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By careful placement of surface electrodes on the body, it is possible to record the complex, compound electrical signal of the heart. This tracing of the electrical signal is the **electrocardiogram (ECG)**, also commonly abbreviated EKG (K coming kardiology, from the German term for cardiology). Careful analysis of t... | {
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"Header 3": "**Electrocardiogram**",
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Occassionally, an area of the heart other than the SA node will initiate an impulse that will be followed by a premature contraction. Such an area, which may actually be a component of the conduction system or some other contractile cells, is known as an ectopic focus or ectopic pacemaker. An ectopic focus may be stimu... | {
"Header 1": "**19.2 | Cardiac Muscle and Electrical Activity**",
"Header 2": "**ECG Abnormalities**",
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In the event that the electrical activity of the heart is severely disrupted, cessation of electrical activity or fibrillation may occur. In fibrillation, the heart beats in a wild, uncontrolled manner, which prevents it from being able to pump effectively. Atrial fibrillation (see **[Figure 19.25](#page-823-0)b**) is ... | {
"Header 1": "**19.2 | Cardiac Muscle and Electrical Activity**",
"Header 2": "**External Automated Defibrillators**",
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By the end of this section, you will be able to:
- Describe the relationship between blood pressure and blood flow
- Summarize the events of the cardiac cycle
- Compare atrial and ventricular systole and diastole
- Relate heart sounds detected by auscultation to action of heart's valves
The period of time that begi... | {
"Header 1": "**19.3 | Cardiac Cycle**",
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Ventricular systole (see **[Figure 19.27](#page-825-1)**) follows the depolarization of the ventricles and is represented by the QRS complex in the ECG. It may be conveniently divided into two phases, lasting a total of 270 ms. At the end of atrial systole and just prior to atrial contraction, the ventricles contain ap... | {
"Header 1": "**19.3 | Cardiac Cycle**",
"Header 3": "**Ventricular Systole**",
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Ventricular relaxation, or diastole, follows repolarization of the ventricles and is represented by the T wave of the ECG. It too is divided into two distinct phases and lasts approximately 430 ms.
During the early phase of ventricular diastole, as the ventricular muscle relaxes, pressure on the remaining blood withi... | {
"Header 1": "**19.3 | Cardiac Cycle**",
"Header 3": "**Ventricular Diastole**",
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One of the simplest, yet effective, diagnostic techniques applied to assess the state of a patient's heart is auscultation using a stethoscope.
In a normal, healthy heart, there are only two audible **heart sounds**: S1 and S2. S1 is the sound created by the closing of the atrioventricular valves during ventricular c... | {
"Header 1": "**19.3 | Cardiac Cycle**",
"Header 3": "**Heart Sounds**",
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SV is normally measured using an echocardiogram to record EDV and ESV, and calculating the difference: SV = EDV – ESV. SV can also be measured using a specialized catheter, but this is an invasive procedure and far more dangerous to the patient. A mean SV for a resting 70-kg (150-lb) individual would be approximately 7... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "CO = HR × SV",
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For an adult, normal resting HR will be in the range of 60–100 bpm. Bradycardia is the condition in which resting rate drops below 60 bpm, and tachycardia is the condition in which the resting rate is above 100 bpm. Trained athletes typically have very low HRs. If the patient is not exhibiting other symptoms, such as w... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Heart: Abnormal Heart Rates**",
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Initially, physiological conditions that cause HR to increase also trigger an increase in SV. During exercise, the rate of blood returning to the heart increases. However as the HR rises, there is less time spent in diastole and consequently less time for the ventricles to fill with blood. Even though there is less fil... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Correlation Between Heart Rates and Cardiac Output**",
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Nervous control over HR is centralized within the two paired cardiovascular centers of the medulla oblongata (**[Figure](#page-832-0) [19.32](#page-832-0)**). The cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, and the cardioinhibitory centers decrease heart act... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Cardiovascular Centers**",
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The cardiovascular center receives input from a series of visceral receptors with impulses traveling through visceral sensory fibers within the vagus and sympathetic nerves via the cardiac plexus. Among these receptors are various proprioreceptors, baroreceptors, and chemoreceptors, plus stimuli from the limbic system.... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Input to the Cardiovascular Center**",
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Extreme stress from such life events as the death of a loved one, an emotional break up, loss of income, or foreclosure of a home may lead to a condition commonly referred to as broken heart syndrome. This condition may also be called Takotsubo cardiomyopathy, transient apical ballooning syndrome, apical ballooning car... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Heart: Broken Heart Syndrome**",
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Using a combination of autorhythmicity and innervation, the cardiovascular center is able to provide relatively precise control over HR. However, there are a number of other factors that have an impact on HR as well, including epinephrine, NE, and thyroid hormones; levels of various ions including calcium, potassium, a... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Other Factors Influencing Heart Rate**",
