The Urinary System Flashcards
Urinary system
Excretion: removal of metabolic waste products from body fluids
Elimination: discharge of wastes from the body
Homeostatic regulation: volume and solute concentration of blood
Kidneys
Produce urine
Urine
Water, ions and small soluble compounds
Urinary tract
Ureters
Urinary bladder
Urethra
Ureteres
Paired tubes that transport urine toward the urinary bladder
Urinary bladder
Muscular sac for temporary urine storage
Urethra
Tube that conducts urine to exterior
Transports semen in males
Micturition
Urination
Urinary bladder contracts and forces urine through the urethra which conducts the urine to the exterior
Homeostatic functions of urinary system
- Regulating blood volume and blood pressure
- Regulating plasma concentrations of sodium, potassium, chloride, and other ions
- Helping to stabilise blood pH
- Conserving valuable nutrients
- Assisting the liver in detoxifying
Where are the kidneys located?
Retroperitoneally in the superior lumbar region
On either side of the vertebral column between vertebrae T12 and L3
Organs located partially or entirely retroperitoneally
SAD PUCKER Suprarenal (adrenal) glands Aorta and inferior vena cava Duodenum Pancreas Ureters Colon Kidneys Esophagus Rectum
What holds the kidneys in position
- Overlying peritoneum
- Contact with adjacent visceral organs
- Supporting connective tissues
Connective tissues stabilise and protecting kidneys
- Fibrous capsule covers outer surface of entire organ
- Preinephric fat surrounding fibrous capsule
- Renal fascia - fibrous outer layer
Hilum
Prominent medial indentation
Point of entry for renal artery and renal nerves
Point of exit for renal vein and ureter
Renal sinus
Internal cavity within the kidneys
Fibrous capsule lines renal sinus
Layers of kidney
Outer renal cortex and inner renal medulla
Renal medulla
Made of renal pyramids
Renal papilla
Tip of renal pyramids that project into renal sinus
Renal columns
Bands of cortical tissue which seperate renal pyramids
Kidney lobe
Consists of a renal pyramid, an overlying area of renal cortex and adjacent tissues of the renal columns
Where is urine produced?
In the kidney lobes
Urine production
Ducts within each renal papilla > minor calyx > major calyx > renal pelvis > renal sinus > ureter
Two types of nephrons in kidneys
Cortical nephrons in the renal cortex and juxtamedullary nephrons in the renal medulla
Renal circulation
Renal artery > segmental artery > interlobar artery > arcuate artery > cortical radiate artery > affarent arteriole > glomerulus > efferent arteriole > pertibular capillaries > venule > cortical radiate vein > arcuate vein > interlobar vein > renal vein
Renal nerves
Innervate kidneys and ureters
Functional unit of kidneys
Nephrons
Nephrons
Renal corpuscle and a renal tobule
Renal corpuscle
Spherical structure containing a capillary network that filters blood
Renal tubule
Long tubular passageway which begins at the corpuscle which empties into the collective system
Collective system
Series of tubes that carry tubular fluid away from the nephron
Renal corpuscle
Contains glomerular capsule and glomerulus
Glomerular capsule
Encapsulate glomerular capillaries
Glomerus
Intertwined capillaries
Blood flow through glomerus
Afferent arteriole > glomerus > efferent arteriole
Capsular outer layer
Outer wall of the capsule
Visceral layer
Covers glomerular capillaries
Capsular space
Separates capsuler outer layer and visceral layer
Podocytes
Cells in visceral layer of the capsule
Foot processes
Feet of podocytes
Filtration slits
Narrow gaps between adjacent foot processes
Glomerulonephritis
Inflammation of the glomeruli that impairs filtration in the kidneys
Intraglomerular mesangial cells
Located among glomerular capillaries
Specialised cells derived from smooth muscle
Filtration membrane
Fenestrated endothelium, basement membrane and foot processes of podocytes
Filtration
Blood pressure forces water and small dissolved solutes out of the glomerular capillaries through this membrane and into the capsular space
Where does filtration take place?
