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Phase 1 > SUGER: Endocrine > Flashcards

SUGER: Endocrine Flashcards

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1
Q

What do progesterone, aldosterone, cortisol, testosterone, and estriol have in common?

A

They are all steroid hormones, made from cholesterol.

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2
Q

What are catecholamines (dopamine, adrenaline, noradrenaline) synthesised from?

A

Tyrosine.

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3
Q

What are thyroid hormones synthesised from?

A

Tyrosine and iodine.

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4
Q

The pituitary gland receives blood via the hypothalamic-hypophyseal portal system. What does this mean?

A

Arterial blood enters the hypothalamus, then travels through the infundibulum to the pituitary gland.

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5
Q

Which part of the pituitary gland releases more hormones, the anterior or posterior?

A

Anterior.
Posterior only releases oxytocin and antidiuretic hormone (ADH).

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6
Q

Which part of the structure of TSH, LH, and FSH (and hCG) is the same?

A

The alpha chain (they have different beta chains).

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7
Q

What hormone released by the hypothalamus stimulates the anterior pituitary gland to release TSH (thyroid stimulating hormone)?

A

TRH (thyrotropin releasing hormone).

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8
Q

What hormone released by the hypothalamus stimulates the anterior pituitary gland to release ACTH (adrenocorticotrophic hormone)?

A

Corticotropin releasing hormone (CRH).

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9
Q

What hormone released by the hypothalamus stimulates the anterior pituitary gland to release FSH (follicle stimulating hormone) and LH (luteinising hormone)?

A

GnRH (gonadotropin releasing hormone).

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10
Q

What hormone released by the hypothalamus inhibits the anterior pituitary gland from releasing prolactin?

A

Dopamine.

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11
Q

The anterior pituitary gland releases ACTH (adrenocorticotropic hormone).
What are the two key functions of ACTH?

A

Acutely stimulates cortisol release.
Stimulates corticosteroid synthesis.

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12
Q

The anterior pituitary gland releases ACTH (adrenocorticotropic hormone). ACTH acutely stimulates cortisol release. What effect does cortisol have on ACTH release?

A

Cortisol has a negative feedback effect on the release of ACTH.

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13
Q

Why should cortisol blood test levels for adrenal insufficiency be taken in the morning?

A

Cortisol has a circadian rhythm, and usually peaks in the morning.

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14
Q

What three bodily states stimulate growth hormone release?

A

Hypoglycaemia, exercise, and sleep.

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15
Q

Growth hormone is important in linear growth in children and acquisition of bone mass. What other five actions does growth hormone have?

A

Stimulates protein synthesis, lipolysis, and glucose metabolism.
Regulates body composition.
Psychological well-being.

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16
Q

What effect does thyroxine have on TSH (thyroid stimulating hormone) release from the anterior pituitary?

A

Thyroxine has a negative feedback effect on the release of TSH.

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17
Q

In the male HPG (hypothalamus, pituitary, gonads) axis, what effect does LH have on the gonads?

A

LH stimulates Leydig cells to secrete testosterone.

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18
Q

How does prolactin work like a contraceptive?

A

Prolactin inhibits gonadal activity through central suppression of GnRH (gonadotropin releasing hormone) and therefore decreases LH/FSH levels.

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19
Q

What cells of the pancreas perform exocrine activity, producing and secreting pancreatic juice?

A

Acinar cells

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20
Q

What cells of the pancreas perform endocrine activity, producing and releasing peptide hormones into the portal vein?

A

Islet cells

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21
Q

What cell type in the islets of Langerhans secretes glucagon?

A

Alpha cells.

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22
Q

Why can insulin, or glucagon, not be taken as a tablet?

A

They are peptide hormones, they would be digested by proteases.

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22
Q

What cell type in the islets of Langerhans secretes insulin?

A

Beta cells.

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23
Q

Insulin increases glucose uptake into insulin sensitive tissues e.g. muscle and fat, and also helps lower blood glucose levels by suppressing four processes. Name these four processes.

