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HORMONAL CORDINATION
A hormone is a chemical substance produced by a gland carried in the blood, which alters the activity of one or more
specific target organs.

THE DIFFERENCE BETWEEN EXOCRINE & ENDOCRINE GLANDS

The exocrine glands are those glands which have ducts, i.e. their secretions are passed through ducts onto the
epithelial surface e.g. tear gland, salivary gland etc. The endocrine glands are ductless (do not have ducts) and their
secretions are carried by the blood.
EXAMPLES OF ENDOCRINE GLANDS & THE HORMONES THEY PRODUCE

GLAND HORMONE
Thyroid Thyroxin
Adrenal Adrenaline
Pituitary ADH, FSH, TSH Legend;
Pancreas Insulin, glucagon ADH – Antidiuretic Hormone
Testis Testosterone FSH – Follicle Stimulating Hormone
Ovaries Oestrogen, Progesterone TSH – Thyroid Stimulating Hormone

locations of glands

Function of Insulin
- Insulin reduces the blood glucose level when its high (regulates the amount of glucose level in the blood) by
stimulating the liver cells to take up glucose from the blood & convert it to glycogen & stored.

Function of glucagon
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- it raises the blood glucose level when its low by stimulating the liver cells to convert the stored glycogen to
glucose.

Functions of adrenaline
This is commonly known as Flight or Fight hormone because it prepares the body for action. It has the following
affects;
- It increases the rate & depth of breathing.
- It increases the rate of heart beat
- Constricts the blood vessels carrying the blood to the gut & skin hence diverting more blood to the muscles
- It also promotes the conversion of the stored glycogen to glucose to raise blood sugar level. (therefore
functions like glucagon)

The above mentioned effects help to provide more glucose & more oxygen to the working muscles.

Function of testosterone
- It controls the production & development of sperms
- Regulates the development of the male secondary sexual characteristics e.g. enlargement of sex organs,
growth of facial hair (beard), muscle enlargement, deepening of the voice etc.

Functions of oestrogen & Progesterone

- It is responsible for the development of secondary sexual characteristics in females, e.g. armpit & pubic hair,
development of breasts, broadening of hips, enlargement of vagina etc
- It prepares the uterus for implantation by making its lining thicker & rich in blood vessels

Comparison between the Nervous & the Endocrine Systems

NERVOUS SYSTEM ENDOCRINE SYSTEM

Information passes as electrical impulses Information passes as a chemical substances (hormone)

Transmission is through the nerves Transmission is through the blood

Rapid Transmission & immediate responses e.g. blinking Slow transmission & usually slow response e.g. growth
of the eye
The response is short lived The response is long lasting

The response is exact since impulses are sent directly to The response is usually widespread because hormones
target organs are dispersed throughout the body

NEGATIVE FEEDBACK
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The Incoming message triggers the release of another message, which brings about
a negative change (of opposite effect).
Example;

- When the blood sugar level is high, the pancreas is stimulated to produce
insulin which in term stimulates the liver cells to convert excess glucose to
glycogen and reduce the blood sugar level.

- The Follicle stimulating hormone (FSH) secreted by the pituitary gland

stimulates the ovaries to produce oestrogen, but the moment the oestrogen
level increases the production of FSH stops, which in turn will lead to a
decrease in oestrogen level. Refer to the figure below
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THE ROLE OF HORMONES IN THE TROPIC RESPONSES OF PLANTS

Geotropism – Is the growth response of a plant to gravity

Phototropism – Is the growth response of a plant to light
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Geotropism & Phototropism in terms of auxins regulating growth (refer to the figure below)

Geotropism
If a plant is placed with its shoot horizontal more auxin reaches the lower of the shoot. The lower side of the shoot
elongates faster than the upper side of the shoot and the shoot curves upwards as it grows. This also applies to the
radicle which in this case shows positive geotropism.

Phototropism
In phototropism less auxin reaches the illuminated side and more reaches the shaded side. The cells on the shaded
side extend more rapidly than those on illuminated side causing the shoot to grow in a curve towards the light source.

The Effect of Removing the apical bud from a plant seedling

The cells near tip of some growing seedling / shoot produce a chemical auxin, which
in certain concentrations accelerates growth in length. The auxins achieve this effect
probably by delaying the loss of plasticity in the walls of the cells in the region of
extension so that at a time when the cells are osmotically active & taking in water,
the increased pressure in the vacuole forces the cell wall to extend.

It has been observed that when the tip of the coleoptile (sheath surrounding &
protecting the plumule of some monocots; especially grasses) is removed, the
growth of the plant is arrested (no elongation). If the tip is cut & auxin applied on the
cut / decapitated coleoptile, growth is resumed which shows that auxin is a growth
stimulating hormone.

Courtesy of Lebsy Mb
Contact; 71726846