Download How do our organ systems maintain homeostasis?

Homeostasis and the Human Body
What is homeostasis?
The human body maintains a stable internal environment by monitoring the internal and external
conditions and responding to indicators of change. Each of the body’s systems maintain this
healthy balance, which is called homeostasis. Here are examples of how the human body responds
to changes in temperature, blood glucose level, and blood calcium level. The body systems that help
to maintain these conditions are the integumentary system, the nervous system, the endocrine
system, and the skeletal and muscular systems.
How do our organ systems maintain homeostasis?
Body Temperature:
The body’s temperature is monitored by the nervous system. If sensory receptors indicate that the
body is too hot or too cold, the brain will send nerve impulses to the skin and muscles, which will
respond to increase or decrease heat loss from the body’s surface. Here are a few ways that the skin
and muscles may respond:

Hairs on the skin trap more warm air if they are standing up, and less if they are lying flat.
Tiny muscles in the skin can quickly pull the hairs upright to reduce heat loss, or lay them
down flat to increase heat loss.

If the body is too hot, glands under the skin secrete sweat onto the surface of the skin, to
increase heat loss by evaporation. Sweat secretion stops when body temperature returns to
normal.

Blood vessels supplying blood to the skin can swell or dilate - called vasodilation. This causes
more heat to be carried by the blood to the skin, where it can be lost to the air. Blood vessels
can shrink down again - called vasoconstriction. This reduces heat loss through the skin once
the body’s temperature has returned to normal.

Muscles can also receive messages from the brain when you are cold. They respond by
shivering, which warms you up.
Blood Glucose Level:
A number of different hormones are active in keeping the blood glucose level at about 0.1%. The
most important of these is insulin. Immediately after eating, the increased glucose concentration
from food stimulates the pancreas to release insulin. Insulin stimulates the conversion of glucose to
glycogen in the liver to decrease the glucose levels in the blood. Between eating, when insulin is not
being produced and as glucose levels in the blood are decreasing, the liver converts glycogen to
glucose to increase the glucose level in the blood. This helps the blood glucose level to remain
constant.
Blood Calcium Levels:
Bones play an important role in regulating blood calcium levels, which must be maintained within
narrow limits for functions such as muscle contraction and membrane potentials to occur normally.
Bone is the major storage site for calcium in the body, and movement of calcium into and out of
bone helps to determine blood calcium levels. Calcium moves into bone as osteoblasts build new
bone and out of bone as osteoclasts break down bone.
Hormones help regulate blood calcium
levels. For instance, calcitonin, secreted by the thyroid gland inhibits osteoclasts and stimulates
osteoblasts, thus decreasing blood calcium levels. Parathyroid hormone is secreted by the glands
on the posterior side of the thyroid. Parathyroid hormone inhibits osteoblasts, stimulates
osteoclasts, reduces the output of calcium by the kidneys and promotes the absorption of calcium
by the small intestines, thus increasing blood calcium levels.
Use this information and your textbook to describe how the nervous system, endocrine system,
muscular and skeletal systems, and the integumentary system help to maintain homeostasis in
the human body, specifically for temperature, blood glucose levels, and blood calcium levels.
Information gathered from:
GCSE Bitesize BBC:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/bodytemprev1.shtml
Mcgraw-Hill Education College Division:
http://www.mhhe.com/biosci/genbio/maderbiology/supp/homeo.html
http://www.mhhe.com/biosci/esp/2001_saladin/folder_structure/su/m2/s6/