Importance of theEndocrine System

Chemical Controls

• The endocrine system consists of a number of glands and their respective hormones.

• The endocrine hormones are chemicals secreted by endocrine glands directly into the blood which affect cells in other areas of the body.

• Hormones may affect a specific target within the body or have a broad-spectrum effect on body function where several organs are affected at the same time by the hormone’s release.

Endocrine Glands

• Pituitary• Pineal• Thyroid• Parathyroid• Thymus• Adrenal• Pancreas• Ovary/Testes

Steroid vs. Protein Hormones

Steroid Hormones• Lipids – made from cholesterol.• They diffuse from blood into the cell and attach to a

receptor molecule.• Taken into nucleus and attaches to chromatin at specific

gene location.• Hormone activates gene and required protein is made.

Protein Hormones• Proteins – made of amino acid chains.• They attach to receptor proteins in cell membrane.• The hormone-receptor complex produces a molecule that

acts as a messenger and activates enzymes within the cell.

See also Section 8.1, Figures 4 & 5

The All-Powerful Pituitary Gland

• Referred to as the “master gland” because it exercises control over the other glands.

• Connected to the hypothalamus.• The pituitary makes and stores hormones and the

hypothalamus tells it when to release them using nerve impulses.

• The pituitary has two lobes – anterior and posterior.• The posterior lobe stores and releases hormones made by

the hypothalamus.• The anterior lobe produces and releases its own

hormones.• See figure 6 on page 376 for examples of the hormones

stored and/or produced by each lobe of the pituitary gland.

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Hormones That AffectBlood Sugar

Blood Sugar Hormones

The pancreas has cells that produce digestive enzymes and those that produce hormones – we will discuss the hormones.

Cells in the Islets of Langerhans (special pancreatic cells) produce insulin and glucagon.

Insulin is a hormone that allows for the uptake of glucose by body cells.

Glucagon is a hormone that promotes the conversion of glycogen to glucose. (A la Unit 1)

Blood Sugar Too High?

Pancreas secretes insulin – cells take in excess glucose from blood.

Liver also converts excess glucose into glycogen.

Glucose levels in the blood drop back to normal because excess glucose has gone from blood into cells or has been stored in the liver as glycogen.

Blood Sugar Too Low?

Pancreas releases glucagon into the blood which goes to the liver.

The liver starts to convert (breakdown) the glycogen it stores into glucose molecules which are then released into the blood.

Insulin and glucagon have opposing actions in terms of blood sugar management.

Diabetes

Diabetes is a chronic disease that occurs when the body cannot produce any insulin, or enough of it, or is unable to use the insulin in makes properly.

Three main types:– Type 1 → occurs when the pancreas is unable to produce insulin

because of degeneration of the cells that make it (onset is usually in childhood).

– Type 2 → is associated with decreased insulin production or ineffective use of insulin (onset is usually in adulthood).

– Gestational diabetes occurs in 2-4% of all preganancies and is associated with a increased risk of diabetes in both mother and child.

Diabetes

What could happen???– After meals, blood sugar spikes (hyperglycemia),

excess glucose exits body in urine and the threat of dehydration exists.

– After time goes by, cells become starved for glucose and have to rely on other fuels. This can result in problems as harmful byproducts of the alternate fuel pathways.

– If energy levels get too low, organs will be shut down and failure occurs.

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Hormones That Affect Metabolism

Glands & Metabolism

• Metabolism is the sum of the chemical reactions required to live.

• Metabolism (metabolic rate) is affected by the thyroid gland, parathyroid glands, and anterior pituitary gland.

• The thyroid gland is situated just below the larynx.

• The parathyroid glands sit on the thyroid.• The pituitary gland is situated just below the

hypothalamus.

The Thyroid Gland• The thyroid is located just below the larynx and it

secretes the hormone thyroxine.• Thyroxine aids in the oxidation (breakdown) of

sugar and nutrients in the body.

T3 (tri-iodothyronine) thyroxine

The Thyroid Gland• People that produce ample amounts of thyroxine

usually can eat a lot of food without gaining any weight because it is broken down very quickly.

• People that have hypothyroidism are the opposite…they have low levels of thyroxine and because of this they do not oxidize nutrients fast enough and they gain weight quickly.

Controlling the Thyroid• The thyroid is brought into action by a negative feedback system

which involves the hypothalamus and pituitary gland.

• Low Metabolic Rate…• Detected by the hypothalamus – it releases thyroid-

releasing hormone (TRH) which goes to the pituitary.

• Pituitary receives TRH and produces thyroid-stimulating hormone (TSH) which goes into blood to get to thyroid gland.

• Upon receiving TSH, the thyroid gland secretes thyroxine which raises metabolic rate.

The Parathyroid Glands

• The parathyroids are four smaller glands found within the thyroid gland.

• Their control/action is not under the influence of the nervous or endocrine systems – the parathyroids respond directly to changes in their immediate surroundings.

• The parathyroids produce parathyroid hormone (PTH) which raises the levels of calcium in the blood.

Growth Hormone

• Growth hormone (somatotropin) is made and released by the anterior pituitary.

• Growth hormone:– causes tissues to increase in number and/or size. In muscles,

the cells increase in size by promoting protein synthesis and inhibiting protein breakdown. In bones, the cells elongate and the skeleton lengthens.

– promotes the breakdown of fats into fatty acids which can actually replace glucose as the primary fuel. Glucose builds up in the blood – good for the brain – while the fatty acids provide a ton of energy for growth. (This is why you often see a loss of fat accompanying a growth spurt.)

• Too much or too little during childhood can result in dwarfism or gigantism.

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