Endocrine Glands Flashcards
(90 cards)
1
Q
How do endocrine glands get their message to target cells?
A
Secrete hormones
- Lack ducts
- Much slower but effect is longer lasting
2
Q
What is a neurohormone?
A
Chemicals that are secreted by specialized neurons into the blood rather than synaptic cleft
-ex: Vasopressin (ADH), Neuroepinephrine
3
Q
What do hormones affect?
A
Metabolism of target organs
-Help regulate total body metabolism, growth and reproduction
4
Q
What are amines?
A
Hormones derived from tyrosine and and tryptophan
-NE, Epi, and T4
5
Q
What are polypeptides?
A
Chains of <100 amino acids in length
-ex: ADH
6
Q
What are protein hormones (glycoproteins)?
A
Polypeptide chains with >100 amino acids
-ex: Growth hormone, LH, FSH
7
Q
What are lipophilic hormones?
A
Lipids derived from cholesterol
- ex: Testosterone, Estradiol, Cortisol, Estrogen, Progesterone
- Will be associated with some kind of protein to travel in blood, will not be free-floating
8
Q
What is cholesterol first converted to?
A
Pregnenolone (a good precursor that can change into many hormones: estradiol, estrogen, progesterone)
9
Q
What can hormones be divided into?
A
1) Polar - NE, Epi
2) Nonpolar (lipophilic) - can gain entry into target cells; steroid hormones and T4
3) Properties of both polar and nonpolar - pineal gland secretes melatonin
10
Q
What is a prohormone?
A
Precursor that is a longer chained polypeptide -> cut and spliced together to make the hormone
-Proinsulin in the inactive form
11
Q
What is a preprohormone?
A
Larger precursor molecule that prohormone is derived from
-Preproinsulin -> Proinsulin (both inactive forms)
12
Q
What is a prehormone?
A
Molecules secreted by endocrine glands that are inactive until changed into hormones by target cells
-T4 (inactive) -> T3 (active)
13
Q
How are neural control systems and endocrine regulation similar?
A
1) Action of some hormones are accompanied by ion diffusion and electrical changes in the target cell.
- Nerve axon boutons release NTs
- Some chemicals are secreted as hormones, and also are NTs (Vasopressin)
2) In order for either a NT or hormone to function in physiological regulation: target cell must have specific receptor proteins; combination of the regulatory molecule with its receptor proteins must cause a specific sequence of changes; and there must be a mechanism to quickly turn off the action of a regulator
14
Q
What is a synergistic effect?
A
When two or more hormones work together to produce a particular result
-Their effects may be additive or complementary
15
Q
What is an example of a synergistic additive effect?
A
The action of NE and Epi on the heart
-Each separately produces an increase in cardiac rate; acting together in the same concentrations, they stimulate an even greater increase in cardiac rate
16
Q
What is an example of a synergistic complementary effect?
A
FSH and testosterone
-Each hormone stimulates different step in the process
17
Q
Prior exposure of uterus to estrogen induces formation of receptors for progesterone, what is this effect called?
A
Permissive effect; when hormone enhances the responsiveness of a target organ to the second hormone, or when it increases the activity of the second hormone
18
Q
What kind of effect do insulin and glucagon have on one another?
A
Antagonistic effect
-Action of one hormone antagonizes the effects of another
19
Q
What does [hormone] in blood reflect?
A
The rate of secretion
- Normal tissue responses are produced only when the hormones are present within physiological range
- Hormones do not generally accumulate in the blood because they are rapidly removed by target organs and by the liver
20
Q
What is a priming effect caused by?
A
Upregulation of receptors (increase number of receptors formed on target cells in response to a particular hormone)
-Greater response by the target cell
21
Q
What is desensitization?
A
Downregulation (decrease number of receptors formed on target cells in response to prolonged exposure to high [polypeptide hormone])
- Less response by the target cell
- Ex: Insulin in adipose cells (in type 2 diabetes, insulin receptor is desensitized)
22
Q
What may prevent downregulation?
A
Pulsatile secretion
-Polypeptide and glycoprotein hormones are secreted in spurts rather than continuously
23
Q
What do hormones of same chemical class share in common?
A
Similar mechanisms of action:
- The location of cellular receptor proteins depends on the chemical nature of the hormone
- The events that occur in the target cells after the hormone has combined with its receptor protein
24
Q
What 3 characteristics do hormones exhibit?
A
1) Specificity - target cell must have specific receptors for that hormone
2) High affinity - hormones bind to receptors with high bond strength
3) Low capacity - possibility of saturating receptors with hormone molecules because of the limited number of receptors per target cell
25
How are lipophilic steroid and thyroid hormones transported and where are their receptors located?
