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How is coordination achieved through the activities of the nervous system and the endocrine system?

•Nervous system - exerts control by the transmission of nerve impulses to and from the various tissues.

•Endocrine system - influences the activity of cells by the release of chemical messengers. (Hormones)


Define Homeostasis.

Homeostasis is the maintenance of a constant internal environment.


Homeostasis ensures that the fluid environment of the cells:

•contains the optimum concentration of nutrients, ions, gases and waters

•stays at a constant temperature - the optimum temperature for normal cell functioning

•is maintained at the optimum pressure


Is the maintenance of this steady state completely constant?

No, instead, there is a dynamic equilibrium in which the input and output of materials and energy are balanced.


What allows the maintenance of homeostasis to take place?

To compensate for those changes, the body must be able to both sense changes in the internal and external environment.

The nervous and endocrine systems are the main sensory and controlling body systems and, in the case of homeostasis, they operate through feedback systems, many of which involve negative feedback.


What is a feedback system?

A feedback system is a circular situation in which the body responds to a change, or stimulus, with the response altering the original stimulus.


What happens during a negative feedback system?

The response causes the stimulus, or variable, to change in a direction opposite to that of the original change.


Example of a negative feedback system.

1. Blood glucose level falling
2. Liver releases glucose into blood
3. Blood glucose level rising
4. Liver absorbs glucose from blood


Negative feedback systems are also known as?

Steady state control systems.


What are common features of cycles involved in Negative Feedback System?

•Stimulus - change in the environment that causes the system to operate.

•Receptor - detects change

•Modulator - a control centre responsible for processing information received from the receptor and for sending information to the effector.

•Effector - carries out a response counteracting the effect of the stimulus.

•Feedback - achieved because the original stimulus has been changed by the response.


What is the role of Exocrine glands?

They secrete into a duct that carries the secretion to the body surface or to one of the body cavities.

Eg. Sweat glands, mucous glands, salivary glands and the glands of the alimentary canal


What is the role of Endocrine glands?

They secrete hormones into the extracellular fluid that surrounds the cells that make up the gland. The secretion then usually passes into the capillaries to be transported by the blood. Endocrine glands are sometimes called ductless glands.


What are Hormones?

Hormones may be proteins, steroids or amines. They are transported throughout the body in the blood. A hormone may affect all the cells of the body or only particular groups of cells, target cells, or particular organs, target organs.


How do cells communicate?

Cells may communicate with other cells in the same tissue by secreting chemicals that diffuse to adjacent cells.


What are Paracrines?

They are sometimes know as local hormones. Paracrines are secreted by all cells in a particular tissue and move through the extracellular fluid. Hormones, however, are secreted only by specialized cells that are transported by the bloodstream.


How are hormones specific?

Hormones are only able to influence cells that have the correct receptor for the hormone. Saturation can also occur, once all receptor molecules are occupied by hormone molecules, the addition of more hormones does not produce any greater effect. (Same with protein receptors)


How do protein and amine hormones work?

They attach to receptor molecules on the membrane of the target cell. The combination if the hormone with the receptor causes a secondary messenger substance to diffuse through the cell and activate particular enzymes.


How do Steroid hormones work?

They enter target cells and combine with a receptor protein inside the cell. The receptor may be on the mitochondria, on other organelles or in the nucleus.


What does the hormone-receptor complex do?

They activate the genes controlling the formation of particular proteins.


How do hormones change the functioning of cells?

They change the type, activities or quantities of proteins produced. They are not enzymes, but in changing the activity of enzymes or by changing the concentration of enzymes.


Hormones may:

•activate certain genes in the nucleus so that a particular enzyme or structural protein is produced.

•change the shape or structure of an enzyme so that it is turned 'on' or 'off'.

•change the rate of production of an enzyme or structural protein by changing the rate of transcription or translation during protein production.


What is enzyme amplification ?

The process of activating thousands of enzyme molecules through just one hormone.

One hormone molecule could trigger the production of more than a billion enzyme molecules. Thus, a very small stimulus can produce a very large effect.


How does Enzyme Amplification work?

The hormone triggers a cascading effect in which the number of reacting molecules involved is increased hundreds or thousands of times for each step along the metabolic pathway.


How does hormone clearance work?

Hormones are broken down. Some
are broken down in the target cells but most are broken down in the liver and kidneys. The degraded hormones are then excreted either in the bike or in the urine.


What regulates hormonal secretions?

Generally Negative feedback systems.


How is the hypothalamus involved in hormonal secretions?

Some negative feedback systems involve the nervous system as it requires the release of regulating factors from the hypothalamus of the brain.


What regulates the function or the pituitary gland?

The regulating factors that are release from the hypothalamus.


What is the main role of hypothalamus in hormonal secretion?

The hypothalamus can secrete releasing factors, which stimulate the release of a hormone, or inhibiting factors, which slow down the secretion of a hormone.


Where is the hypothalamus located?

