Terms in this set (160)
What is the endocrine System?
Deals with hormones and is involved with adaptation to stress
What are the 4 mechanisms of communication between cells?
1. Gap junctions
3. Paracrine hormones
Pores in cell membrane allow signalling molecules, nutrients, and electrolytes to move from cell to cell
Released from neurons to travel from pre- synaptic to post- synaptic neurons
Local hormones secreted into tissue fluids to affect nearby cells
Chemical messengers that travel in the bloodstream to other tissues and organs
Glands, tissues, and cells that secrete hormones
Study of endocrine System and the diagnosis and treatment of its disorders
Organs that are traditional sources of hormones
Chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ -- usually far away
What are the major organs of the endocrine System?
- pineal gland
- pituitary gland
- thyroid gland
- adrenal glands
- parathyroid glands
- gonads -- ovaries, testes
Organs of the endocrine system
What are the 2 types of glands?
- no ducts
- contain dense, fenestrated capillary networks that allow easy uptake of hormones into bloodstream
- internal secretions
- intracellular effects such as altering target cell metabolism
External secretions -- ducts carry secretion to an epithelial surface or the mucosa of the GI tract
- extracellular effects -- food digestion
What chemicals function as hormones and neurotransmitters?
3. Thyrotropin-releasing hormone
5. Antidiuretic hormone
What hormones are secreted by neuroendocrine cells?
Neurons that release secretion in the bloodstream
What chemicals cause overlapping effects on same target cells in the nervous and endocrine systems?
Norepinephrine and glucagon cause glycogen hydrolysis in liver
How do the endocrine and nervous system regulate eachother?
- neurons trigger hormone secretion
- hormones stimulate or inhibit neurons
What are target organs or cells?
Organs or cells that have hormone receptors and can respond to them
Where is the hypothalamus?
Forms floor and walls of third ventricle of the brain
What does the hypothalamus do?
Regulates primitive functions of the body from water balance and thermoregulation to sex drive and childbirth
Many functions carried out pituitary gland
What is the pituitary gland suspended from?
In the hypothalamus by the infundibulum
Where is the pituitary gland housed?
Stella turcica of sphenoid bone
What two structures compose the pituitary gland?
- Adenohypophysis -- anterior pituitary
- Neurohypophysis -- posterior pituitary
Anterior three-quarters of pituitary
- Has two segments
- Linked to hypothalamus by hypophyseal portal system
What is the hypophyseal portal system?
Primary capillaries in hypothalamus connected to secondary capillaries in adenohypophysis by portal venules
What are the 2 segments of the adenohypophysis?
1. Pars Distalis -- anterior lobe
2. Pars Tuberalis -- small mass of cells adhering to stalk
Posterior one-quarter of the pituitary
- Has 3 parts
- Nerve tissue -- not a true gland
*Nerve cell bodies in hypothalamus pass down the hypothalamo-hypophyseal tract and end in posterior lobe
- Hypothalamic neurons secrete hormones that are stored in the neurohypophysis until released into blood
What are the 3 parts of the neurohypophysis?
1. Median Eminence
3. Posterior Lobe
What is the main difference between the adenohypophsis and the neurohypophysis?
Hormones are secreted by the adenohypophysis and stored in the neurohypophysis
Hormones released by the pituitary
How many hormones are produced in the hypothalamus?
8 are produced in the hypothalamus:
- 6 regulate the anterior pituitary
- 2 are released into the capillaries in the posterior pituitary and stored in the posterior pituitary when hypothalamic neurons are stimulated
What are the 6 releasing and inhibiting hormones that stimulate or inhibit the anterior pituitary?
1. TRH -- thyrotropin releasing hormone
2. CRH -- corticotropin releasing hormone
3. GnRH -- gonadotropin releasing hormone
4. GHRH -- growth hormone releasing hormone
5. PIH -- prolactin inhibiting hormone
What are the 4 releasing hormones that stimulate the anterior pituitary?
1. TRH -- thyrotropin releasing hormone
2. CRH -- corticotropin releasing hormone
3. GnRH -- gonadotropin releasing hormone
4. GHRH -- growth hormone releasing hormone
What are the 2 inhibiting hormones that inhibit the anterior pituitary?
1. PIH -- prolactin inhibiting hormone
What do the 4 releasing hormones in the hypothalamus stimulate in the anterior piuitary?
