The Endocrine System

Feedback Mechanisms and Operation of Hormones

Hormones regulate endocrine function on the basis of feedback mechanisms.

There are two types of feedback mechanisms.

1. Negative feedback Mechanism/loop

• A mechanism that works to “reverse” or “decrease” changes in the body.

• E.g Furnace

Ex: Hypothalamus – Pituitary Feedback Mechanism

Operation of the Hypothalamus-Pituitary Feedback mechanism

Operation of the Hypothalamus-Pituitary Feedback mechanism

2. Positive Feedback Mechanism

•A mechanism that serves to “increase” the effect of an action.

•E.g: behaving is positive ways will lead to more positive behaviours

Feedback Mechanisms and Operation of Hormones

Ex: Oxytocin Feedback loop.

Anterior Pituitary Gland Hormones

Anterior Pituitary Gland Hormones

Posterior Pituitary HormonesStores hormones, but does not create any.

ADH and Oxytocin are created by the HYPOTHALAMUS and STORED in the

posterior pituitary.

Problems associated with the Pituitary Gland

• a. Dwarfism– Cause: Insufficient production of HGH during childhood.

– Effect: Causes an abnormally short stature.

– Treatment: Injections of HGH

Problems associated with the Pituitary Gland

• b. Giantism– Cause: Excess production of HGH prior to

puberty.

– Effect: abnormal growth of long bones in the skeleton.

– Treatment: microsurgery of pituitary , radiation treatment of gland tissue.

Problems associated with the Pituitary Gland

• c. Acromegaly– Cause: Excess HGH production during adult years.

– Effect: Causes thickening of bone tissue. Causes abnormal growth of head, hands and feet. Also causes spinal deformities.

– Treatment: Surgical removal of tumor causing too much HGH to be released.

– Radiation of tumor

– Injection of HGH blocking drug.

Problems associated with the Pituitary Gland

• d. Diabetes Insipidus– Cause: Insufficient production of ADH (Antidiuretic

Hormone).

– Effect: increased thirst and dehydration

– Production of high amounts of dilute urine

– Enlarged urinary bladder.

– Treatment: Injections of ADH to reverse effects.

Thyroid Gland Hormones

• Function of Thyroxine– Thyroxine increases metabolism rate and oxygen consumption.– Thyroxine is released from the thyroid gland when stimulated by

TSH from the pituitary.– TSH --------- > Thyroid Gland -------- > releases Thyroxine– TSH and Thyroxine work on a negative feedback loop.– Iodine is needed in diet in order to produce Thyroxine.

• TSH --------- > Thyroid Gland -------- > releases Thyroxine• TSH and Thyroxine work on a negative feedback loop.

• Function of Calcitonin• Moves calcium from the blood and into the bones. This

lowers amount of calcium in the blood

Problems associated with Thyroid GlandA. Hyposecretion of Thyroxine

• 1. Myxedema• Condition where adults become obese, lose appetite

and are often tired because of under production of thyroxine.

• Treatment: drugs that have Thyroxine in them

Problems associated with Thyroid GlandA. Hyposecretion of Thyroxine

• 2. Congenital Hypothyroidism or Cretinism• Condition in children where they are often

short/stalky and often mentally delayed.

• Treatment: drugs having thyroxine

Problems associated with Thyroid GlandA. Hyposecretion of Thyroxine

• 3. Goiter– A condition caused by a lack of iodine in the diet.

– This causes a decreased production of Thyroxine.

– Patients end up with swollen thyroid gland. Looks like a large growth on the neck.

– Treatment: increase iodine intake.

– Governments have added iodine to salt for years (Iodized salt) to counteract this problem.

Problems associated with Thyroid GlandB. Hypersecretion of Thyroxine

• i. Grave’s Disease– Condition where there is an increased

metabolism (“hyperness”) in a person.

– Increased sweating

– Muscle weakness

– Protruding eyes

– Treatment: Surgical removal of thyroid gland

– Thyroid blocking drugs.

Parathyroid Gland(s) Hormone

• PTH (Parathyroid Hormone)• Causes bones to release calcium into the blood

stream.

• Causes kidneys to reabsorb calcium from blood thus increasing amount of calcium in the body.

Pineal Gland• Melatonin

• Causes a feeling of “sleepiness” and aids with sleep.

