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Digestive System
Digestive System - analyze the functional inter-relationships of the structures of the digestive system, describe the components, pH, and digestive actions of salivary, gastric, pancreatic, and intestinal juices.
Chapter 38: Digestive and Excretory Systems Section 38.1 - Food and Nutrition Section 38.2 - The Process of Digestion Organs of Digestion Body Mass Index Impact of Alcohol Reflexes in the Colon Relationship of Nutrient needs to Age and Gender Three Phases of Gastric Secretion |
Video: Section 38.2
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Human Digestion: Structures & Functions
The mouth is responsible for the mechanical and chemical digestion of food. In the mouth, saliva mixes with food to form a food ball or bolus.
The tongue functions in taste as well as in moving, mixing, and positioning food for chewing and swallowing.
The teeth cut and crush food increasing surface area and mixing with saliva.
Every day the salivary glands produce about a litre of saliva. It contains salivary amylase, which begins the hydrolysis of starch into maltose.
The pharynx or throat is the passageway for both the food bolus to the esophagus and for air to enter the trachea. The process of swallowing takes place in the pharynx.
The epiglottis meets with the glottis when swallowing takes place. It covers the opening to the trachea and allows food to move into the esophagus.
The esophagus or food tube is about 25 centimetres long. Smooth muscle contractions of the esophagus, also referred to as peristalsis, move the food bolus to the stomach.
The cardiac sphincter is a ring of muscle located at the entrance to the stomach. It keeps digested food (acid chime) in the stomach, preventing reflux during digestion in the stomach.
The stomach is a muscular organ that mechanically and chemically digests food. It produces hydrochloric acid that lowers the pH in the stomach. The low pH activates the pepsinogen enzyme, which helps to digest proteins into peptides.
The pyloric sphincter controls the amount of acid chyme that enters the duodenum by releasing small quantities at regular intervals.
The duodenum, the first section of the small intestine, is important for the digestion and absorption of nutrients. It produces enzymes such as maltase and peptidases, and it also receives enzymes and bicarbonate from the pancreas and bile from the liver, via the gallbladder. The bicarbonate neutralizes the acid and the bile emulsifies fats. The absorption of nutrients is facilitated by numerous villi that line the inside of the duodenum.
The liver produces bile that is stored in the gall bladder. Bile is released into the small intestine to emulsify fats.
The gall bladder stores bile for the emulsification of fats/lipids.
The pancreas makes pancreatic juice that contains numerous digestive enzymes, as well as bicarbonate ions that neutralize acid chime entering the small intestine.
The small intestine is essential in the chemical digestion and absorption of nutrients.
The appendix is a projection of the cecum at the entrance to the large intestine. It may have a role in the immune function in humans.
The large intestine (colon) is important for the absorption of water and production of vitamins.
The rectum functions in the storage of feces and defecation.
The anus is a sphincter involved in the defecation reflex.
Digestion Video Animation
The tongue functions in taste as well as in moving, mixing, and positioning food for chewing and swallowing.
The teeth cut and crush food increasing surface area and mixing with saliva.
Every day the salivary glands produce about a litre of saliva. It contains salivary amylase, which begins the hydrolysis of starch into maltose.
The pharynx or throat is the passageway for both the food bolus to the esophagus and for air to enter the trachea. The process of swallowing takes place in the pharynx.
The epiglottis meets with the glottis when swallowing takes place. It covers the opening to the trachea and allows food to move into the esophagus.
The esophagus or food tube is about 25 centimetres long. Smooth muscle contractions of the esophagus, also referred to as peristalsis, move the food bolus to the stomach.
The cardiac sphincter is a ring of muscle located at the entrance to the stomach. It keeps digested food (acid chime) in the stomach, preventing reflux during digestion in the stomach.
The stomach is a muscular organ that mechanically and chemically digests food. It produces hydrochloric acid that lowers the pH in the stomach. The low pH activates the pepsinogen enzyme, which helps to digest proteins into peptides.
The pyloric sphincter controls the amount of acid chyme that enters the duodenum by releasing small quantities at regular intervals.
The duodenum, the first section of the small intestine, is important for the digestion and absorption of nutrients. It produces enzymes such as maltase and peptidases, and it also receives enzymes and bicarbonate from the pancreas and bile from the liver, via the gallbladder. The bicarbonate neutralizes the acid and the bile emulsifies fats. The absorption of nutrients is facilitated by numerous villi that line the inside of the duodenum.
The liver produces bile that is stored in the gall bladder. Bile is released into the small intestine to emulsify fats.
The gall bladder stores bile for the emulsification of fats/lipids.
The pancreas makes pancreatic juice that contains numerous digestive enzymes, as well as bicarbonate ions that neutralize acid chime entering the small intestine.
The small intestine is essential in the chemical digestion and absorption of nutrients.
The appendix is a projection of the cecum at the entrance to the large intestine. It may have a role in the immune function in humans.
The large intestine (colon) is important for the absorption of water and production of vitamins.
The rectum functions in the storage of feces and defecation.
The anus is a sphincter involved in the defecation reflex.
Digestion Video Animation
The Stomach
The stomach is a muscular organ that mechanically and chemically digests food. The muscular walls of the stomach contract to mix the food with acid and enzymes, resulting in the production of acid chyme. Cells in the stomach lining produce hydrochloric acid, the pepsinogen enzyme, and mucus. The low pH caused by the production of hydrochloric acid kills bacteria and activates pepsinogen, which, as pepsin, digests proteins into peptides. Pepsin has optimal activity in the low pH of the stomach. The mucus protects the stomach from its acidic contents. The following chart summarizes the components and function of gastric juice.
The pyloric sphincter controls the amount of acid chyme that enters the duodenum by releasing small amounts at regular intervals.
The duodenum is important for the digestion and absorption of nutrients, and it makes enzymes like maltase and peptidases. From the pancreas it receives enzymes and bicarbonate that neutralize acid. From the liver, via the gall bladder, it receives bile that emulsifies fats. The function of the small intestine, accessory organs, and the large intestine are the topics of later lessons in this section.
