Homeostasis2

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H.1.1 State that homeostasis involves maintaining
internal environment
State that homeostasis involves maintaining internal environment at a constant
level or between narrow limits, including blood pH, water potential, oxygen and
carbon dioxide concentrations, blood glucose and body temperature.
Things maintained by homeostasis:
blood pH (controlled by both nervous and endocrine system)
water potential (controlled by the endocrine system, kidney and ADH)
Oxygen and Co2 concentrations (controlled by the nervous system, ventilation
rate etc)
blood glucose (controlled by the endocrine system, glucagon and insulin)
body temperature (controlled by the nervous and endocrine systems)
H.1.2 Explain that homeostasis involves monitoring
levels of variables and correcting changes in levels
Explain that homeostasis involves monitoring levels of variables and correcting
changes in levels by negative feedback mechanisms.
H.1.3 Describe the control of body temperature
Describe the control of body temperature, including the roles of sweat glands,
hairs, skin arterioles and shunt vessels, shivering, hormones (thyroxin, TRH, TSH),
anterior pituitary gland, hypothalamus and thyroid.
Heat is sensed by the skin and the hypothalamus, as both contain thermo
receptors. External environment temperature is sensed by the skin, and internal
environment temperature is sensed by the hypothalamus.
When it is cold outside, messages are sent from the themoreceptors in the skin or
from deep thermal receptors or via the blood to the cerebrum and the
hypothalamus. The cerebrum makes the person aware of being cold, and can
cause behavioral changes which are voluntary to, for example, put on a sweater.
When the message has reached the hypothalamus, a series of reactions follow.
TRH (thyroid releasing hormone) is released by the hypothalamus, its target organ
being the anterior lobe of the pituitary gland. When TRH reaches the pituitary
gland, it releases TSH (thyroid stimulating hormone) into the blood stream. The
target organ of TSH is the thyroid gland. Upon receiving TSH, the thyroid then
produces thyroxin. Thyroxin increases cellular metabolism to make heat.
Other things that happen:
vasoconstriction (blood diverted from skin to keep heat)
reduced sweating
skin hairs raised (erector pilli muscle contracted)
shivering
increased metabolic rate
When it is too warm, messages are sent in the same way to the hypothalamus.
This causes:
increased sweating to release heat via water
vasodilation (blood diverted to skin to lose heat)
skin hairs lowered
reduced metabolic rate

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H.1.4 Explain the control of water potential
Explain the control of water potential including the roles of the hypothalamus, the
posterior pituitary gland and feelings of thirst.
Osmoreceptors in the hypothalamus detect the water potential of the body. If the
water potential is too low, then it will act in a way to keep more water in the
body. If it is too high, then it will act in a way to excrete more water in the body.…read more

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