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Caffeine and nicotine are not found naturally within the body. Both of these nonregulated drugs have an excitatory effect on membranes of neurons in general and have a stimulatory effect on the cardiac centers specifically, causing an increase in HR. Caffeine works by increasing the rates of depolarization at the SA no... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Caffeine and Nicotine**",
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HR can be slowed when a person experiences altered sodium and potassium levels, hypoxia, acidosis, alkalosis, and hypothermia (see **[Table 19.1](#page-834-0)**). The relationship between electrolytes and HR is complex, but maintaining electrolyte balance is critical to the normal wave of depolarization. Of the two ion... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Factors Decreasing Heart Rate**",
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Preload is another way of expressing EDV. Therefore, the greater the EDV is, the greater the preload is. One of the primary factors to consider is **filling time**, or the duration of ventricular diastole during which filling occurs. The more rapidly the heart contracts, the shorter the filling time becomes, and the lo... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Preload**",
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It is virtually impossible to consider preload or ESV without including an early mention of the concept of contractility. Indeed, the two parameters are intimately linked. Contractility refers to the force of the contraction of the heart muscle, which controls SV, and is the primary parameter for impacting ESV. The mor... | {
"Header 1": "**19.4 | Cardiac Physiology**",
"Header 3": "**Contractility**",
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By the end of this section, you will be able to:
- Describe the embryological development of heart structures
- Identify five regions of the fetal heart
- Relate fetal heart structures to adult counterparts
The human heart is the first functional organ to develop. It begins beating and pumping blood around day 21 o... | {
"Header 1": "**19.5** | Development of the Heart",
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**afterload** force the ventricles must develop to effectively pump blood against the resistance in the vessels
- **anastomosis** (plural = anastomoses) area where vessels unite to allow blood to circulate even if there may be partial blockage in another branch
- **anterior cardiac veins** vessels that parallel the s... | {
"Header 1": "**19.5** | Development of the Heart",
"Header 3": "**KEY TERMS**",
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Bachmann's bundle) group of specialized conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium
- **interatrial septum** cardiac septum located between the two atria; contains the fossa ovalis after birth
- **intercalated disc** physical junction between adjacent card... | {
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"Header 3": "**KEY TERMS**",
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the difference between EDV and ESV
- **sulcus** (plural = sulci) fat-filled groove visible on the surface of the heart; coronary vessels are also located in these areas
- **superior vena cava** large systemic vein that returns blood to the heart from the superior portion of the body
- **systemic circuit** blood flow to... | {
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"Header 3": "**KEY TERMS**",
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The heart resides within the pericardial sac and is located in the mediastinal space within the thoracic cavity. The pericardial sac consists of two fused layers: an outer fibrous capsule and an inner parietal pericardium lined with a serous membrane. Between the pericardial sac and the heart is the pericardial cavity,... | {
"Header 1": "**19.5** | Development of the Heart",
"Header 3": "**[19.1 Heart Anato](#page-790-1)[my](#page-791-0)**",
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The heart is regulated by both neural and endocrine control, yet it is capable of initiating its own action potential followed by muscular contraction. The conductive cells within the heart establish the heart rate and transmit it through the myocardium. The contractile cells contract and propel the blood. The normal p... | {
"Header 1": "**19.5** | Development of the Heart",
"Header 3": "**[19.2 Cardiac Muscle and Electrical Activity](#page-812-0)**",
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The cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0.8 seconds. Beginning with all chambers in diastole, blood flows passively from the veins into the atria and past the atrioventricular valves into the ventricles. The atria begin to contract (atr... | {
"Header 1": "**19.5** | Development of the Heart",
"Header 3": "**[19.3 Cardiac Cycle](#page-825-0)**",
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The heart is the first organ to form and become functional, emphasizing the importance of transport of material to and from the developing infant. It originates about day 18 or 19 from the mesoderm and begins beating and pumping blood about day 21 or 22. It forms from the cardiogenic region near the head and is visible... | {
"Header 1": "**19.5** | Development of the Heart",
"Header 3": "**[19.5 Development of the Heart](#page-839-0)**",
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By the end of this section, you will be able to:
- Compare and contrast the three tunics that make up the walls of most blood vessels
- Distinguish between elastic arteries, muscular arteries, and arterioles on the basis of structure, location, and function
- Describe the basic structure of a capillary bed, from the ... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
