Chapter 18: Endocrine System

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What are the four types of communication between cells?

Direct communication, paracrine communication, endocrine communication, and synaptic communication

What is direct intercellular communication?

2 cells of the same type with extensive physical contact

What is paracrine intercellular communication?

use of chemical messengers to communicate between cells

What is a hormone?

a chemical messenger secreted into the bloodstream and transported to target cells in other parts of the body where they alter cellular activity

What is endocrine intercellular communication?

hormones coordinate cellular activity in distant parts of the body

What is synaptic intercellular communication?

quick communication between neurons with neurotransmitters

What is the goal of the endocrine system?

To preserve homeostasis in the body

What three affects can a hormone have on a target cell?

1. increase production of enzymes and proteins through gene activation in the nucleus 2. decrease production of enzymes and proteins by affecting transcription or translation 3. turn an enzyme or channel on or off by altering its shape

How can you define the endocrine system?

all the cells and tissues that produce hormones or paracrine factors to effect other parts of the body

What is the difference between endrocrine and exocrine cells?

endocrine secretes into extracellular fluid and exocrine secretes through ducts onto epithelial surfaces

What are the three classes of hormones?

1. amino acid derivatives 2. peptide hormones 3. Lipid derivatives

What are two types of amino acid hormones? Give examples of each.

tyrosine (thyroid hormones and catecholamines: E, NE, and dopamine) and tryptophan (melatonin from the pineal gland)

What are the two categories of peptide hormones? Give examples of each.

glycoproteins (TSH, LH, and FSH from the pituitary gland) and Short polypeptides and small proteins (ADH, Oxytocin, GH, Prolactin)

What are the two categories of Lipid hormones? Give examples of each.

Eicosanoids (leukotrienes and prostaglandins) and Steroid hormones (androgens, estrogens, progestins, corticosteroids, calcitriol)

What important process do eicosanoids affect?

blood clotting

What are leukotrienes?

eicosanoids released by white blood cells that respond to injury or disease

What are prostaglandins?

eicosanoids that affect local cellular activities

Where are androgens produced?

testes

Where is estrogen produced?

ovaries

Where are progestins produced?

ovaries

Where are corticosteroids produced?

adrenal glands

Where is calcitriol produced?

kidneys

Once in the blood stream, what two courses of action may a hormone take?

can circulate freely or bind to a carrier protein

What is a first messenger?

a hormone that binds to cell membranes

What is a second messenger?

it's triggered by the first messenger and it changes the rate of metabolic reactions

What are three common second messengers?

cyclic AMP (derivative of ATP), cyclic GMP (derivative of GTP), and calcium ions

Explain up regulation.

if there is an absence of a hormone that a cell needs, it will increase its number of receptors for that hormone thereby increasing its sensitivity to it

Explain down regulation.

If there is an overabundance of a hormone that a cell needs, it will decrease its number of receptors for that hormone thereby decreasing its sensitivity to it

What is a G protein?

the link between the first and second messenger

When a G protein is activated by a hormone, it can activate cAMP. Describe this process.

1. G protein activates enzyme adenylate cyclase
2. Adenylate cyclase converse ATP to cAMP
3. cAMP activates kinase which attaches a high energy phosphate group to another molecule; phosphorylation
4. important enzymes are activated and ion channels are opened

What enzyme inactivates cAMP?

phophodiesterase (PDE)

When a G protein is activated by a hormone, it can open ion channels or release Ca ions from intracellular storage. Describe this process.

1. G protein activates phospholipase C (PLC) leading to a receptor cascade
2. Diacylglycerol (DAG) and inositol triphosphate are produced (IP3) from membrane phospholipids
3. IP3 diffuse into cytoplasm and triggers release of Ca2+ from intracellular reserves (in smooth ER)
4. DAG and intracellular Ca2+ activate membrane protein kinase C (PKC).
5. The activation of PKC leads to the phosphorylation of calcium channel proteins, which open the channel and allows extracellular Ca2+ to enter the cell
6. Protein calmodulin binds to Ca2+ and activates specific cytoplasmic enzymes

Which types of hormones bind to the cell membrane activating the G protein?

