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Unit 14 Flashcards

1
Q

What 2 classes of hormone are derived from tyrosine?

A

Thyroid and adrenal medullary

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2
Q

Where are receptors for protein hormones typically found?

A

Cell membrane

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3
Q

Where are receptors for steroid hormones typically found?

A

Cytoplasm

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4
Q

Where are receptors for catecholamine hormones typically found?

A

Cell membrane

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5
Q

Where are receptors for thyroid hormones typically found?

A

Nucleus

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6
Q

What hormones are synthesised from cholesterol?

A

Steroid and thyroid

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7
Q

Which hormones are secreted from the anterior pituitary?

A

GH
TSH
ACTH
Prolactin
FSH/LH

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8
Q

Which hormones are secreted from the posterior pituitary?

A

ADH
Oxytocin

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9
Q

What hormones are secreted from the hypothalamus?

A

GHRH
CRH
TRH
GnRH
Somatostatin (growth hormone-inhibitory protein)
Dopamine (prolactin-inhibitory hormone)

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10
Q

What are the metabolic effects of GH?

A

Increased protein synthesis
Increased fatty acid mobilisation
Decreased glucose utilisation

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11
Q

What factors stimulate GH release?

A

Decreased BG
Decreased blood FFA
Increased blood amino acids
Starvation
Exercise
Testosterone
Sleep
GHRH
Ghrelin

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12
Q

What factors inhibit GH release?

A

Increased BG
Increased FFA
Aging
Obesity
Somatostatin
Exogenous GH
Insulin-like growth factors

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13
Q

Describe the structure of the thyroid gland

A

Composed of follicles filled with colloid
Lined with cuboidal epithelial cells

C cells - secrete calcitonin

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14
Q

What is the main constituent of colloid?

A

Thyroglobulin

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15
Q

What is the main influencer of iodine trapping in the thyroid?

A

TSH

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16
Q

How is iodide transported out of the cell across the apical membrane into the follicle?

A

Via iodine/chloride transporter - Pendrin

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17
Q

Briefly describe the steps of thyroid hormone formation

A

Thyroglobulin produced in thyroid cells, transported into follicle
Iodide transported into follicle via pendrin
Iodide oxidised by peroxidase and H2O2
Iodide binds with thyroglobulin - produces T4
Stored in follicle
Reabsorbed back into cell by pinocytosis

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18
Q

How do T3/T4 circulate in blood?

A

Small free fraction
Bound to thyroxine-binding globulin, thyroxine-binding prealbumin and albumin

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19
Q

What layer of the adrenal gland secretes aldosterone?

A

Zona glomerulosa

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20
Q

What stimulates aldosterone secretion?

A

AngII and potassium

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21
Q

Where is the majority of cholesterol for synthesis of adrenocortical hormones from?

A

LDLs

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22
Q

In which organelles are adrenal steroids synthesised?

A

Mitochondria and endoplasmic reticulum

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23
Q

Why doesn’t cortisol activate the renal mineralocorticoid receptor?

A

11B-hydroxysteroid dehydrogenase converts cortisol => less potent cortisone

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24
Q

Where is the main site of aldosterone action?

