Venous

Venules

Small veins that collect blood from capillaries and return it to the heart.

Characteristics of Venules

Very porous, allowing fluid and white blood cells to pass into tissues.

Postcapillary Venules

The smallest venules made mostly of endothelium that are porous.

Large Venules

Contain 1 or 2 layers of smooth muscle and thin tunica externa.

Veins

Thinner walled vessels with larger lumens and lower pressure that serve as blood reservoirs.

Venous Valves

Prevent backflow of blood, especially in limbs, formed from folds of tunica intima.

Blood Reservoirs

Veins contain approximately 65% of the total blood volume.

Anastomoses

Interconnections between blood vessels that allow alternate routes for blood flow if one vessel is blocked. Locations: Common in joints, heart, brain, abdominal organs.

Blood Flow

The volume of blood flowing through a vessel or organ per time, equal to cardiac output.

Blood Pressure

The force exerted by blood on vessel walls, measured in mmHg.

Pressure Gradient

The difference in pressure that drives blood flow from high to low pressure.

Resistance

Opposition to blood flow, influenced by blood viscosity, vessel length, and diameter.

Cardiac Output

The volume of blood pumped by the heart per minute.

Systolic Blood Pressure

The pressure in arteries during ventricular contraction, average is 120 mm Hg.

Diastolic Blood Pressure

The pressure in arteries during elastic recoil when the heart is filling, average is 80 mm Hg.

Mean Arterial Pressure (MAP)

Average pressure that drives blood to tissues, calculated as Diastolic + 1/3(Pulse Pressure).

Capillary Blood Pressure

Low pressure ranging from ~35 mmHg to 15 mmHg, Prevents rupture; allowing nutrient exchange.

Venous Blood Pressure

Very low blood pressure in veins, ranging from ~15 mmHg to 0 mmHg.

Respiratory Pump

Pressure changes in the thoracic cavity during breathing that help move blood toward the heart. Inhale → pressure changes → blood moves toward heart.

Muscular Pump

Contraction of skeletal muscles that squeezes veins to push blood toward the heart.

Sympathetic Venoconstriction

Contraction of veins due to sympathetic nervous system activity, pushing blood to the heart. reduces the volume of blood in veins

Blood Pressure Measurement

Using a sphygmomanometer to measure the pressure exerted by blood on artery walls. Expansion/recoil of arteries; felt at pressure points.

resistance source 

Blood viscosity: Thickness of blood (↑ viscosity → ↑ resistance).

Total vessel length: Longer = more resistance.

Vessel diameter: Small diameter → ↑ resistance (main regulator).

 Blood Pressure

Pumping fluids (blood) in a closed system, Pump = Heart (pressure highest closer to the pump), Heart Contractions result in blood flow.