Lecture 20- Urinary tract 3 Flashcards
What are the basic functions of the kidney?
- Control of blood composition (fluid and electrolyte balance):
- Regulation of osmolarity
- Maintenance of ion balance
- Homeostatic regulation of pH
- Control of blood volume
- Control of blood pressure
- Production of hormones by the kidney: erythropoietin
and calcitriol (active component of Vitamin D) - Excretion of waste: urea, urate & creatinine in urine
Recap the osmotic gradients
What is the modulation of osmolarity?
What is the movement of ions in water?
What is the countercurrent exchange principle?
Where does reabsorption occur?
Why do we refine filtrate and where?
Modulation of osmolarity through movement of water
and ions
* Descending limb is permeable to water only
* highest osmolarity at the bottom of the loop of Henle
* Ascending limb impermeable to water
* Filtrate entering the loop is similar to that in the
collecting duct
* Movement of ions and water from the filtrate into the
interstitial fluid
* generates a medullary osmotic gradient
* enables the exchange ofsolutes with contents in
capillaries of the vasa recta
* Coutercurrent exchanger shift in in blood supply
* Reabsorption in prox. & dist. Tubule
* Refining filtrate for excretion in collecting duct
* removal of water
Can osmolarity and volume change independently of each other and why?
- Osmolarity and volume can change independently (permeability differences in
nephron), although they effect each other
What happens to blood composition during dehydration and how is it compensated?
- Dehydration decreases blood volume/pressure, and increases osmolarity
Can changes in blood composition affect pH? Why?
Compensation involves cardiovascular responses coordinated by hormones;
Angiotensin II (ANG II), Antidiuretic hormone (ADH/vasopressin), and thirst
response to maintain blood volume/pressure
* pH changes (defined by presence of H+ ions):
* H+ concentration is closely regulated because it can alter three-dimensional
structure of proteins
* Abnormal pH affects the nervoussystem
* Acidosis: neurons become less excitable; CNS depression
* Alkalosis: hyperexcitable
* pH disturbances (often associated with K+ disturbances) affect membrane potential
What can an abnormal pH affect?
Abnormal pH affects the nervoussystem
* Acidosis: neurons become less excitable; CNS depression
* Alkalosis: hyperexcitable
* pH disturbances (often associated with K+ disturbances) affect membrane potential
What is ADH? What is its function and what releases it? What is the purpose of ADH?
ADH (vasopressin) is a peptide hormone produced by the posterior pituitary gland.
- Paraventricular neurons and supraoptic
nucleus neurons release ADH (vasopressin) - antidiuretic function (e.g. when dehydrated)
- prevents the production of diluted urine
- increases permeability of the collecting duct
to water entering the interstitial fluid and
systemic circulation by osmosis - net effect is to increase water reabsorption
by the kidney
How can the body determine we are dehydrated?
using Osmoreceptorsin the hypothalamus detect an increase in blood osmolality (decrease in blood volume with the same amount of ions so concentration of ions increases) which means an decrease in blood volume which equates to dehydration
Go through the steps of ADH secretion. What kind of feedback system is this and why?
negative feedback system
- Osmoreceptorsin the hypothalamus detect an
increase in blood osmolality - ADH is produced in cells of the hypothalamus
(supraoptic and paraventricular nuclei) - ADH is transported to the posterior pituitary
- ADH is released into the blood & travelsto the kidney
- Upon reaching the nephron epithelium ADH
stimulates an increase in number of water channels - Increased water
reabsorption - Decreased blood
osmolality
What happens during maximal ADH secretion?
- With maximal ADH the collecting duct
is freely permeable to water - Water leaves by osmosis and is carried
away by the vasa recta capillaries
(reabsorbed) - Urine is concentrated
What happens when minimal ADH is secreted and when may this be observed?
- the collecting duct is still impermeable to water
- this means there is no change in solute concentration and therefore osmolality
-there is a large volume and urine is diluted
-can be observed when overhydration occurs
What are the stimulating factors of the thirst mechanism and what are the sensors? Complete the steps of the thirst mechanism
Stimulating factors and sensore: increased blood osmolality (stimulate osmoreceptors in hypothalamus in brain)
decreased blood volume (decreased activity of atrial volume receptors in the heart)
decreased blood pressure decreases activity of baroreceptors in blood vessels in carotid arterie and aortic arch
-decreased blood pressure also increases release of renin from kidneys
dry mouth (direclty stimulates the thirst receptor in hypothalamus)
-all these sensors stimulate the thirst receptors in the hypothalamus
-hypothalamus increases thirst
- thirst increases water intake
-i increase in water intake decreases blood osmolality and increases blood volume, blood pressure and relieves mouth dryness to alleviate all the stimulating factors
- lack of water increases osmolality
- osmoreceptors are stimulated
- supraoptic PVN nuclei is triggered
- ADH release increased
- increased permeability in collecting duct
- water reabsorbed into circulation
What does high osmolality mean?
Osmolality is a measure of the concentration of solute particles in a solution per unit of solvent in terms of osmoles of solute particles per kilogram of solvent (osmol/kg). It quantifies the osmotic pressure exerted by solute particles in a solution and reflects the solution’s ability to induce water movement across a semipermeable membrane.
Draw and summarise the mechanisms that show how ADH and the thirst mechanism work together
- change in plasma osmolality
- osmoreceptors in hypothalamus detect change
- hypothalamus compares and initiates change
- posteriar pituitary releases ADH and Hypothalamus initiates thirst response
- osmolality is returned to the physiological range
Why is acid-based balance so important?
activity of most enzymes is pH dependent and perfomr most efficiently at an optimal
-amino acids within proteins can change their charge and then repel each other which changes the conformation of the proteins and thus the proteins function
-Maintenance of the pH is important for accurate control of tissue biochemical and physiological functions
