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Communicable Diseases Nurse Test
Erythropoiesis
Congenital Heart Disorders – Disorders with Obstruction to Blood Flow
Congenital Heart Disorders – Disorders with Mixed Blood Flow
Congenital Heart Disorders – Disorders with Increase Pulmonary Blood Flow

Posted: 03 Dec 2010 06:12 PM PST

December 2010 Nursing Board Exam Review Questions on Communicable Diseases.

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Erythropoiesis

Posted: 03 Dec 2010 04:57 PM PST

Red Blood Cells

Red Blood Cells (RBC's) also called erythrocytes, are oxygen carrying cells. It is derived from the Greek words "erythros" meaning "red," "kytos" meaning "hollow" and "cyte" translated as "cell" in modern language. These cells are anuclaeted (without nucleus) and contain hemoglobin. Hemoglobin is the iron-containing component of the RBC and is responsible for oxygen transport.

Site of RBC Production

Erythrocytes are produced in the red marrow, a process known as ERYTHROPOIESIS. Red marrow is the site of active blood cell production and constitutes as the major blood-producing organ. This organ is highly vascular and it consists of connective tissues that contain free cells. The simplest structures of free cells are called stem cells. The stem cells are the precursor of two different cell lines namely:

Myeloid line – includes erythrocytes, leukocytes and platelets
Lymphoid line – differentiates into lymphocytes

Red Blood Cell Production

The kidney is responsible for initiating the red blood cell production. Juxtaglomerular cells are present inside the kidneys. These cells are sensitive to the levels of oxygen in the blood. Low levels of oxygen detected in the blood (hypoxemia) delivered in the renal arterial supply stimulates the juxtaglomerular cells in the kidney to release erythrogenin. Erythrogenin is a renal erythropoietic factor that stimulates the kidney to form, produce and release the very important hormone in red blood cell production, erythropoietin (EPO).

Erythropoietin is the hormone that stimulates red blood cell production in the red marrow. Mature red blood cells are formed from stem cells in the bone marrow. With the presence of erythropoietin, red cell pathway starts to form proerythroblast from stem cells. At this point the cell still contains nucleus. However, as the development progresses the nucleus becomes smaller and the cytoplasm becomes basophilic due to the presence of ribosome, thus the cell is now called basophilic erythroblast. As the cell becomes older it also becomes smaller and eventually when it begins to produce hemoglobin it is now termed as polychromatic erythroblast. Later on the cytoplasm will become more eosinophilic and the cell is now called orthochromatic erythroblast, which will then extrude its nucleus as the cells slowly fill with hemoglobin before entering the circulation as reticulocytes. Reticulocytes will mature to form the anucleated red blood cells.

Final reticulocyte maturation takes place in the bloodstream. Within a few days the reticulocytes completely loses all its nuclear components and becomes a mature red blood cell. In a blood sample, reticulocytes can be differentiated from RBC's because the former still contain flecks of their nucleus. The lifespan of a fully mature RBC is 4 months or 120 days. After this period, the old and damaged RBCs are removed from the circulation by macrophages in the spleen and liver.

Dietary Requirements

Dietary elements are essential for RBC production. The following are needed by the red marrow to produce erythrocytes:

Iron – for hemoglobin synthesis
Folic Acid – for DNA synthesis
Vitamin B12 – for DNA synthesis

image from nlds.sdsu.edu

Congenital Heart Disorders – Disorders with Obstruction to Blood Flow

Posted: 03 Dec 2010 04:55 PM PST

Disorders with Obstruction to Blood Flow

Obstruction to the blood flow in the heart may be caused by narrowing of vessels or valves. As a result, the pressure before the narrowed part increased while it decreases after the narrowed area. This prevents the heart from reaching the lungs for oxygenation or the rest of the body. Disorders under this category include pulmonary stenosis, aortic stenosis and coarction of aorta. These heart diseases can cause back-pressure of the heart thereby overwhelming it.

Pulmonary Stenosis

The word stenosis means narrowing of a specific part. Pulmonary stenosis is the narrowing of the pulmonary valve or the pulmonary artery itself distal to the valve. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. A pulmonary valve is a flap of tissue that opens with pressure to allow blood to enter the pulmonary circulation. Inability of the right ventricle to evacuate blood to the pulmonary artery would result to right ventricular hypertrophy.

Clinical Manifestations

Some infants with pulmonary stenosis may be asymptomatic or have mild signs of right –sided heart failure. Severe narrowing of the pulmonary artery may cause the following manifestations:

Cyanosis
Typical systolic ejection murmur (grade IV or V crescendo-decrescendo quality) – loudest at the upper left sternal border
Thrill at the upper left sternal border

Aortic Stenosis

Oxygenated blood is pumped from the left ventricle to the aorta. Presence of a stricture or stenosed aortic valve prevents blood from flowing to the systemic circulation. The heart's inability to evacuate blood in the left ventricle results to increased pressure and hypertrophy of the left ventricle. If the left ventricle's pressure becomes acute, pressure in the left atrium increases that would result to back-pressure in the pulmonary veins and possible pulmonary edema.

Clinical Manifestations

Most infants are asymptomatic however generally they present the following physical manifestation:

Typical murmur (rough systolic sound at the second right interspace)
Thrill at the suprasternal notch

For severe cases

Decreased cardiac output
Hypotension
Tachycardia
Poor sucking ability
Chest pain similar to angina (when the child is active)

Coarction of Aorta

The narrowing of the lumen of aorta is a congenital heart failure called coarction of aorta. There are two types of this disorder:

Preductal – coarction is present between the subclavian artery and the ductus arteriosus
Postductal – coarction is present distal to the ductus arteriosus

Difficulty of the blood to enter the systemic circulation through narrowed aorta result to increase the blood pressure before (proximal) the coarction and decreased distal to it.

