NPB101: Cardiovascular Physiology II

UC Davis, A.V. Gomes, SQ2025

Compared to the resting state, which is true of the cardiac cycle during exercise?

both systole and diastole decrease, but there is a greater decrease in diastole

Circulation and blood pressure

Systemic and pulmonary circulation each consist of a closed system of vessels that transport blood to the tissues in parallel

Arteries

Composed of large vessels that carry blood from the heart

Arterioles

small diameter vessels that arise form the branching of arteries when they reach the organs they are supplying

Capillaries

the smallest diameter vessels that are formed when arterioles branch

venules

the vessels that form when capillaries join together

veins

large diameter vessels formed by the merging of venules

Microcirculation

the name given to the collection of arterioles, capillaries and venules

The larger the ____ area, the easier it is for things to be ____

cross-sectional; exchanged

Blood flow is determined by …

1. pressure gradient in the vessels

2. resistance to flow caused by friction and viscosity of the blood

Blood flow equation

F = P/R

• F= flow rate, volume of blood passing through a vessel per unit of time

  • alpha r^4

• P = pressure gradient, difference in pressure btwn the beginning and end of a vessel

• R = Resistance, resistance to flow depends on 3 factors

  • Blood viscosity

  • Vessel Length

  • Vessel radius

Blood Viscosity

friction developed in blood, determined by the concentration of plasma proteins, and the number of circulating red blood cells

Vessel length

friction between blood and the inner surface of a vessel is proportional to the vessel length

Vessel radius

friction btwn blood and inner surface of a vessel is inversely proportional to the 4th power of the vessel radius ( r )

• resistance (R) alpha 1/r^4

• Flow (F) alpha r^4

If all other variables remain constant, which of the following is not true of the amount of fluid that would flow through a vessel?

Doubling the radius of the vessel would result in 4 times more flow

Arteries: good for

large vessels serve as conduit for the low resistance flow of blood and bc of their elasticity they act as a pressure reservoir

Pressure Reservoir

Can serve as a driving force during ventricular diastole. Due to elasticity of the artery walls (smooth muscle, collagen, elastin). Arteries can expand and store the pressure imparted by cardiac contraction. During relation the arterial walls recoil and maintain pressure

Pulse pressure

pressure difference between systolic pressure and diastolic pressure

Mean arterial pressure

pressure that is monitored and regulated by blood pressure reflexes

• Mean arterial pressure = diastolic pressure + 1/3 pulse pressure

Sphygmomanometer

device used to measure systolic and diastolic arterial blood pressure

When cuff pressure is greater than 120 mm Hg …

• no blood flows through the vessel

• no sound is heard

When cuff pressure is between 120 and 80 mm Hg…

• blood flow through the vessel is turbulent whenever blood pressure exceeds cutoff pressure

• Intermittent sounds are heard as blood pressure fluctuates throughout the cardiac cycle

When cuff pressure is less than 80 mm Hg…

• blood flows through the vessel in a smooth, laminar fashion

• no sound is heard

Left ventricular pressure

swings between a low of 0 mm Hg during diastole to a high of 120 mm Hg during systole

Arterial pressure

Fluctuates between a peak systolic pressure of 120 mm Hg an d allow diastolic pressure of 80 mm Hg

Arteriolar pressure

drops dramatically across the length of the arterioles such that the systolic-to-diastolic swings in pressure are converted to a non-pulsatile pressure when blood flows through the arterioles

Pressure

continues to decline (but at a slower rate) as blood flows through the capillaries and venous system

Cardiovascular Response to Exercise

More amount of blood flowing during exercise but the proportion of blood decreases

Arterioles

• Source of vascular resistance in the circulatory system.

• Arteriolar radius is regulated intrinsically and extrinsically to control cardiac output and arterial pressure

Intrinsic (or local) control

• factors intrinsic to an organ or tissue. Subdivided into chemical and physical controls:

  • local chemical control

    • local metabolic changes

  • local physical control

Intrinsic- Local Metabolic Changes

Factors derived from metabolic activity causing dilation.

• O2 concentration: reduced O2 during metabolic demand

• CO2 concentration: increased CO2 during metabolic demand

• pH: increases in CO2 and/or lactic acid lowers the blood pH

• Extracellular K+ concentration: increased neuronal activity that outpaces the Na+/K+ ATPase

• Osmolarity: increased solute concentration resulting from metabolic activity

• Adenosine: released in cardiac muscle in response to metabolic demand

• Prostaglandins: produced from the metabolism of fatty acids

• Histamine release- released when tissues are damaged and leads to vasodilation accompanying an inflammatory response

Smooth muscle tone is controlled by…

the release of mediators, such as Nitric Oxide (NO), from the endothelial cells lining the inner walls of the arterioles

Intrinsic- Local Physical Control

• Temperature: arteriolar smooth muscle tone is inversely proportional to temperature

• Myogenic response: arteriolar smooth muscle responds to stretch by contracting

Which is true of arterial blood pressure during progressive dynamic exercise?