Secreted by the Anterior Lobe:
1. TSH -- thyroid stimulating hormone
2. PRL -- prolactin
3. ACTH -- adrenocorticotropic hormone
4. FSH -- folicle stimulating hormone
5. LH -- luteinizing hormone
6. GH -- growth hormone
What do the 2 inhibiting hormones in hypothalamus inhibit in the anterior pituitary?
1. PRL -- prolactin
2. TSH -- thyroid stimulating hormone
3. GH -- growth hormone
Hypothalamic Hormones and Anterior Pituitary Hormones
What is folicle stimulating hormone?
stimulated secretion of ovarian sex hormones, development of ovarian follicles, and sperm production
What is Luteinizing Hormone?
Stimulates ovulation, stimulates corpus luteum to secrete progestrone, stimulates testes to secrete testerone
What is thyroid stimulating hormone?
Stimulates secretion of thyroid hormone
What is adrenocorticotropic hormone?
Stimulates adrenal cortex to secrete glucocorticoids
What is prolactin?
After birth, stimulates mammary glands to synthesize milk; enhances secretion of testosterone by testes
What is growth hormone?
Stimulates mitosis and cellular differentation
- half0life of 6-20 minutes
What are the two hypothalamic hormones stored in the posterior pituitary?
1. OT -- Oxytocin
2. ADH -- Antidiuretic hormone
What is oxytocin?
- produced in the right and left paraventricular nuclei of the hypothalamus
- transported by hypothalamo-hypophyseal tract
- stored in the posterior pituitary
- surge of hormone released during sexual arousal and orgasm which stimulates uterine contractions and propulsion of semen
- promotes feelings of sexual satisfaction and emotional bonding
- stimulates labor contractions during childbirth
- stimulates flow of milk during lactation that prolactin synthesizes
- emotional bonding between mother and infant
What is antidiuretic hormone?
- produced in the supraoptic nuclei of the hypothalamus
- transported by the hypothalamo-hypophyseal tract
- stored in the posterior pituitary
- increases water retention which reduces urine volume and prevents dehydration
- also called vasopressin because it causes vasoconstriction
Control of pituitary secretion
Rates of secretion are not constant
- regulated by hypothalamus, other brain centers, and feedback from target organs
Hormones and Target Organs
What are the 2 types of hypothalamic and cerebral control?
1. Anterior lobe control
2. Neuroendocrine reflex
What is anterior lobe control?
Releasing and inhibiting hormones from the hypothalamus
- eg. Cold weather pituitary simulated by hypothalamus to release TSH which generates body heat
What is neuroendocrine reflex?
Hormone release in response to nervous system signals or higher brain centers
- eg. Milk ejection reflex can be triggered by a baby cry
- eg. Infant suckling --> simulates nerve endings --> hypothalamus --> posterior lobe --> oxytocin --> milk ejection
- eg. Emotional stress can affect secretion of gonadotropins, disrupting ovulation, menstruation and fertility
Negative feedback in pituitary secretion
Increased target organ hormone levels inhibit release of hormones
Positive feedback in pituitary secretion
Stretching of uterus increases oxytocin release, causes more contractions, causes more uterine stretching, until delivery
Pituitary Positive and Negative Feedback
What body tissues get the most effect from growth hormone?
What is growth hormone effect on the liver?
Induces liver to produce growth stimulants
- eg. Insulin- like growth factors (IGF-I) or somatomedins (IGF-II)
- Protein Synthesis Increases
- Lipid Metabolism Increases
- Carbohydrate Metabolism
- Elwectrolyte Balance
How does the liver produce growth stimulants?
- Target cells are stimulated in diverse tissues
- IGF-I prolongs the action of growth hormone
What is Insulin-Like Growth Factor?
- causes skeletal muscle hypertrophy and activation of osteocytes
- it can also complement the effects of insulin
- Half-life of 20 hours
What is Somatomedins?
- binds to IGF-I receptor and is a growth-promoting hormone during gestation
What is Hormone half life?
the time required for 50% of the hormone to be cleared from the blood
How does GH cause protein synthesis increase?
boots transcription of DNA, production of mRNA, amino acid uptake into cells and supresses protein catabolism
How does GH cause lipid metabolism increase?
fat catabolized by adipocytes (protein-sparing effect) which provides energy for growing tissues
How does GH cause Carbohydrate Metabolism?
- mobilizes fatty acids, reduces the dependance of most cells on glucose -- Will not compete with the brain on glucose
- Makes electrolytes avaiable to growing tissues
How does GH promote electrolyte balance?
