Endocrine System Flashcards
1
Q
Why is the endocrine system slower than the nervous one?
A
It is a regulatory system that uses hormones that travel through the blood to the target organ.
2
Q
What are ductless glands formed of?
A
Formed of epithelial tissues and release hormones directly into the blood or the lymph.
3
Q
What are the general characteristics of hormones?
A
Specific rates and rhythms of secretion
They operate within feedback systems
They affect only cells with appropriate receptors
The liver inactivates hormones, making them more water soluble for renal excretion
4
Q
What are the different characteristics of hormones that control the rhythm and rate?
A
Diurnal: during the day
Pulsatile: a relatively constant level of hormone over a period of time
Cyclic: hormone increases and decreases in a constant pattern.
5
Q
What are the regulations of hormone release?
A
Hormones are regulated by chemical, hormonal, or neural factors.
Negative/positive feedback
6
Q
When are hormones released?
A
In response to a change in the cellular environment
To maintain a regulated level of certain substances or other hormones.
7
Q
Is ACTH inhibitory or stimulating to release of other hormones?
A
Stimulatory
8
Q
How do the different kinds of hormones transport?
A
They are released into the system by endocrine glands.
Water-soluble hormones are free to move around
Lipid-soluble hormones need to bind to a plasma protein
9
Q
What are the two plasma proteins that lipid hormones bind to?
A
Albumin and globulin
10
Q
What are the two different kinds of hormones?
A
Water soluble hormones (catecholamines): heavy molecular weight
Lipid hormones: thyroid, steroid, sex hormones and Vitamin D3
11
Q
Where are the receptors found in each category of hormone?
A
Water soluble: on the surface of the cell membrane since it is hard for them to bypass the lipid bilayer.
Lipid soluble: intracellular receptors
12
Q
What are the chemical classes of the hormones?
A
Steroid (lipid)
Proteins (water)
Amines (water)
Eicosanoids (lipid)
13
Q
Which kind of hormones has second messenger systems and why?
A
Water soluble hormones and it is because of the location of their receptors. Second messenger systems mediate the action of the hormone in the target cell.
14
Q
What are the different types of cell surface receptors?
A
Receptor Kinases (phosphorylation mediated)
Receptor - Linked Kinases (phosphorylation mediated)
G-Protein Coupled Receptors (phosphorylation mediated)
Ligand Gated Ion Channels (non-phosphorylation mediated)
15
Q
What is up and down regulation?
A
The process where receptors are constantly being synthesized or broken down based on the demand.
16
Q
What happens to the receptors when the hormone levels increase/decrease?
A
High blood level of hormone: the number of receptors is reduced
Low hormone levels: number of receptors is increased
17
Q
What is the cellular mechanism of lipid-soluble hormones?
A
They diffuse across the plasma membrane and bind to cytoplasmic or nuclear receptors.
Activate RNA Polymerase and DNA Transcription/Translation
18
Q
What are some examples of steroid hormones?
A
Androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and thyroid hormones.
19
Q
What kind of hormone are steroids hormones?
A
Lipid-soluble
20
Q
What is the cellular mechanism of water-soluble hormones?
A
First messenger
Signal transduction
Second messenger molecules
21
Q
What are some examples of second messenger molecules?
A
Calcium
cAMP
cGMP
22
Q
What is the first messenger?
A
The hormone; it causes some changes to the cell which leads to transduction and the release of the second messenger
23
Q
What are the cell surface second messengers and what are their functions?
A
Adenylate cyclase: catalyzes the conversion of ATP to cAMP
Guanylate cyclase: catalyzes the conversion of GMP to cGMP
Calcium and Caladium system: Ca2+ is 2nd messenger
Phospholipase C system: inositol phosphates and diacyl glycerol are second messengers
24
Q
What are the different controls of hormone release?
A
Hormonal: a hormone causing the release of a hormone
Humoral: change in chemical or ion causing the release of a hormone
Neural: a signal causing the release of a hormone
25
Which part of the pituitary produces the hormones?
