circulation: the heart and blood vessels 137The Cardiovascular System and Blood
The heart pumps blood into blood vessels that transport
blood throughout the body. In this way the system delivers
blood’s cargoes to body cells and carries away potentially
toxic wastes and other unneeded materials.
Blood pressure generated by heart contractions helps keep
blood flowing through the cardiovascular system.
Mechanisms that widen or narrow the diameter of arterioles
and capillaries allow adjustments in blood flow to different
body regions as conditions warrant.
As described in Chapter 8, blood is the medium that
transports nutrients, oxygen, hormones, cell wastes, and
other substances. It also carries and distributes a great deal
of body heat.
Blood’s ability to clot allows the body to sustain minor wounds
without a serious loss of blood.The Cardiovascular System and Blood in Homeostasis
Unless otherwise indicated, all art on this page is © Cengage Learning.Integumentary system
Adjustments to blood flow
at the skin’s surface help
regulate body temperature.
Blood‑clotting mechanisms
help repair skin injuries.Digestive system
The bloodstream circulates nutrients from
food digestion to cells. The liver receives and
processes certain nutrients via the hepatic portal
system.Skeletal system
Stem cells in bone marrow
produce blood cells. Circulating
blood delivers calcium and
phosphate used to form bone
tissue.Immunity and the lymphatic system
The lymphatic system picks up fluid lost from
capillaries and returns it to the bloodstream,
helping to maintain normal blood pressure.
Circulating blood also carries many types of white
blood cells, which function in defense.
Respiratory system
Blood pumped by the heart picks up inhaled
oxygen from the lungs and delivers carbon dioxide
to the lungs to be exhaled.Urinary system
The kidneys filter impurities and other unneeded
substances from blood and form urine that removes
them from the body. The kidney hormone erythro‑
poietin stimulates the formation of red blood cells.
Nervous system
Centers in the brain and spinal cord adjust the
rate and strength of heart contractions and help
maintain proper blood pressure by adjusting the
diameter of arterioles.
Sensory systems
Sensors in the carotid arteries help monitor blood
pressure. Sensory perceptions related to mental
or physiological states may trigger changes in
local blood flow (as in blushing, sexual arousal).
Endocrine system
Nearly all hormones reach their targets via the
bloodstream. Certain cells in the heart atria
release a hormone (ANP) that helps regulate
blood pressure.
Reproductive system
Reproductive hormones, including estrogens and
testosterone, travel in the bloodstream. Arterioles
in organs of sexual intercourse dilate at times
of arousal. Blood vessels of the placenta help
maintain homeostasis in a developing fetus.Muscular system
Circulating blood distributes heat produced
by active skeletal muscles. Contraction of leg
muscles helps return venous blood to the heart.- 11
ConneCTionS
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