Module 4: Renal II Flashcards
Micturition reflex
- What is it?
- What volume does it kick in?
- What volume is its maximum (then what happens)?
- How much is left once micturition is completed?
- The urge to urinate.
- Around 200 mL.
- 500 mL, the internal sphincter is forced open, leading to opening of the external sphincter and loss of voluntary opposition
- 10 mL.
What are the 3 important structures of micturition?
- Detrusor muscle: makes up majority of the bladder wall
- Internal sphincter: smooth muscle, passively contracted
- External sphincter: skeletal muscle, stays contracted
Define incontinence. Give 5 causes.
The inability to control urination voluntarily.
- Infants: corticospinal connections yet to be established
- Damage to internal or external sphincter
- Spinal cord damage
- Aging
- Prostate growth
What four parameters are balanced by homeostatic mechanisms for fluid and electrolyte balance?
- Fluid volume: dictates blood volume, dictates blood pressure
- Osmolarity: dictates cell volume
- pH: protein folding and optimization
- Concentrations of individual ions: Na+, K+, Ca2+
Mass balance: what are the three methods remove excess fluid and molecules from the body?
- Kidneys
- Feces and sweat
- Lungs: lose water and help remove H+ and HCO3 by excreting CO2
What cell in the kidney is important for maintaining cell volume and osmolarity? How does it do this?
Renal tubule cells (Loop of Henle in juxtamedullary nephrons) are constantly exposed to hypertonic ECF and produce organic solutes to match intracellular osmolarity.
What systems integrate fluid and electrolyte balance? How are they controlled and what is their response speed?
-
Cardiovascular
- Neural control
- Rapid
-
Respiratory
- Neural control
- Rapid
-
Renal
- Endocrine and neuroendocrine control
- Slower
Which cells in the body respond to atrial filling?
Volume baroreceptors on the aorta.
What creates concentrated urine? The concentration, or osmolarity, of urine is a measure of how much of what is excreted by the kidneys?
The intersitial space of the renal medulla. Concentration is a measure of how much water is excreted.
If the kidneys are trying to remove excess water they will produce a _____ volume of _____ urine. This is known as diuresis.
Large, dilute.
If the kidneys are trying to conserve water they will produce a _____ volume of _____ urine. This is known as antidiuresis.
Small, concentrated.
How do the kidneys control the urine concentration? Where does this occur?
- What happens in the production of dilute urine?
- What happens in the production of concentrated urine?
What mechanism are these changes made by?
They vary the amounts of water and Na+ reabsorbed in the distal nephron (distal tubule and collecting duct).
- The distal nephron must reabsorb solute without allowing water to follow by osmosis.
- The distal nephron must reabsorb water and little solute.
This is done adding or removing water pores (AQP2) in the apical membrane under the direction of the hormone vasopressin (AVP).
The insertion of AQP2 is a _____ process, depending on the amount of AVP present.
Graded. It is not all or one.
What 4 stimuli control vasopressin secretion?
- Blood pressure
- Blood volume
- Osmolarity
- Increased osmolarity is the most potent stimulus of AVP secretion
- Circadian rhythm (dies down at night)
Production and secretion of vasopressin:
- Controlled by what cells?
- What is osmolarity monitored by?
- How do these signal the control cells?
- Magnocellular neurosecretory cells (MNC’s) in the hypothalamus
- Osmolarity is monitored by osmoreceptor neurons.
- Stretch sensitive neurons that increase firing rate as osmolarity increases (shrink)
- High osmolarity causes firing of the osmoreceptor neurons, signaling the MNC’s, causing the release of AVP.
Activity of MNC’s
- Hypertonic solution:
- Set point:
- Hypotonic solution:
- Hypertonic solution: increased AP’s, increased AVP release, antidiuresis
- Set point: antidiuresis and diuresis both adjust to meet the set point level
- Hypotonic solution: decreased AP’s, decreased AVP, diuresis
MNC’s are always active to some extent
AVP is important for water reabsorption out of the nephron, but the high osmolarity within the medullary interstitium is necessary for what?
To create the concentration gradient for osmotic movement of water out of the collecting duct.
What creates the hyperosmotic interstitium and why isn’t it reduced as water is reabsorbed? (2 reasons)
The renal medulla
- Renal countercurrent exchange system
- Urea
What are the components of the renal countercurrent exchange system? What are the main roles of each?
-
Loop of Henle (countercurrent multiplier)
- Descending limb: allows water to follow to follow its osmotic gradient into the increasingly hypertonic interstitium but does not allow solutes to be transported.
