Urinary Flashcards
What are the goals of the urinary system?
To act as a “water treatment plant”
What is the urinary system comprised of?
Kidneys, ureters, urinary bladder, urethra
What filters wastes from the blood?
The kidneys
Where does waste come from?
All cells and it enters the blood from tissues and cells
Waste is eliminated by…
Urine
What are the additional functions of the kidneys (there are 6)
Regulation of ions and acid base-balance, regulation of blood pressure, elimination of biologically active molecules, helps synthesize calcitrol, Production and release of erythropoietin and Potential to engage in gluconeogenesis.
Layers of the kidney
Fibrous capsule
Perinephric fat
Renal fascia
Paranephric fatq
fibrous capsule def.
Directly adhered to external surface of
kidney – maintains shape, protects from
pathogens
Perinephric fat
External to fibrous capsule – cushions
and supports
Renal fascia
external to perinephric fat – anchors
kidney in place
Paranephric fat
Outermost layer surrounding kidney - cushion and support
What are the two regions of functional tissue within the kidneys
renal cortex and renal medulla
Renal columns
Cortex projections into the medulla
Renal pyramids
Portion of medulla divided by renal columns
corticomedullary junction
Exterior region of pyramids (borders cortex)
renal papilla
Medial apex
Renal lobe
Renal pyramid and portions of adjacent renal columns of cortex
Renal sinus
o Medially located urine drainage
o Minor calyces – funnel-shaped structures of renal pyramids
o Merge to form major calyx
Renal pelvis
Formed from merged major calyces
Merges at medial edge of kidney with ureter
The nephron consists of
renal corpuscle and renal tubule
Nephron
Microscopic functional filtration unit of kidney
Renal corpuscle of nephron
Enlarged bulbous region of nephron within renal cortex
Glomerulus
o Conglomeration of capillary loops within the nephron
o Blood enters via afferent arteriole, exits via efferent arteriole
Vascular pole
side of corpuscle with vessels
Tubular pole
origin of renal tubule
Glomeruli capsules:
o Internal permeable visceral layer
o External impermeable parietal layer
o Capsular space between two layers
Renal tubule
Last part of nephron, 3 sections of tubule
1. Proximal convoluted tubule
2. Nephron loop
3. Distal convoluted tubule
Proximal convoluted tubule
Originates at tubular pole of renal corpuscle
Simple cuboidal epithelium with microvilli to increase surface area
Nephron loop
Descending limb & ascending limb
o Contain thick (simple cuboidal) and thin (simple squamous) segments of epithelium
Distal convoluted tubule
o Lined by simple cuboidal epithelium without microvilli
o Extends to collecting tubule
Two types of nephrons
cortical and juxtamedullary
Cortical nephrons
o Oriented with renal corpuscles near peripheral cortex
o Short nephron loop just penetrating medulla
o Most reside within cortex
(85%)
Juxtamedullary nephrons
o Renal corpuscles adjacent to corticomedullary junction
o Long nephron loops extend deep into medulla
o Help establish salt concentration gradient in interstitial space
(15%)
Nephron drainage
◦ Nephrons drain into a collecting tubule > collecting duct > papillary duct
◦ Both collecting tubules and collecting ducts project toward the renal papilla
Principal cells
Responsive to hormones aldosterone and antidiuretic hormone (ADH)
Intercalated cells
Help regulate urine pH and blood pH
o Type A: eliminates acids (H+)
o Type B: eliminates bases (HCO3-)
Juxtaglomerular apparatus (JG)
◦ Helps regulate blood filtrate formation, systemic blood pressure
◦ Consists of an afferent arteriole next to a DCT
Granular cells
in afferent arteriole
Can contract when stimulated by sympathetic nervous system
o Sympathetic nervous system sends the “don’t pee” signal
o Synthesize, store, and release renin - signals to increase blood volume / pressure
Macula densa cells
In DCT
o Detect changes in NaCl concentration of fluid in lumen of DCT
o Sends signals to granular cells based on NaCl concentrations
Extraglomerular mesangial cells
o In gap between afferent arteriole and DCT
o Can contract
Flow of filtrate
- Blood flows through glomerulus
- Both water and solutes filtered out from blood plasma
- Moves across wall of glomerular capillaries and into
capsular space -> filtrate - Filtrate enters PCT -> tubular fluid
