Cardiovascular system- L7
Faisal I. Mohammed, MD, PhD
Yanal A. Shafagoj MD, PhD
University of Jordan
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Long term Regulation of
BP…cont
3. Renin-Angiotensin-Aldosterone system  1
hour to be effective
Angiotensinogen (14 a.a peptide) converted into Angiotensin I (10
a.a peptide) by Renin that come from afferent arteriolar cell, the
angiotensin I is converted into angiotensin II (8 a.a peptide) by
Angiotensin converting enzyme mainly in the lungs.
Angiotensin II (A II) is very potent vasoconstrictor. AII also
stimulates aldosterone synthesis and secretion from the adrenal
coretx (Zona glomerulosa), aldosterone increases Na+ reabsorption
from the renal nephrone and so water.
AII is also a positive inotropic agent
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Juxtaglomerular Apparatus
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Renin-Angiotensin System

Renin is synthesized and stored in
modified smooth muscle cells in
afferent arterioles of the kidney.

Renin is released in response to a fall
in pressure.

Renin acts on a substance called
angiotensinogen to form a peptide
called angiotensin I.

AI is converted to AII by a
converting enzyme located in the
endothelial cells in the pulmonary
circulation.
Long term Regulation of BP
…cont
4. Atrail Natriuretic peptide (ANP): An
28 a.a peptide released mainly from the Rt.
Atrium in response to stretch. It causes
increase in GFR and thus, increase Na+ and
water excretion . Its concentration decreases
when BP is low and its concentration
increases if BP is high, mainly due volume
overload
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Cardiac Output and Venous return
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Effect of Venous Valves
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Effect Of Gravity on Venous return
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Effect of Venous Valves
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The Capillaries
The Microcirculation
● Important in the transport of nutrients to tissues.
● Site of waste product removal.
● Over 10 billion capillaries with surface area of
500-700 square meters perform function of solute
and fluid exchange.
Diffusion


Most important method
Substances move down their concentration
gradient
 O2 and nutrients from blood to interstitial
fluid to body cells

CO2 and wastes move from body cells to
interstitial fluid to blood
Fluid Exchange - Starling Forces

As blood flows to the tissues of the body,
hydrostatic and osmotic forces at the capillaries
determine how much fluid leaves the arterial end of
the capillary and how much is then reabsorbed at the
venous end. These are called Starling Forces.


Filtration is the movement of fluid through the walls of the
capillary into the interstitial fluid.
Reabsorption is the movement of fluid from the interstitial
fluid back into the capillary.
Fluid Exchange - Starling Forces

Two pressures promote filtration:

Blood hydrostatic pressure (BHP) generated by the
pumping action of the heart - decreases from 35 to 16 from
the arterial to the venous end of the capillary

Interstitial fluid osmotic pressure (IFOP), which is constant
at about 1 mmHg
Fluid Exchange - Starling Forces

Two pressures promote reabsorption:

Blood colloid osmotic pressure (BCOP) is due to the presence
of plasma proteins too large to cross the capillary - averages 36
mmHg on both ends.

Interstitial fluid hydrostatic pressure (IFHP) is normally close
to zero and becomes a significant factor only in
states of edema.
Fluid Exchange - Starling Forces
Fluid Exchange - Starling Forces

Normally there is nearly as much fluid
reabsorbed as there is filtered.



At the arterial end, net pressure is outward at 10 mmHg
and fluid leaves the capillary (filtration).
At the venous end, net pressure is inward at –9 mmHg
(reabsorption).
On average, about 85% of fluid filtered is reabsorbed.
Fluid Exchange - Starling Forces

Fluid that is not reabsorbed (about 3L/ day for the
entire body) enters the lymphatic vessels to be
eventually returned to
the blood.
Net Filtration Pressure (NFP)
Filtration Rate = Kf{(Pc – Pif) – ( c -  if)}
Filtration Rate = Kf{(Pc – Pif) – ( c -  if)}
• Mean capillary hydrostatic pressure (Pc)-tends to force
fluid outward through the capillary membrane.
• Interstitial fluid pressure (Pif)- opposes filtration when
value is positive.
• Plasma colloid osmotic pressure (π c)- opposes filtration
causing osmosis of water inward through the membrane
• Interstitial fluid colloid pressure (π if) promotes filtration
by causing osmosis of fluid outward through the
membrane
• Filtration coefficient (Kf)
Gas And Nutrient Exchange

In contrast to the bulk flow of fluids at the capillaries, the
exchange of gases and small particles (like certain nutrients and
wastes) is a purely passive diffusion process.
 Gases and these other
substances simply
move into or out of
the capillary down their
concentration gradient.
Factors that Facilitate Venous Return
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Thank You
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