Cardiovascular system 2 Physiology 232 BMS

Arterial blood pressure Is the force per unit area exerted on the vessel wall by blood If the amount of blood entering & leaving the elastic arteries in a given period were equal arterial pressure will be constant

Types of arterial blood pressure 1.Systolic pressure As the left ventricle contracts & expels blood into aorta ….. This will lead to stretching the elastic aorta ….. The pressure inside the aorta will reach to its peak, this pressure peak is called: Systolic pressure (Average 120mmHg in healthy adults) 2.Diastolic pressure After that blood will move from aorta to the other blood vessels (Because blood pressure in aorta is higher than in other blood vessels) Aortic valve will close, preventing blood from flowing back into the heart & the walls of aorta will recoil, to keep the blood flowing forward into the other blood vessels During this, aortic pressure will drop to its lowest level called: Diastolic pressure (Average 70 – 80 mmHg in healthy adults)

Types of arterial blood pressure 3.Pulse pressure The difference between systolic & diastolic blood pressure 4.Mean arterial pressure (MAP) The pressure that propels the blood to the tissues pulse pressure MAP = diastolic pressure + ______________ 3

Factors affecting arterial blood pressure Cardiac output Resistance Blood volume Cardiac output increases …… Blood pressure increases Resistance increases …….. Blood pressure increases Blood volume increases ……. Blood pressure increases

Control of arterial blood pressure Short term control Long term control By changing the Resistance By changing the Blood volume ( ↑ R ….. ↑ BP) ( ↑ BV ….. ↑ BP) Short term control 1. Neural control 2. Hormonal control

Control of arterial blood pressure (ABP) 1. Neural control: Baroreceptor reflex action Vasomotor center: Center in the brain Chemoreceptors that controls the changes in the diameter of blood vessels (Cause blood vessels to be in moderate constriction) Baroreceptor: Pressure sensitive receptors If ABP rises …… Baroreceptors Will feel change in blood pressure …… And then will send impulse to the vasomotor center ….. This impulse will inhibit the vasomotor center causing vasodilatation ….. And so decrease in blood pressure

Control of arterial blood pressure (ABP) Chemoreceptors When the oxygen content of the blood drops, or the carbon-dioxide levels rise ……. Chemoreceptors will send impulses to the cardio-acceleratory center ………. Which will increases the cardiac output ….. And so blood pressure will increase …. And will increase blood return to heart & lungs

Control of arterial blood pressure (ABP) 2. Hormonal control: A. Adrenal hormones During periods of stress, the adrenal gland releases nor- epinephrine ….. That enhances the sympathetic response ….. Causing vasoconstriction & increase in blood pressure B. Atrial natriuretic peptide (ANP) The atria of the heart produce the hormone ANP ….. Which decreases blood volume & blood pressure C. Angiotensin II If blood pressure decreases ….. The kidneys will secrete the hormone Renin …. Which leads to the production of Angiotensin II …. Which causes vasoconstriction & increase in blood pressure

Control of arterial blood pressure (ABP) Long term control: It is performed by the kidneys (Direct & Indirect ways) Direct way If blood pressure decreases ….. Kidneys will keep the fluids & return them to the blood stream …. So increases blood volume & blood pressure Indirect way (Renin – Angiotensin mechanism) If blood pressure decreases ….. Kidneys will secrete Renin …… Leads to secretion of Angiotensin II 1. Vasoconstriction …… So increases blood pressure 2. Stimulates secretion of Aldosterone hormone …… ↑ water & salt re-absorption …… So increases blood volume & blood pressure 3. Stimulates secretion of Anti-diuretic hormone (ADH – Vasopressin) from pituitary gland …. ↑ water & salt re-absorption … So increases BP

Alterations in blood pressure 1. Hypotension: Is systolic blood pressure below 100 mmHg Orthostatic hypotension Is a temporary low blood pressure when the person rises suddenly from a sitting position

Alterations in blood pressure 2. Hypertension: Is arterial blood pressure of 140/90 or higher Chronic hypertension is common & dangerous disease, that is called(Silent killer) as it is usually asymptomatic for the first 10 – 20 years It is the main cause of atherosclerosis & cardiovascular diseases Types Primary Secondary With no reason Is due to certain diseases as: kidney diseases

Alterations in blood pressure Primary hypertension Causes which may be involved: 1. Diet: High intake of sodium 6. Stress 2. Obesity 7. Smoking 3. Age: Usually appears after age of 40 4. Diabetes mellitus 5. Hereditary

Gas exchange Gas exchange occurs between: Lungs & Blood And then between: Blood & Tissues (By a process called Diffusion which depends on the movement along a concentration gradient ….. Each substance moves from an area of its higher concentration to an area of its lower concentration) (Oxygen & nutrients pass from the blood, where their concentration is high to the cells – Carbon dioxide & waste products pass from cells, where their concentration is high to the blood) Diffusion The capillary walls consist of semi-permeable membrane that allow small molecules to pass into tissues, & retain large molecules in blood Diffusable substances include: Oxygen, Carbon dioxide, Fatty acids

Gas exchange Hydrostatic pressure: Is the pressure exerted by a fluid against a wall In capillaries: HP is the pressure exerted by the blood on the capillary walls (Capillary hydrostatic pressure HPC ) …. Force fluids to pass from capillaries to outside HPC is opposed by interstitial fluid hydrostatic pressure (Hpif ) acting outside the capillaries & pushing the fluid from outside to inside the capillaries And so Net hydrostatic pressure acting on capillaries = HPC - HPif HPif is usually Zero & so Net hydrostatic pressure = HPc

