1 Flashcards
What is the organ called that forms urine?
Kidneys
What are the accessory structures in the urinary system that store and transport urine?
Ureters, Urethra, & the Urinary Bladder
What is the structure called that water is reabsorbed through and moves across in the tubular epithelial cells?
- Aquaporins
Describe the passive rebasorption of Water.
- Water is reabsorbed passively down its osmotic gradient, which is primarily established by the active transport of sodium
How is chloride rebasorbed across the proximal tubule?
- Chloride moves across the tight junctions of these tubules
Describe the passive rebasorption of chloride.
- The electrochemical gradient for chloride is already established by the active transport of sodium
What is the passive reabsorption of solutes such as chloride, water, and urea dependent on?
- It is dependent on sodium reabsorption
What is the term that refers to the coconcentration of glucose (or any other substance) in the filtrate that causes the transport maximum to be reached ? And, what happens once it is reached?
- Renal threshold
- Once it is reached, glucose will begin to be excreted in the urine
What is the term referred to when transport proteins are saturated and operating at their maximum speeds?
- Maximum rate of transport
Describe the process of glucose reabsorption and how it is relevant to sodium reabsorption
- On the apical membrane, glucose moves across by cotransport with sodium through a secondary transport protein
- On the basolateral membrane, glucose moves across using a facilitated diffusion carrier protein
What is ANP and how does it influence sodium reabsorption in the distal tubule? Also, how does it differ from aldosterone?
- ANP is a hormone released from specialized cardiac atrial muscle cells in response to stretching.
- ANP decreases Na⁺ reabsorption by decreasing the number of Na⁺ channels in the apical membrane of the principal cells of the distal tubule
• ANP also inhibits the secretion of renin and aldosterone,
• ANP inhibits the contraction of smooth muscle cells in the afferent arteriole,
• & ANP inhibits the activity of the sympathetic nervous system.
List the 3 inputs that stimulate granular cells (of the juxtaglomerular apparatus) to secrete renin
- By the decreases in pressure in the afferent arterioles
- By paracrine messengers released from macula densa cells in response to decreased salt concentration in the filtrate
- By increased sympathetic nervous system activity (baroreceptor reflex)
Which system regulates aldosterone secretion?
- The Renin - Angiotensin-Aldosterone System (RAAS)
What is aldosterone and how does it increase sodium reabsorption in the distal tubule?
- A steroid hormone secreted from the adrenal cortex, which increases Na⁺ reabsorption by:
• (1) Increasing the number of Na⁺ channels in the apical membrane
• (2) Increasing the number of Na⁺ / K⁺ -ATPase in the basolateral membrane
List the hormones that regulate sodium reabsorption in the distal tubule
- Aldosterone & Arterial natriuretic peptide (ANP)
Describe the process of sodium reabsorption in the Distal tubule? Including both the Apical and basolateral membranes
- On the Apical membrane, Sodium moves across by cotransport with chloride (Cl-) through a secondary active transport protein or through sodium channels.
- On the Basolateral membrane, Sodium moves across by a primary active transport protein, the Na+/K+-ATPase
Describe the process of sodium reabsorption in the proximal tubule? Including both the Apical and basolateral membranes
- On the apical membrane, Sodium moves across by cotransport or by countertransport through secondary active transport proteins.
- On the basolateral membrane, Sodium then moves across by a primary active transport protein, the Na+/K+-ATPase
Why is sodium reabsorption in the proximal tubule important?
- Because it is important for the reabsorption of other solutes, such as glucose, amino acids, water, chloride (Cl⁻), hydrogen ions (H⁺), and urea
Where is the majority of sodium (67%) reabsorbed? Where is the rest of the sodium reabsorbed (25%)? And, where is the remaining sodium reabsorbed (8%)?
- Proximal tubule (67%)
- Loop of Henle (25%)
- Distal tubule (8%)
What is hyponatremia?
- It is a lower than normal plasma concentration of Na⁺, and is also accompanied by low plasma volume and decreased blood pressure
What is hypernatremia?
- It is a higher than normal plasma concentration of Na⁺, and is also accompanied by water retention and an increased blood pressure
Why is the homeostatic maintenance of Sodium important?
- Important to achieve normal osmotic pressure and for the functioning of excitable cells
What is the primary solute in the ECF?
Sodium
What are the components of the reabsorption barrier in tubular reabsorption?
