Chapter 17 Physiology of the Kidneys Flashcards
The renal systems function is to… (4)
- Regulate blood volume
- Eliminate organic waste
- Regulate balance of electrolytes
- Maintain pH of plasma
Kidneys do what… (4)
- Form urine
- Water and electrolyte balance
- Secretion of toxins and drugs
- Gluconeogensis
What is gluconeogensis
synthesis of glucose from AAs during prolonged fasting
The ureters do what
transfer urine to bladder
Urinary bladder does what
Storage and micturition (urination) via the urethra
Urethra does what
Micturition
What is the outer layer of the kidney
What happens here
Renal cortex
Glomerular filtration
Convoluted tubules
What is the inner part of the kidney
What happens here
Renal medulla
Location of loops of Henle:
Drains the collecting ducts into the renal pelvis and ureter
What is the pathway of micturition
Collecting ducts Renal pelvis Ureters Bladder Urethra
What causes urine to flow from the ureter to the bladder
Contractions of smooth muscle in ureter
Where is the Internal urethral sphincter
At the base of the bladder
Where is the External urethral sphincter
What does it do
below internal, and surrounds the urethra.
Its contraction can prevent urination.
What is the smooth muscle called in the ureter
What does it produce
Detrusor muscle
Contraction produces micturition
What is the nephron
The functional unit of the kidneys, consisting of a renal corpuscle and tubule
Stages that happen at the nephron
- Arterial blood enters kidney through renal artery
- Branching eventually leads to afferent arterioles, which bring blood to the glomerulus
- Glomerulus produces blood filtrate that enters tubule
- Blood remaining in glomerulus (appx 80%) leaves through efferent arteriole to the peritubular capillaries
- This blood drains into veins that exit the kidney as the renal vein
What surrounds the glomerulus
What does it do
Bowman’s capsule
Filtration
Renal corpuscle is made up of
Bowman’s capsule + glomerulus
What does the Proximal convoluted tubule do (3)
- Filtrate from glomerulus enters its lumen
- Reabsorption of salt, water, etc. into peritubular capillaries
- Secretion of substances into filtrate
List the pathway of fluid in the nephron (8)
- Glomerulus
- Bowman capsule
- Proximal convoluted tubule
- Peritubular capillaries
- Descending loop of Henle
- Ascending loop of Henle
- Distal convoluted tubule
- Collecting duct
Steps of glomerular filtration (4)
- Fluid filters out of glomerulus into Bowman’s capsule
- Filters through fenestrae
- Due to hyrdostatic pressure of cardiac pump
- Filtrate is plasma like
What is fenestrae
Large pores in the glomerular capillaries
What is Glomerular Filtration Rate (GFR)
Volume of filtrate produced by both kidneys per minute
What happens with sympathetic stimulation of kidneys (2)
FIGHT OR FLIGHT
- Vasoconstriction of afferent arterioles
2. Reduces GFR to preserve blood volume and drive blood to muscles and heart
What is Renal autoregulation
Afferent arterioles dilate when BP decreases, constrict when BP increases
What is reabsorption
What process allows for this to happen
Return of filtrate from tubules to blood (peritubular capillaries)
Osmosis
How much salt and water is reabsorbed in the:
Proximal tubule
Descending limb of Henle
65%
20%
What allows for water reabsorption to occur
Active transport of Na+ from filtrate into peritubular blood increases osmolarity so that reabsorption via osmosis can occur
Steps of reabsorption from proximal tubules to surrounding epithelial cells (6)
- Lower concentration of Na+ in surrounding cells than filtrate due to low permeability
- Diffusion + active transport of Na+ into epithelial cells
- Cl- moves to high Na concentration due to electrical gradient
- NaCl accumulates - increases osmolarity of epithelial cells
- Water moves from filtrate to surrounding cells
- This salt and water now moves into surround peritubular capillaries to re-enter the bloodstream
In order for water to be reabsorbed the surrounding ISF must be
Hypertonic
Steps in the descending limb of Henle (4)
- Permeable to water but not salt
- Surrounding ISF is hypertonic compared to filtrate here
- Water leaves descending limb by osmosis and enters ISF and then capillaries
- This increases osmolarity of tubular fluid and decreases volume
Steps in the ascending limb of Henle
- Na+ actively pumped into ISF
- Cl- follows Na+ because of electrical attraction
- K+ diffuses passively into the filtrate
