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 dilateb. Perspiration increases and skin capillaries dilatec. Muscle tissue shivers and skin capillaries constrictd. 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 lesssolutes dissolvedin then in the cell)• Ex. Freshwater fish excrete verydilute 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 gillsWater 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?