Lecture 6:Endocrine System
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1. What does the Endocrine System do?
- Acts with the nervous systme to coordinate and integrate the activity of body cells
- Influences metabolic activites by means of hormones transported in the blood
2.True or false, response in the endocrine systme are faster and last longer than the nervous system?
False, Responses occur more slowly, but tend to last longer than those of the nervous system
3.Name the Endocrine Glands
- Adreal Ovary
4.True or False, Some organs produce Hormones and Exocrine products.
True, Sone organs produce both hormones and exocrine products (e.g., pancreas and gonads)
5. True or False, the Hypothalmus has bothe neural and endocrine functions
6.What other organs and tissues produce hormones?
- Adipose cells
- Cells in the walls of the small intestine
7. What are Hormones?
- Long-distance chemical signals that travel int he blood or lymp
- exert systmeic action on a certain target tissue
- secreted by ductless glands
8. What secretes Hormones?
Ductless glands secret Hormones
9. What are Autocrines?
Chemcial that exert effects on the same cells that secrete them
10. What are Paracrines
Locally acting chemical that affect cells other than those that secrete them
11. Are Autocrines and Paracrines considered part of the endocrine system?
NO, because they are local chemical messengers
12. What are the two main chemical classes of Hormones?
- Amino acid-based Hormones...proteins in nature
13. Describe Amino acid-based hormones
pronteins in nature
14. Describe Steroids
- Synthesized from cholesterol (lipids in nature)
- Gonadal and adrenocoritcal hormones
15. What is the Hormone action on target cells?
- Alter plasma membrane permeability and/or membrane potential by opening or close ion channels
- Stimulate synthesis of protiens or regulatory molecules
- Activate or deactivate enzyme systems
- Induce secretory activity
- Stimulate mitosis
16. What are the two mechanisms of Hormone Action?
- Water-soluble hormones
- Lipid-solubele hormones
17. What do the Two mechanisms depend on?
their Chemical Nature
18. Describe Water-soluble hormones
- All amion acid-based hormones EXCEPT Thyroid Hormone
- Cannot enter the target cells
- Act on plasma membrane receptors
- Coupled by G proteins to intracellular second messengers that mediate the target cell
- s response
19. Describe Lipids-Soluble Hormones
- Steroid and Thyroid hormones
- Act on intracellular receptors that directly activate genes
- They CAN enter target cells
20. Name the two Second-Messenger Systems
21. Describe cAMP signaling mechanism (Second-Messenger System)
- Hormone (first messenger) binds to receptor
- Receptor activates G protein
- G protein activates G protein
- G protein activated adenylate cyclase
- Adenylate cyclase converts ATP to cAMP (second messenger)
- cAMP activates protein kinases
- Activated kinases phosphorylate various proteins, activating some and inactivation others
- cAMP is rapidly degraded by the enzyme phosphodiesterase
22. Describe PIP2 (Phosphatidylinositol 4,5-bisphosphate) and Calcium signaling mechanism
- Used by some amino acid-based hormones in some tissues
- Involves a G protien
- G protien activates phospholipase C enzyme
- Phospholipase splits membran phospholipid PIP2 into two second messengers:diacylglycerol (DAG) and IP3
