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Endcrine system notes pdf final

Life Sciences (Renaissance)

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LIFE SCIENCE GRADE 12

THE ENDOCRINE SYSTEM

AND HOMEOSTASIS
NOTES

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The endocrine system

Key words:

1.The endocrine gland- type of gland which pours its secretion’s directly into the blood
Example of an endocrine gland: Hormones are an example of an endocrine gland
since they pour their secretions directly to the blood.
2. The exocrine gland- type of gland which pours its secretions directly into the duct
Example: sperm duct, sweat gland, salivary glands etc. these types of glands pour their
secretions directly into the duct
3. Hormones- these are chemical messenger’s which are protein in nature

. Differences between the endocrine system and the nervous system

Endocrine system Nervous system

Messages are transmitted as HORMONES Message is transmitted as NERVE IMPULSE
BY NEURONS
Takes a long time to react e.g. puberty may Responds quickly to impulses
take years
Targets a wider area Targets a specific area
Hormones control long term changes Nerve impulse controls short term changes

NB: everything inside the endocrine system is regulated by hormones and regulatory organs
/target organs.

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4 How the endocrine system works.

endocrine gland blood target organ

• Endocrine gland- secretes the hormone.

• Blood-transports the hormone
• Target organ- responds to the hormone.

4.1List of hormones we will deal with in this section/topic

➢ ADH
➢ THYROXIN
➢ ADRENALIN
➢ ALDOSTERONE
➢ GROWTH HORMONE
➢ TSH
➢ FSH
➢ PROLACTIN
➢ GLUCAGON
➢ INSULIN
➢ TESTOSTERONE
➢ OESTROGEN
➢ PROGESTERONE

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HOMEOSTASIS AND NEGATIVE FEEDBACK MECHANISM

Key words:
1. Homeostasis- process of maintaining a constant internal environment within narrow
limits, despite the changes that may take place internally and externally.
2. Negative feedback mechanism- when there is an increase from normal, a corrective
mechanism causes a decrease and vice versa to maintain a balanced system.
3. Coordination – joint linking together of systems and activities within the body to bring
about a harmonious response.

How the body reaches homeostasis

control centre
control centre responds by sending
stimulated messages to the
target organ

target organ will

imbalance detected
oppose/reverse the
by RECEPTORS
inbalance

homeostasis(balance
is now restored)

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1. Balancing of water levels

I. Responsible hormone: ADH (antidiuretic hormone)

II. Who produces ADH: the HYPOTHALUMUS
III. Who secretes ADH: the PITUITARY GLAND

Key words:
A. OSMOREGULATION- is the regulation and balancing of water levels in
the body (internal environment)

Water levels increase above the normal Water levels decrease below the
normal
An increase in water levels above the A decrease/drop in water levels
normal
The hypothalamus in the brain is The hypothalamus in the brain is
stimulated, it will produce LESS ADH stimulated, it will produce MORE
ADH
The pituitary gland is also stimulated, The pituitary gland is also
pituitary gland will secrete LESS ADH stimulated, it will secrete MORE
ADH
ADH will decrease the permeability of ADH will increase the
the collecting ducts (renal tubules) permeability of the collecting
ducts (renal tubules)
Less water is re absorbed by blood More water will be reabsorbed
vessels, more water leaves the body
The water levels are returned to The water levels are returned to
normal normal

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2. Balancing of thyroxin levels

Key words:

I. TSH- thyroid stimulating hormone.

II. Goitre- disease caused by a deficiency of the mineral iodine, leading to the
swelling of the thyroid gland.
III. GH- Growth hormone
IV. Gigantism- disease caused by the oversecreting of the growth hormone
(GH)
V. Dwarfism- disease caused by the under secreting of the growth hormone
(GH)
VI. Hyperthyroidism- disease caused by the oversecretion of the hormone
thyroxin.
VII. Hypothyroidism- disease caused by the undersecretion of the hormone
thyroxin.
VIII. Prolactin- stimulates the production of milk in mammary glands.

A. The TSH- it is the thyroid stimulating hormone. Its role is to stimulate the thyroid gland
to produce the hormone thyroxin.

The following shows a flow diagram on how thyroxin is produced.

pituitary Thyroid
TSH Thyroxin
gland gland

B. Importance of the hormone thyroxin

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• Thyroxin controls all the metabolic processes in the body, thus high
levels of thyroxin can lead to increased metabolic rate, leading to
hyperactivity.
• Thyroxin affects the growth and the functioning of the heart.
Low thyroxin levels can affect growth also how the heart functions.

C. Goitre

• Goitre is caused by the deficiency of iodine in the blood.

• Effects: leads to the swelling of the thyroid gland

Figure 1: woman affected by goitre.