The anterior lobe of the pituitary forms hormones and the posterior lobe of the pituitary stores them via neurosecretory cells.
26
What does the hypothalamus produce?
Both releasing and inhibiting hormones, ADH & Oxytocin, CRH
27
What is the function of oxytocin?
Induces labor (positive feedback) & lactation
28
What is the function of ADH?
Inhibits diuresis by water reabsorption, urine volume decreases and blood pressure increases.
29
Where do ADH and oxytocin get released?
ADH: kidney tubules
Oxytocin: mammary glands and uterine muscles
30
Which are the tropic hormones?
Where are they produced?
FSH, TH/TSH, ACTH
Anterior pituitary
31
Which are the non-endocrine targets?
Growth hormone and Prolactin
32
Where is the pineal gland located?
The roof of the third ventricle of the brain
33
What is the function of the pineal gland?
Secretes melatonin which controls circadian cycle
34
What are the hormones produced by the adrenal cortex called?
Corticosteroids
35
What are the three different kinds of corticosteroids?
Mineralocorticoids, glucocorticoids, androgens
36
What are the three divisions of the cortex?
Zona glumerulosa
Zona fasciculata
Zona reticularis
37
What is the function of the zona glomerulosa?
To secrete melanocorticoids
38
What is the function of melanocorticoids?
They are involved in the regulation of electrolytes (sodium and potassium)
39
Which is the most important mineralocorticoid?
Aldosterone
40
What is the function of the zona fasciculata?
Primary secretion of glucocorticoids
41
What is the function of glucocorticoids?
To increase blood glucose levels.
Have additional effects protein and fat metabolism
42
Which is the most important glucocorticoid?
Cortisol
43
What is the function of zona reticularis?
Primary secretion of androgens
44
What is the function of the androgens?
Same effect as the male sex hormone - testosterone
45
What are all adrenal cortex hormones?
Steroids
46
Are adrenal cortex hormones stored?
No, they are synthesised as needed
47
What hormones are synthesised from the cholesterol-steroid ring (corticoids)?
Aldosterone, sex hormones, and cortisol
48
What does cortisol bind to and why?
Cortisol is a lipid-soluble hormone so it needs to bind to a plasma protein. It binds to corticosteroid-binding globulin (CGB)
49
Is cortisol required for long term effect or short term?
Long-term, essential for life. Cortisol secretion needs to continue, otherwise it can be fatal in the long-term.
50
What are the net effects of cortisol
Catabolic (both muscle and fat)
51
What are the physiological actions of cortisol?
- Promotes gluconeogenesis
- Promotes the breakdown of skeletal muscle protein (broken down into amino acids which are then used in gluconeogenesis)
- Enhances lipolysis
- Suppresses immune system
- Breakdown of bone matrix
52
What other hormone has a similar effect to cortisol?
Glucagon
53
What is adrenal diabetes and what causes it?
Cause: hypersecretion of cortisol
Result: very high blood glucose levels.
Prolonged hypersecretion of insulin burns out the beta cells of the pancreas resulting in diabetes mellitus.
54
What are the anti-inflammatory effects of cortisol?
Suppresses the immune system so reduces phagocytic action of WBCs
Suppresses allergic reactions
Wide-spread therapeutic use
55
What is the regulation of cortisol release?
Regulated by ACTH (pituitary gland)
Release follows a daily pattern
Negative feedback by cortisol inhibits the secretion of ACTH (pituitary gland) and CRH (hypothalamus)
56
What is the mechanism of action for cortisol?
- Diffusion through membrane lipids
- Hormone binds to cytoplasmic/nuclear receptors
- Binding hormone - receptor complex to DNA
- Gene activation
- Transcription and mRNA production
- Translation and protein synthesis
- Alternations of cellular structure
57
Feedback loops of cortisol secretion
External stimulus
Hypothalum (CRH)
Anterior pituitary (ACTH)
Adrenal cortex (Cortisol)
Tissue (immune system, liver, muscle, adipose tissue)
58
Is aldosterone essential for long or short term?
