Anatomy and Physiology 12 - Circulatory System PDF

# Stevens - Anatomy and Physiology 12 ## UNIT 7: CIRCULATORY SYSTEM A "BLOODY" BRILLIANT UNIT We have learned earlier that oxygen is necessary to produce energy during cellular respiration. We have also learned that we break down our food into smaller monomers and polymers so we can absorb them i...

# Stevens - Anatomy and Physiology 12 ## UNIT 7: CIRCULATORY SYSTEM A "BLOODY" BRILLIANT UNIT We have learned earlier that oxygen is necessary to produce energy during cellular respiration. We have also learned that we break down our food into smaller monomers and polymers so we can absorb them into our cells to make new biomolecules. How do these nutrients get moved around the body? Where does the force that drives the flow of blood come from? Why does our heart make a "lub-dub" noise? All these questions and more will be explained in our exploration of the circulatory system. ### 7.1: ARTERIES, CAPILLARIES, VEINS #### Arteries **Function:** Arteries transport blood away from the heart. The largest arteries (aorta and pulmonary) are very elastic. They stretch when the ventricles eject the blood from the heart, then recoil, moving blood along. Arteries are often associated with carrying oxygen rich blood (but there are exceptions!) **Leads into:** The large arteries branch to form smaller arteries called arterioles. **Structure:** Thick, muscular, and elastic walls. **Location:** Usually found deep along bones #### Veins **Function:** Transports blood back to the heart **Structure:** Thin walls, contain valves. The valves prevent the backflow of blood. Without them blood would get stuck in your feet and legs. **Location:** Often on the surface, surrounded by skeletal muscles. **Blood from:** Very small veins which collect blood from capillaries called Venules #### Capillaries **Function:** Connect arteries and veins **Structure:** Very thin walls (1 cell thick). It takes ten of these to equal a human hair thickness. **Location:** Everywhere, within a few cells from each other. **How do they work?** They have sphincter muscles that can dilate and constrict the vessel. #### Arterioles and Venules All the features that apply to veins and arteries apply to arterioles and venules on a smaller scale. The arterioles leading to specific organs and regions will have sphincter muscles. When they are triggered they can dilate or constrict to regulate blood pressure by increasing or decreasing blood flow to particular capillary beds. You may see the term "afferent" which means incoming arteriole and "efferent" which means outgoing arteriole. Afferent arteriole = Arriving Q: If all the capillary beds were open at one time, it would decrease the blood pressure. If they were all closed, it would increase blood pressure. Why? A: Blood pressure is by definition; how hard blood is pressing against your arteries. If capillary beds were open and blood could easily flow, there would be lower pressure. If they are constricted, then the blood needs to be pumped with much more force which increases pressure... Imagine if these were on the surface of your skin and open all the time! Papercuts would be deadly! ### 7.2: MAJOR BLOOD VESSELS OF THE BODY #### Aorta **What:** Carries oxygenated blood out of the heart to the rest of the body. **Where:** It leaves the left ventricle and loops over the top of the heart, creating a structure known as the aortic arch and descends along the inside of the backbone. It is the largest artery in the body with the diameter being almost the size of a garden hose. #### Coronary Arteries and Veins **What:** Arteries: The coronary arteries. branches of the aorta are the coronary arteries. They feed and provide nutrients from the heart muscle. **Veins:** They take the oxygenated blood back to the heart. **Where:** These relatively small blood vessels can actually be seen on the surface of the heart. "Spent blood" is low in oxygen and high in carbon dioxide. This is because this term is used to describe blood that has delivered oxygen to the cells and picked up carbon dioxide. Study Tip: Think of a sprinter who is "spent" and has no energy, they would be gasping for breath and wanting more oxygen, like how spent blood has little oxygen. Q: Why does the heart not receive nutrients from blood as it passes through the heart? A: The heart does not receive nutrients from the blood that