Endocrinal control and coordination

Introduction

Control and coordination are the inseparable functional aspects of some of the body systems. This is especially true when it comes to the endocrinal system, musculoskeletal system and the nervous system as they play a predominant role in the mechanism of control and coordination. However, almost every body system is indirectly responsible for the control and coordination of human body. In a vast majority of the mammals including human beings, the nervous system is the master system regulating the locomotion, however, plants produce movements through their hormones- phytohormones. In this article, let us understand the role of the endocrinal system in the locomotion, coordination and control of the human body.

 

Why do we need controla nd coordination

Human body is a complex integration of many cells, tissues and organs that requires some biolofical force to stay integrated and balanced. As each system work on their own, they also need some communication witht he rest of the body system to ensure its limits. In order to either increase or decrease the pace of different functions in the body, brain and endocrinal systems generates impulses that sends signals to all other system so that they determine whether to increase or decrease the rate of functions.For instance, if the digestion process has to be rapid, muscles that help in chewing , swallowing and moving food must work in synchrony which is made possible by the action of endocrinal and neuromuscular systems.

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 

An endocrinal gland is a ductless land that secretes hormone. Homones are the chemical substances responsible to initiate the right  response from the target organs or systems when they reach. Depending upon where they are secreted, hormones are divided into 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. There are 2 types of glands; exocrine and endocrine glands. As the name suggests, endo means within, as the endocrinal hormones are secreted locally, and they do not require ducts to transport their secretions far away from their location. Endocrinal glands are otherwise called ductless glands and the substances they secrete are called hormones. 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 secreted by their neurosecretory cells. The 2 principal types of hormones secreted by the hypothalamus are; the releasing hormones and the inhibiting hormones. Releasing hormones stimulate the secretion of pituitary hormones while the inhibiting hormones help to suppress the secretions . 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  the master of all glands as it indirectly helps to control every other gland. It is located in a space known as the sella tursica where it is attached to a small stalk-like attachement called infundibulum. The gland has 2 partitions, the adenohypophysis and a neurohypophysis. Adenohypophysis is the anterior pituitary region that 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 ( posterior pituitary region) is the melanocyte-stimulating hormone (MSH).

 

The Pineal Gland and its hormones

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

 

Thyroid Gland

The thyroid gland secretes thyroxine 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 gland is composed of follicles and stromal tissues. Each follicle has follicular cells that secrete T3 and T4 where T3 is called the triiodothyronine and T4 is called tetraiodothyronine. Thyroxine is closely linked with iodine regulation in our body. Hence, the deficiency of iodine leads to hypothyroidism. Hypothyroidism is the most primary cause of  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. They are also called suprarenal glands. The glands have 2 types of tissues, namely the adrenal medulla (central region) and the adrenal cortex (external region). The adrenal medulla secretes catecholamines and they 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).

 

Further reading 

1.

 Structure and functions of pancreas         

2 .    

Concept of immunity

3.

Pituitary gland and pituitary hormone

4.

Coordination in plants

5.

Structure and functions of liver

 

Important Questions 

  1. What is the key difference between endocrine glands and exocrine glands?

  2. List the endocrine and exocrine glands in our body.

  3. Name the sex hormones in males and females.

  4. Explain thee role of thyroid hormone sin our body.

  5. What is the role of endocrine and exocrine pancreas?

  6. Which hormone regulates the fluids and electrolytes in our body?

 

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