endocrine-bio 102 handout1 endocrine system rev 12-12 collection of specialized cells, tissues and...

Endocrine-BIO 102 HANDOUT 1

Endocrine System rev 12-12

Collection of specialized cells, tissues and glands that produce and secrete hormones that control many body functions.

Endocrine glands are ductless and secrete their hormones into interstitial fluid, lymph, and blood.

• Exocrine glands secrete products into ducts • Hormones are bloodborne “information” units.

– Come from endocrine glands– Circulate in the bloodstream– Act on specific cells in the body


Endocrine glands are stimulated in one of three ways:

1. By nervous impulses

2. By hormones

3. By humoral stimulation (usually a chemical [glucose, calcium] )regulated by the hormone which activates or inhibits hormone release


Endocrine System Characteristics

• Access to every cell because hormones circulate in the blood

• Each hormone acts only on specific cells (target cells) because only the hormone’s target cells have the appropriate receptor to fit it;

• Endocrine control slower than nervous system• Endocrine and nervous systems interact i.e.

timing of growth and sexual maturation involves a complex sequence of changes in both endocrine and nerve signals; release of some hormones is dependent on input from sensory neurons.


Classification of Hormones

Hormones are classified as “steroid” or “nonsteroid” based on their structure and mechanism of action.

•Steroid hormones:

– Lipid soluble, chemically derived from cholesterol

– Enter target cells, bind to an intracellular receptor and activate genes that produce new proteins

– Slower acting than nonsteroid hormones

Steroid hormones pass through the plasma membrane and act in a two step process.

• Once inside the cell, steroid hormones bind to nuclear membrane receptors, producing an activated hormone-receptor complex.

• The activated hormone-receptor complex binds to DNA and activates mRNA to produce new proteins.



• Nonsteroid hormones:– Water soluble; derived from amino acid protein

building blocks– Bind to receptors on target cell membranes and

converts an inactive molecule within the cell into an active molecule. The activated molecule produces a chemical which is called a second messenger.

– Activate existing enzymes so that even a small amount of hormone can produce a significant cellular change

– Faster action than steroid hormones


Homeostasis is generally maintained by a negative feedback loop.

In a negative feedback loop involving a hormone, the endocrine gland is the control center, the hormone represents the pathway between the control center and the effectors, the hormone’s target cells, tissues, or organs.

• An endocrine system negative feedback loop is a stable, self-adjusting mechanism for maintaining homeostasis of the controlled variable.


Hypothalamus and the Posterior Pituitary GlandHypothalamus

– plays an important role in the regulation of homeostasis--monitors fluid and electrolyte balance, temperature, and carbohydrate metabolism

– Is “the power behind the throne” -- the pituitary gland; is physically connected to the pituitary by a thin strip of tissue called the infidibulum

– produces hormones which stimulate the release of most pituitary hormones

• Has specialized neuroendocrine cells which function as nerve and endocrine cells; they generate nerve impulses which release hormones directly into the circulation; called the neuroendocrine reflex

– Hormones going to the posterior pituitary affect whole body; these hormones are transported on the hypothalamic neurons to the posterior pituitary;

• are actually neurosecretions– Secretes tropic hormones to hypothalamic blood

vessels which delivers them to the anterior pituitary

– Interaction between the hypothalamus and the pituitary demonstrates the relationship between the endocrine and the nervous systems


• http://neuroscience.uth.tmc.edu/s4/chapter02.html

• Fig 2.1=neurosecretion

• Fig 2.4, 2.5= ant pit secretion


http://neuroscience.uth.tmc.edu/s4/chapter02.html

http://neuroscience.uth.tmc.edu/s4/chapter02.html


Pituitary Gland (also called hypophysis) is located beneath the hypothalamus (and right behind the center of the eyes) in a bony cavity at base of brain;

– Called the “master gland” because it secretes 8 different hormones which regulate many of the other endocrine glands;

• Consists of 2 lobes: posterior and anterior− Posterior pituitary lobe (neurohypophysis):Neuroglial-like supporting cells and nerve fibers;

− Anterior pituitary lobe (adenohypophysis)Glandular tissue


Posterior pituitary:– Connection to hypothalamus—may be considered an

extension of the hypothalamus; some hypothalamic hormones are stored in posterior pituitary

– Hormones: nonsteroidal; made by neuroendocrine cells

• Antidiuretic hormone (ADH): causes reabsorption of water in kidneys, regulates water balance in body

• Oxytocin: causes uterine contractions during labor and milk ejection (milk let-down reflex)

– The neurons that make the hormones transport the hormones down their axon to be released into the blood


Hypothalamus and the Anterior Pituitary Gland

• Anterior pituitary:– Releasing and inhibiting hormones from the

hypothalamus travel to anterior pituitary through the pituitary portal system--a special blood supply that runs directly between the hypothalamus and the anterior pituitary.