travels through it because the muscle is too dense and thick, and the blood is travelling through it too hard and fast. Another way of thinking about it would be like driving 100 miles per hour by the McDonalds drive through. It would be difficult to get any food at that speed, just because you are near nutrients doesn't necessarily mean you will get the. #### Anterior (Superior) and Posterior (Inferior) Vena Cava **What:** The largest vein of the body. These vessels collects deoxygenated blood from smaller veins and carries it to the right atrium of the heart. **Where:** The Anterior Vena Cava collects blood from the Upper body, while the Posterior Vena Cava collects blood from the lower body. You may also see the term "inferior" or "superior" Vena Cava. They are synonymous with "posterior" and "anterior” Vena Cava respectively. #### Carotid Arteries **What:** The main purpose of these is to bring oxygenated blood to the brain. They are highly specialized as they contain different types of nerves which are receptors which help to maintain homeostasis. These include chemoreceptors that detect oxygen content and pressure receptors that detect blood pressure changes. **Where:** These branch off the aortic arch and take the blood to the head If the carotid arteries take blood to the brain, what happens when they are blocked? Think of the symptoms of a stroke: dropping face, numbness and weakness of the face, arms, or legs, and difficulty with speech or vision. A cause of up to ⅓ of all strokes comes from carotid artery disease when there is blockage and damage to the carotid arteries which take blood to the head. #### Jugular Veins **What:** They bring deoxygenated blood from the head to the heart. (Opposite of Carotid artery) They do not contain valves (veins normally do) and use gravity for blood flow. **Where:** They conduct blood from the head to the Superior Vena Cava and then to the heart. The COMMON carotid artery and the INTERNAL jugular vein run side by side on the left and right and are the vessels that are bringing up and draining the blood in the brain. #### Subclavian Arteries and Veins **What:** These carry the blood around the arms and connect to the brachial arteries. The brachial artery carries blood towards and the brachial vein carries blood away from the arms and towards the heart. **Where:** Branch from the Aorta and travel under the clavicle. #### Mesenteric Arteries **What:** Bring blood to the organs of the digestive system and picks up newly digested nutrients from the digestive tract. **Where:** They branch off from the aorta as it travels posteriorly (this means towards the rear.) They go to the intestines where they branch into capillaries that can be identified as villi. (remember this word?) **Mesenteric Vein:** A large vein that returns blood from the intestines. You will be learning new terms in this unit which you will see many times in the future. The names of these indicate the part of the body they are connected to. For instance, "renal" refers to the kidneys. In this case "Hepatic" means liver "portal" which indicates that there is a capillary bed on both ends of it. #### Hepatic Portal Vein **What/where:** This is a mesenteric vein which brings blood from the digestive tract to the liver. It has a capillary bed on both ends of it. #### Hepatic Vein **What:** After the liver has cleansed the blood, it must return to the veins. **Where:** From the liver to the inferior vena cava #### Hepatic Artery **What:** Carries blood from the celiac artery to the liver **Where:** From the aorta to the liver. #### Renal Arteries **What:** Take blood to the kidneys **Where:** Branch off dorsal (lower) aorta and pass through the lumbar region (lower back). #### Renal Veins **What:** Take blood away from the kidneys. **Where:** From the kidneys back to the vena cava ### 7.3: THE HEART AND ITS PARTS The heart is essentially a pump made out of muscle. Despite its crude nature, it is an absolute workhorse. It contracts almost once a second all day everyday until you die. We'll look at the anatomy of the heart below. #### Atria (atrium pl.): collecting Chambers **Right:** Collects deoxygenated blood from Vena Cava. **Left:** Collects oxygenated blood from Pulmonary Veins. #### Ventricles: pumps **Right:** Sends blood to the lungs via the Pulmonary Trunk. **Left:** Sends blood to the body via the Aorta **Chordae