- DAG activates protein kinases; IP3 triggers release fo Ca2+
- Ca2+ alters enzymes or channels or binds to the regulatory protien calmodulin
23. Describe Steroid hormones and thyroid hormone Drect Gene Activation
- Diffuse into their target cells and bind with intracellualar receptors
- Receptor-hormone complez enters the nucleus
- Receptor-hormone complex binds to a specific region of DNA
- This prompts DNA transcription to produce mRNA
- The mRNA directs protien synthesis
24. What must target cells have in order to bind Hormones?
Target cells must have specific receptors to which the hormone binds
25. Where are ACTH receptors found?
ACTH receptors are only found on certain cells of the adrenal cortex
26. Where are Thryroxin receptors found?
Thyroxin receptors are found on nearly all cells of the body
27. On what three factors do Target cell activation depend on?
- Blood levels of the hormone
- Relative number of receptors on or in the target cell
- Affinity of binding between receptor and hormone
28. What is Up-regulation?
The influence of hormones on target cells which make them form more receptors in response to the hormone
29. What is Down-regulation?
The influence of hormones on target cells which make them lose receptors in response to the hormone
30. Which is the connection between Obesity and Diabetes, Up-regulation or Down-regulation?
31. Describe Hormones in the blood
- Hormones circulate in the blood eithre free or bound
- Steroids and thyroid hormone are attached to plasma proteins
- All other circulate without carriers
List the ways that Hormones are removed from the blood.
- Degrading enzymes
- Half-life- the time required for a hormone's blood level to decrease by half
One hormone cannot exert its effects without anohter hormone being present as in reproductive system hormones and thyroid hormones.
more than one hormone produces the same effects on a target cell as in glucagon (panceas) and epinephrine (adrenal medulla) acting on the liver to increase blood glucose.
one or more hormone opposes the action of another hormone as in Insulin (decreases glucose in blood) and Glucagon (increases glucose in blood)
How does the dependence hormone-receptor interaction on blood level hormones work?
- It is controlled by negative feedback systems
- Vary only within a narrow desirable range
What are hormones synthesized and released in response to?
- Humoral Stimuli
- Neural Stimuli
- Hormonal Stimuli
Describe how Humoral Stimuli works.
- Changing blood levels of ions and nutrients directly stimulate secretion of hormones
- ex: Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid Hormone)---->PTH causes Ca2+ concentration to rise and the stimulus is removed
True or False Ca2+ in the blood is an example of Humoral Stimuli
- True, Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid Hormone)
- PTH causes Ca2+ concentration to rise and the stimulus is removed
Describe how Neural Stimuli work.
- Nerve fibers stimulate hormone release
- Ex: Sympathetic nervous system fibers stimulate the adrenal medulla to secrete catecholamies
What is another name for Neuroepinephrine and epinephrine?
Describe how Hormonal Stimuli work
- Hormones Stimualte other endorcrine organs to release their hormones
- Ex: Hypothalamic hormones stimulate the release of most anterior pituitary hormones
- Anterior pituitary hormones, inturn, stimulate several targets to secrete more hormones
- Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from the final target organs inhibit the release of the anterior pituitary hormones (NEGATIVE FEED BACK)
PLACE THE FOLLWING IN ORDER TO DEMONSTRATE NEGATIVE FEED BACK:
1Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from the final target organs inhibit the release of the anterior pituitary hormones
2Anterior pituitary hormones, inturn, stimulate several targets to secrete more hormones
3Hypothalamic hormones stimulate the release of most anterior pituitary hormones
Describe what the Nervous System Modulation is
- The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms
- Ex: under severe stress, the hypothalamus and the sympathetic nerovus system are activated--->As a result body gluscose levels rise
True or False: The Pituitary Gland is not controlled by anything
False, the Hypothalamus controls the pituitary gland
Name the major lobes of the pituitary gland
- Posterior pituitary lobe (nerohypohysis)
- Anterior pituitary lobe (adenohypophysis)
What is the Posterior Pituritary lobe made up of?
Pituicytes (glial- like supporting cells) and nerve fibers
What is the Anterior pituitary lobe made up of?
True or False there is a direct neural connection b/w the Hypothalamus and the anterior pituitary lobe ?
False, there is not direct neural connection b/w them.
What is the hypothalmic-hypophyseal tract?
The Neural Connection b/w the Posterior Pituitary lobe and the hypothalamus
True or False, The Posterior Pituitary Lobe is a downgrowth of hypothalamic neural tissue?
What does the nuclei of the hypthalamus synthesize?