Catecholamines, peptide hormones, and eicosanoids

Lipid hormones can pass through the glycolipid bilayer of a cell membrane and bind to receptors inside the cytoplasm. What takes place from that point?

the hormone-receptor complex activates or deactivates specific genes in the nucleus altering the rate of transcription affecting protein synthesis

How do thyroid hormones affect cellular activity? (process)

1. they cross the cell membrane by active transport and bind to receptors in the nucleus and on mitochondria
2. those that bind to receptors in the nucleus change the rate of transcription which affects metabolic activity of the cell by increasing or decreasing enzymes
3. those that bind to mitochondria increase ATP production

What are regulatory hormones?

hormones secreted by the hypothalamus that affect the anterior lobe of the pituitary gland

What hormones does the hypothalamus synthesize and release into circulation within the pituitary gland?

oxytocin and ADH

What is another name for the pituitary gland?

hypophysis

What structure connects the pituitary gland to the hypothalamus?

infundibulum

What is another name for the anterior lobe of the pituitary gland?

adenohypophysis

What three mechanisms does the hypothalmus use to control the body's endocrine system?

1. secretion of regulatory hormones to the anterior lobe of the pituitary gland
2. production of ADH and oxytocin which it releases into the posterior lobe of the pituitary gland
3. control of the sympathetic output to adrenal medullae; affecting secretion of E and NE

The anterior lobe of the pituitary gland can be divided into three regions. What are those regions? Describe their locations.

1. Pars distalis- largest and most anterior portion
2. Pars tuberalis- extension wrapping around the infundibulum
3. Pars intermedia- a narrow band bordering the posterior lobe

What is the function of the hypophyseal portal system?

To transport regulatory hormones from the hypothalamus to the anterior lobe of the pituitary gland

What are portal vessels?

blood vessels that link 2 capillary networks (as in the hypophyseal portal system)

What is the function of the releasing hormones of the hypothalamus?

to stimulate synthesis and secretion of hormones in the anterior lobe of the pituitary gland

What is the function of the the inhibiting hormones of the hypothalamus?

to inhibit the synthesis and secretion of hormones in the anterior lobe of the pituitary gland

What are tropic hormones?

anterior lobe hormones whose purpose is to turn on other endocrine glands in the body

What hormones does the A.L.P.G. synthesize and secrete? (6)

TSH (thyroid stimulating hormone), ACTH (adrenocorticotropic hormone), Gonadotropins, PRL (Prolactin), GH (Growth Hormone), MSH (Melanocyte-stimulating hormone)

Which hypothalamic-releasing hormone triggers TSH?

Thyrotropin-releasing hormone (TRH)

Which hypothalamic-releasing hormone triggers ACTH?

corticotropin-releasing hormone (CRH)

What does ACTH of the A.L.P.G. do?

stimulates the release of steroid hormones by the adrenal cortex (ie. glucocorticoids which affect glucose metabolism)

What do gonadotropins of the A.L.P.G. do?

regulates activities of gonads including reproductive cell and hormone production

What hormone stimulates Gonadotropins?

Gonadotropin-releasing hormone (GnRH) from the hypothalamus

What is hypogonadism?

abnormally low production of gonadotropins resulting in no sexual maturation

What are the two kinds of Gonadotropins?

Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH)

What does FSH do for males and females?

males: sperm maturation
females: promotes estrogen secretion (ie estradiol)

What does LH do for males and females?

males: stimulates androgen production (ie. testosterone)
females: induces ovulation and promotes secretion of estrogen and progestin

What function does progestin serve?

prepares a woman for pregnancy

What function does the hormone Prolactin serve?

stimulates mammary gland development

Explain the two mechanisms by which GH accelerates protein synthesis resulting in cell growth and replication.

1. causes liver to make somatomedins or insulin-like growth factors (IGFs); these bind to cells and increase the uptake rate of amino acids and incorporation into new proteins.
2. stimulates stem cell divisions in epithelia and connective tissue; stimulates breakdown of triglycerides in adipose tissue and tissues break this down generating ATP

What is the diabeticogenic effect?

in the liver, GH stimulates the break down of glycogen reserves resulting in the elevation of glucose in the blood

What hormones regulate the secretion of GH?

Growth Hormone Releasing Hormone (GH-RH) and Growth Hormone Inhibiting Hormone (GH-IH) from the Hypothalamus

What does Melanocyte-stimulating hormone do?

stimulates melanocytes to produce melanin; however, this is non functional in adults because melanin is produced locally in the skin

What is another name for the Posterior Lobe of the Pituitary Gland?

Neurohypophysis because it contains axons of hypothalamus neurons

How and where are Oxytocin and ADH produced?

