Renal - Physiology and Diagnostics Flashcards
What is the functional subunit of the kidney?
The nephron
True or False: Nephron numbers increase over time.
False - they decrease over time; 10% drop in numbers every 10 years after the age of 40
What are the components of the nephron?
Glomerulus and tubules
What is the glomerulus?
a capillary bed
What is the glomerulus surrounded by?
Bowman’s capsule
What does the glomerulus produce?
ultrafiltrate
What surrounds the tubules of the nephron?
peritubular capillaries
What is the function of the tubules?
To transport and alter urine
Where is there high hydrostatic pressure in the nephron? What occurs here? Is it selective or non-selective?
In the globerulus, there is increased filtration and it is non-selective
Where is there low hydrostatic pressure in the nephron? What occurs here? Is this process selective or non-selective?
In the tubules, there is increased reabsorption and it is a selective process
What do the two different capillary systems allow for?
individual adjustments of filtration/reabsorption
What are the subsections of the tubule?
Proximal tubule, loop of henle, juxtaglomerular complex, distal tubule, connecting tubule, collecting tubule, and collecting duct
What is the volume and composition of urine dictated by?
Glomerular filtration rate, tubular reabsorption rate, and tubular secretion rate
What is the filtration fraction through the glomerulus?
20 percent
The ultra-filtrate that the glomerulus produces is almost identical to plasma except for what?
There is a lower protein content and a lower content of protein-bound molecules (calcium and FA)
What are the 3 layers of the glomerulus?
Fenestrated epithelium, basement mebrane, and podocytes (epithelial cells)
Decribe the fenestrated endothelium.
It is composed of large pores and is negatively charged
Describe the basement membrane of the glomerulus.
It is composed of a collagen/proteoglycan mesh and is negatively charged
Describe the podocytes of the glomerulus.
It is separated by slit pores and is negatively charged
What are the consequences for the ultrafiltrate?
Retention of larger, negatively charged molecules within the plasma
What can glomerular diseases cause (think about the ultrafiltrate)?
Urinary loss of larger proteins - albumin and antithrombin
What determines the glomerular filtration rate (GFR)?
Glomerular hydrostatic pressure, capsular hydrostatic pressure, glomerular oncotic pressure, and filtration coefficient
What mechanisms are involved in reapsorbtion/secretion in the tubules?
transporters and pinocytosis
What occurs in the proximal tubule?
reabsorption, pinocytosis, and secretion
What is reabsorbed in the proximal tubule?
65% of Na+ and water, and >98% glucose and amino acids
What molecules undergo pinocytosis in the proximal tubule?
larger molecules
What is secreted in the proximal tubules?
Oxalate, urate, catecholamines, and drugs such as penicillin
What inibitors works at the level of the proximal tubules?
Carbonic anhydrase inhibitors
Normally, the proximal tubules should reabsorb all glucose in the urine. What happens in the proximal tubules in diabetes mellitus patients?
They get overwhelmed by the amount of glucose in the urine and can only reabsorb so much (transport maximum is exceeded). This results in glucosuria
What is Fanconi’s syndrome?
An inherited/acquired disease affecting fucntion of the proximal tubules
What does Fanconi’s syndrome impair in the proximal tubules?
Reabsorption of proteins, glucose, aninoacids, and bicarbonate
What disease can Fanconi’s syndrome progress to?
Chronic kidney disease
What occurs in the thin descending and ascending portions of the Loop of Henle?
There is low metabolic activity - diffusion of urea, Na, and water occurs here
What occurs in the thick ascending portion of the Loop of Henle?
25% of Na, Cl, K, Ca, Mg, and bicarbonate is reabsorbed
What is the thick ascending portion of the Loop of Henle impermeable to?
water
The Loop of Henle is the site of action of what?
Loop diuretics - furosemide
What is reabsorbed in the early distal tubule?
5% of Na and Cl
What is the early distal tubule impermeable to?
water
The early distal tubule is the site of action of what?
Thiazide diuretics - Chlorothiazide
What cells make up the late distal tubule?
Principle cells and intercalated cells
What occurs in the principle cells of the late distal tubule?
Reabsorption of Na and secretion of K
The principle cells of the late distal tubule are the site of action of what?
Anti-diuretic hormone, aldosterone, and spironolactone
The principle cells in the late distal tubule are permeable to water only in the presence of what?
ADH
What does aldosterone do?
Increase Na absorption and K secretion
What occurs in the intercalated cells of the late distal tubule?
H secretion and bicarbonate absorption
What is reabsorbed in the collecting duct?
<10% of Na and water
What is secreted in the collecting duct?
Strong H secretion
What massively increases permeability to water in the collecting duct?
ADH
What is needed to form concentrated urine?
A concentration gradient between the interstitium and tubular lumen (Na and BUN) and antidiuretic hormone (and its receptors)
What are the components of the concentration gradient that is needed to form concentrated urine?
Active Na, K, Cl transport in the thick ascending Henle
Active ion transport in the collecting ducts
Facilitated urea diffusion in the medullary collecting ducts
Limited water diffusion in the distal tubules
What is ADH produced by? Released by?
It is produced by the hypothalamus and released by the posterior pituitary
What triggers the release of ADH?
Increased plasma osmolality and decreased blood volume/blood pressure
What is the effect of ADH?
Inceased vascular tone and water conservation
What does high medullary osmolality allow for in regards to water?
osmotic pull
Where is the juxtaglomerular apparatus located?
at the early distal tubule where it has contact with afferent and efferent arterioles
What does the juxtaglomerular apparatus regulate?
Systemic blood pressure and glomerular filtration rate
What are the two cell types of the juxtaglomerular apparatus?
Macula densa cells and juxtaglomerular (glanular) cells
What occurs in the macula densa cells if GFR decreases due to decreased BP?
Na decreases in the distal tubules and signals the afferent arterioles to dilate
What does dilation of afferent arterioles do?
Increases glomerular hydrostatic pressure and increases GFR
Where are the juxtaglomerular cells located?
In the walls of the afferent and efferent arterioles
What do juxtaglomerular cells secrete and in response to what?
They secrete renin in response to decreases in GFR
When is the renin-angiotensin system activated?
When there is a drop in blood pressure and fluid volume
When the RAAS is activated, what is released from the kidney? What does it do?
Renin is released to convert angiotensinogen (from the liver) into angiotensin I
What converts angiotensin I into angiotensin II? Where is it released from?
ACE - released from the lings
What does angiotensin II act on and what does it do?
It acts directly on the blood vessels stimulating vasoconstriction
It acts directly on the adrenal gland to stimulate release of aldosterone
What does aldosterone do?
It acts on the kidneys to stimulate reabsorption of salt and water
What vessels does Angiotensin II work on especially?
the efferent arterioles
What is the end systemic result of the RAAS?
Maintenance of blood pressure and GFR
What drugs interfere with the RAAS?
Angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARB)
What are the possible side effects of RAAS inhibitors?
Decreased GFR and BP