They are attached to plasma carrier proteins -> hormones dissociate from carrier proteins to pass through lipid component of target plasma membrane -> receptors located within cytoplasm and nucleus
-Vitamin A and D also travel this way
26
What are the receptors for the lipophilic hormones known as?
Nuclear hormone receptors
- Function within the cell to activate genetic transcription
- mRNA directs synthesis of specific enzyme proteins that change metabolism
27
What are the 2 regions in a nuclear hormone receptor?
1) Ligand (hormone)-binding domain
| 2) DNA-binding domain
28
What is the HRE (hormone responsive element)?
Short DNA span, composed of characteristic nucleotide bases, located adjacent to the gene that will be transcribed in response to the hormone-activated nuclear receptor
-Receptor must be activated by ligand-binding domain binding to hormone before DNA-binding domain can bind to HRE
29
What is the mechanism of steroid hormone action?
1) Steroid hormone, transported bound to plasma carrier proteins, dissociate from plasma carriers and pass through plasma membrane of target cell
2) Steroid hormone binds to receptors (in cytoplasm or nucleus)
3) Hormone-bound receptor translocates to nucleus, where DNA-binding domain binds to specific HRE of the DNA
4) Dimerization occurs (process of 2 receptor units coming together at the 2 half-sites) - this is another layer of control
5) Stimulates genetic transcription -> new mRNA synthesis
6) New mRNA codes for synthesis of new proteins -> hormonal effects in the target cell
30
What is the mechanism of thyroid hormone action?
1) Thyoxine (T4) carried to target cell bound to its plasma carrier protein, dissociates from its carrier and passes through plasma membrane of target cell
2) In the cytoplasm, T4 is converted to T3 (triiodothyronine)
3) T3 binds to ligand-binding domain and enters nucleus
4) Other half-site is vitamin A derivative (9-cis reitonic acid) -> this DNA-binding domain can bind to the half-site of the HRE
5) 2 partners can bind to the DNA to activate HRE -> Stimulate synthesis of new mRNA
6) New mRNA codes for synthesis of new proteins -> hormonal effects in the target cell
31
What is required for T3 to stimulate genetic transcription?
9-cis-retinoic acid
| -T3 forms a dimer with the receptor protein for 9-cis-retinoic acid (derivative of vitamin A)
32
How do water-soluble hormones (catecholamines, polypeptdies, and glycoproteins) reach their receptors?
Cannot pass through the plasma membrane, so their receptors are located on the outer surface of the membrane
-Hormone action requires activation of 2nd messengers within the cell (G proteins)
33
Water-soluble hormones will bind to their receptors on the outer surface of the target cell's plasma membrane, causing what? And what does this activate?
Causing dissociation of a subunit of G-protein; G-protein subunit binds to and activates adenylate cyclase
34
What does activated adenylate cyclase catalyze?
Conversion of ATP to cAMP + PPi
35
What does cAMP activate?
Protein kinase
| -cAMP attaches to inhibitory subunit of protein kinase -> inhibitory subunit dissociates and activates protein kinase
36
What does activated cAMP-dependent protein kinase do?
Transfers phosphate groups to (phosphorylates) other enzymes in the cytoplasm
- Activity of specific enzymes is either increased or inhibited by phosphorylation
- Altered enzyme activity mediates the target cell's response to the hormone
37
How is cAMP inactivated?
Phosphodiesterase
| -Hydrolyzes cAMP to inactive fragments
38
How is Ca2+ involved in the 2nd messenger system?
1) Binding of Epi to alpha-adrenergic receptor in plasma membrane activates a G-protein intermediate, phospholipase C
2) Activated phospholipase C splits phospholipids in the membrane to IP3 and DAG (both derivatives serve as 2nd messengers)
3) IP3 diffuses through cytoplasm to ER
4) Binding of IP3 to receptor protein in ER causes Ca2+ channels to open
5) Ca2+ diffuses into cytoplasm and binds to calmodulin
6) Calmodulin activates specific protein kinase enzymes -> Alters the metabolism of the cell -> hormone's effects
39
How many 2nd messenger systems can Epi act through?
2:
1) Epi can stimulate beta-adrenergic receptors -> activation of adenylate cyclase -> production of cAMP -> activates protein kinase
2) Epi can stimulate alpha-adrenergic receptors -> rise in cytoplasmic [Ca2+] -> activates calmodulin -> activates protein kinase
40
What activates tyrosine kinase?
When 2 insulin molecules bind to the insulin receptor, the 2 parts of the receptor phosphorlyate each other (dimerize) -> autophosphorylation occurs -> activates tyrosine kinase
41
What does activated tyrosine kinase activate?
Phosphorylation of signal molecules -> Cascade of effects
- Stimulates glycogen, fat, and protein synthesis
- Stimulates insertion of GLUT-4 carrier proteins
42
What receptors do 30-40% of pharmaceuticals target?
