9.1: The genitourinary system Flashcards
5 functions of the kidneys
Excretion of metabolic products
Extretion of foreign substances
Homeostasis of body fluids, electrolytes and acid-base balance
Regulates blood pressure
Secretes hormones e.g erythropoietin, renin
What is the urinary system composed of?
Kidneys
Ureters
Bladder
Urethra
Renal blood supply into the kidney
Renal artery
Segmental artery
Interlobal artery
Arcuate artery
Interlobular artery
Afferent arteriolar
Into glomerular capillaries
Renal blood supply from the glomerular capillaries
From glomerular capillaries
Efferent arteriolar
Peritubular capillaries
Interlobular vein
Arcuate vein
Interlobular vein
Renal vein
Where does the urine once formed, travel through in the kidney?
Minor calyx to the major calyx and then through ureter
What are the 3 funtions of the peritubular capillaries?
Provide oxygen and nutrients to the nephron to allow them to perform their functions
Help in reabsorption of different substances along the nephron and then take it away to the cirulatory system
Help in secretion of different substances into the tubular fluid
What is the function of the detrusor muscle?
Detrusor muscle - Contracts to build pressure in the urinary bladder to support urination
What does stretching of the trigone to its limit lead to?
Signals sent to the brain about the need for urination
Is it the internal or external sphincter that gives involuntary control to prevent urination?
Internal sphincter - must be relaxed for urination to proceed
External sphincter gives voluntary control to prevent urination
What do abnormalities with the internal or external sphincter cause
Urinary incompetence
What is the function of the bulbourethral gland?
Produces thick lubricant which is added to watery semen to promote sperm survival
What are the 2 different cell type classes in the dital convoluted tubule and the collecting duct and describe their mitochondria density?
- Principal cells - Low density of mitochondria, the main Na+ reabsorbing cells and the site of action of aldosterone K+ sparing diuretics
- Intercalated cells - High density of mitochondria, regulation of acid-base homeostasis
What are the anatomical differences between the juxtamedullary and superficial nephrons?
The glomerulus of the superficial nephron is in the upper cortex, whereas the juxtamedullary nephron has its glomerulus closer to the medullary border
The Loop of Henle in the superficial nephron only extends to the outer medulla, whereas the juxtamedullary nephron has its one extending into the inner medulla
Why does the cortex have a granular appearance, whereas the medulla has a striated appearance?
Loop of Henle extending through the medulla gives it its striated appearance
3 cell types making up the juxtagolmerular apparatus
Extraglomerular mesangial cells
Macula dense
Juxtaglomerular cells
What are the main functions of this juxtaglomerular apparatus?
GFR regulation through tubular-glomerular feedback mechanism
Renin secretion for regulating blood pressure
What are the 4 main renal proccesses?
Glomerular filtration
Reabsorption
Secretion
Excretion
Is glomerular filtration a passive or active process?
Passive
Describe the permeability of the filtration barrier
Highly permeable to fluids and small solutes
Impermeable to cells and proteins
What is the name of the spaces between capillary endothelium and how big are they?
- Fenestrae70nm in diameter
What substances can pass through the fenestra in the kidneys?
Water
Ions
Small proteins
What substances can pass through the slit diaphragm of the glomerular basement membrane?
Water and small solutes only
What are podocytes
Highly specialised cells of the kidney glomerulus that wrap around capillaries and that neighbour cells of the Bowman’s capsule
What is the name of the ‘pulling’ pressure exerted by the solutes?
Oncotic pressure - fluid molecules are drawn in across a semipermeable membrane
Why does the cortex is granular looking whereas medulla has a striated appearance?
In medulla loop of Henley is present which is a tube so gives a striated appearance whereas the cortex contains the glomerulus and bowman’s capsule
What is the name of the force that causes the glomerular filtration from the glomerulus into the Bowman’s capsule?
Hydrostatic pressure from glomerular capillaries
4 main renal processes
Glomerular filtration
Reabsorption
Secretion
Excretion
Process of Reabsorption in the kidneys
Substances from inside of nephron are reabsorbed into the blood
Process of secretion in the kidneys
Body secretes chemicals which enter the kidney nephron to remove substances
Characteristics of epithelial podocytes in the bowman’s space
Thin and porous, water and small solutes can pass
Passive process into the bowman’s capsule
Fluid driven through semipermeable glomerular capillaries into the bowman’s capsule space by hydrostatic pressure of the heart
Characteristics of Filtration barrier into bowman’s capsule
Highly permeable to fluids and small solutes
Impermeable to cells and proteins
Diameter of glomerular basement membrane
70nm
(Lined by negatively charged proteins)
What is the Slit diaphragm
Finger like projections which interlock tightly
How do you calculate the net ultrafiltration pressure?