Clinical Manifestations

Absence of palpable femoral pulses
Elevated blood pressure in the upper part of the body and decreased BP in the lower extremities.
Leg pain on exertion
Exceptional irritability
Epistaxis
Headache
Vertigo

images from marvistavet.com, heart-valve-surgery.com, nlm.nih.gov

Congenital Heart Disorders – Disorders with Mixed Blood Flow

Posted: 03 Dec 2010 04:50 PM PST

Disorders with Mixed Blood Flow

Mixing of the blood from the pulmonary and systemic circulation in the chambers of the heart results in a relative deoxygenation of the blood flowing. The defects under this include transposition of the great arteries, total anomalous pulmonary venous return, truncus arteriosus and hypoplastic left heart syndrome.

Transposition of the Great Arteries

Normally, the pulmonary artery arises from the right ventricle and the aorta from the left ventricle. With transposition of the great arteries, the pulmonary artery arises from the left ventricle while the aorta from the right ventricle. As blood (unoxygenated) enters the right atrium it flows to the right ventricle. Because the aorta is connected to the right ventricular portion of the heart completely deoxygenated blood goes out into the aorta to the different parts of the body. On the other side of the heart oxygenated blood enters the left atrium via the pulmonary veins. It flows to the left ventricle then back to the pulmonary artery then to the lungs and returns to the left atrium. Two closed circulatory systems are present. In most cases, ASD and VSD are present with transposition of the great arteries. This makes the entire heart have a single yet mixed circulation.

Clinical Manifestations

Cyanosis at birth
There may be murmur or there may be various murmurs (depending on the shunting of blood through atrial or ventricular septal defects)

Total Anomalous Pulmonary Venous Return

Normally, the pulmonary vein drains oxygenated blood to the left atrium. In total anomalous pulmonary venous return, the pulmonary veins drain the blood to the right atrium or the superior vena cava. Blood from the right atrium enters the right ventricle to the pulmonary artery, lungs, pulmonary veins and back to the right atrium. Often, an absent spleen is associated with this disorder.

Truncus Arteriosus

Normally aorta and pulmonary artery are separate vessels. In Truncus Arteriosus, one major artery or trunk serves as the common pathway for the pulmonary artery and aorta. This trunk or major artery arises from the right and the left ventricles. Thus, deoxygenated blood (from the pulmonary artery) and oxygenated blood (in the aorta) mixes in one major trunk.

Hypoplastic Left Heart Syndrome

In Hypoplastic left heart syndrome, the left side of the heart is non-functional. The left ventricle, which pumps blood to the systemic circulation, lacks sufficient strength to pump the blood into the systemic circulation. This results to the hypertrophy of the right ventricle as it tries to maintain the adequate heart function and action.

images from healthguide.howstuffworks.com, chw.org, health.allrefer.com

Congenital Heart Disorders – Disorders with Increase Pulmonary Blood Flow

Posted: 03 Dec 2010 04:47 PM PST

Classification of Congenital Heart Diseases

Congenital Heart disorders were formerly classified as either cyanotic and acyanotic heart diseases. Cyanotic heart diseases occur when deoxygenated blood is shunted from the venous circulation to the arterial circulation, resulting to the bluish discoloration of the skin (cyanosis) due to decreased oxygen levels in the systemic circulation. With this classification, blood is shunted directly from the right to the left part of the heart. Acyanotic heart diseases involve narrowing or stricture of the blood that moves the blood from the arterial to the venous circulation (left to right shunt). However, some patients with heart diseases under the cyanotic type do not show cyanosis until they are seriously ill. And those with cyanotic heart diseases can also exhibit cyanosis.

Because of the confusion the former system created a second classification system has been established. This classification system identifies four types of disorders which is classified according to the blood flow patterns of the disease not their signs and symptoms. The following are:

Increased pulmonary blood flow
Obstruction to blood flow
Mixed blood flow
Decreased pulmonary blood flow

Disorders with Increased Pulmonary Blood Flow

Congenital heart disorders classified with increased pulmonary blood flow follows the movement pattern of the blood from the left side of the heart (greater pressure) to the right side of the heart (lower pressure). This abnormal blood movement is due to an opening between two systems or arteries. Disorders of this type include the following:

Ventricular Septal Defect (VSD)

With this cardiovascular defect, an opening between the two ventricles is present. Because pressure in the left side of the heart is greater than the right side, blood will be shunted from the left to the right. Thus, more blood enters the pulmonary circulation (from the right side) and less to the aorta.

Clinical Manifestations:

Easy fatigability
Loud harsh pansystolic murmur at the left sterna border

Atrial Septal Defect (ASD)

Presence of an opening in between the two atria resulting to the shunt of the oxygenated blood from the left side of the heart to the right side is noted with ASD. This congenital heart disease is more common in girls than boys.

Clinical Manifestations:

Harsh systolic murmur (at 2^nd or 3^rd interspace)
Second heart sound auscultated as split (fixed splitting)

Atrioventricular Canal Defect (AVC) or Endocardial Cushion Defect

Endocardial cushion is the septum of the heart at the junction of the atrium and ventricle. When this endocardial cushion fails to fuse the disorder is called AVC or Endocardial Cushion Defect.

Patent Ductus Arteriosus (PDA)

Ductus arteriosus is a fetal accessory that links the pulmonary artery to the aorta. Failure of this accessory structure to close at birth (Patent Ductus Arteriosus) will result to the shunting of the oxygenated blood from the aorta to the pulmonary artery. Blood is shunted from the aorta to the pulmonary artery because of the increase pressure in the aorta.