RTKs (receptor tyrosine kinases)
43
What are the hormones secreted by the anterior pituitary called?
Trophic hormones (trophic means "feed"): GH, TSH, ACTH, FSH, LH, Prolactin
- High blood [hormone] -> target organ will hypertrophy
- Low blood [hormone] -> target organ will atrophy
44
The posterior pituitary stores and releases 2 hormones that are produced in the hypothalamus, what are they?
1) ADH/Vasopressin - promotes retention of H20 by kidneys, less H2O excreted in urine
2) Oxytocin - stimulates contractions of the uterus during parturition, stimulates contractions of the mammary gland alveoli (milk-ejection reflex)
45
What controls the release of hormones in the posterior pituitary?
Neuroendocrine reflexes from the hypothalamus
| -Transported along hypothalamohypophyseal tract
46
What controls the release of hormones in the anterior pituitary?
```
Hormonal control (negative feedback)
-Hypothalamus neurons synthesize releasing and inhibiting hormones -> secreted into hypothalamohypophyseal portal system
```
47
How does negative feedback control the anterior pituitary and hypothalamic secretions?
Negative feedback controlled at 2 levels by the target organs they regulate:
1) The target gland hormone can act on the hypothalamus and inhibit secretion of releasing hormones
2) The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone
48
What is the short feedback loop?
Retrograde transport of blood from anterior pituitary to hypothalamus
-Hormone released by anterior pituitary inhibits secretion of releasing hormone
49
Is there a positive feedback loop that affects the anterior pituitary?
Yes; During the menstrual cycle, estrogen stimulates "LH surge"
-Most hormones have negative feedback effect
50
What is an axis?
The relationship between the anterior pituitary and a particular target gland
-ex: the pituitary-gonad axis refers to action of gonadotropic hormones on the testes and ovaries
51
What are the adrenal glands?
Paired organs that cap the kidneys
| -Each gland consists of an outer cortex and inner medulla
52
What is the adrenal medulla synthesize and secrete?
Synthesizes and secretes catecholamines (mainly Epi but some NE ; complement the sympathetic NS in the "fight-or-flight" rxn)
53
What does the adrenal cortex secrete?
Steroid hormones that participate in the regulation of mineral and energy balance (corticosteroids)
54
What is the main difference of the adrenal cortex and medulla?
Adrenal cortex does not receive neural innervation (adrenal medulla innervated by preganglionic sympathetic axons)
-Adrenal cortex must be stimulated hormonally (ACTH secreted from the anterior pituitary)
55
What are the 3 zones of the adrenal cortex?
Zona glomerulosa, zona fasciculata, zona reticularis
56
Which zone of the adrenal cortex produces mineralcorticoids (aldosterone)?
Zona glomerulosa
| -Aldosterone stimulates kidneys to reabsorb Na+ and secrete K+ (water retention)
57
Which zone of the adrenal cortex secretes glucocorticoids (cortisol)?
Zona fasciculata
| -Cortisol inhibits glucose utilization and stimulate gluconeogenesis (increase blood glucose level)
58
Which zone produces sex steoids (DHEA)?
Zona reticularis
| -Sex steroids are weak androgens that supplement sex steroids secreted by the gonads
59
What is the precursor for mineralocorticoids and glucocorticoids?
Cholesterol
| -Cholesterol -> Aldosterone -> Mineralocorticoids
60
What are the functions of the adrenal medulla?
Via Epinephrine:
- Increase RR
- Increase HR and cardiac output
- Vasoconstrict blood vessels, thus increasing venous return
- Stimulate glycogenolysis
- Stimulate lipolysis
61
What does the non-specific response to stress produce?
GAS (general adaptation syndrome)
- Stress causes a rise in the plasma glucocorticoid levels
- Suppresses the immune response
62
What is the largest of the pure endocrine glands?
Thyroid gland
63
Thyroid follicular cells secrete _________; parafollicular cells secrete _________.
Thyroxine; Calcitonin
64
How is thyroid hormone produced?
1) Thyroid follicles actively accumulate iodide (I-) from the blood and secrete it into the colloid
2) I- in the colloid is oxidized to iodine and attached to tyrosine within thyroglobulin chain
3) Attachment of 1 iodine -> MI ; Attachment of 2 iodine -> DIT
65
When two DIT molecules are coupled together what is produced?
T4 (thyroxine)
66
When one DIT and one MIT are coupled together what is produced?
T3
67
How is T3 and T4 secreted into the blood?
Upon stimulation by TSH, the cells of the follicle take up a small volume of colloid by pinocytosis, enzymes hydrolyze the T3 and T4 from the thyroglobulin, and secrete the free hormones into the blood
68
What is T3 responsible for?