A

Glycogenolysis
Gluconeogenesis
Lipolysis
Breakdown of muscle (decreased ketogenesis)

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24
Glucagon increases hepatic glucose output by stimulating glycogenolysis and gluconeogenesis. Name three other effects of glucagon.
Stimulates lipolysis. Stimulates muscle glycogenolysis & breakdown. Reduces peripheral glucose uptake.
25
Glucose enters beta cells and is metabolised, creating ATP. What does a rise in ATP concentration cause in the beta cell?
Rise in ATP concentration causes potassium (K-ATP) channel to close, depolarising the cell membrane.
26
Glucose enters beta cells and is metabolised, creating ATP. The rise in ATP concentration causes potassium (K-ATP) channel to close, depolarising the cell membrane. What does this depolarisation cause?
Voltage-gated calcium channels open, calcium rushes into the beta cell, stimulating exocytosis of insulin from insulin secretory granules.
27
Why is it important for blood glucose level management that the GLUT2 transporters on the beta cell membranes are "low affinity transporters"?
Low affinity transporters need high concentrations of substrate to function efficiently. Therefore the beta cell is only triggered to secrete insulin by high concentrations of glucose in the blood.
28
What is proinsulin?
The precursor to insulin, formed of alpha and beta chain joined by c-peptide.
29
Where is proinsulin cleaved into insulin?
Inside the secretory granules in the beta cells.
30
Why is insulin release biphasic?
The beta cells first phase response is rapid release of stored insulin from secretory granules. The second phase response is slower because the beta cells release newly synthesised insulin.
31
How does insulin increase glucose uptake in muscle and fat cells?
1. Insulin binds to insulin receptor on muscle/fat cell plasma membrane. 2. This causes a cascade of intracellular signalling, resulting in GLUT4 vesicles being moved to plasma membrane. 3. GLUT4 transporters are integrated into the plasma membrane. 4. Glucose enters the muscle/fat cell via GLUT4.
32
Primary glucose sensors are in the pancreatic islets. Where else in the body are glucose levels sensed?
Gut wall, medulla, hypothalamus, and carotid bodies.
33
Both GLP-1 (glucagon-like peptide) and GIP (glucose-dependent insulinotrophic peptide) are hormones released by the gut called incretins. What is the main function of incretins?
Stimulate the pancreas to release insulin.
33
What enzyme cleaves GLP-1 to inactivate it, preventing GLP-1 from continuing to stimulate insulin release and preventing hypoglycaemia?
DPP-IV (dipeptidyl peptidase IV)
34
What two hormones are produced in neurons in the hypothalamus?
ADH and oxytocin.
35
ADH and oxytocin are produced in neurons in the hypothalamus. How do ADH and oxytocin travel from the hypothalamus to the posterior pituitary to be released?
ADH and oxytocin are transported down axons from the hypothalamus, and are then stored in vesicles in the axon terminals in the posterior pituitary.
36
How does the hypothalamus control release of ADH and oxytocin from the posterior pituitary?
When hypothalamic neurons are activated, this triggers the hormones to be released from the neuron axon terminals in the posterior pituitary.
37
What type of hormone are ADH and oxytocin?
Peptide hormones.
38
Why is copeptin levels tested for as a reliable measure of ADH release?
Copeptin is a byproduct of ADH production within ADH storage vesicles in the posterior pituitary, and is therefore released in proportion to ADH release.
39
What triggers ADH release from the posterior pituitary?
Increased osmolarity (solutes more concentrated because of dehydration).
40
Which part of the nephron does ADH act on?
Collecting tubule (and also DCT).
41
How does ADH increase water reabsorption in the collecting duct and distal convoluted tubule?
ADH binds to membrane receptor. Receptor activates cAMP second messenger system. Cell inserts aquaporins into membrane.
42
ADH release is usually triggered by high osmolarity, detected by osmoreceptors. When might another trigger cause ADH release?
In hypovolaemia, baroreceptors (carotid sinus and aortic arch) send signal to hypothalamus to release ADH from posterior pituitary.
43
What are the three zones of the adrenal cortex, and what categories of hormones do they produce?
Zona glomerulosa = mineralocorticoids Zona fasiculata = glucoticoids Zona reticularis = androgens "GFR" "Salt, Sugar, Sex"
44
By what age does the zona reticularis develop?
Age 8 (because it produces androgens needed for puberty).
45
ACTH (adrenocorticotropic hormone) binds with receptors on adrenal cortex cell membranes. What does this trigger within the cell (5 key steps)?
Activates cAMP secondary messenger system within the cell. Cholesterol enters mitochondria to be altered. Smooth ER processes further. Mitochondria then finalises creation of cortisol. Cortisol released from cell.
46
What effects do glucocorticoids (e.g. cortisol) have on glucose levels?
Increase glucose levels by increased gluconeogenesis (from protein and fat sources).
47
What effects do glucocorticoids have on the immune system?
Dampen the immune response and reduce inflammation (immunomodulation).
48