The hypothalamus is located at the base of the brain.


Why is the hypothalamus so important?

This organ regulates many of the basic functions of the body, such as body temperature, water balance and heart rate. Many of its functions are carried out through the pituitary gland.


Where is the pituitary gland located?

•The pituitary gland or hypophysis lies just under the hypothalamus and is joined go the hypothalamus by a stalk called the infundibulum. It is not much bigger than a large pea, about 13 mm in diameter, but it is absolutely vital to the normal functioning of the body.


Describe the structure of the pituitary gland.

The pituitary consists of an anterior love and a posterior lobe, each of which functions separately.


Describe the anterior (front) lobe.

It has no nerves connecting it to the hypothalamus but it is connected to it by a complex network of blood vessels.


Describe the posterior (rear) lobe.

It is not a true gland because it does not secrete substances. It is joined to the hypothalamus by nerve fibers that come from nerve cell bodies in the hypothalamus and pass through the infundibulum to the posterior lobe.


How are hormones transported from the hypothalamus ?

The hypothalamus produces many different hormones. Some of them are carried by the blood to the anterior lobe of the pituitary where they stimulate or inhibit the release of hormones made in the anterior lobe. Other hormones pass along the nerve fibres from the hypothalamus to the posterior lobe of the pituitary where they are then secreted.


Why is the pituitary gland referred to the as the "Master Gland"?

This is because many pituitary hormones regulate the activity of the endocrine glands.


What's another than do the anterior lobe of the pituitary?



What controls the secretions of the anterior lobe?

They are controlled by releasing and inhibiting factors secreted by the hypothalamus.


How are the secretions of the hypothalamus considered to be hormones?

They are secreted into the extracellular fluid around the cells of the hypothalamus and are carried by the blood to the anterior lobe of the pituitary gland.


What hormones are released by the anterior lobe of the pituitary?

• Gonadotropins
• Follicle Stimulating Hormones (FSH)
• Luteinising Hormone (LH)
• Growth hormone (GH)
• Thyroid Stimulating Hormone (TSH)
• Adrenocorticotropic Hormone (ACTH)
• Prolactin ( PRL)


Explain the function of Gonadotropins.

The affect the gonads, the ovaries and development of the testes.


What is the functions of Follicle Stimulating Hormones (FSH)?

•In the ovary of the female it stimulates the development of the follicles that contain eggs.

•In the males, FSH stimulates the production and maturation of sperm in the testes.


Explain the function of the Luteinising hormone.

•LH, which is another gonadotropin that works with FSH in the female to bring about ovulation and to form a structure called the corpus luteum after ovulation.

•In the male, LH stimulates interstitial cells in the testes to secrete male sex hormones.


Explain the function of the Growth Hormone.

•AKA somatotropin, which stimulates body growth, particularly growth of the skeleton.

•It increases the rate at which amino acids are taken up by cells and built into proteins.

•GH is secreted throughout life as it helps to maintain the size of organs once maturity is reached.


Explain the function of Thyroid Stimulating Hormone (TSH).

Aka thyrotropin, it stimulates production and release of hormones from the thyroid gland.


Explain the function of the Adrenocorticotropic hormone (ACTH).

Aka Adrenocorticotropin, it controls the production and release of some of the hormones from the cortex of the adrenal glands.


Explain the function or the Prolactin (PRL).

Aka lactogenic hormone, it works with other hormones to initiate and maintain milk secretion in females.


Explain the function if the posterior lobe of the pituitary.

Aka neurohypophysis, releases the hormones oxytocin and antidiuretic hormone, but neither is manufactured in the posterior lobe.


Where are the hormones oxytocin and antidiuretic hormone produced?

Both hormones are produced in special nerve cells in the hypothalamus of the brain. These cells have long extensions that pass through the infundibulum to the posterior lobe.


How does the hormones manufactured in the special cells transported? (Posterior lobe of the pituitary gland)

They move down the extensions and are stored trash for release into the bloodstream. The release of the hormones is triggered by nerve impulses intimated in the hypothalamus and conducted along the cell extensions.


Explain the told of Oxytocin (OT).

It is a hormone that stimulates contraction of the muscles of the uterus. It is released in large quantities during labour. It also stimulates contraction of cells in the mammary glands, resulting in release if milk during breast feeding.


Explain the role of the Antidiuretic hormone (ADH).

Aka vasopressin, it causes the kidneys to remove water from urine that is forming. This water is returned do the bloodstream.

Therefore ADH helps to retain fluid within the body. At higher concentrations, ADH can also cause constriction of small arteries, the arteriole a (giving rise to the alternative name, vasopressin).


What is the Mystery Gland?

Pineal Gland, found deep inside the brain and in children is about the size if a pea. After about the age of seven the gland begins to shrink and by adulthood it is just a tiny lump of fibrous tissue. It does secrete hormones but it's role remains a mystery.


Describe the location of the thyroid gland.

