Homeostasis and excretion

1. Homeostasis and excretion Mrs. Jackie

2. Homeostasis include • Maintaining a constant interval environment despite possible fluctuations in the external environment • Include blood pH • Carbon dioxide and glucose concentration • Blood glucose • Body temperature • Water balance

3. An example of homeostasis in a non biological system Detected by thermostat Heater switched off Temperature rises Temperature falls Desired temperature of bath water Temperature rises Temperature falls Detected by thermostat Heater switched on

4. Examples of homeostasis • Oxygen and carbon dioxide concentrations • Maintain in balance due to chemodetectors • Blood glucose • Body temperature • Water balance • Blood PH • Main within narrow limits around 7.4 • Contain buffers to minimize fluctuations in pH

5. Homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms • Negative feedback • The control of a process by the result or effect of the process in such a way that an increase in the results or effects is always reversed. • Requires • Sensors – require to pass the information to a center which knows the desire value and compares the current situation to the norm. If the values are not the same the center activates a mechanisms to bring the current value to normal levels • The center will turn off the mechanisms once it reaches the norm

6. Nervous and endocrine systems are both involved in homeostasis • Thermoregulation is done via nerves • Blood glucose levels are maintain via hormones

7. Nervous system consists of the central nervous system and peripheral nerves composed of neurons • Central nervous system (CNS) • Brain • Spinal chord • Peripheral nerves • Everything else • Made of neurons • Transport messages in the form of electrical impulses to specific sites

8. Control of body temperature • Thermoregulation • Body of mammals/birds has thermo-receptors in the skin and in the heat center in the brain for monitoring temperature changes in the environment as well as changes in the blood temperature • IF the organisms is to hot • Vasodilatation- blood vessels in the skin become wider which increases the flow of blood to the skin. Skin becomes warmer which increases heat loss to the environment. • Sweating- evaporation of fluid from the skin; change of phase(liquid to gas) , requires energy which is taken from the body. • Decreased metabolism- any reaction produces heat as a by product • Behavior adaptations: birds-bating, desert rodent- retreat into humid burrows, dogs- dig holes and allow cool earth to absorb heat from belly

9. Vasodilation

10. Vasoconstriction

11. Control of body temperature • If the organism is too cold • Vasoconstriction- blood vessels in the skin contract which decreases the flow of blood to the skin; as a result the skin becomes colder reducing the heat loss to the environment. • Shivering- any reaction will produce heat as a by product. Muscular contraction produce a lot of heat • Increased metabolism: increase production of heat • Fluffing of hair or feathers: increases the thickness of the insulating layer of air. • Thick layer of brown fat or of blubber: this is a good insulator and reduces radiation and convection and generates heat • Special structure hair: (polar bears) which absorbs UV light

12. Endocrine system • Consist of glands which release hormones that are transported in the blood • Endocrine glands are ductless- they do not release their product into a duct but to the blood • As the hormones passes cells, only those with special receptors will react to the presence of the hormone- TARGET CELLS

13. Control of glucose concentration in blood • Pancreas is both an exocrine and endocrine gland • Exocrine cells in the pancreas produce digestive enzymes which are released into the small intestine via the pancreatic duct. • Endocrine cells are clustered together in groups called the Islets of Langerhans • Produce hormones which help in regulating the blood glucose levels.

14. Control of blood glucose • Islet of Langerhans cells in the pancreas have chemoreceptors which are sensitive to levels of glucose • Levels of glucose can go up after a meal and down after exercise • IF glucose levels are to low (see figure 1 page 138) • The alpha cells in the islets in the pancreas secrete glucagon • Glucagon- protein hormone whose main target is the liver • Hepatocytes- cells of the liver will respond to the presence of glucagon by converting glycogen to glucose and releasing it to the blood. Amino acids and glycerol are also converted to glucose

15. Control of blood glucose • If blood glucose levels are to high • Beta cells in the islets of langerhans in the pancreas secrete insulin • Insulin is a protein hormone travel to all parts of the body. Its presence will make the muscle cells absorbs more glucose • The muscle cells and hepatocytes converte glucose into glycogen • In adipose tissue glucose is converted into fat in the presence of the hormone insulin. • See diagram on figure 2 page 139

16. Excretion

17. Excretion • Removal from an organism of the toxic waste products of metabolism

18. Role of the kidney • Main functions • Maintenance of the water balance in the body and the removal of nitrogenous metabolic waste via excretion. • Two basic process • Ultrafiltration- some components of the blood flowing through the kidney are pushed out of the blood vessels into kidney tubules. Only plasma and small particles can be filtered. Large proteins and cells stay in the blood • Reabsoption- substances useful for the body such as glucose and amino acids are reabsorbed and send back to the blood. The amount of water and salts reabsorbed is regulated to maintain homeostasis. • Unwanted substances become urine and is excreted