Cardiovascular System 2 PDF

Cardiovascular System 2 Dr/ Mai Adawi Lecturer of Physiology FOMSCU  The cardiac output  Cardiac output is the amount of blood pumped from each ventricle. Usually, it refers to left ventricular output through aorta.  Cardiac output is the most important factor in cardiovascu...

Cardiovascular System 2 Dr/ Mai Adawi Lecturer of Physiology FOMSCU  The cardiac output  Cardiac output is the amount of blood pumped from each ventricle. Usually, it refers to left ventricular output through aorta.  Cardiac output is the most important factor in cardiovascular system, because rate of blood flow through different parts of the body depends upon cardiac output. Arterial blood pressure  Arterial blood pressure is defined as the pressure exerted by the column of blood on wall of arteries.  Systolic blood pressure (systolic pressure) is defined as the maximum pressure exerted in the arteries during systole of heart. Normal systolic pressure: 120 mm Hg.  Diastolic blood pressure (diastolic pressure) is defined as the minimum pressure exerted in the arteries during diastole of heart. Normal diastolic pressure: 80 mm Hg.  Mean arterial blood pressure is the average pressure existing in the arteries. Normal mean arterial pressure: 93 mm Hg (80 + 13 = 93). Mean arterial blood pressure = Diastolic pressure + 1/3 of pulse pressure Arterial blood pressure  Mean Arterial Pressure = Cardiac Output × Total Peripheral Resistance  Total peripheral resistance (TPR) is the resistance to blood flow offered by all of the systemic vessels, especially by the arterioles, which are the primary resistance vessels.  Therefore, MAP is regulated by cardiac activity and vascular smooth muscle tone.  Regulation Of Blood Pressure  Arterial pressure control mechanism can be divided into two groups: 1- Those that react rapidly, within seconds or minute. 2- Those that provide long-term arterial pressure regulation (days, months, and years). Neural Control Mechanism Rapidly Acting Pressure Control Mechanisms  Acting Within Seconds or Minutes.  These mechanisms are powerful.  Of the mechanisms that show responses within seconds; there are:  (1) Baroreceptor mechanism.  (2) Chemoreceptor mechanism. The baroreceptor mechanism  Baroreceptors are the receptors, which give response to change in blood pressure. They are situated in the carotid sinus and wall of the aorta. The baroreceptor mechanism The Chemoreceptors mechanism  The chemoreceptors are chemosensitive cells sensitive to oxygen lack, carbon dioxide excess, and hydrogen ion excess ( primary function).  Peripheral chemoreceptors are located in large arteries (common carotid artery, and aorta).  A secondary function of these receptors is to influence MAP by providing input to the vasomotor center. A decrease in blood pressure causes a decrease in blood flow to the carotid and aortic bodies, Leading to adjustment the activity of the autonomic nervous system Long Term Regulation Of Blood Pressure  Kidneys regulate arterial blood pressure by two ways:  1. By regulation of ECF volume:  When the blood pressure increases, kidneys excrete large amounts of water and salt, particularly sodium  When blood pressure decreases, the reabsorption of water from renal tubules is increased.  2. Through renin-angiotensin mechanism.  When blood pressure and ECF volume decrease, renin secretion from kidneys is increased. It converts angiotensinogen into angiotensin I. This is converted into angiotensin II by ACE (angiotensin converting enzyme) in lungs.  Angiotensin II acts directly on the kidneys to cause salt and water retention.  Angiotensin II stimulates the adrenal cortex to secrete aldosterone. This hormone increases reabsorption of sodium & water from renal tubules resulting in increased ECF volume and blood volume. Pharmacy Applied: Antihypertensive drugs Diuretics; A group of therapeutic agents designed to reduce the volume of body fluids. Their mechanism of action is at the level of the kidney and involves an increase in the excretion of Na+ ions and Cl– ions and, consequently, an increase in urine production. Angiotensin converting enzyme inhibitors: ACE inhibitors not only cause vasodilation, they inhibit the aldosterone response to net sodium loss.Typically, aldosterone, which enhances the reabsorption of sodium in the kidney, would oppose diuretic-induced sodium loss. Therefore, the co-administration of ACE inhibitors would enhance the efficacy of diuretic drugs.  The Circulatory Shock  Means generalized inadequate blood flow through the body, to the extent that the body tissues are damaged because of too little flow, as a result of too little oxygen and other nutrients delivered to the tissue cells.  This clinical syndrome characterized by tissue hypoperfusion due to decrease in the cardiac output and arterial pressure.  It occurs as a result of either blood loss (hypovolemic shock) or other conditions in which the blood volume is normal (normovolemic shock).  Normovolemic shock includes:  The cardiogenic shock  The septic shock  Anaphylactic shock  MANIFESTATIONS OF CIRCULATORY SHOCK :  Low blood pressure  Rapid weak pulse  Cold pale skin  Low urinary output  Lack of blood flow to brain tissues produces ischemia resulting in fainting and irreparable damage of brain tissues. Finally the damage of brain tissues and cardiac arrest kill the victim.  The Hypovolemic Shock  This occurs as a result of reduction of the blood volume. Its manifestations are those or acute hemorrhage.  Main causes include:  (1) Acute hemorrhage (hemorrhagic shock)  (2) major surgery (surgical shock)  (3) Loss of large amount of plasma e.g. from extensive bums (burn shock)  (4) Dehydration (e.g. as a in severe diarrhea. Vomiting) Because the skin is pale and cold in this type of shock (due to V.C.). it is also referred to as "cold shock".  The Cardiogenic Shock  This occurs as a result of inadequate pumping action of the heart leads to reduction of the cardiac output and arterial blood pressure.  The main causes of cardiogenic shock include:  (1) Extensive left ventricular infarction  (2) Acute myocarditis  (3) Heart failure.  (4) Certain ventricular arrhythmias.  Because there is congestion in the lungs and viscera in this condition. it is also referred to as "congested shock".  The Neurogenic Shock  This occurs in severe emotions (e.g. fear) as well as in cases associated with severe pain e.g. severe trauma and burns (so traumatic and burn shock have both hypovolemic and neurogenic feature).  In these cases, signals from certain areas in the cerebral cortex inhibit the normal sympathetic V.C. tone.→ resulting in generalized V.D and venodilatation (while the blood volume is normal).  This leads acute drop of the venous return → decreased cardiac output and arterial blood pressure → tissue hypoperfusion → shock, and fainting also often occurs (a condition called vasovagal attack).  The Anaphylactic (allergic) Shock  This occurs in severe allergic conditions  In these cases, there is increased release of histamine during antigen-antibody reactions(= histamine shock)..→ resulting in generalized V.D and venodilatation (while the blood volume is normal).  This leads acute drop of the venous return → decreased cardiac output and arterial blood pressure → tissue hypoperfusion → shock  The Septic Shock  This occurs in certain bacterial infections  In these cases, the endotoxin released from the bacteria causes V.D. (which also occurs by effect of fever) → Shock  There is also some hypovolemic features as the endotoxin also increases capillary permeability with loss of plasma in the tissues.  The endotoxin also causes red cell agglutination & intravascular coagulation. This leads to multiple organ failure and cardiac depression, which makes shock more worse. THANK YOU