Hormonal Communication Flashcards
What are the limitations
They can only control the organ to which they are attached and they have a difficult time maintaining actions for a long period of time. Although a continuous series of impulses could, in theory, be sent down a nerve, this would be a huge drain on ATP supplies in the neurone and so is not feasible in practice.
How is the transmission of hormones different to neurones
It lasts longer (minutes rather than seconds).
Is chemical rather than electrical
Via the blood system rather than via nerves
Since blood travels to all parts of the body, so a hormone in the blood can reach and affect all organs and tissues.
How does the hormone affect the organs or tissues (its target tissues)
Hormones are chemical messengers which are endocrine glands and are carried through the blood. The cell membranes of the target cells have hormone-specific receptors. The hormone binds to these receptors and stimulate a series of events which ultimately creates a response.
What type of hormone is Adrenaline
The fight or flight hormone
This hormone is produced at times of stress or excitement. It affects many organs and helps the body respond to emergency situations.
What can hormones be made of
Many are proteins (e.g insulin,growth hormone) but some are steroids (e.g testosterone, oestradiol). Adrenaline is a catecholamine. Many hormones are peptides, e.g ADH.
Adrenal glands
The two adrenal glands are situated above the kidneys. The adrenal glands consist of two areas: a central medulla and an outer cortisol, which have a variety of functions but are mainly concerned with the control of concentrations of mineral ions, carbohydrates and proteins. The medulla produces adrenaline.
First and second messenger
When a hormone affects a cell, there are messengers involved. The first messenger is the hormone itself, which ‘brings’ the message to the cell from an endocrine gland in a different location from the target tissue. The hormone does not enter the cell, it just binds to a receptor on its surface membrane. A second messenger inside the cell then brings about some effect.
What does the second messenger do when the first messenger in adrenaline
The adrenaline binds to a specific receptor in the membrane, the adrenergic receptor.
This binding activates a G-protein complex inside the cell, which contains guanosine diphosphate (or GDP).
The GDP is converted to guanosine triphosphate (GTP).
The GTP activates a membrane enzyme adenylyl cyclase, which converts ATP to cyclic adenosine monophosphate (cyclic AMP, or cAMP).
The cAMP starts a cascade of reactions that result in the desired effect within that cell
The cAMP is the second messenger
Structure of the pancreas
This is found in the abdomen of mammals and it functions as both an endocrine and exocrine gland. Endocrine glands secrete hormones directly into the blood, whereas exocrine glands secrete substances through a duct. The exocrine function in the pancreas is the production of pancreatic juice that is delivered to the small intestine where the enzymes in the juice act to digest food. Within the organ, the exocrine and endocrine functions are performed by different tissues, which can be clearly seen in microscope sections. Most of the pancreatic cells are responsible for the secretion of digestive enzymes, but throughout the organ there small groups of cells called Islet of Langerhans that are responsible for hormone production. The islets contain two types of cell, the alpha cells, which secrete glucagon, and beta cells, which secrete insulin. The alpha cells are larger but less numerous than the beta cells.
