Week 4 Renal Flashcards
Where are the kidneys located?
Kidneys are in the posterior region of the abdominal cavity, behind the peritoneum. They lie on either side of the vertebral column, with upper and lower poles extending from 12th Thoracic vertebra to 3rd lumbar vertebra.
Define cortex of kidney
Outer layer of kidney, contains all the glomeruli, most of proximal tubules and some of the segments of the distal convoluted tubule
Define Medulla
Inner part of the kidney consisting of regions called pyramids
Define pyramids of kidney
Extend into the renal pelves and contain loops of Henle and collecting ducts
What are the renal columns
extension of the cortex, extend between the pyramids to the renal pelvis
What are the renal calyces
=chambers receiving urine from collecting ducts and form entry of renal pelvis (extension of upper ureter)
What is the structural unit of the kidney, and what is it composed of
Structure unit of the kidney is the lobe. Each love is composed of a pyramid and overlying cortex, with 14-18 lobes in each kidney
What is the functional unit of the kidney? Describe
Nephron is a tubular structure with: 1. Renal Corpuscle 2. Proximal convoluted tubule 3. Loop of Henle 4. Distal convoluted tubule 5. Collecting duct=all help with formation of urine
What are the 3 kinds of nephrons
(1) superficial cortical nephrons (85% of all nephrons), which extend partially into the medulla; (2) midcortical nephrons with short or long loops; and (3) juxtamedullary nephrons (about 12% of nephrons), which lie close to and extend deep into the medulla and are important for the concentration of urine
What is the glomerulus
The glomerulus is a tuft of capillaries that loop into the Bowman capsule (Bowman space), like fingers pushed into bread dough.
What do mesangial cells do
Mesangial cells (shaped like smooth muscle cells) secrete the mesangial matrix (a type of connective tissue) and lie between and support the capillaries. Mesangial cells also have phagocytic abilities=release inflammatory cytokines + can contract to regulate glomerular capillary blood flow
What does the renal corpuscle consist of (3 components)
Combo of glomerulus, the Bowman capsule, and mesangial cells (GBM)
Describe the 3 layers of the glomerular filtration membrane
The glomerular filtration membrane filters blood components through its 3 layers:
(1) an inner capillary endothelium (cells in continuous contact with the basement membrane + has pores)
(2) a middle basement membrane (glycoproteins + mucopolysaccharides)
(3) an outer layer of capillary epithelium (Podocytes from which pedicles (foot projections) stick to basement membrane)
Filtration slits=pedicles interlock with podocytes
Endothelium, basement membrane + podocytes covered with protein molecules with anionic (negative) charges=help with filtration of anionic proteins and prevention of proteinuria
The membrane separates blood of glomerular capillaries + fluid of Bowman space. Filters everything EXCEPT blood, plasma proteins
What blood source is the glomerulus supplied be? Where does blood drain?
Glomerulus: is supplied by the afferent arteriole and drained by the efferent arteriole.
What hormone do juxtaglomerular cells release
renin
Where are juxtaglomerular cells located
around the afferent arteriole where it enters the glomerulus
What is the macula densa? Where is it located?
Macula Densa: (sodium-sensing cells) located Between the afferent+ efferent arterioles on the distal convoluted tubule
What does the juxtaglomerular apparatus consist of? What is are its 3 functions?
Juxtaglomerular Apparatus=Juxta cells + Macula Densa
Function: 1. Control renal blood flow (RBF) 2. glomerular filtration 3. Renin secretion occurs here
Describe the proximal convoluted tubule
Proximal convoluted tubule: Consists of 1 layer of cuboidal epithelial cells+surface layer or microvilli=increases reabsorptive surface area **only surface with microvilli in nephron
Joins the Loop of Henle which extends into Medulla
Describe the loop of Henle
Loop of Henle: Cells of thick segment are cuboidal=transport solutes, no H2O—thin segment is thin squamous cells, no transport
Describe the distal convoluted tubule
The distal convoluted tubule: has straight and convoluted segments. It extends from the macula densa to the collecting duct
Principal cells: reabsorb sodium, secrete potassium
intercalated cells: secrete hydrogen, reabsorb potassium + bicarbonate.
Adjusts acid-base balance by excreting acid into the urine and forming new bicarb ions
Describe the collecting ducts
Collecting duct: a large tubule that descends down the cortex, through the renal pyramids of the inner and outer medullae, draining urine into the minor calyx
What is GFR
Glomerular filtration rate (GFR) – is the measurement of plasma filtration per unit of time.
