The Urinary System Flashcards
What is the organization of the urinary system?
Two kidneys
Two ureters
One urinary bladder
One urethra
What do the kidneys do?
make urine and carry out other vital functions
What do the ureters do?
carry urine to the urinary bladder
What does the urinary bladder do?
collects, stores, and releases urine
What does the urethra do?
empties urine from the body
What are the six functions of the urinary system?
- Eliminating organic waste products, such as urea, uric acid, creatine, and ammonia
- Regulating blood volume and pressure by: adjusting the volume of water lost and releasing erythropoietin and renin
- regulating plasma concentrations of ions;
- helping stabilize blood pH: by controlling loss of hydrogen ions and bicarbonate ions in urine
- conserving nutrients
- assisting the liver in detoxifying poisons
What does the renal lobe of the kidny consist of?
- renal pyramid
- overlying area of renal cortex
- adjacent tissues of renal columns
What is the order that urine production goes in?
urine from renal papilla -> minor calyx -> major calyx -> renal pelvis -> ureter
Compare the anatomy of kidneys between domestic animals
- cattle do not have a distinct renal pelvis
- human, cattle, and pig have multipyramidal or multilobar kidneys
- cat, dog, and horse have unipyramidal or unilobar kidneys
How much cardiac output do kidneys receive?
20-25%
How many ml of blood flow per minute do kidneys receive in humans?
1200 ml
What are the nephrons of the kidney?
the collecting system and functional unit
What do nephrons consist of?
- renal corpuscle
- renal tubule
What are the parts of the renal tubule?
- proximal convoluted tubule (PCT)
- the Loop of Henle
- distal convoluted tubule (DCT)
Describe the renal corpuscle
spherical structure consisting of:
- Bowman’s capsule: forms the outer wall of the renal corpuscle and encapsulates the glomerular capillaries
- glomerulus: capillary network
Describe the parts of the Bowman’s capsule
- Parietal epithelium: a simple squamous epithelium, forms the outer wall. Continuous with visceral epithelium
- Visceral epithelium: covers glomerular capillaries
- Capsular space: separates the parietal and visceral epithelia
Describe the parts of the visceral epithelium
- consists of large cells (podocytes) with complex processes or “feet” (pedicels) that wrap around specialized lamina densa of glomerular capillaries
- Filtration slits: narrow gaps between adjacent pedicels
Describe the glomerulus
- consists of 50 intertwining capillaries
- are fenestrated capillaries
- blood delivered via afferent arteriole
- blood leaves in efferent arteriole: flows into peritubular capillaries which drain into small venules
Describe the proximal convoluted tubule (PCT) of the renal tubule
- first part nearest to Bowman’s capsule
- Loop of Henle which consists of:
a descending limb
a sharp turn
an ascending limb
each limb contains a thick segments and a thin segment
Describe the distal convoluted tubule (DCT) of the renal tubule
convoluted tubule beyond the Loop of Henle
Describe collecting ducts
recieve fluid from many nephrons
each collecting duct:
- begins in cortex
- descends into medulla
- carries fluid to papillary duct that drains into a minor calyx
What are cortical nephrons?
- 85% of all nephrons
- located mostly within cortex
- Loop of Henle is short
- peritubular capillaries surround entire renal tubule
Describe juxtamedullary nephrons
- long loops of Henle deep into medulla
- peritubular capillaries connect to vasa recta
What is the goal of urine production?
to maintain homeostasis by regulating volume and composition of blood and including excretion of metabolic waste products
What are the three organic waste products?
Urea: the most abundant organic waste and produced during the breakdown of amino acids
Creatinine: generated in skeletal muscle tissue by breaking down the high-energy compound, creatine phosphate
Uric acid: formed by recycling of nitrogenous bases from RNA molecules
What is the pathway or urine formation?
renal papilla -> minor calyx -> major calyx -> renal pelvis -> ureter -> urethra
What are the three processes of urine formation?
Filtration: blood pressure forces water and small solutes across membrane into capsular space
Reabsorption: movement of molecules selectively out of the tubule and itno the peritubular blood
Secretion: movement of waste molecules out of peritubular blood and into the tubule for excretion
Describe the filtration membrane
- capillary endothelium: fenestrated, 60-100 nm diameter
- lamina densa
- filtration slits: the finest filters of all: 6-9 nm diater
Describe filtration
hydrostatic pressure forces water and small solute through membrane pores:
- metabolic wastes and excess ions
- glucose, free fatty acids, amino acids, vitamins
Describe filtration pressures:
glomerular filtration is governed by the balance between:
- glomerular hydrostatic pressure (GHP): blood pressure ~ 45-55 mm Hg
-Capsular hydrostatic pressure (CsHP): opposes GHP ~ 15 mm Hg
- Blood colloid osmotic pressure (BCOP): osmotic pressure resulting from presence of suspended proteins ~ 25 mm Hg
Net hydrostatic pressure (NHP): GHP - CsHP = ~ 35 mm Hg
Filtration Pressure (FP): NHP - BCOP = ~ 10 mm Hg
What is Glomerular Filtration Rate (GFR)?
is the amount of filtrate produced in the kidneys each minute
- ~125 ml per min in humans (~10% of fluid delivered to the kidneys)
- 50 gallons (180L)/day, ~70 times the total plasma volume
- 99% is reabsorbed
Any factor that alters the filtration pressure will change the GFR
- are very sensitive to changes in blood pressure
- if blood pressure at the glomeruli drops by 20%, kidney filtration will cease
Describe the autoregulation (intrinsic) of the GFR
Maintains GFR despite changes in local blood pressures and blood flow
Reduce renal blood pressure triggers:
- dilation of afferent arteriole
- dilation of glomerular capillaries
- constriction of efferent arterioles
Rise in renal blood pressure:
- constricts afferent arterioles
- decreases glomerular blood flow
What is the net effect of increased sympathetic activity?
