OCR A2 Biology F214 - Hormones

Everything you need to know about hormone control. Let me know if anything needs either editing or adding in. Thank you!

HideShow resource information
Preview of OCR A2 Biology F214 - Hormones

First 522 words of the document:

Hormonal Control
Stimulus ­ Any change in the environment of an organism that causes a response.
Response ­ The reaction to a stimulus, causing a change in behaviour our physiology.
External Environment ­ Consists of air, water and soil.
Internal Environment ­ Internal cells are bathed in tissue fluid. Metabolic activities use up substances &
produce products that diffuse out into the tissue fluid. Cells alter their own environment.
Cell Signalling ­ How cells communicate. One cell releases a signal that is detected by another, the second cell
responds to the signal released by the first.
Neuronal System ­ An interconnected network of neurons that signal to each other across synapse junctions.
The neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing
Hormonal System ­ Uses blood to transport the signals. Cells in an endocrine organ release the signal (a
hormone) directly into the blood. It is carried all over the body but is only recognised by specific target cells.
The hormonal system longer-term responses to be coordinated.
Negative Feedback ­ The reversal of a change in the internet environment to a steady state or optimum
Positive Feedback ­ Processes that increase any change detected by receptors. This tends to be harmful &
doesn't lead to homeostasis.
Endotherm ­ An organism that can use internal sources of heat, such as heat that is generated from
metabolism in the liver.
Ectotherm ­ An organism that relies on external sources of heat to regulate its body temperature.
Hormone ­ Small protein or lipid molecule which travels through the blood plasma to a specific target cell. E.g.
protein is adrenaline and insulin, lipid is testosterone and oestrogen.
Target Tissue ­ Tissue that is affected by a hormone.
Endocrine Gland ­ Secretes hormones directly into the blood capillaries (duct-less).
Exocrine Gland ­ Secretes substances into a duct that carries the molecules to where they need to be (Duct).
First messenger ­ Is the hormone which binds to the receptor of the target cell e.g. adrenaline.
Second messenger ­ Is activated inside the target cell and can activate enzymes e.g. cAMP.
To keep cells alive and working efficiently, conditions need to be kept constant:
A suitable temperature
A suitable pH
An aqueous environment that keeps the substrates and products in solution
Freedom from toxins and excess inhibitors
A good communication system will be able to:
Cover the whole body
Enable cells to communicate with each other
Enable specific cell communication
Enable rapid communication
Enable both long-term and short-term responses.
Cell Signalling
Cells communicate with each other by the process of cell signalling. There are two major systems of
communication that work by cell signalling: Neuronal and Hormonal System.
Homeostasis - Keeping a constant internet environment despite the external changes.
These include regulating:
Body temperature
Blood glucose concentration
Blood salt concentration
Water potential of the blood
Blood pressure
Carbon Dioxide

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Negative Feedback
In order to maintain a constant internal environment a number of processes must occur.
Any change to the internal environment must be detected.
The change must be signalled to other cells.
There must be a response that reverses the change.
The reversal of a change in the internal environment to return to a steady state or optimum position is known
as Negative Feedback.…read more

Page 3

Preview of page 3

Here's a taster:

What are hormones?
There are two types of hormones ­
Protein and peptide hormones, and derivatives of amino acids (for example adrenaline, insulin and glucagon).
These are not soluble in the phospholipid membrane and do not enter the cell.
Steroid Hormones (for example sex hormones). They can pass through the membrane and actually enter the
cell to have a direct effect on the DNA in the nucleus.
Endocrine glands ­ Hormones are released directly into the blood from endocrine glands.…read more

Page 4

Preview of page 4

Here's a taster:

The pancreas ­ both an exocrine and endocrine gland
The majority of cells in the pancreas manufacture and release digestive enzymes. This is the exocrine function
of the pancreas. The cells are found in small groups surrounding tiny tubules into which they secrete digestive
enzymes. The tubules join to make up the pancreatic duct which carries the fluid containing the enzymes into
the first part of the small intestine.…read more

Page 5

Preview of page 5

Here's a taster:

Insulin is secreted when blood glucose levels rise above 120 mg per 100 cm3,
A high blood glucose concentration is detected by cells, which in response secrete insulin into
the blood. The target cells are the liver cells or hepatocytes, muscle cells and some other body cells
including those in the brain. These possess the specific membrane-bound receptors for insulin. When
the blood passes these cells the insulin binds to the receptors.…read more

Page 6

Preview of page 6

Here's a taster:

Diabetes mellitus
Blood glucose levels never remain constant. After a meal the concentration will rise and during exercise the
concentration will fall. However, using a negative feedback mechanism the body is able to keep control over
the blood concentration fairly well within controlled limits.
Diabetes mellitus is a disease in which the body is no longer able to control its blood glucose concentration.
This can lead to very high concentrations (hyperglycaemia), but it can also lead the concentration to drop too
low (hypoglycaemia).…read more

Page 7

Preview of page 7

Here's a taster:

The heart is supplied by nerves from the medulla oblongata of the brain. These nerves connect to the
SAN. These do not initiate a contraction, but they can affect the frequency of the contractions. Action
potentials sent down the accelerator nerve increase the heart rate. Action potentials send down the
vagus nerve reduces the heart rate.
The heart muscle responds to the presence of the hormone adrenaline in the blood.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »