35. Endocrine Control Of Plasma Flashcards
What are the three classes of hormones?
Protein/polypeptides, steroids, amines (derivatives of tyrosine)
Which hormones are hydrophobic?
Steroid
How do amines behave?
Some (ie thyroxine) behave like steroids, while some (ie adrenaline) behave like peptides
How are peptide hormones synthesised?
As preprohormones that require further processing and cleavage to be active
Where are peptide hormones stored?
In vesicles in gland
Don’t cross membrane easily so can be stored
Why are steroid hormones not stored in the gland?
They are synthesised and used immediately as they easily cross the membrane and leave gland when they are made
How do steroid hormones circulate in the blood?
Bound to proteins, eg albumin
Where are peptide hormones created?
By ribosomes in the ER then mature in the Golgi apparatus
Where are steroid hormones produced?
In the mitochondria or ER
What is the mechanism of action of peptide hormones?
Bind to cell surface receptors and act via secondary messenger systems
What is the mechanism of action of steroid hormones?
Act via intracellular receptors which allow the hormone-receptor complex to enter the nucleus and activate mRNA transcription
What is an ultra-short feedback loop?
Paracrine or autocrine effects
What is a short-loop feedback?
Feedback from pituitary hormone to hypothalamus
What is feed-forward control?
A direct effect of the stimulus on the control system before the action of the feedback signal occurs
Allows for preparation and adaptations
How much of the body weight is made up of ECF?
20% (14L)
What is the main ion present in ICF?
What is the main ion present in ECF?
K+
Na+ and Cl-
What is the ECF?
Plasma and interstitial fluid
What does osmolality represent?
The total solute concentration
What is plasma osmolality related to?
Intracellular osmolality as plasma is the only fluid that circulates through the body and links ICF and ECF compartments
How is sodium and water balance regulated?
Neural and endocrine control
How do osmoreceptors work?
Where are they located?
Change size in response to changing osmolality
Located in or near hypothalamus
What stimulates the hypothalamic thirst centre?
Which has a greater effect?
Decrease in plasma volume, increase in plasma osmolality
Plasma osmolality is more sensitive and thus has a greater effect
Where is ADH stored?
In the posterior pituitary, in secretory granules
How does increased osmolality cause ADH release?
Causes change in membrane permeability, influx of Ca2+
What type of receptors does ADH act on?
What effects do they have?
V1 in arterioles, cause vasopressor action
V2 in collecting tubules, insertion of aquaporins (water transported through tubular cells and back into blood)
What is the main function of aldosterone?
Regulate sodium excretion and reabsorption
Sodium retention
Where is aldosterone synthesised?
The Zona glomerulosa of the adrenal cortex
What is the first step in produced a steroid hormone?
Converting cholesterol into pregnenolone
How does aldosterone affect the kidney?
Stimulates sodium reabsorption and potassium secretion by distal convoluted tubule and CD
What stimulates aldosterone release?
Decreased BP or volume
Decreased Na+ in filtrate
How does aldosterone affect gene transcription?
Produced channels for Na+ to be reabsorbed from the urine into the ICF (Na+/K+ ATPase and epithelial sodium channels)
How do ADH and aldosterone work together?
ADH decreases osmolarity, aldosterone increases blood volume
What stimulates the release of ANP?
Where is it released from?
Increased atrial stretch
Released from atrial cells
Where is BNP released from?
Ventricle cells
What is the function of ANP?
Reduce blood volume by vasodilation of renal blood vessels, inhibit Na+ reabsorption, inhibit renin, aldosterone, and ADH release
