THE URINARY SYSTEM Flashcards
HOW DOES THE KIDNEY MAINTIAN HOMEOSTASIS
- regulating H2O volume and solute concentration in H2O
- maintains long term acid-base balance
- synthesizes vitamin D
- produces erythropoietin and renin
- excretes metabolic wastes, toxins, and drugs
- carries out glucogenesis if needed
- regulates ion concentration in ECF
WHATS LOCATED IN THE RENAL CORPSUCLE
- glomerular capsule. contains podocytes that contain foot processes which create filtration slits to allow filtrate to pass into capsular space
- the glomerulus is a tuft of capillaries composted of fenestrated eipthelium , they are highly porous to allow efficent filtrate formation
WHAT IS FILTRATE?
plasma derived fluid that the renal tubules process to form urine
WHAT ARE THE PARTS OF THE RENAL TUBULE
where are they both confined to?
- proximal convoluted tubule: closest to renal corpsucle, focuses on reabsorption and secretion
- distal convoluted tubule: farthest from renal corpscle, focuses more on secretion than reabsorption. fluid from here drains into the collecting duct
- both confined to renal cortex
WHERE IS THE NEPHRON LOOP LOCATED, WHAT COMPONENTS ARE A PART OF IT AND IT’S FUNCTION?
- Function: formation of dilute vs. concentrated urine
- contains: descending limb continous with proximal convoluted tubule and the ascending limb, continous with distal convoluted tubule
- found: in renal medulla
WHAT ARE THE FUNCTIONS OF THE COLLECTING DUCTS
- receives filtrate from many nephrons
- runs through medullary pyramids (gives them striped appearance)
- ducts fuse together to deliver urine to minor calyces
WHAT ARE THE 2 TYPES OF NEPHRONS
- Cortical nephrons: make up 85% of nephrons and are mainly in the cortex
- juxtamedullary nephrons: long loops deeply penetrate medulla. ascending limbs have a thick and thin segment and are important for concentrating urine
WHAT ARE THE CAPILLARY BEDS ASSOCIATED WITH EACH NEPHRON
- CORTICAL: glomerulus, peritubular capillaries
- JUXTAMEDULLARY: vasa recta
EXPLAIN THE GLOMERULUS. WHAT MAKES IT DIFFERENT?
- capillaries are specialized for filtration, and are different form other capillary beds bc they are fed and drained by arteriole (affarent and efferent)
- arterioles arise from cortical radiate arterues and feed into peritubular capillaries or vasa recta
- has high pressure because affarent arterioles are bigger (wider diamter) than effferent, they are high resistance vessels
EXPLAIN PERITUBULAR CAPILLARIES AND FUNCTION, WHERE DOES IT ARISE FROM
- low pressure porous capillaries adapted for absorption of H2O and solutes
- arrise from efferent arterioles and drain into venules
- cling to adjacent renal tubules in cortex
EXPLAIN THE VASA RECTA AND FUNCTION, WHERE DOES IT ARISE FROM
- long thin walled vessels that are parallel to long nephron loops in juxtamedullary nephrons
- arise from efferent arterioles (in juxtamedullary)
- functions to form concentration urine
WHAT IS THE JUXTAGLOMERULAR COMPLEX? WHAT CELLS ARE IN IT AND WHAT DO THEY DO?
- includes modified portions of the ascending limb, and affarent (sometimes efferent) arterioles
- regulate rate of filtration formation and BP
- macula densa cells: closely packed cells in the ascending limb that contain chemoreceptors detecting NaCl content of filtrate
- granular/ juxtaglomerular cells: enlarged smooth muscle cells of arteriole (vascular). mechanoreceptors that sense Bp in afferent arteriole, also contain secretory granules that contain renin
HOW MUCH FLUID IS PROCESSED, URINE FORMED, AND O2 USED IN THE KIDNEY. WHAT IS INCLUDED IN FILTRATE?