Why are the majority of glucocorticoids (90%) bound to proteins such as CBG (corticosteroid-binding globulin) in the bloodstream?
Glucocorticoids are not water soluble (lipid based steroid hormones). When bound to proteins, they are also inactive, which helps to regulate their effects.
49
What effect does aldosterone have on sodium and potassium reabsorption/excretion in the distal convoluted tubules?
Increases reabsorption of sodium, increases excretion of potassium.
50
What is the most abundant adrenal steroid hormone?
DHEA (dehydroepiandrosterone), a very weak androgen.
51
What cells trigger release of adrenaline from specialised ganglia in the adrenal medulla?
Preganglionic sympathetic neurons from the spinal cord.
52
How does cortisol effect catecholamine synthesis?
Cortisol up-regulates enzymes involved in catecholamine synthesis to increase production of catecholamines. This is called a "permissive effect".
53
Does the adrenal medulla produce more adrenaline or noradrenaline?
Adrenaline (80%, only 20% noradrenaline).
54
Catecholamine release causes tachycardia, cardiac contractility, and redistribution of circulating volume. What effect do catecholamines have on glucose levels?
Increase glucose levels by lipolysis and gluconeogenesis.
55
What glycoprotein produced in the thyroid contains multiple tyrosine residues that can be iodinated to form the building blocks for T3 and T4?
Thyroglobulin.
56
Which thyroid hormone is more abundant, T3 or T4?
T4.
57
Are both T3 and T4 active thyroid hormones?
No, only T3 is active.
58
What transport protein, made in the liver, are the majority of thyroid hormones in the plasma bound to?
Thyroxine binding globulin (TBG).
59
The majority of thyroid hormones travel in plasma bound to thyroxine binding globulin. What other two proteins help to transport thyroid hormones?
Transthyretin. Albumin.
60
What does deiodination of T4 by deiodinase D1 or D2 result in?
Converts inactive T4 into active T3.
61
How do thyroid hormones cross the blood brain barrier? Why is it important for thyroid hormones to cross the blood brain barrier?
Via specialised transporters in capillary endothelial cells. Thyroid hormones are essential for brain development and adult brain functioning.
62
If serum TSH is high, and serum T4 & T3 are low, is this hyperthyroidism or hypothyroidism?
Hypothyroidism; TSH is raised because pituitary is trying to stimulate more T4 & T3 to be released.
63
If serum TSH is high, and serum T4 & T3 are high, what does this suggest the origin of the problem is?
The pituitary gland; it is producing too much TSH.
64
What are the parathyroid glands?
4 small pea-sized glands on the back of the thyroid gland.
65
What key hormone do the parathyroid glands secrete?
PTH (parathyroid hormone).
66
What are the 4 main effects of PTH (parathyroid hormone)?
Increases calcium reabsorption in renal distal tubule. Increases intestinal calcium reabsorption. Increases calcium release from bone. Decreases phosphate reabsorption.
67
What hormone do low calcium or high phosphate levels trigger to be released?
PTH (parathyroid hormone).
68
Why does a blood gas only measure half of serum calcium?
Blood gas is only measuring the 'free' serum calcium (50%), the remaining 50% of serum calcium is bound to albumin. (Lab values also measure bound calcium).
69
How does PTH (parathyroid hormone) increase calcium absorption in the intestines?
PTH stimulates the kidneys to produce calcitriol, the active form of vitamin D.
70
Calcitonin is a hormone produced by C-cells of the thyroid gland in response to hypercalcaemia. What effect does calcitonin have on osteoclasts?
Inhibits bone reabsorption by osteoclasts.
71
Epiphyseal fusion occurs at the end of longitudinal growth, when the epiphyses plate (AKA growth plate) is completely replaced with bone. What hormones cause epiphyseal fusion?
Oestrogens, both in males and females.
72
How is IGF-1 (insulin-like growth factor 1) similar to insulin?
In molecular structure, and also in effect; IGF-1 stimulates uptake of glucose in tissues which lowers blood glucose levels.
73
Where is IGF-1 (insulin-like growth hormone 1) primarily produced?
The Liver.
74
What hormone triggers the liver to release IGF-1 (insulin-like growth hormone 1)?
Growth hormone (which is released by the anterior pituitary).
75
What peptide hormone released by the hypothalamus inhibits the anterior pituitary from releasing growth hormone?
Somatostatin.
76
When body mass reaches certain level, what hormone provides permissive signals which trigger the start of puberty, by initiating the HPG axis?
Leptin (released by fat cells).
77
In late puberty, do levels of LH follow a circadian rhythm?
No, LH follows a circadian rhythm (higher at night) in early-mid puberty, but in later puberty LH pulses throughout day and night.
78
Why do people with differences in sex development often also have adrenal problems?
Embryologically, development of the gonads and the adrenal glands have a shared origin of the adrenogonadal primordium (clump of cells within the urogenital ridge).
79
What enzyme converts testosterone to 5-alpha dihydrotestosterone, which is essential for embryological development of male genitalia?
5-alpha reductase

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