Chapter 10: Internal Regulation

1. Chapter 10: Internal Regulation

2. Homeostasis • This is Latin for ‘same state’ • It is referring to a set of internal processes that keep the body operating within a fixed range on a number of different variables • Body temperature • Set point – this is a single value that the body works to maintain under normal circumstances • Weight

3. Body Temperature • What is meant when an animal is called ‘cold blooded’? • Poikilothermic – body temp matches the environment • Homeothermic – the body expends energy to maintain a constant temp • Why is being homeothermic better? • We can stay active no matter what the ambient temp

4. How we maintain our Temperature • When cold we: • Put on layers or fluff out our fur/hair • Huddle • Circulatory changes • Shiver, activate muscles • When hot we: • Take off layers, shed hair • Circulatory changes • Sweat

5. More about Temp Control • Some of the things we just discussed are behavioral, others are physiological • How does the body know to change circulation or turn on the faucets (i.e. make you sweat)? • An area of your brain is constantly monitoring your temperature & sending signals to the rest of the body to make homeostatic adjustments • The anterior hypothalamus

6. Disorder of Temperature: Fever • Fever occurs when the immune system is activated by a bacterial or viral invader • But the fever is not a direct result of immune system activation • Immune cells release prostaglandins (hormone) into the blood, which stimulate the anterior hypothalamus to increase body temp

7. Anhidrosis • This is the inability to sweat in response to increasing body temperature. • Can be caused by genetic or neurological disorders, or even just taking certain medications or becoming dehydrated. • Treatment/cure is simple for two of the cases above • Otherwise, you just have to monitor and maintain your body temperature using external methods

8. Thirst • There are two kinds of thirst (I bet you didn’t know that!) • Osmotic thirst – this is your every day, eat a bag of chips get thirsty, kind of thirst • Hypovolemic thirst – this is thirst due to loss of blood volume from injury or illness • When you are thirsty, your body conserves water in several ways: no sweat, no urine, increase blood pressure • Result from release of hormone vasopressin

9. Mechanisms of Thirst • In osmotic thirst, an area of the brain called the OVLT senses the body’s osmotic balance • In hypovolemic thirst two things are important: • Baroreceptors in the veins themselves detect pressure • An area of the brain called the subfornical organ (SFO)

10. Hunger • Did you know there are actual biological constraints on what we eat? • Dairy & lactose intolerance • Teeth! • Herbivores • Carnivores • Omnivores • Taste & experience • Sweet vs. bitter • Conditioned aversions

11. What makes us feel full? • Would Willy Wonka’s gum actually make us feel satisfied? • Or could we just fill our stomachs with nutrients and be satisfied? • It turns out that both answers are no. • We require both the early digestive processes (chewing and swallowing) and the filling of the stomach to feel satisfied

12. The Stomach • There are physical and chemical messages from the stomach that tell our brains that we’ve had enough to eat • Stimulation of the vagus nerve tells the brain when the stomach is physically full • Other nerves report to the brain about the nutrient content • CCK is a hormone that is released from the small intestine to start reducing the amount you are bringing in

13. Energy Feedback System • What does the body use as fuel? • Glucose • When you eat, your body produces insulin to help you get that glucose into your cells, makes you less hungry • Glucagon later helps you get that glucose back out of storage • What happens in diabetes?

14. Brain Control of Hunger • The hypothalamus is the hunger Wizard of Oz, there are two areas I want you to know: • Lateral hypothalamus seems to be involved in initiation of eating – if this area is damaged animals won’t eat and lose weight • Ventromedial hypothalamus seems to be involved in satiety and reduction of eating – damage to this area results in animals that will eat a lot more and have overactive insulin

15. Chemical Control of Weight • Leptin is a peptide chemical released by fat cells themselves • The body and brain are able to keep tabs on the current fat stores • Triggers puberty onset • Changes the way we eat • Changes functioning in other physiological systems – i.e. immune system • We have discovered a gene (in mice) that prevents leptin production = obese mice

16. More Chemical Control of Weight • Neuropeptide Y (NPY) is a chemical that acts on the hypothalamus • Specifically it acts on the PVN of the hypothalamus and results in increased meal size • There are approximately 21 other hormones/neurotranmitters that influence when, how frequently and how much we eat – very complex system

17. External Effects on Meal Size Time of week Alone or with others Time of day and culture “Low-fat”

18. Prader-Willi Syndrome • Genetic condition due to a random mutation on chomosome 15. • Symptoms include: • Mild mental retardation/developmental delay • Incomplete sexual development (puberty) • Insatiable appetite – health probs related to obesity • Treatment – food restriction (& I mean RESTRICTION!)

19. Obesity • Obesity is defined as being 20% over your ideal weight • ‘Ideals’ are based on height, age, sex and mass index • About 25% of adults in the U.S. are obese • Major health problems – Type II diabetes, heart disease • Genetics, life style & stress are all contributors

20. Anorexia • This is basically controlled starvation of yourself • Fewer than 800 calories per day, usually from a restricted number of foods • Much more common in women than in men • More common in upper socio-economic & Caucasian women

21. Anorexia • Characteristics of girls who develop anorexia: • Come from overbearing/controlling parents • Anxious personality traits – shyness, perfectionism, social anxiety • Loss of a family member early in life • Depression • Anorexia is not just about wanting to be thin, it is about feeling out of control –it is an anxiety disorder

22. Bulimia This disorder is typified by intense binge eating, followed by purging Purging is usually through vomiting, but can also be achieved through improper use of laxatives Psychological aspects of the disease are similar to those of anorexia Often more difficult to diagnose – secretive behavior and less obvious results

23. Consequences of Eating Disorders Death Osteoporosis Heart and other cardiovascular problems, including stroke Damage to the esophagus, stomach, teeth, mouth