OCR A2 Biology F214 - Hormones

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…

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…

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…

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…

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…

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…

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…