Homeostasis Review

Maintaining a balance Organisms and their cells function best at certain temperatures, pH levels, solute concentrations, etc. They must maintain these levels from becoming too high or low.

Homeostasis- the body’s ability to regulate its internal physiology to maintain stability in response to fluctuations in the outside environment

Homeostasis Our bodies rely on a cycle of monitoring and responding to internal conditions called a negative feedback loop, similar to the way a thermostat operates in a home. It is called a negative feedback loop because any change to the system seen as a negative, such as a drop in temperature, causes the system to return to its original state.

Simple Homeostasis in your body In low light, pupils dilate to allow more light into the eye. This is response to a stimulus, low light, to maintain constant light levels in the eye.

Dynamic Equilibrium Our bodies are in a state of dynamic equilibrium because internal conditions are not perfectly constant; instead they vary slightly as our bodies adjust and adapt to changing external conditions.

Thermoregulation – maintaining a stable body temperature. The hypothalamus regulates many of the body’s internal states, such as temperature. It senses temperature of blood passing through it and can cause: Shivering and/or constriction of capillaries to conserve heat (warming) Perspiration (sweat evaporating and carrying heat away from the body) and /or dilation of capillaries to release heat (cooling)

Warm vs. cold blooded

Warm blooded animals -convert food into energy and generate heat -must eat a lot of food to maintain a constant temperature -only a small amount of food’s energy is used for increases in body mass -endothermic

Warm vs. cold blooded

Cold blooded animals -convert much more of their food into body mass -more active in warm environments and sluggish in cold because muscle activity depends on chemical reactions that are temperature dependent -convert much more of their food into body mass -ectothermic

Osmoregulation – maintaining the balance of water and solutes (dissolved molecules and ions) in an organism.

Organisms that live in aquatic environments face challenges: Fresh water: hypotonic to cells of organisms Saltwater: isotonic to cells, but differing type of solutes found in cells and water (ex> excess Na and Cl from water need to be removed- gill cells)

Organisms that live on land face challenges too: Conserving water: kidneys control reabsorption of water and useful solutes; water is gained from drinking and lost in urine -Loss of 1% of water from body produces sensation of thirst -Loss of water through evaporation, perspiration, and urination- must prevent dehydration

Gas Exchange Carbon dioxide and oxygen levels must be regulated in the blood via passive transport Alveoli are site of gas exchange in the lungs; blood flowing to the alveoli contains excess carbon dioxide and little oxygen Too much carbon dioxide dissolved in blood causes low pH levels which is dangerous

Blood Glucose The pancreas releases insulin to combat high glucose levels; glucose enters the cells of the liver and muscles and is converted to glycogen If blood sugar level fall, glucagon breaks down stored glycogen and releases it to the blood Type 1 diabetes- pancreas does not produce enough insulin Type II- tissues do not respond to insulin

Metabolism – a set of chemical reactions that occur in living organisms in order to maintain life.

stimulus—anything detected in an organism’s environment that causes it to react Ex. light, odor, sound, heat