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Different types of blood vessels vary slightly in their structures, but they share the same general features. Arteries and arterioles have thicker walls than veins and venules because they are closer to the heart and receive blood that is surging at a far greater pressure (**[Figure 20.3](#page-853-0)**). Each type of ... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Shared Structures**",
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The **tunica intima** (also called the tunica interna) is composed of epithelial and connective tissue layers. Lining the tunica intima is the specialized simple squamous epithelium called the endothelium, which is continuous throughout the entire vascular system, including the lining of the chambers of the heart. Dama... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Tunica Intima**",
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The **tunica media** is the substantial middle layer of the vessel wall (see **[Figure 20.3](#page-853-0)**). It is generally the thickest layer in arteries, and it is much thicker in arteries than it is in veins. The tunica media consists of layers of smooth muscle supported by connective tissue that is primarily made... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Tunica Media**",
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An **artery** is a blood vessel that conducts blood away from the heart. All arteries have relatively thick walls that can withstand the high pressure of blood ejected from the heart. However, those close to the heart have the thickest walls, containing a high percentage of elastic fibers in all three of their tunics. ... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Arteries**",
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An **arteriole** is a very small artery that leads to a capillary. Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. The critical endothelial lining of the tunica intima is intact. The tunica media is restricted to one or two smooth muscle cell layers in thick... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Arterioles**",
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A **capillary** is a microscopic channel that supplies blood to the tissues themselves, a process called **perfusion**. Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). The diameter of a capillary lumen ranges from ... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Capillaries**",
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The most common type of capillary, the **continuous capillary**, is found in almost all vascularized tissues. Continuous capillaries are characterized by a complete endothelial lining with tight junctions between endothelial cells. Although a tight junction is usually impermeable and only allows for the passage of wate... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Continuous Capillaries**",
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A **sinusoid capillary** (or sinusoid) is the least common type of capillary. Sinusoid capillaries are flattened, and they have extensive intercellular gaps and incomplete basement membranes, in addition to intercellular clefts and fenestrations. This gives them an appearance not unlike Swiss cheese. These very large o... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Sinusoid Capillaries**",
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A **metarteriole** is a type of vessel that has structural characteristics of both an arteriole and a capillary. Slightly larger than the typical capillary, the smooth muscle of the tunica media of the metarteriole is not continuous but forms rings of smooth muscle (sphincters) prior to the entrance to the capillaries.... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Metarterioles and Capillary Beds**",
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A **vein** is a blood vessel that conducts blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens (see **[Figure 20.7](#page-859-0)**). Because they are low-pressure vessels, larger veins are commonly equipped with valves that promote the unidirectional flow of blood... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Veins**",
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Despite the presence of valves and the contributions of other anatomical and physiological adaptations we will cover shortly, over the course of a day, some blood will inevitably pool, especially in the lower limbs, due to the pull of gravity. Any blood that accumulates in a vein will increase the pressure within it, w... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Cardiovascular System: Edema and Varicose Veins**",
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In addition to their primary function of returning blood to the heart, veins may be considered blood reservoirs, since systemic veins contain approximately 64 percent of the blood volume at any given time (**[Figure 20.9](#page-861-0)**). Their ability to hold this much blood is due to their high **capacitance**, that ... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Veins as Blood Reservoirs**",
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When blood flow needs to be redistributed to other portions of the body, the vasomotor center located in the medulla oblongata sends sympathetic stimulation to the smooth muscles in the walls of the veins, causing constriction—or in this case, venoconstriction. Less dramatic than the vasoconstriction seen in smaller ar... | {
"Header 1": "**20.1 | Structure and Function of Blood Vessels**",
"Header 3": "**Figure 20.9 Distribution of Blood Flow**",
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By the end of this section, you will be able to:
- Distinguish between systolic pressure, diastolic pressure, pulse pressure, and mean arterial pressure
- Describe the clinical measurement of pulse and blood pressure
- Identify and discuss five variables affecting arterial blood flow and blood pressure
- Discuss seve... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
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As shown in **[Figure 20.10](#page-864-0)**, the difference between the systolic pressure and the diastolic pressure is the **pulse pressure**. For example, an individual with a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg would have a pulse pressure of 40 mmHg.