The pyloric sphincter controls the amount of acid chyme that enters the duodenum by releasing small amounts at regular intervals.
The duodenum is important for the digestion and absorption of nutrients, and it makes enzymes like maltase and peptidases. From the pancreas it receives enzymes and bicarbonate that neutralize acid. From the liver, via the gall bladder, it receives bile that emulsifies fats. The function of the small intestine, accessory organs, and the large intestine are the topics of later lessons in this section.
The Pancreas
The Pancreas: Structure and FunctionThe pancreas is both an exocrine and an endocrine gland that externally resembles masses of tiny grapes. Exocrine glands release their products into ducts while endocrine glands release their products directly into the bloodstream. The pancreas does both.
The cells of the exocrine tissue secrete pancreatic juice that flows down the pancreatic duct, into the bile duct, and then to the duodenum. The endocrine tissue consists of groups of cells known as the islets of Langerhans. Those cells primarily secrete the hormones insulin and glucagons, which will be discussed later.
STRUCTURE & FUNCTION:
All enzymes produced in the pancreas act in the small intestine. Pancreatic juice is released into the duodenum through a duct in response to acid chyme from the stomach entering the small intestine. The sodium bicarbonate found in pancreatic juice maintains the pH in the duodenum at 7.5 to 8.5. Sodium bicarbonate neutralizes stomach acid and creates an optima pH for the enzymes that act in the small intestine.
The following chart summarizes the digestive enzymes produced by the pancreas and released into the small intestine.
The cells of the exocrine tissue secrete pancreatic juice that flows down the pancreatic duct, into the bile duct, and then to the duodenum. The endocrine tissue consists of groups of cells known as the islets of Langerhans. Those cells primarily secrete the hormones insulin and glucagons, which will be discussed later.
STRUCTURE & FUNCTION:
All enzymes produced in the pancreas act in the small intestine. Pancreatic juice is released into the duodenum through a duct in response to acid chyme from the stomach entering the small intestine. The sodium bicarbonate found in pancreatic juice maintains the pH in the duodenum at 7.5 to 8.5. Sodium bicarbonate neutralizes stomach acid and creates an optima pH for the enzymes that act in the small intestine.
The following chart summarizes the digestive enzymes produced by the pancreas and released into the small intestine.
The following table summarizes the components and functions of pancreatic juice.
The Small Intestine
Structure and Function:
The small intestine, which is approximately six metres long, is named for its narrow diameter. The small intestine receives small quantities of acid chyme from the stomach, released at intervals by the pyloric sphincter.
The first twenty-five centimetres of the small intestine is called the duodenum. In the duodenum, bile, and pancreatic juice enter the small intestine through a common duct. Bile, produced in the liver and stored in the gallbladder, emulsifies fats in the small intestine. Pancreatic juice adds sodium bicarbonate that neutralizes acid chime and makes the pH slightly basic and digestive enzymes (pancreatic amylase, trypsin, lipase, and nucleases). The cells of the small intestine also produce enzymes (maltase, peptidases, nucleosidases).
In the small intestine, arguably the most important digestive organ, pancreatic juice, intestinal juice, and bile are responsible for the absorption of nutrients into the blood and lymph (tissue fluid) for use by the body. The walls of the small intestine are highly folded and covered with villi. Villi are finger-like extensions that increase the surface area available for absorption of nutrients.
The small intestine, which is approximately six metres long, is named for its narrow diameter. The small intestine receives small quantities of acid chyme from the stomach, released at intervals by the pyloric sphincter.
The first twenty-five centimetres of the small intestine is called the duodenum. In the duodenum, bile, and pancreatic juice enter the small intestine through a common duct. Bile, produced in the liver and stored in the gallbladder, emulsifies fats in the small intestine. Pancreatic juice adds sodium bicarbonate that neutralizes acid chime and makes the pH slightly basic and digestive enzymes (pancreatic amylase, trypsin, lipase, and nucleases). The cells of the small intestine also produce enzymes (maltase, peptidases, nucleosidases).
In the small intestine, arguably the most important digestive organ, pancreatic juice, intestinal juice, and bile are responsible for the absorption of nutrients into the blood and lymph (tissue fluid) for use by the body. The walls of the small intestine are highly folded and covered with villi. Villi are finger-like extensions that increase the surface area available for absorption of nutrients.
The outer cell layer of each villus is made up of columnar epithelial cells. These cells resemble columns packed tightly together and have nuclei near their bases. These cells absorb nutrients and transfer them to the blood capillaries and lacteals. This absorption involves active transport and requires ATP energy. To increase absorption, the outer surfaces of these cells are covered with microvilli (called a brush border) that increase the surface area even more.
Each villus contains blood capillaries and small lymphatic vessels called lacteals. Glucose and amino acids move through the epithelial cells and into the blood capillaries, and travels via the hepatic portal vein to the liver for processing. Fatty acids and glycerol are packaged by epithelial cells and moved into lacteals. The lymphatic vessels later dump them into the bloodstream.
Each villus contains blood capillaries and small lymphatic vessels called lacteals. Glucose and amino acids move through the epithelial cells and into the blood capillaries, and travels via the hepatic portal vein to the liver for processing. Fatty acids and glycerol are packaged by epithelial cells and moved into lacteals. The lymphatic vessels later dump them into the bloodstream.
ENZYMES IN THE SMALL INTESTINE:
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Circulatory System
Circulatory System - describe the inter-relationships of the structures the heart, analyze the relationship between heart rate and blood pressure, analyze the functional inter-relationships of the vessels of the circulatory system, describe the components of blood, describe the inter-relationships of the structures of the lymphatic system. Chapter 37: Circulatory and Respiratory Systems Section 37.1 - The Circulatory System Section 37.2 - Blood and the Lymphatic System Phagocytosis The Immune Response Conducting System of the Heart Fluid Exchange Across the Walls of Capillaries Hemoglobin Breakdown The Cardiac Cycle Flu Jail Cells How are Blood Smears Used to Diagnose Disease What Factors affect the likelihood of Hypertension |
Video: Section 37.1
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Circulatory System
The circulatory system is responsible for transporting materials throughout the entire body. It transports nutrients, water, and oxygen to your billions of body cells and carries away wastes such as carbon dioxide that body cells produce. It is an amazing highway that travels through your entire body connecting all your body cells.
