Hormone Synthesis and action Flashcards
1
Q
what is the endocrine system?
A
- a system of ductless glands and cells that secrete hormones
- regulates many physiological processes
2
Q
Hypothalamus
A
production of ADH, oxytocin and regulatory hormonea
3
Q
pineal gland
A
melatonin
4
Q
parathyroid gland
A
- posterior surface of thyroid gland
- parathyroid hormone
5
Q
heart
A
natriuretic peptides: ANP & BNP
6
Q
kidney
A
- renin
- erythropoietin (EPO)
- calcitrol
7
Q
adipose tissue
A
- leptin
- resistin
8
Q
digestive tract
A
numerous hormones
9
Q
pancreatic islets
A
insulin, glucagon
10
Q
gonads
A
testes
- androgens (especially testosterone), inhibin
ovaries
- estrogens, progestins, inhibin
11
Q
adrenal glands
A
adrenal medulla
- epinephrine, norepinephrine
adrenal cortex
- cortisol, corticosterone, aldosterone, androgens
12
Q
thymus
A
(undergoes atrophy during adulthood)
thymosins
13
Q
pituitary gland
A
anterior lobe
- ACTH, TSH, GH, PRL, FSH, LH and MSH
posterior lobe
- release oxytocin and ADH
14
Q
thyroid gland
A
Thyroxine (t4)
triiodothyronine (t3)
calcitonin (CT)
15
Q
endocrine glands
A
release secretions into blood directly from cells (ductless glands)
16
Q
exocrine glands
A
(not part of endocrine sustem)
release their secretions outside the body and may be ducted e.g. gut secretions, sweat glands
17
Q
mixed glands
A
e.g. pancreas produces digestive juice + insulin, glucagon and somatostatin
18
Q
chemical coordinator of endocrine system
A
hormone - many different types affecting different specific tissue
19
Q
chemical coordinator of nervous system
A
neurotransmitter - few types, secreted only onto target tissue
20
Q
speed of effect of endocrine system
A
generally slow
21
Q
speed of effect nervous system
A
generally rapid
22
Q
duration of effect of endocrine system
A
generally long lasting
23
Q
duration of effect of nervous system
A
generally short lived
24
Q
localisation of effect of endocrine system
A
secreted into blood therefore widespread
25
localisation of effect of nervous system
secreted onto target cell so effect very localised
26
neuro-endocrine
boundaries become blurred because some hormones are secreted from nerve endings
27
what is a hormone?
- a substance secreted directly into the blood by specialised cells
- carries in blood to receptors on target organs (endocrine, autocrine, paracrine)
- present in only minute concentrations in blood and bind specific receptors in target cells to influence cellular reactions
28
intracrine system
generated by a chemical acting within the same cell
29
autocrine signals
those in which a chemical acts on the same cell
30
paracrine mechanism
chemical communication between neighbouring cells within a tissue or organ
31
classic endocrine and neuroendocrine signalling mechanism
a chemical released by a specialised group of cells into the circulation and acting on a distant target tissue
32
control of action at a distance
stimulus ➡️ gland ➡️ hormone ➡️ target tissue ➡️ action or hormone
33
what is negative feedback?
process by which body senses change and activates mechanism to reduce it (the final product of an endocrine cascade acts to inhibit the release of hormones higher up the cascade)
34
what is positive feedback?
