N 15. Blood vessels. Circulatory Systems

Simply click on a region of the heart on the diagrams or the hyperlinks listed below to learn more about the structures of the heart.

Coronary Arteries

Because the heart is composed primarily of cardiac muscle tissue that continuously contracts and relaxes, it must have a constant supply of oxygen and nutrients. The coronary arteries are the network of blood vessels that carry oxygen- and nutrient-rich blood to the cardiac muscle tissue.

The blood leaving the left ventricle exits through the aorta, the body’s main artery. Two coronary arteries, referred to as the "left" and "right" coronary arteries, emerge from the beginning of the aorta, near the top of the heart.

The initial segment of the left coronary artery is called the left main coronary. This blood vessel is approximately the width of a soda straw and is less than an inch long. It branches into two slightly smaller arteries: the left anterior descending coronary artery and the left circumflex coronary artery. The left anterior descending coronary artery is embedded in the surface of the front side of the heart. The left circumflex coronary artery circles around the left side of the heart and is embedded in the surface of the back of the heart.

Just like branches on a tree, the coronary arteries branch into progressively smaller vessels. The larger vessels travel along the surface of the heart; however, the smaller branches penetrate the heart muscle. The smallest branches, called capillaries, are so narrow that the red blood cells must travel in single file. In the capillaries, the red blood cells provide oxygen and nutrients to the cardiac muscle tissue and bond with carbon dioxide and other metabolic waste products, taking them away from the heart for disposal through the lungs, kidneys and liver.

 

When cholesterol plaque accumulates to the point of blocking the flow of blood through a coronary artery, the cardiac muscle tissue fed by the coronary artery beyond the point of the blockage is deprived of oxygen and nutrients. This area of cardiac muscle tissue ceases to function properly. The condition when a coronary artery becomes blocked causing damage to the cardiac muscle tissue it serves is called a myocardial infarction or heart attack.

Superior Vena Cava

The superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.

Inferior Vena Cava

The inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.

The inferior vena cava (or IVC), also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart.

It is posterior to the abdominal cavity and runs alongside of the vertebral column on its right side (i.e. it is a retroperitoneal structure). It enters the right atrium at the lower right, back side of the heart.

Drainage patterns

 

The IVC is formed by the joining of the left and right common iliac veins and brings blood into the right atrium of the heart. It also anastomoses with the azygos vein system (which runs on the right side of the vertebral column) and venous plexuses next to the spinal cord.

 

The caval opening is at T8. The specific levels of the tributaries are as follows:

Superior vena cava, inferior vena cava, azygos vein and their tributaries.

Because the IVC is not centrally located, there are some asymmetries in drainage patterns. The gonadal veins and suprarenal veins drain into the IVC on the right side, but into the renal vein on the left side, which in turn drains into the IVC. By contrast, all the lumbar veins and hepatic veins usually drain directly into the IVC.

 

The tributaries of Inferior vena cava can be remembered using the mnemonic, "I Like To Rise So High", for Illiac vein (common), Lumbar vein, Testicular vein, Renal vein, Suprarenal vein and Hepatic vein.

 

Note that the vein that carries de-oxygenated blood from the upper half of the body is the superior vena cava.

 

Pathologies associated with the IVC

 

Health problems attributed to the IVC are most often associated with it being compressed (ruptures are rare because it has a low intraluminal pressure). Typical sources of external pressure are an enlarged aorta (abdominal aortic aneurysm), the gravid uterus (aortocaval compression syndrome) and abdominal maligancies, such as colorectal cancer, renal cell carcinoma and ovarian cancer. Since the inferior vena cava is primarily a right-sided structure, unconscious pregnant females should be turned on to their left side (the recovery position), to relieve pressure on it and facilitate venous return. In rare cases, straining associated with defecation can lead to restricted blood flow through the IVC and result in syncope (fainting).

 

Occlusion of the IVC is rare, but considered life-threatening and is an emergency. It is associated with deep vein thrombosis, IVC filters, liver transplantation and instrumentation (e.g. catheter in the femoral vein).

Embryology

 

In the embryo, the IVC and right atrium are separated by the Eustachian valve, also known in Latin as the valvula venae cavae inferioris (valve of the inferior vena cava). In the adult, this structure typically has totally regressed or remains as a small endocardial fold.

Diagram showing completion of development of the parietal veins.

Base and diaphragmatic surface of heart.

The arch of the aorta, and its branches.

The abdominal aorta and its branches.

 

Inferior vena cava

 The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.

Transverse section of human embryo eight and a half to nine weeks old.

