Ch 13 Intro To A&p

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Endocrine System

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the endocrine system releases hormones into interstitial fluid (fluid that surrounds cells) and then into the bloodstream. The circulating blood then delivers hormones to virtually all cells throughout the body, and cells that recognize a particular hormone will respond.

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What is the basic difference between endocrine glands and exocrine glands?

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Secretions of endocrine glands diffuse into interstitial fluid and then into the blood; exocrine secretions flow into ducts that lead into body cavities or to the body surface

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endocrine gland secretions

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secrete their products (hormones) into interstitial fluid, the fluid that surrounds tissue cells. Then, the hormones diffuse into blood capillaries, and blood carries them throughout the body.

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Lipid-soluble hormones

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diffuse through the lipid bilayer of the plasma membrane and bind to their receptors within target cells

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Lipid soluble hormone effects

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A lipid-soluble hormone detaches transport protein in the bloodstream. The free hormone diffuses from blood into interstitial fluid through plasma membrane into a cell.

The hormone binds to and activates receptors within the cell. The activated receptor–hormone complex turns specific genes on or off.

As the DNA is transcribed, new messenger RNA (mRNA) forms, leaves the nucleus, and enters the cytosol. It directs synthesis of a new protein, often an enzyme, on the ribosomes.

The new proteins alter the cell's activity and cause the responses typical of that specific hormone.

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water-soluble hormones

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water-soluble hormones bind to receptors that protrude from the target cell surface.

When a water-soluble hormone binds to its receptor at the outer surface of the plasma membrane, it acts as the first messenger

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Second messenger

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An intracellular mediator molecule that is produced in response to a first messenger (hormone or neurotransmitter) binding to its receptor in the plasma membrane of a target cell.

Initiates a cascade of chemical reactions that produce characteristic effects for that particular target cell.

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Cyclic AMP

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Molecule formed from ATP by the action of the enzyme adenylate cyclase; serves as second messenger for some hormones and neurotransmitters.

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Why is cAMP called a “second messenger”?

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It brings the message of the first messenger, the water-soluble hormone, into the cell.

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Hormone secretion is regulated by

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(1) signals from the nervous system

(2) chemical changes in the blood

(3) other hormones

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relationship between the hypothalamus and the pituitary gland

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hypothalamus synthesize at least nine hormones

the pituitary gland secretes seven (also called hypophysis)

regulation of virtually all aspects of growth, development, metabolism, and homeostasis

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Which lobe of the pituitary gland does not synthesize the hormones it releases? Where are its hormones produced?

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The posterior pituitary releases hormones synthesized in the hypothalamus

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Pituitary Gland

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controlled by the hypothalamus (hypophysis) Nickname "Master Gland" - releases hormones which activate the other gland

Human Growth Hormone and Insulinlike Growth Factors
Thyroid-Stimulating Hormone
Adrenocorticotropic Hormone
Prolactin
Follicle-Stimulating Hormone and Gonadatrophin
Antidiuretic Hormone
Oxytocin
Melanocyte-stimulating Hormone

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Functions of the Thyroid

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Thyroxine (T4)Increases metabolic rate and cardiac output; stimulates
growth; development, growth, and activity of the nervous system. It is the major hormone secreted by the thyroid follicles.

Triiodothyronine (T3) --Same functions as T4. Formed at the target tissues by conversion of T4 to T3.

Calcitonin -- Pulls calcium from blood into the bones. Inhibits bone breakdown (osteoclast activity) and bone resorption (pulling of calcium out of bones into blood). Has a bone sparing effect

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Thyroid gland

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Largest endocrine gland - butterfly shaped
anterior neck overlying the trachea (just below the voice box) with right and left lateral lobes on either side of the trachea connected by an isthmus

secretes thyroxine (T4), triiodothyronine (T3), and calcitonin (CT)

Activated by adrenocorticotropic hormone

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Control of Thyroid Hormone Secretion

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Thyrotropin-releasing hormone (TRH) from the hypothalamus

and thyroid-stimulating hormone (TSH) from the anterior pituitary

stimulate synthesis and release of thyroid hormones

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Thyroid hormone process

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Low blood level of thyroid hormones or low metabolic rate stimulate the hypothalamus to secrete TRH.

TRH is carried to the anterior pituitary, where it stimulates secretion of thyroid-stimulating hormone (TSH).

TSH stimulates thyroid follicular cell activity, including thyroid hormone synthesis and secretion, and growth of the follicular cells.

The thyroid follicular cells release thyroid hormones into the blood until the metabolic rate returns to normal.

An elevated level of thyroid hormones inhibits release of TRH and TSH (negative feedback).

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Calcitonin

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The hormone produced by the parafollicular cells of the thyroid gland

Calcitonin can decrease the level of calcium in the blood by inhibiting the action of osteoclasts, the cells that break down bone

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Parathyroid gland

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One of usually four small endocrine glands embedded in the posterior surfaces of the lateral lobes of the thyroid gland.

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Parathyroid hormone (PTH)

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A hormone secreted by the chief (principal) cells of the parathyroid glands that increases blood calcium level and decreases blood phosphate level.

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glucagon

Insulin

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The main action of glucagon is to increase blood glucose level when it falls below normal, which provides neurons with glucose for ATP production

Insulin, by contrast, helps glucose move into cells, especially muscle fibers, which lowers blood glucose level when it is too high.