Short term
59
What is aldosterone responsible for?
Responsible for regulating Na+ reabsorption in the distal tubule and the cortical collecting duct
60
What cells are associated with aldosterone?
Principal cells
61
Is there a dilution effect, if so why?
There is no dilution effect because both water and salt are reabsorbed, not just water.
62
What factors stimulate aldosterone release directly?
Increase of extracellular K+
Decrease of osmolarity
ACTH
63
What factors stimulate aldosterone release indirectly?
Decrease in blood pressure
Decrease of macula dense blood flow
64
What causes the lack of aldosterone?
Increase of Na+, Cl- and water loss
Decrease in EFC volume
Hypokalemia
Increase in RBC concentration
Decrease of cardiac output
Shock
65
What causes hypersecretion of aldosterone?
Increase of Na+, Cl- and water retention,
Increase in ECF volume
Hypokalaemia
66
What are the functions of the adrenal medulla?
Extension of the sympathetic nervous system,
Acts as a peripheral amplifier
Activated by same stimulus as sympathetic nervous system
67
What are the hormones of the adrenal medulla?
Catecholamines: adrenaline, epinephrine, noradrenaline, norepinephrine
68
Where are catecholamines secreted and released?
Secreted and stored in the adrenal medulla
Released in response to appropriate stimulus
69
Which receptor is norepinephrine more suitable for?
α - receptor
70
Which receptor is epinephrine more suitable for?
β - receptor
71
What are the differences between epinephrine & norepinephrine?
Epinephrine is better for cardiac stimulation --> greater cardiac output, because of the β - receptors
Epinephrine is better in terms of increasing metabolism
Norepinephrine is better in terms of constriction of blood vessels --> increased peripheral resistance --> increased arterial pressure because of α - receptors
72
What are the functions of catecholamines?
Stimulate "fight or flight" response
Increase plasma glucose levels
Increase cardiovascular function
Increase metabolic rate
Decrease gastrointestinal and genitourinary function
73
Where are adrenal glands located?
Near superior poles of kidneys
74
What is medulla formed of?
Neural crests
75
What are the three different kinds of cells found in the pancreatic islet cells?
α cells: release glucagon (25%)
β cells: release insulin (90%)
δ cells: somatostatin (5%)
76
What is the function of somatostatin?
Can stop reaction of both insulin and glucagon
77
Where is insulin synthesised?
In the RER of β cells
78
What is the pro hormone from which insulin is produced?
Preproinsulin
79
Explain the different stages of preproinsulin to get to insulin
RER of β cells: Preproinsulin, has thiol groups attached to it.
Transported to Golgi: packaged together and C-peptide is removed it becomes proinsulin.
Insulin has no C - peptide and is inserted into secretory vesicles to fuse out of the cell and into blood.
80
How many amino acids do the A chain and B chain have?
A chain: 21
B chain: 30
81
Where do the main steps of synthesis and secretion of insulin happen?
β cells in the islets of Langerhans
82
What happens after insulin is released into the blood?
Insulin does not need to attach to a plasma protein as it is water soluble and its receptors are attached to its surface.
83
What receptors are attached to an insulin molecule?
Two α subunits (hormone binding) outside the cell and two β subunits (ATP binding) on the inside
84
How are the receptors linked with one another?
By disulphide bonds
85
How does glucose enter a cell?
By facilitated diffusion with the help of GLUT transporters
86
Which GLUT transporter is stimulated by insulin?
GLUT 4 which is found in the muscles and adipose tissues.
87
How is glucose transported into the intestines and kidneys?
By secondary active transport
88
Cycling of GLUT 4
Insulin receptors activation
Activation of phosphoinositide - 3- kinase
Translocation of GLUT4 to cell membrane
GLUT 4 mediates glucose transport into the cell
89
What stimulates the secretion of insulin?