Human kidneys viewed from behind with spine removed

Liver and gallbladder

Inferior vena cava

Inferior vena cava

Inferior vena cava

Inferior vena cava

Inferior vena cava

Inferior vena cava

 

Aorta

The aorta is the largest single blood vessel in the body. It is approximately the diameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.

Schematic view of the aorta and a number of its most important branches

The course of the aorta

Course of the aorta in the thorax (anterior view), starting posterior to the main pulmonary artery, but then anterior to the right pulmonary arteries, the trachea and the esophagus, but then turning posteriorly to course dorsally to these structures

The aorta is usually divided into five segments/sections:

1.     Ascending aorta—the section between the heart and the arch of aorta

The ascending aorta and arch of aorta with their branches

Components

 

The aortic root is the portion of the ascending aorta beginning at the aortic annulus and extending to the sinotubular junction. Between each commissure of the aortic valve and opposite the cusps of the aortic valve, three small dilatations called the aortic sinuses.

 

The sinotubular junction is the point in the ascending aorta where the aortic sinuses end and the aorta becomes a tubular structure.

 

Relations

 

At the union of the ascending aorta with the aortic arch the caliber of the vessel is increased, owing to a bulging of its right wall.

 

This dilatation is termed the bulb of the aorta, and on transverse section presents a somewhat oval figure.

 

The ascending aorta is contained within the pericardium, and is enclosed in a tube of the serous pericardium, common to it and the pulmonary artery.

 

The ascending aorta is covered at its commencement by the trunk of the pulmonary artery and the right auricula, and, higher up, is separated from the sternum by the pericardium, the right pleura, the anterior margin of the right lung, some loose areolar tissue, and the remains of the thymus; posteriorly, it rests upon the left atrium and right pulmonary artery.

 

On the right side, it is in relation with the superior vena cava and right atrium, the former lying partly behind it; on the left side, with the pulmonary artery.

 

Branches

 

The only branches of the ascending aorta are the two coronary arteries which supply the heart; they arise near the commencement of the aorta from the aortic sinuses which are opposite the aortic valve.

Front view of heart and lungs

Thumb|Fetal ascending aorta

Ascending aorta

Ascending aorta

Ascending aorta

Ascending aorta

Ascending aorta

2.     Arch of aorta—the peak part that looks somewhat like an inverted "U". The arch of the aorta or the transverse aortic arch (English pronunciation: /eɪˈɔrtɪk/) is the part of the aorta that begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta.

Related structures

 

The ligamentum arteriosum connects the commencement of the left pulmonary artery to the aortic arch. The blood bypasses the lungs through the ductus arteriosus during embryonic circulation. This becomes the ligamentum arteriosum postnatal as pulmonary circulation begins.

 

The aortic knob is the prominent shadow of the aortic arch on a frontal chest radiograph.

 

Aortopexy is a surgical procedure in which the aortic arch is fixed to the sternum in order to keep the trachea open.

Diagram showing the origins of the main branches of the carotid arteries.

Course and distribution of the glossopharyngeal, vagus, and accessory nerves.

Heart left lateral view

It thus forms two curvatures: one with its convexity upward, the other with its convexity forward and to the left. Its upper border is usually about 2.5 cm. below the superior border to the manubrium sterni. It lies within the mediastinum.

3.     Descending aorta—the section from the arch of aorta to the point where it divides into the common iliac arteries. he descending aorta is part of the aorta, the largest artery in the body. The descending aorta is the part of the aorta beginning at the aortic arch that runs down through the chest and abdomen. The descending aorta is divided into two portions, the thoracic and abdominal, in correspondence with the two great cavities of the trunk in which it is situated. Within the abdomen, the descending aorta branches into the two common iliac arteries which serve the pelvis and eventually legs.

The thoracic aorta, viewed from the left side

4.     Thoracic aorta—the half of the descending aorta above the diaphragm. The thoracic aorta is contained in the posterior mediastinal cavity. It begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth thoracic vertebra, at the aortic hiatus in the diaphragm where it becomes the abdominal aorta. At its commencement, it is situated on the left of the vertebral column; it approaches the median line as it descends; and, at its termination, lies directly in front of the column. The vessel describes a curve which is concave forward; as the branches given off from it are small, its diminution in size is insignificant. It has a radius of approximately 1.16 cm.

Histopathological image of dissecting aneurysm of thoracic aorta in a patient without evidence of Marfan's trait. The damaged aorta was surgically removed and replaced by artificial vessel. Victoria blue & HE stain.

Thoracic aorta

Transverse section of thorax, showing relations of pulmonary artery

Relations

 

It is in relation, anteriorly, from above downward, with the root of the left lung, the pericardium, the esophagus, and the diaphragm; posteriorly, with the vertebral column and the azygos vein; on the right side, with the hemiazygos veins and thoracic duct; on the left side, with the left pleura and lung.