In the Hypothalamus, neurons, supraoptic and Paraventricular nuclei manufacture them and transport them to the posterior lobe of the pituitary gland

What triggers the release of ADH?

high solute concentration in blood or fall in the volume or pressure of blood

What function does ADH serve?

to decrease water loss at the kidneys thereby increasing blood volume and decreasing solute concentration of the blood

What does drinking alcohol cause frequent urination?

it inhibits ADH resulting in excessive water loss at the kidneys

What is diabetes insipidus?

posterior lobe does not secrete ADH; causes frequent urination and thirst

What does oxytocin do?

stimulates smooth muscle contraction in the uterus and the ejection of milk

thyroid anatomy:
What is a thyroid follicle?

a hollow sphere

thyroid anatomy:
What is a follicle cavity?

holds colloid which has lots of protein

thyroid anatomy:
What is thyroglobulin?

the follicle cells produce this globular protein and secrete it into the colloid. These molecules contain tyrosine which forms thyroid hormones

Explain the process by which the thyroid gland synthesizes and secretes T3 and T4.

1. TSH opens follicle channels to admit I-
2. Iodide ions from the diet are transported into cytoplasm of follicle cells.
3. Iodide ions are converted to I+ by thyroid peroxidase; one or two I- are attached to thyrosine portion of thyroglobulin
4. These thyrosine-I- complexes form covalent bonds with one another to make thyroid hormones thyroxine T4 (has 4 I-) and Triiodothyronin T3 (has 3); These remain incorporated into thyroglobulin.
5. Follicle cells remove thyroglobulin from follicles by endocytosis
6. Lysosomal enzymes break thyroglobulin into amino acids and thyroid hormones.
7. T3 and T4 enter the bloodstream
8. Most T4 and T3 attach to thyroid-binding globulins; the rest attach to transthyretin

Explain the process by which T3 and T4 hormones affect target cells.

1. They bind to cytoplasmic receptors of target cells to affect storage
2. They bind to mitochondria to increase ATP production
3. they bind to receptors in the nucleus to accelerate the production of an enzyme responsible for the sodium-potassium pump

What is the ultimate effect that T3 and T4 have on a target cell?

increase the metabolic rate

What is the calorigenic effect?

heat generation as a result of consumed energy in the cell

Why is most of the body's iodide reserve stored in the thyroid gland?

TSH stimulates iodide from the diet to be actively transported to thyroid follicle cells

When there is too much Ca+ in the blood, what do the thyroid glands produce?

C cells produce calcitonin which results in decreased Ca+ levels

What do high Ca+ levels cause?

decreased permeability to Na+

What do low Ca+ levels cause?

increased permeability to Na+ and muscle spasms

Where are the parathyroid glands located?

2 pairs in the posterior surface of the thyroid

What are the two types of cells in parathyroid glands?

chief cells and oxyphils

What is the function of the chief cells?

to monitor Ca2+ levels in the blood; they act in opposition of C cells; while C cells respond to high levels of Ca2+ by secreting calcitonin, chief cells respond to low levels by secreting parathyroid hormone (PTH) which increases Ca2+

Does calcitonin activate osteoclasts or osteoblasts in the bone? PTH?

osteoblasts; osteoclasts

What effect does PTH have on the body? (specific)

1. stimulates osteoclasts and inhibits osteoblasts
2. enhances reabsorption of Ca2+ at the kidneys
3. stimulates calcitriol at kidneys which enhances Ca 2+ absorption at the digestive tract.

Why is the Adrenal cortex yellow?

stored lipids

What are the steroids of the adrenal cortex called?

Adreno-corticosteroids

Why can a person not live without corticosteroids?

they are in charge of which genes are transcribed and at what rate

What are the three layers of the adrenal cortex from outermost to innermost?

zona glomerosa, zona fasciculata, zona reticularis

What hormone does the zona glomerosa produce?

mineralcorticoids (specifically aldosterone) which affect electrolyte levels in the blood

What does aldosterone do?

stimulates conservation of Na+ and elimination of K+

What does the zona fasciculata produce?

glucocorticoids

What do glucocorticoids do?

accelerate glucose synthesis and glycogen formation; anti-inflammatory- inhibits white blood cells; can be used to control allergies

Which hormone triggers the zona fasciculata to produce glucocorticoids?

adreno cortico tropic hormone from the anterior lobe of the pituitary gland

What are two glucocorticoids?

cortisol and corticosterone

What can the liver convert cortisol into ?

cortisone

What hormones does the zona reticularis produce and what effect do they have on the body?

androgens that are converted to estrogens; stimulate pubic hair; important for muscle mass, blood cell formation and libido in adult women

Why is the adrenal medulla not a typical endocrine gland?

Its hormone production is triggered by the autonomic nervous system (sympathetic division)

What hormones does the adrenal medulla produce and secrete?

epinephrine and norepinephrine

How do the effects of E and NE differ from any other response from the sympathetic nervous system?

the effects last several minutes; other responses last mere seconds

Where is the pineal gland located

posterior roof of the third ventricle

What are the secretory cells of the pineal gland called and what do they secrete?

pinealocytes; melatonin

What is the function of melatonin?