Tendineae:** Strong, fibrous strings that support the AV valves. Keeps the valves from inverting with the force of blood flow. **Pulmonary Trunk:** Branches off to form the pulmonary Arteries. Receives blood from the right ventricle. **Septum:** The wall of the Heart. It Separates the left and right sides of the Heart The mitral valve is named after a very famous hat...that of the Pope! #### Valves **Atrioventricular Valves:** Valves between the atria and ventricles. Prevent backflow of blood from the ventricles into the atria. There are two kinds: 1. Right hand side "tricuspid": three cusps, or flaps 2. Left hand side bicuspid/mitral - two cusps **Semi-Lunar Valves:** Between ventricles and arteries exiting the heart There are two kinds: 1. Pulmonary Valve: Prevents back flow of blood from Pulmonary Trunk into right ventricle. 2. Aortic Valve: Prevents back flow of blood from aorta into left ventricle. Think of "Try, Performing, Better, Always" or (Tricuspid, Pulmonary, Bicuspid, and Aortic) to help you remember the positions of the heart valves and the order in which blood flows through the heart. Feel free to access the optional link/ QR code provided here for additional information about heart structure and function: https://www.nhlbi.nih.gov/health-topics/how-heart-works ### 7.4: CIRCUITS AND CROSS-SECTIONAL AREA - THE HARD STUFF There are technically two paths that blood is taking which can be considered "Circuits" because they loop back around on each other. This is called a double loop. The pulmonary circuit is comprised of the pulmonary trunk and arteries that deal strictly with the heart and lungs. #### Pulmonary Circuit: aka Heart and Lungs This circuit carries carbon dioxide filled blood to lungs for cleaning and returns oxygen rich blood to heart. *From right ventricle → pulmonary trunk → pulmonary arteries → lung capillaries → pulmonary veins left atrium* #### Systemic Circuit: Carries oxygen rich blood to the body tissues and returns the CO2 filled blood to the heart. *Vena cava → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve left ventricle → aortic valve, aorta → tissues of the body → repeat* You MUST memorize these pathways! Rather than straight up memorizing the terms, try to understand why they take these paths by looking at the structure of the heart and flow path. One way to look at it could be: Atria before ventricle because the atria are higher. Starting on the right they pass through the tRI(ght)cuspid to the right ventricle then to the lungs so use the "pulmonary terms". Back from the lungs is similar just on the other side starting at the left atrium then to the ventricle past the bicuspid. It has already been to the lungs so now it needs to go to the rest of the body, so it goes through the aorta. #### Cross Sectional Area This is a tricky diagram, but it refers to the relationship between blood vessels, pressure and cross-sectional area. Total cross sectional area of the blood vessels (sum of the cross-sectional area of all blood vessels of one type) has a major effect on blood flow. As cross-sectional area increases, velocity of the blood decreases. Velocity of the blood decrenses from arteries to arterioles to capillaries and increases in venules and veins. As CSA increases, blood pressure decreases. Once the blood pressure is lost in the capillaries it cannot be regained even though CSA of venules and veins increases, decreases? Take a look at the graph above. Check your understanding and see if you can answer these questions: 1. Which type of blood vessel has the highest blood pressure? 2. Which type of blood vessel has the lowest blood pressure? 3. Which type of blood vessel has the highest velocity? 4. Which type of blood vessel has the lowest velocity? 