 

The esophagus, with its accompanying plexus of nerves, lies on the right side of the aorta above; but at the lower part of the thorax it is placed in front of the aorta, and, close to the diaphragm, is situated on its left side.

 

Branches

 

Branches before thoracic aorta

 

The initial part of the aorta, the ascending aorta, rises out of the left ventricle, from which it is separated by the aortic valve. The two coronary arteries of the heart arise from the aortic root, just above the cusps of the aortic valve.

 

The aorta then arches back over the right pulmonary artery. Three vessels come out of the aortic arch, the brachiocephalic artery, the left common carotid artery, and the left subclavian artery. These vessels supply blood to the head, neck, thorax and upper limbs.

 

Branches of thoracic aorta

 

The aorta gives off several paired branches as it descends in the thorax. In descending order, these include the

·        Bronchial arteries

·        Mediastinal arteries

·        Esophageal arteries

·        Pericardial arteries

·        Superior phrenic artery

5.     Abdominal aorta—the half of the descending aorta below the diaphragm. The abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta (of the thorax).

Path

 

It begins at the level of the diaphragm, crossing it via the aortic hiatus, technically behind the diaphragm, at the vertebral level of T12. It travels down the posterior wall of the abdomen, anterior to the vertebral column. It thus follows the curvature of the lumbar vertebrae, that is, convex anteriorly. The peak of this convexity is at the level of the third lumbar vertebra (L3).

 

 Abdominal aorta

 

It runs parallel to the inferior vena cava, which is located just to the right of the abdominal aorta, and becomes smaller in diameter as it gives off branches. This is thought to be due to the large size of its principal branches. At the 11th rib, the diameter is 122mm long and 55mm wide and this is because of the constant pressure

Branches

 

The abdominal aorta supplies blood to much of the abdominal cavity. It begins at T12, and usually has the following branches:

Abdominal aorta

Note that the bifurcation (union) of the inferior vena cava is at L5 and therefore below that of the bifurcation of the aorta.

 

Contrast enhanced MRA of the abdominal aorta demonstrating normal paired arteries.

Note that the bifurcation (union) of the inferior vena cava is at L5 and therefore below that of the bifurcation of the aorta.

1.     inferior phrenic a.

2.     celiac a.

1.     left gastric a.

2.     splenic a.

1.     short gastric arteries (6)

2.     splenic arteries (6)

3.     left gastroepiploic a.

3. common hepatic a.

1.     cystic a.

2.     right gastric a.

3.     gastroduodenal a.

1.     right gastroepiploic a.

2.     superior pancreaticoduodenal a.

4. right hepatic a.

5. left hepatic a.

1.     1. superior mesenteric a.

1.     jejunal and ileal arteries

2.     inferior pancreaticoduodenal a.

3.     middle colic a.

4.     right colic a.

5.     ileocolic a

1.     anterior cecal a.

2.     posterior cecal a. – appendicular a.

3.     ileal a.

4.     colic a.

1.     middle suprarenal a.

2.     renal a.

3.     testicular or ovarian a.

1.     four lumbar arteries

1.     inferior mesenteric a.

1.     left colic a.

2.     sigmoid arteries (2 or 3)

3.     superior rectal a.

1.     median sacral a.

1.     common iliac a.

1.     external iliac a.

2.     internal iliac a.

Abdominal aorta

 

Relations

 

The abdominal aorta lies slightly to the left of the midline of the body. It is covered, anteriorly, by the lesser omentum and stomach, behind which are the branches of the celiac artery and the celiac plexus; below these, by the lienal vein(splenic artery), the pancreas, the left renal vein, the inferior part of the duodenum, the mesentery, and aortic plexus.

 

Posteriorly, it is separated from the lumbar vertebrж and intervertebral fibrocartilages by the anterior longitudinal ligament and left lumbar veins.

 

On the right side it is in relation above with the azygos vein, cisterna chyli, thoracic duct, and the right crus of the diaphragm—the last separating it from the upper part of the inferior vena cava, and from the right celiac ganglion; the inferior vena cava is in contact with the aorta below.

 

On the left side are the left crus of the diaphragm, the left celiac ganglion, the ascending part of the duodenum, and some coils of the small intestine.

 

Relationship with inferior vena cava

 

The abominal aorta's venous counterpart, the inferior vena cava (IVC), travels parallel to it on its right side.

Above the level of the umbilicus, the aorta is somewhat posterior to the IVC, sending the right renal artery travelling behind it. The IVC likewise sends its opposite side counterpart, the left renal vein, crossing in front of the aorta.

