Endocrine and Skin Flashcards
Pituitary gland - where is it located?
At the base of the brain, connected to the hypothalamus by the infundibulum/pituitary stalk.
Consists of 2 lobes- anterior and posterior pituitary
describe the blood supply of the anterior pituitary gland - why is this significant?
Has a portal venous blood supply, the hypothalamic-hypophyseal portal system -no arterial blood supply.
Receives portal venous circulation from the hypothalamus, allowing transport of hormones.
what are the different types of hormone structures?
derived from:
e.g.
- steroids: derived from cholesterol, e.g. cortisol
- peptides: proteins e.g. insulin
- thyroid hormones: derived from 2 modified tyrosine - thyroxine
- catecholamines: stress hormones synthesised from tyrosine, e.g. adrenaline and noradrenaline
2 different ways in which hormones communicate with other cells
- cell surface receptors: G protein coupling
- intracellular receptors
what structure is located just anteriorly to the pituitary gland?
the optic chiasm
Which is the most stored thyroid hormone?
How is its active form forced?
T4 most stored.
Iodase is cleaved off by deiodinases to form active T3.
Action similar to steroid hormones.
6 Key hormones of the anterior pituitary
what type of hormones are they?
Growth hormone
Prolactin
ACTH
= polypeptides
FSH and LH
TSH
= glycoproteins
Anterior pituitary Growth hormone: - regulatory hormone(s) from the hypothalamus: - effect of regulatory hormone - effect of hormone
- regulatory hormone(s): GHRH and somatostatin
- effect of regulatory hormone: GHRH increases levels, SST inhibits
- effect of hormone: acts on liver to secrete IGF-1. Stimulates protein synthesis, carb and lipid metabolism
Anterior pituitary Thyroid Stimulating hormone (TSH) - regulatory hormone(s) from the hypothalamus: - effect of regulatory hormone - effect of hormone
- regulatory hormone(s):TRH
- effect of regulatory hormone: increases TSH release
- effect of hormone: stimulates the thyroid gland to release T3 and T4
Anterior pituitary Prolactin - regulatory hormone(s) from the hypothalamus: - effect of regulatory hormone - effect of hormone
- regulatory hormone(s): dopamine
- effect of regulatory hormone: inhibits release
- effect of hormone: breast development and milk production
Anterior pituitary Adrenocorticotropic hormone (ACTH) - regulatory hormone(s) from the hypothalamus:: - effect of regulatory hormone - effect of hormone
- regulatory hormone(s): CRH
- effect of regulatory hormone: increases release
- effect of hormone: stimulates the adrenal cortex to secrete cortisol
Anterior pituitary FSH and LH - regulatory hormone(s) from the hypothalamus: - effect of regulatory hormone - effect of hormone
- regulatory hormone(s): GnRH
- effect of regulatory hormone: increased release
- effect of hormone: gonads: germ cell development and secretion of sex hormones (androgens)
How do regulatory hormones reach the anterior pituitary gland?
- regulatory hormones secreted by the neuroendocrine cells in the hypothalamus.
- axons project to the median eminence at the base of the brain
- at this site the neuroendocrine cells can release substances (hormones) into the Hypothalamo-hypophyseal portal vessels that travel directly to the anterior pituitary gland
where do neuroendocrine cells have their cell bodies?
In supraoptic and paraventricular nuclei
Most releasing hormones (from the hypothalamus) increase production of their respective hormones from the anterior pituitary.
What are 2 releasing hormones that have an inhibitory affect?
- dopamine is released to inhibit prolactin release
- somatostatin is released as an inhibitor to growth hormone (GHRH increases release)
What does the posterior pituitary consist of?
Not glandular like the ant. pituitary.
Largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary, and serve as a site for the secretion of neurohypophysial hormones (oxytocin and ADH) directly into the blood.
What is the hypothalamic–neurohypophyseal system composed of?
the hypothalamus (the paraventricular nucleus and supraoptic nucleus), posterior pituitary, and the axonal projections extending from nuclei –> pituitary.
What are the neurohypophysial hormones?
ADH and oxytocin - secreted from the posterior pituitary
Which nuclei in the hypothalamus has neurosecretory cells which secrete oxytocin?
Paraventricular nucleus
Which nuclei in the hypothalamus has neurosecretory cells which secrete ADH?
Supraopticnucleus
Arterial supply of the thyroid gland
- superior thyroid artery
- inferior thyroid artery from subclavian artery, ascending branch supplies parathyroid
3 main hormones produced by the thyroid gland
- Thyroxine (T4) – Reservoir for T3
- Tri-iodo-thyronine (T3) – Major thyroid hormone
- Calcitonin
Which cells of the thyroid secrete thyroid hormone?
Follicular epithelial cells
Which cells of the thyroid secrete calcitonin?
Parafollicular cells
How is thyroxine/triiodothyronine made?
enzyme?
Iodination of Thyroglobulin (in thyroid follicle lumen).
Iodinated Tyrosines on Thyroglobulin combine to make T3 and T4.
Enzyme – Thyroid Peroxidase.
Steps are stimulated by TSH.
What does T3 do?