The main parts of the circulatory system are the heart, arteries, capillaries, and veins. Each of these parts is discussed in detail within this section. Additional topics include the lymphatic system and fetal circulation. Did you know one drop of blood contains a half a drop of plasma, 5 MILLION red blood cells, 10 thousand white blood cells, and 250 thousand platelets? |
Types of Blood Vessels
An average adult human has approximately 100 000 kilometres of blood vessels. Arranged end to end, they would circle the Earth two and a half times. These blood vessels transport blood on a non-stop journey from the heart into the arteries, which branch into arterioles, which lead to capillaries that merge into venules, which merge into veins that return to the heart.
Arteries and Arterioles
Arteries carry blood away from the heart toward a specific part of the body. The walls of arteries have three main layers. The inside layer that is in direct contact with blood is made up of simple squamous epithelium surrounded by connective tissue containing elastic fibres. Smooth muscle makes up the thick middle layer and the outer layer is more connective tissue. These three layers make up a strong, elastic vessel that can contract or relax to regulate blood flow and moderate changes in blood pressure between heartbeats.
Arterioles are small arteries. One artery may branch into many arterioles that supply blood to the tissues. Smooth muscles in arterioles control blood pressure by constricting or dilating. Sphincters (rings of smooth muscle) at the entrance to capillary beds also control blood flow.
Capillaries
Capillaries are very small vessels, approximately 10 micrometres wide. Capillary walls are one cell thick, which allows for easy exchange of gases, nutrients, and wastes with the tissues. Oxygen and nutrients are delivered to tissues by the blood, and carbon dioxide and wastes are carried away from the tissues by blood that exits the capillaries.
Capillary beds are found everywhere in the body, and this explains why bleeding takes place anywhere an injury occurs. In locations where blood enters a capillary bed, such as at the end of an arteriole, sphincters (rings of muscle) control the flow of blood into the capillary bed. These sphincters allow blood to be actively directed (shunted) toward areas that require increased blood flow. After a meal, the capillaries of the intestines require more blood flow. During exercise, muscles need the oxygen carried by red blood cells.
Veins & Venules
Venules are small veins. Venules collect the blood that drains from capillary beds. The blood from many capillaries converges into a single venule and moves back towards the heart. Venules and veins have the same three layers as arteries but the smooth muscle and connective tissue layers are thinner.
Veins are larger blood vessels that collect blood and return it to the heart. They have thinner walls and a larger lumen than arteries. Blood flow in the veins is promoted by movement of the body (muscle contraction) and the presence of one-way valves in veins that do not allow the backflow of blood. These valves allow for the return of blood to the heart from the lower body against the downward pull of gravity. About 70% of the blood in the body is held in veins.
Blood Pressure
Blood pressure is the pressure blood exerts on the walls of blood vessels. Blood pressure drops with increased distance from the heart due to the branching of the blood vessels and the resulting increases in cross-sectional area. The effect is much like a mighty river fanning out into a delta. Once the pressure has dropped in the capillary beds it cannot be increased until it returns to the heart. The lower pressure in veins explains the importance of one-way valves and muscular movement to return blood to the heart.
Blood pressure is greatest in the arteries and this is why arteries have thick, elastic, muscular walls. Blood pressure is lowest in the vena cava (0 to 20 mmHg), which is furthest from the heart. As blood moves away from the heart, the branching of arteries into arterioles into capillaries reduces blood pressure and blood velocity. This reduction is due to a huge increase in cross-sectional area in the capillaries. Blood leaving the capillaries converges into venules and then veins. The resulting decrease in cross-sectional area increases the velocity of blood flow but the pressure remains low.
Blood Pressure: Online Activity
Arteries carry blood away from the heart toward a specific part of the body. The walls of arteries have three main layers. The inside layer that is in direct contact with blood is made up of simple squamous epithelium surrounded by connective tissue containing elastic fibres. Smooth muscle makes up the thick middle layer and the outer layer is more connective tissue. These three layers make up a strong, elastic vessel that can contract or relax to regulate blood flow and moderate changes in blood pressure between heartbeats.
Arterioles are small arteries. One artery may branch into many arterioles that supply blood to the tissues. Smooth muscles in arterioles control blood pressure by constricting or dilating. Sphincters (rings of smooth muscle) at the entrance to capillary beds also control blood flow.
Capillaries
Capillaries are very small vessels, approximately 10 micrometres wide. Capillary walls are one cell thick, which allows for easy exchange of gases, nutrients, and wastes with the tissues. Oxygen and nutrients are delivered to tissues by the blood, and carbon dioxide and wastes are carried away from the tissues by blood that exits the capillaries.
Capillary beds are found everywhere in the body, and this explains why bleeding takes place anywhere an injury occurs. In locations where blood enters a capillary bed, such as at the end of an arteriole, sphincters (rings of muscle) control the flow of blood into the capillary bed. These sphincters allow blood to be actively directed (shunted) toward areas that require increased blood flow. After a meal, the capillaries of the intestines require more blood flow. During exercise, muscles need the oxygen carried by red blood cells.
Veins & Venules
Venules are small veins. Venules collect the blood that drains from capillary beds. The blood from many capillaries converges into a single venule and moves back towards the heart. Venules and veins have the same three layers as arteries but the smooth muscle and connective tissue layers are thinner.
Veins are larger blood vessels that collect blood and return it to the heart. They have thinner walls and a larger lumen than arteries. Blood flow in the veins is promoted by movement of the body (muscle contraction) and the presence of one-way valves in veins that do not allow the backflow of blood. These valves allow for the return of blood to the heart from the lower body against the downward pull of gravity. About 70% of the blood in the body is held in veins.