Below the level of the umbilicus, the situation is generally reversed, with the aorta sending its right common iliac artery to cross its opposite side counterpart (the left common iliac vein) anteriorly.

 

Collateral circulation

The collateral circulation would be carried on by the anastomoses between the internal thoracic artery and the inferior epigastric artery; by the free communication between the superior and inferior mesenterics, if the ligature were placed between these vessels; or by the anastomosis between the inferior mesenteric artery and the internal pudendal artery, when (as is more common) the point of ligature is below the origin of the inferior mesenteric artery; and possibly by the anastomoses of the lumbar arteries with the branches of the internal iliac artery.

The celiac artery and its branches; the stomach has been raised and the peritoneum removed

Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas

CT scan showing the liver and a kidney

A transverse contrast enhanced CT scan demonstrating an abdominal aortic aneurysm of 4.8 by 3.8 cm

Ultrasound image of a normal abdominal aorta measuring 1.9 cm (0.75 in) in diameter.

Abdominal aorta

Abdominal aorta

 

 

Pulmonary Artery

The pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs. A common misconception is that all arteries carry oxygen-rich blood. It is more appropriate to classify arteries as vessels carrying blood away from the heart.

Pulmonary Vein

The pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium. A common misconception is that all veins carry de-oxygenated blood. It is more appropriate to classify veins as vessels carrying blood to the heart.

The pulmonary veins are large blood vessels that carry oxygenated blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung. They carry oxygenated blood, which is unusual since almost all other veins carry deoxygenated blood.

 

Path

 

The pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart. In humans there are normally four pulmonary veins, two from each lung. As part of the pulmonary circulation they carry oxygenated blood back to the heart, as opposed to the veins of the systemic circulation which carry deoxygenated blood.

 

Occasionally the three veins on the right side remain separate, and not infrequently the two left pulmonary veins end by a common opening into the left atrium. Therefore, the number of pulmonary veins opening into the left atrium can vary between three and five in the healthy population.

 

The right pulmonary veins (contains deoxygenated blood) pass behind the right atrium and superior vena cava; the left in front of the descending thoracic aorta. At the root of the lung, the superior pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the hilus of the lung and on a plane posterior to the upper vein. Behind the pulmonary artery is the bronchus. Within the pericardium, their anterior surfaces are invested by the serous layer of this membrane.

Diagram of the alveoli with both cross-section and external view.

Bronchial anatomy

Bronchi, bronchial tree, and lungs

Pulmonary circuit

Alveolus diagram

Heart seen from above.

Base and diaphragmatic surface of heart.

Left atrium

 

Right Atrium

The right atrium receives de-oxygenated blood from the body through the superior vena cava (head and upper body) and inferior vena cava (legs and lower torso). The sinoatrial node sends an impulse that causes the cardiac muscle tissue of the atrium to contract in a coordinated, wave-like manner. The tricuspid valve, which separates the right atrium from the right ventricle, opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle.

Right Ventricle

The right ventricle receives de-oxygenated blood as the right atrium contracts. The pulmonary valve leading into the pulmonary artery is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the right ventricle contracts, the tricuspid valve closes and the pulmonary valve opens. The closure of the tricuspid valve prevents blood from backing into the right atrium and the opening of the pulmonary valve allows the blood to flow into the pulmonary artery toward the lungs.

Left Atrium

The left atrium receives oxygenated blood from the lungs through the pulmonary vein. As the contraction triggered by the sinoatrial node progresses through the atria, the blood passes through the mitral valve into the left ventricle.

Left Ventricle

The left ventricle receives oxygenated blood as the left atrium contracts. The blood passes through the mitral valve into the right ventricle. The aortic valve leading into the aorta is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the left ventricle contracts, the mitral valve closes and the aortic valve opens. The closure of the mitral valve prevents blood from backing into the left atrium and the opening of the aortic valve allows the blood to flow into the aorta and flow throughout the body.

 

Papillary Muscles

The papillary muscles attach to the lower portion of the interior wall of the ventricles. They connect to the chordae tendineae, which attach to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. The contraction of the papillary muscles opens these valves. When the papillary muscles relax, the valves close.

Chordae Tendineae

The chordae tendineae are tendons linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. As the papillary muscles contract and relax, the chordae tendineae transmit the resulting increase and decrease in tension to the respective valves, causing them to open and close. The chordae tendineae are string-like in appearance and are sometimes referred to as "heart strings."

The chordae tendineae, or heart strings, are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart.

 

Chordae tendineae are approximately 80% collagen, while the remaining 20% is made up of elastin and endothelial cells.

Interior of right side of heart

Mechanism

 

During atrial systole, blood flows from the atria to ventricles down the pressure gradient. Chordae tendineae are relaxed because the atrioventricular valves are forced open.

