Week 5 Endocrinology Intro Flashcards
What is the difference between and endocrine and exocrine gland?
Endocrine glands:
- Do not have ducts, products are secreted directly into blood:
e.g. pituitary, thyroid, adrenal, parathyroid glands, gonads (testis & ovaries)
Exocrine glands:
- Products secreted via ducts to epithelial surfaces inside or outside the body:
e.g. sweat, salivary, mucus, mammary gastric, prostate glands, liver bile duct
Some glands, e.g. pancreas, do both:
Endocrine:
insulin, glucagon, somatostatin & pancreatic polypeptide
Exocrine:
digestive enzymes secreted via pancreatic duct to the small intestine
What are the two types of endocrine signalling?
‘Classical’ endocrine signalling:
hormone carried by blood
to receptors on ‘target’ cells
Intracrine signalling:
inactive prohormone enters a cell
activated intracellularly
(e.g. sex steroids)
A hormone which is an example of classical endocrine signalling?
Thyroxine
A hormone which is an example of intracrine signalling?
Testosterone/ Oestrogen
What are the two subtypes of endrocrine signalling where hormones diffuse straight through fluid in tissues rather than the blood?
Paracrine (local) signalling:
hormone diffuses through tissue fluids …
to receptors on ‘target’ cells
Autocrine (local) signalling:
hormone diffuses through tissue fluids …
to receptors on the same cell
Difference between peptide, steroid and amine hormones?
Peptide hormones are peptides and are water soluable
Amine hormones bind to plasma proteins
Steroid protiens also bind to plasma proteins but contain a cholesterol backbone and can pass through the lipid membrane of a cell
Give an example of a steroid hormone?
Testosterone and Oestrogen
Give two examples of amine hormones
Adrenaline and thyroxine
Give an example of a peptide hormone
Adrenocorticotropic hormone (ACTH)
What is the diffuse endrocrine system?
Anything that has something to do with hormones that isn’t either the HP axis or the classic endocrine organs which interact with the HP axis
Signalling hormones or End Organ hormones - which has a shorter half life?
‘Signalling’ hormones:
short half-life - only a few mins
‘End-organ’ hormones:
long-lived - hours to days
Where are hormones broken down?
Broken down int he liver and kidneys
How does metabolism affect hormone levels?
The rate at which hormones are broken down is dependent on metabolism
If metabolism is increased then hormones go down and they are broken down faster
What is the main interface between the central nervous system and the endocrine system?
Hypothalamus
What is the difference in the way that the anterior and posterior pituitrary recieve signals?
The anterior pituriary recieves signals via hormones in the portal system from the hypothalamus
The posterior has a direct neural connection with the thalamus
Complete this statement about the anterior pituitrary cells and corresponding hypothalamic releasing hormones
CRH: Corticotropin-releasing hormone
GNRH: Gonadotrophin releasing hormone
TRH: Thyrotropin-releasing hormone
DA: Dopamine
GHRH: Growth hormone-releasing hormone
Complete this statement about the anterior pituitrary cells and corresponding hypothalamic releasing hormones
CRH: Corticotropin-releasing hormone
GNRH: Gonadotrophin releasing hormone
TRH: Thyrotropin-releasing hormone
DA: Dopamine
GHRH: Growth hormone-releasing hormone
Complete this statement about which anterior pituitary hormones are released by which cells
ACTH: Adrenocorticotropic hormone
TSH: Thyroid stimulating hormone
FSH&LH: Follicle stimulating hormone & Luteinising hormone
GH (somatotrophin): Growth hormone
PRL: Prolactin
Complete this statement about which anterior pituitary hormones are released by which cells
ACTH: Adrenocorticotropic hormone
TSH: Thyroid stimulating hormone
FSH&LH: Follicle stimulating hormone & Luteinising hormone
GH (somatotrophin): Growth hormone
PRL: Prolactin
What two hormones are made in the posterior pituitary?
Oxytocin and Vasopressin
Fill in the target organs and corresponding physiological or hormonal resonse
Describe the general levels of aterior pituitary hormone and target gland hormone you would see with a hormone producing tumour in the target gland
Describe the general levels of aterior pituitary hormone and target gland hormone you would see with a hormone producing tumour in the anterior pituitary
Describe the general levels of aterior pituitary hormone and target gland hormone you would see with target gland failure
Describe the general levels of aterior pituitary hormone and target gland hormone you would see with anterior pituitary failure
Which is these statements applies to Hypothalamic hormones, Pituitary hormones or Target tissue hormones:
Hormones rarely measured in plasma (measure by petrosal sinus sampling)
Hormones often measured in plasma for
diagnosis
Hormones measured in plasma for diagnosis
AND to monitor hormone reduction or replacement
Hormones rarely measured in plasma (measure by petrosal sinus sampling) - Hypothalamic hormones
Hormones often measured in plasma for diagnosis - pituitary hormones
Hormones measured in plasma for diagnosis AND to monitor hormone reduction or replacement - target tissue hormones
What are steroid hormones made from?