5. Which type of blood vessel has the highest CSA? 6. Which type of blood vessel has the lowest CSA? 1. Arteries 2. Veins 3. Arteries, but an increase is seen back at the veins 4. Capillaries, need time to exchange nutrients and waste with cells 5. Capillaries 6. Arteries and veins as higher velocity ### Putting it Together Right, now you know about the parts of the heart, the major veins and arteries in the body, and the pathways that they take. Using what you know, trace the pathway of a red blood cell from the starting point to the ending point below. This is a good halfway point tester so ensure that you understand the content up to this point, because soon we will be going more in depth about what happens at the capillaries. **Trace the path of blood:** 1. From the head to your toes 2. From the arm to the liver 3. From the heart muscle to the kidney? Answers to Putting it together on page 13: 1. Juglar vein to the vena cava to the right atrium to the right ventricle to the pulmonary artery to the lungs to the pulmonary vein to the left atrium to the left ventricle to the aorta to the iliac artery 2. Subclavian vein to the VC to the RA to the RV to the PA to the lungs to the PV to the LA to the LV to the aorta to the mesentric artery to the small intestine to the hepatic portal vein to the liver 3. Cardiac vein to the VC to the RA to the RV to the PA to the lungs to the PV to the LA to the LV to the aorta to the renal artery to the kidney ### 7.5 CAPILLARY-TISSUE FLUID EXCHANGE This picture will be your new best friend... #### Arterial end **Blood pressure is higher than osmotic pressure.** Liquid part of blood is forced out to form tissue fluid. #### Venous end **Osmotic pressure is higher than blood pressure.** Tissue fluid is reabsorbed. Capillaries are where fluids, gases, nutrients, and wastes are exchanged between the blood and body tissues by diffusion. Capillary walls contain small pores that allow certain substances to pass into and out of the blood vessel. This is called fluid exchange which controlled by blood pressure within the capillary vessel (hydrostatic pressure) and osmotic pressure of the blood within the vessel. The osmotic pressure is produced by high concentrations of salts & plasma proteins in the blood. The capillary walls allow water & solutes to pass between its pores but do not allow proteins to pass through. As blood enters the capillary bed on the arteriole end the blood pressure in the capillary vessel is greater than the osmotic pressure of the blood in the vessel. The net result is that fluid moves from the vessel to the tissues. At the middle of the capillary bed, blood pressure in the vessel equals the osmotic pressure of the blood in the vessel. The net result is that fluid passes equally between the capillary vessel and the body tissue. Gasses, nutrients, and wastes are exchanged at this point. On the venule end of the capillary bed, blood pressure in the vessel is less than the osmotic pressure of the blood in the vessel. The net result is that fluid, carbon dioxide and wastes are drawn from the body tissue into the capillary vessel. Tip to remember this better: "BAP" - Blood Pressure higher in Arterioles and VOP = Osmotic Pressure is higher in Venules Make sure that you understand the process behind capillary fluid exchange. As practice, draw the above image and explain what is happening to a friend. ### 7.6 FETAL CIRCULATION Now that you know the heart and its workings, you should know how it applies to tiny humans. There are a few pieces of anatomy unique to the fetus. These modifications are so blood avoids organs not currently in use! 1. **Oval Opening** aka (foramen ovale) There is an opening or small hole in the wall between the between the 2 atria chambers of the heart. It is covered by a flap of tissue that acts like a valve The blood flows directly from the right atrium to the left atrium. This allows blood to bypass the lungs, which do not work yet. 2. **Arterial Duct** (ductus arteriosus) This connects the pulmonary Artery and the Aorta. It also allows for the blood to bypass the lungs. 3. **Umbilical Artery and Vein** The Umbilical Artery takes wastes (aka carbon Dioxide and Urea) from the fetus to the placenta. The umbilical Vein takes nutrients (aka Oxygen and Glucose and Amino Acids) to the placenta to the fetus. 4. **Venous Duct** (ductus venosus) This connects the Umbilical Vein and the vena cava. Blood from the umbilical vein passes directly to the vena cava through the venous duct which allows blood to bypass the liver How many lungs can a human live with? 1. How many lungs can a baby live with? They need 2. Why? This is because more gas exchange occurs over a larger surface area so as when you are older when the lung surface area increases then you can live with 1 lung rather than 2. Let's trace this new blood path! Remember this is for a FETUS not an ADULT 1. Blood arrives via the umbilical vein. 2. The ductus venosus shunts oxygenated blood from the placenta away from the semi-functional liver and toward the heart 