Blood PressureBlood Pressure

The maintenance of blood pressure is The maintenance of blood pressure is dependent upon intrinsic (stroke volume, dependent upon intrinsic (stroke volume, heart rate and cardiac output) , reflex heart rate and cardiac output) , reflex (baroreceptors and chemoreceptors), (baroreceptors and chemoreceptors), hormonal, renal, and micro vascular hormonal, renal, and micro vascular control systems control systems

Blood pressureBlood pressure

Blood pressure changes by:Blood pressure changes by:

1.1. Blood flow (blood volume)Blood flow (blood volume)

2.2. Resistance (blood vessels area)Resistance (blood vessels area)

3.3. Both 1 and 2Both 1 and 2

Blood VolumeBlood Volume

Blood volume is determined by the amount Blood volume is determined by the amount of water and sodium :of water and sodium :

1.1. IngestedIngested

2.2. Excreted by the kidneys, gastrointestinal Excreted by the kidneys, gastrointestinal tract, lungs and skintract, lungs and skin

How Blood Volume Affects Blood How Blood Volume Affects Blood PressurePressure

An increase in blood volume An increase in blood volume

1.1. Increases Increases central venous pressurecentral venous pressure

2.2. IncreaseIncrease atrial atrial andand ventricular pressure ventricular pressure

3.3. IncreasesIncreases stroke volume stroke volume andand cardiac cardiac outputoutput

What alters blood volume?What alters blood volume? Removing HRemoving H22O from the body decreases the volume O from the body decreases the volume

of bloodof blood; ; i.e.i.e., failing to retain H, failing to retain H22O by failing to retrieve O by failing to retrieve

it from urine when that is concentrated in the kidney it from urine when that is concentrated in the kidney causes blood volume to decrease along with blood causes blood volume to decrease along with blood pressure. pressure. VP/ADH stimulates the kidney distal VP/ADH stimulates the kidney distal tubules to recapture the Htubules to recapture the H22O in urine passing through O in urine passing through

the tubules.the tubules.

Increasing the osmotic or ionic content of blood will Increasing the osmotic or ionic content of blood will increase blood volume by drawing Hincrease blood volume by drawing H22O from body O from body

tissues to dilute dissolved materialstissues to dilute dissolved materials, , e.g.e.g., glucose, or , glucose, or ions, ions, e.g.e.g., Na, Na++. . Sodium ion recovery from urine is Sodium ion recovery from urine is stimulated by the Renin-Angiotensin-Aldosterone stimulated by the Renin-Angiotensin-Aldosterone system which is stimulated by low blood pressure.system which is stimulated by low blood pressure.

How are changes in blood pressure detected?How are changes in blood pressure detected?

Brain, heart, & kidney respond to changes in blood pressure via pressure receptors, baroreceptors, & to

changes in ionic composition of blood via osmoreceptors.

Baroreceptors exist in large blood vessels, heart, & the kidney glomerulus (maculodensa).

Osmoreceptors occur in hypothalamic & glomerulus (juxtaglomerular) cells.

Hormonal Regulation of the Hormonal Regulation of the Cardiovascular SystemCardiovascular System

Several hormones affect blood pressure (BP) Several hormones affect blood pressure (BP) and flow by acting on the heart, by altering and flow by acting on the heart, by altering blood vessel diameter, or adjusting the total blood vessel diameter, or adjusting the total blood volumeblood volume. .

Examples of Hormones that affect BPExamples of Hormones that affect BPThese include (but not all): These include (but not all): 1) 1) Renin-angiotensin-aldosterone (RAA) systemRenin-angiotensin-aldosterone (RAA) system - angiotensin - angiotensin

II raises BP by causing vasoconstriction, elevating CO, and II raises BP by causing vasoconstriction, elevating CO, and stimulating aldosterone and ADH secretion to raise total stimulating aldosterone and ADH secretion to raise total blood volume (review aldosterone and ADH).  It also blood volume (review aldosterone and ADH).  It also stimulates thirst. stimulates thirst. 

2) 2) Epinephrine and norepinephrineEpinephrine and norepinephrine - from adrenal medulla, act - from adrenal medulla, act to increase CO and selective vasoconstriction/vasodilation to increase CO and selective vasoconstriction/vasodilation to adjust blood flow in flight/fight.to adjust blood flow in flight/fight.

3) 3) Antidiuretic hormoneAntidiuretic hormone - How would this affect total blood - How would this affect total blood volume and therefore BP? It also has vasomotor abilities.volume and therefore BP? It also has vasomotor abilities.

4) 4) Atrial natriuretic peptide (ANP)Atrial natriuretic peptide (ANP) - lowers BP by causing - lowers BP by causing vasodilation and promoting loss of salt and water in urine to vasodilation and promoting loss of salt and water in urine to decrease total blood volume.decrease total blood volume.

5) 5) ErythropoietinErythropoietin stimulates RBC production if BP declines or stimulates RBC production if BP declines or blood becomes hypoxic.  This will elevate blood volume (by blood becomes hypoxic.  This will elevate blood volume (by addition of cells) and improve its oxygen-carrying capacity.addition of cells) and improve its oxygen-carrying capacity.