Blood flow, pressure, and resistance are key components of circulation. Resistance depends on vessel length and diameter, with smaller diameters resulting in greater resistance. Blood pressure includes systolic, diastolic, and mean arterial pressures. The circulatory system is regulated through neural, chemical, and renal mechanisms to maintain homeostasis. Issues like hypotension, hypertension, and shock can occur if regulation is compromised.

1. Circulation

2. Blood flow, blood pressure, and
resistance
Blood flow is the actual volume of blood
flowing through a vessel, and organ, or the
entire circulation in a given period of time.
Blood pressure is the force per unit area
exerted on the wall of a blood vessel by its
contained blood.

3. Resistance is opposition to flow and is a
measure of the amount of friction blood
encounters as its passes through the vessels.
Peripheral resistance is resistance
encountered in the peripheral circulation.

4. Blood viscosity is the internal resistance to
flow and is related to the thickness of a
fluid.
The longer the total vessel length, the
greater the resistance encountered.
The smaller the vessel diameter, the greater
the resistance encountered.

5. Arterial blood pressure
Systolic pressure is the pressure exerted by
ventricular contraction, and is measured in
the aortic arch at about 120mm Hg.
Diastolic pressure is the pressure exerted by
the arteries when the ventricles are in
diastole.

7. Pulse pressure is the difference between
systolic and diastolic pressure.
Mean arterial pressure (MAP) is responsible
for actually propelling the blood to the
tissues: = diastolic + pulse pressure/3.

8. Venous blood pressure
The respiratory pump is a lessening of
pressure created by pressure changes
occurring the in the body cavity during
breathing.
The muscular pump is pressure created by
the contraction of skeletal muscles.

11. Neural controls
The neural center that oversees changes in
the diameter of blood vessels is the
vasomotor center, which is located in the
medulla.

12. The vasomotor center transmits impulses in
a fairly steady stream along sympathetic
efferents called vasomotor fibers.
Vasomotor tone is a state of moderate
constriction of arterioles as a result of
inervation by vasomotor fibers.

14. The carotid sinus reflex protects the blood
supply to the brain due to acute changes in
blood pressure.
The aortic reflex maintains adequate blood
pressure in the systemic circuit as a whole.

15. Chemical controls
Adrenal medulla hormones enhance the
sympathetic response, either by increasing
cardiac output (epinephrine), or by
vasoconstriction (NE).
Atrial natriuretic peptide causes blood
volume and blood pressure to decline by
promoting excretion of sodium and water
by the kidneys.

16. Antidiuretic hormone stimulates the kidneys
to conserve water, and also causes
vasoconstriction in order to increase blood
pressure.
Angiotensin II causes intense
vasoconstriction, and is generated in
response to renin release by the kidneys.

17. Nitric oxide promotes systemic and
localized vasodilation.
Alcohol causes blood pressure to drop by
inhibiting ADH release.

20. Renal regulation
The renin-angiotensin system is an indirect
renal mechanism used to raise blood
pressure due to a decline in arterial blood
pressure.
Angiotensin II is a vasoconstrictor produced
by the enzyme renin, which increases renal
perfusion, and stimulates the adrenal cortex
to secrete aldosterone.

21. Monitoring circulatory efficiency
Vital signs are measurements of pulse and
blood pressure.
A pulse is the alternating expansion and
recoil of elastic arteries during each cardiac
cycle.
Pressure points are areas where blood flow
can be compressed due to trauma, or to take
a pulse measurement.

23. Systemic arterial blood pressure is
measured indirectly by the auscultatory
method, which measures blood pressure in
the brachial artery using a
sphygmomanometer.

24. Alterations in blood pressure
Hypotension is low blood pressure, and is
generally considered to be a systolic
pressure of < 100 mm Hg.
Hypertension is high blood pressure, and is
generally considered to be > 140/90.
Elevated diastolic pressure is more
significant clinically, because it indicates
progressive occlusion or arteriosclerosis.

25. Primary hypertension accounts for 90% of
all cases, and has no underlying cause.
Secondary hypertension accounts for 10%
of cases, and is due to identifiable disorders.

26. Blood flow through body tissues
Tissue perfusion is blood flow through the
body.
Autoregulation is the automatic adjustment
of blood flow to each tissue in proportion to
its requirements at any point in time.

29. Myogenic responses are stimulation of
vascular smooth muscle due to changes in
arteriolar blood pressure, and keep tissue
perfusion fairly constant.
Reactive hyperemia is the dramatic increase
in blood flow into a tissue that occurs after
the blood supply to an area has been
temporarily blocked.

30. When blood flow increases to skeletal
muscles in direct proportion to their greater
metabolic activity, it is called active
hyperemia.

31. Blood flow through capillaries
Vasomotion is the slow and intermittent
flow of blood through capillaries, and is due
to the opening and closing of precapillary
sphincters.
Gases, most chemical nutrients, and
metabolic wastes pass between the blood
and interstitial fluid by diffusion.

34. Hydrostatic pressure is the force exerted by
a fluid pressing against a wall.
Capillary hydrostatic pressure tends to force
fluids through the capillary walls.
Interstitial fluid hydrostatic pressure is the
pressure acting outside the capillaries,
which opposes blood pressure.

35. Capillary colloid osmotic pressure is due to
plasma proteins in capillaries, such as
albumin, that draw water into the
capillaries.
The net filtration pressure is a result of all
forces acting at the capillary bed.
NFP = (HPc-HPif) - (OPc-OPif)

37. Circulatory shock
Circulatory shock is any condition in which
blood vessels are inadequately filled and
blood cannot circulate normally.

38. Types of circulatory shock
Hypovolemic shock results from large-scale
loss of blood, as might follow acute
hemorrhage.
Vascular shock is due to a huge drop in
peripheral resistance due to extreme
vasodilation.

39. Cardiogenic shock occurs when the heart is
so inefficient that it cannot sustain adequate
circulation.