Generally, a pulse pressure shou... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Pulse Pressure**",
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**Mean arterial pressure (MAP)** represents the "average" pressure of blood in the arteries, that is, the average force driving blood into vessels that serve the tissues. Mean is a statistical concept and is calculated by taking the sum of the values divided by the number of values. Although complicated to measure dire... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Mean Arterial Pressure**",
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After blood is ejected from the heart, elastic fibers in the arteries help maintain a high-pressure gradient as they expand to accommodate the blood, then recoil. This expansion and recoiling effect, known as the **pulse**, can be palpated manually or measured electronically. Although the effect diminishes over distanc... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Pulse**",
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Blood pressure is one of the critical parameters measured on virtually every patient in every healthcare setting. The technique used today was developed more than 100 years ago by a pioneering Russian physician, Dr. Nikolai Korotkoff. Turbulent blood flow through the vessels can be heard as a soft ticking while measuri... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Measurement of Blood Pressure**",
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Jean Louis Marie Poiseuille was a French physician and physiologist who devised a mathematical equation describing blood flow and its relationship to known parameters. The same equation also applies to engineering studies of the flow of fluids. Although understanding the math behind the relationships among the factors ... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**A Mathematical Approach to Factors Affecting Blood Flow**",
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The relationship between blood volume, blood pressure, and blood flow is intuitively obvious. Water may merely trickle along a creek bed in a dry season, but rush quickly and under great pressure after a heavy rain. Similarly, as blood volume decreases, pressure and flow decrease. As blood volume increases, pressure an... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Blood Volume**",
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Viscosity is the thickness of fluids that affects their ability to flow. Clean water, for example, is less viscous than mud. The viscosity of blood is directly proportional to resistance and inversely proportional to flow; therefore, any condition that causes viscosity to increase will also increase resistance and decr... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Blood Viscosity**",
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The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood. Likewise, if the vessel is shortened, the resistanc... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Vessel Length and Diameter**",
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Recall that we classified arterioles as resistance vessels, because given their small lumen, they dramatically slow the flow of blood from arteries. In fact, arterioles are the site of greatest resistance in the entire vascular network. This may seem surprising, given that capillaries have a smaller size. How can this ... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**The Roles of Vessel Diameter and Total Area in Blood Flow and Blood Pressure**",
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Compliance allows an artery to expand when blood is pumped through it from the heart, and then to recoil after the surge has passed. This helps promote blood flow. In arteriosclerosis, compliance is reduced, and pressure and resistance within the vessel increase. This is a leading cause of hypertension and coronary hea... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Cardiovascular System: Arteriosclerosis**",
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In many body regions, the pressure within the veins can be increased by the contraction of the surrounding skeletal muscle. This mechanism, known as the **skeletal muscle pump** (**[Figure 20.15](#page-871-0)**), helps the lower-pressure veins counteract the force of gravity, increasing pressure to move blood back to t... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Skeletal Muscle Pump**",
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The **respiratory pump** aids blood flow through the veins of the thorax and abdomen. During inhalation, the volume of the thorax increases, largely through the contraction of the diaphragm, which moves downward and compresses the abdominal cavity. The elevation of the chest caused by the contraction of the external in... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Respiratory Pump**",
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Although vessel diameter increases from the smaller venules to the larger veins and eventually to the venae cavae (singular = vena cava), the total cross-sectional area actually decreases (see **[Figure 20.15](#page-871-0)a** and **b**). The individual veins are larger in diameter than the venules, but their total numb... | {
