Homeostasis and Negative Feedback.
Homeostasis: ‘The physiological process by which the internal
systems of the body are maintained at equilibrium, despite
variations in the external conditions’ (Minidictionary for Nurses
2003).
When an imbalance occurs in any cell the automatic and selfregulating mechanism will come into effect to counteract and
rebalance. This process is called negative feedback. Negative
feedback involves the hypothalamus, the pituitary gland, and the
target gland. Negative feedback usually inhibits the release of a
hormone.
Positive feedback works in a similar way to negative feedback
except that the changes made have the effect of inducing further
change to occur. Positive feedback is beneficial (has a positive
effect) in situations such as childbirth where it maintains
contractions of the uterus. However most positive feedback
causes harm, even death, if homeostatic balances remain
disrupted (for example in shock due to severe bleeding). Positive
feedback acts to continue and imbalance rather than stopping or
reversing it. Positive feedback usually promotes the release of
other hormones.
Hypothalamus: Small structure in the brain (approximately the
size of a sugar lump). The hypothalamus works closely with the
pituitary gland to monitor and regulate blood flow, body
temperature, food intake, sleep-wake cycle, water-salt balance
and the activity of hormones.
Pituitary Gland. This is known as the ‘Master Gland’ because it
controls all the other endocrine glands.
Endocrine glands are the organs of the endocrine system.
Endocrine glands secrete hormones directly into the bloodstream,
(rather than a duct or tube), and are involved with many body
functions such as sexual reproduction, growth and metabolism.
Endocrine glands include; Pituitary gland, thyroid gland,
parathyroid glands (4), adrenal glands (2), pancreas and gonads.
Negative Feedback and Regulation of Blood Glucose.
 Carbohydrate is taken into the body.
 Carbohydrates are broken down into glucose to be absorbed
into the blood via the capillaries of the villi in the small
intestine.
 Glucose is transported by the blood to the liver.
The Liver.
 The liver has many functions that require a lot of energy.
Glucose is required for energy production.
 Some glucose remains in the circulating blood. Normal blood
glucose levels are around 4-7millimoles per litre (mmol/L).
 Glucose not required for immediate use is converted into
glycogen for storage in the liver and muscles.
 When blood glucose and glycogen levels are within normal
limits, any left over glucose is converted into fat and stored
under the skin in fat depots.
 Insulin is necessary for glucose to be converted into glycogen.
 When carbohydrates are taken into the body, unless they are
broken down and used or stored appropriately we would have
excess glucose in our blood.
 Normal metabolism of carbohydrates require insulin.
 Insulin is a hormone that is secreted by Beta Cells in the Islets
of Langerhans in the pancreas.
 Hormones are chemicals that are released straight into the
blood so they can create a quick response.
 Insulin allows the liver to convert glucose into glycogen for
storage, therefore maintain blood glucose within its normal
levels.
 If insulin levels get too high then the Negative Feedback kicks
in. Alpha Cells within the Islets of Langerhans secrete
glucagon.
 Glucagon inhibits the action of insulin and causes the liver to
convert glycogen back to glucose, thus the levels of blood
glucose remain within normal limits (4-9mm/1ltr).
 Somatostatin, (in Delta cells), are also found in the Islets of
Langerhans. Delta cells regulate the production of insulin and
glucagon.