endocrine system 3

• Are two small glands located superior to each kidney.

• Each adrenal gland has an inner part, called adrenal medulla, and outer part, called adrenal cortex.

ENDOCRINE GLANDS AND THEIR HORMONES Adrenal Gland

Adrenal Medulla• Epinephrine or adrenaline is the principal

hormone released from the adrenal medulla and small amounts of norepinephrine.

• These are released in response to stimulation by the sympathetic nervous system.

• Epinephrine and norepinephrine are referred to as fight-or-flight hormones.


Major effects of hormones from adrenal medulla:

• Increase the breakdown of glycogen to glucose in the liver, release of glucose into the blood and release of fatty acids from fat cells. These serves as energy sources to maintain the body’s increased rate of metabolism.

• Increased heart rate, which causes blood pressure to rise.


Major effects of hormones from adrenal medulla:

• Stimulation of smooth muscle in the wall off arteries supplying the internal organ and the skin. Blood flow to internal organs and the skin decreases, blood flow through skeletal muscles increases.

• Increased blood pressure due to smooth muscle contraction in the walls of blood vessels in the internal organs and the skin.

• Increased metabolic rate of several tissues. Specially in skeletal muscle, cardiac muscle, and nervous tissue.


In general:• Responses to hormones fro the adrenal

medulla reinforce the effect of the sympathetic division of the autonomic nervous system.

• It prepares the body for physical activity and to produce fight-or-flight response and other responses to stress.


Adrenal Cortex• Secretes 3 classes of steroid hormones:– Mineralocorticoids– Glucocorticoids– Androgens


• Secreted by the outer layer of adrenal cortex• Helps regulate blood volume and blood levels

of K+ and Na+

ENDOCRINE GLANDS AND THEIR HORMONES Adrenal Gland - Mineralocorticoids

binds to receptor molecules of kidney

and also affects intestine, sweat glands

and salivary gland.

causes Na+ and H2O to be retained in the body

and increase elimination of K+

Blood levels of K+ and Na+ directly affect the

adrenal cortex to influence aldosterone

secretion.

More sensitive to changes in blood K+

levels than to changes in blood Na+ levels.

increases when blood K+ levels increase or

when blood Na+ levels decrease.

Aldosterone


• Changes in blood pressure indirectly affect the rate of aldosterone secretion.

• Low blood pressure causes the release of a protein molecule called renin from the kidney, which acts as an enzyme.

• Renin causes a blood protein called angiotensinogen to be converted to angiotensin I.


• Angiotensin –converting enzyme causes angiotensinogen I to be converted to angiotensin II.

• Angiotensin II causes the smooth muscle in blood vessels to constrict and it also increases aldosterone secretion.

• Increases in blood volume causes by aldosterone and blood vessel constriction help raise blood pressure.


• Secreted by the middle layer of adrenal cortex.• It regulates blood nutrient levels.

ENDOCRINE GLANDS AND THEIR HORMONES Adrenal Gland - Glucocorticoids


increases the breakdown of protein and fat and their

conversion to form energy.

causes liver to convert amino acids to glucose, it acts on

adipose tissue, causing fat to be broken to fatty acids. Glucose and

fatty acids are released into the blood, taken up by tissues, and

convert it to energy.

breaks down protein to amino acids, which are then released

into the blood.

reduces inflammatory and immune responses.

CORTISOL

• A steroid, cortisone, or other similar drug, can reduce inflammation caused by injuries, allergic reactions, rheumatoid arthritis and asthma.

• In stressful conditions, cortisol is secreted in larger amount; thus, it helps the body by providing energy sources for tissues.

• If stressful conditions are prolonged, it can be harmful it can lead to hypertension, heart disease, ulcers, etc.

• Adrenocorticotropic hormone (ACTH) stimulates cortisol secretion. Without ACTH adrenal cortex will be dysfunctional and loses its ability to secrete cortisol.


Secreted by the inner layer of the adrenal

cortex.

Stimulates the development of male

sexual characteristics. in adult males androgens are

secreted by the testes.

In adult females, androgens influence the

female sex drive.

ENDOCRINE GLANDS AND THEIR HORMONES Adrenal Gland - Androgens

• If the secretion of sex hormones from the adrenal cortex is abnormally high, exaggerated male characteristics develop in both males and females.

• This condition is most apparent in females and in males before puberty

ENDOCRINE GLANDS AND THEIR HORMONES Adrenal Gland - Androgens

• Endocrine part of the pancreas consist of pancreatic islets, which are dispersed among the exocrine portion off the pancreas.

• These two islets secretes two hormones – insulin and glucagon – which help regulate blood levels of nutrients specially glucose.

ENDOCRINE GLANDS AND THEIR HORMONES Pancreas, Insulin and Diabetes

Beta cellssecretes insulin.

Alpha cellssecretes glucagon

• It is very important to maintain normal blood glucose levels. A below-normal blood glucose level causes the nervous system to malfunction because glucose is the main source of energy. Other tissues rapidly break down fats and proteins to provide an alternative energy source.


converts some fatty acids to acidic ketones which are released into

the blood.


• The breakdown of fats can cause release of enough fatty acids and ketones that reduce the pH of the body fluids below a normal range, a condition called acidosis.