- Fluid enters papillary duct -> urine
Urine formed from 3 processes:
Glomerular filtration
Tubular reabsorption
Tubular secretion
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 in to the blood
Tubular secretion
The movement of substances from blood into the tubular fluid
Glomerular filtration membrane characteristics
◦ Porous, thin, negatively charged structure
◦ Formed by glomerulus and visceral layer of glomerular capsule
Basement membrane of glomerulus (middle)
Glycoprotein and proteoglycan molecules
Endothelium of glomerulus (inner)
Fenestrated, allows plasma and dissolved substances to be filtered
Visceral layer of glomerular capsule
Outermost layer
podocytes
o Long processes, pedicels wrap around glomerular capillaries
o Support capillary wall but don’t completely enclose it
o Separated by thin spaces, filtration slits
o Restrict passage of most small proteins
3 types of substances in the blood
̶
1. Freely filtered – pass easily through filtration membrane
o Small substances
o E.g., water, glucose, amino acids, ions
̶
2. Not filtered – cannot pass
o Formed elements and large proteins
̶
3. Limited filtration – usually blocked
o Proteins of medium / large size – very small proteins can pass
o Due to size or due to negative charge
Mesangial cells
◦ Modified smooth muscle cells positioned in/between glomerular capillary loops
◦ Phagocytose any foreign matter stuck in the system
◦ Can contract when stimulated, shrinking the glomerulus > less filtrate formed
Pressure driving filtration:
◦ Glomerular hydrostatic (blood)
pressure
o “Pushes” water and some solutes out of glomerulus
o Pushed into capsular space of renal corpuscle
o Higher than blood pressure of other systemic capillaries
˗ Required for filtration to occur
˗ Larger diameter of afferent
arteriole
Pressures opposing filtration:
◦ Blood colloid osmotic pressure (OPg)
o Osmotic pressure exerted by dissolved
solutes
˗ E.g., plasma proteins
o Draws fluid back into glomerulus
◦ Capsular hydrostatic pressure
o Pressure in glomerular capsule due to
filtrate
o Impedes movement of additional fluid
Net filtration pressure
the difference between driving and opposing forces,
determines if filtration occurs
Glomerular filtration rate (GFR)
o Rate at which the volume of filtrate is formed
◦ Helps kidney control urine production based on physiologic conditions
◦ Processes within kidney itself (intrinsic controls)
◦ Processes external to kidney (extrinsic controls)
Influenced by net filtration pressure
Renal autoregulation: intrinsic
Intrinsic ability of kidney to maintain constant blood pressure and GFR
2 parts include myogenic response and Tubuloglomerular feedback mechanism
Myogenic response for low system pressure
Compensates for lower system pressure
-Decreased blood pressure, less stretch of smooth muscle in arteriole causes
smooth muscle cells to relax > vessels to dilate
̶ Allows more blood into glomerulus
Myogenic response for high system pressure
With increased blood pressure, more stretch of smooth muscle in arteriole, causes smooth muscles to contract -> vessel constriction
Allows less blood into glomerulus
Tubuloglomerular feedback mechanism
“Backup” to myogenic mechanism response to increased blood pressure
̶If glomerular blood pressure increased
o Amount of NaCl in tubular fluid also increased
o Results in further vasoconstriction of afferent arteriole
Extrinsic controls: Neural and hormonal
control
Sympathetic stimulation
̶Decreases GFR through vasoconstriction
̶Reduces blood flow into the glomerulus
̶Causes granular cells of JG apparatus to release renin
̶Stimulates myofilaments within mesangial cells to contract
̶Results in decrease in surface area of filtration membrane
̶Decrease in urine production
GFR stands for
Glomerular filtration rate
Atrial natriuretic peptide (ANP)
̶Peptide hormone released from cardiac muscle cells based on tension in heart cambers
̶Relaxes afferent arteriole and inhibits release of renin
̶Causes relaxation of mesangial cells which increases filtration membrane area
̶Net increase in GFR with increased urine volume
Transport process
◦ Substances secreted when they move from blood to the nephron (not in glomerulus)
◦ Substances reabsorbed when they move from the nephron back in to the blood
◦ Highly regulated
