Renal Physiology II ( Lecture 54 - 56 ) Flashcards
The ability to produce _______ is a major determinant of the ability to survive with limited water intake
hyperosmotic urine
The kidney can produce HIGHLY concentrated urine with a maximal concentration of _____ mOsmol / L almost ____ times the osmolarity of plasma which is _______ mOsmol / L.
1400
5
300
Where does urinary concentration take place.
Explain
Urinary concentration takes place as tubular fluid flows through the medullary collecting duct.
The interstitial fluid around it is hyperosmotic, therefore, with the presence of Vasopressin, water diffuses out of the ducts to the interstitial fluid and returns to the capillaries
Compare the descending and ascending limbs of the Loop of Henle
Descending
- permeable to water
- not permeable to solutes
Ascending
- not permeable to water
- permeable to solutes ( Na/ K/ Cl tranporters)
Limbs travel in opposite directions ( countercurrent)
Explain the countercurrent multiplier system
Because of osmolarity differences that exist, each horizontal level gradient is “multiplied” as it goes deeper into the medulla, hence, calling it the countercurrent multiplier system.
(T/F) Loop of Henle directly forms concentrated urination
False
The Loop of Henle is important when needed to form concentrated urination, however, vasopressin and the medullary collecting duct is also needed.
What is the only way water can leave the medullary collecting duct by _______
By Aquaporins stimulated by the Vasopressins
What will happen if there was no vasopressin
concentrated urination will not be produced since water will not be reabsorbed in the medullary collecting duct.
_______ in the ______ monitors the osmolarity of the extracellular fluid
Osmoreceptors in the hypothalamus
If osmolarity increases …. ADH…
If osmolarity decreases …. ADH…
If osmolarity increases, ADH secretion is stimulated and increases water reabsorption
If osmolarity decreases, ADH secretion is inhibited, which decreases water reabsorption and increases water excretion
______ that can detect ____ and _____ also has an influence on ADH secretion
Baroreceptors blood volume and pressure
What has an effect on ADH secretion
Baroreceptors in the atria
osmoreceptors (in the hypothalamus) that stimulates ADH from the posterior pituitary
What are baroreceptors
Baroreceptors located in the atria detect and respond to changes in the blood volume and those in the aortic arch and carotid sinus respond to changes in the blood pressure.
As blood volume / pressure increases …. ADH…
As blood volume / pressure increases, the action potential of the baroreceptors increases. This causes a decrease in ADH secretion, which decreases water reabsorption, thus decreasing blood volume and pressure.
As blood volume / pressure decreases… ADH…
As blood volume/ pressure decreases, the action potential of baroreceptors decrease. This causes an increase in ADH secretion, which increases water reabsorption, thus increasing blood volume and water pressure.
The _____ (structure) prevents countercurrent gradient from being washed away
hairpin loop of the vasa recta
A low extracellular volume _____ vasopressin secretion from baroreceptors reflexes and a high extracellular volume _____ it
stimulates
inhibits
_____ is a steroid hormone released from the _____ that regulates both ______ and ______.
Aldosterone
adrenal cortex
Na+ reabsorption and K+ secretion
Explain the mechanism of how aldosterone promotes Na+ reabsorption and K+ secretion ( 5 steps)
- Aldosterone binds to cytosolic receptors in the renal tubule cells of teh distal tubule and collecting duct
- The hormone receptor complex initiates transcription in the nucleus
- This stimulates new protein c
The most important factor in control of the aldosterone release is the ______
renin-angiotensisn-aldosterone system (RAAS)
Where is Renin secreted
granular cells in the juxtaglomerular appartus
What is the Macula Densa ? Function?
When arterial pressure is low, the GFR is also low which causes a low concentration in Na and Cl ions. In response to the low arterial pressure, the macula densa cells of the distal tubules secrete paracrine factors that act on granular cells.
Paracrine factors acts on granular cells to tell them to secrete renin. Therefore, when sodium concentration of the tubular fluid decreases, renin secretion increases
When sodium concentration in the tubular fluid _____, renin secretion _____
Decreases
Increases
Where is the juxtaglomerular apparatus formed
It is formed where the distal tubules travel close to the afferent and efferent arterioles
3 distinct inputs to the granular cells to trigger renin release
- a decrease in blood pressure is a primary stimulus for renin release. Specifically, a decrease in afferent arteriole pressure, because granular cells are directly sensitive to the degree of stretch of the afferent arterioles
- A large decrease in mean arterial pressure ( MAP) also decreases GFR, which leads to a decrease in Na anc Cl concentration in the distal tubules. This drop in Na and Cl is detected by the macula densa and secretes a chemical signal to stimulate renin release from the granular cells.
