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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 ADH – Antidiuretic Hormone
Pancreas Insulin, glucagon FSH – Follicle Stimulating Hormone
Testis Testosterone
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
- 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
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Comparison between the Nervous & the Endocrine Systems

NERVOUS SYSTEM ENDOCRINE SYSTEM

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

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

THE ROLE OF HORMONES IN THE TROPIC RESPONSES OF PLANTS

 Geotropism – Is the growth response of a plant to gravity

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.

 Photo tropism
In photo tropism 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 auxin 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 stimulation.