Increased blood glucose
Increased amino acids (can lead to gluconeogenesis)
Increased free fatty acids (can lead to gluconeogenesis)
Glucagon
90
What inhibits the secretion of insulin?
Decreased blood glucose
Decreased amino acids
Decreased free fatty acids
Somatostatin
91
What are the effects of insulin on carbohydrate metabolism?
Inhibiting glycogenolysis
Stimulating glycogenesis
Stimulating glucose uptake
Stimulating glycolysis
Inhibiting gluconeogenesis
92
What are the effects of insulin on fat metabolism?
Reduces rate of release of free fatty acids
Stimulates de novo synthesis of fatty acids
Conversion of fatty acids into triglycerides in the liver
93
What happens to the body if there is a lack of insulin?
Lipolysis
Increased plasma cholesterol
Increased phospholipid concentration
94
Why are diabetes patients so thin?
They lack insulin so fatty acids are continuously broken down
95
What are the effects of insulin on protein metabolism?
Stimulates transport of amino acids across the plasma membrane (liver and muscle)
Stimulates protein synthesis
Reduces release of amino acids from muscle
96
Where is glucagon released from?
α cells when blood glucose levels are too high
97
Which organ is glucagon's primary target?
The liver
98
What are the functions of glucagon?
Stimulates glycogenolysis
Stimulates gluconeogenesis
Stimulates lipolysis and ketogenesis
Inhibits glycolysis
99
What is diabetes mellitus?
Consistent hyperglycemia
100
What are the two different types of diabetes?
Type 1: insulin deficiency due to autoimmune destruction of islets
Type 2: insulin resistance, may be due to deficiency of GLUT receptor, or genetic defects in insulin receptors.
101
What causes destruction of β cells which can lead to Type 1 diabetes?
Autoimmune disease or increased levels of cortisol
102
What are some symptoms of diabetes?
Hyperglycemia
Glucosuria
Polydypsia
Polyuria
Polyphagia
Ketosis, acidosis
103
Why does polyuria occur?
Excess blood glucose filtered by kidneys cannot be reabsorbed and eliminated at the expense of water.
104
Why does polydipsia occur?
Osmotic diuresis of glucose and subsequent tissue dehydration. Thirst is mediated by hypothalamus
105
Why does polyphasic occur?
Poor utilization of carbohydrates, results in the depletion of stored fats, protein, and carbohydrates. Glucose cannot enter the cell so it gives off the signal that there is no insulin present.
106
What are the two kinds of cells found in the thyroid gland?
Follicle and Parafollicular cells
107
What separates the two lobes of the thyroid gland?
Isthmus
108
What are the three thyroid gland hormones?
Thyroxine, T4 (lipid soluble)
Triiodothyronine T3 (lipid soluble)
Calcitonin (water soluble)
109
Which hormones come from the follicular cells and which ones from the parafollicular?
Thyroxine and triiodothyronine are from the follicular cells and calcitonin is from the parafollicular
110
What is the target of each thyroid hormone?
T3 and T4 target most cells while calcitonin targets mostly bone
111
What is the action of T3 and T4?
Increase basal metabolic rate
112
What is the action of calcitonin?
Decrease calcium
113
What are the functions of the thyroid hormones?
Increase overall BMR --> increase in heat production (calorigenic effect)
Increase oxygen consumption & energy expenditure
Increase of catecholamines (epinephrine and norepinephrine) (sympathomimetic effect)
114
What is the duration of thyroid gland hormones?
Slow action long duration
115
How are thyroid hormones synthesised?
- Thyroglobulin is synthesized and discharged in the follicle lumen.
- Iodide (I-) is trapped
- Iodide is oxidized to iodine
- Iodine is attached to tyrosine in colloid, forming DIT (dioidityrosine) and MIT (monoiodotyrosine)
- Iodinated tyrosines are linked together to form T3 and T4
- Thyroglobulin colloid is endocytose and combines with a lysosome.
