Download Control of arterial blood pressure

Physiology
232 BMS
Dr/Nahla Yacout
2016/2017
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
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)
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
1. Cardiac output
2. Resistance
3. 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
By changing the Resistance
( ↑ R ….. ↑ BP)
Long term control
By changing the Blood volume
( ↑ 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
With no reason
Secondary
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:
NFP = (HPc - Hpif ) – (OPc – OPif )
= (35 – 0) – (26 – 1) = (35 – 25)
= 10 mmHg
HP > OP & so fluid passes
from capillaries into the tissues
At venous end of the capillaries:
NFP = (HPc - Hpif ) – (OPc – OPif )
= (17 – 0) – (26 – 1) = (17 – 25)
= -8 mmHg
HP < OP & so fluid passes from
the tissues into the 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
Osmotic pressure = 25 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
 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
 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
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
 Arterial blood pressure: Is the force per unit area exerted on the vessel wall
by blood
 Types of arterial blood pressure:
1. Systolic pressure: During contraction
2. Diastolic pressure: During relaxation
3. Pulse pressure: Difference between systolic & diastolic pressures
4. Mean arterial pressure (MAP): The pressure that propels the blood to the
tissues
 Factors affecting ABP:
1. Cardiac output:
COP ↑ ……. ABP ↑
2. Resistance:
Resistance ↑ …… ABP ↑
3. Blood volume:
Blood volume ↑ …….. ABP ↑
 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)
 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 )
 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
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