- Stimulates protein synthesis
- Promotes maturation of nervous system
- Stimulates rate of cellular respiration by: production of uncoupling proteins, increase active transport by Na+/K+ pumps, and lower cellular [ATP}
- Increases metabolic heat
- Increases metabolic rate (stimulates increased consumption of glucose, fatty acids, and other molecules)
69
What does insufficient iodine in the diet cause?
Endemic goiter
- Abnormal growth of thyroid gland
- In the absence of sufficient iodine, cannot produce adequate amounts of T4 and T3
- Lack of negative feedback inhibition -> stimulates TSH -> abnormal growth of the thyroid
- Seen in 3rd world countries
70
What can severe hypothyroidism result in?
Adult myxedema
- Accumulation of mucoproteins and fluid in subcutaneous tissues and viscera
- Symptoms: decreased metabolic rate, weight gain, decreased ability to adapt to cold, lethargy
71
What is Grave's disease?
```
Autoimmune disorder (hyperthyroidism)
-Autoantibodies exert TSH-like effects on thyroid and are not inhibited by negative feedback -> high secretion of thyroxine cannot turn off excessive stimulation of thyroid
```
72
What does hypothyroidism during the end of 1st trimester to 6 months postnatally cause?
Cretinism -> severe mental retardation
73
What glands are embedded in the posterior surfaces of the lateral lobes of the thyroid gland?
Parathyroid gland
74
What is the only hormone secreted by the parathyroid gland and what important function does it have?
Parathyroid hormone (PTH); single most important hormone in the control of blood [Ca2+]
75
What is PTH stimulated by and what does it cause?
By decreased blood [Ca2+] ; promotes rise in blood [Ca2+] by acting on bones, kidneys and intestines
-Negative feedback
76
What do the alpha cells of the pancreatic islets (islets of langerhans) secrete?
Glucagon
- Stimulus: decrease in blood [glucose]
- Stimulates: glycogenolysis, lipolysis, and conversion of fatty acids to ketones
77
What do the beta cells of the pancreatic islets (islets of langerhans) secrete?
Insulin
- Stimulus: increase in blood [glucose]
- Stimulates: cellular uptake of blood glucose, glycogenesis, conversion of glucose to fat, and aids entry of amino acids into cells
78
What does the pineal gland secrete?
Melatonin
- Secretion of melatonin increases with darkness and peaks in the middle of the night
- May inhibit GnRH and may function in onset of puberty
79
What is the thymus?
Site of production of T cells (thymus-dependent cells), which are lymphocytes
- Lymphocytes are involved in cell-mediated immunity
- Secretes hormones that are believed to stimulate T cells after they leave thymus
80
T or F: Thymus gland size is small in newborns and children and grows after puberty.
False; Size is large in newborns and children, regresses after puberty and becomes infiltrated with strands of fibrous tissue
81
What are the gonads and what do they secrete?
The testes and ovaries ; secrete sex hormones - testosterone, estradiol (after menopause, produces estrone), progesterone
-All are made in both males and females, what differs is the levels of each
82
What does the placenta secrete?
Large amounts of estriol, progesterone, hCG (human chorionic gonadotropin), hCS (human chorionic somatomammotropin, also called hPL)
83
What is autocrine regulation?
Produced and act within the same tissue of an organ
- All autocrine regulators control gene expression in target cells
- "Local" regulation
- Prostaglandins are autocrine regulators
84
What is paracrine regulation?
Produced within one tissue and regulate a different tissue of the same organ
-"Traveling further" regulation
85
What are the most diverse group of autocrine regulators?
Prostaglandins
- Produced in almost every organ
- Wide variety of functions
86
What are some effects exerted by prostaglandins?
- Immune sx: promote inflammatory process
- Reproductive sx: play role in ovulation
- Digestive sx: inhibit gastric secretion (CCK)
- Circulatory sx: vasoconstrict/vasodilate
- Urinary sx: vasodilate
87
How are prostaglandins formed?
Upon stimulation by hormones or other agents, arachidonic acid is released from phospholipids in the plasma membrane and may enter one of 2 possible metabolic pathways:
1) Arachidonic acid -> (by enzyme cyclooxygenase) -> prostaglandin -> converted by other enzymes into other prostaglandins
2) Arachidonic acid -> (by enzyme lipoxygenase) -> leukotrienes
88
What do NSAIDs block?
COX-1 inhibit conversion of arachidonic acid -> prostaglandin
- Decrease inflammation, platelet aggregation...
- Aspirin is an irreversible inhibitor
89
What role do prostaglandins play in the respiratory system?
May bronchoconstrict or bronchodilate
-They play a role in producing DMPC and DPPC (lung surfactants); around 25 weeks there is a big surge in DMPC and sphingo myelin (high risk of ARDS in infants that do not produce enough surfactant)
90
What do celecoxib and rofecoxib inhibit?
COX2