"Header 1": "**20.2 | Blood Flow, Blood Pressure, and Resistance**",
"Header 3": "**Pressure Relationships in the Venous System**",
"token_count": 271,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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By the end of this section, you will be able to:
- Identify the primary mechanisms of capillary exchange
- Distinguish between capillary hydrostatic pressure and blood colloid osmotic pressure, explaining the contribution of each to net filtration pressure
- Compare filtration and reabsorption
- Explain the fate of f... | {
"Header 1": "**20.3 | Capillary Exchange**",
"token_count": 269,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The primary force driving fluid transport between the capillaries and tissues is hydrostatic pressure, which can be defined as the pressure of any fluid enclosed in a space. **Blood hydrostatic pressure** is the force exerted by the blood confined within blood vessels or heart chambers. Even more specifically, the pres... | {
"Header 1": "**20.3 | Capillary Exchange**",
"Header 3": "**Hydrostatic Pressure**",
"token_count": 212,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The net pressure that drives reabsorption—the movement of fluid from the interstitial fluid back into the capillaries—is called osmotic pressure (sometimes referred to as oncotic pressure). Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in. Osmotic pressure is determin... | {
"Header 1": "**20.3 | Capillary Exchange**",
"Header 3": "**Osmotic Pressure**",
"token_count": 427,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The normal unit used to express pressures within the cardiovascular system is millimeters of mercury (mm Hg). When blood leaving an arteriole first enters a capillary bed, the CHP is quite high—about 35 mm Hg. Gradually, this initial CHP declines as the blood moves through the capillary so that by the time the blood ha... | {
"Header 1": "**20.3 | Capillary Exchange**",
"Header 3": "**Interaction of Hydrostatic and Osmotic Pressures**",
"token_count": 606,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Since overall CHP is higher than BCOP, it is inevitable that more net fluid will exit the capillary through filtration at the arterial end than enters through reabsorption at the venous end. Considering all capillaries over the course of a day, this can be quite a substantial amount of fluid: Approximately 24 liters pe... | {
"Header 1": "**20.3 | Capillary Exchange**",
"Header 3": "**The Role of Lymphatic Capillaries**",
"token_count": 275,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
By the end of this section, you will be able to:
- Discuss the mechanisms involved in the neural regulation of vascular homeostasis
- Describe the contribution of a variety of hormones to the renal regulation of blood pressure
- Identify the effects of exercise on vascular homeostasis
- Discuss how hypertension, hemo... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"token_count": 286,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Neurological regulation of blood pressure and flow depends on the cardiovascular centers located in the medulla oblongata. This cluster of neurons responds to changes in blood pressure as well as blood concentrations of oxygen, carbon dioxide, and hydrogen ions. The cardiovascular center contains three distinct paired ... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**The Cardiovascular Centers in the Brain**",
"token_count": 394,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Baroreceptors are specialized stretch receptors located within thin areas of blood vessels and heart chambers that respond to the degree of stretch caused by the presence of blood. They send impulses to the cardiovascular center to regulate blood pressure. Vascular baroreceptors are found primarily in sinuses (small ca... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Baroreceptor Reflexes**",
"token_count": 549,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
In addition to the baroreceptors are chemoreceptors that monitor levels of oxygen, carbon dioxide, and hydrogen ions (pH), and thereby contribute to vascular homeostasis. Chemoreceptors monitoring the blood are located in close proximity to the baroreceptors in the aortic and carotid sinuses. They signal the cardiovasc... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Chemoreceptor Reflexes**",
"token_count": 385,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The renin-angiotensin-aldosterone mechanism has a major effect upon the cardiovascular system (**[Figure 20.19](#page-879-0)**). Renin is an enzyme, although because of its importance in the renin-angiotensin-aldosterone pathway, some sources identify it as a hormone. Specialized cells in the kidneys found in the juxta... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Renin-Angiotensin-Aldosterone Mechanism**",