Puf = HPgc - HPbw - πgc
Puf - Net ultrafiltration pressure
HPgc - hydrostatic pressure in glomerular capillaries
HPbw - hydrostatic presure in bowman’s capsule
πgc - Oncotic pressure of plasma proteins in glomerular capillaries
What is meant by the glomerular filtration rate and how do you calculate it?
Amount of fluid filtered from the glomeruli into the Bowman’s capsule per unit time (ml/min)
GFR = Puf x Kf
Kf - ultrafiltration coefficient (membrane and surface area available for filtration)
What is the GFR for a healthy male and female respectively?
90-140ml/min
80-125ml/min
What does a fall in GFR show about the excretory products in the plasma?
That there is an increase in the excretory products in the plasma
Describe the myogenic mechanism used to regulate the GFR when arterial pressure is high
Arterial pressure increases
Afferent arteriole stretches
Ateriole contracts
Vessel resistance rises
Blood flow reduces
GFR stays the same
Describe the tubulo-glomerular feedback mechanism used to regulate the GFR
Increase/Decrease in GFR
Increased/Decreased NaCl in Loop of Henle
Change detected by macula densa
Increased/Decreased ATP and adenosine discharged
Afferent arteriole constricts/dilates
GFR stabilises
What is meant by renal clearance?
Number of litres of plasma that are completely cleared of the substance per unit time
Therefore it is only concerned with the excretory role of the kidneys
How would you calculate renal clearance?
C x P = U x V therefore C = (U x V)/P
C = Renal Clearance
U = Concentration of substance in urine
V - Rate of urine production
P = Concentration of substance in plasma
If a substance is only filtered in the kidneys and not reabsorbed or secreted, then what value is the GFR the same as?
Renal clearance
Give an example of a molecule that is only filtered and so it follows the principle of GFR=renal clearance ?
Insulin
(Not found in mammals, so must be transfused )
How can creatinine be used to assess renal function?
It’s Renal function is stable , the creating amount in urine is stable
Low creative clearance or high plasma creative may indicate renal failure
Why is creatinine not the ideal molecule like inulin and why is it still commonly used despite this?
It is secreted in small amounts into the nephron
However, the process for estimating creatinine in the blood and urine can account for that to allow for GFR calculations
What is the renal plasma flow?
Volume of plasma that reaches the kidney (afferent arteriole) per unit time
If the total amount of a molecule entering the kidney equals amount excreted, then the renal clearance of this molecule is the same as the renal plasma flow
What molecule is therefore used to measure the renal plasma flow?
Para aminohippurate - all of it is removed from the plasma passing through the kidney through filtration and secretion
What is meant if a substance is freely filtered
Means they can be found in the ultrafiltration and plasma at same concentration
What is meant by the filtration fraction and how is this calculated?
Ratio of amount of plasma filtered, and which arrives via the afferent arteriole is defined by Filtration Fraction
FF = GFR/RPF
e.g - a value of 0.15 implies that 15% of the plasma has been filtered
What is the difference betwen primary and secondary active transport?
Primary - Uses ATP directly to transport molecules in and out of the cell
Secondary - Movement of one solute along its electrochemical gradient provides energy for the other solute to move against its own electrochemical gradient
Is endocytosis a primary or secondary active transport mechanism?
Primary - small proteins are reabsorbed in the PCT using an ATP molecule
Explain how the Na+Glucose symporter works
Na+ moves down its electrochemical gradient into the cell
This provides the energy to transport glucose against its electrochemical gradient into the cell
- Explain how the Na+/H+ antiporter works
Na+ moves down its electrochemical gradient into the cell
This provides energy to actively transport H+ against its electrochemical gradient out of the cell
In the epithelial cell layer of the renal tubules, how does water follow the transcellular pathway?
It is transported from tubular fluid —> epithelial cells —> blood via aqua poring in the epithelial cells
How does trancellular Na+ reabsorption occur in the renal tubules?
3Na+ is transported from epithelial cells into blood via Na+/K+ ATPase
This creates a concn. gradient for Na+ as it is lower in the epithelial cell so Na+ from the tubular fluid diffuses into cell
2 K+ is transported from blood into epithelial cells via Na+/K+ ATPase so this is an active transport as ATP is used
What is meant by the paracellular pathway in the renal tubules?