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What are the primary target tissues for

PTH

calcitonin

calcitriol?

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PTH are bone and kidneys

the target tissue for calcitonin is bone

the target tissue for calcitriol is the gastrointestinal (GI) tract

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Pancreatic islet

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A cluster of endocrine gland cells in the pancreas that secretes insulin, glucagon, somatostatin, and pancreatic polypeptide

Also called an islet of Langerhans

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Insulin actions

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Insulin acts on various cells in the body to promote facilitated diffusion of glucose into cells, especially skeletal muscle fibers;

to speed synthesis of glycogen from glucose; to increase uptake of amino acids by cells; and to increase protein synthesis.

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adrenal glands

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There are two adrenal glands, one lying atop each kidney

Each adrenal gland has regions that produce different hormones:

the outer adrenal cortex - secretes steroid hormones

the inner adrenal medulla - secretes epinephrine and norepinephrine

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Cortisol and other glucocorticoids have the following actions:

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Protein breakdown

Glucose formation

Breakdown of triglycerides

Anti-inflammatory effects

Depression of immune responses

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Ovary

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Female gonad that produces oocytes and hormones

estrogens
progesterone
inhibin
relaxin

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Pineal gland

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A cone-shaped gland located in the roof of the third ventricle that secretes melatonin.

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Melatonin

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A hormone secreted by the pineal gland that helps set the timing of the body's biological clock.

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Stress response

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Wide-ranging set of bodily changes, triggered by a stressor, that gears the body to meet an emergency. Also known as general adaptation syndrome (GAS)

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fight-or-flight response

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initiated by nerve impulses from the hypothalamus to the sympathetic division of the autonomic nervous system (ANS) including the adrenal medullae

brings huge amounts of glucose and oxygen to the brain, skeletal muscles, the heart

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Hormones

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Chemical messengers that are released directly in the bloodstream.

They function to regulate growth, metabolism, reproduction, and behavior.

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Target tissue

Receptors

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Target tissue: tissue acted on by each hormone

Receptors: sites in the cell membrane to which a hormone may attach.

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Chemically, hormones fall into the following categories:

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Amino acid compounds --Most hormones fall into this category

Steroids -- hormones derived from lipids produced by the adrenal cortex and sex glands

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Negative feedback

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Self-regulating system in which the concentration of the hormone itself acts as a brake on further secretion of a hormone.

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Tropic hormones

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stimulate or inhibit the release of hormones

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Hypothalamus location

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Neural tissue in the brain that links the nervous system to the endocrine
system

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Hypothalamus function

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a neuroendocrine organ - both neural and endocrine functions

Neurons secrete tropic hormones which stimulate or inhibit the
release of hormones from their target cells

releasing hormones (ex: growth hormone releasing hormone, prolactin releasing hormones, Gonadotropin releasing hormone)

inhibiting hormones (Growth hormone inhibiting hormone, prolactin inhibin hormone)

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Pituitary Gland Structure

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Infundibulum -- stalk which suspends the pituitary gland in the brain

Anterior pituitary (adenohypophysis)
-composed of glandular tissue. Manufactures and releases a number of hormones.

Posterior pituitary (neurohypophysis)
Actually part of the brain. It derives from a downgrowth of hypothalamic tissue and maintains a neural connection with the Hypothalamus

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Hormones secreted by the Anterior pituitary gland

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1. Human growth hormone

2. Thyroid stimulating hormone

3. Adrenocorticotropic hormone

4. Prolactin

5. Gonadotrophins
a. Follicle-stimulating hormone -- production of eggs in the ovaries, and sperm in the testes.
b. Luteinizing hormone (LH) -- ovulation in females, sex hormone secretion in both males and females

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HGH disorders

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Disorders associated with human growth hormone:

Hypersecretion:
Gigantism -- occurs during growing years. Child grows to Extremely tall (7+ feet)
Acromegally -- occurs during adult years. Characterized by distored features.

Hyposecretion:
Pituitary dwarfism: Caused by deficient GH in children. May interfere with development of secondary sex characteristics

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Hormones of the Posterior Pituitary

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Hormones of the Posterior Pituitary

Antidiuretic hormone (Vasopressin) Increases blood pressure by promoting the reabsorption of water from the kidney tubules, thus decreasing the excretion of water. Abbreviated as ADH.

Oxytocin -- Causes contraction of the muscles of the uterus during labor; ejection of milk from breast during breast feeding.

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Disorders of related to the Posterior Pituitary gland

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Antidiuretic hormone
Hyposecretion of Posterior pituitary hormones
Diabetes insipidus -- caused by the insufficient production of vasopressin by the posterior portion of the pituitary gland

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Disorders associated with the Thyroid gland:

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T3 and T4:
Hypersecretion:
Graves disease -- Characterized by increased metabolic rate which
results in weight loss, intense nervousness, rapid pulse, sweating, tremors. autoimmune disorder

Hyposecretion:
Cretinism: Condition resulting from severe hypothyroidism in infants and children, may have mental retardation if condition is not caught early enough to provide hormone replacement therapy

Myxedema: Results from atrophy of the thyroid in the adult, sluggishness, weight gain due to low metabolic weight; thick, dried skin; puffy eyes; goiter if caused by a lack of iodine