- The baroreceptor reflex in response to a decrease in blood pressure increases activity in the sympathetic activity which stimulates renin release by direct input to granular cells
RAAS tends to ____ blood pressure
increase
How does renin act to increase MAP and sodium reabsorption (3)
- Renin acts on the protein Angiotensinogen, that is always secreted in the plasma by the liver
- Renin cleaves off some AA from the Angiotensiongen and converts it to Angiotensin I
- Angiotensin I is converted to Angiotensin II by the ACE, which is bound to the inner surfaces of the capillaries.
3 important functions of Angiotensin II
- the stimulation of Aldosterone release from the adrenal cortex
- The increase in MAP by acting as a vasoconstrictor
- Acting in the hypothalamus to stimulate vasopressin release and thirts
Angiotensin increases MAP by 4 mechanisms
- Angiotensin II stimulates vasoconstriction of systematic arterioles, which increases MAP
- Angiotensin II activates hypothalamic neurons to stimualte thirst and fluid intake, which by increasing plasma volume increases MAP
- Angiotensin II stimulates posterior pituitary to secrete Vasopressin, which increases water reabsorption by minimizing fluid loss and maintains plasma volume, this maintains mean arterial pressure.
- Angiotensin II stimulates the adrenal cortex to secrete Aldosterone, which increases Na reabsorption and causes water reabsorption to increase se
Where is the Atrial Natriuretic peptide (ANP) secreted ? And when is it secreted.
ANP is secreted by cells in the atria of the heart.
It is secreted in response to the distention of atrial walls ( swelling), which happens when plasma volume increases
Function of renin
Renin responds to low blood pressure.
They cause an increase in sodium retention which is accompanied by water retention
How does ANP cause and increase in Na excretion
- ANP increases sodium excretion by increasing GFR and decreasing Na reabsorption
- ANP also causes the dilation of the afferent arteriole and constriction of the efferent arteriole. This increases the glomerular capillary pressure which increases GFR and increases the filtered sodium load.
- ANP can also decrease sodium directly by decreasing the number of sodium channels in membranes of the renal tubular cells
(T/F) ANP decreases secretion of aldosterone
True.
ANP decreases the secretion of both aldosterone and renin.
This causes a decreased absorption of Na, and increases the amount of NA excreted.
This lowers the osmolarity of the body fluid, which increases the excretion of the water from the body
The fluid that remains after ____, ______, ____, and ____ is excreted as urine
Filtration, reabsorption,
Excretion,
Secretion
What are the detrusor muscles
The wall of the bladder contains smooth muscle fibers that are connected by gap junctions as a unit. Together, these fibers are called detrusor musecles
Two rings of the detrusor muscle, the _____ and ______ acts as ________ to regulate the flow of urine from the bladder
Internal and external urethral sphincters
Valves
How does the micturition reflex occur.
Micturition reflex causes the voiding of the bladder when the detrusor muscles contract, and the internal and external urethra sphincters relax and open
Micturition is regulated by the _____ that can be overridden by ______.
Spinal reflex
Voluntary control
Explain how the micturition is regulated through voluntary control
When the bladder fills, the expansion of the wall is detected by stretch receptors that transmits to the spinal cord
In the spinal cord, signals are relayed via interneruons to 3 sets of neurons that project back to the bladder and associated structures
This neuronal signaling results in the detrusor muscle contraction, which increases pressure on the bladder content causing the internal urethral sphincter to open.
At the same time, the stretch receptor inhibits sympathetic and somatic neuron activity, allowing the h internal and external sphincters to open
When the bladder is at rest the _______ which is a smooth muscle controlled by the ______ NS keeps it _______ . ______ controlled by the skeletal muscle is _____.
internal sphincter
sympathetic
contracted
External sphincter
also contracted
When the bladder is fired with urine ….
- Stretch receptors sends signals via sensory neurons to the spinal cord.
- The stimulus of a full bladder excites parasympathetic neurons leading to the smooth muscle in the bladder wall
- The smooth muscle contracts, increasing the pressure on the bladder contents
- At the same time, somatic motor neurons leading to the external sphincter are inhibited by inhibitory interneruons within the spinal cord. Also, sympathetic neurons into the internal sphincter stop firing.
- Contraction of the bladder occurs that pushes urine to the urethra. Pressure exerted by the urine forces the internal sphincter open while external sphincter relaxes.
- Urine then passes through the urethra and out of the body.
