CV Regulation
BP
Dr. Meg-angela Christi Amores
Blood Pressure
• Patient: Doc, pila akong BP?
• Doctor: 110/70 mmHg
• Ever wonder why BP is measured in
millimeters mercury?
Blood Pressure
• the mercury manometer has been used since
antiquity as the standard reference for
measuring pressure
• blood pressure means the force exerted by the
blood against any unit area of the vessel wall
• Pressure of 50 mmHg - means that the force
exerted is sufficient to push a column of
mercury against gravity up to a level 50 mm
high
Summary of the Integrated,
Multifaceted System for Arterial
Pressure Regulation
• first line of defense against acute changes in
arterial pressure is the nervous control system
• second line of defense achieved mainly by
kidney mechanisms for long-term control
• However, there are other pieces to the puzzle
• Pressure Control Mechanisms That Act After
Many Minutes
• (1) the renin-angiotensin vasoconstrictor mechanism,
(2) stress-relaxation of the vasculature, and (3) shift of
fluid through the tissue capillary walls in and out of the
circulation
• Within 30 mins to several hours
• Rapidly Acting Pressure Control Mechanisms,
Acting Within Seconds or Minutes
• acute nervous reflexes or other nervous responses
• SECONDS: (1) the baroreceptor feedback mechanism,
(2) the central nervous system ischemic mechanism,
and (3) the chemoreceptor mechanis
• (1) to cause constriction of the veins and provide
transfer of blood into the heart, (2) to cause increased
heart rate and contractility of the heart to provide
greater pumping capacity by the heart, and (3) to cause
constriction of most peripheral arterioles to impede
flow of blood out of the arteries
• Long-Term Mechanisms for Arterial Pressure
Regulation.
• renal-body fluid pressure control mechanism
• decrease in arterial pressure leads within minutes to an
increase in aldosterone secretion
Cardiac Output, Venous Return
• Cardiac output is the quantity of blood
pumped into the aorta each minute by the
heart
• Venous return is the quantity of blood flowing
from the veins into the right atrium each
minute
Cardiac Output
• Factors: (1) the basic level of body
metabolism, (2) whether the person is
exercising, (3) the person's age, and (4) size of
the body
• young, healthy men, resting cardiac output
averages about 5.6 L/min
• women, this value is about 4.9 L/min
Venous Return
• principal factors that affect venous return to
the heart from the systemic circulation:
– Right atrial pressure, which exerts a backward
force on the veins to impede flow of blood from
the veins into the right atrium
– Degree of filling of the systemic circulation
– Resistance to blood flow between the peripheral
vessels and the right atrium
Local control of blood flow
• Delivery of oxygen to the tissues
• Delivery of other nutrients, such as glucose,
amino acids, and fatty acids
• Removal of carbon dioxide from the tissues
• Removal of hydrogen ions from the tissues
• Maintenance of proper concentrations of other
ions in the tissues
• Transport of various hormones and other
substances to the different tissues
Variations in Blood Flow in Different
Tissues and Organs
ORGAN
PERCENT
Brain
14
Heart
4
Bronchi
2
Kidneys
22
Liver
27
Muscle
15
Bone
5
Skin
6
Thyroid
1
Adrenal glands
0.5
Others
3.5
Phases of blood flow control
• Acute Control
• achieved by rapid changes in local vasodilation or
vasoconstriction of the arterioles, metarterioles, and
precapillary sphincters
• Long term control
• slow, controlled changes in flow over a period of days,
weeks, or even months
• increase or decrease in the physical sizes and numbers
of actual blood vessels supplying the tissues
Long term blood flow regulation
• to change the amount of vascularity of the
tissues
• actual physical reconstruction of the tissue
vasculature to meet the needs of the tissues
• the final degree of response is much better in
younger tissues than in older
• Vascularity Is Determined by Maximum Blood
Flow Need, Not by Average Need
Humoral control of the circulation
• control by substances secreted or absorbed
into the body fluids-such as hormones and
ions
• Vasoconstrictors:
– Norepinephrine and epinephine
– Angiotensin II
– Vasopressin
– Endothelin
Humoral control of the circulation
• Vasodilators:
– Bradykinin
– Histamine
• IONS:
• Inc calcium ion concentration causes vasoconstriction
• Inc potassium ion concentration causes vasodilation
• Inc Mg and Hydrogen - vasodilation