think about… 18.1the concept of homeostasis 18.2regulation of blood glucose level

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Think about…18.1 The concept of homeostasis18.2 Regulation of blood glucose levelRecall ‘Think about…’Summary concept map

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18.1 The concept of homeostasis

Do you know what homeostasis is?

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• ability of the body to maintain a stable internal environment

What is homeostasis?18.1 The concept of homeostasis

• important for body to function properly

- composition of blood and tissue fluid

- body temperature

- blood pressure

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For example:Our body is exposed to changes in the external environment, e.g. air temperature

homeostasis

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For example:The condition of blood and tissue fluid is kept constant for proper functions of cells

capillaryblood

body cell bathed in tissue fluid

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Parameters of the internal environment to be kept stable


What parameters must be kept

constant in our body?

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affects

1 Water content in blood18.1 The concept of homeostasis

water content in blood

water potential of tissue fluid

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If water potential of tissue fluid is different from that of the cells, water will …

enter the cells

leave the cells

or

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If too much water is gained …

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If too much water is lost …

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If too much water is lost …cells cannot function properly and may even die

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• regulated by kidneys ( 腎 )

kidneys ureters

urinary bladder urethra

mammalian urinary system

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2 Glucose level in blood18.1 The concept of homeostasis

• for respiration in cellsglucose + O2

energy + CO2 + water

- level in blood is kept steady to ensure a sufficient supply

- as it is water soluble, any change in level affects water potential of the tissue fluid

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2 Glucose level in blood18.1 The concept of homeostasis

In humans,• normal range is 90–100 mg/cm3

• maintained by

liver pancreas

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3 Gas content in blood18.1 The concept of homeostasis

• in respirationglucose + O2


content in blood is kept steady to ensure a sufficient supply

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• in respirationglucose + O2


dissolves in blood

affects pH of blood and tissue fluid

affects enzyme activity

too much / too little

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• regulated by

breathing heartbeat

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4 Body temperature18.1 The concept of homeostasis

• normal range is 36.5–37C • kept steady for enzymes to function

properly• regulated by

skin

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What are the effects of failing to regulate body temperature?

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C4442

>37.5

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deathCNS breakdownfever

loss of consciousness

muscle failure

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Mechanism of homeostasis18.1 The concept of homeostasis

• by negative feedback mechanism (負反饋機制 )What does that mean?

Let me explain with an example.

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When the room temperature (RT) is higher than the set temperature (S) …

Negative feedback mechanism

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thermostat turns compressor on, cooling the air back to set temperature

RT > S


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When the room temperature (RT) is lower than the set temperature (S) …


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thermostat turns compressor off, allowing room temperature to increase

RT < S


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Three components:Receptor Detects changes in the level

of the parameterControl centre

Processes information from receptor and coordinates different organs


nervous system or endocrine system

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Three components:Receptor Detects changes in the level

of the parameterControl centre

Processes information from receptor and coordinates different organs

Effector Produces a response opposite to the original change


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normal level of parameter

When level of parameter is higher than normal,

receptor control centre effector

response to decrease the level

back to normal


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When level of parameter is lower than normal,

receptor control centre effector

Negative feedback mechanismresponse to

increase the level back to normal

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1 is the ability of the body to maintain a stable internal environment.

Homeostasis


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2 Homeostasis is important for the of organisms because it provides a stable internal environment for cells to function.

survival


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3


Parameter Importance of regulating the parameter

Water content in blood

• To keep a stable water potential in cells so that they can carry out metabolic activities properly

waterpotential

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3



Glucose content in blood

• To provide sufficient glucose to cells for

• To keep a stable water potential in blood

respiration

potentialwater

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3



Gas content in blood

• To provide sufficient oxygen to cells for respiration

• To maintain a stable for enzymes to work

oxygen

pH

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3



Body temperature

• To maintain a stable temperature that is optimal for to work

enzymes

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4 The system and the system coordinate different organs to achieve homeostasis.

nervousendocrine


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5 results in responses that have opposite effects to the changes in the parameter, so that the level of the parameter can be restored to normal.



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18.2 Regulation of blood glucose level

How do the liver and pancreas regulate our blood glucose level?

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Roles of liver and pancreas18.2 Regulation of blood glucose level

• pancreas secretes hormones

insulin glucagon

both act on liver but with opposite effects

• they work together

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body cells


Insulin decreases blood glucose levelexcess glucose

liver cells glycogenstored in

muscles liver

Body cells take in more glucose

glucose CO2 + water

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liver cells


Glucagon increases blood glucose levelstored

glycogenglucose

Let’s see how blood glucose level is

regulated by negative feedback mechanism.

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normal blood glucose level

higher than

normal

pancreas secretes more insulin and

less glucagon

liver cells and body

cells

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Decrease level by:1 converting more glucose to

glycogen in liver cells2 increasing glucose uptake and

oxidation by body cells

higher than

normal

pancreas secretes more insulin and

less glucagon

liver cells and body

cells

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lower than

normal

pancreas secretes more glucagon and less insulin

Increase level by:converting stored glycogen to glucose

liver cells

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Failing to regulate blood glucose level


What will happen if blood glucose level is too high?

