Homeostasis & Excretion

6.5.7, Homeostasis Homeostasis is the process by which organisms maintain a stable internal environment. The internal environment fluctuates very little, unlike the external environment. Failure to adjust results in disease or loss of function. Some homeostatic components include osmolarity, temperature, pH, ion balance, blood glucose, and oxygen vs carbon dioxide levels. The 2 systems which are most important to maintaining homeostasis are the nervous and endocrine systems. The nervous system is involved in sending electrical impulses (from the central nervous system to neurons to tissues) and the endocrine sends chemical hormones (from glands through lymph and blood to tissues.)

6.5.9 Homeostasis (cont’d) Negative feedback mechanisms are homeostatic, Both hormones and nerves work to maintain the setpoint (create a response based on environmental changes.) Recall negative feedback- Homeostasis involves a range, but if the fluctuation from the setpoint is too great, (Positive feedback is not homeostatic- a change is brought about- oxytocin produces uterine contractions right before birth- more oxytocin, more contractions- out pops a monster!)

Control of Body Temp Body temperature is maintained by a negative feedback system, The hypothalamus of the brain monitors the internal temp,

Body Temp Regulation (cont’d) If body temp is too high: 1. Sweat glands 2. Metabolic rate 3. Blood vessels in the skin 4. Take off them clothes! Sit down in the shade!

Body Temp (cont’d) If body temp is too low: 1. Blood vessels 2. Shivering and 3. Hug someone (conduction), eat candy, roll up into a ball, run around, sit near a radiator (radiation), put your clothes back on! Don’t sweat!

Body Temp (cont’d) 4. Another circulatory adaptation is a special arrangement of blood vessels Arteries carrying warm blood are in close contact with veins conveying cool blood back toward the core. - **Humans don’t use this as much as other animals (birdfeet)

Control of Blood Glucose The regulation of blood glucose levels is a crucial metabolic component. The regulation of blood glucose levels is a crucial metabolic component. The pancreas produces 2 hormones, The pancreas produces 2 hormones, Insulin, a hormone, is responsible for Insulin, a hormone, is responsible for The glucose can be taken up by cells Glucagon, antagonistic to insulin, is responsible for Glucagon, antagonistic to insulin, is responsible for In the pancreas, the cells responsible for regulating glucose concentration are called

Glucose Regulation (cont’d) Right after a meal, insulin levels At night or during fasting, glucagon levels **** If glycogen and/or fat stores are low, proteins can also be catabolized in cellular respiration.

Diabetes Type 1 This is known as juvenile-onset diabetes. This is known as juvenile-onset diabetes. Treatment is insulin injections (used to come from pigs.) Treatment is insulin injections (used to come from pigs.) Patients can go from hyperglycemic to hypoglycemic. Patients can go from hyperglycemic to hypoglycemic. Hypo- Hypo- Hyper – Hyper – Result can be ketoacidosis, where dehydration occurs & pH of blood drops- can result in coma and death. Result can be ketoacidosis, where dehydration occurs & pH of blood drops- can result in coma and death.

Type 2 This is insulin resistant diabetes. Common treatment is diet and exercise. This form of diabetes is one of the fastest growing diseases in the country. While causation is not certain, children who are obese and inactive have higher incidence of diabetes. Historically, this diabetes was diagnosed after age 50. Now, it is not uncommon for children to get the disease.

Other Hormones We’ve talked about adrenaline, as well as reproductive hormones. The thyroid produces 2 hormones T3 and T4. Thyroxine (T4) has mainly metabolic functions. T4 functions:

Leptin & Ghrelin These 2 hormones affect hunger and satiety. Leptin is released by Ghrelin is released by As you can guess, eating is not simply based on the levels of these 2 hormones (obesity often leads to cells being resistant to leptin, even though levels are higher in the blood.)

Melatonin Produced in the Melatonin regulates the sleep cycle- It is thrown off when travel to different time zones occurs, or when we stare at bright screens at night. Also interacts with leptin,