Blood Pressure
Blood pressure is the pressure blood exerts on the walls of blood vessels. Blood pressure drops with increased distance from the heart due to the branching of the blood vessels and the resulting increases in cross-sectional area. The effect is much like a mighty river fanning out into a delta. Once the pressure has dropped in the capillary beds it cannot be increased until it returns to the heart. The lower pressure in veins explains the importance of one-way valves and muscular movement to return blood to the heart.
Blood pressure is greatest in the arteries and this is why arteries have thick, elastic, muscular walls. Blood pressure is lowest in the vena cava (0 to 20 mmHg), which is furthest from the heart. As blood moves away from the heart, the branching of arteries into arterioles into capillaries reduces blood pressure and blood velocity. This reduction is due to a huge increase in cross-sectional area in the capillaries. Blood leaving the capillaries converges into venules and then veins. The resulting decrease in cross-sectional area increases the velocity of blood flow but the pressure remains low.
Blood Pressure: Online Activity
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COPY CODE SNIPPET
Blood
Blood is a form of liquid body tissue that has many functions in the body. It transports oxygen and nutrients to the tissue fluid surrounding cells, and it carries away carbon dioxide and other cellular waste products. Blood also helps balance fluid levels, body temperature, ion concentrations, and pH within the body. Formed elements (cells) in blood have important roles in fighting disease and forming clots to heal tissue damage.
Blood is composed of two main parts. The liquid component of blood, called plasma, is mainly water (92%) with many dissolved substances. Plasma makes up 55% of the volume of blood. The remaining 45% of the blood volume is composed of formed elements or blood cells of various kinds. These are red blood cells, white blood cells, and platelets, which are actually cell fragments.
Blood Plasma
Blood plasma is mainly water, which acts as the solvent the substances dissolved in it. These dissolved substances include:
Blood is a form of liquid body tissue that has many functions in the body. It transports oxygen and nutrients to the tissue fluid surrounding cells, and it carries away carbon dioxide and other cellular waste products. Blood also helps balance fluid levels, body temperature, ion concentrations, and pH within the body. Formed elements (cells) in blood have important roles in fighting disease and forming clots to heal tissue damage.
Blood is composed of two main parts. The liquid component of blood, called plasma, is mainly water (92%) with many dissolved substances. Plasma makes up 55% of the volume of blood. The remaining 45% of the blood volume is composed of formed elements or blood cells of various kinds. These are red blood cells, white blood cells, and platelets, which are actually cell fragments.
Blood Plasma
Blood plasma is mainly water, which acts as the solvent the substances dissolved in it. These dissolved substances include:
- plasma proteins—albumin (maintains blood volume), immunoglobulins (fight infection), and fibrinogen (blood clotting)
- salts—sodium ions, potassium ions, chloride ions, calcium ions, etc.
- nutrients—glucose, amino acids, fatty acids, certain vitamins
- gases—mainly carbon dioxide, in the form of bicarbonate ion, from the tissues
- waste—urea from the liver
- hormones—many are found in plasma, e.g., thyroxin, insulin, adrenalin, estrogen
Blood Cells
All of the following types of blood cell are produced in red bone marrow. Red bone marrow is located in the ribs, vertebrae, skull, and the ends of long bones in the arms and legs.
Red Blood Cells—Erythrocytes
All of the following types of blood cell are produced in red bone marrow. Red bone marrow is located in the ribs, vertebrae, skull, and the ends of long bones in the arms and legs.
Red Blood Cells—Erythrocytes
Biconcave shape contain hemoglobin that carries oxygen produced in bone marrow
The majority of cells found in the blood are red blood cells or erythrocytes. RBCs are shaped like biconcave disks and have no nuclei. The flattened shape increases the surface area for gas exchange and aids in transport through the capillaries. A single millilitre of blood will normally contain 4 to 6 billion RBCs. RBCs function in the blood for up to four months. New RBCs are continually being produced from stem cells in the red bone marrow to replace worn out ones. As mentioned previously, the liver plays a role in recycling iron and breaking down of the heme groups to make bile.
RBCs carry oxygen from the lungs and deliver it to the body tissues in the capillaries. They contain proteins called hemoglobin, and each hemoglobin molecule is composed of four polypeptide chains (an example of quaternary protein structure). Each of the four polypeptides has a heme group that contains iron. The heme group binds to oxygen and releases it to the tissues of the body. If hemoglobin levels in the blood decrease—a condition called anemia—more of the hormone erythropoietin is produced, which increases the number of RBCs produced in the bone marrow. Recombinant forms of this hormone (EPO, which is created to treat patients with anemia from many different causes) are now misused by athletes to increase the oxygen carrying capacity of the blood.
White Blood Cells—Leukocytes
White blood cells are large cells that vary in colour and contain nuclei. WBCs are spherical in shape. WBC are produced in red bone marrow. Some require further maturing before they are active and this is done ususally in tissues of the lymphatic system.
White blood cells:
Neutrophils, the most common WBC, have a multi-lobed nucleus. They are phagocytic, meaning they engulf and ingest foreign substances or invaders, such as like bacteria and other pathogens, and destroy them.
Lymphocytes mature in lymphatic tissues, such as the thymus and spleen. There are two main types—B lymphocytes and T lymphocytes. Both produce antibodies and provide secondary immunity.
Antibodies are Y-shaped protein molecules that travel in blood and lymph, and attach to specific foreign antigens with a lock and key mechanism similar to enzymes. Antibodies help to prevent disease. They are produced to recognize a specific antigen—a foreign substance that is recognized by the immune system as non-self and needs to be destroyed. Antibodies attach to foreign antigens by and promoting phagocytosis by other WBCs, clump pathogens together, or form complexes with pathogens and prevent them from attaching to cells in the respiratory tract and digestive tract.
Monocytes, the largest WBCs, develop into large macrophages in the body tissues and have the ability to phagocytize pathogens during infection. Eosinophils are involved in the control of allergic and inflammatory responses. Basophils release histamine that increases blood flow to sites of tissue injury.
