Introduction to kidneys and body fluid Flashcards
What is the total body water as a %?
→ 60%
How much is intracellular water?
→ 40%
How much is extracellular water?
→ 20%
What is osmoregulation?
→ process where the concentration of solutes is regulated
Why is osmoregulation needed?
→ to avoid large disruptive movements of water between ICF and ECF
What is the plasma compartment sometimes called?
→ Effective circulating volume
What do starling forces determine?
→ Fluid and solute movement between plasma and interstitial fluid
What is osmolarity?
→ total concentration of osmotically active solutes
Why must osmolarity be kept the same?
→ Avoid excessive shifts of water between ECF and ICF
What is the principal electrolyte of the ECF?
→ Sodium
Why can ECF be regulated?
→ It is continuous
How many compartments is the ICF made from?
→ 1x10^14
What are the concentrations of Na+ in mmol/L in ICF and ECF?
ECF : 135-145
ICF - 5-10
What are the concentrations of K+ in mmol/L in ICF and ECF?
ECF : 3-5
ICF : 130-150
What will large shifts between ECFV and ICFV cause?
→ disrupts tissue function and structure
What does tissue perfusion depend on?
→ Balance between circulating volume and interstitial volume
What do salt and water balance depend on?
→ Osmoregulation
→ Volume regulation
What does osmoregulation maintain?
→ Maintains osmotic equilibrium between ICFV and ECFV
What does volume regulation maintain?
→adequate ECFV to support plasma volume
What is the equation for investigating plasma osmolarity?
→2[Na] + 2[K] + [Glucose] + [Urea] (all in mmol L-1)
What is the ion that has the biggest impact on osmolarity?
→ Na+
Why can other ions be neglected as contributing to osmolarity?
→they are present in much lower concentrations
What are the two ways to change the osmolarity of a solution?
→Add/Remove Solute
→Add/Remove Water
How do the kidneys respond when plasma osmolarity rises?
→ More water needed
→Kidneys respond by producing a small volume of concentrated urine (water retention)
How do the kidneys respond when plasma osmolarity falls?
→ Too much water
→Kidneys respond by producing a large volume of dilute urine (water excretion)
What volume does volume regulation refer to?
→Circulating plasma volume
What are volume changes detected by?
→Stretch and pressure receptors in the CVS
What is a fall in blood volume opposed by?
→ Sodium retention
→ water follows osmotically
→restoring the volume
Why does an increase in sodium not cause a huge change in osmolarity?
→the concentration (and hence osmolarity) is little changed because the retained sodium brings water with it.
What is the kidneys central function?
→ Salt and water balance
How does the kidney carry out its central function?
→regulating the amount of urine to conserve or excrete, water, and its concentration, the amount of salt
What is a by product of kidney function?
→ Urine
What is the urinary tract important for?
→ Temporary storage and removing the urine from the body
What are the 7 functions of the kidney?
→Osmoregulation
→Volume regulation
→Acid-base balance
→Regulation of electrolytes 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 (EPO)
What is the nephron?
→ Functional unit of the kidney
What does the nephron consist of?
→special blood vessels and elaborate tubules (tiny tubules)
What are the 4 major structures in a nephron?
→Blood vessels
→The glomerulus
→Bowman capsule
→The renal tubule
Describe the blood flow entering the nephron
Renal artery ↓ Segmental arteries ↓ Interlobar arteries ↓ Arcuate arteries ↓ Interlobular arteries ↓ Afferent arterioles ↓ Nephrons
Describe the blood flow leaving the nephron
Nephron ↓ Venules ↓ Interlobular veins ↓ Arcuate veins ↓ Interlobar veins ↓ Renal vein
What is the whole kidney supplied by?
→ Renal artery
What does the renal artery subdivide into?
→ Many renal arterioles supplying each nephron
Where does the kidney drain into?
→ The renal vein
What is the renal vein supplied by?
→venules coming away from each nephron
→joining together into larger veins which merge into the renal vein.
What are the 4 basic processes of renal function?
→Glomerular Filtration
→Tubular Reabsorption
→Tubular Secretion
→Excretion of Water and Solutes in the Urine
What is the blood filtered through every few minutes?
→The entire blood plasma volume is filtered through the Bowman’s capsule every few minutes
What is reabsorption?
→Things you want are grabbed back from the filtrate as it makes its way along the nephron
Where is the plasma filtered?
→glomerulus
→renal tubule
What is the driving force behind glomerular filtration?
→Hydrostatic pressure which is due to the blood pressure of the afferent arteriole
What drives filtration?
→The pressure gradient between the afferent and efferent arteriole
What is filtration opposed by?
→It will be opposed by forces favouring reabsorption due to plasma proteins which aren’t filtered out of the capillaries
What Is the amount of filtrate the kidneys produce each minute?
→ GFR
What happens to GFR during renal failure?
→ It is reduced
What can be used as an index for GFR?
→ Plasma creatinine
What does hydrostatic pressure do to fluids and solutes?
→Hydrostatic pressure forces fluids and solutes through the glomerular capillary membrane
What leads to the production of ultra filtrate in Bowmans capsule?
→Small molecules pass readily
→Large ones (proteins) and cells cannot pass
What are selectively reabsorbed in the primary filtrate?
→Water and solutes in the primary filtrate are selectively reabsorbed
Where are substances reabsorbed from and to?
→ from the tubular lumen into the peritubular capillaries
What is tubular secretion important for?
→Disposing of substances which are not already in the filtrate
→Eliminating undesirable substances such as urea and uric acid
→Ridding the body of excess potassium ions
→Controlling blood pH
What is excreted as urine?
→Whatever is left in the renal tubule at the end of these processes is excreted as urine
What is the control of water balance based on?
→The control of water balance (osmoregulation) is based on the control of the osmolarity of the ECFV
What should the total water balance be?
→ 0
What is the physiological response to water restriction?
→Loss of water (sweat, breathing).
What is the response when plasma osmolality rises?
→ increased secretion of ADH (Antidiuretic hormone, also known as vasopressin)
→A decreased urine volume
→An increased urine osmolality
What is the physiological response to an increased water intake?
→Increase in water absorption through GIT
What is the response when plasma osmolality falls?
→The response the reduced secretion of ADH
→Urine volume increases
→Urine osmolality decreases
What is osmolality related to?
→ Total solute concentration
What is the biggest contributor to osmolality?
→ Na
What is the sodium retaining system?
→ RAAS system
What is the sodium eliminating system?
→ ANP (cardiac natriuretic peptides)
What is ECF volume determined by?
ECF volume is determined by the amount of Na+ in this compartment.
The sympathetic nervous system, the renin-angiotensin-aldosterone system, and natriuretic peptides are important components of the system needed to maintain steady-state Na+ balance.
What must be balanced to maintain constant ECF volume?
→To maintain constant ECF volume (i.e., euvolemia), Na+ excretion must match Na+ intake.
What is the major route for eliminating Na+ from the body?
→ Kidneys
Where are volume sensors located and what do they monitor ?
→ located primarily in the vascular system
→monitor volume and pressure.
What happens when ECF volume expansion occurs?
→ neural and hormonal signals are sent to the kidneys to increase the excretion of NaCl and water
→ thereby restore euvolemia.
What are 3 important components in maintaining a steady state Na+ balance?
→The sympathetic nervous system
→the renin-angiotensin-aldosterone system
→natriuretic peptides
