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Control Systems

The Endocrine System : Overview

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Outcomes

Learners will be able to: Compare the effects of the nervous system and the

endocrine system in controlling the body. Describe the functions of hormones Explain the mechanism by which hormones are

regulated Identify the glands of the endocrine system on a

diagram List the hormones produced by each endocrine

gland and describe the effects of each on the body

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Outcomes (continued)

Describe how the hypothalamus controls the anterior and posterior pituitary

Describe the effects of hyposecretion and hypersecretion of various hormones

List the tissues other than the endocrine glands that produce hormones

Explain how the endocrine system responds to stress

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The Endocrine SystemA group of glands that produce regulatory chemicals called hormones.

The endocrine system’s effects occur more

slowly and over a longer period of time than the nervous system and involves chemical stimuli only.

•The Endocrine and nervous systems work together to control and coordinate all other systems of the body

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Hormones are Chemical Messengers Secreted into the Blood from

Endocrine Glands

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• Regulating growth, metabolism, reproduction and behaviour.

• Some hormones can affect many tissues whilst others are very specific in the ‘target tissue’ they affect.

• The cells of these target tissues have ‘receptors’ in their plasma membrane or within their cytoplasm to which the hormone attaches.

Hormones

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Hormones ‘target’ cells with specific receptors

When attached to the cell the hormone affects cells activities by regulating the manufacture of

proteins, changing the permeability of the membrane or by affecting metabolic reactions

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Some Hormones Influence ‘Second Messengers’

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Hormones fall into two main categories

• Amino acid compounds: All hormones except those secreted by the adrenal gland and the sex organs fall into this category.

Most hormones are proteins or related

compounds also made of amino acids.

• Steroids: These hormones are derived from lipids (fats) and are produced by the adrenal cortex and the sex glands.

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Regulation of hormones.

The amount of each hormone that is secreted is normally kept within a specific range.

•Negative feedback is the method used to regulate these levels.

•Hormone release may fall into a rhythmic pattern

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Trophic or Tropic Hormones

These hormones stimulate secretion of other hormones: (e.g., adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to secrete cortisol etc.)

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Non-Tropic Hormones These

hormones have a DIRECT effect upon target cells: e.g. Insulin and Glucagon.

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Hypothalamus & Pituitary (hypophysis) Gland

Hormone release

The hormones produced in the anterior pituitary are not released from the gland until chemical messengers called releasing hormones arrive from the hypothalamus.

Releasing hormones are then sent to anterior pituitary by way of a special type of circulatory system called a portal systemThis circulatory detour means that blood leaving the hypothalamus travels to capillaries in the anterior pituitary before returning to the heartAs the blood circulates through the capillaries it delivers the hormones that stimulate the release of the anterior pituitary secretions.

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Exceptions

ADH and oxytocin are stored in the posterior pituitary.

They are produced in the hypothalamus and stored in the posterior pituitary.

Their release is controlled by nerve impulses that travel over pathways (tracts) between the hypothalamus and the posterior pituitary.

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Thyroid Hormones

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Hormonal Deficiency: Thyroxine Hypothyroidism

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Hormone Excess: Thyroxine Hyperthyroidism

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Hormone Deficiency:Replacement Therapy

e.g. Thyroxine

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Surgical Removal of Thyroid Mass

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The Parathyroid glands

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The Parathyroid glands – calcium metabolism

The parathyroid hormone is one of three substances that regulate calcium metabolism.

The other two are calcitonin (produced by the thyroid gland) and hydroxycholecalciferol (the active form of vitamin D, produced by modification of the vitamin in the liver and then in the kidney)

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Calcium metabolism

• PTH promotes the release of calcium from bone tissue, thus increasing the amount of calcium in the bloodstream. It also causes the kidney to retain calcium.

• Calcitonin lowers the amount of calcium circulating in the bloodstream by promoting the deposit of calcium in bone tissue.

• Hydroxycholecalciferol increases the reabsorption of calcium by the intestine to increase blood calcium levels

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The Adrenal GlandsThe cortex and medulla

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The Pancreas

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Insulin

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Insulin• Insulin is active in the transport of glucose

across the plasma membranes and once inside a cell it is metabolised for energy.

• Insulin also increases the rate at which the liver changes excess glucose into fatty acids which can then be converted to fats and stored as adipose tissue.

• Through these actions insulin has the effect of lowering the level of sugar in the blood.

• Other metabolic effects include the uptake of amino acids into cells and improves the manufacture of these into proteins.

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Typical Effects of Insulin & Glucagon

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Disorders of the Islets

If the Islets fail to produce insulin glucose cannot be taken into the cells cells to produce energy energy.

– glucose remains in the blood and then must be removed and excreted by the kidneys in the urine.

•This condition called diabetes mellitis is the most common endocrine disorder.

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Diabetes Mellitis – two types

• Insulin dependent diabetes mellitus (Type I)

(IDDM) is less common bit more severe.

• Usually appears by the age of 30 and is brought

on by autoimmune (self) destruction of the

insulin-producing cells in the islets.

