6.5: (Nerves, Hormones, &) Homeostasis Pg 110-

Homeostasis The human body works best under the following conditions: Body temperature of 37°C O.1 % blood sugar level Blood pH level of ~7.4 The external environment can alter these levels Ex: Outside temperature, physical activity, meals…

HOMEOSTASIS HOMEOSTASIS is the maintenance of the internal environment within an acceptable range, despite fluctuations in the external environment. It creates a dynamic equilibrium: a stable condition with fluctuating limits

Homeostasis Requires constant monitoring and feedback about body conditions. Homeostasis requires the interaction of several regulatory systems I.e.: Nervous system, respiratory system, endocrine system, the excretory system, the circulatory system….

Ex of Biological Homeostasis: Blood pH Carbon dioxide concentration Blood glucose concentration Body temperature Water balance Blood pressure

What’s wrong with this graph?

Blood pH Homeostatic level is pH 7.4 Narrow acceptable range: < 7.35 = acidosis >7.45 = alkalosis Non-homeostatic levels can cause blood proteins and enzymes to ionize and change shape and function.

Blood pH Blood pH is maintained by the carbonic acid- bicarbonate buffer system BUFFER: substance that maintains pH H2O + CO2 H2CO3 HCO3 - + H + water carbon carbonic bicarbonate hydrogen dioxide acid ion ion

Low pH Ex: after eating a vinaigrette salad, H + ions will enter the bloodstream, and the blood will become too acidic (pH to low!) The increase in H + means that there is a greater chance of HCO3 - ions finding a H + and forming H2CO3, thus increasing the pH

High pH When a base enters the blood stream, the pH will rise making it more basic because the base will bond with H + and remove them from the blood. To compensate, H2CO3 ionizes to replace the missing H + and lower the pH back to acceptable ranges

Carbon Dioxide Concentration Oxygen and Carbon Dioxide concentration are maintained with the aide of chemoreceptors in the walls of certain blood vessels that can cause an increase or decrease in breathing rate.

Negative Feedback Systems Mechanisms that make adjustments to bring the body back within an acceptable range (like a thermostat) The result of a process causes a reversal of the result. Homeostasis relies on negative feedback systems to maintain homeostatic levels

Negative Feedback A thermostat is an example of negative feedback. Temperature Rises Temp change Detected by Thermostat Heater switched off Temp Decreases Temp change Detected by Thermostat Heater switched on Temperature Rises

All homeostatic control system have 3 functional components 1. A monitor/sensor Measure the current situation 2. A coordinating center Compares the current situation to the homeostatic norm Can activate a mechanism to adjust situation 3. Regulator A mechanism to restore normal balance

Example During exercise, CO2 levels increase Chemoreceptors in the arteries are stimulated (sensor) They send a message to the medulla oblongata (coordinating center) The medulla sends impulses to the intercostal muscles (regulator) to increase the rate of breathing to flush out excess CO2 from the body

Thermoregulation Maintenance of body temperature within a range that allows cells to function efficiently Different optimal temperatures and ranges exist for each animal

Thermoregulation and Invertebrates Invertebrates, most fish, amphibians, and reptiles are also known as ECOTHERMS These animals depend on air temperature to regulate metabolic rates. Ex: reptiles sun themselves on rocks or retreat to shaded areas to regulate their body temperature

Thermoregulation and Vertebrates Mammals and birds are ENDOTHERMS They are able to maintain a constant body temperature regardless of surroundings. Thermoreceptors in the skin and in the hypothalamus of the brain monitor temperature changes in the environment and in the blood.

If an organism is too hot, it can cool down by using one or more of the following mechanisms: Vasodilation Sweating The evaporation of fluid from the skin requires energy, which is taken from body heat. Decreased metabolism Many biochemical reactions produce heat as a by-product Behavioural adaptations

Vasodilation Blood vessels in the skin dilate (become wider) This increase blood flow to the skin. Blood will bring heat. Skin will become warmer and the heat will dissipate into the environment

Behavioural Adaptations Birds: bathing Dessert Rodents: retreat into burrows Dogs: dig holes and allow cool earth to absorb heat from belly

If an organism is too cold, it can warm up using one or more of the following mechanisms: Vasoconstriction Shivering Muscular contractions that produce heat a by-product Increased metabolism Biochemical reactions often produce heat as a by-product Fluffing of hair or feathers Thick layer of brown fat or blubber Provides insulation, and generates heat Special structures Ex: polar bears have hairs that can absorb UV light

Vasoconstriction Blood vessels in the skin contract (get narrower) This decreases blood flow to the skin Less heat loss to the environment

Fluffing of hair or feathers Increases the thickness of the insulating layer of air Goosebumps: when you are cold, nerve message are carried to the muscle that surround the hair follicles in your skin – causing the hair to “stand up” The small bump made by the contraction of the muscle creates the goose bump The hair traps warm air next to the surface of your skin and helps reduce heat loss

Maintaining Blood Glucose The pancreas is both an exocrine gland (producing digestive enzymes) and an endocrine gland As an endocrine gland it produces 2 hormones essential to maintaining blood sugar levels within homeostatic ranges

The islets of Langerhans, are the cells in the pancreas that produce insulin and glucagon α cells of Islets of Langerhans: secrete glucagon β cells of Islets of Langerhans: secrete insulin

Insulin When blood glucose levels are too high, insulin is secreted. It causes the muscle cells to absorb more glucose (from the bloodstream) hepatocytes and muscle cells to covert glucose to glycogen In fat tissue (adipose tissue), glucose to be converted into fat

Glucagon Secreted by the pancreas when glucose levels are too low. It travels throughout the body but its main target is the liver. Causes hepatocytes to convert glycogen to glucose and release it to the blood

Diabetes Mellitus Disorder in which a person does not produce enough insulin or in which a person does not react to insulin. Can lead to hyperglycemia: high blood glucose Can cause nerve damage, retina damage, blood vessel damage, kidney failure, comas, and even death.

Type I Diabetes Also called “juvenile diabetes” because diagnosed as a child Individual doesn’t make insulin, or makes insufficient levels of insulin. Causes: often by the body producing antibodies against insulin or β cells of Islets of Langerhans Treatment: insulin injections, pancreas transplant, diet regulation

Type II Diabetes Occurs later in life, as an adult Insufficient amounts of insulin are produced or the body has become less sensitive to insulin Causes: obesity, age, family history, lifestyle If the individual has a high glucose diet, their body will become desensitized to insulin. Treatment: regulated diet, exercise, medications to increase insulin production and lower blood glucose levels.