- 180L processes but onyl 1.5L of urine formed
- consumes 20-25% of O2
- filtrate is essentially blood plasma minus plasma proteins and cells
- urine is less than 1% original filtrate
WHAT ARE THE 3 STEPS OF URINE FORMATION
- Glomerular filtration: creates protein and cell free filtrate
- tubular reabsorption: selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts
- tubular secretion: selectively moves substances from blood to filtrate in renal tubules and collecting ducts
GENERALLY EXPLAIN GLOMERULAR FILTRATION. WHAT PRESSURES ASSIST IN IT. IS IT AN ACTIVE OR PASSIVE PROCESS?
- it is a passive process (no metbolic energy required)
- hydrostatic pressure forces fluids and solutes through filtration membrane into glomerular capsule
- no reabsorption into glomerulus occurs
WHAT IS THE FILTRATION MEMBRANE
- porous membrane between blood and interior of glomerular capsule
- allows water and solutes smaller than plasma proteins to pass (and no cells)
- has 3 layers
- fenestrated endothelium: of glomerular capillaries
- basement membrane: fused basal laminae of the other 2 layers
- food processes of podocytes: contains filtraiton slits, their diaphragms repel macromolecules
WHAT TYPES OF SUBSTANCES ARE ALLOWED TO PASS THROUGH THE FILTRATION MEMBRANE. WHY DO PLASMA PROTEINS REMAIN IN THE BLOOD?
- molecules smaller than 3 nm: water, glucose, amino acids, nitrogenous wastes
- Plasma proteins remain in the blood to maintain colloid osmotic pressure. this prevents loss of all water to capsular space
- proteins in filtrate indicates membrane problem
WHAT OUTWARD PRESSURES AFFECT FILTRATION
- OUTWARD: hydrostatic pressure in glomerular capillaries (HPgc): is basically glomerular blood pressure.
- CHEIF FORCE: force pushing water, solutes out of blood, 55mm/hg compared to 26 mm/hg seen in more capillary beds
high because efferent arteriole is highresistane and smaller than afferent
WHAT ARE SOME INWARD PRESSURES AFFECTING FILTRATION
INWARD PRESSURES
- forces inhibiting filtrate formaiton
- hydrostatic pressure in capsular space (HPcs): filtrate pressure in capsule, 15 mm/hg
- colloid pressure in capillaries (OPgc): pulls proteins into blood, 30 mm/hg
WHAT IS NET FILTRAITON RATE? WHAT DOES IT DETERMINE?
it is the sum of all forces, it is
NFP= (forces out)-(forces in)
basically NFP= ( 55:HPgc)- (15:HPcs + 30 OPgc)= 10 mm/hg
this is the main factor determining glomerular filtration rate (GFR)
WHAT IS GLOMERULAR FILTRATION RATE? WHAT IS PROPORTIONAL TO?
GFR= Volume of filtrate formed per minute by both kidneys (normal= 120-125 ml/min).
- Net filtration rate: primary pressure is glomerular hydrostatic pressure
- total SA available for filtration: glomerular mesangial cells control this by contracting
- filtration membrane permeability: much more permeable that other capillaries
HOW IS GFR REGULATED? WHY IS IT IMPORTANT
- Constant GFR is important bc it allows kindye sto make filtrate and mantian extraceullar homeostasis
- intrinsic controls regulate GFR (local renal autoregulation)
- extrinsic controls maintain systemic blood pressure, through nervous system and endocrine (hormonal) controls
EXPLAIN THE INTRINSIC CONTROLS (RENAL AUTOREGULATION)
- maintaints near constant GFR when MAP is in range of 80-180 mm/Hg. there are 2 types of renal autoregulation: myogenic mechanism, tubuloglomerular feedback mechanism
EXPLAIN THE MYOGENIC MECHANISM
local smooth muscle contracts when streched
- increase bp > muscles strech > constriction of afferent arterioles
- restricts bloodflow into glomerulus and protext from damaging high BP
- decreased Bp= dilation of arterioles.
- both maintian normal GFR despite flunctuating Blood pressures.