- Tubular epithelial cells (With apical and basolateral membranes), basement membrane, peritubular space, and peritubular capillary endothelial cells
Why is tubular reabsorption a highly selective process?
- Because most solutes require the presence of a transport protein to facilitate movement across the reabsorption barrier.
Where does most reabsorption occur, and is unregulated?
- The proximal tubule
On the topic of tubular reabsorption, describe the reabsorption concentration concept
- With the exception of the plasma proteins, all solutes are in the same concentration in the glomerular filtrate as in the plasma
What is Tubular reabsorption?
- It is the movement of solutes and water from the tubules, back into the plasma in the peritubular capillaries
How does the sympathetic nervous system extrinsically regulate GFR?
- Through the baroreceptor reflex (Involved in the short- and long- term regulation of MAP)
- And through the mesangial cells ( Which are modified smooth muscle cells that surround the glomerular capillaries, and upon SNS innervation, they decrease the surface area available for filtration)
How are the extrinsic mechanisms of regulating GFR different from the intrinsic ones? And what is the goal of the extrinsic mechanisms of regulating GFR?
- Extrinsic mechanisms can override intrinsic ones, allowing for changes to GFR even when MAP is within the range of 80-180 mm Hg and is subjected to intrinsic regulation
- Goal is to maintain MAP, through the SNS
Describe Tubuloglomerular feedback intrinsic regulation of GFR, and its response to changes in MAP?
- Intrinsic response of the macula densa cells of the juxtaglomerular apparatus (distal tubule) in response to an increase in the salt concentration of the fluid in the filtrate.
- In an increase in MAP, and increase in salt concentrations, Macula densa secrete adenosine (paracrine chemical messenger), causing neighbouring afferent arterioles to vasoconstrict
- In a decrease in MAP, results in less adenosine secretion by macula densa cells, thus less vasoconstriction or vasodilation of afferent arterioles
Describe Myogenic intrinsic regulation of GFR, and its response to changes in MAP?
- Is an intrinsic response to a stretching of the smooth muscles in the walls of the afferent arteriole.
- In an increase in MAP, the afferent arterioles stretch, causing vasoconstriction, increasing resistance, and decreasing GC hydrostatic pressure, thus decreasing GFR
- Opposite sequence goes for a decrease in MAP
What are the intrinsic mechanisms for the regulation of GFR? And, their function
- Myogenic regulation & Tubuloglomerular feedback
- They function to allow for GFR to remain constant with changes in MAP over the range of 80-180 mm Hg
List some examples of unregulated pathological changes that affect GFR?
- Severely burned patients (lose protein-rich plasma, decrease GC oncotic pressure, & increasing GFR)
- Dehydration diarrhea patient (increase in plasma-protein, increase GC oncotic pressure, & decreasing GFR)
- Glomerular capillary damage ( protein filters into bowman’s capsule, increasing BC oncotic pressure, & increasing GFR)
- Kidney stones or an enlarged prostate ( Increasing BC hydrostatic pressure, decreasing GFR)
What are the unregulated pathological changes that affect GFR?
- Includes changes in GC oncotic pressure and BC oncotic & hydrostatic pressures
What is the regulated variable that affects GFR?
- The glomerular capillary hydrostatic pressure
- Which occurs in response to an increase in MAP (GFR increases as well)
Why is it important to regulate GFR?
- Because small increases in GFR result in large increases in the volume of fluid filtered and excreted
What is the filtration fraction?
- It is the fraction of plasma that enters the Bowman’s capsule as filtrate during glomerular filtration -> on average 20% of plasma enters Bowman’s capsule as filtrate
How is the filtration coefficient determined?
- by the glomerular surface area available for filtration & the glomerular membrane permeability
What are the 2 variables that GFR depends on?
- Net glomerular filtration pressure & the filtration coefficient (Kf)
What is the Glomerular filtration rate (GFR)
- Is it the rate of filtration through the glomerular capillaries
What is the net glomerular filtration pressure? And, how is it calculated?
