Endocrine system

Water balance Uterine contractions and milk release Growth, metabolism, and tissue

maturation Ion regulation Heart rate and blood pressure regulation Blood glucose control Immune system regulation Reproductive functions control

› Are molecules released from one location that move to another location to produce a response.

Intracellular chemical signals› Are produced in one part of a cell (cell

membrane) and travel to another part of the same cell and bind to receptors (cytoplasm or nucleus).

Intercellular chemical signals› Are released from one cell, are carried in the

intercellular fluid, and bind to their receptors, which are found in some cells, but usually not all cells in the body.

Autocrine chemical signals› Are released by cells and have a local effect on the

same cell type from which the chemical signals are released

Paracrine chemical signals› Released by cells that have effects on other cell types

near the cells from which they are released, without being transported in blood

Neuromodulators and neurotransmitters› Are intercellular chemical signals, secreted by nerve

cells, which play important roles in the function of the nervous system

Pheromones› Are chemical signals secreted into the environment that

modify the behavior and the physiology of other individuals.

Receptors - are proteins or glycoproteins where in ligands bind to produce a response.

Receptor site – portion of each receptor molecule where a chemical signal binds.

Specificity – the tendency for each receptor site to bind to a specific chemical signal and not to others.

Membrane-bound receptors› Extend through the cell membrane, with

their receptor sites on the outer surface.› Respond to large water-soluble molecules

that do not diffuse through the cell membrane.

Intracellular receptors› Located in either the cytoplasm or the

nucleus.› Intercellular chemical signals diffuse

through the cell membrane then bind to receptor sites on intracellular receptors.

Receptors that directly alter membrane permeability› Intercellular chemical signals bind to

receptor sites, causing ion channels in the cell membrane to open or close.

› The change in membrane permeability alters the movement of ions across the cell membrane, which is responsible for the cells response.

Receptors and G Proteins› Activation of a complex of proteins at the inner

surface of the cell membrane called G proteins› The inactive G protein complex has alpha (α), beta

(β), and gamma (γ) subunits.› Bound to the alpha (α) subunit is Guanosine

diphosphate (GDP)› The binding of intercellular chemicals causes the

conversion of Guanosine diphosphate (GDP) to Guanosine triphosphate (GTP).

› The alpha (α) subunit with GTP bound to it can either Open or close membrane channels, to produce a

response Activate enzymes that produce intracellular

chemical signals Affect gene expression

Receptors that directly alter the activity of enzymes› Some intercellular chemical signals bind to

receptor sites and directly increase or decrease the activity of enzymes

Membrane-bound receptor responses › Produce rapid responses cascade

effect Intracellular receptor responses

› Several hours

Derived from the Greek word endo and krino meaning “within” and “to separate”

The word implies that intercellular chemical signals are produced within and secreted from endocrine glands, but the chemical signals have effects at locations that are away from, or separate from, the endocrine glands that secreted them.

Intercellular chemical signals secreted by the endocrine system.

Derived from the Greek word hormon meaning “set into motion”

Defined as an intercellular chemical signal, produced in minute amounts by a collection of cells, that is secreted into the interstitial fluid and enters the circulatory system to be transported some distance, and that acts on tissue at another site in the body to influence their activity in a specific way.

Target tissue – are certain tissues that respond to each type of hormone and are made up of cells that have receptor molecules for the hormone.

Proteins› Amino acids bound together by peptide

bonds› Carbohydrate molecules are bound to

some of the protein hormones.› Hormones of the anterior pituitary gland

Peptide hormones› Short chains of amino acids› Hormones of the posterior pituitary gland

Amino Acids› Consist of single amino acids that have

been chemically modified.› Hormones secreted by the adrenal medulla

Steroid Hormones› Derived from cholesterol› Produces mostly by the adrenal cortex

and the gonads› Diffuse across the cell membrane

Eicosanoids› Make up a class of chemicals derived

from the fatty acid arachidonic acid.› Include prostaglandins, thromboxanes,

prostacyclins, and leukotrienes

› Controlled by negative feedback

Blood Levels of Chemicals Hormones Nervous system

Is also called the hypophysis Small gland about the size of a pea Rests in the depression of the sphenoid

bone inferior to the hypothalamus Anterior pituitary is made up of

epithelial cells derived from the embryonic oral cavity

Posterior pituitary is an extension of the brain and is made up of nerve cells.

“Master Gland”

Endocrine control center of the brain located inferior to the thalamus

The pituitary gland is controlled in 2 ways by the Hypothalamus:› Neurohormones, produced and secreted

by neurons of the hypothalamus, act on cells of the anterior pituitary gland.

› Secretion of hormones from the posterior pituitary is controlled by nervous system stimulation of nerve cells within the hypothalamus.

