Lecture 3 Flashcards
Function of Antidiuretic Hormone - ADH
Inhibits diuresis / urine output by regulating amount of H2O reabsorbed
- Does so by making principal cells of collecting ducts more permeable to H2O by inserting aquaporins into their apical membranes
… thus increasing water reabsorption / decreasing water secretion - Amount of ADH = determines amount of aquaporins
Formation of Concentrated Urine
Occurs when dehydrated
posterior pituitary will ↑ ADH –> causing urine solute concentration to ↑ (*up to 1200 mOsm, ICF in deepest parts of medulla)
MAX ADH SECRETION = up to 99 % water reabsorbed from filtrate to be returned to blood
only 0.5 L of concentrated urine will then be excreted as a result
Why is there a constant low level of ADH secreted ?
Due to the high filtration rate of H2O in urine, most of the time we will need to conserve water
The low level of ADH will ↑ as the plasma osmolarity exceeds over 300 mOsm
ADH cannot add water to make us more hydrated, only conserves whatever water is there. Must act in conjunction with thirst mechanism
________________ water reabsorption is regulated based on the body’s needs
Facultative
Formation of Dilute Urine
Occurs when overhydrated
↓ ADH –> causing urine osmolality to ↓ (as low as 100 mOsm)
- If aldosterone hormone is present, DCT & collecting duct can remove Na (salt) + other ions from filtrate at the top of ascending limb –> causing osmolality to ↓ as low as 50 mOsm
Collecting ducts remain impermeable to water, NO water channels will be open
The presence / amount of ADH is dependent on :
- the medullary gradient
- presence of urea ( ↓ in severely malnourished ppl which ↓ plasma osmolarity –> cannot conserve water as efficiently as a result )
What are diuretics ?
Enhance urinary output
Any substance that :
- NOT reabsorbed
- EXCEEDS renal absorption ability (eg. diabetes)
Alcohol interferes w/ urine formation by inh. ADH release –> need to pee more, dehydrated next day
Caffeine & other diuretics inhibit Na (salt) reabsorption [ water follows salt ]
What is Renal Clearance ?
V of plasma from which kidneys clear (completely remove) particular substance per given time
RC = UV / P
U = conc of substance in urine (mg / ml)
V = flow rate of urine formation (ml / min)
P = conc of substance in plasma (mg / ml)
Inulin
High mw plant polysaccharide used as a set point (standard) bc it is NOT reabsorbed by kidneys
RC (inulin) = GFR
U (inulin) = 125 mg/ml
V (inulin) = 1 ml / min
P (inulin) = 1 mg/ml
RC (inulin) = 125 ml / min
[ all inulin present in 125 ml of plasma cleared per 1 min ]
If RC (substance) < RC (inulin) :
eg. urea (RC = 70 mg / ml)
SOME of the substance gets reabsorbed into blood (55 ml), rest (70 ml) cleared from filtrate
If RC (substance) = 0 :
eg. glucose & amino acids in healthy individual
substance is COMPLETELY REABSORBED, none filtered
If RC (substance) > RC (inulin) :
eg. creatinine (RC = 140 ml / min) & drug metabolites
125 ml of substance filtered, secreted in small amounts
If RC (substance) = RC (inulin) :
NO net reabsorption / secretion
Physical Characteristics of Urine - Colour & Transparency
clear / pale to deep yellow due to urochrome –> pigment from heme degradation
- Deepness of yellow indicates how concntrated urine is (water dilutes - paler, dehydrated - darker)
- Cloudiness indicates infections / UTI
- Colour can be altered by drugs / vitamins
- Abnormal colours as a result of certain foods, presence of bile pigments or blood in urine
Physical Characteristics of Urine - Odour
will develop *ammonia odour if left to sit due to bacterial metabolism of urea
- Can be altered by drugs, vegetables & DM ( ketone bodies –> acetone gives fruity aroma )
