Compare and contrast the actions of the nervous system and the endocrine system

Question

Compare and contrast the actions of the nervous system and the endocrine system to control body function.

Identify the major endocrine glands and their location within the body, with a particular focus on the pituitary gland, thyroid gland, Adrenal gland as well as how pancreas acts as an endocrine organ. (We will discuss gonads at end of semester)

Define a local hormone and explain the difference between autocrine and paracrine.

Identify the hypothalamus, anterior vs. posterior pituitary and thyroid glands and describe regulatory relationship between the hypothalamus, pituitary and thyroid in detail.  

Explanation / Answer

1). Neurons conduct impulses through electrical signal within a neuron, but to transmit that signal to the effector cell or to the postsynaptic neuron, a neurotransmitter is needed that is called as a chemical messenger.

The endocrine system organizes various body functions by its hormonal secretions. The hormone is a chemical messenger secreted from an “endocrine gland” (ductless glands) which is transported to a distant site from its origin, where it produces its action (paracrine action).

The nervous system sends speedy signals onto cells via neurotransmission & action potentials finally vanish as quickly as possible. The endocrine system generates hormones from specific endocrine glands to act on specific target cells to produce signal transduction mechanism via receptor activity & takes longer to produce cellular activity, for example, steroid hormones.

So, both nervous system and endocrine system both need chemical messengers to send signals to target cells, but they do differ in their speed of transmission and organs or tissues they regulate.

2).  The major endocrine glands present in the birds are the pituitary gland, thyroid gland, parathyroid gland, adrenal gland, gonads (testes and ovaries), thymus gland, and pancreas.

Thus, pituitary gland regulates the blood levels of hormones through the negative feedback mechanism. The two lobes of the pituitary gland are,

The pituitary gland secretes endocrine hormones (trophic hormones) under the influence of releasing hormones secreted by the hypothalamus. For example, the thyrotropin-releasing hormone (TRH), released by the hypothalamus stimulates the pituitary gland to release the thyrotropin into the circulation. If the blood levels of the pituitary hormone are found high, immediately it sends signals to the hypothalamus to stop sending particular releasing hormones. This is an example of negative feedback regulation.

The posterior pituitary secretions are regulated by the hypothalamus by sending the nerve signals down the stalk. These signals command the release of anti-diuretic hormone (ADH) and oxytocin whenever needed.

The thyroid gland is an endocrine gland located just below the larynx or voice box, on either side of the trachea. The thyrotrophic releasing hormone released by the hypothalamus acts on anterior pituitary to release the thyroid stimulating hormone (TSH). The TSH stimulates the thyroid gland to release the thyroid hormones. The thyroid gland is an endocrine gland, and it secretes two hormones, namely, triiodothyronine (T3) and thyroxine (T4). Iodine is necessary for the synthesis of thyroid hormones. The TSH regulate the release of thyroid hormones by a negative feedback loop.

Pancreas elongated organ located posterior to the stomach. It acts as both endocrine and exocrine gland. It secretes digestive juices (carbonate) directly into the digestive tract (duodenum of the small intestine). It is the exocrine function of the pancreas. The endocrine function of the pancreas is to maintain the blood glucose levels by releasing the insulin and glucagon. Insulin converts glucose into glycogen, whereas the glucagon converts glycogen into glucose.

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