How is GFR regulated?
GFR is autoregulated via the perfusion pressures (capillary hydrostatic pressure, oncotic pressure, hydrostatic pressure of Bowmans space) of the glomerular capillaries.
What substance cannot pass through the glomerular capilleries into Bowmans capsule?
The glomerular capillaries do not allow RBCs and plasma proteins to pass into the Bowmans capsule, because the glomerular filtration barrier consists of 3 layers that eliminate loss of RBC and prevent proteinuria. This then only leaves a small amount of filtrate (a combination of substances: water, solutes like Na+) to circulate in the tubules, approx. 125ml.
What hormones affect blood flow to the kidney?
Adrenaline and Angiotensin II increase arterioles (afferent and efferent) resistance which in turn decrease renal blood flow and decreases GFR. These hormones are stimulated in order to raise BP and stimulate reabsorption.
Atriopeptin (ANP) (secreted via Atria) and Brain Natriuretic Peptide (BNP) (secreted via ventricles) decreases arterioles resistance which in turn increase renal blow flow and increases GFR. These peptides are stimulated in order to help lower BP and excrete substances.
What is Autoregulation of Renal Blood Flow
-local mechanism with kidney – will keep renal blood flow and GFR constant over a range of systemic blood pressures (80mmHg – 200mmHg)
What is the myogenic mechanism?
Myogenic mechanism – smooth muscle cells contract when stretched because of high volumes/pressures of blood. Once cells are stretched, the afferent and efferent arterioles contract.
What is the Tubuloglomerular Mechanism
Tubuloglomerular Mechanism – involves distal convoluted tubule and glomerulus. The macula densa cells – chemoreceptors - sense when GFR is up or down based on quantity of Na+ or Cl- ions floating thru tubules.
-If increase in BP = Increase renal blood flow = increase GFR therefore more fluid and more dissolved ions reach macula densa which in response will release adenosine causing the afferent arteriole to constrict, decreasing GFR.
What is the vasa recta
Vasa Recta – network of capillaries that is the only blood supply to the medulla (contributes to formation of concentrated urine). The capillaries form loops and closely follows the loop of Henle.
Describe the process of urine formation
Glomerular Filtration: Movement of fluid and solutes across the glomerular capillary membrane into the bowman space
- Water, electrolytes (sodium, chloride, and potassium), and organic molecules (creatinine, urea, glucose) are filtered at the glomerulus.
- Protein free
Tubular reabsorption: Movement of fluids and solutes from the tubular lumen to the peritubular capillary plasma
reabsorption of h20 by osmosis- occurs when ADH is present
Reabsorption of sodium by active transport. More sodium is conserved when aldosterone is secreted
Glucose by active transport
Tubular Secretion: Transfer of substances from the plasma of the peritubular capillary to the tubular lumen
- Secretion of ammonia, hydrogen, and potassium by active transport.
What factors determine GFR
Factors determining GFR are related to the pressures that favour or oppose filtration.
Obstruction of outflow (ex. Strictures, stones, tumours) can cause an increase in hydrostatic pressure at bowman space and a decrease in GFR
Low levels of plasma protein in the blood can results in a decrease in capillary oncotic pressure resulting in an increase in GFR
Excessive loss of protein-free-fluid from vomiting diarrhea or use of diuretics can increase capillary oncotic pressure and decrease GFR
Where does urine concentration primarily occur
Urine concentration/dilution occurs primarily in the loop of Henle, distal convoluted tubules and collecting ducts
What determines final urine composition
Final urine composition is determined by the distal convoluted tubules and collecting duct according to what the body needs
What is the countercurrent exchange system
The production of concentrated urine involves a countercurrent exchange system in which fluid flows in opposite directions through the parallel tubes of the loop of Henle
What is substance is transported out of the ascending limb of Henle to the descending limb of vasa recta/ interstitium
NaCl
As urine flows _________________ in the collecting tubule, it encounters higher and higher concentrations of solutes in the interstitium. Hence it goes on losing water due to osmosis. This is how urine is concentrated.
downwards
Define tubular reasbsorption
Tubular reabsorption is the movement of fluids and solutes from the tubular lumen to the peritubular capillary plasma.
Define tubular secretion
Tubular secretion is the transfer of substances from the plasma of the peritubular capillary to the tubular lumen…for eventual excretion.
Define excretion
Excretion is the elimination of a substance in the final urine
Where is the primary site of sodium reabsorption
Proximal Convoluted tubule:
Primary site of sodium reabsorption.
