What would kill you first if your body’s homeostasis systems failed?Think about which organ systems do what as you rank them.A change in body temperatureAn increase in the concentration of carbon dioxideA change in the concentration of oxygenA change in concentration of electrolytesAn increase in the concentration of waste A change in concentration of blood sugar

The kidneys sense that the oxygen levels in the blood are low. The kidney sends a hormone signal to the bone marrow to make more red blood cells. The number of red blood cells increases, so more oxygen is carried in the blood.A.This is a positive feedback loopB.This is a negative feedback loopC.This is not a feedback loop

10. An example of feedback is seen in blood clotting. Part of the complex biochemical pathway of clotting is the production of an enzyme that forms the matrix of the blood clot, but also speeds up the production of still more thrombin. That is, it has a self- catalytic , self-accelerating effect, so that once the clotting process begins, it runs faster and faster until, ideally, bleeding stops. Thus, this positive feedback loop is part of a larger negative feedback loop, one that is activated by bleeding and ultimately works to stop the bleeding.A.This is a positive feedback loopB.This is a negative feedback loopC.This is not a feedback loop

What type of feedback loop is this?Feedback is seen in protein digestion, where the presence of partially digested protein in the stomach triggers the secretion of hydrochloric acid and pepsin, the enzyme that digests protein. Pepsin digests proteins, casing more HCl and pepsin to be released.

INTRODUCTION TO HOMEOSTASIS

Important variables within the body:blood sugarfluid balancebody temperatureoxygen levelsblood pressurepH

These variables must stay within certain ranges.

Changes in the external environment can cause these variables to change.

Homeostasis:

The process by which a constant internal environment is maintained despite changes in the external environment.

The hypothalamusPart of the brain

Often serves as the co-ordinating centre:Receives messages from monitors

Initiates a hormonal/nervous response

Dynamic equilibriumHomeostasis is also called dynamic equilibrium:

Conditions do fluctuate, but within an acceptable range

How is dynamic equilibrium maintained?Feedback systems

Negative feedbackPositive feedback

Negative feedbackNegative feedback: Response triggered by changed

conditions serves to reverse the change

E.g., Body temperature increases Skin blood vessels dilate Body temperature decreases

Example: Blood Pressure Regulation

Positive feedbackPositive feedback: The response triggered by changing

conditions serves to move the variable even further away from its steady state

E.g., uterine contractions are stimulated by oxytocin baby moves towards cervix more oxytocin is released

Thermoregulation

Maintaining body temperature

Body temperatureAverage human body temperature: 37°CCore body temperature is slightly higherInterindividual variation

ThermoregulationThermoregulation: The maintenance of body

temperatures within a range that enables cells to function effectivelyRecall: Enzymes have optimal temperaturesHigh temperatures can denature proteins

Types of temperature stressHeat stressCold stress

Response to Heat Stress

Response to Heat StressCo-ordinating centre is the hypothalamus

Responses:Skin blood vessels will dilateSweat glands will produce perspiration

Both responses serve to lower body temperature Return to normal range

Response to Cold Stress

Response to Cold StressCo-ordinating centre is the hypothalamus

Responses:Skin blood vessels will constrictSkeletal muscle will contract rapidly (shivering),

increasing metabolismSmooth muscle around hair follicles will contract,

producing goosebumps

Responses serve to raise body temperature Return to normal range

Prolonged exposure to cold stressMay cause an increase in the rate of metabolismSpecial fat cells called “brown fat”

Particularly important for babies

Hypothermia: Occurs when core body temperature drops below normal range.Usually results in coma, then death

Summary of thermoregulationStimulus Physiological

responseAdjustment

Cold •constriction of blood vessels in skin•hairs on body erect•shivering

•heat is conserved

•heat is generated by increasing metabolism

Heat •dilation of blood vessels in skin•sweating

•heat is released

Homeworkpg.111 Answer All Questions