Stimulates the growth of bones, muscles, and other organs by increasing protein synthesis

Resists protein breakdown during periods of food deprivation and favors fat breakdown.

The secretion of growth hormone is controlled by 2 hormones from the hypothalamus (releasing hormone and inhibiting hormone)

Daily peak levels of GH occur during sleep and also increase during periods of fasting and exercise

In addition to GH, genetics, nutrition and sex hormones influence growth

GIANTISM Excess growth hormone is present before

bones complete their growth in length therefore exaggerated bone growth occurs.

DWARFISM Result from decrease GH secretion during

childhood The features of the body develop in

appropriate proportion to one another, but the rate of development is greatly decreased.

ACROMEGALY Excess GH is secreted after growth in bone

length is complete, growth in bone diameter, but not in length, continues

Enlargement is especially marked in bones of the hands and feet, cranium, noses, bosses of the forehead, supraorbital ridges, lower jawbone, and portions of the vertebrae.

The lower jaw protrudes forward, the forehead slants forward, the nose increase to as much as twice normal size, the feet requires size 14 or larger shoes, and the fingers become extremely thickened so that the hands develop a size almost twice normal

Develop kyphosis (hunched back).

Binds to membrane-bound receptors on cells of the thyroid gland and cause the cells to secrete thyroid hormone

The rate of TSH secretion is increased by a releasing hormone from the hypothalamus.

Binds to membrane-bound receptors on cells in the cortex of the adrenal glands.

Increases the secretion of a hormone from the adrenal cortex called Cortisol also called Hydrocortisone.

Required to keep the adrenal cortex from degenerating

Also bind to melanocytes in the skin and increases skin pigmentation.

The rate of ACTH is increased by a releasing hormone from the hypothalamus.

Bind to membrane-bound receptors on the cells of the gonads

Regulate the growth, development, and functions of the gonads

Luteinizing Hormone (LH)› In females causes ovulation of the oocytes

and the secretion of the sex hormones estrogen and progesterone from the ovaries

› In males, stimulates the secretion of sex hormone testosterone from the testes. It is sometimes referred to as Interstitial Cell-Stimulating Hormone (ICSH) because it stimulates interstitial cells of the testes to secrete testosterone.

Follicle-stimulating Hormone› Stimulates the development of follicles in the

ovaries and sperm cells in the testes.

Binds to membrane-bound receptors in cells of the breast and helps promote development of the breast during pregnancy and stimulates the production of milk in the breast following pregnancy.

Binds to membrane-bound receptors on melanocytes and causes them to synthesize melanin.

Binds to membrane-bound receptors and increases water reabsorption by kidney tubules

Can also cause blood vessels to constrict when released in large amounts

Sometimes called vasopressin Reduced ADH released from the posterior

pituitary results in the formation of large amounts of dilute urine.

Lack of ADH secretion causes diabetes insipidus – production of a large amount of dilute urine therefore resulting in an increase in the osmolality of the body fluids and the loss of important electrolytes such as Ca2+, Na+, and K+ in the large urine volume.

Binds to membrane-bound receptors and causes contraction of the smooth muscle cells of the uterus and milk ejection, or milk “let-down,” from the breast in lactating women

Made up of 2 lobes connected by a narrow band called Isthmus located on either side of the trachea, just inferior to the larynx.

One of the largest endocrine glands and is highly vascularized

Thyroid follicles› Small spheres with walls that consist of simple

cuboidal epithelium› Filled with proteins to which thyroid hormones

are attached› The cells synthesized thyroid hormones, which

are stored in the follicles Parafollicular cells

› A network of loose connective tissue located between follicles that contains capillaries.

Bind to intracellular receptors in cells and regulate the rate of metabolism in the body

Iodine is required to synthesize thyroid hormone and is taken up by the thyroid follicles in which synthesis occurs.

Thyroxine or tetraiodothyronine contains 4 iodine atoms T4

Triiodothyronine contains 3 iodine atoms T3 If the quantity of iodine is not sufficient, the

production and secretion of the thyroid hormone decreases.

Thyroid hormones are stored in combination with a protein called thyroglobulin (located within the thyroid follicle)

Regulated by TSH from the anterior pituitary Have a negative-feedback effect on the

hypothalamus and pituitary.

From the parafollicular cells Secreted if the blood concentration

Ca+ becomes too high, and it causes Ca+ levels to decrease to their normal range

Bind to membrane-bound receptors of osteoclasts and reduces the rate of Ca+ resorption from bone by inhibiting them.

Results in an elevated rate of metabolism, extreme nervousness, and chronic fatigue› Grave’s Disease – results from the

production of abnormal proteins by the immune system that are similar in structure and function to TSH. Grave’s disease is often accompanied by exophthalmia.

