The Endocrine Systemand Homeostasis

ENDOCRINE GLANDS

Hormones are secreted directly into the bloodstream, which transports the hormones throughout the body.

Examples include: pituitary and adrenal glands

Two types of glands

EXOCRINE GLANDS

• are glands that secrete their products (hormones) into ducts

• Examples include sweat, salivary, mammary glands and the many glands of the digestive system.

Chemical Signals regulate homeostasis

TWO TYPES OF HORMONES:

• Lipid Soluble: these hormones can easily diffuse through the lipid bilayer of cell membranes. This interaction activates specific genes, causing changes in the cell.

EXAMPLES: Steroid hormones, such as testosterone, estrogen, and cortisol.

• Water Soluble (protein or protein-related hormones): these hormones cannot diffuse across the cell membrane.

EXAMPLES: Epinephrine, human growth hormone, thyroxine, and insulin.

HORMONES are chemical messengers which “excite” or “set in motion” a series of reactions.

Negative Feedback Loops

Once the hormone’s message has been delivered, enzymes inactivate the hormone – thus causing a NEGATIVE FEEDBACK LOOP.Main regulatory gland is the Hypothalamus.

United Streaming video: Endocrine System – Biologix – Hypothalamus/Pituitary gland – Video Segment #2

Example: Affects on Blood Pressure

In the example to the right blood pressure has increased.

Therefore, receptors in the carotid arteries detect the change in blood pressure and send a message to the brain.

The brain will cause the heart to beat slower and thus decrease the blood pressure.

DECREASING HEART RATE HAS A NEGATIVE EFFECT ON BLOOD PRESSURE.

Gland secretes at least eight hormones.

Involved in the body’s metabolism, growth, development, reproduction and other critical life functions.

Controlled by the hypothalamus – secretes only 2 hormones – directs activities of other glands.

The two lobes are called the anterior and posterior gland -- each lobe is a separate gland and they release different hormones

The MASTER gland:The Pituitary

HypothalamusPituitary Gland

United Streaming: Endocrine System – Biologix: Hypothalamus/Pituitary – Segment #4

Anterior Pituitary GlandAnterior pituitary: hormone-

synthesizingit’s cells produce and release six major

hormones, including:hGHPRLTSHACTHFSHLH

Human Growth Hormone (hGH)

• Stimulates the liver to secrete growth hormones called growth factors.• Protein synthesis• Cell division and growth• Metabolic breakdown and

release of fats stored in adipose tissue

• Stimulates the growth of muscles, connective tissue and the growth of plates at the end of long bones.

GIGANTISM – is a disorder caused by excessive amounts of hGH during childhood.DWARFISM – low amount of hGHACROMEGALY – after reaching adulthood, overproduction of hGH

Disorders caused by hGH

THYROID GLAND

Hormone, thyroxine produced in the thyroidRegulates body metabolism and the growth and differentiation of tissues.Individuals who secrete higher levels of thyroxine oxidize sugars and other nutrients at a faster rate.Lower levels of thyroxine do not break down sugars as quickly. Excess blood sugar is eventually converted into liver and muscle glycogen. Unfortunately, if blood sugar is too high, the excess sugar is converted to fat.Hypothyroidism – low thyroid secretionsHyperthyroidism – high thyroid secretions

Goiters - Thyroid Gland disorder

CRETINISM causes very serious retardation of physical and mental development; if the condition is left untreated, growth is stunted and the physical stature attained is that of a dwarf.

GRAVES DISEASE symptoms may include:Anxiety Irritability Difficulty sleeping Fatigue A rapid or irregular heartbeat A fine tremor of your hands or fingers An increase in perspiration Sensitivity to heat Weight loss, despite normal food intake Brittle hair Enlargement of your thyroid gland (goiter) Light menstrual periods Frequent bowel movements

Parathyroid gland

Functions of the Parathyroid and PTH (parathyroid hormone)

Maintenance of the body's calcium levelWhen blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood.Parathyroid hormone has effects antagonistic to those of calcitonin. It increases blood calcium levels by stimulating bone cell breakdown and, thus, the release of calcium.