 

When the ventricles of the heart contract in ventricular systole, the increased blood pressures in both chambers push the tricuspid valve and mitral valve to close simultaneously, preventing backflow of blood into the atria. Since the blood pressure in atria is much lower than that in the ventricles, the flaps attempt to evert to the low pressure regions. The chordae tendineae prevent the eversion, prolapse, by becoming tense thus pulling the flaps, holding them in closed position.[1]

 

Tendon of Todaro

 

The tendon of Todaro is a continuation of the Eustachian Valve of the Inferior vena cava and the Thebesian valve of the coronary sinus. Along with the opening of the coronary sinus and the septal cusp of the tricuspid valve, it makes up the triangle of Koch. The centre of the triangle of Koch is the location of the atrioventricular node.

Papillary muscles and chordae tendinae

Papillary muscles and chordae tendinae

 

Tricuspid Valve

The tricuspid valve separates the right atrium from the right ventricle. It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle. It closes as the right ventricle contracts, preventing blood from returning to the right atrium; thereby, forcing it to exit through the pulmonary valve into the pulmonary artery.

Mitral Value

The mitral valve separates the left atrium from the left ventricle. It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. It closes as the left ventricle contracts, preventing blood from returning to the left atrium; thereby, forcing it to exit through the aortic valve into the aorta.

Pulmonary Valve

The pulmonary valve separates the right ventricle from the pulmonary artery. As the ventricles contract, it opens to allow the de-oxygenated blood collected in the right ventricle to flow to the lungs. It closes as the ventricles relax, preventing blood from returning to the heart.

 

Aortic Valve

The aortic valve separates the left ventricle from the aorta. As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body. It closes as the ventricles relax, preventing blood from returning to the heart.

Blood vessels

The blood vessels are part of the circulatory system and function to transport blood throughout the body. The most important types, arteries and veins, carry blood away from or towards the heart, respectively.

Anatomy

All blood vessels have the same basic structure. The inner lining is the endothelium and is surrounded by subendthelial connective tissue. Around this there is a layer of vascular smooth muscle, which is highly developed in arteries. Finally, there is a further layer of connective tissue known as the adventitia, which contains nerves that supply the muscular layer, as well as nutrient capillaries in the larger blood vessels.

Capillaries consist of little more than a layer of endothelium and occasional connective tissue.

When blood vessels connect to form a region of diffuse vascular supply it is called an anastamosis (pl. anastomoses). Anastomoses provide critical alternative routes for blood to flow in case of blockages.

Laid end to end, the blood vessels in an average human body will stretch approximately 62,000 miles. 2.5 times around the earth

Types

There are various kinds of blood vessels:

• Arteries
• Aorta (the largest artery, carries blood out of the heart)
• Branches of the aorta, such as the carotid artery, the subclavian artery, the celiac trunk, the mesenteric arteries, the renal artery and the iliac artery.
• Arterioles
• Capillaries (the smallest blood vessels)
• Venules
• Veins
• Large collecting vessels, such as the subclavian vein, the jugular vein, the renal vein and the iliac vein.
• Venae cavae (the 2 largest veins, carry blood into the heart)

They are roughly grouped as arterial and venous, determined by whether the blood in it is flowing toward or away from the heart. The term "arterial blood" is nevertheless used to indicate blood high in oxygen, although the pulmonary artery carries "venous blood" and blood flowing in the pulmonary vein is rich in oxygen.

Physiology

Blood vessels do not actively engage in the transport of blood (they have no appreciable peristalsis), but arteries - and veins to a degree - can regulate their inner diameter by contraction of the muscular layer.This changes the blood flow to downstream organs, and is determined by the autonomic nervous system. Vasodilation and vasoconstriction are also used antagonistically as methods of thermoregulation.

Oxygen (bound to hemoglobin in red blood cells) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95-100%) with oxygen. In all veins apart from the pulmonary vein, the hemoglobin is desaturated at about 70%. (The values are reversed in the pulmonary circulation.)

The blood pressure in blood vessels is traditionally expressed in millimetres of mercury (1 mmHg = 133 Pa). In the arterial system, this is usually around 120 mmHg systolic (high pressure wave due to contraction of the heart) and 80 mmHg diastolic (low pressure wave). In contrast, pressures in the venous system are constant and rarely exceed 10 mmHg.

Vasoconstriction is the constriction of blood vessels (narrowing, becoming smaller in cross-sectional area) by contracting the vascular smooth muscle in the vessel walls. It is regulated by vasoconstrictors (agents that cause vasoconstriction). These include paracrine factors (e.g. prostaglandins), a number of hormones (e.g. vasopressin and angiotensin) and neurotransmitters (e.g. epinephrine) from the nervous system.

