Blood: Bringing life & PROTECTIon
Blood is an amazing component of our bodies. Without blood, our tissues would not receive oxygen and they wouldn't survive to grow--tissues would die off. Blood is composed of both solid components & liquid components. The solid components include red blood cells eryhtrocytes (the cells that carry oxygen), white blood cells or leukocytes (cells that are a part of the body's immune response), and platelets (components responsible for clotting). The liquid component is plasma, making up about 55% of the blood volume.
White blood cells are divided into 5 categories:
1. Neutrophils: Multi-lobed nuclei, these attack bacteria and make up about 50% of WBC's
2. Eosinophils: Bi-lobed nuclei, these target tapeworms and make up 1-3% of WBC's
3. Basophils: It's hard to see a nucleus here, these release histamines. Very large but only make up <1% of WBC's
4. Lymphocytes: The nucleus takes up all of the cell. Can be T-cells (target tumors) or B-cells (antibodies). Make up 25% of WBC's
5. Monocytes: Kidney shaped nucleus, also called "macrophage", these target bacteria and viruses. They make up 3-9% of WBC's
Note: Lymphocytes and monocytes are classified as "agranulocytes" (cytoplasm has no granules) whereas #1-3 are "granulocytes" (cytoplasm has granules).
White blood cells are divided into 5 categories:
1. Neutrophils: Multi-lobed nuclei, these attack bacteria and make up about 50% of WBC's
2. Eosinophils: Bi-lobed nuclei, these target tapeworms and make up 1-3% of WBC's
3. Basophils: It's hard to see a nucleus here, these release histamines. Very large but only make up <1% of WBC's
4. Lymphocytes: The nucleus takes up all of the cell. Can be T-cells (target tumors) or B-cells (antibodies). Make up 25% of WBC's
5. Monocytes: Kidney shaped nucleus, also called "macrophage", these target bacteria and viruses. They make up 3-9% of WBC's
Note: Lymphocytes and monocytes are classified as "agranulocytes" (cytoplasm has no granules) whereas #1-3 are "granulocytes" (cytoplasm has granules).
UnDERSTANDING BLOOD TYPES
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The 4 kinds of blood types are A, B, AB, and O. We all have our own different blood type, sometimes Rh+ and sometimes Rh-. If you have B+ blood type, you have type B blood with the Rh antigen on your cell. You also have B antigen and anti-A antibodies (your body will "attack" any type A blood).
An interesting situation to think about is when an Rh- woman is giving birth to an Rh+ baby. During the first birth, her body will not have time to react to the Rh antigen of the baby, but come second birth there is a problem. When her second birth comes around, her body has had time to create Antibody D (an antibody that binds to Rh+ blood cells). If the second baby's blood (Rh+) comes in contact with her Rh- blood, there will be agglutination (clotting up) in the fetal blood, causing swelling and rupture of the baby's red blood cells.
To better understand blood components and Rh factors, click below to watch a video.
An interesting situation to think about is when an Rh- woman is giving birth to an Rh+ baby. During the first birth, her body will not have time to react to the Rh antigen of the baby, but come second birth there is a problem. When her second birth comes around, her body has had time to create Antibody D (an antibody that binds to Rh+ blood cells). If the second baby's blood (Rh+) comes in contact with her Rh- blood, there will be agglutination (clotting up) in the fetal blood, causing swelling and rupture of the baby's red blood cells.
To better understand blood components and Rh factors, click below to watch a video.
The Human Heart
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The heart is composed of three layers, (from outside to inside) the pericardium, myocardium, and the endocardium. The pericardium is either fibrous or serous (can be serous parietal or serous visceral) and it lines the inside of the pericardium and surrounds the heart itself. The myocardium is entirely muscle and is much thicker in the left ventricle (this ventricle needs to pump blood throughout the entire body as opposed to just the lungs). The endocardium lines the inside of the heart and is also continuous with the lining of blood vessels in the body.
The heart is made up of four chambers, 2 ventricles and 2 atria. The Atria sit on the top portion of the heart whereas the ventricles dominate the bottom portion with their larger size. Look to the picture below to understand the arrangement.
The heart is made up of four chambers, 2 ventricles and 2 atria. The Atria sit on the top portion of the heart whereas the ventricles dominate the bottom portion with their larger size. Look to the picture below to understand the arrangement.