EXPLAIN THE TUBULOGLOMERULAR FEEDBACK MECHANISM
- flow dependednt mechanism directed by macula densa cells
- GFR increases > filtrate flow increases > reabsorption time decreases (bc its moving fast) > high NaCl lvl in filtrate > feedback mechanism causes contriction of afferent arteriole which will lower NFP and GFR allowing for more time for NaCl to reabsorb
- oposite mechanism for decreased GFR
EXPLAIN THE EXTRINSIC CONTROLS
- neural and hormonal
- purpose is to regulate GFR to maintain systemic blood pressure
- extrinsic controls will override intrinsic if blood volume needs to increase
EXPLAIN THE NEURAL MECHANISM
SYMPATHETIC NERVOUS SYSTEM
- normal conditions= renal blood vessels dilated and renal autoregulation prevails
- abnormal conditions (below 80 or above 180 MAP/ low ECF volume)
- norepinephrine and epinephrine released> systemic vasoconstriciton which increases Bp > contriction of afferent arteriole which decreased GFR > blood volume and pressure increases
EXPLAIN THE HORMONAL MECHANISM
renin-angiotensin-aldosterone mechanism
- is the main mechanism for increasing Bp. there are 3 pathways for renin release from granular cells
- direct stimulation of granular cells from** sympathetic nervous system**
- stimulation by activated macula densa cells when NaCl content is low
- reduced strech from granular cells
WHAT DOES TUBULAR REABSORPTION DO? HOW ARE SUBSANCES SELECTED AND WHAT ROUTES DO THEY TAKE?
- Tubular reabsorption: quickly reclaims most of tubular content back into blood
- almost all organic nutrients are reabsorbed
- water and ion reabsorption are hormonally regulated and adjusted
- involved active and passive tubular reabsorption
- 2 pathways include transcellular and paracellular
DRAW OUT A DIAGRAM EXPLAINING NA, GLUCOSE, AMINO ACIDS, IONS, VITAMINS, UREA AND WATER REABSORPTION IN THE RENAL TUBULES
answer on ipad
WHAT IS A TRANSPORT MAXIMUM
- transcellular transport systems are specific and limted
- transport maximum (Tm) exists for almost every reabsorbed substance (number of carriers in renal tubules that are able to facilitate diffusion)
- when carriers are saturated, excess is secreted in urine (like glucose in urine bc of hyperglycemia)
WHAT SPECIFIC SUBSTACES ARE ABSORBED IN THE PROXIMAL CONVOLUTED TUBULE. WHAT MAINLY OCCURS?
- SITE OF MOST REABSORPTION
- all nutrients, like glucose and amino acids are reabsorbed
- 65% of H20 and Na+ reabsorbed
- may ions, almost all uric acid
- half of urea (will be secreted back into filtrate)
WHAT SPECIFIC SUBSTANCES ARE REABSORBED AT THE NEPHRON LOOP? DIFFERENCIATE BETWEEN THE ASCENDING AND DESCENDING LIMBS
- ascending limb: H2O CAN’T leave, solutes can
- descending limb: H2O CAN leave, solutes can’t (Na, K+, Cl-)
WHAT SPECIFIC SUBSTANCES ARE REABSORBED AT THE DISTAL CONVOLUTED TUBULE? HOW IS IT REGULATED?
- reabsorption is typically hormally regulated in the DCT
- anti-diuretic hormone (vassopressin) is released by posterior pituitary and causes princible cells to insert aquaporins to increase water reabsorption
- aldosterone: increases Na+ reabsorption (water follows), as a result little Na leaves the body. also functions to increase Bp and lower K+ levels
- this occurs in the collecting duct as well
- without it, daily loss of filtered Na+ would be 2% which is incompatible with life
WHAT IS THE ROLE OF ATRIAL NATRIUETIC HORMONE?
-inhibits Na+ reabsorption in the collecting ducts
reduces Na+ in the blood which causes reduced Blood pressure
- released by cardiac atrial cells if blood volume or pressure is elevated
- directly counteracts effects of aldosterone
WHERE DOES TUBULAR SECRETION MAINLY OCCUR? WHAT SUBSTANCES ARE SECRETED?
- mainly occurs in the proximal convoluted tubule
- K+, H+, NH4+ (ammonia), creatinine, organic acids and bases, HCO3 (synthesized in tubule cells) are also secreted
WHY IS TUBULAR SECRETION IMPORTANT?