1. inhibits reproductive function
2. protects against damage by free radicals
3. sets circadian rhythms

What other body system is the pancreas a part of? Why?

digestive system; makes digestive enzymes

Which portion of the pancreas has an endocrine function?

pancreatic islets

What four types of cells are in the pancreatic islets?

alpha, beta, delta, and F cells

What do the alpha cells of the pancreatic islets produce?

glucagon

What effect does glucagon have on the body?

raises blood glucose levels

What do the beta cells of the pancreatic islets produce?

produce insulin

what effect does insulin have on the body?

lowers blood glucose levels

What two antagonistic hormones do the pancreatic islets produce?

glucagon and insulin

What do the delta cells of the pancreatic islets do?

suppress glucagon and insulin release

What hormone do the F cells of the pancreatic islets produce and secrete?

pancreatic polypeptide (PP)

What effect does pancreatic polypeptide (PP) have on the body?

inhibits gallbladder contractions

What characterizes insulin-dependent cells?

they have insulin receptors and require insulin to absorb glucose

What characterizes insulin-independent cells and where are these cells located in the body?

they do not have insulin receptor and do not require insulin to absorb glucose; brain, kidneys, digestive tract, and red blood cells

What effect does insulin have on the cells it binds to?

stimulates glucose utilization to support growth and establishment of glycogen and triglyceride reserves

What effects does glucagon have on the body?

mobilizes glycogen reserves for use
1. stimulates the break down of glycogen in muscle and liver
2. stimulates the break down of triglycerides in adipose tissue
3. stimulates glucose production in liver

What controls most digestive processes?

local hormones

What hormones do the kidneys produce and secrete?

Calcitriol, Erithropoietin (EPO) and Renin

What triggers the release of Calcitriol from the kidneys?

low Calcium levels in the blood trigger the release of Parathyroid hormones which trigger the release of Calcitriol

What is Cholecalciferol?

Vitamin D that is synthesized in the skin when exposed to sun; can be converted to calcitriol

What effect does Calcitriol have on the body?

stimulates Calcium and Phosphate ion absorption along digestive tract

What triggers the production and release of Erithropoietin (EPO) by the kidneys?

low oxygen levels in the kidneys

What does EPO accomplish in the body?

stimulates the production of red blood cells by bone marrow

What stimulates the production and release of Renin from the kidneys?

sympathetic stimulation and decline in kidney blood flow

What effect does Renin secretion from the kidneys have on the body?

increases blood pressure and volume by retricting salt and water loss at the kidneys

How are heart endocrine glands antagonistic to kidney endocrine glands?

Renin from the kidneys responds to low blood pressure and increases it; the heart's endocrine glands respond to high blood pressure and lower it

How do the endocrine cells in the heart detect high blood pressure?

They are cardiac muscle cells in the wall of the chambers; when blood volume increases, they get stretched and are mechanically triggered

What hormone do the heart's endocrine glands secrete?

natriuretic peptides

What effect do natriuretic peptides have on the body?

they promote loss of Na+ and water at the kidneys, suppress thirst, and prevent E and NE from elevating blood pressure

Where is the thymus located?

the mediastinum

What hormone does the thymus produce?

thymosin

What effect does thymosin have on the body?

promotes development of lymphocytes

What two types of endocrine cells are in a male's gonads?

1. interstitial cells
2. sustentacular cells

What hormone do the interstitial cells of the testes release?

androgens, eg. testosterone

What hormone do the sustentacular cells of the testes release?

inhibin

What effect does inhibin have on the body?

inhibits FSH and GnRH; supports differentiation and physical maturation of sperm

What hormones do adipose tissue release?

leptin and resistin

What effect does leptin have?

feelings of fullness

What effect does resistin have?

reduces insulin sensitivity

How does resistin correlate with obesity and diabetes?

Obese people have more adipose tissue that releases more resistin. Resistin causes less sensitivity to insulin resulting in higher blood sugar.

What is antagonistic effect?

two hormones inhibit one another (PTH and calcitonin)

What is a synergistic effect?

the result of two hormones is greater than the sum

What is a permission effect?

the first hormone is needed for the second hormone

What is an integrative effect?

2 hormones produce a different but complementary effect (work well together)

Without thyroid hormones during fetal development what is the result?

mental retardation

What is the result of low thyroid prior to puberty?

normal skeletal development cannot occur

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