3. Oxygenated blood enters the atrium via inferior vena cava 4. The foramen ovale allows oxygenated blood in the right atrium to reach the 5. The ductus arteriosus connects the aorta with the pulmonary artery, further shunting blood away from the lungs and into the aorta 6. Mixed blood travels to the head and body, and back to the placenta via the aorta ### 7.7 WHAT MAKES YOUR HEARTBEAT? #### Seat Activity Put your hand on your heart. Did you place your hand on the left side of your chest? Many people do, but the heart is located almost in the center of the chest, between the lungs. It is tipped slightly so that a part of it sticks out and taps against the left side of the chest, which is what makes it seem as though it is located there. Hold out your hand and make a fist. If you are a child, your heart is about the same size as your fist, and if you are an adult, it is about the same size as two fists. DOES YOUR HEART REALLY BEAT TO THE BEAT OF THE DRUM?!?! Thanks KEЗНА... A heartbeat is a two-step process. **Systole:** Contraction of the Heart **Diastole:** Relaxation of the Heart Each heartbeat or cardiac cycle follows the following with the average rate of 70 beats per min. | Time | Atria | Ventricle | |:--:|:--:|:--:| | 0.15 sec | Systole | Diastole | | 0.30 sec | Diastole | Systole | | 0.40 sec | Diastole | Diastole | |=0.85 sec | | | Q: Why do the ventricles have a longer and stronger contraction? A: After the blood leaves the ventricles, it must be pumped throughout the entire body. Q: When you place your head on someone's chest and you can hear their heartbeat, what creates the sound you hear? Yes, your heart contracts, but when you contract your biceps. A: The opening and closing of valves! The signature lub - dub sound is due to the closing of valves, starting with atrioventricular and then semi-lunar. The beat of the heart is said to be intrinsic. This means it will beat without any nervous system stimulation. This also means it can be removed from the body and still continue beating (aka your favorite vampire shows are realistic). The beat is controlled by a special type of tissue called nodal tissue which has both muscular and nervous tissue characteristics. #### Key Terms: 1. **SA Node** (Sinoatrial Node) Found in the upper wall of the right atrium 2. **AV Node** (Atrioventricular Node) Pound at the bottom of the right atrium near the septum. 3. **Bundle of His** (The atrioventricular bundle) Passes into the ventricular septum and divides into two bundle branches -, the left and right bundles. 4. **Purkinje Fibers** The bundles of His are called Purkyně or Purkinje fibers. #### How it Works: SA is before/above AV. The signals are sent from SA to AV. Remember: San Antonio Spurs are better than the Atlanta Hawks. The SA Node (also called the pacemaker) initiates the heartbeat and sends out an excitation impulse every 0.85 seconds. The impulse causes both atria to contract. The impulses are sent to the AV node which controls the heart rate. The AV node serves as an electrical relay station, slowing the electrical current sent by the sinoatrial (SA) node to ensure the atria fully contract before the signal is permitted to pass down through to the ventricles. The Purkinje Fibers (in the walls of the ventricles and the septum) stimulates both ventricles to contract from the bottom upwards. The electrical signals produced by the different steps of your heart's contractions and relaxations can be tracked. You'll have seen this before in medical dramas where doctors or nurses look at an EKG readout and someone "flatlines". Their heart has stopped producing electrical signals...they're having a bad day! The chart on the right shows the voltage change (electrical signal) on an electrocardiogram during a heartbeat. Electrodes attached to the patient register the voltage change across the surface of the heart as it beats. The letters PQRST are the standard labels used to identify the parts of the ECG. The **P Curve** records the simultaneous contraction of the atria as they drive the blood out into their ventricles. The **QRS** is the contraction of the ventricles as they drive the blood out into their respective arteries. Note the much higher peak of the QRS phase of the cardiac cycle in the picture above. This is due to the much longer and stronger contraction of the ventricles pushing blood out of the heart. The **T** marks the recovery