Vasodilation is a similar process mediated by antagonistically acting mediators. The most prominent vasodilator is nitric oxide (termed endothelium-derived relaxing factor for this reason).

Permeability of the endothelium is pivotal in the release of nutrients to the tissue. It is also increased in inflammation in response to histamine, prostaglandins and interleukins, which leads to most of the symptoms of inflammation (swelling, redness and warmth).

Role in disease

Blood vessels play a role in virtually every medical condition. Cancer, for example, cannot progress unless the tumor causes angiogenesis (formation of new blood vessels) to supply the malignant cells' metabolic demand. Atherosclerosis, the formation of lipid lumps (atheromas) in the blood vessel wall, is the prime cause of cardiovascular disease, the main cause of death in the Western world.

Blood vessel permeability is increased in inflammation. Damage, due to trauma or spontaneously, may lead to haemorrhage. In contrast, occlusion of the blood vessel (e.g. by a ruptured atherosclerotic plaque, by an embolised blood clot or a foreign body) leads to downstream ischemia (insufficient blood supply) and necrosis (tissue breakdown).

Vasculitis is inflammation of the vessel wall, due to autoimmune disease or infection.

The Present Perfect Tense - When to use

 

Uses of the Present Perfect - Practice

---

Exercise: choose for or since.

1.     You have broken my watch

2.     I have never been to Paris

3.     How long have you been here

4.     Angela has bought a new flat

5.     How many times have you been married

6.     We haven't worked on a farm

7.     This building has been an office since 1998

 

 

Vascular Systems

Humans, birds, and mammals have a four-chambered heart that completely separates oxygen-rich and oxygen-depleted blood, as is shown in Figure 10. Fish have a two-chambered heart in which a single-loop circulatory pattern takes blood from the heart to the gills and then to the body. Amphibians have a three-chambered heart with two atria and one ventricle. A loop from the heart goes to the pulmonary capillary beds, where gas exchange occurs. Blood then is returned to the heart. Blood exiting the ventricle is diverted, some to the pulmonary circuit, some to systemic circuit. The disadvantage of the three-chambered heart is the mixing of oxygenated and deoxygenated blood. Some reptiles have partial separation of the ventricle. Other reptiles, plus, all birds and mammals, have a four-chambered heart, with complete separation of both systemic and pulmonary circuits.

The Heart

The heart is a muscular structure that contracts in a rhythmic pattern to pump blood. Hearts have a variety of forms: chambered hearts in mollusks and vertebrates, tubular hearts of arthropods, and aortic arches of annelids. Accessory hearts are used by insects to boost or supplement the main heart's actions. Fish, reptiles, and amphibians have lymph hearts that help pump lymph back into veins.

The basic vertebrate heart, such as occurs in fish, has two chambers. An auricle is the chamber of the heart where blood is received from the body. A ventricle pumps the blood it gets through a valve from the auricle out to the gills through an artery.

Amphibians have a three-chambered heart: two atria emptying into a single common ventricle. Some species have a partial separation of the ventricle to reduce the mixing of oxygenated (coming back from the lungs) and deoxygenated blood (coming in from the body). Two sided or two chambered hearts permit pumping at higher pressures and the addition of the pulmonary loop permits blood to go to the lungs at lower pressure yet still go to the systemic loop at higher pressures.

Establishment of the four-chambered heart, along with the pulmonary and systemic circuits, completely separates oxygenated from deoxygenated blood. This allows higher the metabolic rates needed by warm-blooded birds and mammals.

 

The human heart, as seen in Figure 11, is a two-sided, four-chambered structure with muscular walls. An atrioventricular (AV) valve separates each auricle from ventricle. A semilunar (also known as arterial) valve separates each ventricle from its connecting artery.

The heart beats or contracts approximately 70 times per minute. The human heart will undergo over 3 billion contraction cycles, as shown in Figure 12, during a normal lifetime. The cardiac cycle consists of two parts: systole (contraction of the heart muscle) and diastole (relaxation of the heart muscle). Atria contract while ventricles relax. The pulse is a wave of contraction transmitted along the arteries. Valves in the heart open and close during the cardiac cycle. Heart muscle contraction is due to the presence of nodal tissue in two regions of the heart. The SA node (sinoatrial node) initiates heartbeat. The AV node (atrioventricular node) causes ventricles to contract. The AV node is sometimes called the pacemaker since it keeps heartbeat regular. Heartbeat is also controlled by nerve messages originating from the autonomic nervous system.