(DIT + MIT --> T3) (DIT + DIT --> T4)
- Lysosomal enzymes cleave T3 and T4 from thyroglobulin and hormones diffuse into bloodstream.
116
How are thyroid hormones transported when in the bloodstream?
99% of T3 and T4 are bound to plasma proteins
1% of them are free to produce hormone actions.
117
What are the plasma proteins which transport the thyroid hormones?
Thyroxine-binding globulin (TBG): present in low concentrations but has very high affinity, binds 70 to 80% of the circulating hormones.
Albumin: has lower affinity and binds 15 to 20% of the circulating hormones
118
How are the thyroid hormones controlled?
Thyrotropin Releasing Hormone (TRH): is released from the hypothalamus which stimulates
Thyroid Stimulating Hormone (TSH): from the anterior pituitary gland to the thyroid and therefore to the target organs.
It is a negative feedback loop.
119
What are the effects of thyroid hormones on metabolism?
Na-K pump
Gluconeogenic enzymes
Respiratory enzymes
Myosin heavy chain
β - adrenergic receptors
Increase BMR
Stimulate carbohydrate metabolism and lipolysis
Increase the body's sensitivity to catecholamines
120
What is hypothyroidism?
Low levels of thyronine
Could occur because of Hashimoto's thyroiditis or surgical removal
121
What are the different kinds of hypothyroidism?
Cretinism and Myxedema
122
What is cretinism?
- Occurs during fetal development
- Could be as a result of congenital defect in thyroid development
- Causes severe mental retardation and poor overall development and growth retardation
123
What is myxoedema?
- Hypothyroidism in the adult
- May result from autoimmune destruction of the thyroid or thyroid injury or surgical removal
- Presents with signs of hypometabolism.
- Appearance of edema on the face, hands and ankles.
124
What are the signs of hypometabolism?
Cold intolerance, weight gain, fatigue, bradycardia, cool, dry skin, anorexia and constipation
125
What is goiter?
The enlargement of the thyroid regardless of the production of thyroid hormones.
A common cause is iodine deficiency
126
What is goiter?
The enlargement of the thyroid regardless of the production of thyroid hormones.
A common cause is iodine deficiency
127
What is hyperthyroidism?
Increased levels of thyroxine hormones,
Elevated levels of T3 and T4 due to hyperfunction of the thyroid gland
128
What can cause hyperthyroidism?
Grave's disease (exophthalmos)
129
How can you treat hyperthyroidism?
Anti-thyroid drugs
Radioactive iodine
Surgery
Glucocorticoids
130
What happens to the thyroid during hyperthyroidism?
The thyroid gland increases in size about two to three times
Hyperplasia and in-folding of the follicular cell
Hypermetabolic state of the thyroid
131
What does calcitonin do?
Regulates Ca++ levels by depositing it into the bones
It is an antagonist of parathyroid hormone
132
Where is calcitonin produced?
Parafollicular cells of thyroid gland
133
Where are the parathyroid glands located?
Posterior to the thyroid gland
134
What hormones do the the parathyroid glands produce?
Parathyroid hormone (water soluble)
135
What is the function of the parathyroid hormone?
Increase blood calcium levels, through a humoral control. When the blood calcium levels are low then parathyroid hormone increases and so does bone destruction so parathyroid hormone is released to increase calcium
It increases Ca++ absorption in the GIT and re-absorption from kidneys
136
What happens to the size of the thymus as you get older?
It decreases
137
What is the function of the thymus?
To produce a hormone called thymosin
138
What is the function of thymosin?
Matures T-lymphocytes
Important role in developing the immune system
139
What are the gonads?
Sperms in male
Eggs in females
140
What is the function of the gonads?
To produce sex hormones (oestrogen and progesterone & testosterone)