Neruohormones Oxytocin and Antidiuretic Hormone (ADH)
True or False, Neruohormones are transported to the posterior pituitary
True they are made in neurosecretory cells in the hypthalmus and then sent to the Posterior Pituitary
What are the Hypophyseal portal systems?
- Primary capillary plexus
- Hypophyseal portal veins
- Secondary capillary plexus
What type of Hormones does the Hypophyseal portal system release, and what do they do?
Releasing (RH) and Inhibiting hormones (IH) to the anterior pituitary to regulate hormone secretions.
Name the six Anterior Pituitary Hormones, and their Abbreviations.
- Growth Hormone (GH)
- Thyroid-Stimulating Hormone (TSH)
- Adrenocoticotropic Hormone (ACTH)
- Follice-stimulating Hormone (FSH)
- Luteinizing Hormone (LH)
- Prolactin (PRL)
True or false, All of the Anterior Pituitary Hormones are Lipids
False they are all proteins
Which of the Anterior Pituitary Hormones DOES NOT activate cyclic AMP second-messenger systems at their targets
Growth Hormone (GH)
What four hormones are tropic hormones, and what endocrine gland do they secrete?
- TSH- thyroid
- ACTH-adrenal cortex
- LH gonads
- PRL gonads
What does the Growth Hormone stimulate?
Simulates most cells but targets Skeletal muscle and bones
Whot promotes protien synthesis and encourages the use of fats for fuel?
Growth Hormone (GH)
What mediates indirectly the effects fo GH?
insulin-like growth factors (IGFs)
How GH regulated by the hypothalamus?
Via the Growth Hormone-Relasing Hormon (GHRH) & Growth Hormone
What does direct action of GH do?
- Stimulaes liver, skeletal muscles, bones, and cartilage to produce insulin-like growth factors
- Mobelizes fats,elevates blood glucose by decreasing glucsoe uptake by cells and encourageming glycogen breakdown (anti-insuling effect of GH)
What happens to CHILDREN with Hypersecretion of Growth Hormone (GH)?
What happens to ADULTS with Hypersecretion of Growth Hormone (GH)?
- Acromegaly- features expand
What happens to CHILDREN with Hyposecretion of GH?
- Results in Pituitary Dwarfism
What does TSH stand for?
Thyroid-Stimulating Hormone (thyrotropin)
What does Thyroid-Stimulating Hormone (TSH) do?
Stimulates the normal development and secretory activity of the thyroid
What is TSH (thyrotropin) stimulated by?
Stimulated by thyrotropin-releasing hormone (TRH)
What is TSH inhibited by?
Inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus
What does Adrenocorticotropic Hormone (ACTH) do?
Stimulatees the adrenal cortex to release corticosteroids
What causes Adrenocorticotropic Hormone to be release?
Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm
How can the alter the release of ACH?
Internal and external factorrs such as fever, hyoglycemia, and stressors can alter the release of CRH
What are Hormones are Gonadotropins?
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
What does FSH do?
Stimiuates gamete (egg or sperm) production
What does LH do?
It promotes production of gonadal hormones
True or false, FSH and LH are present in prepubertal boys and girls.
False, it is absent from the blood in prepubertal boys and girls
What triggers the release of gonadotropins?
Triggered by the gonadotropin-releaseing hormone (GnRH) during and after puberty
What surppresses gonadotropins?
They are suppressed by gonadal hormones (feedback)
What does PRL stand for?
What does Prolactin do?
It stimulates milk production
How does milk production become possible in pregant women?
PRL blood levels rise toward the end of pregnancy
What stimulates PRH release and promotes continued milk production?
What does the posterior pituitary contain?
Axons of hypothalamic neurons
What does the posterior pituitary store?
Antiduretic hormone (ADH) and oxytocin
ADH and oxytocin are released in response to what?
True or false, both ADH and Oxytocin use PIP-calcium second-messenger mechanism at their targets
What does Oxytocin do and how?
