon dioxide to the capillaries of the alveoli. Since the partial pressure of oxygen is greater in the alveolar space that in the surrounding capillaries, oxygen readily diffuses down its pressure gradient into the capillaries. On the other hand, since the partial pressure of carbon dioxide is greater within the capillaries than in the alveolar space, the carbon dioxide diffuses out of the capillaries and into the alveolar space. The pulmonary venules then carry the oxygenated blood to the pulmonary veins, which carry it to the left atrium of the heart.
Surfactant in Alveoli and Surface Tension: When a droplet of water is placed on the surface of a table, that droplet will form a spherical shape. This is a result of the strong and stabilizing hydrogen bonds that exist between the water molecules. When a detergent is added to the water droplet, the water will lose its spherical shape and spreads out along the surface of the table. This is because the detergent has hydrophobic and hydrophilic regions. The hydrophilic regions will interact with the water to form intermolecular bonds while the hydrophobic sections will orient as far away form the water as possible. This in turn will break some of the hydrogen bonds in the water and this will cause it to lose its spherical shape. The detergent also lowers the water's surface tension. This is because the detergent replaces the water molecules found on the surface and makes it much easier for an applied force to break the surface bonds. Within the alveoli of our lungs there is a complex substance called pulmonary surfactant (composed of phospholipids and proteins). This substance acts in a similar way to the detergent acting on water. Inside each alveolus is a thin layer of polar fluid that contains a relatively high surface tension. Alveolar type II cells release this surfactant and when it mixes with the alveolar fluid, it decreases its surface tension. This in turn decreases the pressure needed to inflate the balloon-like alveoli and makes it much easier for us to inhale during respiration. It also prevents the alveolar from collapsing onto themselves during the process of exhalation.
Hemoglobin, Cooperativity and Oxygen Dissociation Curve: Oxygen is a non-polar diatomic molecule and will not readily dissolve within the blood plasma, which is a polar substance. Hemoglobin is the protein that binds oxygen and carries it within our blood, thereby protecting it from the polar surroundings. Hemoglobin consists of four polypeptide subunits that each have a heme group. The heme group contains a single iron atom that can undergo an oxidation-reduction reaction to bind a single diatomic oxygen molecule. Therefore, a single hemoglobin can carry a maximum of four oxygen molecules because it contains four of these heme groups. Deoxyhemoglobin refers to a hemoglobin that contains no oxygen molecules. On the other hand, a fully saturated hemoglobin is called oxyhemoglobin. Hemoglobin displays something called positive cooperativity. This means that when deoxyhemoglobin binds a single oxygen, it causes the other heme groups to become much more likely to bind other oxygen molecules. Likewise, when hemoglobin is fully saturated, dissociating one oxygen makes the other oxygen much more likely to dissociate. This positive cooperativity behavior creates a sigmoidal curve called the oxygen-hemoglobin dissociation curve. On this curve, the x-axis is the partial pressure of oxygen in the surrounding area while the y-axis is the percent of hemoglobin that is fully saturated with oxygen. This curve tells us that within the pulmonary lungs, about 98% of the hemoglobin will be fully saturated with oxygen. The hemoglobin then carries these oxygen molecules through the blood vessel system and to our tissues. Since our tissues have an average partial pressure of 40 mmHg for oxygen, the curve tells us that much less of the hemoglobin will be saturated because some of it will begin unloading the oxygen to the tissues.
Hemoglobin and Bohr Effect: As cells carry our their metabolic processes as a higher rate, they will produce more waste by-products. One of the major waste by-products is carbon dioxide. Carbon dioxide is a non-polar molecule and that means it cannot easily dissolve inside the blood (a polar substance). The way that our cells solve this problem is by first transferring the carbon dioxide to the red blood cells located in nearby capillaries. Once inside the red blood cells, an enzyme called carbonic anhydrase combines gaseous carbon dioxide with liquid water to produce aqueous carbonic acid. Carbonic acid, which is a weak acid, readily dissociates into a hydrogen ion and bicarbonate ion. Since these two ions are polar, they readily and easily dissolve inside the polar blood plasma. These two molecules can bind to hemoglobin at special allosteric sites and change the conformation of the protein in such as way as to decrease its affinity for oxygen. Therefore, by increasing the concentration of carbon dioxide, we increase the concentration of hydrogen and therefore decrease the pH (make the blood more acidic). This decreases hemoglobins affinity for oxygen and shifts the oxygen-hemoglobin dissociation curve to the right. On the other hand, if we increase our pH, we shall shift the curve to the left and increase hemoglobin's affinity for oxygen.
Effect of Temperature on Hemoglobin Dissociation Curve: When cells have a high metabolic rate, they produce an excess amount of thermal energy as a waste by-product. This thermal energy is typically transferred into the blood plasma of nearby capillaries via the process of heat. Once inside the blood, it increases the average kinetic energy of the molecules and particles within the plasma, thereby increasing its temperature. A higher temperature is correlated to the cells working harder and therefore means they need a higher supply of oxygen to keep them going. Therefore at higher blood plasma temperatures, the hemoglobin becomes less likely to bind to oxygen and much more likely to unload to into the cells of the tissue. Therefore, as temperature increases, this shifts the entire oxygen-hemoglobin dissociation curve to the right. This ultimately means that the exercising cells will receive more oxygen.
2,3 BPG and Hemoglobin: 2,3-biphosphoglycerate or simply 2,3-BPG is a biological molecule that is produced as an intermediate during the process of glycolysis. When a cell is exercising and has a high metabolic rate, it will produce excess 2,3-BPG molecules. Some of these 2,3-BPG molecules will exit the cell and enter the blood plasma of nearby capillaries. Once inside the blood plasma, the biphosphoglycerate can then enter the red blood cells and bind to deoxyhemoglobin. Only deoxyhemoglobin contains a cavity (space) between the two beta subunits that is large enough for 2,3-BPG to actually bind to via electrostatic forces. Oxyhemoglobin does not contain this space and therefore 2,3-BPG does not readily bind to it. Once bound, the 2,3-BPG changes the shape of the deoxyhemoglobin and makes it much less likely to actually bind to oxygen. Therefore it shifts the entire oxygen-hemoglobin dissociation curve to the right. This ultimately bring more oxygen molecules to the exercising cells of our tissue.
Carbon Monoxide and Hemoglobin: Carbon monoxide is a competitive inhibitor to oxygen when it comes to binding to the heme group of hemoglobin. In fact, carbon monoxide is about 250 times as likely to actually bind to the heme group of hemoglobin than is oxygen. Due to its very high affinity, it is also very difficult to actually unbind the carbon dioxide. However, increasing the concentration of oxygen can cause it to outcompete carbon monoxide for the heme group since we are dealing with competitive inhibition. When carbon monoxide binds to hemoglobin, it shifts the entire oxygen-hemoglobin curve not only to the left but also down. The leftward shift takes place because when carbon monoxide binds to the hemoglobin, it makes the other unoccupied heme groups much more likely to bind to oxygen (increases its affinity). This also means that the hemoglobin will be much less likely to release that oxygen to the tissues and this can lead to suffocation ( this is known as carbon monoxide poisoning). The downward shift is a result of the carbon monoxide molecules binding to the heme group and preventing other oxygen molecules from binding to that same location. Therefore, this decreases the total oxygen-carrying capacity of the hemoglobin proteins.