process by which body senses change and activates mechanism to amplify it
35
endocrine axis
- the target tissue for one hormone may be another endocrine gland (a tropic hormone stimulates another endocrine gland)
- the functional grouping of endocrine glands
- faults may occur along this axis
36
process of hypothalamic-pituitary axis
NO - neurons in the hypothalamus secrete
RABBITS - thyrotropin releasing hormone which stimulates cells in the
ALTER - anterior pituitary to secrete
SEXUALLY - thyroid stimulating hormone
EXCITED - TSH binds to epithelial cells in the thyroid gland stimulating
SNAKES - synthesis and secretion of thyroid hormones
37
negative feedback of hypothalamic - pituitary axis
When blood concentrations of thyroid hormones increase above a certain threshold, TRH secreting neurons in the hypothalamus are inhibited and stop secreting TRH
38
thyroid action
BMR, growth
39
parathyroid action
Ca2+ regulation
40
cortisol action
glucose regulation, inflammation
41
aldosterone action
BP, N’a+ regulation
42
catecholamines action
BP, stress
43
oestradiol action
menstruation, femininity
44
testosterone action
sexual function, masculinity
45
insulin action
glucose regulation
46
ANP action
Na+ regulation
47
vitamin D action
Ca2+ regulation
48
overview of protein and peptide hormones
- most common type of hormone, of amino acids
- water soluble (hydrophilic) - happy in blood but unable to get through cell membrane (not lipid soluble)
- performed and stored in membrane bound vesicles ready for release by exocytosis
- produced by ribosomes (RER) as large precursor molecule - pre-prohormone
49
what is thyrotropin releasing hormone?
- tripeptide, synthesised from a large precursor protein (mol wt ~29000) which contains several copies
50
what does a large precursor allow?
structural specificity
51
how to form insulin?
preproinsulin ==> proinsulin (cleavage of signal peptide and covalent - S-S bonds formed) + C-peptide ==> insulin
Endoprotease PC2 & PC3 and carboxypeptidase
52
What are common things glycoproteins hormones can have?
- common a subunits
| - b subunit which is unique and confers specificity
53
Steroid hormone overview
- all made from cholesterol
- normally from adrenal glands
- hormones from adrenal cortex and sex hormones
- lipid soluble
- synthesised as required and diffuse out of the cell
- synthesised in SER from cholesterol derived from diet or from acetate
54
what is the first and rate-limiting step in steroid hormones?
cholesterol to pregnenolone
| - formed in mitochondrion but moved to endoplasmic reticulum for processing to hormones
55
how are steroid hormone synthesised?
- hydrolysis of esters and release of cholesterol
- cholesterol to pregnenolone in mitochondria - movement of cholesterol to mitochondrion is regulated by steroid acute regulatory protein (StAR). ACTH regulated StAR activity and processing of cholesterol
- processing of pregnenolone in SER
- egress by diffusion or facilitated -
56
3 examples of enzymes within adrenal 3 cortical regions
zona glomerulolsa - aldosterone
zona fasciculata - cortisol
zona reticularis - adrenal androgens
57
secretion and excretion of steroid hormones
- newly synthesised steroid hormones are rapidly secreted from the cell with little if any storage
- increases in secretion reflect accelerated rates of synthesis
- steroid hormones are eliminated by inactivating metabolic transformations and excretion in urine or bile
58
what are thyroid hormones?
- tyrosine derivatives bound together
- contain 4 iodine atoms (T4) - less active
- contain 3 iodine atoms (T3) - active
- small, non-polar molecules
- soluble in plasma membranes
59
synthesis of T4 in the thyroid
- from endoplasmic reticulum - thyroglobulin secretion (in thyroid follicular cell)
- exocytosis in follicle colloid
- from blood - through Na/I symporter to form I- and Na+, then through pendrin where oxidation changes I- to I0
- I0 + thyroglobulin (iodination)
- conjugation
- endocytosis into thyroid follicular cell
- proteolysis to thyroxine and triiodothyronine
60
why are steroid and thyroid hormones transported in blood by carrier proteins?
- increase solubility in blood
- increase half- life
- create readily accessible reserve in blood
61
what are the types of binding proteins?
- specific binding proteins e.g. thyroid binding globulin (TBG) and cortisol binding globulin (CBG)
- non specific binding proteins e.g. albumin - loose binding. aldosterone binds to albumin.
- bound and free hormone are in equilibrium
62
what are the site of action of hormones?
- peptide - cell surface receptors
| - steroid - intracellular receptors
63
what are the cellular actions of protein and peptide hormones?
- receptors located on surface of target cell
- hormone binding activated second messenger cascade
- ultimately there is phosphorylation of proteins within the cell and the activated proteins bring about a change in cellular function
64
what does chemistry of hormones do?
determines its mode of action
65
what are endocrine disorders?
