Urinary System 2 Flashcards
What are the implications for renal function?
Need to maintain solute/H2O balance in body
Intake is ‘unpredictable’
Therefore need both hypertonic and hypotonic urine ( hypertonic sol - greater conc of solutes than another etc)
Filtration into nephrons
125 ml/min (180 L/day, 60x plasma vol)
Protein-free plasma
Topologically on surface of body
Reabsorption back into peritubular capillaries
Major task is to reabsorb most of 180 L/day
(Secretion is important, but fairly minor in comparison)
Circa 99% fluid reabsorbed
H2O only ever moves via osmotic & hydrostatic forces
Renal relies on osmotic forces
How is urine formed?
FILTRATION
Passive ultrafiltration at Bowmans Capsule
ACTIVE TRANSPORT (reabsorption and secretion)
Energy driven retrieval of valuable substances along nephron
OSMOSIS (reabsorption)
Mainly in Loop PCT+ Collecting duct
Summarise the renal processes
Filtration (BC)
Mass movement of water and solutes from plasma to the renal tubule
Depends on Glomerular capillary pressure (high)
Reabsorption
Movement of water and solutes from the tubule back into the plasma
Secretion
Secretion of additional substances into the tubular fluid
Excretion: Components of urine
amount excreted = amount filtered - amount reabsorbed + amount secreted
What are some further details on the renal corpuscle?
*Renal corpuscle: combination of glomerulus and Bowman’s capsule
*Filtration takes place in the renal corpuscle
*Epithelium around glomerular capillaries -modified into podocytes.
Go into details on filtration in the renal corpuscle
*Movement a balance between osmotic/hydrostatic forces
Barriers:
*Glomerular capillary *basement membrane
*Basal lamina/membrane
*Bowmans capsule epithelia (podocytes)
Filtered substances pass through endothelial pores and filtration slits.
What are the details of general filtration?
*GFR high 125 ml/min (vol of fluid /unit time )
*1/5 plasma filtered into BC (4/5 plasma, proteins, cells PTC ie not filtered)
*Lumen of efferent arteriole smaller than afferent (so high pressure)
*Capillary Pressure Causes Filtration (net pressure and flow into tubule)
Some components retained in plasma (not filtered)
Cells: Fenestrations in capillary wall
Proteins: Basement lamina membrane ‘-’ charged, proteins also ‘-’charged –like charges repel
Size (> 7nm 40KDa excluded AND charge)
What is hematuria?
*Red blood cells in urine
Normal?
*Sign of damage (to barrier)
*Maybe from outside or inside kidney
Outside:
Kidney stones, tumors (renal pelvis, ureter, urinary bladder, prostate, urethra)
UTI (inflammation of urinary bladder, urethra, prostate)
May also get WBC in urine
Inside:
Inflammation of glomeruli (eg glomeruli nephritis) – affects filtration
Infarct – necrosis of kidney
What is proteinuria?
Protein in urine
Normal?
Why?
CHARGE, SIZE
Albumin slightly < 7nm (urine minute amounts)
Some protein hormones smaller but actively reabsorbed
V little protein found in the urine of healthy people
Question
Haemoglobin smaller than albumin
V little passes from blood to filtrate – v little found in filtrate?
What is tubular re-absorption?
180/day liters fluid filtered into the tubules
Only about 1.5/2 liters excreted
>99% of fluid entering the tubules must be reabsorbed into the blood
Most takes place in the LH (fluid)/
proximal tubule (solutes)
Some in the distal segments of nephrons (fine tuning)
Re-absorption may be Active or Passive
Water regn through solute (Na) regn
Describe re-absorption in the PCT
*Reabsorption of most solutes is linked to the diffusion of Na +
*Carrier molecules for other molecules that co-transported
*Each of these carrier molecules binds specifically to that substances to be transported and to Na+
*Move with Na + into tubule cell
*As solutes are transported out of the lumen, through the proximal convoluted tubule cells, and into the interstitial fluid, water follows by osmosis.
*volume has been reduced by approximately 65%.
Describe some facts about secretion
Transfer of molecules from extracellular fluid into the nephron
Metabolites produced in the body / substances brought into the body / or xenobiotics ( eg drugs)
Make excretion is even more efficient
Depends mostly on membrane transport systems
What are the structures involved in the loop of henle + functions?
*Cortical (80%) and Juxtamedullary (20%) Nephrons
*Juxtamedullary nephrons: hypertonic medulla
Vasa recta: counter current
Long peritubular capillaries that dip into the medulla
Blood flow in the vasa recta moves in the opposite direction from filtrate flow in the loops of Henle
*hypertonic environment in medulla
What does the loop of henle do? + what parts do what?
Further resorption of NaCl and H2O by
COUNTERCURRENT MULTIPLIER
Descending Loop
Permeable to water
Ascending Loop
Impermeable to water
Actively transports Na+ into interstitial space followed by Cl-
Describe the osmotic gradient in the medulla (different regions involved)?
Descending limb: Filtrate becomes more concentrated as it loses water
Ascending limb: pumps out ions, filtrate.
Multiply the concentrations of Na+ deep in the medulla
(hypertonic, high concentration of solutes)
Blood in the vasa recta removes water leaving the loop of Henle.
Hyperosmotic in medulla: hyposmotic filtrate leaving the LH
Describe the fine tuning of urine (DCT + CD)
Hormonal mechanisms
Renin-angiotensis-aldosterone (RAAS) mechanisms
Antidiuretic hormone (ADH) mechanism
Atrial naturetic peptide (ANP) mechanisms
RAAS and ANP: more sensitive to changes in BP
ADH: more sensitive to blood concentration
Describe what happens in fine tuning under hormonal control (LOWBP) Angiotensin only
Angiotensin (RAAS)
Macula Densa cells senses low Na in filtrate in dct
JG cells also detect reduced stretch in afferent arteriole
Renin release from kidney (from JGC)
Converts angiotensinogen (found in plasma) into angiotensin I
ACE (pulmonary capillaries) converts angiotensin I into angiotensin II
Angiotensin II: vasoconstrictor
Increases TPR
Stimulates release of aldosterone (and thirst)
Describe what happens in fine tuning under hormonal control (LOWBP) Aldosterone
Aldosterone
Steroid hormone / Released from adrenal cortex
Travels to DCT and CD
Bind to receptors
Stimulates Na+ reabsorption from CD into capillaries
Cl- co-transported
Water follows
Increases Blood volume
Increases BP
Describe what happens in fine tuning under hormonal control (LOWBP) ADH
Normally dct and collecting ducts impermeable to water
Anti-Diuretic Hormone (ADH)
Released from posterior pituitary
Release sensitive to…
Osmoreceptors (hypothalamus) –
sense when body fluids become concentrated
Volume stretch receptors (right atrium) (decrease)
High osmolarity or low blood pressure cause vasopressin (ADH) release
ADH release:
Increases permeability of dct and collecting ducts to water
Increases reabsorption in collecting ducts
Small volume concentrated urine
Describe fine tuning of urine under normal hormonal control (ANP)
Atrial Natriuretic Peptide (ANP) Opposite effect: Na+ excretion increased
ANP Released from right atrium when blood volume increases
Leads to increased loss/excretion of Na+
Decreases Na+ reabsorption
Na + remains in tubules
Water moves towards Na +
Increases Urine volume while reducing blood volume and BP
*Can inhibit ADH
