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Homeostasis
BIO.A.4.2.1
homeostasis
• Maintaining a stable internal environment.
Thermoregulation
• Maintaining a certain temperature.
• Negative feedback loop – cycle of monitoring
and responding to internal conditions.
• Ex. Room temperature, air conditioning turns
on if it gets too hot, furnace turns on if it gets
too cold.
Body Temp
• Normal human body
temperature is 37 C (98.6 F).
• When the temperature
changes the hypothalamus of the brain senses the
temperature of the blood passing through it.
• If temperature is too high or low, the
hypothalamus sends signals to parts of the body
that cause it to release or retain heat.
• Ex. Shivering, perspiration, dilation or constriction
of blood vessels.
Homeostatic mechanism
• System(s) in body that regulate homeostasis in
body.
Question
The human body maintains a constant internal
temperature of 98.6 F. Which changes occur when
the hypothalamus detects a temperature of 100.1
F?
a. Muscle tissue shivers and skin capillaries dilate
b. Perspiration increases and skin capillaries dilate
c. Muscle tissue shivers and skin capillaries
constrict
d. Perspiration increases and skin capillaries
constrict.
Osmoregulation
• Controlling water and solutes in the body.
• Organisms that live in freshwater environments
are always in a state of hypotonic.
(solution has less
solutes dissolved
in then in the cell)
• Ex. Freshwater
fish excrete very
dilute urine to
eliminate excess
water.
Osmoregulation
• Organisms in saltwater are isotonic to their
environment.
• They must find ways to retain the solutes they
need and eliminate the excess sodium and
chloride ions in seawater.
• Marine fish have specialized gill cells that
excrete excess chloride ions.
Osmoregulation
• Land animals – need to conserve water.
• Their urine is much more concentrated than
their blood, containing a high ratio of solutes
to water. Ex. NaCl in blood is 5:1
• Allows them to excrete excess solutes while
conserving water.
Kidneys
• The kidneys control the reabsorption of water
and useful solutes.
• The kidneys control how concentrated urine is.
• The brain sends signals to the mouth and throat
that produce a feeling of dryness. –thirst
• Blood vessels and the hypothalamus of the brain
detect water balance in the the body.
• Hormones are sent to kidney to regulate water
loss.
Water loss
• Land animals lose water through evaporation,
perspiration, and urination.
Paramecium
• Single-cell protist (eukaryote)
• Has a contractile vacuole that pumps water
out of the cell.
• What kind of environment do parameciums
have?
Gas Exchange
• The levels of dissolved oxygen and carbon dioxide
in the blood must be regulated to allow
respiration to take place.
• Ex. Fish perform gas exchange through gills
Water flows over the capillaries in the gills, which
contain a higher concentration of carbon dioxide
and a lower concentration of oxygen than the
surrounding water.
The differences causes carbon dioxide to move into
the water and oxygen to move into the
bloodstream, through passive transport. (diffusion)
Gas-exchange
• In mammals occurs in lungs by passive transport.
• Capillaries – tiny blood vessels, surround each of
the microscopic air sacs in the lungs called
alveoli.
• Blood flowing to the alveoli contains more carbon
dioxide than oxygen.
• So carbon dioxide crosses through blood cell
membrane into the air in the lungs.
• Oxygen passes through blood cell membrane into
the blood cell.
Regulation of Blood Glucose
• Glucose – is the macromolecule, carbohydrate.
• Monomer – simple sugar
• Human body requires a blood
Glucose level of around 90 mg/100mL.
If it falls too low or rises too high, homeostatic mechanisms
bring it back into range.
• The pancreas senses blood glucose levels.
• When glucose is too high the pancreas releases the
hormone insulin.
• Insulin causes the cells of the muscles, liver, and other
tissues to allow more glucose to cross the plasma
membrane
Blood sugar levels
• The liver then converts this glucose to
glycogen.
• Glycogen is how animals store carbohydrates.
• When blood glucose is low, the pancreas
secretes another hormone, glucagon.
• Glucagon causes the liver to break down
stored glycogen and release the glucose into
the bloodstream.
Question
After skipping a meal and exercising, a body’s
blood glucose falls to 85 mg/100mL. What
changes will occur in the body?