• People with IDDM need close monitoring of

blood sugar levels and injections of insulin

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Replacement of Hormone Deficiency: Insulin

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Diabetes Mellitis – two types• Non-insulin dependent diabetes mellitus (NIDDM) or type

II diabetes characteristically occurs in overweight adults.

• Insulin is secreted in varying amounts depending upon the severity of the disease but the ability of the body cells to respond to the hormone is diminished.

• This disease can be controlled by diet, oral medication to improve insulin production and increase its effectiveness and for the obese individual weight reduction is required.

• Treatment with injectable insulin may be required during illness or other stress.

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Hormonal Deficiency: InsulinComplications:

• Abnormal fat metabolism

• Damage to arteries

• Damage to peripheral nerves

• Decreased transport of amino acids – weakness, poor tissue repair and reduced resistance to infection.

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Insulin Receptors: Insulin stimulates a Glucose Transporter

Mechanism in the Cell Membrane

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The Sex Glands• The gonads (ovaries of the female and the

testes of the male) produce the sex cells and are also important endocrine organs.

• Hormones are needed in the development of sexual characteristics during puberty

• Once adulthood has been reached hormone output is responsible for maintaining reproductive organs.

• .

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Male sex hormones

• The main male sex hormone or ANDROGEN produced by the male sex glands is TESTOSTERONE

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In the female the hormones that most nearly parallel testosterone in their actions are

ESTROGENS.

Estrogens contribute to the development of female secondary sex characteristics and stimulate the development of the mammary glands, the onset of menstruation and the development and functioning of the reproductive organs.

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The PINEAL glandA small, flattened cone shaped structure located posterior to the midbrain and connected to the roof of the third ventricle.

•Produces the hormone MELATONIN during the dark period of each day and little of this hormone is produced during the daylight hours.

•This pattern of hormone secretion influences the regulation of sleep-wake cycles.

•Melatonin also appears to delay the onset of puberty.

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The THYMUS Gland Lymphoid tissue that lies in the

upper part of the chest above the heart.

Important in the development of immunity.

It’s hormone THYMOSIN assists in the maturation of certain white blood cells known as T cells (T lymphocytes) after they have left the thymus gland and taken up residence in lymph nodes throughout the body

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Other hormone producing tissues

Hormone secretions come from other tissues other than endocrine glands.

•Various substances produced in the body that have regulatory actions either locally or at a distance from where they are produced.

•Many body tissues produce substances that have strong effects in regulating the local environment.

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Some other hormone-producing organs

• Stomach secretes hormone that stimulates digestive activity

• Small intestine produces hormone to stimulate the production of digestive juices and help regulate the digestion process.

• Kidneys produce erythropoietin which stimulates red blood cell production in the bone marrow – produced when there is a decreased supply of oxygen in the blood.

• The atria of the heart produce a substance called atrial natriuretic peptide (ANP) in response to increased filling of the atria and increases loss of sodium by the kidneys and lowers blood pressure.

• The placenta produces several hormones during pregnancy to cause changes in the uterine lining and later in pregnancy help to prepare the breasts for lactation. (pregnancy tests are based upon the presence of placental hormones)

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Scientific Research & Discovery

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Uses of natural and synthetic hormones

• Growth hormone - from recombinant DNA techniques. To treat deficiency in children.

• Insulin – either from recombinant DNA or obtained from animal pancreas.

• Adrenal steroids – primarily glucocorticoids, used for the relief of inflammation (e.g. asthma, rheumatoid arthritis) immunosuppression (e.g.after organ transplantation) and relief of stress symptoms of shock.

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Uses of natural and synthetic hormones

Adrenaline has many uses: Stimulation of cardiac

muscle when a rapid response is required (e.g. cardiac arrest)

Treatment of asthmatic attacks by relaxation of the muscles of the small bronchial tubes.

Treatment of acute allergic reaction called

ANAPHYLAXIS

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Uses of natural and synthetic hormones

• Thyroid hormones: Replacement therapy after surgical removal of the thyroid gland or to treat hypothyroid conditions like cretinism or myxoedema

• Oxytocin; used to contract the uterine muscle

• Androgens: testosterone and androsterone used in severe chronic illness to aid tissue building and promote healing.

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Uses of natural andsynthetic hormones

Occasionally give rise to nausea and more rarely they cause serious complications such as blood clots (thrombosis) or hypertension.

Any woman taking birth control pills should have BP checked every 6 months

Preparations of ESTROGEN and PROGESTERONE are used to treat the symptoms associated with menopause

ESTROGEN and PROGESTERONE as

purified synthetic drugs are used as oral

contraceptives. They are highly effective in

preventing pregnancy.

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Homeostasis

StressCreates Imbalance of

Homeostasis

The Body in Balance

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Cortisones decrease the immune response leaving the body more open to infection!!

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Control Systems respond to and regulate imbalances in Homeostasis

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Age Related Hormonal Disturbances

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Hormone Replacement Therapy

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Steroid Hormones Influence Gene Expression

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Steroid Hormones Influence Gene Expression