- It stimulates uterine contrations during childbirth by mobilizing Ca2+ through a PIP2-Ca2+ second-messenger system
- Triggers milk ejection ("letsown" reflex in women producing milk
- Plays a role in sexual arousal and orgasm in makes and females
What does ADH stand for?
What responds to changes in the solute concentration fo the blood?
What happens if solutes concentration is high?
- Osmoreceptors depolarize and transmit impulses to hypothalamic neurons
- ADH is synthesized and release. It increases water reabsorption by the kidney tubules and thus reduces urine production (output)
What happens if concentration is low?
ADH is not released allowing water loss
What inhibits ADH release and increases urine output?
What does ADH deficiency result in?
- Diabetes insipidus : syndrome marked by the output of huge amounts of urine and intense thirst
- Also increases blood volume which in turn causes high blood pressure.
Name some reasons for ADH hypersecretion
- after neurosurgery
- or secreted by cancer cells
What may happen due to ADH hypersecretion?
- SIADH or syndrome of inappropriate ADH secretion
- this is when cells absorb too much water and burst, sodium levels increase, blood vessel tone increases and so, BP increase
What is the Thyroid Gland composed of?
- Consists of tow lateral lobes connected by a median mass called the isthmus
- Composed of follicles that produce the glycoprotein thyroglobulin
- Colloid (thyroglobulin +iodine) fills the lumen of the follicles and is the precursor of thyroid hormone
- Parafollicular cells produce the hormone calcitonin
What are colloids?
- they are thyroglobulin & iodine
- fill the lumen of the follicles
- is the precursor of thyroid hormone
What produce the hormone calcitonin?
Parafollicular cells produce the hormone calcitonin
What are thyroid hormones?
two related compounds T4 and T3
What is T4 (thyroxine) made up of?
2 tyrosine molecules & 4 bound iodine atoms
What is T3 made up of?
2 tyrosines & 3 bound iodine atoms
What does T4 and T3 target?
All body cells
True or false Thyroid hormone is a major metabolic hormone?
Thyroid Hormone has a calorigenic effect, what does that mean?
It increases metabolic rate and heat production
What does TH play a role in?
- the Thyroid Hormone plays a role in:
- maintenance of blood pressure
- regulation of tissue growth
- development of skeletal and nervous systems
- reproductiove capabilities
True or false T4 is 10x more active than T3?
Flase, T3 is 10x more active than T4
Describe how the TH is synthesized
- Thyroglobulin is syntheszied and dischared into the follicel lumen
- Iodides (I-) are actively taken into the cell, oxidized to iodine (I2) and released into the lumen
- Iodine attached to tyrosine, mediated by peroxidase enzymes
- Iodinated tyrosines linke together to form T3 and T4
- T3 and T4 are cleaved and diffused into the bloodstream
What are T4 and T3 transported by?
T4 and T3 are transported by thyroxine-binding globulins (TBGs)
True or false, only T4 binds to target receptors
False both T3 and T4 bind to target receptors
Describe how TH is regulated by negative feedback
- Rising TH levels provide negative feedback inhibition on release of TSH
- Hypothalamic thyrotropin-releaseing hormne (TRH) can overcome the negatibe feedback during pregnancy or exposure to cold
What happens in adults who have hyposecrtion of TH?
What happens in infants who have hyposecretion of TH?
- Hypothyroidism (cretinism)
- children become mentally challenged
What happens if there is hypersecretion of TH?
- Hyperthyroidism (Graves' disease)
What is Calcitonin produced by?
the Parafollicular (c) cells
What is Calcitionin a antagonist to?
PTH (parathyroid hormone)
What does Calcitonin do?
- Inhibits osteoclast activity and release of Ca2+ from bone matrix
- Stimulates Ca2+ uptake and incorporation inot bone matrix
- Regulated by a humoral (Ca2+ concentration in the blood) megative feedback mechanism
What are parathyroid glands?