"token_count": 389,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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Chemical signals work at the level of the precapillary sphincters to trigger either constriction or relaxation. As you know, opening a precapillary sphincter allows blood to flow into that particular capillary, whereas constricting a precapillary sphincter temporarily shuts off blood flow to that region. The factors in... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Chemical Signals Involved in Autoregulation**",
"token_count": 342,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The **myogenic response** is a reaction to the stretching of the smooth muscle in the walls of arterioles as changes in blood flow occur through the vessel. This may be viewed as a largely protective function against dramatic fluctuations in blood pressure and blood flow to maintain homeostasis. If perfusion of an orga... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**The Myogenic Response**",
"token_count": 1019,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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The heart is a muscle and, like any muscle, it responds dramatically to exercise. For a healthy young adult, cardiac output (heart rate × stroke volume) increases in the nonathlete from approximately 5.0 liters (5.25 quarts) per minute to a maximum of about 20 liters (21 quarts) per minute. Accompanying this will be an... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Effect of Exercise on Vascular Homeostasis**",
"token_count": 785,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Chronically elevated blood pressure is known clinically as **hypertension**. It is defined as chronic and persistent blood pressure measurements of 140/90 mm Hg or above. Pressures between 120/80 and 140/90 mm Hg are defined as prehypertension. About 68 million Americans currently suffer from hypertension. Unfortunatel... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Hypertension and Hypotension**",
"token_count": 268,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Minor blood loss is managed by hemostasis and repair. Hemorrhage is a loss of blood that cannot be controlled by hemostatic mechanisms. Initially, the body responds to hemorrhage by initiating mechanisms aimed at increasing blood pressure and maintaining blood flow. Ultimately, however, blood volume will need to be res... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Hemorrhage**",
"token_count": 382,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The loss of too much blood may lead to **circulatory shock**, a life-threatening condition in which the circulatory system is unable to maintain blood flow to adequately supply sufficient oxygen and other nutrients to the tissues to maintain cellular metabolism. It should not be confused with emotional or psychological... | {
"Header 1": "**20.4 | Homeostatic Regulation of the Vascular System**",
"Header 3": "**Circulatory Shock**",
"token_count": 865,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
By the end of this section, you will be able to:
- Identify the vessels through which blood travels within the pulmonary circuit, beginning from the right ventricle of the heart and ending at the left atrium
- Create a flow chart showing the major systemic arteries through which blood travels from the aorta and its m... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"token_count": 928,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
As you learn about the vessels of the systemic and pulmonary circuits, notice that many arteries and veins share the same names, parallel one another throughout the body, and are very similar on the right and left sides of the body. These pairs of vessels will be traced through only one side of the body. Where differen... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Figure 20.22 Interaction of the Circulatory System with Other Body Systems**",
"token_count": 628,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Recall that blood returning from the systemic circuit enters the right atrium (**[Figure 20.23](#page-887-0)**) via the superior and inferior venae cavae and the coronary sinus, which drains the blood supply of the heart muscle. These vessels will be described more fully later in this section. This blood is relatively ... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Pulmonary Circulation**",
"token_count": 534,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The **aorta** is the largest artery in the body (**[Figure 20.25](#page-889-0)**). It arises from the left ventricle and eventually descends to the abdominal region, where it bifurcates at the level of the fourth lumbar vertebra into the two common iliac arteries. The aorta consists of the ascending aorta, the aortic a... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**The Aorta**",
"token_count": 497,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
There are three major branches of the aortic arch: the brachiocephalic artery, the left common carotid artery, and the left subclavian (literally "under the clavicle") artery. As you would expect based upon proximity to the heart, each of these vessels is classified as an elastic artery.