Platelets—Thrombocytes
Platelets are cell fragments that break away from larger cells in the red bone marrow. A millilitre of blood contains up to 300 million platelets. Platelets are involved in blood clotting following tissue injury. Blood clotting is a complex process involving platelets, many clotting factors, the proteins fibrinogen and prothrombin, vitamin K found in green vegetables and produced by bacteria in the large intestine, and calcium ions. In the clotting process following an injury, platelets act as a first line of defense by forming a platelet plug that seals the leak. Later, a complex series of events form a protein net that traps RBCs around the platelet plug. As tissue repair takes place, the plug is dissolved and blood flow resumes.
The Pathway of Blood through the Heart
Go to Voyage of the Blood now to see how blood flows through the heart.
Blood flows through the heart structures in the following sequence:
The majority of cells found in the blood are red blood cells or erythrocytes. RBCs are shaped like biconcave disks and have no nuclei. The flattened shape increases the surface area for gas exchange and aids in transport through the capillaries. A single millilitre of blood will normally contain 4 to 6 billion RBCs. RBCs function in the blood for up to four months. New RBCs are continually being produced from stem cells in the red bone marrow to replace worn out ones. As mentioned previously, the liver plays a role in recycling iron and breaking down of the heme groups to make bile.
RBCs carry oxygen from the lungs and deliver it to the body tissues in the capillaries. They contain proteins called hemoglobin, and each hemoglobin molecule is composed of four polypeptide chains (an example of quaternary protein structure). Each of the four polypeptides has a heme group that contains iron. The heme group binds to oxygen and releases it to the tissues of the body. If hemoglobin levels in the blood decrease—a condition called anemia—more of the hormone erythropoietin is produced, which increases the number of RBCs produced in the bone marrow. Recombinant forms of this hormone (EPO, which is created to treat patients with anemia from many different causes) are now misused by athletes to increase the oxygen carrying capacity of the blood.
White Blood Cells—Leukocytes
White blood cells are large cells that vary in colour and contain nuclei. WBCs are spherical in shape. WBC are produced in red bone marrow. Some require further maturing before they are active and this is done ususally in tissues of the lymphatic system.
White blood cells:
- fight infection
- develop immunity
- phagocytize foreign particles
Neutrophils, the most common WBC, have a multi-lobed nucleus. They are phagocytic, meaning they engulf and ingest foreign substances or invaders, such as like bacteria and other pathogens, and destroy them.
Lymphocytes mature in lymphatic tissues, such as the thymus and spleen. There are two main types—B lymphocytes and T lymphocytes. Both produce antibodies and provide secondary immunity.
Antibodies are Y-shaped protein molecules that travel in blood and lymph, and attach to specific foreign antigens with a lock and key mechanism similar to enzymes. Antibodies help to prevent disease. They are produced to recognize a specific antigen—a foreign substance that is recognized by the immune system as non-self and needs to be destroyed. Antibodies attach to foreign antigens by and promoting phagocytosis by other WBCs, clump pathogens together, or form complexes with pathogens and prevent them from attaching to cells in the respiratory tract and digestive tract.
Monocytes, the largest WBCs, develop into large macrophages in the body tissues and have the ability to phagocytize pathogens during infection. Eosinophils are involved in the control of allergic and inflammatory responses. Basophils release histamine that increases blood flow to sites of tissue injury.
Platelets—Thrombocytes
Platelets are cell fragments that break away from larger cells in the red bone marrow. A millilitre of blood contains up to 300 million platelets. Platelets are involved in blood clotting following tissue injury. Blood clotting is a complex process involving platelets, many clotting factors, the proteins fibrinogen and prothrombin, vitamin K found in green vegetables and produced by bacteria in the large intestine, and calcium ions. In the clotting process following an injury, platelets act as a first line of defense by forming a platelet plug that seals the leak. Later, a complex series of events form a protein net that traps RBCs around the platelet plug. As tissue repair takes place, the plug is dissolved and blood flow resumes.
The Pathway of Blood through the Heart
Go to Voyage of the Blood now to see how blood flows through the heart.
Blood flows through the heart structures in the following sequence:
- deoxygenated blood is returned to the right atrium from the body
- the right atrium pumps the blood through the atrioventricular valve into the right ventricle
- the right ventricle pumps blood through the semilunar (pulmonic) valve into the pulmonary truck and into the pulmonary arteries to both lungs
- oxygenated blood is returned to the left atrium
- the left atrium pumps the blood through the atrioventricular valve into the left ventricle
- the left ventricle pumps the blood under high pressure through the semilunar (aortic) valve to the body
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Respiratory System
Respiratory System - analyze the functional inter-relationships of the structures of the respiratory system, analyze the processes of breathing, analyze internal and external respiration.
Chapter 37: Circulatory and Respiratory Systems Section 37.3 - The Respiratory System Alveolar Pressure Changes During Inspiration & Expiration Gas Exchange During Respiration Movement of Oxygen and Carbon Dioxide |
Video: Section 37.3
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Respiratory System
All the cells in your body require oxygen. Without it, they couldn't move, build, reproduce, and turn food into energy. In fact, without oxygen, they and you would die! How do you get oxygen? From breathing in air which your blood circulates to all parts of the body.
This section discusses how the respiratory system functions to enrich our bodies with oxygen.
You may want to check with your local teacher to see about an optional assignment for this section. If your local teacher purchased the Teacher's Guide to this course they will have the optional assignment information.
All the cells in your body require oxygen. Without it, they couldn't move, build, reproduce, and turn food into energy. In fact, without oxygen, they and you would die! How do you get oxygen? From breathing in air which your blood circulates to all parts of the body.
This section discusses how the respiratory system functions to enrich our bodies with oxygen.
You may want to check with your local teacher to see about an optional assignment for this section. If your local teacher purchased the Teacher's Guide to this course they will have the optional assignment information.
The Nasal Cavity – Air from outside the body passes through two nostrils or nares and into the nasal cavities. Ciliated cells in the upper parts of the nasal cavities are odor receptors and are responsible for the sense of smell.
Pharynx or Throat – The pharynx is a common passage way for both the respiratory and digestive systems.
Larynx or Voice Box – The larynx, a structure located below the epiglottis, acts as a passageway for air between the pharynx and trachea. The larynx contains the vocal cords.