• Thymus Gland

• Thymosin• Causes the production and maturation of

lymphocytes into T-cells. T-cells help the immune system fight infection.

Adrenal Glands• Adrenal Cortex: Releases three major hormones.

– Aldosterone: Regulates blood pressure and salt levels in the blood.

– Cortisol: Reduces inflammation and causes glucose to be made by the liver.

– Sex Hormones: Males hormones called “Androgens”

Females hormones called “Estrogens”

• Adrenal Medulla: Releases two major hormones– Adrenaline (epinephrine) and Noradrenaline (norepiniphrine)

• Released during times of stress. The “Fight or Flight” hormone.– Increases heart rate, respiration rate, release of glucose by liver etc.

Gonads: Ovaries and Testes• Ovaries – found in females

– Estrogen: controls secondary sex characteristics in females

• Prepares the uterus for pregnancy

– Progesterone: Maintains uterus during pregnancy

• Testes – found in males• Testosterone: Controls secondary sex

characteristics in males.*Secondary sex characteristics are any of a number of manifestations, as

development of breasts or beard, muscularity, distribution of fat tissue, and change of pitch in voice, specific to each sex and incipient at puberty but not essential to reproduction.

Pancreas (Islets of Langerhans)• Located near small intestine.• Helps regulate blood glucose levels.• Contain specialized endocrine cells called Islets of

Langerhans• Which are made up of Alpha and Beta cells.

• Secretes Insulin and Glucagons.

• á cellsi) secrete hormone called glucagon– ii) when blood-sugar levels drop, glucagon

stimulates the release of glucose into the bloodstream (liver converts glycogen to glucose, adipose cells convert fat to glucose, muscles convert protein to glucose).

cells – i) secrete a hormone called insulin– ii) when blood-sugar level is too high, insulin

stimulates the storage of sugar (liver stores glucose as glycogen, adipose cells store glucose as fat & muscles store glucose as proteins).

http://www.youtube.com/watch?v=qX4HLMY_1Bg&feature=channel

The Discovery of Insulin– two Canadian scientists: Fredrick Banting and

Charles Best. • They worked with dogs and first discovered the link

between the pancreas and diabetes in that dogs that had their pancreas removed developed symptoms of diabetes. In addition, they found the islet cells of the pancreas were responsible for preventing diabetes.

• Later on, they did an experiment. They extracted the islet secretions from a healthy dog and put them in the system of a diabetic dog (removed pancreas). As expected, the diabetic dog’s blood sugar did go back to normal.

– After several tests and modifications, this extract was given to a human patient with success. It was named insulin after the Latin word for island.

Diabetes– a disorder where blood sugar levels are elevated

constantly. Can cause circulatory disorders, blindness, and/or weight loss

• (1) Type 1 Diabetes (Diabetes Mellitus)• also called juvenile diabetes

• insulin dependent (pancreas doesn’t make any insulin)

• suggested to be an autoimmune disorder; body’s own cells attack the pancreas and destroy the cells which make insulin

• (2) Type 2 Diabetes• adult-onset diabetes

• insulin produced but body less sensitive to it or it is not produced enough

• - 90% of all diabetics are type 2

• Lab: p. 436-437

Adrenal Gland and Stress

• Cortex and Medulla do not interact, but they are both controlled by the hypothalamus.

Adrenal Gland and Stress

• Adrenal cortex: – Cortisol: stimulates the synthesis of

carbohydrates.– Aldosterone: regulates salt and water balance,

which affects blood pressure. (osmoregulation)

• Both hormones contribute to long term stimulation of immune system.

• Adrenocorticotropic hormone (ACTH): controls the production of cortisol and aldosterone.

• Adrenal medulla:– Adrenaline: “stress hormone” – Noradrenaline:– Both increases heart rate, trigger the release of glucose,

from energy stores, and increasing blood flow to skeletal muscles.

• Adrenal medulla functions with the sympathetic nervous system via direct connection to the hypothalamus. – Adrenaline and noradrenaline may act as

neurotransmitters.

What do you think?– “Should doctors prescribe HGH as a

treatment for individuals who have normal levels of human growth hormone in their system, yet are genetically shorter than average, simply as a

– means to increase their height?”

– “Should steroids (performance enhancing drugs) be legalized for use by all athletes?”

– “Should random drug testing of athletes be permitted or is it an invasion of privacy?”

– “Should hormones be used within the beef industry to increase production?”