• The amino acids of proteins are broken down and used by the liver to synthesize glucose.


If glucose levels are too high, the kidneys produce large

volumes of urine containing a lot of glucose

Rapid loss of water in the form of urine will occur and dehydration can result

Insulin from beta cells is released in response to elevated blood glucose levels and increased parasympathetic stimulation

Increase in blood levels of certain amino acids also

stimulate insulin secretion

Decreased insulin secretion results from decreasing blood

glucose levels and from stimulation pancreas by the sympathetic division of the

nervous system

Decreased insulin level therefore allows glucose to be conserved to provide the brain

w/ adequate glucose and to allow other tissues to

metabolize fatty acids and glycogen stored in the cells


• The major target tissues for insulin are the liver, adipose tissue, muscles and the area of the hypothalamus that controls appetite, called the satiety center.

• Insulin increases the rate of glucose and amino acid uptake in these tissues.


Glucose Glycogen or Fat Amino Acids Protein

Diabetes mellitus – has many causes: • Type 1 diabetes mellitus occurs when too

little insulin is secreted from pancreas. Tissues cannot take up glucose effectively causing blood sugar levels to become very high, a condition called hyperglycemia.

• Type 2 diabetes mellitus is caused by insufficient numbers of insulin receptors on target cells or by defective receptors.


• Because glucose enter the cells of the satiety center of the brain, the satiety center responds as if there were too little blood glucose, causing an exaggerated appetite.

• The excess glucose in the blood in excreted in the urine, making the urine volume much greater than normal.

• Because of this the person has a tendency to become dehydrated and thirsty.


• Fats and proteins are broken down to provide an energy source for metabolism because levels of blood glucose is not in a normal range, thus causing malfunction in the nervous system.

• When too much insulin is injected or when a person is injected with insulin who has not eaten after the injection, blood glucose levels become very low thus making the brain malfunction because it depends primarily on glucose for an energy source, this condition is called insulin shock.


blood glucose levels are low

Glucagon is released from the alpha cells

It binds with the membrane-bound

receptors of the liver

causing the glycogen in the liver to be

converted to glucose

released it into the blood to increase blood

glucose levels

After a meal, when blood glucose are

elevated, glucagon secretion decreased



blood glucose levels

Insulin secretion

Glucagonsecretion

blood glucose levels

Glucagon secretion

Insulinsecretion

Target Tissues Insulin Response Glucagon ResponseSkeletal muscles, cardiac muscles, cartilage, bone fibroblasts, blood cells, mammary glands

Increase glucose uptake and glycogen synthesis; increases uptake of amino acids.

Has little effect

Liver Increases glycogen synthesis; increases use of glucose for energy

Causes rapid increase in the breakdown of glycogen to glucose and release of glucose into the blood increases the formation of glucose from the amino acids and to some degree from fats; increases metabolism of fatty acids.

Adipose cells Increases glucose uptake, glycogen synthesis, far synthesis.

High concentrations cause breakdown of fats; probably unimportant under most conditions.

Nervous System Has little effect except to increase glucose uptake in the satiety center

Has no effect

• Testes of the male and ovaries of the female secretes sex hormones in addition to producing sperm cells and oocytes.

ENDOCRINE GLANDS AND THEIR HORMONES Testes and Ovaries


Testosterone is the main sex hormone in the male which is secreted by the testes. It is responsible for the growth and development of the male reproductive structures, muscle enlargement, growth of body hair, voice changes, and the male sexual drive.


In the female, there are two sex hormones secreted by the ovary: estrogen and progesterone.Together these hormones contribute to the development of female sexual characteristic and female reproductive structures. Such as the enlargement of the breast and the distribution of fats which influences the shape of the hips, breasts, and thighs. Female menstrual cycle is also controlled by the sex hormones.

• Luteinizing Hormone (LH) and Follicle-stimulating Hormone (FHS) stimulate the secretion of hormones from the ovaries and testes. Hypothalamus controls the rate of LH and FHS, in turn, LH and FHS controls the secretion of hormones from the ovaries and testes.


• Lies in the upper part of the thoracic cavity. Important in the function of the immune system.

• Secretes hormone called thymosin, which aids in the development of white blood cells called T cells. White blood cells fight infections and protects the body against foreign organisms.

• Thymus is most important early in life, without this a newborn cannot develop the immune system normally.

ENDOCRINE GLANDS AND THEIR HORMONES Thymus

• Is a pinecone-shaped structure located superior and posterior to the thalamus of the brain.

ENDOCRINE GLANDS AND THEIR HORMONES Pineal Gland

• Produces a hormone called melatonin.• This decreases the release of hypothalamic-

releasing hormones and secretion of LH and FHS thus melatonin inhibits the functions of reproductive system.


• Animal studies show that the amount of available light controls the rate of melatonin secretion. In short, less light increases melatonin secretion and more light decreases melatonin secretion.

• Some evidence suggest that melatonin plays an important role in the onset of puberty in humans.


SUMMARY OF ENDOCRINE GLANDS

endocrine system 3

Science

blood flow

blood levelsof

intothe blood

blood nutrient levels

increased blood pressure

orwhen blood na

changesin blood na

low blood pressure