Increase in thyroxin levels above the normal decrease in thyroxin levels below the
normal
increase in thyroxin levels above the normal, Decrease in thyroxin levels below the
the pituitary gland is stimulated normal, the pituitary gland is stimulated
Pituitary gland will secrete LESS TSH Pituitary gland will secrete MORE TSH
There will be less stimulation of the thyroid TSH will stimulate the thyroid gland to
gland to produce thyroxin produce MORE thyroxin
Less thyroxin is produced by the thyroid MORE thyroxin is produced by the thyroid
gland gland
Thyroxin levels are returned to normal Thyroxin levels are returned to normal

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3. Balancing of salt levels

Regulatory organ: the adrenal gland

Responsible hormone: aldosterone

A. where is the adrenal gland found?

It is located on top of the kidneys.

Increase in salt levels above the normal Decrease in salt levels below the normal
Increase in salt levels above the normal, the decrease in salt levels below the normal, the
adrenal gland is stimulated adrenal gland is stimulated
Adrenal gland will secrete LESS aldosterone Adrenal gland will secrete MORE
aldosterone
This will decrease the re absorption of This will INCREASE the re absorption of
salt(ions) in the kidneys and the collecting salt(ions) in the kidneys and the collecting
duct duct
More salt is excreted/leaves the body e.g. as LESS salt is excreted/ LESS SALT leaves the
part of urine body e.g. as part of urine
Salt levels in the blood are returned to Salt levels in the blood are returned to
normal normal

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4 How the body is prepared to meet emergency

(the fight or flight hormone)

Key word:
a. adrenaline- is the fight or flight hormone, it prepares the body to meet
emergency.
b. Who secretes adrenaline? - adrenal gland.
What changes will occur because of adrenaline, during emergency situations?

• During an emergency situation, the adrenal gland is stimulated.

• The adrenal gland will secrete the hormone adrenaline.
• Adrenaline will cause certain changes in the body to occur:
I. The heart will start beating faster.
II. blood pressure will increase.
III. The rate and dept of breathing will increase.
IV. Blood vessels of the skin and the digestive will CONSTRICT, to allow blood that
is rich in oxygen, nutrients, and glucose to flow into the skeletal muscles and
the brain.
V. The liver will be stimulated to convert glycogen back to glucose, to increase
the blood glucose levels.

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5.Thermoregulation (balancing of the body

temperature)
Key words:
a. Thermoregulation- is the process of maintaining a constant body temperature.
b. Vasodilation-The widening of blood vessels in the skin
c. Vasoconstriction- the narrowing of the blood vessels in the skin

During a hot day During a cold day

Increase in body temperature above normal decrease in body temperature below
limits, the hypothalamus is stimulated normal limits, the hypothalamus is
stimulated
It will send nerve impulses to the blood it will send nerve impulses to the blood
vessels of the skin to dilate (vasodilation will vessels of the skin to constrict
occur) (vasoconstriction will occur)
More blood will flow to the surface of the less blood will flow to the surface of the skin
skin
Sweat glands become activated, and will Sweat glands become inactive, no sweat is
produce more sweat produced
Therefore, more heat will be lost/released Therefore, less heat will be lost/released via
via evaporation (of sweat) evaporation (of sweat)
Body temperature is returned to normal Body temperature is returned to normal

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6.Balancing of glucose levels

Key words:
a. Insulin- hormone which converts glucose into glycogen, thus it decreases the blood
glucose levels.
b. Glucagon- converts glycogen (stored glucose) back to glucose, thus it increases the
blood glucose levels.
c. Pancreas (islets of Langerhans)- produce the hormones glucagon and insulin.
d. Diabetes mellitus- disease that results when insulin stops working or when the body
does not produce enough insulin, may be due to unhealthy diet.

Increase in blood glucose levels Decrease in blood glucose levels

Pancreas (islets of Langerhans) will be
stimulated by an increase in blood glucose Pancreas (islets of Langerhans) will be
levels stimulated by a drop in blood glucose
levels
Islets of Langerhans will secrete the Islets of Langerhans will secrete the
hormone insulin, which will convert glucose hormone glucagon, which will convert
to glycogen. glycogen back to glucose
Glycogen is then stored in the liver Stored glycogen is now converted back to
glucose
Blood glucose levels are returned to normal Blood glucose levels are returned to normal

NB: LERNER MUST KNOW THE TWO TYPES OF DIABETES MELLITUS, TYPE
1 AND 2

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7. Balancing of carbon dioxide levels

When the CO2 level in the blood increases above normal

levels

• CO2 levels in the blood increase above normal levels

• Receptor cells in the carotid artery in the neck are
stimulated
• To send impulses to the medulla oblongata in the brain
• Medulla oblongata stimulates breathing muscles
(intercostal muscles and diaphragm) and hear
• Breathing muscles contract more actively – increases the
rate and depth of breathing. The heart beats faster
• More CO2 is taken to and exhaled from the lungs
• The CO2 level in the blood returns to normal

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