- It is the forces that exist across the walls of glomerular capillaries
- It is calculated by totalling the starling forces favouring filtration and subtracting them by the starling forces favouring absorption across the glomerular capillaries
Describe the Bowman’s Capsule hydrostatic pressure (Pbc). And answer whether it favours filtration or absorption across the glomerular capillaries
- It is the pressure exerted by the filtrate in the bowman’s capsule -> 15 mm Hg
- It favours absorption across the glomerular capillaries
Describe the Bowman’s Capsule oncotic pressure (πBC). And answer whether it favours filtration or absorption across the glomerular capillaries
- It results from proteins present in the bowman’s capsule -> 0 mm Hg under normal healthy conditions
- It favours filtration across the glomerular capillaries
Describe the Glomerular capillary oncotic pressure (πGC). And answer whether it favours filtration or absorption across the glomerular capillaries
- It results from proteins present in the glomerular capillaries - > 29 mm Hg
- It favours absorption across the glomerular capillaries
Describe the Glomerular capillary hydrostatic pressure (Pgc). And answer whether it favours filtration or absorption across the glomerular capillaries
- It is the blood pressure exerted on the glomerular capillaries -> at 60 mm Hg
- It favours filtration across the glomerular capillaries
List the 4 starling forces involved in glomerular filtration
- Glomerular capillary oncotic pressure & Glomerular capillary hydrostatic pressure
- Bowman’s capsule oncotic pressure & Bowman’s capsule hydrostatic pressure
What is the pathway for the glomerular filtration process? (step by step)
- Glomerular filtration occurs through the glomerular membrane, by moving solutes and fluid through the fenestrations in the capillary endothelial cells
- Then across the basement membrane
- And finally, through the filtration slit pores in the tubule epithelial cells (podocytes)
What is the glomerular filtration process?
- It is the mechanism of action where protein-free plasma filters through the glomerular capillaries to the Bowman’s capsule
Describe Tubular secretion in its role in urine formation?
- Is the selective transfer of substances from the peritubular capillaries to the tubular lumen
Describe Tubular reabsorption in its role in urine formation?
- As filtrate flows through the tubules, substances of value are returned to the peritubular capillaries’ plasma
Describe glomerular filtration in its role in urine formation?
- 1st step in urine formation, occurs in the renal corpuscle
- Where 20% of the blood entering the glomerulus via the afferent arterioles filters into the Bowman’s capsule and becomes filtrate
Which renal processes are involved in the formation of urine?
- Glomerular filtration, Tubular reabsorption, & Tubular secretion
Describe Juxtamedullary nephrons, and list their location. What is the % of nephrons that are of this type? What is their function?
- 15-20% of nephrons are juxtamedullary, and they have long loops of Henle located deep into the medulla.
- They also play an important role in establishing the medullary vertical osmotic gradient (allowing for water reabsorption)
Describe cortical nephrons, and list their location
- Most nephrons are cortical nephrons (80-85%)
- They are located in the renal cortex
What are the 2 types of nephrons called? And, how are they distinguished?
- They are the cortical and juxtamedullary nephrons
- They are distinguished based on their anatomical locations
What structure do the Granular cells of the juxtaglomerular apparatus belong to? And what is their function?
- Surround the afferent arterioles
- They secrete the enzyme renin, which functions to regulate blood volume and blood pressure
What structure do the macula densa cells of the juxtaglomerular apparatus belong to? And what is its function?
- Belong to the epithelial cells of the distal tubule
- Function in the detection of salt concentrations in the filtrate
What is the Juxtaglomerular Apparatus in the nephron?
- It is the region where the distal tubule and the afferent arteriole meet, leading into the glomerulus
Describe the Collecting duct in the tubular component of the nephrons?
- Distal tubule finally empties the filtrate here.
- The filtrate leaves the collecting ducts as urine, as its emptied into the minor calyx
What is the structure called that the distal tubule collects the filtrate from? And, where is the distal tubule located in the nephron?
- Following the loop of Henle, which lies entirely in the renal cortex
Describe the Loop of Henle in the Tubular component of the nephrons? What is the structure called that it collects the filtrate from? And, where is it’s loops located
- Following the proximal tubule, forming a U-shape, with ascending and descending loops, that dip into the renal medulla and rise into the renal cortex
Describe the Proximal tubule in the tubular component of the nephrons?
- Following Bowman’s capsule, filtered fluid enters here.
- Is it located in the renal cortex
Describe the Bowman’s capsule in the tubular component of the nephrons?
- Tubular component begins here, following glomerular filtration, it collects the filtrate from the glomerular capillaries
What is the function of the tubular component of the nephron?
- It forms the urine within the nephron
Describe the Venules in the vascular component of the nephrons?
- Peritubular capillaries rejoin to form venules, which exit the kidneys as the renal vein