HORMONAL COORDINATION IN MAMMALS

Endocrine system

Is the System that regulates the internal environment of the animal. The system consists of ductless glands which produce hormones. Since they have no ducts or tubes, the hormones are secreted directly into the blood stream. The hormones are transported through the blood to the target organ or tissue or cell.

Endocrine glands control slow and long term activities such as growth and sexual development e.g. sex hormones preparing female for ovulation, pregnancy, birth and lactation. But some are for particular moment e.g. adrenaline.

Feed back and interaction

For effective control, two opposing systems are needed like brakes and accelerator in the car. E.g. Adrenaline promotes the release of sugar into the blood, while insulin removes sugar the blood and stores it.

Feed back is needed so that the glands can adjust their output accordingly.

Diagram. Position of endocrine glands in human body.

Similarity between Nervous system and Endocrine system

1.      They are both set into action by a stimulus to produce a response.

2.      They both involve chemical transmission.

3.      They both provide means of communication in the body of an organism.

4.      The target organs in hormonal co-ordination are like the effector organs in the nervous co-ordination.

Differences between nervous system and Endocrine system

Activity	Nervous	Endocrine-Hormones
Methods of transmission	Neurone or Nerve impulse	Blood stream
Speed	Rapid	Usually slow
Duration of response	Short lived	Long lasting
Message or stimuli	Impulse	Hormone
Origin of message	Receptor and brain	Endocrine gland
Effector	Muscle or gland	Target organ or muscle

The endocrine glands

Endocrine means internal secretion. The endocrine glands Are ductless glands which secretes hormones into the blood stream. Hormones are organic compounds which are proteinous in nature. Hormones have either a generalized co-ordinating effect on the body or have localized (specific) co-ordinating effect in a particular target organ.

Some glands like pancreas are compound glands ie. They perform both endocrine and exocrine functions.

The exocrine glands

Are glands which have ducts or tubes through which the secretion move to the part of the body where they produce response. Examples are salivary gland, sweat glands and pancreas.

 Endocrine glands and their functions.

1.      Pituitary Gland

It is also called the master gland because it controls activities of other endocrine glands. It is found at the base of the fore brain attached to the Hypothalamus. It secretes several hormones. Examples:-

-Anterior lobe secret Trophic hormone which stimulate other endocrine glands to secrete hormones e.g. adrenocorticotropic hormone, thyroid stimulating hormone and gonadotropic hormone like luteinizing hormones.

-posterior lobe secret antidiuretic hormone.

Functions of pituitary hormones:-

• Growth Hormone: For stimulating growth.

                                Over secretion leads to -gigantism in infants

          -acromegaly in adults

                               Under secretion leads to dwarfism.

• Somatotrophin hormone: Stimulates protein synthesis and growth of long bones

• TSH- Thyroid stimulating hormone: is for thyroid gland stimulation

• FSH- Follicle stimulation hormone:

Female, ripening of follicle in the ovary.

Male, ripening of perms

• Oxytocin (Birth inducing hormone) for strong contraction of uterus during birth and production of milk.

• prolactin for production of milk

• lutenising hormone, brings about ovulation

• ADH- Anti-diuretic hormone: increase absorption of water from kidney.

2.      Thyroid gland.

It produces Thyroxine. Is a butterfly shaped gland in the neck in front of the wind pipe below the larynx.

• Functions.

-Produces thyroxine and amino acids containing iodine

-Regulates rate of metabolism and respiration

-Influence mental and physical development and growth.

Complications:

• Deficiency

-Cretinism in infants i.e. dwarfness and mental retardation.

Can be cured by administration of thyroxine in the early stage.

-Myxoedema in adults ie. Reduced metabolic rate, overweight, sluggish activity, thick skin, coarse hair and premature ageing

-Colloid Goitre: enlargement of thyroid gland

• Excess:

-In adults, thinness, restlessness, over activity/excited and mentally unstable.

-Hyperthyroidism ie. Exopthalmic Goitre: enlargement of thyroid gland

3.      Parathyroids

-Are found within thyroid gland

-They produce parathormone in response to a lack of calcium in the blood, resulting in increase absorption.

4.      Pancreas (Islets of Langerhans)

Pancreas is a compound gland: Exocrine part produces digestive enzymes while endocrine part produces tow hormones ie. Insulin and Glucagon.

-Insulin which convert glucose into glycogen for storage in the liver and muscles.

-Glucagon which convert glycogen into glucose to be used in the body.

• Complications: too little insulin causes Diabetes Mellitus ie. Excess of glucose in the blood.

• Functions of Insulin

-promotes the uptake of glucose from blood by muscle cells.

-accelerate conversion of glucose into glycogen in the liver

-increases protein synthesis in some cells.

5.      Adrenal glands

Are situated just above the kidney.

• The outer layer (Adrenal cortex) produces two hormones

-Glucocorticoids e.g. cortisol which accelerate glucose formation from non-carbohydrate sources like protein.

-Mineralocorticoid e.g. Aldesterone which stimulate re-absorption of sodium ions in the kidney ie.  controls the salt balance.

• The inner zone (medulla) produces Adrenaline when stimulated by nervous system e.g. impulses of danger or other situations which need vigorous actions. Therefore, Adrenaline prepares body for emergency by rising blood pressure, increase heart beat and breathing rates, increasing blood sugar levels, increasing blood supply to the muscles while decreasing supply to the gut (alimentary canal) and skin.

• Under secretion: causes Addison disease ie. Anaemia and weakness

• Over secretion: Adrenogenital syndrome ie. Bearded lady.

• Causes Cushing

6.      Gonads - Sex hormones (Gonadohormornes)

Are produced by ovaries of female and testes of male mammals.

• Female sex hormones:

+Oestrogen  (from the ovary), Functions:-

-development of female secondary sexual characteristics.

-prepares uterus to receive a ripe, fertilised ovum.

-maintain the uterus in a state where by it can nourish and protect the developing embryo ie. Prevent the contraction of uterus until the baby is due to be born.

-in some mammals, it brings female to "HEAT"

+Progesterone

-promotes proliferation of uterine wall (inhibits eggs)

-formation of mammary glands (development of breasts)

Male sex hormone:

+Androgen or Testosterone from testis;

-development of male secondary sexual characteristics.

-production of sperms.

Complications for both females and males:

Delay or lack of development of secondary sexual characteristics.

7.      Duodenum

Food stimulates the lining of the duodenum to produce hormone Secretin, which on reaching the pancreas in the blood stream initiate the production of pancreatic enzymes. The enzymes are secreted only when the food is present.

Conclusion

Hormones and nervous systems affect each other and therefore the whole body. Any disturbance in this interrelationship can have far reaching effects all over the body, sometimes with disastrous consequence.

Hormones and nerves affect the person's behaviour but the person's behaviour can also affect his/her hormones and nerves. E.g. excessive stress may cause a permanent damage.