– This allows minute quantities of hypothalamic hormones to get to the anterior pituitary and not be diluted in the systemic circulation



– Hormones: nonsteroidal: these hormones are made in the pituitary but released only upon hypothalamic stimulation

• Adrenocorticotropic hormone (ACTH): stimulates adrenal cortex

– Stimulates the adrenal cortex to release glucocorticosteroids (steroid hormones involved in stress related conditions and the metabolism of glucose)

– TSH-Thyroid Stimulating Hormone• Stimulates the thyroid gland to produce thyroid

hormone



– Follicle stimulating hormone (FSH): induces egg development and sperm development

– Luteinizing hormone (LH): promotes ovulation and testosterone. These hormones are absent until ages 10-13 years and their production stimulates sexual maturation and development of the secondary sexual characteristics

– Prolactin (PRL): stimulates the development of mammary gland cells and production of milk

– Growth hormone (GH): widespread effects on growth


Pituitary Disorders

Endocrine disorders tend to be chronic conditions of hypersecretion or hyposecretion

• Syndrome of inappropriate ADH secretion (SIADH): hypersecretion of ADH, excessive water retention so the body is out of balance—symptoms: headache, vomiting

• Diabetes insipidus: hyposecretion of ADH, inability to save water appropriately; frequent urination


Pituitary Disorders

• Gigantism: hypersecretion of growth hormone during childhood and adolescence; usual cause is a tumor of the anterior lobe of the pituitary. Person has relatively normal body proportions

• Acromegaly: hypersecretion of growth hormone in adulthood; overgrowth of hands, feet and face

• Both can cause headaches, poor vision, sinus congestion, congestive heart failure, impotence, kidney stones, weakness, arthritis and a shortened life span

• Pituitary dwarfism: hyposecretion of growth hormone during childhood; immediate treatment with growth hormone during childhood


Pancreas: Endocrine FunctionsPancreas is both an endocrine gland and an

exocrine gland (secreting products into the digestive tract)

Endocrine cells are located in the Islets of Langerhans; clusters of cells throughout the pancreas

• Hormones: nonsteroidal: all work to regulate blood glucose (sugar)– Glucagon: made by alpha cells; raises blood sugar– Insulin: made by beta cells, lowers blood sugar – Somatostatin: made by delta cells, inhibits secretion of

glucagon and insulin, regulates other hormones


Disorders of the Endocrine System

Since the endocrine system is one of 2 primary systems for controlling body functions, any disruption can have a widespread effect

Diabetes mellitus: DM—poor control of blood sugar inability to get glucose into cells.

• glucose stays in the circulatory system and overwhelms the kidney’s ability to resorb the sugar excreted in the urine.

• person also excretes a large amount of water


– Person becomes dehydrated and very thirsty, tired, has blurred vision, frequent infections, slow healing cuts, tingling in feet and hands.

• When glucose can’t be metabolized correctly, the body will metabolize fat and proteins. This causes other problems—cardiovascular and neural diseases, renal failure, blindness, and potentially leg amputations.


• There are 2 types of diabetes:– Type I -caused by the failure of the pancreas

to secrete enough insulin possibly caused by a virus that causes the immune system to attack the beta cells of the pancreas• Person is insulin dependent for the rest of

his/her life


– Type II -thought to be insulin resistance—cells fail to respond adequately to insulin • Usually occurs in adults over 40 years• Treatment: lifestyle changes• Oral pills: drugs to stimulate the pancreas

to secrete more insulin; drugs that increase the uptake of glucose by the liver and muscle cells

• New: inhalable insulin


Adrenal Glands

Adrenal glands are located just above the kidneys– Have an outer layer—cortex – an inner layer--medulla

• Adrenal cortex:– Secretion: mediated through hypothalamus-

pituitary secretions– Hormones: steroidal


Adrenal Gland-Cortex– Glucocorticoids: cortisol assists glucagon in

maintaining glucose levels during prolong fasting by promoting using fats and amino acids (liver can use amino acids to make glucose) AND

• Suppresses inflammation after infection or injury

• Also secreted when we are under emotional stress

– Mineralocorticoids: aldosterone--primarily regulates minerals (sodium and potassium)

• Also helps maintain body water balance


Adrenal Gland: Medulla

• Adrenal medulla: neuroendocrine organ – when these are released into blood stream, function

as hormones; when work as neurotransmitters, are nervous system transmitters

– Secretion: sympathetic nervous system

– Hormones: nonsteroidal:

• Epinephrine and norepinephrine: enhance function of sympathetic nervous system (fight-or-flight response)

• Play role in metabolism and controlling blood pressure and heart activity


Adrenal glands:• Addison’s disease: failure of adrenal

cortex to secrete sufficient cortisol and aldosterone• Lack of cortisol decreases blood sugar levels• Lack of aldosterone lowers blood sodium

levels• Symptoms: fatigue, weakness, abdominal

pain, weight loss • Treatment is medicine to replace hormones


• Cushing’s syndrome: excessive cortisol production causing– Excessive production of glucose and retention

of salt and water.– Blood sugar rises and muscle mass

decreases because protein is used to make sugar.

