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.