of the ventricles-(restoration of the normal electrical condition, preparing them for the next contraction). The rate of the heart can also be controlled by the nervous system. The heart rate center is located in the medulla of the brain. The SA Node is connected to the brain by the **Vagus** nerve (cranial nerve #10). This nerve pathway, part of the Autonomic Nervous System (not under conscious control), has two systems that affect the Heart Rate: 1. **Parasympathetic System** - Causes the heartbeat to slowdown 2. **Sympathetic System** - Causes the heartbeat to increase during times of stress Study Tip Ways to remember which is which: Sympathetic is like sympathy to other's stress which will increase stress/heartbeat, diastole sound like disaster, which is what will happen if you relax too much and don't study! ### 7.8 WHAT MAKES YOUR HEART NOT BEAT? Ventricles pump a volume of blood (approx. 70 ml) each time they contract. The arteries must have elastic, expandable walls to withstand this pressure. The force of blood against the blood vessel walls is simply known as **blood pressure** The term **systolic pressure** (or systole) refers to the pressure when the ventricles contract. This is the highest blood pressure reading. The term **diastolic pressure** (diastole) refers to the blood pressure when the heart is at rest. This is the lowest blood pressure reading. Blood pressure is normally measured along the brachial artery of the arm. **Pulse:** As blood is pumped through arteries, the arterial walls swell, and then recoil. This swelling can be felt in any artery that runs close to the surface. #### Cardiovascular Conditions **Hypertension - High (High) blood pressure** Example: 140/90 or 125/90 **Contributing Factors:** * Plaques aka atherosclerosis formed by the fatty deposits from digested foods; lines the walls of the arteries and make the radius smaller increasing the blood pressure. * High Salt intake retain water - greater fluid volume leads to blood in greater volume which results in increased blood pressure. * Stress * Smoking * Age, biological sex, race * Stimulants (class of drugs) * Lack of exercise * Diet **Cause is vitamin deficiency in the cells of the arteries which results in thickening and spasms of the arterial walls and an increase in blood pressure.** Natural prevention and natural treatment are an optimum intake of the following essential nutrients: Vitamin C (citrus fruits like oranges), Arginine (sesame seeds), Coenzyme Q-10 (fatty fish like trout), Magnesium (green leafy vegetables) **Hypotension - Low Blood Pressure** Example: 90/60 **Reasons:** Cuts or amputated limbs/ Drugs/ Hormones Blood does not reach all organs. Proper kidney function can only be maintained if there is a sufficient pressure for filtration. Luckily, the body can adjust blood pressure to some degree. Monitored by the hypothalamus in them or constrict (narrow) them to raise the blood pressure. This adjustment is an example of homeostasis. How does this apply to you and the way you need to live your life? According to hard data, five harmful habits herald the coming of heart disease. These five are: * smoking * being inactive * carrying too many pounds * eating poorly * drinking too much alcohol Alone and together, they set the stage for artery-damaging atherosclerosis and spur it onward. They do this by deranging metabolism and changing how cells and tissues work. They also disturb the markers of health we worry about so much: blood pressure, cholesterol, and blood sugar. All too often, the result of these five habits is a heart attack, stroke, peripheral artery disease, valve problem, aortic aneurysm, or heart failure. The damage they cause is not limited to the cardiovascular system, but extends to the kidneys, bones, and brain. Q: What can making healthier life choices do for your health and longevity? A: Consider this provocative finding from the Nurses' Health Study: "Non-smoking women with a healthy weight who exercised regularly, and consumed a healthy diet were 83% less likely to have had a heart attack or to have died of heart disease over a 14-year period, compared with all the other women in the study." The results were almost identical in a similar study in men. In these two studies, more than two-thirds of all cardiovascular events could be chalked up to smoking, excess weight, poor diet, and drinking too much alcohol.