Renal System Flashcards
Where are the kidneys and what size are they?
Located on inner surface of lower back.
Small organs 1% of body weight.
What % of Cardiac output to kidneys receive?
25%
Discuss the internal structure of the kidney?
Outer renal capsule surrounds renal cortex surrounds renal medulla.
Renal medulla composed of renal pyramids. The renal pyramids join to the renal papilla at the minor calyx which joins to major calyx and then renal pelvis which leads to the ureter.
Permeating the pyramids are nephrons which are the functional units of the kidneys
What are kidney nephrons?
The function unit of the kidney. An intricate epithelial tube of simple cuboidal epithelia specialised for secretions and absorption.
Discuss the structure of a nephron.
Afferent Arteriole - Glomerulus - Efferent arteriole.
Glomerulus surrounded by glomerular capsule - Proximal convoluted tubule - loop of henle descending and ascending- distal convoluted tubule - collecting duct - renal papilla
Discuss the cell specialisation of the proximal convoluted tubule
Cells have microvilli on apical surface, joined by tight junctions.
Cells have brush border so huge surface area. This promotes reabsorption of water nutrients into blood and secretion of other substances back into systemic circulation
Discuss the filtration membrane of the glomerulus blood vessels.
The blood vessels have fenestrations in the squamos epithelia surrounded by a basement membrane.
Podocytes are cells which surround blood vessels which wrap vessels forming pedicels which leave gaps exposing the basement membrane. These are filtration slits.
What does the filtration membrane at the glomerulus do?
Large particles like rbc & proteins cannot cross barrier but water nutrients, glucose, ions can.
What does the loop of henle do?
Site of water reabsorption to adjust osmotic gradient that allows water & sodium reabsorption and to concentrate urine in collecting duct
What does the distal convoluted tubule do?
Further reabsorption of material including BICARBONATE ions as well as secretion of hydrogen. This adjusts blood ph assisting to maintain acid base balance.
What does the collecting duct do?
Serves multiple nephrons. Final site of water reabsorption determining final concentration of urine
How many litres of water are filtered each day?
180 Litres
How much of filtered water is reabsorbed
99%
How many grams of sodium are filtered per day?
630g
How much of filtered sodium is reabsorbed?
95.5%
How many grams of glucose are filtered each day?
180g
How much of filtered glucose is reabsorbed?
100%
How many grams of urea are filtered per day?
54g
How much of filtered urea is reabsorbed?
44%
How much water, sodium, glucose, urea is excreted each day?
Water - 1.8 litres
Sodium - 3.2g
Glucose - 0
Urea - 30g
What happens to the substances that are reabsorbed and those that are not?
Reabsorbed enter systemic circulation, the rest is excreted as urine
What do tight junctions in the nephron do?
Tight junctions restrict diffusion between lumen and extracellular space. Make nephrons watertight.
What is the Glomerulus?
Part of nephron. A network of capillaries with a relatively high bp. The high bp works to push fluid out of capillaries into space of bowman capsule
What is reabsorbed in the proximal convoluted tubule?
Water, glucose, Vitamin C, some salts
75% of filtered sodium is reabsorbed here
What are the three main processes involved in urine formation?
Filtration
Reabsorption
Secretion
What is the Glomerular Filtration Rate?
The measure of how much filtrate is produced. About 180 Litres a day in a normal person.
GFR is an important indicator of kidney health/ function
How is eGFR (estimation of GFR) standardised?
By correcting for body surface area.
What drives filtration?
- The sieve like walls of the capillary walls
- Pressure gradients resulting from glomeruli bp being high compared to bowman capsule (assisted by presence of plasma proteins in capillary blood)
What is glomerular capillary blood pressure?
60 mmHG
This pushes blood out
What is the bowman capsule blood pressure?
20mmHg
This acts to push fluid back into capillaries
What is the Capillary osmotic pressure (plasma proteins)
30mmHg
Acting to pull water from bowman capsule back into capillaries
What is the overall filtration pressure out of the glomerular capillaries?
10mmHg
Acting in outward direction.
Describe the reabsorption of sodium ions in the proximal convoluted tubule?
75% OF S
Describe the reabsorption of sodium ions in the proximal convoluted tubule?
75% OF Sodium ions reabsorbed here.
It is an ACTIVE PROCESS using membrane pumps and ATP.
What ions are taken along with sodium ions during reabsorption and why?
Chloride ions are dragged along with sodium ions as they are negatively charged and help to maintain eletrochemical neutrality by counteracting the positively charged sodium ions.
Water is also reabsorbed to maintain osmotic balance.
What is the maximum amount of material that can be transported from the filtrate back into plasma known as?
The Transport Maximum (Tm)
Once beyond the transport maximum no more can be reabsorbed.
At what point would a substance such as sodium appear in the urine?
Only once the transport maximum for sodium has been reached and exceeded.
Discuss diabetes mellitus in terms of glucose excretion and the transport maximum.
Glucose not absorbed and level in plasma increases.
Filtered glucose increases and exceeds transport maximum. Transport systems overwhelmed.
Glucose now appears in urine
What is glucose in the urine called?
Glycosuria
Why does glycosuria result in increased urine volume?
The presence of glucose in the urine exerts an osmotic gradient pulling water into the tubule. Thus there is an increased volume of urine.
What is secreted in the distal convoluted tube?
Potassium Ions
HYDROGEN Ions
Ammonia
These substances are now added to the filtrate for excretion
What does the reabsorption of bicarbonate and secretion of hydrogen in the distal convoluted tube achieve?
Bicarbonate is alkaline.
Hydrogen is acidic.
This process increases the acidity of urine and in REGULATING PLASMA PH (acid base balance)
What is the normal PH of plasma?
7.4
What hormone influences the collecting duct?
Anti-diuretic hormone which helps to reabsorb water
What does ADH do in terms of the collecting duct?
Influence the volume and concentration of urine. Increases water reabsorption and fluid retention in plasma.
This is important in regulating plasma volume and therefore blood pressure.
What stimulates release of ADH from the posterior pituitary gland?
Dehydration, blood loss, shock
Discuss dehydration and ADH as a negative feedback loop?
Dehydration
ADH released
Water reabsorption increased and plasma fluid retention increased.
Increases blood volume
Increased blood volume = less ADH released