HOw the heart works
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We think of the heart as a blob of muscle that pumps blood. The question is, how does it actually pump blood throughout our body? It has a two part system. One part of the heart is receiving blood and the other part is discharging blood. On the right side of the heart, the system is called the pulmonary circuit, which moves blood/oxygen to and from the lungs only. The left side of the heart houses the systemic circuit, which transports blood to and from the entire body--this is why the left ventricle is thicker and stronger--it must send blood through the legs and arms (against gravity sometimes) unlike the right ventricle, which sends only a short distance to the lungs.
The blood that is coming into the heart is colored red on this chart (because it came from the lungs, oxygenated). The blood that is leaving the heart is colored blue (because it is deoxygenated and is on its way to the lungs to collect oxygen).
Remember that when looking at an image of the heart, you must tell right and left based on the heart being in someone's body, not from your point of view. The blue part of the heart in the image above is the right side, not the left.
The heart has its atria, ventricles, and it also has valves. The 4 valves of the heart are the atrioventricular valves (bicuspid, tricuspid) and the semi-lunar valves (pulmonary semilunar, aortic semilunar). These valves create pressure in the heart as they close and therefore permit the heart to pump blood through vessels. See these valves on the image below.
The blood that is coming into the heart is colored red on this chart (because it came from the lungs, oxygenated). The blood that is leaving the heart is colored blue (because it is deoxygenated and is on its way to the lungs to collect oxygen).
Remember that when looking at an image of the heart, you must tell right and left based on the heart being in someone's body, not from your point of view. The blue part of the heart in the image above is the right side, not the left.
The heart has its atria, ventricles, and it also has valves. The 4 valves of the heart are the atrioventricular valves (bicuspid, tricuspid) and the semi-lunar valves (pulmonary semilunar, aortic semilunar). These valves create pressure in the heart as they close and therefore permit the heart to pump blood through vessels. See these valves on the image below.
The direction of heart flow can be understood by following the diagram of flow on the image. Blood comes into the heart deoxgenated, used up, goes out of the heart into the lungs (pulmonary circuit) to be re-oxygenated, then goes back through the heart to be pumped out to the body so that body tissues receive oxygen (systemic circuit).
Coronary Circulation: We often don't think of the heart needing blood because it is constantly pumping it! However, there is such thing as a blood supply for the heart called "coronary circulation". There are blood vessels along the surface of the heart, see the image below to see how they wrap around the whole heart. There is a special artery in the heart that is usually the cause of heart attacks called the anterior interventricular arteries.
Coronary Circulation: We often don't think of the heart needing blood because it is constantly pumping it! However, there is such thing as a blood supply for the heart called "coronary circulation". There are blood vessels along the surface of the heart, see the image below to see how they wrap around the whole heart. There is a special artery in the heart that is usually the cause of heart attacks called the anterior interventricular arteries.
The microscopic heart & excitation
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The picture to the left is cardiac muscle. Cardiac muscle cells are short and fat. They branch out to each other as to allow faster communication between cells. The lines between the cells are intercalated disks (either desmosomes that keep cells stuck together or gap junctions that allow ions to pass--like doorways). The intercalated disks allow all cells to act together as a unit. How the heart muscle contracts is a whole different story!
Intrinsic conductionTHE SA NODE: Also called the pacemaker, this node generates impulses 75x/minute (called sinus rhythm). On its own, it beats 100x per minute and is naturally slowed down by the vagus nerve (releasing acetylcholine) to the lower 75x per minute.
THE AV NODE: This node is pretty cool. If the SA node is not working, this node will take over and keep the heart beating at 50x per minute on its own. The AV node delays impulses and allows the heart to fill with blood after the atria contract. (If this node is defective, it can result in total or partial heart block). These two nodes are responsible for the beat of a heart along with these steps! 1. SA node "ignites" 2. AV node depolarizes 3. AV bundle of HIS is excited (only electrical connection between atria & ventricles) 4. Right/Left bundle branches of the interventricular septum carry impulses down the heart to the apex (bottom point of heart). 5. Purkinje fibers spread the current through the apex and throughout the ventricular walls Note: The AV bundle of HIS and Purkinje fibers can keep the heart beating at 30 BPM without the AV or SA nodes. There are a lot of backup systems in the heart! |
Extrinsic conductionOutside of the heart, the beat is held together by the Autonomic Nervous System. The part of the brain that externally controls the heart is the medulla oblongata, labeled on the image below. There is a cardioacceleratory center (innervates SA & AV nodes) and a cardioinhibitory center (inhibits the nodes through parasympathetic fibers in the vagus nerve--Cranial X--which throws Acetylcholine at the SA node to slow it down). Sympathetic fibers are stimulated by stress and release norepinephrine to increase the HR. Parasympathetic fibers release acetylcholine (as mentioned above).