- dispossing of substances, like drugs, that are bound to plasma proteins
- eliminating undesirable substances that were passivley reabsorbed (urea, uric acid)
- ridding body of excesss K+ (aldosterone effect)
- controlling blood Ph by altering amounts of H+ or HCO3 in urine
WHAT LEVEL DO WE WANT BODY FLUID OSMOTIC CONCENTRATION TO BE AT? WHEN DO WE PRODUCE LARGER OR SMALLER AMOUNTS OF URINE?
- body fluid osmotic concentration aims to be 300 mOsm
- produce less urine when fluids are hypertonic (dehydrated) (>300 mOsm), more urine when fluids are hypotonic (overhydrated) (<300 mOsm)
WHAT IS COUNTERCURRENT MECHANISM? WHAT ARE THE 2 TYPES
- countercurrent mechanism: is fluid flow in opposite directions in 2 adjacent segments of the same tube with a hairpin turn
- countercurrent multiplier: interaction of filtrate flow in ascending/descending limbs of nephron loops of juxtamedullary nephrons. CREATES GRADIENT
- countercurrent exchanger: blood flow in ascending/descending limbs of vasa recta. PERSERVES GRADIENT
COLLECTING DUCT USES GRADENT TO VARY URINE CONCENTRATION
GOES FROM 300-1200 mOsm
HOW DOES THE COUNTERCURRENT EXCHANGER WORK?
- vasa recta is highly permeable to water and solutes
- blood inside remains isoosmotic, it can absord water and solutes without disturbing the gradient by countercurrent multiplier
- prevents rapid removal of salt from interstitial space
- removing reabsorbed water
WHERE DOES WATER COME FROM IN THE VASA RECTA?
water in ascending vasa recta comes from descending vasat recta or it is reabsorbed from nephron loop and collecting duct, thus volume of blood at the end of vasa recta is greater than beginning
WHAT WOULD HAPPEN IF A GRADIENT WAS NOT PRESENT?
the established medullary osmotic gradient can now be used to form diluted or concentrated urine
- without it, it can’t raise {urine} > 300 mOsm to conserve water
WHAT PROMPS ADH RELEASE?
- decreased extracellular fluid osmolarity. it recuruits aquaporins to the collecting duct (no aquaporins=fluid excreted)
DRAW THE DIAGRAMS FOR OSMOLARITY WITH AND WITHOUT ADH, AS WELL AS THE ONES IN THE NEPHRON REGULARLY
WHAT ARE SOME THINGS THAT ENHANCE URINARY OUTPUT
- adh inhibitors (alcohol)
- Na+ reabsorption inhibitors (caffeine)
- loop diuretics
- osmotic diuretics
WHAT IS RENAL CLEARANCE? WHAT CAN IT DETECT?
- volume of plasma kidneys can clear of a particular substance in a given time.
- can detect glomerular damage or progress of renal disease
- as well as GFR
WHAT IS THE CHEMICAL COMPOSITION OF URINE
- 95% water, 5% solutes
- nitrogenous wastes: Urea (largest component), uric acid (nucelic acid breakdown), creatinine (metabolite of creatine phosphate)
- Na+, K+, PO4 3-, SO4 2-. Ca2+, Mg2+, HCO3-
WHAT ARE PHYSICAL CHARACTERISTICS OF URINE
- Clear
- pale to deep yellow
- odour is slighlt aromatic when fresh
- slighly acidic (~6, 4.4-8)
- specific gravity: 1.001-1.035
WHAT IS MICTURITION? WHAT ARE THE NEURAL CONTROLS SURROUNDING IT?
micturition is also called urinating or voiding. 3 events must simultaneously occur
1. **contraction of detrusor muscle ** (ANS, Parasympathetic>sympathetic)
2. opening of internal urethral sphincter (ANS, parasympathetic>sympathetic)
3. opening of external urethral sphincter (somatic nervous system- relaxation)
WHAT IS THE PONTINE CONTROL CENTERS, WHEN DO THEY MATURE AND WHAT ARE THE 2 TYPES?
- mature between 2-3
-pontine storage center: inhibits micturition by inhibiting parasympathetic pathways and excited sympathetuc and somatic efferent pathways - pontine micturition center:excites parasympathetic pathways and inhibits sympathetic and somatic efferent pathways
