Renal an intro to kidneys and body fluids Flashcards
What equilibrium must the ICF and ECF be in?
The ICF and ECF must be in osmotic
equilibrium
What will a change in solute concentration in either ICF or ECF generate?
Change in solute concentration in either ICF or ECF will generate osmotic gradient, resulting in shifts of water between compartments
Why is osmolarity of the ECF regulated to avoid?
Osmolarity of the ECF is regulated to avoid
osmotic shifts of water between ICF and ECF
volumes
What is the normal range of osmolarity?
Normal range 280-300 mOsm/L
What is osmoregulation?
Osmoregulation is the physiological
process that maintains constant
ECF osmolarity
-control of salt concentration in the ECF by adjusting
the amount of pure water in the body
What is the ECF compartment subdivided into?
- Interstitial (or extravascular) compartment (about 75% of ECF)
- Plasma (or vascular) compartment (about 25% of ECF)
What is volume regulation?
Volume regulation is control of the ECF volume to ensure appropriate plasma volume and blood pressure
What does maintaining salt and water balance require?
Maintaining salt and water balance requires
integration of osmoregulation and volume
regulation
What is volume regulation?
control of the amount of salt and water in the ECF
and hence, ECF volume
What is the central funciton of the kidney and what is its by-product?
Homeostasis is the central
function of the kidney
-Production of urine is the by-product
what do renal functions include?
- Osmoregulation
- Volume regulation
- Acid-base balance
- Regulation of electrolyte balance (eg potassium, calcium, phosphate)
- Removal of metabolic waste products from blood
- Removal of foreign chemicals in the blood (e.g. drugs)
- Regulation of red blood cell production (erythropoietin)
What is the nephron?
The nephron is the functional unit of the kidney
What does the nephron consist of?
The nephron consists of special
blood vessels and elaborate
tubules
Structural organization of the nephron: renal tubule
Look at slides for structure
Structural organization of the nephron: blood
vessels
Look at slides for structure
What are the 4 basic processes of renal function?
- Glomerular Filtration
- Tubular Reabsorption
- Tubular Secretion
- Excretion of water and solutes in
the urine
What are the steps involved in glomerulara filtration?
- Balance of Starling forces drive water and solute across the capillary membrane
- Small molecules pass readily – large ones (proteins) and cells cannot pass
- This leads to a plasma ultrafiltrate in the Bowman’s capsule, the first step in the production of urine
What is glomerular filtration rate(GFR)/
The amount of filtrate produced by the kidneys each minute
What is the average GFR?
Averages 125 ml/min (approx 20% of renal plasma flow)
When is GFR reduced?
Very important clinical indicator (reduced in renal failure)
What can be used as an index of GFR?
Plasma creatinine can be used as an index of GFR
What are the steps involved in tubular reabsorption?
Many substances are filtered and then reabsorbed from the tubular lumen into the peritubular capillaries
About 70% of filtered salt and water reabsorbed from proximal tubule
20-25% from loop of Henle
Variable fraction of remaining 5-10% is reabsorbed from distal tubule and collecting duct
What are the steps involved in tubular secretion?
Tubular secretion is important for disposing of substances beyond their level in the filtrate
Eliminating toxins and metabolic by-products
In tubular secretion, where is excess K+ secreted?
Potassium balance: excess K+ secreted in DT and CD
In tubular secretion, what does acid-base balacne rely on?
Acid-base balance relies on H+ secretion in DT and CD
What are the steps involved in excretions of water and solutes in urine?
The tubular fluid remaining after filtration, reabsorption and secretion is excreted as urine.
How can amount excreted in urine be measured?
Amount filtered-amount absorbed+amount secreted
Why can you estimate GFR from plasma concentration?
creatinine is filtered but not reabsorbed; can estimate GFR from plasma concentration
What are the physiological response to water restriction?
Loss of water (skin, lungs)
* Plasma osmolality rises
Response is
* Increased thirst
* Increased secretion of hormone, vasopressin (also called antidiuretic hormone, ADH)
What does ADH increase and how?
ADH increases renal water reabsorption
* Decreased urine volume
* Increased urine osmolality
What are physiological repsonse to increase in water intake?
Increase in water absorption through GIT
* Plasma osmolality falls
Response is
* Decreased thirst
* Reduced secretion of ADH
Results in
* Urine volume increases
* Urine osmolality decreases
What is ECF volume determined by?
ECF volume is determined by the amount of sodium in this
compartment
Where are the main volume sensors for ECF?
Main volume sensors are in the cardiovascular system
What is a fall in blood volume opposed by?
A fall in blood volume is opposed by hormonal signals promoting
sodium retention; water follows osmotically, restoring volume
Why must sodium intake and secretion be balaned?
Sodium intake and excretion must be balanced to maintain constant
ECF volume
What does RAAS do in sodium balance?
- Increases renal Na reabsorption
- Increases ECF volume
What does cardiac natriuretic peptides do in sodium balance?
- Decreases renal Na reabsorption
- Decreases ECF volume