- they are four to eight tiny glands embedded in the posterior aspect of the thyroid
- Contain oyphil cells (funciton unknown) and chief cells that secrete parathyroid hormen (PTH) or parathormone
- PTH- most important horme in Ca2+ homeostasis
True or false, PTH is the most important hormone in Ca2+ homeostasis?
What are the functions of the Parathyroid Hormone?
- Stimulate osteoclasts to digest bone matrix
- Wnhance reabosrption of Ca2+ and secretion of phosphate by the kidneys
- Promotes activation of vitamin D (by the kidneys); increase absorption of Ca2+ by intestinal mucosa
What inhibits PTH release?
Negative feedback control: rising Ca2+ in the blood inhibits PTH release
What causes Hyperparathyroidsim?
What does Hyperparathyroidism do?
- Softnes and deforms bones
- Elevated Ca2+ depresses the nervous system and contributes to formation of kidney stones
What are Adrenal (Suprarenal) Glands?
- Paired, pyramid-shaped organs on top of the kidneys
- Structurally and functionally, they are two glands in one the Adrenal medulla and Adrenal cortex
What is the Adrenal medulla?
nervous tissue, part of the sympathetic nervous system
What is the Adrenal Cortex?
Three layers of glandular tissue that synthesize and secrete corticosteroids
True or false, ACTH targets the Adrenal Cortex?
What are the three layers of the Adrenal Cortex and what corticosteroid do they produced?
- Zona Glomerulosa- mineralocorticoids (Mainly Aldesterone)
- Zona Fasciculata- glucocorticoids
- Zona Reticularis- sex hormones, or gonadocorticoids
What do Mineralocortioids do?
- They Regulate electrolytes (primarily Na+ and K+) in ECF
- Aldosterone is the most potent mineralocorticoid
What is the importance of Na+?
- affects ECF volume
- blood volume
- blood pressure
- levels of other ions
What is the Importance of K+
sets RMP of cells
What does Aldesterone do?
Stimulates water and NA+ reabsorption in exchange with K+ secretion by kidneys
What are the Mechanisms of Aldosterone Secretion?
- Renin-angiotensin mechanism: decreased blood pressure stimulates kidneys to release renin, triggers formation of angiotensin II which is a potent stimulator of aldosterone release
- Plasma concentratrion of K+: Inceased K+ directly influences the zona glomerulos cells to release aldosterone
- ACTH: cause small increases of aldosterone during stress
- Atrial natriuretic petide (ANP): blocks renin and aldosterone secretion to decrease blood pressure
What is Aldosterone hypersecretion and what is it due to?
- Aldosteronism, is hypersecrtion of Aldosteron which is due to:
- an Adrenal tumor
- Hypertension and edema due to excessive Na+
- Excretion of K+ leading to abonormal function of neurons and muscle
What do Glucocorticoids do?
- Keep blood sugar levels relatievely constant
- maintain blood pressure by increasing the action of vasoconstrictors
Which is the most important Glucocorticoid?
What is Cortisol released in response to?
- patterns of eating and activity
What is the prine metabolic effect of Cortisol?
Gluconeogenesis which is the formation of glucose from fats and proteins
What is Gluconeogenesis?
the formation of glucose from fats and proteins
True or false, Cortisol is the most important anti-inflamitory, anti-allergic agent in the body?
True or False, Cortisol inhibits the rise in blood glucose, fatty acids, and amino acids
False, it Promontes
What does hypersecretion of Glucocorticoids do?
What is Cushing's Syndrome?
- Depresses cartilage and bone formation
- Inhibits inflammation
- Depresses the immune system
- Promotes changes in cardiovascular, neural and gastrointestinal function
What does Hyposecretion of Glucocorticoids do?
- Addison's disease
- also involves deficits in mineralocorticoids
What is Addison's disease?
- its caused by hyposecrtion of flucocorticoids and a deficit in mineralocorticoids
- Decrease in glucose and Na+ levels
- Weight loss, severe dehydration and hypotension
What are Gonadocorticoids?
