Endocrinal control and coordination

Introduction

Control and coordination is the combined effort of the nervous system, endocrinal system and the musculoskeletal system. It is difficult to understand the exact mechanism behind the locomotion process. In the majority of the mammals including human beings, the nervous system is the master system regulates the locomotion, however, plants produce movements through the phytohormones. Since the nerve fibres do not innervate all cells of the body, endocrinal system partly assist in movement . hence it is important to understand the fact that, both the nervous system and the endocrine system participate in coordination and movement.

Table Of Contents

1. Introduction

2. Endocrinal glands 

 

    2.1 The Hypothalamus

    2.2 Pituitary hormones

    2.3 The Pineal Gland and its hormones

    2.4 Thyroid Gland

    2.5 Parathyroid Gland

    2.6 Thymus

    2.7 Adrenal Gland

    2.8 Pancreas

3. Sex hormones 

4. How do hormones work

 

 

 

Endocrine system: 1. The pineal gland, 2. Pituitary gland, 3. Thyroid gland, 4. Thymus, 5. Adrenal gland, 6. Pancreas, 7. Ovary, 8. Testicle

 

Endocrinal glands 

There are 2 types of glands; exocrine and endocrine glands. As the name suggests, endo means within, hence endocrinal hormones are secreted locally therefore they do not require ducts to transport their secretion. They are otherwise called ductless glands and the substances they secrete are called hormones. A hormone is a chemical substance produced by glands. Depending upon where they are secreted, hormones are; endocrinal and exocrinal in nature. The secreted hormones are released into the bloodstream to carry them to target locations. Hormones released by the glands will alter the physiological, chemical and biological characteristics of individuals resulting in useful bodily processes such as digestion, growth and coordination. Human endocrine glands are; pituitary glands, pineal glands, thymus gland, gonads (testis in males and ovary in females) thyroid gland, adrenal gland, pancreas and parathyroid glands. This post is designed to brief the structure and functions of most important glands and their hormonal actions that assist the balance and coordination.

The Hypothalamus

It is located at the basal part of the forebrain. It helps to regulate a wide spectrum of bodily functions through the secretions from their neurosecretory cells. 2 types of hormones secreted by the hypothalamus are; the releasing hormones and the inhibiting hormones. Releasing hormones stimulate the secretion of pituitary hormones whereas the inhibiting hormones help to inhibit the secretions of pituitary hormones. For example, Gonadotropin-releasing hormone (GnRH) assists in stimulating the pituitary synthesis whereas somatostatin secreted by the hypothalamus inhibits the release of growth hormone from the pituitary.

Pituitary hormones

The pituitary is called the master of all glands as it indirectly helps to control other hormones. The gland is located in a space known as the sella tursica. The pituitary is attached through a small stalk; infundibulum. The gland has 2 partitions, the adenohypophysis and a neurohypophysis. Adenohypophysis is commonly called anterior pituitary help to release growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The only hormone secreted by the Neurohypophysis is a melanocyte-stimulating hormone (MSH).

The Pineal Gland and its hormones

The pineal gland is present in the dorsal side of the forebrain. pineal gland secretes a hormone known as melatonin. Melatonin regulates our sleep cycle, body temperature metabolism, pigmentation, and to some extent, the menstrual cycle.

Thyroid Gland

The thyroid gland secretes thyroxin hormones. It is located on either side of the trachea –voice box. It has 2 lobes interconnected with a connective tissue known as the isthmus. The thyroid gland is composed of follicles and stromal tissues. The follicle has follicular cells that secrete T3 and T4. T3 is the triiodothyronine and T4 is called tetraiodothyronine. Thyroxin is closely linked with iodine regulation in our body. Hence, the deficiency of iodine leads to hypothyroidism characterized by enlargement of the thyroid gland (goitre). Thyroid hormones also help in maintaining the BMR (basal metabolic rate) by indirectly controlling the metabolism of carbohydrates, proteins, and fats. The hormone is directly responsible for water and electrolyte balance in our body.

Parathyroid Gland

They are located on the ventral side of the thyroid gland. Parathyroid gland also has 2 lobes and the secretions are known as PTH (Parathyroid hormone). The secretion of PTH helps to raise the Ca2+ levels in the blood. They help in the bone desorption (mineral dissolution) process, therefore, the hormone is primarily responsible for the calcium balance in the body.

Thymus

The thymus is a small, irregular-shaped gland located on the top portion of the chest- just under the breastbone in between the lungs. The mediastinum is a space between the 2 lungs where thymus is attached. The thymus has a lobular structure to help in the development and maintenance of the immune system. Thymus secretions are known as thymosins. They assist in the differentiation of T- lymphocytes. Indirectly, they help in cell-mediated immunity during infections and foreign body attacks.

Adrenal Gland

Adrenal glands are the paired structures located just above the 2 kidneys, it is also called suprarenal gland. The glands have 2 types of tissues, namely the adrenal medulla (central region) and the adrenal cortex (external region). The adrenal medulla secretes catecholamines. Catecholamines are of 2 types, adrenaline (epinephrine) and noradrenaline (norepinephrine). Both the hormones help to raise the heartbeat, the strength of heart contraction and the rate of respiration. They also participate in the breakdown of glycogen into glucose in the body.  Anatomically, the adrenal cortex has 3 layers, called zona reticularis as an inner layer, zona fasciculata in the middle and the outermost layer - zona glomerulosa .the secretions are known as the corticoids. There are 2 types of corticoids namely, glucocorticoids (regulate the water and electrolytes and the other one is the mineralocorticoids regulating mineral metabolism.

Pancreas

Pancreas work as both exocrine and endocrine. The endocrine part has cells known as ‘Islets of Langerhans containing 2 types of cells ; the Alpha cells and Beta cells. The pancreas plays a major role in body sugar maintenance through insulin and glucagon secretions secreted from alpha and beta cells. Pancreatic hormones participate in glycolysis ( breaking glucagon into glucose) as well as gluconeogenesis( formation of new glucose). The deficiency of pancreas hormones cause diabetes mellitus-one of the most chronic and dangerous illness.

 

Sex hormones 

Secretions by Testis

They are the paired structures located within the scrotum. The testis is the most vital part of reproduction. They perform 2 functions. They act as sex organs as well as an endocrine gland. A testis has a seminiferous tubules and the interstitial tissue. The Leydig cells or interstitial cells secrete androgens (testosterone) which in turn regulates sperms.

Secretions by Ovaries

Ovaries are the primary female sex organs assist in the production ovum by a process called menstruation. Ovaries also regulate steroid hormones called estrogen and progesterone. The estrogen is released from the growing ovarian follicles to help in nourishing the embryo after fertilization.

 

How do hormones work?

Hormones work on a memory system in which the hormones get attached to a transporter that will deliver the secretions to target areas. They produce their effects by binding to specific proteins known as hormone receptors located in the target tissues only. Such binding of the hormone to its receptor leads to the formation of a hormone-receptor complex

 

Material nature of hormones

  1. Peptide, polypeptide, protein hormones (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones, etc.)

  2. Steroids (e.g., cortisol, testosterone, estradiol and progesterone)

  3. Iodothyronines (thyroid hormones)

  4. Amino-acid derivatives (e.g., epinephrine).

 

 



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