Blood flows through the heart from veins to atria to ventricles out by arteries. Heart valves limit flow to a single direction. One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause. Normal cardiac cycles (at rest) take 0.8 seconds. Blood from the body flows into the vena cava, which empties into the right atrium. At the same time, oxygenated blood from the lungs flows from the pulmonary vein into the left atrium. The muscles of both atria contract, forcing blood downward through each AV valve into each ventricle.

Diastole is the filling of the ventricles with blood. Ventricular systole opens the SL valves, forcing blood out of the ventricles through the pulmonary artery or aorta. The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound. Lub is associated with closure of the AV valves, dub is the closing of the SL valves.

Human heartbeats originate from the sinoatrial node (SA node) near the right atrium. Modified muscle cells contract, sending a signal to other muscle cells in the heart to contract. The signal spreads to the atrioventricular node (AV node). Signals carried from the AV node, slightly delayed, through bundle of His fibers and Purkinjie fibers cause the ventricles to contract simultaneously. Figure 13 illustrates several aspects of this.

Heartbeats are coordinated contractions of heart cardiac cells, shown in an animate GIF image in Figure 14. When two or more of such cells are in proximity to each other their contractions synch up and they beat as one.

An electrocardiogram (ECG) measures changes in electrical potential across the heart, and can detect the contraction pulses that pass over the surface of the heart. There are three slow, negative changes, known as P, R, and T as shown in Figure 15 . Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction. ECGs are useful in diagnosing heart abnormalities.

Diseases of the Heart and Cardiovascular System

Cardiac muscle cells are serviced by a system of coronary arteries. During exercise the flow through these arteries is up to five times normal flow. Blocked flow in coronary arteries can result in death of heart muscle, leading to a heart attack.

Blockage of coronary arteries, shown in Figure 16, is usually the result of gradual buildup of lipids and cholesterol in the inner wall of the coronary artery. Occasional chest pain, angina pectoralis, can result during periods of stress or physical exertion. Angina indicates oxygen demands are greater than capacity to deliver it and that a heart attack may occur in the future. Heart muscle cells that die are not replaced since heart muscle cells do not divide. Heart disease and coronary artery disease are the leading causes of death in the United States.

Hypertension, high blood pressure (the silent killer), occurs when blood pressure is consistently above 140/90. Causes in most cases are unknown, although stress, obesity, high salt intake, and smoking can add to a genetic predisposition. Luckily, when diagnosed, the condition is usually treatable with medicines and diet/exercise.

The Vascular System

Two main routes for circulation are the pulmonary (to and from the lungs) and the systemic (to and from the body). Pulmonary arteries carry blood from the heart to the lungs. In the lungs gas exchange occurs. Pulmonary veins carry blood from lungs to heart. The aorta is the main artery of systemic circuit. The vena cavae are the main veins of the systemic circuit. Coronary arteries deliver oxygenated blood, food, etc. to the heart. Animals often have a portal system, which begins and ends in capillaries, such as between the digestive tract and the liver.

Fish pump blood from the heart to their gills, where gas exchange occurs, and then on to the rest of the body. Mammals pump blood to the lungs for gas exchange, then back to the heart for pumping out to the systemic circulation. Blood flows in only one direction.

Blood

Plasma is the liquid component of the blood. Mammalian blood consists of a liquid (plasma) and a number of cellular and cell fragment components as shown in Figure 21. Plasma is about 60 % of a volume of blood; cells and fragments are 40%. Plasma has 90% water and 10% dissolved materials including proteins, glucose, ions, hormones, and gases. It acts as a buffer, maintaining pH near 7.4. Plasma contains nutrients, wastes, salts, proteins, etc. Proteins in the blood aid in transport of large molecules such as cholesterol.

Red blood cells, also known as erythrocytes, are flattened, doubly concave cells about 7 ΅m in diameter that carry oxygen associated in the cell's hemoglobin. Mature erythrocytes lack a nucleus. They are small, 4 to 6 million cells per cubic millimeter of blood, and have 200 million hemoglobin molecules per cell. Humans have a total of 25 trillion red blood cells (about 1/3 of all the cells in the body). Red blood cells are continuously manufactured in red marrow of long bones, ribs, skull, and vertebrae. Life-span of an erythrocyte is only 120 days, after which they are destroyed in liver and spleen. Iron from hemoglobin is recovered and reused by red marrow. The liver degrades the heme units and secretes them as pigment in the bile, responsible for the color of feces. Each second two million red blood cells are produced to replace those thus taken out of circulation.

