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6.5: (Nerves, Hormones, &) Homeostasis6.5.8 -
Pg 110-
Homeostasis
The human body works best under the following conditions:Body temperature of 37°CO.1 % blood sugar levelBlood pH level of ~7.4
The external environment can alter these levelsEx: 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
HomeostasisRequires 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 pHCarbon dioxide concentrationBlood glucose concentrationBody temperatureWater balanceBlood pressure
What’s wrong with this graph?
Blood pHHomeostatic level is pH 7.4Narrow acceptable range: 7.35-7.45< 7.35 = acidosis>7.45 = alkalosis
Non-homeostatic levels can cause blood proteins and enzymes to ionize and change shape and function.
Blood pHBlood pH is maintained by the carbonic acid-
bicarbonate buffer systemBUFFER: substance that maintains pH
H2O + CO2 H2CO3 HCO3 -
+ H+
water carbon carbonic bicarbonate hydrogen
dioxide acid ion ion
Low pHEx: 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 pHWhen 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 SystemsMechanisms 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 FeedbackA thermostat is an example of negative
feedback.
Temperature
Rises
Temp changeDetected by Thermostat
Heater switched
off
Temp Decreases
Temp Decreases
Temp changeDetected 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
ExampleDuring exercise, CO2 levels increaseChemoreceptors 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
ThermoregulationMaintenance of body temperature within a
range that allows cells to function efficiently
Different optimal temperatures and ranges exist for each animal
Thermoregulation and InvertebratesInvertebrates, 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 VertebratesMammals 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
VasodilationBlood 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 AdaptationsBirds: bathingDessert Rodents: retreat into burrowsDogs: 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:VasoconstrictionShivering
Muscular contractions that produce heat a by-productIncreased metabolism
Biochemical reactions often produce heat as a by-product
Fluffing of hair or feathersThick layer of brown fat or blubber
Provides insulation, and generates heatSpecial structures
Ex: polar bears have hairs that can absorb UV light
VasoconstrictionBlood vessels in the skin contract (get
narrower)This decreases blood flow to the skinLess heat loss to the environment
Fluffing of hair or feathersIncreases 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 GlucoseThe 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
InsulinWhen 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
GlucagonSecreted 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 MellitusDisorder 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 glucoseCan cause nerve damage, retina damage, blood
vessel damage, kidney failure, comas, and even death.
Type I DiabetesAlso 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 DiabetesOccurs 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, lifestyleIf 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.