The brachiocephalic artery is... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Aortic Arch Branches**",
"token_count": 1443,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
| Vessel | Description ... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Aortic Arch Branches and Brain Circulation**",
"token_count": 856,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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The thoracic aorta begins at the level of vertebra T5 and continues through to the diaphragm at the level of T12, initially traveling within the mediastinum to the left of the vertebral column. As it passes through the thoracic region, the thoracic aorta gives rise to several branches, which are collectively referred t... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Thoracic Aorta and Major Branches**",
"token_count": 552,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
After crossing through the diaphragm at the aortic hiatus, the thoracic aorta is called the abdominal aorta (see **[Figure 20.28](#page-893-0)**). This vessel remains to the left of the vertebral column and is embedded in adipose tissue behind the peritoneal cavity. It formally ends at approximately the level of verteb... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Abdominal Aorta and Major Branches**",
"token_count": 1164,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
As the subclavian artery exits the thorax into the axillary region, it is renamed the **axillary artery**. Although it does branch and supply blood to the region near the head of the humerus (via the humeral circumflex arteries), the majority of the vessel continues into the upper arm, or brachium, and becomes the brac... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Arteries Serving the Upper Limbs**",
"token_count": 833,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The external iliac artery exits the body cavity and enters the femoral region of the lower leg (**[Figure 20.33](#page-900-0)**). As it passes through the body wall, it is renamed the **femoral artery**. It gives off several smaller branches as well as the lateral **deep femoral artery** that in turn gives rise to a **... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Arteries Serving the Lower Limbs**",
"token_count": 1182,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Systemic veins return blood to the right atrium. Since the blood has already passed through the systemic capillaries, it will be relatively low in oxygen concentration. In many cases, there will be veins draining organs and regions of the body with the same name as the arteries that supplied these regions and the two o... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Overview of Systemic Veins**",
"token_count": 667,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The **superior vena cava** drains most of the body superior to the diaphragm (**[Figure 20.36](#page-904-0)**). On both the left and right sides, the **subclavian vein** forms when the axillary vein passes through the body wall from the axillary region. It fuses with the external and internal jugular veins from the hea... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**The Superior Vena Cava**",
"token_count": 600,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Circulation to the brain is both critical and complex (see **[Figure 20.37](#page-906-0)**). Many smaller veins of the brain stem and the superficial veins of the cerebrum lead to larger vessels referred to as intracranial sinuses. These include the superior and inferior sagittal sinuses, straight sinus, cavernous sinu... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Venous Drainage of the Brain**",
"token_count": 554,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The **digital veins** in the fingers come together in the hand to form the **palmar venous arches** (**[Figure 20.38](#page-908-0)**). From here, the veins come together to form the radial vein, the ulnar vein, and the median antebrachial vein. The **radial vein** and the **ulnar vein** parallel the bones of the forear... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Veins Draining the Upper Limbs**",
"token_count": 531,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Other than the small amount of blood drained by the azygos and hemiazygos veins, most of the blood inferior to the diaphragm drains into the inferior vena cava before it is returned to the heart (see **[Figure 20.36](#page-904-0)**). Lying just beneath the parietal peritoneum in the abdominal cavity, the **inferior ven... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**The Inferior Vena Cava**",
"token_count": 614,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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The superior surface of the foot drains into the digital veins, and the inferior surface drains into the **plantar veins**, which flow into a complex series of anastomoses in the feet and ankles, including the **dorsal venous arch** and the **plantar venous arch** (**[Figure 20.41](#page-913-0)**). From the dorsal veno... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Veins Draining the Lower Limbs**",
"token_count": 745,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The liver is a complex biochemical processing plant. It packages nutrients absorbed by the digestive system; produces plasma proteins, clotting factors, and bile; and disposes of worn-out cell components and waste products. Instead of entering the circulation directly, absorbed nutrients and certain wastes (for example... | {
"Header 1": "**20.5 | Circulatory Pathways**",
"Header 3": "**Hepatic Portal System**",
"token_count": 624,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
By the end of this section, you will be able to:
- Describe the development of blood vessels
- Describe the fetal circulation