Lack of thyroid hormones› Cretinism – hypothyroidism in infants

where in the person is mentally retarded and has a short stature with abnormally formed skeletal structures

› In adults, this would result in reduced rate of metabolism, sluggishness, a reduced ability to perform routine tasks, and myxedema which is the accumulation of fluid and other molecules in the subcutaneous tissue.

Essential in the regulation of blood Ca levels. Binds to membrane-bound receptors of renal

tubules, which increases active vitamin D formation which in turn causes the epithelial cells of the intestine to increase Ca+ resorption.

Binds to receptors on osteoblasts which release substances that increase osteoclast activity and cause resorption of bone tissue to release Ca+ into the circulatory system

Binds to receptors on cells of the renal tubules and decreases the rate at which Ca+ are lost in urine

Acts on its target tissues to raise blood Ca+ levels to normal.

Increasing blood Ca+ levels cause a decrease in PTH secretion results in a reduction in blood Ca+ levels

Increasing blood Ca+ levels stimulate calcitonin secretion, which also causes blood Ca+ levels to decline.

Can result from a tumor of a parathyroid gland

Elevated blood levels of PTH increase bone resorption and elevated blood Ca+ levels soft, deformed, and easily fractured bone

Makes nerve muscle less excitable resulting in fatigue and muscle weakness

The excess Ca+ can be deposited in soft tissue of the body and kidney stones can result.

Result of injury or the surgical removal of the thyroid and parathyroid glands.

Decrease blood Ca+ levels nerves and muscles become excitable and produce spontaneous action potential frequent muscle cramps or tetanus can affect the respiratory muscles: breathing stops, resulting in death.

Occurs mainly in children Results from calcium or phosphate

deficiency in the extracellular fluid, usually caused by lack of vitamin D

Rickets in adults “Adult Rickets”

Results in diminished organic bone matrix

Causes:› Lack of physical stress on the bones

because of inactivity› Malnutrition to the extent that sufficient

protein matrix cannot be formed\› Lack of vitamin C› Postmenopausal lack of estrogen secretion› Old age› Cushing’s disease

Epinephrine or adrenalin and small amounts of norephinephrine

Released in response to stimulation by the sympathetic nervous system, which becomes most active when a person is excited or physically active

Membrane-bound receptors in their target tissue

Stress and low blood glucose levels can also result in increased sympathetic stimulation of the adrenal medulla

Fight-or-flight hormones

› Increases in the breakdown of glycogen to glucose in the liver, the release of the glucose into the blood, and the release of fatty acids from fat cells.

› Increase in heart rate, which causes blood pressure to increase

› Stimulation of smooth muscle in the walls of the arteries supplying the internal organs and the skin, but not those supplying skeletal muscles.

› Increase in blood pressure because of smooth muscle contraction in the walls of blood vessels in the internal organs and the skin.

› Increase in the metabolic rate of several tissues, especially skeletal muscles, cardiac muscles, and nervous tissue.

Secretes 3 classes of steroid hormones that enter their target cells and bind to intracellular receptor molecules

Help regulate blood nutrient levels in the body Cortisol

a major glucocorticoid increases the breakdown of protein and fat and increases their conversion to forms that can be used as energy sources by the body.

Cortisol reduces the inflammatory and immune responses.

Secreted in large amounts in response to stressful conditions.

Aids the body in responding to stressful conditions by providing energy sources for tissues.

When blood glucose levels decline, cortisol secretion increases: low blood glucose acts on the hypothalamus ↑secretion of ACTH-releasing hormone stimulates ACTH secretion from the anterior pituitary ACTH stimulates cortisol secretion

ACTH molecules bind to membrane-bound receptors and regulate the secretion of cortisol from the adrenal cortex.

Help regulate blood volume and blood levels of K+ and Na+

Aldosterone› Binds to receptor molecules primarily in

the kidney, but it also affects the intestine, sweat glands, and salivary glands.

› Causes Na+ and H2O to be retained in the body and increase the rate at which K+ are eliminated.

› The rate of aldosterone secretion increases when blood K+ levels increase or when blood Na+ levels decrease.

Renin› Protein molecule released from the kidneys

when there is low blood pressure› Acts an enzyme that causes a blood

protein angiotensinogen to converted to angiotensin I angiotensin-converting enzyme converted to angiotensin II which causes smooth muscle in blood vessels to constrict and acts on adrenal cortex to increase aldosterone secretion causes retention of sodium and water which causes an increase in blood volume.