Promotes Sodium, Potassium and Chloride retention in kidneys and enhances Calcium absorption in the intestines
How does GH affect bone growth?
It influences thickening and remodeling especially during childhood and adolesence (osteoblasts for rebuliding and osteoclasts for remodeling)
- secretion of GH is high during first 2 hours of sleep
- GH can peak in response to vigorous exercize
- GH levels can decline with age
- Lack of protein snthesis contributes to aging of tissues and wrinkling of the skin
Where is the pineal gland?
attached to roof of third ventricle beneath the posterior end of the corpus callosum
What 3 systems does the thymus affect?
Where is the thymus?
Bilobed gland in the mediastinum superior ot the heart and goes through involution (shrinking) after puberty
- site of maturation of T cells
What hormones are secreted by the thymus?
Stimulate development of lymphatic organs and cause T cell activity
What is the thyroid gland?
Largest endocrine gland
- bilobed with an isthmus below the larynx
- rich blood supply
What are thyroid follicles?
sacs that compose most of thyroid and are lined with follicular cells which are simple cuboidal epithelium
What hormones are secreted by the thyroid?
1. Thyroxine (T4)
2. Triiodothyronine (T3)
What is Thyroxine?
The major hormone T4 derived from the thyroid an is a prohormone of triiodothyronine and is activated from TSH which is secreted from TRH with a half-life of 6.5 days
What is Triiodothyronine?
A hormone in the thyroid that is produced from T4 Thyroxine and has a half-life of 2.5 days. It is responsible for increasing metabolic rate, oxygen consumption, heat production, appetite GH secretion, alertness and quicker reflexes
- stimulates production of RNA polymerase
- potentiates the effects of beta receptors on glucose metabolism
- stimulates breakdown of cholestrol
What are parafollicular cells?
Located adjacent to the thyroid follicles in the connective tissue that secrete calcitonin
What is calcitonin?
Stimulates osteoblast activity and bone formation
What are parathyroid glands?
Usually 4 glands partially embedded in the posterior surface of the thyroid gland
- from hyoid bone to aortic arch
What hormone do parathyroid glands secrete?
What is parathyroid hormone?
- increases blood calcium levels
- promotes synthesis of calcitrol
- increases absorption of calcium
- decreases urinary excretion
- increases bone resorption
What are they adrenal glands?
small gland that sits on top of each kidney
- adrenal cortex and adrenal medulla are formed by merger of two fetal glands with different origins and functions
What are the layers of the adrenal glands?
- Zona Glomerulosa
- Zona Fasciculata
- Zona Reticularis
What is the adrenal medulla?
Inner core of the adrenal gland
- functions as both an endocrine gland and a sympathetic ganglia
- innervated by preganglionic fibers
- responsible for "fight or flight"
- increases blood pressure, heart rate, blood flow to muscles, pulmonary airflow, and metabolic rate
- decreases digestion and urine
What do the adrenal glands secrete?
What is the effect of the adrenal glands with glucose?
- Glucose-sparing effect which inhibits insulin secretion and saves glucose for brain
- glycogenolysis to break down glycogen and make glucose
- gluconeogenesis which generates glucose from non-carbs
What is the adrenal cortex?
Superfical layer of the adrenal glands that produces more than 25 steroid hormones called corticosteroids or corticoids
What are the major steroid hormones secreted from the adrenal cortex?
- sex-steroids libido
What is mineralocorticoid?
Secreted from the zona glomerulosa of the adrenal cortex
- regulates the body electrolyte balance
What is glucocorticoids?
Secreted from the zona fasciculate of the adrenal cortex
- regulates metabolism of glucose and other fuels
What are the pancreatic islets?
Exocrine digestive gland and endocrine cell clusters found retroperitoneal, inferior and posterior to stomach
What do the pancreatic islets release?
4. Pancreatic polypeptide
What is glucagon?
Secreted by A alpha cells
- released between meals when blood glucose concentration is falling
- in liver, similar glucogenesis and glucogenolysis raising blood glucose level
- in adipose tissue, stimulates fat catabolism
- released to rising amino acid levels and provides cells with raw material for gluconeogenesis
What is insulin?
Secreted by B beta cells
- secreted when glucose and amino aid blood levels are rising
- stimulates cells to absorb nutrients and store them lowering blood glucose level
- synthesizes glycogen
- brain, liver, kidneys, and RBCs absorb glucose without insulin
What is somatostatin?
