HORMONAL COORDINATION IN MAMMALS

HORMONAL COORDINATION IN MAMMALS

Hormonal coordination in mammals involves the two systems which are endocrine system and exocrine system. Before I dig deep into this lesson I would like to give out a brief explanation of the two systems as below.

Endocrine system
Is the system that consists of ductless glands which produce hormone, hormone produced from endocrine glands is used to regulate the internal environment of the body. 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 cells.

Endocrine glands control slow and long term activities such as growth and sexual development like sex, hormone preparing female for ovulation, pregnancy, birth and lactation. Adrenaline is secreted for a particular moment.

Feedback and interaction

For effective control, two opposing systems are needed like brakes and accelerator in the car. Adrenaline promotes the release of sugar in the blood, while insulin converts blood sugar into energy to be used by the body. Feedback is needed so that the gland can adjust their output accordingly.

Similarities between nervous system and endocrine system

Because endocrine system work in connection with nervous system i have at least  to touch their similarities in below.

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 organ of an organism.

4)      The target organs in hormonal coordination are like the effector organs in the nervous coordination.

Difference between nervous system and exocrine system

Activity	Nervous	Endocrine hormones
Method of transmission	Neurone or nerve impulse	Blood stream
speed	rapid	Usually slow
Duration of response	Short lived	Long lasting
Message or stimuli	Impulse	hormones
Origin of message	Receptor and brain	Endocrine gland
Effector	Muscle or gland	Target organ or muscle

 The endocrine glands

The endocrine means internal secretion. The endocrine glands are ductless glands which secret hormones into the blood stream. Hormones are organic compounds which are proteins in nature. Hormone has either a generalised coordinating effect in the body or localized coordinating effects on a particular target organ. Some glands like pancreas are compound glands such that 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 a 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. For example:

                                  i.            The anterior lobe secretes trophic hormone which stimulates other endocrine glands to secrete hormones like adrenocorticotropic hormones, thyroid stimulating hormone and gonadotropic hormone like luteinizing hormones.

                                ii.            The posterior lobe secret antidiuretic hormone.

Function of pituitary hormones

Ø  Growth hormone for stimulating growth, over secretion leads to gigantism in infants, acromegaly in adults. Under secretion leads to dwarfism.

Ø  Thyroid stimulating hormone stimulates the thyroid gland.

Ø  Follicle stimulating hormone which stimulates the ripening of follicular cell in the ovary and ripening of sperm in male.

Ø  Prolactin for production of milk.

Ø  Oxytocin for strong contraction of uterus during birth and production of milk.

Ø  Luteinising hormone, bring about ovulation

Ø  Anti-diuretic hormone for increasing absorption of water from kidney.

 

2)      Thyroid gland

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

Function of thyroid gland

Ø  Produce thyroxin and amino acids containing iodine.

Ø  The hormone it produces regulates rate of metabolism and respiration.

Ø  The hormones it produces influence mental and physical development as well as growth.

Deficiency of thyroxin hormone may lead to;

        i.            Cretinism in infants such as dwarfism and mental retardation. Cretinism can be cured by administration of thyroxin in the early stage.

      ii.            Myxoedema in adults may reduce metabolic rate, overweight, sluggish activity, thick skin, coarse hair and premature ageing.

    iii.            Colloid Goitre: enlargement of thyroid gland.

Excess of thyroxin hormone may lead to;

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

      ii.            Hyperthyroidism such as exophthalmic goitre and enlargement of thyroid glands.

 

      3)      Parathyroid

Found within thyroid gland. They produce parathormone in response to a lack of calcium in the blood, resulting in increased absorption.

4)      Pancreas ( Islets of Langerhans)

Pancreas is a compound gland: exocrine part produces low hormones such as insulin and glucagon hormone. Insulin converts glucose into glycogen for storage in the liver and muscle while glucagon converts glycogen into glucose to be used in the body.

Deficiency of insulin in the body may lead to;

Little insulin causes Diabetes mellitus which result when glucose increases in the blood.

Function of insulin

Ø  Promotes the uptake of glucose from blood by muscle cells.

Ø  Accelerate conversation of glucose into glycogen in the liver.

Ø  Increases protein synthesis in some cells

 

     5)      Adrenal glands

These are situated just above the kidney. The outer layer (adrenal cortex) produce two hormones.