Substances such as water, Ca2+, K+, Cl- and urea are transported through the tight junctions between the epithelial cells
How does Na+ and Bicarbonate reabsorption occur in the early proximal convoluted tubule?
- Na+/K+ ATPase creates a low Na+ concn. in the epithelial cellCO2 enters epithelial cell by diffusion and binds to H20, catalysed by carbonic anhydrase to form bicarbonate and H+Na+/H+ antiporter then transports Na+ down its concn. gradient into the cell from tubular fluid and H+ out into the tubular fluid against concn. gradient using the energy from transportation of Na+Na+/HCO3- symporter transports Na+ down concn. gradient into blood and bicarbonate is transported into blood against conc. gradient using energy from transportation of Na+
How does Angiotensin II regulate the Na+ reabsorbed?
By increasing the number of Na+/H+ antiporters
How does glucose reabsorption occur in the early PCT
Na+/K+ ATPase creates concn. gradient with less Na+ in the epithelial cell
Na+/Glucose symporter (SGLT2) transports Na+ from tubular fluid into epithelial cell and this provides energy to transport glucose against its gradient from the tubular fluid into the epithelial cell
Glucose transporter (GLUT2) transports glucose into the blood from the epithelial cell via facilitated diffusion
Explain the general processes of reabsorption involving the Loop of Henle occurs
Na+Cl- passively leaves thin ascending limb into the medulla and leaves actively from the thick ascending limb
This creates a low water potential in the medulla and so water leaves through the descending limb passively
Describe and explain the osmolarity of the tubular fluid in the different parts of the loop of Henle
At the point where the descending limb enters the ascending limb, the tubular fluid is hyperosmolar as water has been passively reabsorbed from the descending limb however since it is impermeable to Na+Cl-, the fluid is hyperosmolar
At the tip of the thick ascending limb, the tubular fluid is hypoosmolar as the salt has been reabsorbed far more
How does Na+Cl- reabsorption in the thick ascending limb of the Loop of Henle occur?
Na+/K+ ATPase creates concn. gradient with low conc. in the epithelial cell
Na+/K+/2Cl- symporter transports these ions from the tubular fluid into the epithelial cell
K+ is recycled back out into the tubular fluid
K+/Cl- symporter allows reabsorption of these ions back into the blood from the epithelial cell
How does Na+ and Cl- reabsorption occur in the early distal convoluted tubule?
Na+/K+ ATPase creates concn. gradient with low concn. in the epithelial cell
Na+/Cl- symporter transports Na+ and Cl- into the epithelial cell from the tubular fluid into the epithelial cell
K+/Cl- symporter then transports the K+ and Cl- from the epithelial cell into the blood
Is the early DCT permeable to water?
No
How does Active Ca2+ reabsorption occur in the early distal convoluted tubule?
Na+/K+ ATPase creates concn. gradient with low concn. in the epithelial cell
Na+/Ca2+ antiporter transports Na+ into epithelial cell from the blood and Ca2+ is transported from the epithelial cell into the blood against its concn. gradient
Ca2+ ATPase pump transports CA2+ against its concn. gradient as well into the blood from the epithelial cell
How do principal cells work to correct hyperkalaemia?
By transporting the K+ out of the epithelial cells and into the tubula r fluid
Is the later part of the DCT permeable to water?
Yes, it contains aquaporins
How does aldosterone increase Na+ reabsorption?
By increasing the apical Na+ channels and basolateral Na+/K+ ATPase pumps
How does ADH increase water reabsorption?
Basolateral aquaporins are almost always present
How does Na+ reabsorption and K+ secretion occur in the principal cells of the DCT and Collecting duct?
Na+/K+ ATPase creates concn. gradient with low concn. in the epithelial cell so Na+ is reabsorbed
K+ is transported into the epithelial cell from the blood and so it is secreted actively
How do the alpha and beta intercalated cells of the DCT and Collecting duct maintain an acid-base balance?
The alpha intercalated cells facilitate HCO3- reabsorpion and H+ secretion, whereas the beta intercalated cells facilitate HCO3- secretion and H+ reabsorption
Alpha intercalated cells have Cl-/HCO3- antiporters on the basolateral side, whereas beta intercalated cell have them on the apical side
Then the H+ ATPase pump is on the apical side on the alpha intercalated cells and on the basolateral side on the beta intercalated cells
These two cell types work together to act as a buffer to changes in pH