CalcitoninCalcitonin, produced in the thyroid gland, has the ability to decrease blood calcium levels at least in part by effects on two well-studied target organs: Bone: Calcitonin suppresses reabsorption of bone calciumKidney: Calcium and phosphorus are prevented from being lost in urine by reabsorption in the kidney tubules. Calcitonin inhibits tubular reabsorption of these two ions, leading to increased rates of their loss in urine.

THE ADRENAL GLANDS

• Two adrenal glands located above the kidney

• Composed of an inner layer (adrenal medulla) and an outer layer (adrenal cortex)

Adrenal MedullaSHORT TERM

RESPONSES

• Considered a neuro-endocrine structure

• produces two closely related hormones (epiniphrine and norephinephrine)

• Flight or fight response by increasing metabolism

ADRENAL CORTEXLong Term Stress Response

• Glucocorticoids increase blood sugar

• Mineralocorticoids increase pressure

• Gonadocorticoids, female and male sex hormones, supplement the hormones produced by the gonads

CORTISOL – glucocorticoid which is regulated by the anterior pituitary and the adrenal glands

It has several functions including:– helps to regulate blood pressure. – helps to regulate the immune system. – helps to balance the effect of insulin to keep the blood sugar

level normal. – helps the body to respond to stress.

Aldosterone

MineralcorticoidStimulates the distal and collecting tubules of the kidneys to increase the absorption of sodium into the bloodstream.This increases the solute concentration of the blood, which then draws in more water from the nephrons, raising blood pressure.Addison’s disease can result, if the adrenal cortex is damaged. In this case, the body secretes inadequate amounts of mineralocorticoids and glucocorticoids.

THE PANCREAS (exocrine gland)

Pancreas contains two types of cells: digestive enzymes and hormones.

Islets of Langerhans – produce insulin and glucagon (both hormone producing)

Exocrine – means this gland secretes its products through ducts

INSULIN

Regulation of blood sugarInsulin is produced in the beta cells of the islets of Langerhans and is released when the blood sugar level is high.Insulin increases glucose utilization by making many cells of the body permeable to glucose.

Glucagon – produced in the alpha cells and works with insulinReleased when blood sugar levels are low.Promotes the conversion of glycogen to glucose. As glycogen is converted to glucose in the liver, the blood sugar level returns to normal.Other hormones, such as hGH, cortisol, and epinephrine also contribute to increasing the level of blood glucose.

Insulin causes a decrease in blood sugar level, and glucagon causes an increase in blood sugar level.

The effects of glucose imbalance

Diabetes Mellitus

• Hyperglycemia: high blood sugar

• Without insulin, cells remain relatively impermeable to glucose and cannot obtain enough from the blood.

The loss of glucose in the urine causes the osmotic gradient across the nephrons of the kidneys. Large volumes of water therefore follow the glucose.Untreated people with diabetes mellitus experience low energy and great thirst (SHORT TERM).

LONG TERM: can lead to blindness, kidney failure, nerve damage and gangrene in the limbs.

Two types of diabetes mellitusType 1 diabetes

• Juvenile and/or insulin-dependent diabetes

• Immune system produces antibodies that attack and destroy the beta cells of the pancreas.

• The beta cells degenerate and are unable to produce insulin.

Type 2 diabetes

• Develops gradually because the insulin receptors on the body’s cells stop responding to insulin.

• Also, another way, the beta cells of the pancreas produce less and less insulin over time.

• People who are overweight have a greater chance of developing type 2 diabetes.

Posterior Pituitary Gland

Considered part of the nervous system

DOES NOT PRODUCE HORMONES

Hypothalamus, produces, ADH and oxytocin—posterior pituitary stores them for use