Trachea or Windpipe – The trachea lies in front of the esophagus and directs air between the larynx and the bronchi. The trachea consists of a number of cartilaginous rings stacked on top of each other. These rings prevent the trachea from collapsing when the pressure in the thoracic cavity decreases during inhalation.
Bronchi (one is a bronchus) – The bronchi branch off the trachea and supply air to the lungs. Each main bronchus branches into many secondary bronchi that have smaller diameters, thinner walls, and less cartilage for support. Secondary bronchi lead to the smaller tubes called bronchioles.
Bronchioles – Bronchioles, the smallest tubes within the lungs, carry air to the alveoli. Each bronchiole supplies air to a lobule within the lung. Each lobule contains many alveoli.
Thoracic Cavity – The thoracic cavity is the enclosed space within the ribcage. The diaphragm is at the bottom of the thoracic cavity. This cavity allows breathing to take place, and it protects the heart, large blood vessels, and other vital organs.
Diaphragm – The diaphragm is a dome-shaped muscle that separates the thoracic cavity and abdominal cavity. When the diaphragm contracts, the muscles shorten and flatten out the dome-shaped diaphragm, increasing the volume of the thoracic cavity and pushing down on the abdomen.
Ribs – The ribs are bones attached to the spine and sternum. They form the structure of the thoracic cavity. Intercostal muscles between the ribs contract to pull the ribs up and out during inhalation and relax during exhalation.
Pleural Membranes – The pleural membranes are made up of two layers that lie between the lungs and the chest wall. The inner membrane encases the lungs, and the outer membrane adheres to the chest wall. A thin layer of fluid between the two membranes prevents friction and allows easy movement between the lungs and chest wall. The complete seal and the low pressure between these layers prevent the lungs from collapsing.
Alveoli (one is an alveolus) – Alveoli are the air sacs within the lungs. They have thin walls made of simple squamous epithelial cells and are surrounded by blood capillaries (another layer of simple squamous epithelium). Gas exchange occurs in the alveoli. Oxygen gas is in higher concentration in the alveoli than in the blood and so it diffuses into the blood through this thin layer of cells. Carbon dioxide is in higher concentration in the blood than in the alveoli, so it diffuses into the alveoli through this thin layer. The inner surface of the alveolus is covered in a thin lipoprotein layer called pulmonary surfactant. This layer prevents the alveoli from collapsing during exhalation.
Pharynx or Throat – The pharynx is a common passage way for both the respiratory and digestive systems.
Larynx or Voice Box – The larynx, a structure located below the epiglottis, acts as a passageway for air between the pharynx and trachea. The larynx contains the vocal cords.
Trachea or Windpipe – The trachea lies in front of the esophagus and directs air between the larynx and the bronchi. The trachea consists of a number of cartilaginous rings stacked on top of each other. These rings prevent the trachea from collapsing when the pressure in the thoracic cavity decreases during inhalation.
Bronchi (one is a bronchus) – The bronchi branch off the trachea and supply air to the lungs. Each main bronchus branches into many secondary bronchi that have smaller diameters, thinner walls, and less cartilage for support. Secondary bronchi lead to the smaller tubes called bronchioles.
Bronchioles – Bronchioles, the smallest tubes within the lungs, carry air to the alveoli. Each bronchiole supplies air to a lobule within the lung. Each lobule contains many alveoli.
Thoracic Cavity – The thoracic cavity is the enclosed space within the ribcage. The diaphragm is at the bottom of the thoracic cavity. This cavity allows breathing to take place, and it protects the heart, large blood vessels, and other vital organs.
Diaphragm – The diaphragm is a dome-shaped muscle that separates the thoracic cavity and abdominal cavity. When the diaphragm contracts, the muscles shorten and flatten out the dome-shaped diaphragm, increasing the volume of the thoracic cavity and pushing down on the abdomen.
Ribs – The ribs are bones attached to the spine and sternum. They form the structure of the thoracic cavity. Intercostal muscles between the ribs contract to pull the ribs up and out during inhalation and relax during exhalation.
Pleural Membranes – The pleural membranes are made up of two layers that lie between the lungs and the chest wall. The inner membrane encases the lungs, and the outer membrane adheres to the chest wall. A thin layer of fluid between the two membranes prevents friction and allows easy movement between the lungs and chest wall. The complete seal and the low pressure between these layers prevent the lungs from collapsing.
Alveoli (one is an alveolus) – Alveoli are the air sacs within the lungs. They have thin walls made of simple squamous epithelial cells and are surrounded by blood capillaries (another layer of simple squamous epithelium). Gas exchange occurs in the alveoli. Oxygen gas is in higher concentration in the alveoli than in the blood and so it diffuses into the blood through this thin layer of cells. Carbon dioxide is in higher concentration in the blood than in the alveoli, so it diffuses into the alveoli through this thin layer. The inner surface of the alveolus is covered in a thin lipoprotein layer called pulmonary surfactant. This layer prevents the alveoli from collapsing during exhalation.
The Anatomy of the Respiratory System
At rest, the body moves 10 litres of air into and out of the lungs every minute. This movement of air into and out of the lungs is called breathing. The human lungs contain 300 million alveoli with a surface area forty times greater than that of the skin. The alveoli are responsible for the exchange of oxygen and carbon dioxide between the lungs and the blood. This lesson introduces the anatomy of the respiratory system and the functions of each individual organ.
The respiratory system is responsible for the process of breathing, and it cooperates with the circulatory system in the process of respiration. Breathing involves the organs of the respiratory tract. These organs transport oxygen-rich air to the blood in the capillaries of the alveoli and remove carbon dioxide and water taken to the lungs from the tissues.
There are three types of respiration. External respiration exchanges oxygen and carbon dioxide in the alveoli of the lungs. Internal respiration is the exchange of gases between the capillaries and the tissue fluid. In cellular respiration, cells use oxygen to burn glucose to produce ATP energy and the waste products carbon dioxide and water.
At rest, the body moves 10 litres of air into and out of the lungs every minute. This movement of air into and out of the lungs is called breathing. The human lungs contain 300 million alveoli with a surface area forty times greater than that of the skin. The alveoli are responsible for the exchange of oxygen and carbon dioxide between the lungs and the blood. This lesson introduces the anatomy of the respiratory system and the functions of each individual organ.