- (Sex Hormones)
- Most are androgens (male sex hormones) that are converted to testosterone or estrogens
- May contribute to:
- The onset of puberty
- The appearance of seconday sex characteristics
- Sex drive
What do Chromaffin cells secrete and how much of it?
- Epinephrine 80%
- Norepinephrine 20%
What does Epinephrine and Norepinephrine do?
- Cause: Blood glucose levels to rise
- Blood vessels to constrict
- The heart to beat faster
- Blood to be diverted to the brain, heart, and skeletal muscle
What does Epinephrine stimulate?
Stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and the heart
What does Norepinephrine influence?
peripheral vasoconstriction and blood pressure, increase
Describe the Pineal Gland
small gland hanging from the rooof of the third ventricle
What does Pinealocytes secrete?
secretes melatonin derived from serotonin
What may melatonin affect?
- timing of sexual maturation and puberty
- Day/night cycles
- Physiological processes that show rhythmic variations ( body temperature, sleep, appetite)
Describe the Pancreas
Its a triangular gland behind the stomach
True, or false the pancreas has only exocrine cells?
False the Pancreas has both exocrine and endocrine cells
What are acinar cells?
they are exocrine cells that produce an enzyme-rich juice for digestion
What does the Pancreatic islets (islets of Langerhans) contain?
endocrine cells; Alpha and Beta
What do Alpha cells from the Pancreatic islets do?
produce glucagon (a hyperglycemic hormone)
What do Beta cells cells from the Pancreatic islets do?
produce insulin ( a hypoglycemic hormone)
What is the major target of Glucagon?
What does Glucagon promote in the liver?
- Release of Glucose to the blood through:
What are the effects of insulin ?
- Lowers blood glucose levels
- enhances membrane transport of glucose into fat and muscle cells
- participates in neuronal development and learning and memory
- Inhibits glycogenolysisi and gluconeogenesis
What actions does insulin have on cells?
- Activates a tyrosine kinase enzyme receptor
- Cascade leads to increased glucose uptake and enzymatic activities that:
- 1. Catalyze the oxidation of glucose for ATP production
- 2.Polymerize glucose to form glycogen
- 3.Convert glucose to fat (particularly in adipose tissue)
What do you get when you have an imbalance of Insulin
Diabetes mellitus (DM)
What are the three cardinal signs of Diabetes Mellitus (DM)
- Polyuria- huge urine output
- Polydipsia- excessive thirst
- Polyphagia- excessive hunger and food consuption & lose weight
What is Hyperinsulinism?
Excessive insulin secretion; results in hypoglycemia, disorientation, unconsciousness
What do ovaries and placenta do?
- Gonads produce steroid sex hormones
- Ovaries produce estrogens and progesterone.
Ovaries produce estrogens and progesterone are responsible for?
- Maturation of female reproductive organs
- Appearance of female secondary sexual characteristics
- Breast development and cyclic changes in the uterine mucosa
What does the placenta secrete?
- human chorionic gonadotropin (hCG)
What do testes produce?
What does testosterone do?
- initiates maturation of male reproductive organs
- causes appearance of male secondary sexual characteristics and sex drive
- is necessary for normal sperm production
- maintains reproductive organs in their functional state
List other Hormone-Producing structures
- The heart
- Gastrointestinal tract
What hormone does the heart produce?
Atrial natriuretic peptide (ANP)
What does ANP do?
reduces blood pressure, blood volume, and blood Na+ concentration
What do enteroendocrine cells in the Gastrointestinal tract do?
- Gastrin stimulates release of HCL
- Secretin stimulates liver and pancreas
- Cholecystokinin stimulates pancreas, gallbladder, and hepatopancreatic sphincter
What do the kidneys produce?
What does Erythropoietin signal?
production of red blood cells
What does the Renin initiate?
the renin- angiotensin mechanism
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