- Ascending limb: actively transports solutes (Na+, Cl-, K+) into the interstitium. Filtrate leaving is hypoosmotic.
- Main job: create the hypertonic interstitium
-
Peritubular capillaries (vasa recta) (countercurrent exchanger)
- Moves in the opposite direction to the multiplier.
- Removes water
- Main job: prevent the washout (dilution) of the hypertonic interstitium
25% of sodium and potassium reabsorption occurs in the ascending limb of the Loop of Henle. This is done using _____ transport and what kind of transporter? Describe it’s mechanism.
Active transport using NKCC transporters on the apical membrane. Uses energy stored in the Na+ concentration gradient to move Na+, K+ and 2 Cl- into the epithelial cells. Na+ is pumped against it’s concentration gradient on basolateral membrane.
Why doesn’t the water entering the interstitium via the decending limb dilute the hyperosmotic medulla?
The opposite direction loop of the vasa recta picks some solute up and loses some water as it travels by the ascending limb creating hyperosmotic blood. This then creates a gradient allowing much of the water transported from the ascending limb to move into the vasa recta.
What role does urea play in the creation of the hyperosmotic interstitium?
Large amounts of urea in the medulla interstitium contribute to the hyperosmotic state.
Aldosterone
- What is it?
- Where is it produced?
- What role does it play?
- What channels does it act on?
- Steroid hormone
- Produced in the zona glomerusola cells
- Responsible for altering Na+ reabsorption and K+ excretion.
- ENaC (Na+ reabsorption channel) and ROMK (K+ excretion channel)
When aldosterone binds to _____ receptors in _____ cells, what two things happen?
Cytoplasmic mineralocorticoid receptor in P cells.
-
Increased opening of Na+ channels and possibly K+ channels, enhancing Na+ reabsorption and K+ excretion
- Increased Na+ entry speeds up Na+-K+ pump, increasing reabsorption of Na+, while increasing intracellular K+, leading to increased K+ secretion
- Hormone ligand complex transports to cell nucleus, increasing transcription of apical Na+ channels, apical Na/K pumps, and possibly apical K+ channels, further enhancing reabsorption and secretion
What 3 things can trigger aldosterone release? What thing can inhibit it?
Activate:
- Abnormally large drop in Na+
- K+ will act on the adrenal cortex to stimulate production, protecting the body from hyperkalemia
- RAS pathway: decreased blood pressure usually controls aldosterone secretion initiating a pathway that results in the production of angiotensin II which triggers aldosterone release
Inhibit:
- Increased osmolarity acts on adrenal cortex during dehydration, inhibiting aldosterone release
Renin-angiotensin system/pathway
- Role?
- Assists which reflex?
- Works with what system?
- Begins with secretion of what?
- Maintains blood pressure
- Assists baroreceptor reflex
- Works with the cardiovascular control center
- Begins with the secretion of renin
Give three stimuli that begin the RAS. What are these all driven by?
- Low blood pressure in renal arterioles causes granular cells to secrete renin
- Sympathetic neurons activated by CVCC when blood pressure decreases terminate on granular cells to secrete renin
- Paracrine feedback (prostaglandins) from macula densa cells signal to the granular cells to secrete renin
These are all driven by a drop in blood pressure.
What is the main role of renin?
To convert angiotensinogen to angiotensin I.
What enzyme converts ANG I to ANG II?
Angiotensin converting enzyme (ACE).
What are the 5 effects of ANG II?
- Increases vasopressin secretion (ANG receptors in the hypothalamus)
- Stimulates thirst
- Vasoconstriction
- Increased sympathetic output to heart and blood vessels (ANG II receptors in the CVCC)
- Increases proximal tubule Na+ reabsorption (apical Na+/H+ exchanger), increasing water reabsorption
Atrial natriuretic peptide (ANP)
- Where is it produced and secreted from?
- What stimulates production?
- What is its role?
- What is its receptor and how does it work?
- Produced and secreted by specialized myocardial cells primarily in the atria of the heart.
- Stimulated by increased stretch of the atria.
- Causes loss of water and Na+ (works in complete opposition to ANG II).
- ANP receptor, acts through a cGMP second messenger system
ANP primarily affects 4 regions of the body, what are they and how does ANP affect them?
-
Kidney
- Relaxes afferent arterioles (increases GFR)
- Reduces renin release from granular cells
- Reduces Na+ reabsorption at the collecting duct
-
Hypothalamus
- Reduces AVP release
-
Adrenal cortex
- Inhibits aldosterone release
-
Medulla
- Acts on the CVCC to decrease blood pressure
