urinary system i Flashcards
urinary system organs
Kidneys - major excretory organs
Ureters - transport urine from kidneys to urinary bladder
Urinary bladder - temporary storage reservoir for urine
Urethra transports urine out of body
Kidney Main Functions
- water
- endocrine
- vitamin
- glucose
- regulate water volume/ solute concentration
- regulate ECF ion concentration
- ensure long-term acid-base balance
- remove metabolic waste/toxic drugs
- renin to regulate BP
- erythropoeitin to regulate RBC production
- activation of vit D: calcitriol
8 gluconeogenesis during fasting
Internal anatomy (cortex and medulla)
Renal cortex
-Granular-appearing superficial region
Renal medulla
- -Composed of cone-shaped medullary (renal) pyramids
- Pyramids separated by renal columns (Inward extensions of cortical tissue)
Papilla, lobe, and pelvis
Papilla
-Tip of pyramid; releases urine into minor calyx
Lobe
-Medullary pyramid and its surrounding cortical tissue; ~ 8/kidney
Renal pelvis
-Funnel-shaped tube continuous with ureter
calyces
Minor calyces
-Drain pyramids at papillae
Major calyces
- Collect urine from minor calyces
- Empty urine into renal pelvis
urine flow
Renal pyramid minor calyx major calyx renal pelvis ureter
kidney blood supply
- Rich blood supply
- arteries deliver 25% of cardiac output to kidneys each min
- arterial flow into and venous flow out of kidneys along similar path
nerve supply to kidneys
sympathetic fibers from renal plexus
NO parasympathetic innervation
blood flow path
aorta renal artery segmental artery interlobar artery arcuate artery cortical radiate artery afferent arteriole glomerulus capillaries efferent arteriole peritubular capillaries or vasa recta cortical radiate vein arcuate vein interlober vein renal vein inferior vena cava
how many nephrons per kidney?
over a million
tubular parts of nephron
Glomerular (Bowman’s) capsule Proximal convoluted tubule (PCT) Nephron loop (loop of Henle) Descending limb → Ascending limb Distal convoluted tubule (DCT) Multiple nephron tubules drain into Collecting Duct (CD)
blood vessel components of nephron
Afferent arteriole Glomerulus Efferent arteriole Peritubular capillaries Vasa recta (if juxtamedullary nephron)
two parts of renal corpuscle
Glomerulus
-Tuft of capillaries; fenestrated endothelium highly porous allows filtrate formation
Glomerular capsule (Bowman's capsule) -Cup-shaped, hollow structure surrounding glomerulus
glomerular capsule anatomy
Parietal layer - simple squamous epithelium
Visceral layer - branching epithelial podocytes
- Extensions terminate in foot processes that cling to basement membrane
- Filtration slits between foot processes allow filtrate to pass into capsular space
proximal convoluted tubule
cells
function
location
Cuboidal cells with dense microvilli (brush border –> high surface area); large mitochondria
Functions in reabsorption and secretion
Confined to cortex
nephron loop
Descending and ascending limbs
Proximal descending limb continuous with proximal tubule
Distal descending limb = descending thin limb; simple squamous epithelium
Thick ascending limb
-Cuboidal to columnar cells; thin in some nephrons
distal convoluted tubule
cell
function
location
Cuboidal cells with very few microvilli
Function more in secretion than reabsorption
Confined to cortex
Collecting duct’s cells
Principal cells
- Sparse, short microvilli
- Maintain water and Na+ balance
Intercalated cells
-Cuboidal cells; abundant microvilli; two types –>A and B; both help maintain acid-base balance of blood
collecting duct func
receive filtrate from many nephrons
run thru medullary pyramids –> look stripy
fuse together to get urine thru papillae into minor calyces
2 types of nephrons
Cortical nephrons—85% of nephrons; almost entirely in cortex
–have peritubular capillaries
Juxtamedullary nephrons
- Long nephron loops deeply invade medulla
- Ascending limbs have thick and thin segments
- Important in production of concentrated urine
- Have vasa recta
Nephron capillary beds (2 kinds)
glomerulus = all renal tubules (specialized for filtration)
Peritubular capillaries (for cortical nephrons) or vasa recta (for juxtamedullary nephrons)
why is bp high in glomerulus
- afferent arterioles larger in diameter than efferent arterioles
- arterioles are high-resistance vessels
peritubular capillaries
Low-pressure, porous capillaries adapted for absorption of water and solutes
Arise from efferent arterioles
Cling to adjacent renal tubules in cortex
Empty into venules
vasa recta
Long, thin-walled vessels parallel to long nephron loops of juxtamedullary nephrons
Arise from efferent arterioles serving juxtamedullary nephrons
-Instead of peritubular capillaries
Function in formation of concentrated urine
Juxtaglomerular complex
-one per nephron
Involves modified portions of
- distal portion of ascending limb of nephron loop (some references say it involves the first part of the distal convoluted tubule)
- afferent arteriole
Important in regulation of rate of filtrate formation and BP
includes macula densa cells, granular cells, and extraglomerular mesangial cells
macula densa cells
Tall, closely packed cells of ascending limb (or first part of DCT)
Chemoreceptors; sense NaCl content of filtrate
granular cells
Enlarged, smooth muscle cells of arteriole
Secretory granules contain enzyme renin (so now we do not just say renin comes from the kidney! We know exactly where it comes from.)