Secreted by D delta cells
- supresses secretion of glucogen and insulin
- inhibits nutrient absorption and digestion to prolong
What is pancreatic polypeptide?
Secreted by PP or F cells
- inhibits gallbladder and intestinal contractions and secretion of stomach acid and pancreatic digestive enzymes
What is gastrin?
Secreted by G cells
- stimulates stomach acid secretion, motility, and emptying
What are the 6 hyperglycemic hormones?
Raise blood glucose level
What is the hypoglycemic hormone?
Lowers blood glucose level
How does the endocrine system affect skin?
Keratinocytes convert a cholestrol like steroid into cholecalciferol with UV
What hormones are produced by the liver?
- converts cholecalciferol into calcidiol
- angiotensinogen which is a precursor of angiotensin II regulates blood pressure
- 15% of erythropoietin which stimulates bone marrow
- hepcidin which promotes intestinal absorption of iron
- IGF-I which controls action of GH
How does the endocrine system affect the kidneys?
Play role in production of 3 hormones
What 3 hormones are produced by the kidneys?
- convert calcidiol to calcitriol
- 85% of erythropoietin
What is calcitriol?
Active form of vitamin D
- increases calcium absorption by intestine and inhibits loss in the urine
What is renin?
Secreted by the kidneys that converts angiotensinogen to angiotensin I
- angiotensin II created by converting enzyme in lungs
What is erythropoietin?
Stimulates bone marrow to produce RBCs
How does the endocrine system affect the heart?
Cardiac muscle secretes:
- atrial natriuretic peptides
- brain natriuretic peptides
In response to an increase in blood pressure
- decrease blood volume and blood pressure by increasing sodium and water output by kidneys and oppose action of angiotensin II
How does the endocrine system affect the stomach and small intestine?
Secrete at least 10 enteric hormones by enteroendocrine cells
- peptide YY
Coordinate digestive motility and glandular secretion
What does adipose tissue secrete?
Leptin which slows appetite
What do osteoblasts secrete in osseous tissue?
- increases number of pancreatic beta cells, pancreatic insulin output and insulin sensitivity
- inhibits weight gain and onset of type II diabetes
What are the 3 chemical classes of hormones?
2. Peptides & Glycoproteins
What are steroids?
- derived from cholestrol
- secreted by gonads and adrenal glands
What are the 7 steroid hormones?
What are peptides and glycoproteins?
- Created from chains of amino acids
- Secreted by pituitary and hypothalamus
What are monomines?
- Derived from amino acids
- secreted by adrenal, pineal and thyroid glands
What are the 4 monomine hormones?
4. Thyroid Hormone
What are all hormones made from?
Cholestrol or Amino Acids
- when a carbohydrate is added it makes a glycoprotein
What are the steps of making a peptide?
1. Inactive preprohormone is made in the cytosol
2. first several amino acids create a signal peptide that guides preprohormone into the cisterna of the rough ER
3. Signal peptide is removed in the rough ER
4. Prohormone is formed
5. Final transformation into hormone is processed in the golgi
6. Hormone is released for secretion
What are the steps to make insulin?
1. Preproinsulin --> proinsulin
2. When connecting peptide is removed, 2 polypeptide chains form to make insulin
What is melatonin?
is synthesized from the amino acid tryptophan and the monomine seratonin from tyrosine
What is thyroid hormone composed of?
What do follicular cells do?
Absorb iodide ions from the blood and store if in the lumen of a blood capillary as a reactive form of iodine
What are the steps of storing iodine from a follicular cell?
1. Iodide absorption and oxidation from the lumen?
2. Thyroglobulin systhesis and secretion
3. Iodine added to tyrosines of thyroglobulin
4. Thyroglobulin uptake and hydrolysis
5. Release of T4 and a small amount of T3 into the blood
What hormone chemicals are hydrophilic?
Most monomines and peptides
- mix easily with blood plasma
What hormone chemicals are hydrophobic?
Steroids and thyroid hormone
- bind to transport proteins (albumins and globulins)
Bound vs Unbound hydrophobic hormones?
- Bound hormones have a longer half life because they are protected from liver enzymed and kidney filtration
- Unbound hormones leave the capillary to reach the target cell
How do transport proteins assist hormones?