A

Principal cells in collecting tubules

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25
What acid base disturbance is seen with aldosterone excess?
Metabolic alkalosis H+ secreted in exchange for K+ in intercalated cells of collecting ducts
26
Where in the cell does aldosterone act?
Cytoplasm - mineralocorticoid receptor
27
What factors increase aldosterone secretion?
^K+ ^AngII
28
What factors decrease aldosterone secretion?
^Na ^ANP
29
What effect does ACTH have on the rate of aldosterone secretion?
Very little, however, is necessary for secretion
30
How does cortisol affect CHO metabolism?
Stimulates gluconeogenesis - increases enzymes required for aa => glucose, mobilises amino acids, antagonises insulin's antagonist effects on gluconeogenesis Reduces cellular glucose utilisation - reduces GLUT4 translocation
31
How does ACTH stimulate steroid synthesis?
Activates adenyl cyclase, which activates cAMP Activates protein kinase A - converts cholesterol to pregnenolone - rate-limiting step of steroid synthesis
32
What are the 3 cell types of the endocrine pancreas and what are their secretions?
Alpha cells - glucagon Beta cells - insulin Delta cells - somatostatin PP cells - pancreatic polypeptide
33
Insulin half life
6 minutes
34
How is insulin degraded?
Insulinase (liver)
35
What is the main energy source for muscle, how does this change in different states?
Rest - fatty acids Exercise - muscle contraction increases translocation of GLUT4 to membrane - glucose Following meal - insulin allows transport of glucose into cells - glucose
36
How does insulin affect glucose handling in the liver?
Inactivate phosphorylase - prevents glycogen breakdown Activates glucokinase - increases glucose uptake Activates glycogen synthase - increases glycogen synthesis
37
How is glucose handling in the liver affected by lack of low glucose (and insulin) levels)
Phosphorylase activated - glycogen breakdown Glucose phosphatase activated - allows release of free glucose
38
Briefly describe the mechanism of insulin secretion by the pancreatic beta cells
Glucose entters via GLUT-2 channel Phosphorylated to glucose-6-phosphate (glucokinase) Oxidised to ATP Inhibits ATP K channels Depolarises cell Opens voltage-gated calcium channels Exocytosis of insulin-containing vesicles
39
Other than glucose, what factors increase insulin secretion?
Amino acids (small effect when BG normal, when BG high potentiate glucose stimulation) GI hormones - GLP-1 and GIP most potent (also gastrin, secretin and CCK) Other hormones - glucagon, GH, cortisol, progesterone/oestrogen
40
What are the effects of glucagon on metabolism?
Increased glycogenolysis Increased gluconeogenesis Increases amino acid uptake by liver Activates adipose cell lipase - increases fatty acids Inhibits storage of triglycerides
41
What stimulates glucagon release?
Increased BG Increased blood amino acids Exercise
42
How does hypocalcaemia affect the nervous system and why?
Increased excitability Increased neuronal permeability to sodium
43
How is calcium handled in the kidneys?
Protein-bound not filtered in glomerulus, rest is 99% reabsorbed 90% in PT, LOH and DT 10% in CD - more variable
44
What is bone composed of?
Organic matrix and calcium salts
45
What is the composition of organic matrix of bone?
90-95% collagen fibres Remained ground substance - extracellular fluid, proteoglycans (chrondroiton sulphate and hyaluronic acid)
46
What ions are present in bone salts?
Calcium, phosphate, magnesium, sodium, potassium, carbonate
47
What prevents precipitation of hydroxyapatite in extracellular fluid?
Inhibitors - eg pyrophosphate
48
How is calcium salt deposition in osteoid regulated?
Inhibited by pyrophosphate Levels regulated by tissue-nonspecific alkaline phosphatase, secreted by osteoblasts
49
What 3 substances are secreted by osteoblasts?
Tissue-nonspecific alkaline phosphatase - inhibits pyrophosphate Nucleotide pyrophosphate phosphodiesterase 1 - produces pyrophosphate outside the cells Ankylosis protein - transports pyrophosphate from inside to surface of cell
50
What is the main regulator of osteoclast activity? How does the regulation take place?
PTH Indirectly - osteoblasts signal osteoclast precursors to mature - RANKL and macrophage colony-stimulating factor
51
How to osteoblasts prevent bone respiration?
Secrete osteoprotegerin (OPG) - binds RANKL and prevents binding to osteoclasts
52
How to PTH and Vit D affect osteoclast signalling?
Inhibit OPG production Stimulate RANKL production
53
What regulates the rate of conversion of cholecalciferol to 25-hydroxycholecalciferol and where does conversion occur?
Liver Feedback inhibition
54
What regulates the rate of conversion of 25-hydroxycholecalciferol to 1,25-hydroxycholecalciferol and where does conversion occur?
PTH Proximal tubule of kidney
55
Where in the cell are vitamin D receptors found?
Nuclei
56
What are the effects of vitamin D?
Increases intestinal absorption of calcium and phosphorus Decreases renal excretion of potassium and phosphorus Promotes bone calcification in small quantities Increases bone resorption in extreme quantities
57
How does vitamin D increase intestinal absorption of calcium?
Increasing formation of calbindin in intestinal epithelial cells
58
How does PTH affect the kidneys?
Increased calcium reabsorption Reduced phosphate reabsorption Increases reabsorption of magnesium and hydrogen ions Decreases reabsorption of sodium, potassium and amino acids Increased formation of 1.25-dihydroxycholecalciferol
59
Where does renal calcium reabsorption increase in response to PTH?
Thick ascending LOH Distal tubules
60
How is PTH secretion regulated?
Calcium-sensing receptor G-protein-coupled receptor Stimulated by calcium - activates phospholipase C - increases inositol triphosphate and DAG formation => stimulates calcium release from intracellular stores => PTH secretion decreased
61
Where is calcitonin secreted?
Thyroid gland Parafollicular (C) cells
62
How does calcitonin act?
Decreases osteoclast activity Decreases osteoclast formation
63
What is the first line of defence against hypocalcaemia?
Buffer function of exchangeable calcium - predominantly in bones but also mitochondria especially of liver and intestine

Guyton (10 decks)

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