Chapter 24: Urinary System Flashcards
processes that occur as filtrate is converted to urine:
- elimination of metabolic wastes
- regulation of ion levels
- regulation of pH balance
- regulation of blood pressure
- elimination of biologically active molecules
other functions of the kidney
- formation/conversion of calcitriol from vit. D
- production and release of erythropoietin
- potential to engage in gluconeogenesis
filtrate
- 180 L/day
- filtered sample of plasma with small solutes and minimal protein
- caught within capsular space and funneled into PCT
- materials not filtered remain in blood
filtrate occurs in the
renal corpuscle
tubular fluid
modified filtrate in the process
tubular fluid flows through
- PCT
- nephron loop
- DCT
- enters collecting tubules
- empties into collecting ducts
urine
final product for elimination
urine flows through
- papillary duct
- minor calyx
- major calyx
- renal pelvis
- ureter
- urinary bladder
- urethra
glomerular filtration
the movement of substances from the blood within the glomerulus into the capsular space
tubular reabsorption
the movement of substances from the tubular fluid back into the blood
tubular secretion
the movement of substances from the blood into the tubular fluid
most tubular reabsorption occurs at the
PCT
tubular secretion is ____________ at the DCT
highly variable
___________ strongly affect the DCT
hormones
filtration membrane
- composed of three sandwiched layers
- to enter filtrate, must pass through three layers
filtration slits are the
gaps between the podocytes
pedicels
processes on podocytes that wrap around the glomerulus to support the capillary wall
holes within the glomerular capillaries are called
fenestrations
filtration membrane can be damaged by high
blood pressure
Should formed elements be in the filtrate?
no
filtrate includes
- water
- glucose
- amino acids
- ions
- urea
- some hormones
- vitamins B and C
- ketones
- very small amounts of protein
glomerular hydrostatic pressure (HPg)
blood pressure in the glomerulus that pushes water and some solutes out of the blood into the capsular space
- driving force
- usually 60 mmHg
blood colloid osmotic pressure (OPg)
pressure of albumin in blood
- opposes filtration
- osmotic pressure exerted by dissolved solutes
- usually 32 mmHg
capsular hydrostatic pressure (HPc)
fluid pressure in the nephron
- detects any obstructions in the nephron or urinary tract
- opposes filtration
- usually 18 mmHg
finding the net filtration pressure (NFP)
HPg - (OPg + HPc) = NFP
average of NFP
10 mmHg
glomerular filtration rate (GFR)
rate at which the volume of filtrate is formed
increased HPg and NFP leads to
- increases GFR
- decreases filtrate reabsorption
- more solutes and H2O remain in tubular fluid and urine
GFR is tightly regulated based on
physiological conditions
GFR regulated by
- intrinsic controls
- extrinsic controls
intrinsic controls
autoregulation of the kidneys
extrinsic controls
something from outside the kidneys is influencing it (hormones and nervous system)
renal autoregulation
intrinsic control
- ability of kidney to maintain consistent GFR despite fluctuations in systematic arterial pressure
decreased systematic BP results in
vasodilation of afferent arteriole
increased systematic BP results in
vasoconstriction of afferent arteriole
neural and hormonal control
extrinsic controls
- physiological processes that intentionally change GFR
- different from renal autoregulation which maintains GFR
increasing GFR through
atrial natriuretic peptide (ANP)
increasing GFR through ANP’s net effect
GFR increased and filtrate increased; more fluid eliminated in urine, which decreases blood volume
decreasing GFR through
sympathetic stimulation
decreasing GFR through sympathetic stimulation’s net effect
GFR decreased and filtrate decreased; more fluid retained in blood, which maintains blood volume
peritubular capillary
- low hydrostatic pressure
- high colloid osmotic pressure
paracellular transport
movement of substances between epithelial cells
transcellular transport
movement of substances across epithelial cells
transport maximum (Tm)
maximum rate of substance that can be reabsorbed
renal threshold
max blood plasma concentration of substance that can be “contained” in blood without appearing in the urine
glucosuria (glycosuria)
- excretion of glucose in urine
- glucose acts as an osmotic diuretic
PCT reabsorption
- 100% of nutrients
- majority of water
- majority of ions:
- Na+
- Cl-
- K+
- Ca++
- HCO3-
PCT secretion
- some drugs
- nitrogenous wastes
nephron loop reabsorption
- Na+ and Cl-
- water
most sodium reabsorption occurs at the
PCT
what hormones affect sodium reabsorption at the DCT
aldosterone and ANP
DCT and collecting duct reabsorption
- Na+ (regulated by aldosterone and ANP)
- water (regulated by aldosterone and ADH)
- Ca++ ( increased by PTH)
where does most water reabsorption occur
PCT
what hormone affects water reabsorption at the DCT
ADH
water is attracted to
- colloids
- sugars
- sodium
where potassium is absorbed the most
PCT
DCT and collecting duct secretion
- K+ (in exchange for Na+)
- H+ (if pH is low)
- HCO3- (if pH is high)
nitrogenous waste
metabolic waste containing nitrogen
main nitrogenous waste products
- urea
- uric acid
- creatinine
urea
- both reabsorbed and secreted
- a molecule produced from protein breakdown
uric acid
- produced from nucleic acid breakdown in liver
- both reabsorbed and secreted
creatinine
- produced from creatinine metabolism in muscle
- only secreted
substances eliminated as waste products: drugs and bioactive substances
most secretions occuring in PCT
- certain drugs (penicillin, aspirin)
- other metabolic wastes (urobilin)
- some hormones (human chorionic gonadotropin)
GFR can be measured with
- insulin injection
- creatinine clearance test
urine composition
- 95% water
- 5% solutes (salts, nitrogenous wastes, some hormones, drugs, ketone bodies)
urine volume
- 1-2 L per day
- minimum of 0.5 L to eliminate wastes
urine pH
normally between 4.5-8.0
- more acidic- protein or wheat
- less acidic- fruits and vegetables
urine specific gravity
- density of a substance compared water
- urine slightly greater than H20
urine color
ranges from almost clear to dark yellow
urinoid
normal smell of fresh urine
micturition
expulsion of urine from the bladder
