11.10.16 Topic 6.6 (pt. 1)  Homeostasis Overview

Homeostasis Homeostasis - maintaining a balanced internal environment Internal environment = blood and the interstitial fluid different balances depending on their functions. Variables include: pH Dissolved gas concentration (oxygen and carbon dioxide) Blood glucose levels Temperature Balance of water and ions (salts)

Homeostasis uses negative feedback Response: Heater turned off Homeostasis uses negative feedback Room temperature decreases Stimulus: Control center (thermostat) reads too hot Set point: 20ºC Figure 40.8 A nonliving example of negative feedback: control of room temperature Stimulus: Control center (thermostat) reads too cold Room temperature increases Response: Heater turned on

Homeostasis uses negative feedback Sensory neuron detects a change  sends information to the CNS. CNS processes information and directs a response via motor neurons. The effectors bring the variable back to the normal range. Normal Range reached  sensory neuron stops sending messages to the control center Nervous & Endocrine systems Changes in: behavior, anatomy (structure), and physiology (function).

Thermoregulation - keeping body temperature within a tolerable range. WHY? Optimum temperature of metabolic processes. Rates can increase 2-3x for every 10 degrees increased. Too hot? Metabolic activity stops enzymes denature. Membrane properties change more or less fluid Changes efficiency of transport of ions and larger materials across membranes.

How heat is exchanged? Radiation Evaporation Convection Conduction Fig. 40-10 Radiation Evaporation How heat is exchanged? Convection Figure 40.10 Heat exchange between an organism and its environment Conduction

Heat Exchange Radiation: heat emitted as infrared rays from objects that are not in direct contact. Warming up by standing near a hot car. Evaporation: heat loss from the surface of a liquid by vaporization of the most active molecules. Cooling off by sweating. Convection: heat transfer by movement of air or liquid past a surface. Cooling off by standing in the wind. Conduction: heat transfer by direct contact between objects Warming up by sitting on a hot car.

Maintaining body temperature The hypothalamus in the brain is the biological thermostat, directing heating and cooling mechanisms as needed. Heating Mechanisms Cooling Mechanisms Skin arterioles constrict to limit blood flow and heat loss from the extremities Skeletal muscle shivering Behavior changes Skin arterioles dilate to allow more blood flow, dumping excess heat into the environment Sweat glands produce moisture for evaporative cooling Behavior changes

Sweat glands secrete sweat, which evaporates, cooling the body. Fig. 40-16 Sweat glands secrete sweat, which evaporates, cooling the body. Thermostat in hypothalamus activates cooling mechanisms. Blood vessels in skin dilate: capillaries fill; heat radiates from skin. Body temperature decreases; thermostat shuts off cooling mechanisms. Increased body temperature Homeostasis: Internal temperature of 36–38°C Body temperature increases; thermostat shuts off warming mechanisms. Decreased body temperature Figure 40.16 The thermostatic function of the hypothalamus in human thermoregulation Blood vessels in skin constrict, reducing heat loss. Thermostat in hypothalamus activates warming mechanisms. Skeletal muscles contract; shivering generates heat.

Countercurrent heat exchange Canada goose Bottlenose dolphin Blood flow Artery Vein Vein Artery 35ºC 33º Figure 40.12 Countercurrent heat exchangers 30º 27º 20º 18º 10º 9º Countercurrent heat exchange

Cardiac Cycle Practice. Check yesterday’s assignment Clarifying questions. Work on today’s Lab tomorrow! Come ready to go!

The endocrine system The endocrine system consists of multiple glands, which are collections of cells that release various hormones into the bloodstream, where they are transported to effector sites. Hormones are long-distance chemicals that can effect a wide range of changes in many different cells in order to produce a systemic change. They may be proteins, amines (derived from amino acids) and steroids (derived from lipids). Hormone-secreting glands include the hypothalamus, pituitary, thyroid, pancreas, adrenal glands and gonads (and others). The endocrine system often works in conjunction with the nervous system.

Homeostasis of blood glucose level The amount of glucose in the blood is controlled by antagonistic reactions of two hormones– insulin and glucagon. Both insulin and glucagon are produced in the pancreas, in small clusters of endocrine cells called islets of Langerhans. Each cluster has alpha cells, which produce glucagon, and beta cells, which produce insulin. Glucose levels must be maintained at about 90 mg/100 mL in order for cells to have enough glucose for cellular respiration and to produce other organic compounds.

Maintaining blood glucose level When blood sugar gets too high When blood sugar gets too low Beta cells of the pancreas produce insulin and release it into the blood Insulin causes cells to open glucose channels and glucose is taken into cells. Insulin stimulates liver cells to convert glucose into glycogen Both result in the blood glucose level decreasing Alpha cells of the pancreas produce glucagon and release it into the blood Glucagon stimulates the liver and muscle cells to break down glycogen, turning it into glucose This results in the blood glucose level increasing

Diabetes Diabetes is a disorder of the mechanism of glucose homeostasis. It is caused by insulin deficiency or decreased response to insulin in the cells of the tissues. When there isn’t enough glucose for cellular respiration, fat becomes metabolized, but acidic biproducts of these processes build up and lower blood pH dangerously. Uncontrolled diabetes can lead to retina damage, kidney failure, nerve damage, increased risk of cardiovascular disease and poor wound healing.

Types of diabetes Type I diabetes (10%) Type II diabetes (90%) This is an autoimmune disorder in which the beta cells of the pancreas are destroyed by the immune system, so they cannot make insulin. People with type I diabetes take daily shots of synthetic insulin, thus allowing their cells to absorb glucose, and keep the blood glucose level at the set point. This shows up later in life and is caused by a change in insulin receptors on cells so that they do not allow the cells to take up glucose as well. Research shows that excessive weight and poor diet increase the chances of getting this disorder, but genetics and ethnicity also play roles. Type II diabetes can usually be managed by strict diet and regular exercise.