◦ If not reabsorbed, they are excreted as urine
◦ Most reabsorption occurs in the PCT
Paracellular transport
movement between epithelial cells
Transcellular transport:
movement of substances through epithelial cells
potassium reabsorption
◦ Potassium
◦ Can be reabsorbed or secreted into tubular fluid depending on concentration gradients
◦ Aldosterone release > principal cells > secrete K+
◦ Low blood K+ > type A intercalated cells > reabsorb K+
Calcium and phosphate reabsorption
Parathyroid hormone = release phosphate / reabsorb calcium
Hydrogen ions and bicarbonate ions
◦ Influenced by diet and activity of type A and type B intercalated cells
◦ Closely monitor blood pH – urine pH is not nearly as important
Elimination of nitrogenous waste (components)
Main products include urea, uric acid and creatinine
Urea
molecule produced from protein breakdown
◦ 50% excreted in the urine – the rest reabsorbed
◦ Fluid is cycled between collecting duct and nephron to allow for hyper-concentration of wastes
Uric acid
produced from nucleic acid breakdown in liver
Creatinine
produced during creatine metabolism in muscle
Fifty percent of urea is
reabsorbed at the collecting tubules, leaving the remaining
50% to be excreted through urine
o “Recycling” – so we can concentrate our urine
Countercurrent multiplier
establishes gradient
Countercurrent exchange
maintains gradient
Works with aquaporins to reabsorb water / concentrate urine
Urine
◦ Product of filtered and processed blood plasma, sterile
◦ Characteristics: composition, volume, pH, specific gravity, color and turbidity, smell
Composition of PISS
o 95% water, 5% solutes
˗ Salts, nitrogenous wastes, some hormones drugs, ketone bodies
Volume of piss
o Average 1 to 2 L per day
o Variations due to fluid intake, blood pressure, temperature, diuretics, diabetes, other
fluid excretion
o Minimum of 0.5 L to eliminate wastes from body
o Below 0.40, wastes will accumulate in blood
pH of dah pee pee
o Normally between 4.5 and 8.0, average at 6.0
o Influenced by metabolism, infection, diet
Specific gravity
o Density of a substance compared to density of water
o Specific gravity slightly higher than water due to solutes
Color
o Ranges from almost clear to dark yellow
◦ Depends on concentration of urobilin (urochrome; yellow chemical)
o With increased volume of urine, lighter color
Smell
o Urinoid, normal smell of fresh urine
o May develop ammonia smell if allowed to stand
o Fruity smell in diabetes
Ureters
◦ Long epithelial-lined fibromuscular tubes
◦ Urine from kidney > bladder
Ureter walls
◦ 1. Mucosa
o Transitional epithelium
o Distensible and impermeable to urine
o Folds to fill lumen when no urine present
◦ 2. Muscularis
o Inner longitudinal and outer circular layer of smooth muscle cells
o Contracts to propel urine to bladder
◦ 3. Adventitia
o External layer of ureter wall
o Areolar CT, collagen and elastic fibers, prevents backflow
Urinary bladder
◦ Expandable, muscular container
◦ Retroperitoneal reservoir for urine
◦ Inverted pyramidal shape when
empty
o Oval shape when full
Trigone – funnel to urethra
◦ Posteroinferior triangular area of bladder wall
o Formed by imaginary lines connecting ureter openings and urethra
o Remains immobile as bladder fills and empties
Urethra
fibromuscular tube
Internal urethral sphincter
o Involuntary, superior sphincter
o Surrounds neck of bladder
o Involuntary - autonomic nervous
system
External urethral sphincter
o Inferior to internal urethral sphincter
o Voluntary sphincter - somatic nervous system
o “Toilet training” muscle
Female urethra
o Single function: to transport urine from urinary bladder to exterior
o Shorter, easier for infections to enter the body
Male urethra
o Passageway for urine and semen
o Three segments: prostatic urethra, membranous urethra, spongy urethra
Storage reflex
◦ Continuous sympathetic stimulation
o Causes relaxation of detrusor to accommodate urine
o Stimulates contraction of internal urethral sphincter
o External urethral sphincter remains contracted
Micturition
◦ Expulsion of urine from the bladder
◦ Associated with two reflexes
o Storage reflex (sympathetic) and `micturition (parasympathetic) reflex
o Baroreceptors sense stretch > brain
o Reflexively relaxes internal
o Pudendal nerve > consciously relaxes
external sphincter