The respiratory system is responsible for the process of breathing, and it cooperates with the circulatory system in the process of respiration. Breathing involves the organs of the respiratory tract. These organs transport oxygen-rich air to the blood in the capillaries of the alveoli and remove carbon dioxide and water taken to the lungs from the tissues.
There are three types of respiration. External respiration exchanges oxygen and carbon dioxide in the alveoli of the lungs. Internal respiration is the exchange of gases between the capillaries and the tissue fluid. In cellular respiration, cells use oxygen to burn glucose to produce ATP energy and the waste products carbon dioxide and water.
Alveoli Structure and Function
This is the site of external respiration—the exchange of gases between the alveoli and blood capillaries.
This is the site of external respiration—the exchange of gases between the alveoli and blood capillaries.
The following table summarizes the alveoli structure and its function.
The Roles of Cilia and Mucus
Cilia are short hair-like structures made of microtubules (9 + 2 arrangement) that are able to produce movement. In the respiratory system, cilia are found on the ciliated columnar epithelial cells that line the tubes of the lungs. The movement of the cilia sweeps mucus and debris out of the lungs. The tubes of the lungs also contain mucus-producing goblet cells similar to those of the digestive system. Foreign particles in air, such as dust, are trapped by the mucus and swept by the cilia out of the airway into the throat where they are coughed up or swallowed.
Chemicals in cigarette smoke are known to reduce the activity and even permanently disable cilia in the respiratory tract. Read page 299 in your Inquiry Into Life textbook for information related to smoking and lung health. Please don't smoke.
Cilia are short hair-like structures made of microtubules (9 + 2 arrangement) that are able to produce movement. In the respiratory system, cilia are found on the ciliated columnar epithelial cells that line the tubes of the lungs. The movement of the cilia sweeps mucus and debris out of the lungs. The tubes of the lungs also contain mucus-producing goblet cells similar to those of the digestive system. Foreign particles in air, such as dust, are trapped by the mucus and swept by the cilia out of the airway into the throat where they are coughed up or swallowed.
Chemicals in cigarette smoke are known to reduce the activity and even permanently disable cilia in the respiratory tract. Read page 299 in your Inquiry Into Life textbook for information related to smoking and lung health. Please don't smoke.
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The Lymphatic System
The Lymphatic SystemThe lymphatic system is a network of lymph vessels and lymphoid organs found throughout the body. This system of lymphatic veins and nodes has the following three main functions. It drains excess fluid (lymph) from the tissues and moves it back into the circulatory system at the right and left subclavian veins. It collects lipids in lacteals found in the villi of the small intestine and transports them to the bloodstream. It aids the immune system to help protect the body from pathogens.
The lymphatic system is made up of lymph capillaries, lymph vessels, and lymph nodes. Other organs involved in immune function are the tonsils, thymus, liver, spleen, appendix, and bone marrow. They work cooperatively with lymphatic vessels and nodes to fight infections and disease.
Lymph Capillaries
The lymph capillaries are the starting point of the one-way lymphatic system. Lymph capillaries originate in tissues and drain excess tissue fluid that has not been reabsorbed into the bloodstream and move it into lymph veins. This prevents swelling or edema (collection of fluid in the tissues).
Lymph Veins
The lymph veins collect lymph from many lymph capillaries and move it into lymph ducts for transport to the subclavian veins, where the fluid is returned to the bloodstream. The movement of fluid in the lymph veins relies on muscular movements to squeeze the fluid along. These veins, like those that make up the circulatory system, contain one-way valves that keep the fluid moving toward the thoracic cavity or chest where it is returned to the circulatory system.
Lymph Nodes
Lymph nodes are lymphoid organs, along with the tonsils, spleen, thymus and bone marrow. They are bean-shaped structures with a cortex and medulla, similar to many other body organs.
The cortex (outside) of a lymph node contains many lymphocytes (a type of white blood cell) that are activated to fight off pathogens. Lymphocytes produce antibodies (Y-shaped proteins) that combine with antigens (proteins or polysaccharides on foreign cells) to form inactive antigen-antibody complexes, as shown in the following illustration.
In the medulla (middle) of the lymph nodes, macrophages, another form of white blood cell, engulf (phagocytize) foreign debris and clean up lymph fluid. Lymph nodes are found along lymph vessels and are most numerous in the groin, neck, and armpits. Swollen lymph nodes are a sign that an infection is present.
The lymphatic system is made up of lymph capillaries, lymph vessels, and lymph nodes. Other organs involved in immune function are the tonsils, thymus, liver, spleen, appendix, and bone marrow. They work cooperatively with lymphatic vessels and nodes to fight infections and disease.
Lymph Capillaries
The lymph capillaries are the starting point of the one-way lymphatic system. Lymph capillaries originate in tissues and drain excess tissue fluid that has not been reabsorbed into the bloodstream and move it into lymph veins. This prevents swelling or edema (collection of fluid in the tissues).
Lymph Veins
The lymph veins collect lymph from many lymph capillaries and move it into lymph ducts for transport to the subclavian veins, where the fluid is returned to the bloodstream. The movement of fluid in the lymph veins relies on muscular movements to squeeze the fluid along. These veins, like those that make up the circulatory system, contain one-way valves that keep the fluid moving toward the thoracic cavity or chest where it is returned to the circulatory system.
Lymph Nodes
Lymph nodes are lymphoid organs, along with the tonsils, spleen, thymus and bone marrow. They are bean-shaped structures with a cortex and medulla, similar to many other body organs.
The cortex (outside) of a lymph node contains many lymphocytes (a type of white blood cell) that are activated to fight off pathogens. Lymphocytes produce antibodies (Y-shaped proteins) that combine with antigens (proteins or polysaccharides on foreign cells) to form inactive antigen-antibody complexes, as shown in the following illustration.