– Some glucose is converted to fat but in specific areas of the body—the face, abdomen and back of the neck (a hump of fat can be seen by the neck)

– Symptoms include weakness, fatigue, edema and high blood pressure


Thyroid Gland

Located below larynx at the front of the trachea.• linked to the parathyroid gland. Both help

regulate calcium balance.

Thyroid gland helps control metabolism.• Secretion: mediated through hypothalamus–

pituitary secretions• Steroidal hormones:

– Thyroxine (T4) and Triiodothyronine (T3): both regulate production of ATP from glucose, affect metabolic rate


Thyroid GlandIodine deficiency causes decrease in production of

thyroid hormones• This causes goiter which is a result of the failure of the

feedback inhibition of production of TRH and TSH.– Hypothalamus secretes thyrotropin releasing hormone (TRH)

which stimulates your pituitary to release TSH. – TSH stimulates the thyroid to make thyroid hormones. – TSH causes increase in size of thyroid gland as a result of the

gland trying to produce more hormones which it can’t do because of lack of iodine

• Calcitonin: decreases rate of bone resorption – lowers blood calcium levels by stimulating the intake of

calcium by bone and increasing bone mass

• Especially important for bone development



Thyroid:– Hyperthyroidism: overactive thyroid gland;

hyperactivity, nervousness, agitation and weight loss• Graves’ disease: an autoimmune disease

in which the person’s antibodies stimulate the thyroid to produce too much thyroxine. Accompanied by protruding eyes (called exopthalmos, caused by fluid accumulation behind the eyes)



Thyroid:– Hypothyroidism: underactive thyroid gland

slows body growth, changes brain development, delays the onset of puberty• Children: cretinism—mental retardation and

stunted growth• Adults: myxedema—swelling under the

skin, lethargy, weight gain, low body temperature


Parathyroid Glands

Located in the back of the thyroid gland• Hormone: parathyroid hormone (PTH),

nonsteroidal:– Removes calcium and phosphate from bone– Increases absorption of calcium by the

digestive tract– Increases retention by the kidneys of calcium

and excretion of phosphate • PTH increases the calcium concentration in the

blood and is secreted in response to lowered blood calcium levels


Reproductive Hormones

The gonads (testes and ovaries) are responsible for the production of sperm and eggs and production of the sex hormones.

The testes, located in the scrotum, produce androgens, the male sex hormone.

• Hormone: in males: the androgen testosterone (steroidal):– Functions:

• Regulates development and normal functioning of sperm, male reproductive organs, male sex drive

• Development of male secondary sex characteristics and bone and muscle growth at puberty


Ovaries

• Hormones (steroidal) and functions:– Estrogen: initiates development of secondary

sex characteristics, regulates menstrual cycle– Progesterone: regulates menstrual cycle


Other Hormone Sources• Thymus: thymosin and thymopoietin, assist

maturation of T lymphocytes (non-steroidal hormone)

• Pineal gland: melatonin– Receives input from the eyes; melatonin secretion is

higher in the dark; important in synchronizing the body’s rhythms to the daily light/dark cycle (Circadian cycle or rhythm)

• Heart: atrial natriuretic hormone (ANH) (non-steroidal hormone); secreted by the atria to help regulate blood pressure by increasing the rate at which sodium and water are excreted in urine thus decreasing blood volume


Other Hormone Sources

• Digestive system: gastrin, secretin, cholecystokinin; they stimulate activities of the stomach, pancreas and gallbladder

• Kidney: Erythropoietin stimulates RBC production– Renin stimulates aldosterone secretion and

constricts blood vessels


Other Chemical Messengers

Function in ways similar to hormones but aren’t secreted directly into the bloodstream. – Actions of these are primarily local– Actions short because they are either quickly

destroyed or reabsorbed by the cells that produced them

• Histamine: inflammation– Mast cells release into local interstitial fluid in

response to tissue injury or allergen presence• Histamine increases local mucus secretion, dilates

blood vessels and increases the leakiness of capillaries


• Prostaglandins: local control of blood flow; – Can constrict or dilate blood vessels depending on

what is needed; contribute to the inflammatory response; involved in blood clotting at injury site

• Nitric oxide: multiple functions– Regulates local blood flow, regulating smooth muscle

contraction in the digestive tract; fights bacteria, interferes with clotting mechanisms

• Growth factors: local acting to modify development of specific tissues; influence when a cell will divide

endocrine-bio 102 handout1 endocrine system rev 12-12 collection of specialized cells, tissues and...

Documents

nonsteroid hormones

hormones target cells

ducts hormones

nervous system endocrine

handout2 endocrine glands

endocrine control slower

hormone release slide

handout1 endocrine system