What would kill you first if your body’s homeostasis systems failed 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 temperature An increase in the concentration of carbon dioxide A change in the concentration of oxygen A change in concentration of electrolytes An 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 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 loop B. This is a negative feedback loop C. This is not a feedback loop

10. An example of feedback is seen in blood clotting 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 loop B. This is a negative feedback loop C. 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 sugar fluid balance body temperature oxygen levels blood pressure pH 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 hypothalamus Part of the brain Often serves as the co-ordinating centre: Receives messages from monitors Initiates a hormonal/nervous response

Dynamic equilibrium Homeostasis is also called dynamic equilibrium: Conditions do fluctuate, but within an acceptable range

How is dynamic equilibrium maintained? Feedback systems Negative feedback Positive feedback

Negative feedback Negative feedback: Response triggered by changed conditions serves to reverse the change E.g., Body temperature increases  Skin blood vessels dilate  Body temperature decreases

Normal body temperature Body temperature increases Hypothalamus sends a message to blood vessels Skin blood vessels dilate Body temperature decreases Normal body temperature

Example: Blood Pressure Regulation

Positive feedback Positive 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

Maintaining body temperature Thermoregulation Maintaining body temperature

Body temperature Average human body temperature: 37°C Core body temperature is slightly higher Interindividual variation

Thermoregulation Thermoregulation: The maintenance of body temperatures within a range that enables cells to function effectively Recall: Enzymes have optimal temperatures High temperatures can denature proteins

Types of temperature stress Heat stress Cold stress

Response to Heat Stress

Response to Heat Stress Co-ordinating centre is the hypothalamus Responses: Skin blood vessels will dilate Sweat glands will produce perspiration Both responses serve to lower body temperature  Return to normal range

Response to Cold Stress

Response to Cold Stress Co-ordinating centre is the hypothalamus Responses: Skin blood vessels will constrict Skeletal muscle will contract rapidly (shivering), increasing metabolism Smooth muscle around hair follicles will contract, producing goosebumps Responses serve to raise body temperature  Return to normal range

Prolonged exposure to cold stress May cause an increase in the rate of metabolism Special 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 thermoregulation Stimulus Physiological response Adjustment 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

Homework pg.111 Answer All Questions