The human endocrine system

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High school biology

Course: High school biology > Unit 8

The nervous and endocrine systems review

Key terms

Term Meaning
Nervous system The body system that collects, processes, and responds to information using electrical signals
Neuron A nerve cell; the basic unit of the nervous system
Glial cell A cell that supports and protects neurons
Central nervous system Part of the nervous system containing the brain and spinal cord
Peripheral nervous system Part of the nervous system containing associated nerves that are not part of the brain or spinal cord
Endocrine system The body system that regulates cells and organs using chemical substances called hormones
Hormone Chemical messenger that acts as a regulatory substance
Gland Organ that secretes chemical substances, such as hormones

The nervous system

The nervous system uses electrical impulses to collect, process and respond to information about the environment.

Nervous system cells

The unique structure of neurons makes them specialized for receiving and transmitting electrical impulses throughout the body. Neurons are supported by glial cells, which surround, protect, and insulate them.

All neurons have several features in common, including a cell body, dendrites, and an axon. These structures are important for transmitting neural impulses, electrical signals that allow neurons to communicate with one another.

  • Sensory neurons carry impulses from sense organs, such as the eyes or ears.
  • Motor neurons carry impulses to muscles and glands.
  • Interneurons transfer signals between sensory and motor neurons, as well as in between other interneurons.

In a resting neuron, there is a separation of ions in the cell regulated by sodium-potassium pumps. If a neuron receives a large enough signal, the resting potential changes, producing an electrical impulse called an action potential. Once an impulse begins, it moves down the axon until it reaches the axon terminal.

Parts of the nervous system

The nervous system is made up of two parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

The CNS is made of the brain and spinal cord. Commands to the body originate in the brain and the spinal cord connects the brain with the rest of the nerves in the body.

  • The somatic nervous system (SNS) regulates voluntary activities such as muscular movement. It also controls reflexes, such as pulling your hand away from the hot surface of a stove.
  • The autonomic nervous system (ANS) regulates activities that are not under conscious control and has two divisions that are opposite of one another: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system prepares the body for “fight-or-flight” responses, while the parasympathetic nervous system is active during restful periods.

The endocrine system

Like the nervous system, the endocrine system is a regulatory system. However, instead of using electrical impulses for signaling, it produces and uses chemical signals called hormones, which travel through the bloodstream and control the actions of cells and organs.

Common hormones and glands

Hormone Gland produced in Role
Thyroid hormone Thyroid Regulates metabolism
Adrenaline (epinephrine) Adrenal gland Involved in “fight or flight” response
Cortisol Adrenal gland Involved in “fight or flight” response, regulates metabolism and immune responses
Estrogen Ovaries Sexual and reproductive development, mainly in women
Testosterone Testes, sometimes adrenal glands or ovaries Sexual and reproductive development, mainly in men
Insulin Pancreas Blood sugar regulation, fat storage
Glucagon Pancreas Blood sugar regulation

Regulation of the endocrine system

The endocrine system is regulated by negative feedback mechanisms that work to maintain homeostasis. The concentration of hormones, and how they effect other body systems, are controlled in this manner.

For example, blood glucose regulation is controlled by insulin and glucagon, hormones produced by the pancreas.

When blood glucose increases, the pancreas releases insulin, which stimulates the uptake of glucose from the blood. This prevents blood glucose from getting too high.

When blood glucose concentration drops, the pancreas releases glucagon, which stimulates the breakdown of glycogen and releases glucose into the blood. This raises blood glucose back to normal levels.

Negative feedback loop of blood glucose. As blood glucose increases, insulin is released, causing the blood glucose to drop.

Blood glucose is regulated by a negative feedback loop between insulin and glucagon, two opposing hormones made by the endocrine system.

Common mistakes and misconceptions

  • While neurons are often the most recognized nervous system cell, they are not the only ones! In fact, glial cells outnumber neurons by almost 10 times. Glial cells (also known as neuroglia) support the neurons, guiding and protecting them, and provide myelin sheaths around their axons.

Hormones are not just part of the reproductive system. Although there are reproductive hormones, such as testosterone and estrogen, most hormones are not involved in or regulated by the reproductive system. Many hormones control regular body functions, such as hunger or sleepiness.

Although both the endocrine system and the nervous system are both regulatory, there are a few fundamental differences. For one, the endocrine system uses chemical signaling (hormones, produced by glands) while the nervous system uses electrical signaling (neural impulses). The signal transmission of the nervous system is fast because neurons are interconnected, but the functions are more short-lived. Signal transmission in the endocrine system is slow, since hormones must travel through the bloodstream, but the responses tend to last longer.

Want to join the conversation?

Glial cells surround neurons. For example, Schwann cells are wrapped around the axon. They insulate the axon, allowing more efficient transmission of the electrical impulse. I assume that other glial cells can surround the neuron in different places; in the picture of types of neuroglia, the satellite cells appear to be surrounding the surface of the soma (cell body). Hope that helps you!

Common mistake and misconception: Glial cells are 10* more numerous than neurons. This is incorrect.

Azevedo, F. A., Carvalho, L. R. B., Grinberg, L. T., Farfel, J. M., Ferretti, R. E. L., Leite,
R. E. P. et al. (2009). Equal numbers of neuronal and nonneuronal cells make the
human brain an isometrically scaled-up primate brain. Journal of Comparative
Neurology, 513, 532–541.

its a lock and key structure. The substrate which binds with enzyme is key and enzyme is the lock and it has a special site called active site, whats where the substrate binds to it and activates it. the specific substrate attaches with specific active site.

I believe if that were the case, then our nervous system will work just fine while the endocrine system will not. We would receive signals thanks to our receptors and the signals would travel via our neurones to reach our brain, but if the nervous system stopped working with the endocrine system, then glands won’t be triggered. So the endocrine system is essentially dormant, thus you would only see the effects of your nervous system.
This would be detrimental to the body as hormones help with homeostasis as they help to regulate metabolic rates (TRH, TSH, Thyroxine) and regulate water levels (ADH) etc. Without hormones, our bodies will spiral out of control, resulting in complications such as death

The endocrine system is linked to the nervous system by effects of the hypothalamus on the pituitary gland, as seen in the adjacent image.
The pituitary gland is known as the ‘master gland’ because its secretions control the activity of other endocrine glands. The activity of the pituitary gland is however controlled by the hypothalamus which as well as being an endocrine gland, is also part of the nervous system.
Along with the nervous system, the endocrine system coordinates the body’s functions to maintain homeostasis during rest and exercise. The nervous and endocrine systems also work together to initiate and control movement, and all the physiological processes movement involves.
Where the nervous system acts quickly (virtually instantly) delivering messages by nerve impulses, the endocrine system has a slower but longer lasting response which compliments the nervous system. The endocrine system regulates growth, development and reproduction and augments the body’s capacity for handling physical and psychological stress.