ElectrocardiographyWhen you go to the hospital or doctors office, you may have seen or experienced an EKG, or electrocardiogram. This measures the action potential activity of all parts of the heart. There are 3 waves: P wave (depolarization of SA node), QRS complex (ventricular depolarization), and the T wave (ventricular repolarization).
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Heart rate & Developmental aspects
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Aside from what's mentioned above, chemicals like epinephrine work to enhance heart rate. Epinephrine comes from the adrenal medulla. Thyroxine is another hormone that increase heart rate, but enhances the effects of norepinephrine and epinephrine. Too much thyroxine in a lifetime can cause serious heart damage. In addition to hormones, there must be a a balance of Ca2+ ions and K+ ions for normal heart function.
FACTORS THAT INFLUENCE HEART RATE: Age (infants have faster HR), Gender, Exercise, and what temperature your body is (the higher your temperature, the higher your HR)
Tachycardia is abnormally fast HR (above 100) and bradycardia is an abnormally slow HR (below 60).
HEART DEVELOPMENT: Development of the heart begins in the fetus. One heart structures that is special to the fetus is the foramen ovale. Because a fetus does not use lungs, they do not have a working pulmonary circuit because they simply do not need it. To keep blood flowing through the body and to "distract" it from the lungs, the foramen ovale exists. This is a small opening that connects the two atria so blood doesn't go through the pulmonary circuit. This opening closes shortly after birth when the infant takes her first breath. Defects of the infant heart cause mixing of systemic and pulmonary blood and involved narrowed valves or vessels that put more stress on the baby's heart. One defect is called a coarctation, shown in the image above. This is where the infant is born with a heart that has a narrowed aorta, increasing the work of the left ventricle. Click on the video link below to learn more about the fetal heart.
FACTORS THAT INFLUENCE HEART RATE: Age (infants have faster HR), Gender, Exercise, and what temperature your body is (the higher your temperature, the higher your HR)
Tachycardia is abnormally fast HR (above 100) and bradycardia is an abnormally slow HR (below 60).
HEART DEVELOPMENT: Development of the heart begins in the fetus. One heart structures that is special to the fetus is the foramen ovale. Because a fetus does not use lungs, they do not have a working pulmonary circuit because they simply do not need it. To keep blood flowing through the body and to "distract" it from the lungs, the foramen ovale exists. This is a small opening that connects the two atria so blood doesn't go through the pulmonary circuit. This opening closes shortly after birth when the infant takes her first breath. Defects of the infant heart cause mixing of systemic and pulmonary blood and involved narrowed valves or vessels that put more stress on the baby's heart. One defect is called a coarctation, shown in the image above. This is where the infant is born with a heart that has a narrowed aorta, increasing the work of the left ventricle. Click on the video link below to learn more about the fetal heart.
Blood vessels
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Arteries: carry blood away from heart, thicker muscle layer, causes higher BP. They are thicker in muscle so they can withstand the strength of incoming blood from the heart.
Veins: carry blood to the heart, thin muscle layer, causes lower BP. These have valves inside them as to ensure that blood going back to the heart (from the foot) does not keep getting pulled downward (the blood can move against gravity with valves). These rely more on breathing and muscle movement to move blood rather than a heartbeat. Veins have a wider lumen to allow for easier passage of blood as it fight gravity.
Capillaries: connect arteries & veins and are the destination of arteries (only made of tunica intima to allow passage of more particles at their oxygen exchange sites.
3 layers to a blood vessel:
1. Tunica intima: smooth tissue, lines the lumen (space) of all vessels
2. Tunica media: smooth muscle and sheets of elastin. This layer is responsible for vasodilation & constriction via the sympathetic nervous system.
3. Tunica externa: outer layer made of collagen that protects and reinforces vessel shape. Larger vessels contain what's called vaso vasorum that provides bloody supply to the blood vessel itself.
