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Unit 9 Homeostasis
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- PEARSON (PEARSON)
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Homeostatic control of body systemsHormones are chemical messengers. They are produced in organs called hormone-producing (endocrine)
glands. These glands are hormone-producing cells that have accumulated around blood vessels. The
hormones are secreted directly into the bloodstream and not through duct systems, which is common for
other types of glands. Together with the nervous system, the hormones coordinate and control the
function of many of the body's various tissues and organs, so that they work together in an appropriate,
effective, and correct way.
When a hormone is released into the bloodstream, it circulates to all parts of the body, but it only works
on certain parts of the body. These parts are called target organs. The amount of hormone that is secreted
into the bloodstream is determined based on the needs of the body at the time. The levels of hormones in
the blood change because of e.g., infection, stressful situations, and changes in the chemical composition
of the blood. Homeostasis is also responsible for the normal blood pressure in the body. If it is violated,
there will be signals of this from the heart to the brain. The brain responds to the problem and uses
impulses to help the heart lower high blood pressure.
In some cases, the level of one hormone in the blood regulates the level of another hormone. As an
example, the pituitary gland regulates the number of hormones that are produced by other endocrine
glands, the thyroid gland, adrenal glands, testicles, and ovaries. What we need to keep in mind is that
homeostasis is the set of processes that take place in our body and that enables us to maintain a dynamic
balance depending on external conditions. All of these processes are essential to life.
The pituitary gland is a gland the size of a pea that sits on the underside of the brain, just behind the
eyes. The pituitary gland plays a vital role in the coordination of the various endocrine glands, but is
controlled by the hypothalamus, which is located just above the pituitary gland. The hypothalamus
registers the number of hormones in the blood, and it picks up signals which cause adjustments in the
production of hormones. It sends messages to the pituitary gland to alter the secretion of hormones that
control the other endocrine glands in the body.
The pancreas as a hormone-producing gland
Glucose is a form of sugar that is found in several types of food. Glucose is used for energy in the body
cells. Insulin stimulates the cells to absorb enough glucose from the blood so that the cells get the
required amount of energy. The stored glucose is called glycogen. Glycogen is broken down again into
glucose as it is needed e.g., at night or in connection with fasting. While this is happening. The pancreas
will be responsible for lowering or higher blood sugar levels. It does it through the endocrine part.
The endocrine part consists of small cell groups located in the exocrine tissue. These accumulations of
cells are called islets of Langerhans and can consist of anything from a few to several hundred cells. In it
endocrine tissues exist in a total of five different cell types: alpha cells, beta cells each having its own
function.
The most important hormones in this context are glucagon and insulin. Insulin is a small protein
molecule, which plays a crucial role in several metabolic processes. Insulin increases those anabolic
processes in the liver, muscles, and adipose tissue by stimulating the formation of protein, glycogen, and
fatty acids. However, the main function of insulin is to ensure that glucose can be transported through cell
membranes in fat and muscle cells so that the body's cells can get energy. Glucagon is a small polypeptide
that works in many ways as opposed to insulin. Glucagon binds to a receptor on the liver cells. The
binding causes degradation of glycogen to glucose, which is released into the blood, thereby raising blood
, sugar. Somatostatin is excreted by stimulation from i.a. high blood sugar and acts in the pancreas by
inhibiting excretion from the alpha, beta and gamma cells.
Osmoregulation is the process in an organism that is about maintaining a certain osmotic pressure in the
body fluids, regardless of changes in the water and salt content of the food, evaporation of water through
the skin and lungs, sweating and so on. This form of equilibrium is achieved by a regulation of the water
and salts excreted via the kidneys. Kidney function is regulated by nerve centers in the midbrain. From
here, hormones are secreted that affect the kidneys directly and indirectly via the adrenal glands.
Tonicity is the measure of pressure. There will not be any osmotic reaction if the concentration on both
sides of the membrane is the same. The solutions are isotonic in relation to each other. There is usually an
imbalance between solutions between inside and outside the membrane. If you are unclear about osmotic
pressure and tonicity, it may be because you are confused about the difference between diffusion and
osmosis. Potassium plays a crucial role in maintaining the cell's osmotic concentration. Potassium is
necessary for normal nerve, muscle and kidney function.
It has been shown that variations of one percent in the water content of the blood are registered by the
nerve cells in the mentioned area in the midbrain. Upon stimulation, i.e., at elevated salt concentration,
the pituitary gland secretes the so-called antidiuretic hormone (ADH). ADH is produced in the
hypothalamus and reduces the excretion of water (diuresis) through the kidneys. With increased excretion
of ADH, the water excretion is thus counteracted.
Consequently, the blood is not concentrated beyond a certain limit, instead less urine is produced. When
the osmotic pressure in the blood decreases, the production of ADH decreases, and water excretion via
the kidneys increases again.
Nephron, functional unit of the kidneys, is the structure that produces urine in the process of removing
waste and excess substances from the blood. There are about 1,000,000 nephrons in each human kidney.
Minerals
Sodium, potassium and chloride are called electrolytes, and the concentration and balance of these
minerals play a crucial role in regulating fluid balance. The use of feeds that have a high content of
electrolytes or a skewed relationship between them is important. This is not only because these
electrolytes are important for nerve and muscle functions, acid balance and pH in the stomach, but also
because they control the fluid balance in the body.
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