Endocrine System Lesson 2 Negative Feedback, Blood Glucose Levels, and Plant hormones!

Endocrine System Lesson 2Negative Feedback, Blood Glucose Levels, and Plant hormones!

Review Quiz

1) Some hormones affect only one target organ, but most affect more than one.

When the hormone has had the desired effect, further production of the hormone needs to be controlled.

Hormone production is controlled by a process called negative feedback.

The regulation of blood glucose level is an example of negative feedback.

Negative feedback

How do hormones affect their targets?

No receptor, no effect!

Negative Feedback – Glucose Production (quick summary)2) Glucose from ingested lactose or carbohydrates is absorbed into the blood in the intestine and the level of glucose in blood rises. Elevated blood glucose concentration stimulates

endocrine cells in the pancreas to release insulin. Insulin speeds up glucose metabolism in cells, and

blood glucose levels decrease. When the level of blood glucose falls sufficiently, the

stimulus for insulin release disappears and insulin is no longer secreted.

This whole process is monitored by the pituitary gland!

Nervous System’s Control over the Endocrine System3) The hypothalamus synthesizes and secretes neuro-hormones, often called hypothalamic-releasing hormones, which stimulate or inhibit the secretion of pituitary hormones.

The hypothalamus, through its action on the pituitary gland, controls body temperature, hunger, thirst, fatigue, childbirth, salt and water balance, sleep, and many other things!

What is feedback?

Negative Feedback4) A typical negative feedback system has three parts:

Receptor: Detects changes in the values of a variable (e.x. hormone production levels, body temperature, etc.)

Control Center: Monitors changes, and signals a response through the effector… typically the hypothalamus + pituitary gland.

Effector: Begins action to bring the system back to ‘normal’ levels.

What’s the Receptor, Control Centre and Effector in this situation?

Negative Feedback to maintain homeostasis – Some simple Examples!!

E.x. SweatingReceptor Trigger

Control Centre Effector’s Response:

If response fails?

High body temperature

Hypothalamus Sweating, seeking shade, lethargy

Hyperthermia (Sun-stroke!)

High Blood Pressure

Brain (Cardiovascular centre)

Blood vessels relax; heart beat slows down

Hypertension

Low Blood Pressure

Brain (Cardiovascular centre)

Constricts blood vessels; increases speed and force of heart-beat

Hypotension

Low Body Temperature

? ? ?

Effects of Alcohol – Disrupting negative feedback!

6) Alcohol inhibits the pituitary secretion of anti-diuretic hormone (ADH), which acts on the kidney to reabsorb water.

When ADH levels drop, the kidneys do not reabsorb as much water… Your body “thinks” you’re over-hydrated, and consequently, the kidneys produce more urine… Result?

http://health.howstuffworks.com/kidney.htm

http://science.howstuffworks.com/h2o.htm

Negative Feedback VisualWhat is the receptor, control center and effector in this system?

?

Just right!

‘Negative feedback’ loop

signals hormone production to stop once that

‘just right’ level is reached.

© Boardworks Ltd 200413 of 31

Negative feedback – high blood glucose

The pancreas detects the level of glucose in the blood, and notifies the brain (pituitary / hypothalamus region)

When the level of blood glucose increases above normal, what hormone does the pancreas release?

“Check out these glucose levels, Brain!”

Receptor



The pancreas is stimulated to release insulin. What effect does this have?

The insulin stimulates the liver to convert glucose into insoluble glycogen, which is stored in the liver, and stimulates body cells to metabolize glucose. insulin

“Glucose levels are too high!Time to make some hormones,

Mr. Pancreas!” says Brain.

ReceptorControl center


The level of glucose in the blood decreases, causing the pancreas to stop producing insulin.

What would happen if the pancreas kept on producing insulin?

blood glucose returns to normal


Insulin production stops


Effector

“Glucose levels are just right! No more need for insulin, Mr. Pancreas!”

1

2

3


Negative feedback also occurs when the blood glucose level decreases below normal.

This time the brain detects decreased blood glucose and so the pancreas is stimulated to release which hormone?

Negative feedback – low blood glucose


Effector

“Glucose levels are too LOW!!Time to make some hormones,

Mr. Pancreas!” says Brain.


The pancreas produces the hormone glucagon.

Glucagon stimulates the liver to convert glycogen back to glucose and release this glucose into the bloodstream.


decreased blood glucose glucagon


Effector


The level of glucose in the blood increases, causing the pancreas to stop producing glucagon.

What would happen if the pancreas kept on producing glucagon?


decreased blood glucose

blood glucose returns to normal

glucagon


Effector

Blood glucose activity

Plant growth

Shoots will grow towards the light (against gravity)

Roots will grow towards moisture

(with gravity)

These responses are controlled by PLANT HORMONES

Heliotropism – Hormones and negative feedback in plants

Sunflowers are among several plant species – especially desert plants – that have the ability to either grow or move in response to stimuli from sunlight.

Increased sunlight triggers hormone secretion.

Known as heliotropism, the phenomenon can either make a plant move to face towards or away from a light source (phototropism) or the sun (heliotropism).What is the advantage of this?

Maximizes photosynthesis + growth!

Hormone secretion triggers special cells to swell or shrink in response to changes in turgor (pressure) determined by the amount of water in the cell.

Other interesting facts…In shoots, light causes hormones to collect in the shaded part of the stem, causing the shoot to grow towards the sunlight.

Hormones are sent to shaded parts of the plant, to increase turgor (water) pressure in the cells.

Cells on the shaded side stretch and swell (from

increased water pressure),

forcing the plant to bend towards

the light.

Light triggers the release of

special hormones.

What happens next? Where does negative feedback come into play?

Weed Killers!Artificial hormones can also be used to kill weeds, control when a plant ripens, to help many plants grow from one stem, and many other exciting uses…

8) What would be a powerful advantage of using hormones as a pesticide?

Clue:

Weed Killers!A common herbicide (weed killer) is a synthetic version of auxin, a plant hormone that regulates and coordinates plant cell growth and division, specifically in broad-leaf plants (which includes many species of weeds!).

Synthetic auxin pesticides causes the plant to grow abnormally, and often die… but doesn’t disrupt other plant growth, like corn!

Unintended side-effects… Scary stuff! Atrazine, a common herbicide

used all over the world since 1958, has unintended side-effects on hormone production in frogs!

Check out this video about Atrazine, a pesticide you might hear more about in the future……….

Biological Ethics Question… Corn and Rice are extremely important cash

crop, and provides food for hundreds of millions of people. Suddenly banning a pesticide, like Atrazine, could disrupt food production and severely damage the economy… Thailand included (it’s the 7th most popular pesticide in the country)!

Should potential health risks for future generations outweigh the needs of starving people today??!!?!?!?

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Endocrine System Lesson 2 Negative Feedback, Blood Glucose Levels, and Plant hormones!