Organization of the Cardiovascular System

Interstitial fluid

the fluid filling the space between cells, makes up 1/6 of total body volume

Interstitial fluid relation to blood

nutrients leave blood and enter interstitial fluid, then enter cells

Blood composition

• 55% plasma

• 45% red blood cells

• <1% white blood cells

Transportation function of the cardiovascular system

blood distributes essential substances

• Oxygen from lungs → tissues

• CO₂ from tissues → lungs

• Nutrients (glucose, amino acids, fats) to cells

• Waste products to organs for elimination

• Hormones, cytokines, growth factors throughout the body

• Immune cells for tissue repair and defense

Thermoregulation function of cardiovascular system

blood is the warmest part of the body

• When vessels dilate, more warm blood reaches the skin → body cools.

• When vessels constrict, heat is conserved

Pulmonary circulation loop

Heart → lungs → heart

Pulmonary circulation function

oxygenate the blood

Systemic circulation

Heart → rest of body → heart

Systemic circulation function

deliver oxygenated blood and collect CO₂

Arteries

• Always carry blood away from the heart

• Usually oxygen-rich (except pulmonary artery)

Veins

• Carry blood toward the heart

• Usually oxygen-poor (except pulmonary veins)

Structure of the heart

• Right atrium

• Right ventricle

• Left atrium

• Left ventricle

Left ventricle

thicker muscle because it pumps blood to the entire body

Valves

ensure one-way flow

• tricuspid

• pulmonary

• mitral

• aortic

Cardiac diastole

• The heart relaxes

• The ventricles fill with blood

Cardiac systole

• The heart contracts

• Blood is ejected from the ventricles

End-diastolic volume (EDV)

blood volume in ventricles at the end of filling

End-systolic volume (ESV)

blood volume after contraction

Ejection fraction

% of EDV ejected in one heartbeat

Normal ejection fraction

50-75%

Stroke volume (SV)

the volume of blood ejected per beat

SV = EDV - ESV

Cardiac output (CO)

amount of blood pumped per minute

CO = SV*HR

Normal adult CO

5-6 L/min

CO relationship with exercise and heart failure

CO increases with exercise, decreases with heart failure

Blood vessel pathway

Artery → arteriole → capillary → venule → vein

Artery pressure

high

Capillary function

nutrient/gas exchange

Vein pressure

low pressure + volume reservoir

Three layers of blood vessels

1. tunica intima

2. tunica media

3. tunica externa

Tunica intima

inner endothelial layer

Tunica media

smooth muscle layer

Tunica externa

outer connective tissue

Vasa vasorum

tiny blood vessles that supply nutrients to the walls of large arteries/veins

Nervi vasorum

nerves that control vessel diameter, important in vasoconstriction/vasodilation

What do veins rely on for blood movement?

• skeletal muscle contraction: muscles squeeze the vein → pushing blood toward heart

• one-way venous valves → prevents backflow

Pericytes

cells that wrap around capillaries

Pericyte function

• Maintain microvessel structure

• Help with contraction

• Communicate with endothelial cells

• Important in wound healing and blood-brain barrier stability

Capillary beds in lymph vessels

• Return excess interstitial fluid to bloodstream

• Help remove waste and fight infections

Where is blood pressure highest?

aorta/arteries

Where does blood pressure drop?

arterioles

Where is blood pressure lowest?

veins

Where is blood pressure usually measured?

• brachial artery

• radial artery used for heart rate by palpation

Mean arterial pressure

average pressure in arteries over time

MAP = 1/3 aortic systolic pressure + 2/3 aortic diastolic pressure

Normal adult blood pressure

<120 / <80 mmHg