Cholesterol
What is the key concept for how steroids are made?
Cholesterol side groups are cleaved or modified.
The hydrophobic 6 carbon side chain is removed making steroid hormones more water soluble than cholesterol
What are the 6 main endogenous steroid hormone’s we have to know about
Aldosterone
Cortisol
Androstenedione
Progesterone
Testosterone
Oestrogen
Out of these 6 steroid hormones which ones are adrenal and which are gonadal:
Aldosterone
Testosterone
Androstenedione
Progesterone
Cortisol
Oestrogen
Adrenal:
Aldosterone
Cortisol
Androstenedione
Gonadal:
Progesterone
Testosterone
Oestrogen
What is an axample of a mineralocorticoid?
Aldosterone
Regulates sodium/potassium
What is an example of a glucocortcoid?
Cortisol
glucose synthesis
protein & lipid metabolism
inflammation, immune response
What is an example of an adrenal androgen?
Androstenedione
Fetal steroids & growth
What is the group of enzymes involved in the cleaving or modifying cholesterol side groups during steroidgenesis?
cytochrome P450s
Clue P45 is what you get when you leave a job, so cholesterol gets this when it leaves being cholesterol
What does cholesterol side chain cleavage enzyme do?
P450scc converts cholesterol into pregnenolone which is the first step in steroidgenesis
What type of enzyme is involved in interconverting steroid from active to inactive form?
Steroid dehydrogenases/reductases
They come in pairs and convert steroid form active forms to inactive forms
What is the purpose of inactivating hormones or binding the active ones to plasma proteins?
It saves them for the target tissues.
Bound + inactive hormones are transported in the plasma hormones are re-activated in target tissues
Adosterone has a classical genomic steroid mechanism but also has a non-genomic mechanism mimicing that of a peptide or amine hormone.
What are these functions?
Kindneys:
Slow action (>30 mins-48hr)
Aldosterone-regulated synthesis of kidney epithelial sodium channel (ENaC) subunits
Rapid signalling (< 1 min)
Aldosterone-mediated vasoconstriction of vascular smooth muscle & endothelial cells
What are the two structures of the adrenal glands?
Cortex: 80-90% of normal gland
Make steroid hormones:
Mineralocorticoids
Glucocorticoids
adrenal androgens
Medulla: 10-20% of normal gland
Make catecholamines:
adrenaline (epinephrine)
noradrenaline (norepinephrine)
What part of the adrenal gland is involved in the hypothalamic-pituitary-adrenal (HPA) axis
Adrenal cortex, specifically the zona fasciculata and zona reticularis as it is cortisol and androstenedione that is released in response to ACTH
The adrenal cortex can be subdivided into what?
What do each of these parts make?
zona glomerulosa (ZG) - mineralocorticoids
zona fasciculata (ZF) - glucocorticoids
zona reticularis (ZR) - adrenal androgens
In a diurnal circadian rythym when is ACTH highest and when is Cortisol highest?
Diurnal CRH release regulates ACTH release:
high in the early morning (04.00-08.00)
lower later in the day
ACTH regulates cortisol synthesis:
High on waking (06.00-10.00)
lower later in the day (with ‘stress’ activity spikes)
lowest in the middle of the night
Metabolically how does the action of cortisol oppose that of insulin?
Generally speaking it opposes the action of insulin
Anabolic:
Increased gluconeogenesis & liver glucose output
Catabolic:
Inhibition of glucose uptake by peripheral muscle & fat tissue
Immune system suppression
Increased muscle protein breakdown
Increased fat breakdown
Increased bone resorption
Increased appetite & central fat deposition
How is androstenedione converted in oestrogen and testosterone?
Intracrine conversion to testosterone & oestradiol in peripheral tissues
What are the main roles of Dehydroepiandrosterone (this is whats is actually made in the ZR and androstenedione is an intermediary to the final androgens)
Regulates secondary sexual characteristics:
- Facial & body hair, pelvic build, upper body musculature, body fat composition, etc.
Prenatal DHEA production:
- Role in maintaining oestrogenic environment
- Role in foetal development??
Postnatal DHEA production:
- Role in initiation of puberty (adrenarche)??
- Main source of androgens & post-menopausal oestrogen in females
- Role in longevity; elixir of life??
In the gonadal hormone feeback loop what is the extra hormone that inhibits the hypothalamus and pituitary ?
Inhibin
What is desmopressin?
A synthetic vassopressin
What is urine osmolality?
The concentration of chemicals in urine.
What another name for anti-diuretic hormone?
Vasopressin