In the medulla (middle) of the lymph nodes, macrophages, another form of white blood cell, engulf (phagocytize) foreign debris and clean up lymph fluid. Lymph nodes are found along lymph vessels and are most numerous in the groin, neck, and armpits. Swollen lymph nodes are a sign that an infection is present.
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Fetal Circulation
A human fetus (Latin = offspring) resembles a small person by three months. Hair is appearing, some cartilage begins to harden into bone, and it may be possible to determine the sex of the fetus. By four months, the fetal heartbeat can be heard with a stethoscope. By five months, the movement of the fetus can be felt by the mother. This lesson discusses the specialized features of fetal circulation that make it different from adult circulation.
Fetal circulation is modified to allow it to develop in the mother's uterus. One of the main differences is the transport of oxygenated blood from the mother to the fetus via the placenta. The fetus does not use its own pulmonary circuit and lungs until birth.
There are four main differences between the circulatory system of a fetus and an adult human. Two of these—umbilical cord and venous duct—are related to the exchange of oxygen between the fetal and maternal blood supply via the placenta.
In the placenta, fetal capillary beds are in close proximity to maternal capillary beds. Carbon dioxide and wastes from the fetus moved through the umbilical arteries are exchanged for oxygen and nutrients supplied by the mother. Note that fetal and maternal blood do not mix, and this exchange occurs across membranes by the process of diffusion.
The other two differences—oval opening and arterial duct—are temporary structural changes in the heart and blood vessels that allow the fetal circulation to bypass the lungs because the fetus does not breathe while in the uterus.
Refer to the diagram below and see Figure 22.15 on page 455 of your Inquiry Into Life textbook.
A human fetus (Latin = offspring) resembles a small person by three months. Hair is appearing, some cartilage begins to harden into bone, and it may be possible to determine the sex of the fetus. By four months, the fetal heartbeat can be heard with a stethoscope. By five months, the movement of the fetus can be felt by the mother. This lesson discusses the specialized features of fetal circulation that make it different from adult circulation.
Fetal circulation is modified to allow it to develop in the mother's uterus. One of the main differences is the transport of oxygenated blood from the mother to the fetus via the placenta. The fetus does not use its own pulmonary circuit and lungs until birth.
There are four main differences between the circulatory system of a fetus and an adult human. Two of these—umbilical cord and venous duct—are related to the exchange of oxygen between the fetal and maternal blood supply via the placenta.
In the placenta, fetal capillary beds are in close proximity to maternal capillary beds. Carbon dioxide and wastes from the fetus moved through the umbilical arteries are exchanged for oxygen and nutrients supplied by the mother. Note that fetal and maternal blood do not mix, and this exchange occurs across membranes by the process of diffusion.
The other two differences—oval opening and arterial duct—are temporary structural changes in the heart and blood vessels that allow the fetal circulation to bypass the lungs because the fetus does not breathe while in the uterus.
Refer to the diagram below and see Figure 22.15 on page 455 of your Inquiry Into Life textbook.
Umbilical Vein and Umbilical Arteries
The umbilical vein and the umbilical arteries are inside the umbilical cord that attaches the placenta to the umbilicus (future belly button) of the fetus. The umbilical vein carries oxygenated blood with maternal nutrients from the placenta to the fetus. The umbilical arteries carry deoxygenated blood with fetal waste from the fetus to the placenta. The umbilical arteries receive blood from the fetal heart via the dorsal aorta and both iliac arteries of the legs where they branch off to the umbilical cord.
The umbilical vein and the umbilical arteries are inside the umbilical cord that attaches the placenta to the umbilicus (future belly button) of the fetus. The umbilical vein carries oxygenated blood with maternal nutrients from the placenta to the fetus. The umbilical arteries carry deoxygenated blood with fetal waste from the fetus to the placenta. The umbilical arteries receive blood from the fetal heart via the dorsal aorta and both iliac arteries of the legs where they branch off to the umbilical cord.
Venous Duct
The venous duct receives blood from the umbilical vein and directs it to the posterior/inferior vena cava. This venous duct acts as a liver bypass and moves blood into the fetal systemic circulation. The liver bypass means it is possible for harmful substances in the mother's blood to be passed on to the fetus.
Oval Opening
The oval opening is a passage between the right and left atria of the heart. This opening is covered with a flap that allows blood to move from the right atrium to the left atrium only. This movement is aided by higher blood pressure in the right atrium than in the left because little blood returns to the left atrium from the lungs. Movement of blood from the right atrium to the left atrium bypasses the lungs and delivers most of the oxygenated blood from the placenta directly to the body.
Following birth and cutting the umbilical cord, blood begins to flow in and out of the lungs. Blood returning from the lungs to the left atrium closes the flap between the two atria. In some cases, the flap does not close and causes a “blue baby” whose lungs do not receive enough blood to be oxygenated. This condition may require surgery to be corrected.
Arterial Duct
The arterial duct is a connection between the pulmonary artery and the aorta. This duct directs blood away from the lungs and into systemic circulation. At birth, cells grow over the opening to the arterial duct and it closes.
The venous duct receives blood from the umbilical vein and directs it to the posterior/inferior vena cava. This venous duct acts as a liver bypass and moves blood into the fetal systemic circulation. The liver bypass means it is possible for harmful substances in the mother's blood to be passed on to the fetus.
Oval Opening
The oval opening is a passage between the right and left atria of the heart. This opening is covered with a flap that allows blood to move from the right atrium to the left atrium only. This movement is aided by higher blood pressure in the right atrium than in the left because little blood returns to the left atrium from the lungs. Movement of blood from the right atrium to the left atrium bypasses the lungs and delivers most of the oxygenated blood from the placenta directly to the body.
Following birth and cutting the umbilical cord, blood begins to flow in and out of the lungs. Blood returning from the lungs to the left atrium closes the flap between the two atria. In some cases, the flap does not close and causes a “blue baby” whose lungs do not receive enough blood to be oxygenated. This condition may require surgery to be corrected.
Arterial Duct
The arterial duct is a connection between the pulmonary artery and the aorta. This duct directs blood away from the lungs and into systemic circulation. At birth, cells grow over the opening to the arterial duct and it closes.
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