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diabetes mellitus

blood glucose level too high

water leaves cells by osmosis

glucose passes out in urine

normal metabolism affected

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diabetes mellitus

it results when the pancreas fails to produce or does not

produce enough insulin

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blood glucose level (mg/100cm3)

100

200

150

time (hrs)1 2 3

normal

glucose intake

healthy personlevel returns to normal within a short time

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100

200

150

time (hrs)1 2 3

normal

glucose intake

diabeticlevel remains high and then drops very slowly

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100

200

150

time (hrs)1 2 3

normal

glucose intake

diabeticthe drop is due to the loss of glucose in urine

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glucose level in urine

1 2 3glucose intake

time (hrs)

diabetic

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Diabetics need insulin injections

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100

200

150

time (hrs)1 2 3

normal

glucose intake

injection of insulin

level drops quicklydiabetic

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How about if the blood glucose level is too low?

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person becomes unconscious

blood glucose level too low

insufficient supply of glucose for respiration

neurones cannot function

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Pancreatic hormones regulate blood glucose levels

– The pancreas secretes two hormones• Insulin

– Signals cells to use and store glucose

• Glucagon– Signals cells to release stored

glucose into the blood

Pancreatic hormonesPancreatic hormones

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http://www.sunyniagara.cc.ny.us/val/pancreas2.jpg

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http://www.cytochemistry.net/microanatomy/Endocrines/pancreas2.jpg

The insulin producing cells are called cells and make up about 70% of the islet cells.

The glucagon producing cells are called cells and make up about 15 - 20% of the islet cells.

The islets are composed of three cell types: alpha cells, beta cells, and delta cells. These cells cannot be readily distinguished without special stains.

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SECRETORY SECRETORY ROLEROLE

CELL CHARACTERISTICSCELL CHARACTERISTICS

cells of islets cells of islets of Langerhansof Langerhans

Glucagon 15 - 20% of the islet cells; generally more peripherally located in the islet; more uniform in size; cytoplasm appears to be more densely packed than the cells

cells of islets cells of islets of Langerhansof Langerhans

Insulin 70% of the islet cells; generally more centrally located in the islet

Acinus cellsAcinus cells Digestive enzymes

Usually oriented in a circular pattern

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Body

cells

take up moreglucose

Insulin

Blood glucose leveldeclines to a set point;stimulus for insulinrelease diminishes

Stimulus:

Declining bloodglucose level(e.g., afterskipping a meal)

Alphacells ofpancreas stimulatedto release glucagoninto the blood

Glucagon

Liverbreaks downglycogen andreleases glucoseto the blood

Blood glucose levelrises to set point;stimulus for glucagonrelease diminishes

Stimulus:

Rising blood glucoselevel (e.g., after eatinga carbohydrate-richmeal)

Homeostasis: Normal blood glucose level

(about 90 mg/100mL)

Beta cells

of pancreas stimulatedto release insulin intothe blood Liver takes

up glucoseand stores it asglycogen

High blood

glucose level

GlucoseGlucosebalancebalance

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– Diabetes can be detected• By a test called a glucose tolerance test

Blo

od g

luco

se (m

g/10

0mL)

0

50

100

150

200

250

300

350

400

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1 2 3 4 5

Diabetic

Normal

0Hours after glucose ingestion

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Diabetes is a common endocrine disorder

– Diabetes mellitus• Results from a lack of insulin or a failure of cells to

respond to it (absolute or relative inadequacy)

– 2 types of diabetes• Type I (insulin-dependent)

– Autoimmune disease– Beta cells destroyed, no insulin made

• Type II – Body cells fail to respond to insulin

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Diabetes type I and type IIDiabetes type I and type IIType I - autoimmune disorder (destroys ability to produce insulin)

Type II - due to aging, lifestyle, heredity and other lifestyle (diet) factors decreased responsiveness by cells of target organs to insulin

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Complications Complications related to related to DiabetesDiabetes

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Insulin PumpInsulin Pump

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People with diabetes mellitus (糖尿病 ) need to check blood glucose level and

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People with diabetes mellitus (糖尿病 ) need to receive insulin injections

several times a day…

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This greatly affects our daily activities.

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A new device consists of a glucose sensor and an insulin pump

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The sensor checks the blood glucose level

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A suitable amount of insulin is released automatically into the body

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1



high blood glucose level

more and less secreted

blood glucose level falls

1 more is converted to

in liver2 more is oxidized by body cells

insulinglucagon

glucose

glycogenglucose

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stored is converted to in liver

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low blood glucose level

blood glucose level rises

more and less secretedinsulin

glucagonglucose

glycogen

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2a If the blood glucose level is too high, cells water by osmosis and their metabolic activities will be affected. Glucose may be lost in .urine

lose


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2bIf the blood glucose level is too low, cells cannot obtain enough energy for metabolism and they may die.energy


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What is the relationship between1When the pancreas fails to secrete enough insulin, a person will have diabetes mellitus.

diabetes mellitus and insulin?

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Why do people with diabetes mellitus 2Since the blood glucose level varies with body activities, it is necessary to check the level and inject suitable amounts of insulin regularly.

need to check their blood glucose levels and receive insulin injections regularly?

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What other modern advances in 3Other than insulin injections, diabetes mellitus may be controlled or cured by pancreas transplant.

science and technology may help control or cure diabetes mellitus?

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is brought about by

through

nervous system

Homeostasis

endocrine system

negative feedback mechanism

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parameters include

is the maintenance of a

stable internal environment

Homeostasis

water content in blood

glucose level in blood

gas content in blood

body temperature

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is regulated by

act on

pancreassecreted by

glucagon

glucose level in blood

insulin

liver body cells

think about… 18.1the concept of homeostasis 18.2regulation of blood glucose level

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