The thyroid gland is located in the neck, just behind the larynx. It consists of two lives that lie on either side of the trachea and are joined by a narrow piece of tissue that lies across the front of the trachea.


What is the main hormone secreted by the thyroid gland?

The thyroxine, it is made from iodine and an amino acid and is continuously manufactured in the thyroid gland.


What is the main role of the Thyroxine?

It controls body metabolism by regulating reactions in which complex molecules are broken down to release energy, and other reactions in which complex molecules are synthesized from simple ones.


What is the overall effect of Thyroxine?

Is to bring about the release of energy and, since some of the energy released is in the form of heat, to maintain body temperature.


When is thyroxine secreted?

Thyroxine is secreted in response to thyroid stimulating hormone from the anterior lobe of the pituitary.


How many parathyroid glands do we have?

There are 4 parathyroid glands, although some people have none. Each is about the size of a small pea and they are embedded in the rear surface of the lobes of the thyroid gland.


What hormones does the Parathyroid glands secrete?

They secrete parathyroid hormones (DUH....) (PTH of parathormone) which controls calcium and phosphate levels in the blood.


Where is the thymus located?

It is located in the chest just above the heart and just behind the sternum (breastbone).


Explain the main function so the Thymjs.

It secretes a group of hormones called thymosins, these hormones influence the maturation of disease-fighting cells called T lymphocyes.

Like the pineal gland, the humus is largest in infants and children but begins to shrink after puberty.


Describe the structure of the Adrenal Glands.

There are 2, one immediately above each kidney. Each adrenal gland has an inner a adrenal medulla and an outer adrenal cortex. These 2 parts are quite different in their structure and function. Thus, each adrenal gland is really two separate endocrine glands.


What hormones are produced by the Adrenal Medulla?

•Adrenaline (epinephrine)
•Nonadrenaline ( norephine)


Explain the function of the Adrenaline.

Adrenaline, also called epinephrine, had an effect similar to that of the sympathetic division of the autonomic nervous system. It helps to prepare the body for reaction to a threatening situation; that is, it is concerned with fight-or-flight responses.


Explain the function of the Nonadrenaline hormone.

It has effects similar to those of adrenaline. In particular, it increases the rate and force of the heartbeat.


What hormones are produced by the Adrenal Cortex.

More than 20 different hormones are produced in the adrenal cortex and they are known collectively as corticosteroids. The two main ones are:

• aldosterone
• cortisol


Explain the function of the Aldosterone.

It acts on the kidney to reduce the amount of sodium and increase the amount of potassium in the urine.


Explain the role of the cortisol.

With related hormones, it promotes normal metabolism, helping the body to withstand stress, and also helps with repair of damaged tissues.


Where is the pancreas located?

The pancreas lies just below the stomach alongside the duodenum, the first part of the small intestine.


What type of glands does the Pancreas act as?

It is both an exocrine gland and endocrine gland.


Explain the role of these glands. (pancreas)

The exocrine part secretes digestive enzymes into the small intestine through the pancreatic duct. Within the pancreas are clusters of special cells called islets of Langerhans. The islets are the endocrine part of the pancreas and they secrete two important hormones.


What two important hormones does the islet (endocrine part) secrete?



Explain the function of insulin.

Reduces the amount of glucose in the blood, that is the blood sugar level. A reduction in blood sugar is achieved by promoting the uptake of glucose from the blood by the cells of the body.

The level of secretion of insulin from the pancreas is determined by the amount of sugar in the blood and is controlled through a negative feedback system.

•Liver - causes the conversion of glucose to glycogen and fat.

• Fat storage tissues - causes glucose to be converted into fat.


Explain the role of Glucagon.

It acts in the opposite way to insulin. It works to increase the blood sugar level, mainly by promoting the breakdown of glycogen to glucose in the liver. Glucagon also stimulates the breakdown of fat in the liver and in fat storage tissues.


What are the gonads?

They are the testes and ovaries. They produce hormones as well as sperm and eggs.


Explain the function of Androgens.

They are the male sex hormones produced by the tested. These hormones are responsible for the development and maintenance of the male sex characteristics.


Explain the function of Oesteogens and progesterone.

They are the female sex hormones produced by the ovaries. They stimulate the development and maintenance of the pituitary, they also regulate the menstrual cycle and are involved in changes that occur during pregnancy.


List the other endocrine tissues.

• Stomach and Small Intestine
• Kidneys
• Heart
• Placenta


Explain the function of hormones secreted in the stomach and small intestine.

They both secrete hormones that coordinate the exocrine glands of the digestive system.


Explain the function of hormones secreted in the kidneys.

Hormones secreted include erythropoietin (EPO), a hormone that stimulates production if red blood cells by the bone marrow.


Explain the function of hormones secreted in the heart.

Helps reduce blood pressure.


Explain the function of hormones secreted in the placenta.

Secretes a number of hormones during pregnancy that help to maintain the pregnancy, stimulate development if the foetus and stimulate the mother's mammary glands.