In a developing embryo,the heart has developed enough by day 21 post-fertilization to begin beating. Circulation patterns are clearly established by the fourth week of embryonic life. It is ... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"token_count": 1241,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
**abdominal aorta** portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries
**adrenal artery** branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands
**adrenal vein** drains the adrenal or suprarenal glands that are immediately superior to the kidneys; ... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**KEY TERMS**",
"token_count": 1405,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
and flows into the internal jugular vein - **phrenic vein** drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein leads to the left renal vein - **plantar arch** formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply t... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**capacitance vessels** veins",
"token_count": 1714,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
of a vessel (except capillaries) **tunica intima** (also, tunica interna) innermost lining or tunic of a vessel **tunica media** middle layer or tunic of a vessel (except capillaries) - **ulnar artery** formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**capacitance vessels** veins",
"token_count": 619,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Blood pumped by the heart flows through a series of vessels known as arteries, arterioles, capillaries, venules, and veins before returning to the heart. Arteries transport blood away from the heart and branch into smaller vessels, forming arterioles. Arterioles distribute blood to capillary beds, the sites of exchange... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**[20.1 Structure a](#page-850-1)[nd Function of Blood Vessels](#page-851-0)**",
"token_count": 311,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Blood flow is the movement of blood through a vessel, tissue, or organ. The slowing or blocking of blood flow is called resistance. Blood pressure is the force that blood exerts upon the walls of the blood vessels or chambers of the heart. The components of blood pressure include systolic pressure, which results from v... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**[20.2 Blood Flow, Blood Pressure, and Resistance](#page-863-0)**",
"token_count": 321,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Neural, endocrine, and autoregulatory mechanisms affect blood flow, blood pressure, and eventually perfusion of blood to body tissues. Neural mechanisms include the cardiovascular centers in the medulla oblongata, baroreceptors in the aorta and carotid arteries and right atrium, and associated chemoreceptors that monit... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**[20.4 Homeostatic Regulation of the Vascular System](#page-874-0)**",
"token_count": 204,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The right ventricle pumps oxygen-depleted blood into the pulmonary trunk and right and left pulmonary arteries, which carry it to the right and left lungs for gas exchange. Oxygen-rich blood is transported by pulmonary veins to the left atrium. The left ventricle pumps this blood into the aorta. The main regions of the... | {
"Header 1": "**20.6 | Development of Blood Vessels and Fetal Circulation**",
"Header 3": "**[20.5 Circulatory Pathways](#page-884-0)**",
"token_count": 213,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
After studying this chapter, you will be able to:
• Identify the components and anatomy of the lymphatic system
- Discuss the role of the innate immune response against pathogens
- Describe the power of the adaptive immune response to cure disease
- Explain immunological deficiencies and over-reactions of the immun... | {
"Header 1": "**Introduction**",
"Header 2": "**Chapter Objectives**",
"token_count": 548,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
A major function of the lymphatic system is to drain body fluids and return them to the bloodstream. Blood pressure causes leakage of fluid from the capillaries, resulting in the accumulation of fluid in the interstitial space—that is, spaces between individual cells in the tissues. In humans, 20 liters of plasma is re... | {
"Header 1": "**21.1 | Anatomy of the Lymphatic and Immune Systems**",
"Header 3": "**Functions of the Lymphatic System**",
"token_count": 456,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The lymphatic vessels begin as open-ended capillaries, which feed into larger and larger lymphatic vessels, and eventually empty into the bloodstream by a series of ducts. Along the way, the lymph travels through the lymph nodes, which are commonly found near the groin, armpits, neck, chest, and abdomen. Humans have ab... | {
"Header 1": "**21.1 | Anatomy of the Lymphatic and Immune Systems**",
"Header 3": "**Structure of the Lymphatic System**",
"token_count": 271,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
**Lymphatic capillaries**, also called the terminal lymphatics, are vessels where interstitial fluid enters the lymphatic system to become lymph fluid. Located in almost every tissue in the body, these vessels are interlaced among the arterioles and venules of the circulatory system in the soft connective tissues of th... | {
"Header 1": "**21.1 | Anatomy of the Lymphatic and Immune Systems**",
"Header 3": "**Lymphatic Capillaries**",
"token_count": 453,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The lymphatic capillaries empty into larger lymphatic vessels, which are similar to veins in terms of their three-tunic structure and the presence of valves. These one-way valves are located fairly close to one another, and each one causes a bulge in the lymphatic vessel, giving the vessels a beaded appearance (see **[... | {
"Header 1": "**21.1 | Anatomy of the Lymphatic and Immune Systems**",
"Header 3": "**Larger Lymphatic Vessels, Trunks, and Ducts**",
"token_count": 439,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
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