Mechanoreceptors; sense blood pressure in afferent arteriole
extraglomerular mesangial cells
Between arteriole and tubule cells
Interconnected with gap junctions
May pass signals between macula densa and granular cells
how much urine is produced per day vs the amount of fluid processed?
What are the 3 processes of urine formation
180 L processed/day –> 1.5 L urine/day
- glomerular filtration
- tubular reabsorption
- tubular secretion
definitions of the 3 processes
glomerular filtration = produces cell-and protein- 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
- how many times a day do the kidneys filter the body’s plasma volume?
- how much of the body’s oxygen do the kidney’s use at rest?
- from what is the urine produced?
60 times
20-25%
From filtrate (from glomerular filtration) = blood plasma minus proteins
Urine = <1% of oringinal filtrate –> contains metabolic wates and inneeded substances
energy requirements of glomerular filtration
- passive
- no metabolic energy required
- hydrostatic pressure forces fluids and solutes thru filtration membrane
- no reabsorption into capillaries of glomerulus
Filtration membrane
definition and layers
Porous membrane between blood and interior of glomerular capsule
-Water, solutes smaller than plasma proteins pass; normally no cells pass
- Fenestrated endothelium of glomerular capillaries
- Basement membrane (fused basal laminae of two other layers)
- Foot processes of podocytes with filtration slits; slit diaphragms repel macromolecules
Filtration membrane: what can pass and what can’t
Macromolecules “stuck” in filtration membrane engulfed by glomerular mesangial cells
Allows molecules smaller than 3 nm to pass
(Water, glucose, amino acids, nitrogenous wastes)
Plasma proteins remain in blood maintains colloid osmotic pressure prevents loss of all water to capsular space
Proteins in filtrate indicate a filtration membrane problem. Protein in urine is abnormal!
pressures that affect filtration
Outward:
hydrotatic pressure in glomerular capillaries = glomerular bp
-chief force pushig water and solutes out of blood
-high (55 mm Hg) –> most capillary beds = 26 mm Hg
Inward: Hydrostatic pressure in capsular space -pressure of filtrate in capsule (15 mm Hg) Colloid osmotic pressure in capillaries -"pull" of proteins in blood (30 mm Hg)
Sum:
Net filtration pressure
-outward force of 10 mm Hg
-resposible for filtrate formation and glomerular filtration rate
Glomerular filtration rate
Volume of filtrate formed per minute by both kidneys (normal = 120–125 ml/min)
GFR directly proportional to
- NFP – primary pressure is hydrostatic pressure in glomerulus
- Total surface area available for filtration – glomerular mesangial cells control by contracting
- Filtration membrane permeability – much more permeable than other capillaries
regulation of glomerular filtration: intrinsic
Intrinsic controls (renal autoregulation)
- act locally within kidney to maintain GFR
- if glomerular hydrostatic pressure falls by only 18%, GFR = 0
- maintains constant GFR w/in MAP of 80-180
- 2 methods: myogenic mechanism and tubuloglomerular feedback mechanism
Myogenic Mechanism
smooth muscle contracts when stretched
high BP = smooth muscle stretch –> constriction of afferent arterioles = restricted blood flow into glomerulus (protects from damage)
low bp –> dilation of afferent arterioles
Tubuloglomerular Feedback Mechanism
Flow dependent mechanism directed by macula densa cells –> respond to filtrate NaCl concentration
If GFR is high –> filtration flow rate is high –> there’s a shorter reabsorption time –> there’s high filtrate NaCl levels –> there’s constriction of afferent arteriole –> decreases NFP and GFR –> more time for NaCl reabsorption
opposite for low GFR
Extrinsic controls of glomerular filtration
Extrinsic controls maintain systemic blood pressure
- sympathetic NS and Renin-Angiotensin-Aldosterone mechanism –> can negatively affect kidney func
- takes precedence over intrinsic controls if systemic BP <80 or >180 mm Hg
Extrinsic controls: sympathetic NS
If extracellular fluid volume extremely low (bp is low)
- NE released by SNS and Epitnephrine released by adrenal medulla
- systemic vasoconstriction and higher bp
- constriction of afferent arterioles –> lower GFR –> increased blood volume and pressure
Extrinsic Controls: Renin-Angiotensin- Aldosterone Mechanism
Main mechanism for increasing blood pressure –Three pathways to renin release by granular cells
- Direct stimulation of granular cells by sympathetic nervous system
- Stimulation by activated macula densa cells when filtrate NaCl concentration low
- Reduced stretch of granular cells in afferent arteriole