Stimulate the development of male sexual characteristics

Secreted in both male and female Male: secreted by the testes Female: influence the female sex drive

Hypoadrenalism Failure to produce adrenocortical

hormones Mineralocorticoid deficiency – decrease in

renal tubular sodium allowing sodium ions, chloride ions, and water to be lost into urine great decrease in extracellular fluid volume. Hyponatremia, hyperkalemia, and mild acidosis develops because of failure of potassium and hydrogen ions to be secreted in exchange for sodium reabsorption ↓in plasma volume RBC concentration rises markedly cardiac output decreases patient dies in shock

Glucocorticoid deficiency – difficulty in maintaining normal blood glucose concentration between meals because he cannot synthesize significant quantities of glucose by gluconeogenesis. Lack of cortisol reduces the mobilization of both proteins and fats from the tissues, thereby depressing many other metabolic functions of the body.

Melanin pigmentation – melanin is deposited in blotches especially in thin skin areas such as the lips, and the thin skin of the nipples.

Hypersecretion of the adrenal cortex Results from either a cortisol-secreting

tumor of one adrenal cortex or general hyperplasia of both adrenal cortices increase secretion of ACTH

Mobilization of fat from the lower part of the body, with concomitant extra deposition of fat in the thoracic and upper abdominal regions, giving rise to a buffalo torso.

Excess secretion of steroids edematous appearance of the face

Androgenic potency of some of the hormones acne and hairsutism

“Moon Face”

Pancreatic cells called islets of langerhans which secretes 2 hormones insulin and glucagon which function to help regulate blood nutrient levels especially blood glucose

Alpha cells glucagon; beta cells insulin ↓ blood glucose level nervous system

malfunction fats and proteins are broken down rapidly by other tissues to provide an alternative source of energy some of the fatty acids are converted by the liver to acidic ketones released into the circulatory system cause the pH of the body fluids to decrease below normal acidosis

↑ blood glucose level kidney produce large volumes of urine containing substantial amounts of glucose dehydration

Released in response to the elevated blood glucose level and increased parasympathetic stimulation that is associated with digestion of a meal

Stimulated when there is an increase in blood levels of certain amino acids

↓insulin secretion results from decreasing blood glucose levels and from stimulation by the sympathetic nervous system occurs during physical activity allows blood glucose to be conserved to provide the brain with adequate glucose and to allow other tissues to metabolize fatty acids and glycogen stored in the cells.

Major target tissue: liver, adipose tissue, muscles, area in the hypothalamus that controls appetite satiety center

DM type I› Secretion of too little insulin from the

pancreas› Tissues cannot take up glucose effectively

blood glucose become very high hyperglycemia glucose cannot enter cells in the satiety center exaggerated appetite excess glucose is excreted in urine ↑ in urine volume dehydration and being thirsty

DM type II› Insufficient numbers of insulin receptors on

target cells or defective receptors that do not respond normally to insulin

Released when blood glucose levels are low

Bind to membrane-bound receptors primarily in the liver and cause the conversion of glycogen in the liver to glucose glucose is released into the blood to increase blood glucose levels

Secrete sex hormones Testosterone

› Males› Secreted by the testes› Responsible for growth and development of

the male reproductive structures, muscle enlargement, growth of body hair, voice changes, male sexual drive

Estrogen and progesterone› Contribute to the development and function of

female reproductive structures and other female sexual characteristics

› Enlargement of the breasts and distribution of fat, which influences the shape of the hips, breasts, and thighs

› Control female menstrual cycle

Lies in the upper part of the thoracic cavity

Important in the function of the immune system

Thymosin› Helps in the development of T cells which

help protect the body against infection by foreign organisms

Important early in life, becoming smaller in older adults

A small pinecone-shaped structure located superior and posterior to the thalamus of the brain

Melatonin› Decrease the secretion of LH and FSH

by decreasing the release of hypothalamic-releasing hormones

› Act to inhibit the functions of the reproductive system

Hormones that stimulate the production of digestive juices from the stomach, pancreas, and liver

Aid in the process of digestion by causing secretion of digestive juices when food is present in the digestive system

Hormones secreted in the small intestine also help regulate the rate at which food passes from the stomach into the small intestine, so that food enters the small intestine at an optimal rate

Function as intercellular signals Function mainly as autocrine or

paracrine chemical signals effects occur in the tissues where they are produced

Some causes relaxation of smooth muscles such as contraction of the uterus during delivery

Play a role in inflammation released by damage tissues and causes blood vessel dilation, localized swelling, and pain necessary for blood clotting

Secreted in the kidneys to reduced oxygen levels in the kidneys

Acts on the bone marrow to increase the production of RBC

Important source of hormones that function to maintain pregnancy and stimulate breast development

Include estrogen, progesterone, and human chorionic gonadotropin