There is a progressive increase in systolic blood pressure and mean blood pressure but diastolic pressure changes very little

Capillary Exchange

• exchange of materials btwn the blood and the interstitial space

• Occurs by diffusion and bulk flow

  • interstitial fluid (plasma membrane) takes on the same composition as the arterial blood

Capillary Exchange: Diffusion

substances in the blood move independently of one another down their concentration gradients

Transport across a typical capillary wall

1. lipid-soluble substances

2. small water-soluble substances

3. plasma proteins

4. exchangeable proteins

• lipid-soluble substances pass through the endothelial cells

• Small water-soluble substance pass through the pores

• Plasma proteins generally cannot cross the capillary wall

• Exchangeable proteins are moved across by vesicular transport

Capillary Exchange: Bulk Flow

• mechanism for maintaining fluid balance btwn the blood and the extracellular space

• pores in capillary walls permit the flow of plasma, but not proteins or blood cells

Ultrafiltration

bulk flow into the tissues, occurs when the net pressure is positive

reabsorption

bulk flow into the capillaries, occurs when the net pressures negative

Which types of blood vessels carries blood away from the heart?

arteries

What are capillaries

tiny blood vessels that connect arteries to veins

4 Factors that influence bulk flow and net pressure equation

1. capillary blood pressure (P_c)

2. plasma-colloid osmotic pressure (π_p)

3. interstitial fluid hydrostatic pressure (P_IF)

4. interstitial fluid-colloid osmotic pressure (π_IF)

• net pressure = (P_c + π_IF) - (P_IF + π_p)

1. Capillary blood pressure (P_c)

hydrostatic pressure exerted on the inside of the capillaries. Forces fluid out of the capillaries and into the interstitial fluids

2. Plasma-colloid osmotic pressure (π_p)

Osmotic force pushing water into the capillaries from the interstitial fluid. Controlled by the concetration of protein in the blood plasma

3. Interstitial fluid hydrostatic pressure (P_IF)

hydrostatic pressure exerted on the outside of the capillary walls. Forces fluid into the capillaries from the interstitial fluid

4. Interstitial fluid-colloid osmotic pressure (π_IF)

osmotic force pushing water out of the capillaries into the interstitial fluid

What capillary exchange/bulk flow variables are outward pressure

(P_c) - capillary blood pressure

(π_IF) - interstitial fluid-colloid osmotic pressure

→ (P_c + π_IF)

What capillary exchange/bulk flow variables are inward pressure

(π_p) - plasma-colloid osmotic pressure

(P_IF) - interstitial fluid hydrostatic pressure

→ (P_IF + π_p)

Net Filtration and net reabsorption along the vessel length

the inward pressure (P_IF + π_p) remains constant throughout the length of the capillary whereas the outwards pressure (P_c + π_IF) progressively declines throughout the capillary’s length

Net filtration pressure is calculated by…

subtracting the blood colloid osmotic pressure from the capillary hydrostatic pressure

T/F: plasma proteins suspended in the blood cross the capillary cell membrane and enter the tissue fluid via facilitated diffusion. Why?

False; plasma proteins suspended in blood cannot cross the semipermeable capillary cell membrane and so they remain in the plasma within the vessel, where they account for the blood colloid osmotic pressure

Veins

vessels serve as a reservoir for blood and conduit for blood flow back to the heart

venous capacity

• volume of blood the veins can accommodate

• depends on the distensibility of the venous walls and the influence of any externally applied force

venous return

volume of blood entering each atrium per minute. Influenced by several factors

Factors influencing venous return (5)

1. sympathetic activity

2. skeletal muscle activity

3. venous valves

4. respiratory activity

5. cardiac suction

Factors influencing Venous Return: Sympathetic Activity

sympathetic stimulation produces vasoconstriction to increase venous pressure and enhance venous return

Factors influencing Venous Return:: Skeletal Muscle Activity

contraction of skeletal muscles compresses veins and increases venous pressure which counteracts the effect of gravity

Factors influencing Venous Return: Venous Valves

located within the lumen of large veins and prevent the back flow of venous blood

a. without venous valves, contracted skeletal muscle would squeeze blood both towards and away from the heart

b, with venous valves, contracted skeletal muscle squeezes blood towards the heart (valves prevent back flow)

Factors influencing Venous Return: Respiratory Activity

Pressure within the chest cavity transiently decreases during respiration. This increases the pressure gradient between the veins in the lower exterminates and the chest

Factors influencing Venous Return: Cardiac Suction

during ventricular contraction atrial pressure transiently falls below 0mm go Hg. This increases the venous pressure gradient and sucks venous blood into the atria

Baroreceptor reflex

• autonomically regulates cardiac output and total peripheral resistance

• respond to changes in arterial blood pressure by elevating or reducing their rate of firing

• signals alter the ratio of activity in the parasympathetic and sympathetic neurons of the cardiovascular control centers

Baroreceptors: when arterial pressure increases and decreases what happens to firing rate?

• are mechanoreceptors sensitive to changes in both mean arterial pressure and pulse pressure

• constantly provide information about blood pressure

• when arterial pressure increases, the firing rate of their afferent neuron increases. When arterial pressure decreases, the firing rate of their afferent neuron decreases

Hypertension, 2 classes of hypertension

• blood pressure above 140/90 mm Hg

  • Primary hypertension: unknown cause accounts for 90% of cases

  • Secondary: occurs secondary to another known primary problem, accounts for 10% of cases

Hypotension

Blood pressure below 100/60 mm Hg

How many major types of blood have scientists discovered?

4: Types A, B, AB, O