BIOLOGY · HUMAN BODY SYSTEMS
The Cir cu lator y System
A Complete High School Biology Reference
Life's delivery network — pumping oxygen, nutrients, and signals to every cell in the human
body, unceasingly, from birth to last breath.
, The Circulatory System | High School Biology
SECTION 01
W hat Is the Cir cu lator y System ?
The circulatory system — also called the cardiovascular system — is the body's internal transport
network. It is a closed loop of organs and vessels that continuously moves blood throughout the body to
deliver oxygen and nutrients to tissues and remove carbon dioxide and metabolic waste.
Without it, cells would be starved of oxygen within minutes. It works every second of every day —
roughly 100,000 beats per day, never resting — making it one of the most vital systems in the human
body.
Th r ee Cor e Com ponen ts
The circulatory system has three main parts: (1) the Heart — the pump; (2) Blood Vessels —
the pipelines; and (3) Blood — the transport fluid. Together, they form a continuous,
pressurised loop roughly 60,000 miles long if laid end to end.
K ey Facts at a Glance
25 20
60,000 5 Litr es 100,000
Miles of blood vessels Blood in adult body Heartbeats per day tr illion seconds
Red blood cells Full circuit time
Fig. 1 — Overview of the human circulatory system showing the heart and major vessels.Red = oxygenated blood (arteries); Blue =
deoxygenated blood (veins).
Page 2 of 10
The Cir cu lator y System
A Complete High School Biology Reference
Life's delivery network — pumping oxygen, nutrients, and signals to every cell in the human
body, unceasingly, from birth to last breath.
, The Circulatory System | High School Biology
SECTION 01
W hat Is the Cir cu lator y System ?
The circulatory system — also called the cardiovascular system — is the body's internal transport
network. It is a closed loop of organs and vessels that continuously moves blood throughout the body to
deliver oxygen and nutrients to tissues and remove carbon dioxide and metabolic waste.
Without it, cells would be starved of oxygen within minutes. It works every second of every day —
roughly 100,000 beats per day, never resting — making it one of the most vital systems in the human
body.
Th r ee Cor e Com ponen ts
The circulatory system has three main parts: (1) the Heart — the pump; (2) Blood Vessels —
the pipelines; and (3) Blood — the transport fluid. Together, they form a continuous,
pressurised loop roughly 60,000 miles long if laid end to end.
K ey Facts at a Glance
25 20
60,000 5 Litr es 100,000
Miles of blood vessels Blood in adult body Heartbeats per day tr illion seconds
Red blood cells Full circuit time
Fig. 1 — Overview of the human circulatory system showing the heart and major vessels.Red = oxygenated blood (arteries); Blue =
deoxygenated blood (veins).
Page 2 of 10
