Introduction to Bodily Fluids Flashcards
What is the total body water as a %?
→ 60%
50% in females
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)
→Microscopic structures, 1.25 million per kidney
What are the 4 major structures in a nephron?
→Blood vessels
→The glomerulus
→Bowman capsule
→The renal tubule
Bowman’s capsule
Proximal tubule (proximal convoluted tubule, PCT)
Loop of Henle
Distal tubule (DCT)
Collecting duct (CD)
CDs join and ultimately drain into ureter
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 in DT and CD
→Controlling blood pH relies on H+ secretion in DT and CD
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) target renal tubule
→A decreased urine volume
→An increased urine osmolality
What is the physiological response to an increased water intake?
→Increase in water absorption through GIT
Continued water restriction beyond this point will increase ECF osmolality
What is the response when plasma osmolality falls?
→The response the reduced secretion of ADH
→Urine volume increases
→Urine osmolality decreases
Decreased thirst
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 peptide
How does ADH stimulate water reabsorption?
insertion of “water channels” or aquaporins into the membranes of kidney tubules.
→channels transport solute-free water through tubular cells and back into blood, leading to a decrease in plasma osmolarity
What is the structural organisation of the nephron blood vessels?
→Afferent arteriole- enters interstitial space in the glomerulus
→Glomerulus
→Efferent arteriole- divides into capillary network
→Peritubular capillaries
→Vasa recta- surrounding loop of henle
Describe tubular reabsorption
→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
→Fractional reabsorption is important in controlling salt and water balance