- increases metabolic rate
- growth and development
- increased catecholamine effect (sympathetic NS)
Structure of thyroid gland
2 lateral lobes connected by isthmus.
posteriorly, superior and inferior parathyroid glands
Describe the feedback loop of PTH
- low calcium level
- Parathyroid glands stimulated
- increased production of PTH
- acts on bone to increase calcium resorption, acts on kidney to increase calcium reabsorption and phosphate excretion
- indirectly acts on small intestine - calcitriol from kidney –> increased vitamin D –> increased calcium absorption in the small intestine
OVERALL: increased calcium
Effect of PTH on bone
increases calcium resorpton
effect of PTH on kidney
increased calcium reabsorption and phosphate excretion, calcitriol produced
effect of PTH on small intestine
indirect effect -
calcitriol from kidney –> increased vitamin D –> increased calcium absorption
effect of increased plasma insulin from beta cells of pancreas on muscle
- increased glucose uptake and utilisation
- glycogen synthesis
- amino acid uptake
- protein synthesis
effect of increased plasma insulin from beta cells of pancreas on adipocytes
increased glucose uptake and utilisation
triglyceride synthesis
effect of increased plasma insulin from beta cells of pancreas on liver
- decreased gluconeogenesis
- glycogen and triglyceride synthesis
- no ketone synthesis
Shape of R vs L adrenal glands
R = pyramid L = semilunar
Blood supply of adrenal glands
- Inferior phrenic arteries (abdo aorta)
- Middle suprarenal arteries (abdo aorta)
- Inferior suprarenal arteries (renal artery)
Layers of the adrenal cortex from out –> medulla
- Zona Glomerulosa
- Zona Fasciculata
- Zona Reticularis
- Medulla
What does the Zona Glomerulosa produce?
Aldosterone
In response to decreased blood volume
What does the Zona Fasciculata produce?
Glucocorticoids (cortisol)
What does the Zona Reticularis produce?
sex hormones e.g. androgens
What does the medulla produce?
adrenaline/noradrenaline
What is the RAAS
the renin–angiotensin–aldosterone system (RAAS) is a hormone system that regulates blood pressure and fluid balance.
Effects of cortisol from the zona fasciculata
4
Produced during stress
- Metabolism: protein to aas, triglyceride to FFAs and glycerol, gluconeogenesis
- Circulation: increased vasoconstriction
- Decreased inflammation and specific immune response
- Decreased nonessential functions, e.g. reproduction and growth
WHat are the 3 main catecholamines secreted from the adrenal medulla?
80% adrenaline
20% noradrenaline
small amounts of dopamine
Actions of catecholamines secreted by the adrenal medulla (sympathetic nervous system)
- increased glycogenolysis
- increased breakdown of adipose tissue triglyceride
- increased cardiac function
- diversion of blood from viscera to skeletal muscles by vasocontriction (in viscera) and vasodilation (in muscles)
- increased lung ventilation - stimulates brain breathing centres, dilates airways
Endocrine roles of the kidney
- produces erythropoietin: stimulates RBC production
- converts 25-OH vit D to active 1,25-OH vit D
- calcium metabolism
Where does normal proliferation of the skin occur?
In the basal layer
Functions of the skin
- barrier to infection
- thermoregulation
- protection against UV
- vitamin D synthesis
- regulate H2O loss
3 basic layers of the skin
Epidermis, dermis, subcutaneous tissue
What are the layers of the epidermis?
Outer Stratum corneum stratum granulosum stratum spinosum stratum basale
What is the stratum corneum of the epidermis made up of? why is this important?
Made up of corneodesmosomes and desmosomes.
Corneodesmosomes are adhesion molecules which keep the corneocytes together.
no.s increase in psoriasis, decrease in atopic excema
In a healthy skin barrier, what does filaggrin produce?
natural moisturising factor (NMF)
what is the importance of NMF?
Fills corneocytes, helping to maintain the skins hydration
Also helps to maintain an acidic environment at the outer surface of the stratum corneum
What is desquamanation?
In order to balance the introduction of new cells in the basal layer of the epidermis, mature corneocytes are shed from the surface.
Involves degradation of the extracellular corneo-desmosomes by protease enzymes.
What is the role of the lipid lamellae of the skin?
Keeps water inside the skin cells, protects against irritants and allergens.
What are all skin flare ups caused by?
allergens which are able to penetrate into the skin, where they are met with lymphocytes which release chemicals that induce inflammation.
endocrine roles of the kidney?
- Produces erythropoeitin which stimulates bone marrow maturation of red blood cells.
Levels increase in response to anaemia, decrease in polycthaemia - Vitamin D activation - calcitriol formed, increasing calcium reabsorption
What does ADH secreted by the posterior pituitary do?
- aquaporins –> collecting duct, retaining fluid in the body
- acts as a vasoconstrictor to increase blood pressure
where is ADH primarily synthesised?
in the supraoptic nuclei of the hypothalamus
what does oxytocin secreted by the posterior pituitary do?
Stimulates the contraction of the smooth muscles of the breasts for milk ejection during lactation in response to suckling.
Stimulates the contraction of uterine smooth muscles until the baby is born
Promotes the onset of labour
what receptor type do all pituitary and hypothalamic hormones act on?
G-protein coupled receptors