- overproduction of a hormone
- underproduction of a hormone
- non-functional receptors that cause target cells to become insensitive to hormones
66
excess endocrine disorders
- often caused by tumours
- or exogenous administration of hormones
- treatment = surgical removal of part of gland
67
deficient endocrine disorders
primary - primary organ inadequate, tropic hormone - feedback
secondary - tropic hormone deficient
- autoimmune organ destruction most common cause
treatment = replacement therapy (orally absorbed, long half-life e.g. steroid (corticosteroid), thyroid (thyroxine) hormones/ injections e.g. GH, insulin - peptide hormones. otherwise degraded in GI tract)
68
growth hormone
deficiency - growth hormone deficient (dwarfism - proportionate)
excess - gigantism (children), acromegaly (adults)
69
antidiuretic
deficiency - diabetes insipidus
| excess - hypervolaemia (SIADH)
70
thyroid
deficiency - hypothyroidism (1/2/3), hashimoto’s thyroiditis (1), congenital hypothyroidism (iodine deficiency)
excess - hyperthyroidism (Graves disease)
71
parathyroid
deficiency - hypoparathyroidism - tetany
| excess - hyperthyroidism (1/2/3) bone resorption
72
insulin
deficiency - diabetes mellitus
| excess - coma
73
cortisol
deficiency - adrenal insufficiency (addisons disease)
| excess - cushings syndrome
74
aldosterone
deficiency - hypoaldosteronism
| excess - 1: aldosteronism (Conn’s), 2: aldosteronism
75
why would blood flow to endocrine glands change?
- endocrine glands work in tandem to the blood flow in order to transport hormones around the body
- aging may change this : less of a hormone = less blood flow
- stress - more adrenaline = higher blood flow
76
what is the embryologic origin of the thyroid gland?
- the primitive pharynx - median thyroid and neural crest - rudimentary lateral thyroid
- develops near base of neck and descends in week 7
- week 10 : can develop thyroglossal duct cyst if not descended properly
77
Simple lateral cross section of thyroid gland (top to bottom)
- thyroid cartilage
- cricoid cartilage
- thyroid gland
- trachea
78
cross section of thyroid gland (outside in)
- sternocleidomastoid muscle
- strap muscles
- thyroid lobes
- trachea
- oesophagus
also includes internal jugular vein and internal carotid artery
79
what triggers release of T3 & T4?
- triggered by hypothalamus releasing in thyrotropin- releasing hormone which stimulates pituitary gland to produce TSH
80
which nerves, vessels and structures are at risk during a thyroidectomy?
- vagus nerve - regulation of internal organ functions e.g. digestion
- external branch of superior laryngeal nerve - inner ages the cricothyroid muscle (CTM) to promote lengthening and thinning of vocal cord and therefore pitch
- inferior laryngeal nerve - main motor nerve of intrinsic laryngeal muscles and provides sensory innervation to larynx
81
what is the embryological origin of parathyroid glands?
From pharyngeal pouches
82
what cells are in parathyroid glands?
- chief cells
| - oxyphil cells
83
what hormone is secreted by parathyroid glands?
low calcium levels trigger the release of the parathormone
84
what are the consequences of removal of parathyroid glands?
- blood calcium levels drop, leading to confusion, depression, forgetfulness, stiff/achy muscles
- would need to take calcium supplements
- hyperplasia - cells don’t increase but glands get bigger
85
at what vertebral levels do adrenal glands lie?
12th thoracic - above and slightly medial to kidneys within renal fascia
86
what produces mineralcorticoids?
zona glomerulosa
87
what produces glucocorticoids?
zona fasciculata
88
what produces sex hormones?
zona reticularis
89
what does central adrenal medulla produce?
epinephrine and norepinephrine
90
how might the pancreas be damaged ?
- chronic pancreatitis - inflammation
- heavy alcohol use
- high levels of calcium/fats in blood
- medications
- autoimmune conditions