Capillary Exchange: In the capillaries, there is diffusion of oxygen and other nutrients as well as carbon dioxide and wastes from other tissues. Fat-soluble (lipid soluble) dissolve through endothelial cells (shown in image above). Water soluble components pass through the openings, clefts (openings between cells) & fenestrations (openings in the endothelium). Molecules like proteins must travel through the capillary via pinocytotic vesicles.
Veins: carry blood to the heart, thin muscle layer, causes lower BP. These have valves inside them as to ensure that blood going back to the heart (from the foot) does not keep getting pulled downward (the blood can move against gravity with valves). These rely more on breathing and muscle movement to move blood rather than a heartbeat. Veins have a wider lumen to allow for easier passage of blood as it fight gravity.
Capillaries: connect arteries & veins and are the destination of arteries (only made of tunica intima to allow passage of more particles at their oxygen exchange sites.
3 layers to a blood vessel:
1. Tunica intima: smooth tissue, lines the lumen (space) of all vessels
2. Tunica media: smooth muscle and sheets of elastin. This layer is responsible for vasodilation & constriction via the sympathetic nervous system.
3. Tunica externa: outer layer made of collagen that protects and reinforces vessel shape. Larger vessels contain what's called vaso vasorum that provides bloody supply to the blood vessel itself.
Capillary Exchange: In the capillaries, there is diffusion of oxygen and other nutrients as well as carbon dioxide and wastes from other tissues. Fat-soluble (lipid soluble) dissolve through endothelial cells (shown in image above). Water soluble components pass through the openings, clefts (openings between cells) & fenestrations (openings in the endothelium). Molecules like proteins must travel through the capillary via pinocytotic vesicles.
CEntral venous pressure & Blood pressure
Central venous pressure refers to the pressure within the right atrium of the heart. The pressure within this atrium affects pressure in all peripheral veins. This is almost like a car jam, where one major road is backed up, and then smaller roads experience problems too. The atrium becomes backed up with blood (especially with low BP) and the peripheral veins become backed up (this is often the cause of edema, as the blood is forced into tissues because it has no where else to go).
Blood pressure is the force the blood exerts on the walls of blood vessels throughout your body. It usually means the pressure in your systemic (throughout your body) arteries. If you go to the doctor and your reading is 120/80, the 120 is the systole (ventricle contraction) and the 80 is the diastole (ventricles relax). These are called the systolic and diastolic measurements.
Blood pressure is the force the blood exerts on the walls of blood vessels throughout your body. It usually means the pressure in your systemic (throughout your body) arteries. If you go to the doctor and your reading is 120/80, the 120 is the systole (ventricle contraction) and the 80 is the diastole (ventricles relax). These are called the systolic and diastolic measurements.
Wanna know something cool?
Something called vasomotor control helps to keep blood pressure under watch and at a normal level. Baroreceptors and chemoreceptors are a part of this phenomenon. Baroreceptors react to PRESSURE and when they are stretched by pressure, they signal the brain to dilate blood vessels to help decrease the BP and give blood more freedom in its path. They are located in the carotid sinus (protects the brain from high BP) and in the aortic arch (to protect the systemic--body circuit--from high BP). Amazing huh?
There are also chemoreceptors, these are sensitive to oxygen, pH, and carbon dioxide levels. These are located in the carotid artery and in the aorta. The main function of chemoreceptors is to regulate the rate of respiration. Once they sense low oxygen levels, they send signals to the cardioacceleratory center to move blood faster and stronger through the body. They ALSO signal the vasomotor center to constrict blood vessels to increase blood pressure. Increasing speed of blood flow and narrowing blood vessels brings blood back to the heart faster to ensure oxygen transport. Does this sound familiar to you when you're doing a tough workout at the fitness center?
There are also chemoreceptors, these are sensitive to oxygen, pH, and carbon dioxide levels. These are located in the carotid artery and in the aorta. The main function of chemoreceptors is to regulate the rate of respiration. Once they sense low oxygen levels, they send signals to the cardioacceleratory center to move blood faster and stronger through the body. They ALSO signal the vasomotor center to constrict blood vessels to increase blood pressure. Increasing speed of blood flow and narrowing blood vessels brings blood back to the heart faster to ensure oxygen transport. Does this sound familiar to you when you're doing a tough workout at the fitness center?