Hemodynamics and the Urinary System
Hemodynamics:
● Blood pressure (mean arterial pressure)
- Hydrostatic pressure of blood against vessel wall
- mmHg
Blood Pressure:
● Systolic blood pressure (SBP)
- Pressure in arteries when ventricles contract
● Diastolic blood pressure (DBP)
- Pressure in arteries when ventricles relax
● Blood pressure = systolic bp/ diastolic bp
Mean Arterial Pressure (MAP)
● Include % of time spent in each phase of the cycle
● Why is the control of mean arterial pressure important?
1) To maintain and control blood flow (perfusion) to organs, tissues, etc.
2) To influence bulk movement (filtration) across capillary walls
Flow
● Blood flow (perfusion) = Amount blood/time moving past a given point or into or out
of an organ
● To change flow, must change pressure or resistance
Blood Pressure in Various Parts of the Cardiovascular System
● Roughly the same in aorta and arteries
● SBP and DBP disappear as you move towards capillaries
● Low pressure in capillaries
● Very low pressure in venules and veins
Blood Flow Between Two Points
● If R were very large, flow would be very small, moving toward 0
What Determines P and R at a Single Point?
Resistance
● Forces opposing liquid movement
● Resistance is influenced by several factors:
Resistance is Directly Proportional to:
● Viscosity of liquid (U)
- Composition
- Temperature
● Length of tube (L)
- Obesity
● Blood Volume (not in formula; assumed to be constant)
- But not if your bleeding
● Radius of tube (r)
- Small changes in radius change resistance dramatically
- Immediate with autonomic nervous system
● Changing resistance changes:
- Pressure
- Flow
Arterial Blood Flow and Pressure
● Arterial blood flow:
- Amt/min coming out of LV
- Also called cardiac output (CO)
● In respiratory system:
- Amt/time = amt/breath X breaths/min
● In cardiovascular system:
- Amt/time = amt/beat X beats/min
● CO = amt/time
● Heart rate (HR) = beats/min
● Stroke volume (SV) = amt/be
Venous Blood Flow
● Venous flow mostly due to skeletal muscle contraction
Factors that Increase CO
Increase SV (Stroke Volume):
● Increase preload (stretch) increases force of contraction
- Frank-Starling law of the heart
● Increase strength of contraction:
● Increase of sympathetic nervous stimulation
● Hormones epinephrine and norepinephrine
● Increase calcium inflow
● Decrease afterload:
- Decrease amount of blood in ventricles at end of systole
● Hypertension and atherosclerosis increase afterload
Increase HR (Heart Rate):
● CV center in medulla oblongata
- Increase sympathetic nervous stimulation
- Decrease parasympathetic nervous stimulation
● Hormones: epinephrine and norepinephrine
● Increase calcium
● Age and gender
● Increase in temperature
Factors that Influence Blood Pressure
● Increased venous return
● Increased resistance
● Radius
- Increase sympathetic
- Epinephrine and angiotensin
Factors that Influence Venous Return
● Skeletal muscle pump (valves)
● Respiratory pump
● Gravity
● Increased blood vol...