- Not permeable to water so fluid in ascending limb becomes diluted
- NaCl accumulates in the ISF here
What does the countercurrent multiplier system create (2)
High osmotic pressure in ISF
High osmolarity of fluid in tubule
Descending vessels gain and lose what
Gain = salt + urea Lose = water
Ascending vessels gain and lose what
Gain = water Lose = salt and urea
What is urea
a waste product of amino acid metabolism that is excreted in urine
What happens to Urine at the terminal portion of the collecting ducts (2)
Diffuses out into ISF
Then is trapped there due to countercurrent exchange
What is the state of ISF surrounding collecting ducts and the fluid entering the collecting ducts
ISF = hypertonic
Fluid = hypotonic
Collecting ducts are permeable to what
Water but not salt
When plasma osmolarity increases, what does ADH then do (3)
Increases permeability of collecting ducts to water due to insertion of aquaporin channels
This causes more water to exit into renal medulla and peritubular via osmosis
This increases reabsorption
What happens when there is a absence of ADH
Aquaporin channels are in vesicles
What does ADH do in collecting ducts
Stimulates the fusion of vesicles with the plasma membrane thus inserting aquaporin channels
How do osmoreceptors work to change levels of ADH
Changes in water activate hypothalamic osmoreceptors
Release of ADH altered to affect reabsorption
What is the minimal amount of water needed to eliminate the bodys waste
This is known as
400ml/day
Obligatory water loss
What is Renal Plasma clearance
Volume of plasma that is “cleared” of a substance by kidneys per unit time
What reduces clearance
Reabsorption
What is secretion
Where does it occur most
The active transport of substances from the peritubular capillaries into the tubular fluid.
Most reabsorption and secretion occur in the proximal tubule.
Clearance of inulin is equal to
GFR
What is inulin
What is unique about it
Polysaccharide injected into blood to measure GFR
Is filtered but not reabsorbed or secreted
What is the formula for clearance
mass of substance excreted per unit time / plasma concentration of substance
Cs = VUs/ Ps
V = urine volume per unit time Us= urine concentration of S Ps= plasma concentration of S
What is completely reabsorbed in the proximal tubule
By what process
Glucose and AAs
Secondary active transport
What is the process of glucosuria
When the concentration of glucose exceeds the capacity of the transporter molecules
Therefore glucose is excreted in the urine
What activates the Rein-angiotensin-aldosterone system
Decreased plasma Na+
Decrease blood volume
What stimulates aldosterone
Increased plasma K+
What does aldosterone stimulate (2)
Na+ reabsorption in the distal tubule and collecting duct
K+ secretion in distal and collecting duct
What happens when aldosterone stimulates Na reabsorption (3)
- Na/K pump activated
- Passive movement of Na from filtrate to cytoplasm
- Drives pass reabsorption of Cl-
What happens when aldosterone stimulates K secretion (3)
- K pumped into epitherlial cell
- Then diffuses into duct due to potential difference caused by Na reabsorption
- Increased Na absorption = increased K secretion
What substance is filtered from the glomerulus
Potassium
What is the juxtaglomerular apparatus
What does it secrete
The intersection of the macula densa in the distal tubule with the afferent and efferent arterioles
endocrine signal known as renin into blood in the afferent arteriole
What does Atrial natriuretic peptide stimulate
Salt excretion when blood volume increases
How do the kidneys regulate blood pH (2)
- Excrete H+ in the urine
2. Reabsorb bicarbonate
Steps of reabsorbing bicarbonate (7)
- Na/H pump moves H+ into filtrate and Na out
- Bicarbonate binds with H+ in filtrate to form carbonic acid
- Carbonic acid converted to CO2 + H2O
- CO2 diffuses into tubule
- CO2 and H20 bind to form carbonic acid in tubule
- Carbonic acid dissociates to bicarbonate and H+ in tubule
- The Bicarbonate from the tubule diffuses into the blood
Why is the urine acidic
Distal tubule secretes H+ into filtrate using pumps
What buffers the urine
Ammonia and phosphate buffers
What is Alkalosis (4)
pH > 7.45
Decreased plasma H+
Less H+ in filtrate
Less Bicarbonate is reabsorbed to compensate
What is Acidosis
pH < 7.35
Increased plasma H+
More H+ in filtrate
Bicarbonate is made to compensate, which enters the blood