White blood cells, also known as leukocytes, are larger than erythrocytes, have a nucleus, and lack hemoglobin. They function in the cellular immune response. White blood cells (leukocytes) are less than 1% of the blood's volume. They are made from stem cells in bone marrow. There are five types of leukocytes, important components of the immune system. Neutrophils enter the tissue fluid by squeezing through capillary walls and phagocytozing foreign substances. Macrophages release white blood cell growth factors, causing a population increase for white blood cells. Lymphocytes fight infection. T-cells attack cells containing viruses. B-cells produce antibodies. Antigen-antibody complexes are phagocytized by a macrophage. White blood cells can squeeze through pores in the capillaries and fight infectious diseases in interstitial areas

Platelets result from cell fragmentation and are involved with clotting, as is shown by Figures 17 and 18. Platelets are cell fragments that bud off megakaryocytes in bone marrow. They carry chemicals essential to blood clotting. Platelets survive for 10 days before being removed by the liver and spleen. There are 150,000 to 300,000 platelets in each milliliter of blood. Platelets stick and adhere to tears in blood vessels; they also release clotting factors. A hemophiliac's blood cannot clot. Providing correct proteins (clotting factors) has been a common method of treating hemophiliacs. It has also led to HIV transmission due to the use of transfusions and use of contaminated blood products.

Figure 2. Human Red Blood Cells, Platelets and T-lymphocyte (erythocytes = red; platelets = yellow; T-lymphocyte = light green) (SEM x 9,900).

 

 

The Lymphatic System

Water and plasma are forced from the capillaries into intracellular spaces. This interstitial fluid transports materials between cells. Most of this fluid is collected in the capillaries of a secondary circulatory system, the lymphatic system. Fluid in this system is known as lymph.

Lymph flows from small lymph capillaries into lymph vessels that are similar to veins in having valves that prevent backflow. Lymph vessels connect to lymph nodes, lymph organs, or to the cardiovascular system at the thoracic duct and right lymphatic duct.

Lymph nodes are small irregularly shaped masses through which lymph vessels flow. Clusters of nodes occur in the armpits, groin, and neck. Cells of the immune system line channels through the nodes and attack bacteria and viruses traveling in the lymph.

VIDEO

Blood Vessels Structure and Function

Present Perfect Progressive
A. Meaning
The main difference between the present perfect and the present perfect progressive is that the progressive tense emphasizes the duration of an activity that began in the past and is continuing in the present.  The event is still happening in the present time.  The present perfect progressive tense occurs often with for, since, all morning, all day, all week, etc.

        Tim has been studying for a test since last week.  He will do very well on it.  (He started studying last week and is still studying because the test is some time in the future.)
        I have been running errands all day long.  (I started running errands in the morning and I'm not done yet.)
        My sister has been making her own clothes for many years now.  (She started making her own clothes a long time ago and is still making them.)

Note:  You cannot put stative verbs in the present perfect progressive tense.  They can only be in the present perfect tense.

        wrong        I have been knowing John for seven years.
        right          I have known John for seven years.
        wrong       George has been having his car since 1998.
        right         George has had his car since 1998.

Some common words and expressions used with the present perfect progressive tense are recently, lately, these days, which indicate that the action started a short time ago and has continued to the present time.  It implies that the action or event is fairly new or recent.

        My teacher has been giving us a lot of homework lately.  (He didn't use to give us a lot of homework.  But a few days ago, he started to give us a lot more.)
        Kelly has been dating.  We're very happy for her.  (She started dating not too long ago.  This is her new boyfriend.)

B. Form

• Affirmative statements:                    has/have + been + verb-ing

                Mr. Davis has been teaching for twelve years.
                We have been waiting for the bus since 5 o'clock.

• Negative Statements:                       has/have + not + been + verb-ing

                Mr. Davis has not been teaching since 1995.
                I have not been working since I got laid off last month.

• Questions:                                        has/have + subject + been + verb-ing

                Has Mr. Davis been teaching for a long time?
                What have you been doing with your free time lately?

 

Literature:

1. Адамчик М.В. Великий англо-український словник. – Київ, 2007.

2. Англійська мова за професійним спрямуванням: Медицина: навч. посіб. для студ. вищ. навч. закл. IV рівня акредитації / І. А. Прокоп, В. Я. Рахлецька, Г. Я. Павлишин ; Терноп. держ. мед. ун-т ім. І. Я. Горбачевського. –  Тернопіль: ТДМУ : Укрмедкнига, 2010. – 576 с.

3. Балла М.І., Подвезько М.Л. Англо-український словник. – Київ: Освіта, 2006. – Т. 1,2.

4. Hansen J. T. Netter’s Anatomy Coloring Book. – Saunders Elsevier, 2010. – 121 p.

5. Henderson B., Dorsey J. L. Medical Terminology for Dummies. – Willey Publishing, 2009. – P. 189-211.