Gas exchange Osmotic pressure: The force opposing hydrostatic pressure, is created by the presence of large non-diffusible molecules (Such as: Plasma proteins) that are unable to cross the capillary wall (Against hydrostatic pressure, it pulls fluid back to the capillaries) The presence of plasma proteins in the capillaries will produce (Capillary osmotic pressure OPC = 26 mmHg) Interstitial fluid contains small amount of proteins & so it has (Interstitial fluid osmotic pressure OPif ….. But it is low = 1mmHg) And so Net osmotic pressure that pulls fluid back into the capillaries = OPc – OPif = 26 – 1 = 25 mmHg (The same in arterial & venous ends)

Gas exchange And so to determine whether fluid will pass into the capillaries or away from the capillaries we must calculate Net filtration pressure (NFP) NFP = (HPc - Hpif ) – (OPc – OPif ) At arterial end of the capillaries: = (35 – 0) – (26 – 1) = (35 – 25) HP > OP & so fluid passes = 10 mmHg from capillaries into the tissues At venous end of the capillaries: = (17 – 0) – (26 – 1) = (17 – 25) HP < OP & so fluid passes from = -8 mmHg the tissues into the capillaries

Arterial end of capillaries Venous end of capillaries Gas exchange Arterial end of capillaries Venous end of capillaries At the arterial end of the capillaries: Hydrostatic pressure = 35 mmHg Osmotic pressure = 25 mmHg & so HP > OP inside the vessel This causes the movement of blood (Carrying Oxygen) & some solutes from the capillaries into tissues At the venous end of the capillaries: Hydrostatic pressure = 17 mmHg & so HP < OP inside the vessel This causes the movement of blood (Carrying Carbon-dioxide) & some waste products from tissues into capillaries Not all waste products return to the capillaries ….. The excess is drained away from tissues into lymph capillaries (Similar to blood capillaries but more permeable) & then pass into the blood

Some heart diseases Tachycardia: Abnormally fast heart rate (More than 100 beats/min) Bradycardia: Abnormally slow heart rate (Less than 60 beats/min) Congestive heart failure: COP is below the normal level (And so the circulating blood is not sufficient or the tissue needs) Coronary atherosclerosis: The coronary arteries are blocked by fatty materials, which impairs blood & oxygen delivery to the cardiac cells, & so the heart begins to contract insufficiently Multiple myocardial infarctions: Pumping ability of the heart ↓, as the dead heart cells are replaced by non-contractile fibrous tissue

Some heart diseases Pulmonary congestion: If the left side of the heart fails …. The right side continues to give blood to the lungs …. But the left side fails to eject blood into the circulation …. So pressure in the lungs will increase causing pulmonary edema Peripheral congestion: If the right side of the heart fails …. Blood will stay in body organs & will not return to the heart …. This will cause edema

Some heart diseases Hypertrophic cardiomyopathy (HCM): Enlargement of cardiac muscle cells & thickening of the heart wall …. This will cause the heart to pump strongly but doesn’t relax well during diastole Ventricular tachycardia: Rapid ventricular contractions Myocarditis: Inflammation of the cardiac muscle

Summary Arterial blood pressure: Is the force per unit area exerted on the vessel wall by blood Types of arterial blood pressure: Systolic pressure: During contraction Diastolic pressure: During relaxation Pulse pressure: Difference between systolic & diastolic pressures Mean arterial pressure (MAP): The pressure that propels the blood to the tissues Factors affecting ABP: Cardiac output: COP ↑ ……. ABP ↑ Resistance: Resistance ↑ …… ABP ↑ Blood volume: Blood volume ↑ …….. ABP ↑

Summary Control of ABP: 1. Short term control: By changing resistance Neural control: Baroreceptor reflex action Chemoreceptors Hormonal control: Adrenal hormones Atrial natriuretic peptide Angiotensin II 2. Long term control: By changing blood volume Direct way Indirect way (Renin – Angiotensin mechanism)

Summary Alterations in ABP: 1. Hypotension: Is systolic blood pressure below 100 mmHg 2. Hypertension: Is arterial blood pressure of 140/90 or higher Types: Primary: With no reason Secondary: Is due to certain diseases as: kidney diseases Gas exchange: Hydrostatic pressure: Is the pressure exerted by a fluid against a wall Osmotic pressure: The force opposing hydrostatic pressure To determine whether fluid will pass into the capillaries or away from the capillaries we must calculate Net filtration pressure (NFP) NFP = (HPc - Hpif ) – (OPc – OPif )

Summary At arterial end of the capillaries: HP > OP & so fluid passes from capillaries into the tissues At venous end of the capillaries: HP < OP & so fluid passes from the tissues into the capillaries Some heart diseases: Tachycardia: Abnormally fast heart rate (More than 100 beats/min) Bradycardia: Abnormally slow heart rate (Less than 60 beats/min) Congestive heart failure: COP is below the normal level Coronary atherosclerosis: The coronary arteries are blocked by fatty materials, which impairs blood & oxygen delivery to the cardiac cells, & so the heart begins to contract insufficiently Multiple myocardial infarctions: Pumping ability of the heart ↓ Pulmonary congestion: If the left side of the heart fails …. The right side continues to give blood to the lungs …. But the left side fails to eject blood into the circulation …. So pressure in the lungs will increase causing pulmonary edema

Summary Peripheral congestion: If the right side of the heart fails …. Blood will stay in body organs & will not return to the heart …. This will cause edema Hypertrophic cardiomyopathy (HCM): Enlargement of cardiac muscle cells & thickening of the heart wall …. This will cause the heart to pump strongly but doesn’t relax well during diastole Ventricular tachycardia: Rapid ventricular contractions Myocarditis: Inflammation of the cardiac muscle