5.4.1 The Endocrine System Flashcards
What are homeostatic mechanisms?
Homeostatic mechanisms help organisms to keep their internal body conditions near constant
Three key homeostatic mechanisms are:
Thermoregulation – the control of body temperature
Osmoregulation – the control of the water potential of body fluids
The control of blood glucose concentration
These homeostatic mechanisms in mammals require information to be transferred between different parts of the body
One of the coordination systems in mammals that does this is the endocrine system
What is the endocrine system?
A hormone is a chemical messenger produced by an endocrine gland and carried by the blood
They are chemicals which transmit information from one part of the organism to another and bring about a change
They alter the activity of one or more specific target organs
Hormones are used to control functions that do not need instant responses
The endocrine glands that produce hormones in animals are known collectively as the endocrine system
A gland is a group of cells that produces and releases one or more substances (a process known as secretion)
Endocrine glands have a good blood supply as when they make hormones they secrete them directly into the bloodstream (specifically the blood plasma)
The hormones are then transported around the body via the blood to target cells/tissues to bring about a response
Hormones come into contact with a lot of different cells in the body but they only affect cells with receptors that the hormone can bind to
These are either found on the cell surface membrane
Receptors have to be complementary to hormones for there to be an effect
What is a first messenger?
The first messenger is the hormone that brings the “information or signal” from the endocrine gland
Hormones don’t actually enter the cell, they bind to a receptor on the cell surface membrane
What is a second messenger
A second messenger inside the cell causes the effect
What is the mode of action for the hormone adrenaline?
Adrenaline binds to specific receptors on the membrane of liver cells
This causes the enzyme adenylyl cyclase to change shape and become activated
Activated adenylyl cyclase catalyses the conversion of ATP to the second messenger molecule cyclic AMP (cAMP)
cAMP binds to protein kinase A enzymes, activating them
Active protein kinase A enzymes initiate a series of enzyme activations that result in the breakdown of glycogen to glucose; this process is known as glycogenolysis
The enzyme cascade described above amplifies the original signal from adrenaline and results in the release of extra glucose by the liver to increase the blood glucose concentration
What are the differences between the endocrine system and the nervous system?
Nervous System:
- Brain, Spinal Cord, nerves/neurones
- Is an electrical Impulse
- Effectors are muscles or glands
- Very fast transmission
- Short effect until electrical impulses stop
Endocrine System:
- Glands
- Is a chemical hormone
- Transmitted through the bloodstream
- Target cells are in specific tissues
Slower transmission
- Longer effect until hormone is broken down
What are adrenal glands?
Situated above each kidney is a gland known as the adrenal gland
Adrenal glands are an example of endocrine glands
Both adrenal glands have the same structure and function, consisting of two main areas: a central medulla and an outer cortex
The cortex produces steroid hormones:
Aldosterone regulates levels of salts (sodium and potassium) and the water balance in the blood, this has an impact on blood volume and pressure
Cortisol is the primary stress hormone which regulates metabolism of glucose, proteins and fats to release usable energy
The medulla produces adrenaline, a hormone produced at times of stress or excitement that affects many body organs, preparing the body to respond to emergency situations
Adrenaline initiates the “fight or flight” response in the body