Protect circulating hormones from being broken down by enzymes in the plasma and liver and from being filtered out of the blood by the kidneys
How do hormone receptors work?
Hormones stimulate only those cells that have receptors for them
- receptors are protein or glycoprotein molecules on plasma membrane, in the cytoplasm or in the nucleus
- turn on metabolic pathways when hormones bind to them
- usually each target cell has a few thousand receptors for a given hormone
- receptor-hormone interaction has specificity and saturation
How does specifity work in hormone receptors?
Specific receptor for each hormone
What does saturated mean in hormone receptors?
all receptor molecules are occupied by hormone molecules
How do hydrophobic hormones bind to a receptor?
1. penetrate plasma membrane and enter nucleus
2. act directly on the genes changing cell physiology
3. take several hours to days to show effect due to lag of protein synthesis
How do hydrophillic hormones bind to a receptor?
Cannont penetrate into a target cell
- Must stimulate physiology indirectly
How does the second messenger system work in hormone receptors?
Second messengers relay signals to the target molecules from the surface of the cell for hydrophillic hormones such as monomines and peptides
- eg. cAMP
Hormone Receptor Action
one hormone molecule from a small stimulus can trigger the synthesis of many enzyme molecules creating a great effect
- hormone saturates receptors
- receptors create influx of enzymes
- enzymes create a mass reaction/effect
How is target cell sensitivity adjusted?
Changing the number of receptors
What are the 2 types of target cell sensitivity adjustment?
What is up-regulation?
Number of receptors in increased and sensitivity is increased
What is down-regulation?
Number of receptors is decreased and sensitivity is decreased
- happens with long-term exposure to high hormone concentrations where they bind to other receptors and are converted to a different hormone
Can cells be sensitive to more than one hormone?
Most cells are sensitive to more than one hormone and have interactive effects
What are the different types of interactive effects for hormones?
Hormones can sit on same cell receptor
Multiple hormones act together for a greater effect
- eg. prolactin to synthesize milk and oxytocin to stimulate lactation
One hormone enchances the target organ's response to a second later hormone
- eg. thyroid hormone increases the amount of receptors for epinephrine
One hormone opposes the action of another
- eg. insulin lowers blood glucose evels while glucagon raises blood glucose levels
How are hormones disposed of?
Hormone signals must be turned off when their purpose has been served
- most hormones are degraded by the liver and kidneys and excreted by bile or urine
What is the metabolic clearance rate?
Rate of hormone removal from blood
- faster the MCF, the shorter the half-life
What is half-life?
time required to clear 50% of hormone from the blood
What is stress?
Any situation that upsets homeostasis and threatens ones physical or emotional well-being
What is general adaptation syndrome?
consistent way the body reacts to stress which normally involves elevated levels of epinephrine and glucocorticoids
What are the 3 stages of general adaptation syndrome?
1. Alarm Reaction
2. Stage of Resistance
3. Stage of Exhaustion
What is alarm reaction of GAS
Initial Response mediated by norepinephrine from SNS and epinephrine from adernal medulla
- stored glycogen is consumed
- increases aldosterone and angiotensin levels
What does angiotensin do in the alarm reaction
raise blood pressure
What does aldosterone do in the alarm reaction?
promotes sodium and water conservation
What is the stage of resistance in GAS
Glycogen reserves gone, but brain still needs glucose
- provide alternative fuels for metabolism
- dominated by cortisol
- hypothalamus secretes corticotropin-releasing hormone
- pituitary secretes an increase in adrenocorticotropic hormone
What does ACTH do in the stage of resistance?
- stimulates the adrenal cortex to secrete cortisol and other glucocorticoids
- promotes the breakdown of fat and protein for gluconeogenesis
What is gluconeogenesis?
Making glucose from glycerol, fatty acids and amino acids
What is the glucose sparing effect?
Cortisol in the stage of resistance inhibits protein synthesis leaving amino acids free for gluconeogenesis
- can depress immune functions
- can increase susceptibility to infection and ulcers
What is the stage of exhaustion in GAS?
Homeostasis is overwhelmed when fat reserves are gone
- rapid decline and death
- protein breakdown and muscle wasting
- adrenal cortex stops producing glucocorticoids
- aldosterone promotes water retention and hypertension by conserving sodium and eliminating potassium and hydrogen
- death results from heart and kidney infection or other infection
What are paracrines?
chemical messengers that diffuse short distances and stimulate nearby cells
- secreted by a cell and only affect the cell
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