moderate decrease in GFR
Describe reabsorption and secretion
- second step in urine formation
- glomerular filtration produces a filtrate with a composition similar to blood plasma but with few, if any, plasma proteins
reabsorption: recovers useful materials from filtrate
secretion: ejects waste products, toxins, and other undesirable solutes
How does reabsorption and secretion work?
occur in every segment of nephron
- except renal corpuscle
by different mechanisms: passive and active transport
relative importance changes from segment to segment
reabsorbed materials enter peritubular fluid: and diffuse into peritubular capillaries and vasa recta
Describe reabsorption and secretion in the proximal convoluted tubule:
reabsorb:
- 60-70% of the volume of filtrate
- 99-100% of glucose, amino acids, and other organic nutrients
- 60-70% Na+, K+, and HCO3
secrete:
- H+, NH4+, creatinine, drugs, and toxins
Describe reabsorption in the Loop of Henle
Reabsorbs about 1/2 of water, and 2/3 of sodium and chloride ions remaining in tubular fluid by the process of countercurrent multiplication
Two parallel segments of Loop of henle have very different permeability characteristics:
- thin descending limb: permeable to water; impermeable to solutes
- thick ascending limb: impermeable to water, active solute transport
Describe countercurrent multiplication and concentration of urine
positive feedback loop:
- pumping out of Na+ and Cl- from the thick ascending limb elevates the osmotic concentration in the peritubular fluid around the thin descending limb
- the result is an osmotic flow of water out of the thin descending limb
- the arrival of the highly concentrated solution in the thick ascending limb accelerates the transport of Na+ and Cl- into the peritubular fluid
Describe tubular secretion and solute reabsorption at the distal convoluted tubule
only 15-20% of initial filtrate volume reaches DCT
arriving tubular fluid no longer resemble blood plasma
reabsorption of water (~5%):
- under ADH stimulation
reabsorption of Na+:
- under aldosterone stimulation
Secretion of H+, NH4+, creatinine, drugs and toxins
Describe reabsorption and secretion along the collecting system
the collecting ducts receive tubular fluid from many nephrons
along the concentration gradient in the medulla
reabsorption of water (~9%)
- under ADH stimulation
reabsorption of Na+
- under aldosterone stimulation
secretion of H+ or HCO3- to control body fluid of pH
Describe the relevance of kidney and urinary stones:
when the concentration of some substances (e.g. calcium, oxalate, magnesium-ammonium-phosphate etc.) gets so high under certain conditions, the participate to form kidney stones (nephrolithiasis) or urinary tract stones (urolithiasis)
quite common in dogs, cats, and ruminants
Describe the control of urine volume
urine volume and osmotic concentration are regulated by controlling water reabsorption
obligatory water reabsorption:
- water absorption in the proximal convoluted tubule and the descending limb of the loop of Henle
- can not be adjusted; recovers ~85% od filtrate
facultative water reabsorption:
- the amount of water reabsorbed along the distal convoluted tubule and the collecting system
- can be precisely controlled, because these segments are relatively impermeable to water except in the presence of ADH
What hormones control urine volume?
- AHD
- Aldosterone
- Atrial natriuretic hormones (ANH)
How does ADH participate in the control of urine volume?
- controls the permeability of the distal convoluted tubule and collecting system to water by increasing special water channels in the apical cell membranes
How does aldosterone participate in the control of urine volume?
- controls sodium ion pumps along most of the distal convoluted tubule and the proximal portion of the collecting system
- raise the sodium concentration of blood and thus promoting reabsorption of water
How does atrial natriuretic hormones (ANH) participate in the control of urine volume?
- promotes loss of sodium via urine
- opposes aldosterone
- cause the kidney to reabsorb less water and thereby produce more urine
What is the relevance of diabetes insipidus?
- deficient release of ADH or reduced responsiveness of the kidney to AHD
- intense thirst and heavy urination (>20 L/day in humans)
What does the vasa recta do?
- to return solutes and water reabsorbed in medulla:
- to general circulation without disrupting the concentration gradient
What is the normal average pH of arterial blood?
7.4
What is acidemia?
- when the pH of plasma falls below 7.35
- the physiological state that results is acidosis
What is alkalemia?
- when the pH of plasma rises above 7.45
- the physiological state that results is called alkalosis
What range of pH can animals not survive in?
animals can not survive long with an ECF pH below 6.8 or above 7.7
What does an animal body do to control the pH?
the buffer systems:
- the carbonic acid-bicarbonate buffer system: CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
- phosphate buffer system: H2PO4- <-> H+ + HPO42-
- protein buffer system
respiratory compensation: affecting the carbonic acid-bicarbonate buffer system by pulmonary ventilation
renal compensation: the kidneys excrete alkaline or acid urine as needed
Describe respiratory and renal compensation in regulating pH
- in renal compensation, the kidneys vary their rates of H+ secretion and HCO3- reabsorption, depending on the pH of the ECF
What is the micturition reflex?
stretch receptors in bladder -> afferent fibers -> sacral spinal cord
- efferent fibers -> stimulates detrusor muscle (smooth muscle) contraction
- interneuron -> cerebral cortex -> inhibits the micturition reflex or voluntary relaxation of external urethral sphincter (skeletal muscle)