Renal corpuscle
Filtrate
Protein-free solution similar to blood plasma
Renal tubule
Proximal convoluted tubule and distal convoluted tubule
Separated by nephron loop/loop of Henle
Tubular fluid
Filtrate travelling along renal tubule
Proximal convoluted tubule
- 1st segment
- Reabsoprtion of critical ions
Nephron loop
Descending limb: fluid flows toward renal pelvis
Ascending limb: fluid flows toward the renal cortex
Distal convoluted tubule
- 3rd segment
- Reabsorption water and selected ions
- Active secretion of undesirable substances
Juxtaglomerular complex
Helps regulate BP and filtrate formulation
Macula densa
Chemoreceptors or baroreceptors
Juxtaglomerular cells
Secrete renin
Monitor BP in the afferent arteriole
Extraglomerular mesangial cells
Located in the triangle space between afferent efferent glomerular arterioles
Provide feedback control between macula densa and juxtaglomerular cells
Collecting system
Collecting duct > papillary duct > minor calyx
Cortical nephron
- Most common
- Nephron loop is relatively short
- Efferent arteriole delivers blood to a network of pertibular capillaries which surround entire renal tubule
Juxtamedullary nephron
- Long nephron loop
- Efferent arterioles connect to vasa recta
Function of urine
To maintain homeostasis by regulating volume and composition of blood
3 types of metabolic wastes
- Urea
- Creatinine
- Uric acid
Creatinine
Generated by skeletal muscle tissue through the breakdown of creatine phosphate
Uric acid
Waste formed during the recycling of the nitrogenous bases from RNA molecules
Urine formation
- Filtration
- Reabsorption
- Secretion
Filtration
BP forces water and solutes across the walls of glomerular capillaries and into the capsular space where small enough molecules pass through filtration membrane
Reabsorption
- Removal of water and solutes from the filtrate
- Water and solute movement across tubular epithelium into peritubular fluid
Secretion
Transport of solutes from the peritubular fluid across the tubular epithelium and into tubular fluid
Where does filtration exclusively occur?
Renal corpuscle
Where does water reabsorption occur?
- Primarily along the PCT and the descending thin limb of nephron loop
- Variably in the DCT
Where does solute reabsorption occur?
Along the PCT, thick ascending limb of the nephron loop, the DCT and collecting system
What drives glomerular filtration in kidney nephrons?
Hydrostatic pressure
Glomerular filtration
Blood plasma is forced through special pores of the filtration membrane and small molecules are called along
Colloid osmotic pressure
Pressure due to materials in solution on each side of the capillary walls
Typical glomerular hydrostatic pressure (GHP)
50mm
Capsular hydrostatic pressure (CsHP)
Opposes GHP
Results from resistance to flow along the nephron and conducting system
Net hydrostatic pressure (NHP)
Difference between GHP and CsHP
Blood colloid osmotic pressure (BCOP)
Osmotic pressure resulting from suspended proteins in the blood
Normally, very few plasma proteins so no BCOP
When glomeruli are damaged, BCOP is created and fluid loss in urine is increased
Net filtration pressure (NFP)
Difference between NHP and BCOP
Glomerular filtration rate (GFR)
Amount of filtrate the kidneys produce each minute
Depends on the NFP - anything affecting NFP affects GFR
Regulation of the GFR
- Autoregulation occurring at the local level
- Hormonal regulation initiated by kidneys
- Autonomic regulation maintained primarily by the sympathetic division of the autonomic nervous system
Autoregulation of the GFR
Maintains an adequate GFR despite changes in local BP and flow
Changes in diameters of arteries, etc.
Hormonal regulation of the GFR
Regulated by the hormones of RAAS and the natriuretic peptides
RAAS
Release of renin restricts water and salt loss in the urine by stimulating reabsorption by the nephron
Triggers for the release of renin by the JGC
- Decrease in BP, systemic pressures or blockage in renal artery
- Stimulation of JG cells by sympathetic innervation
- Decrease in the osmotic concentration of the tubular fluid at the macula densa
Autonomic regulation of the GFR
Sympathetic postganglionic fibres
Vasoconstriction of afferent glomerular arterioles, decreasing GFR
Functions of the renal tubule
- Reabsorbing all the useful organic nutrients in the filtrate
- Reabsorbing more than 90% of the water in the filtrate
- Secreting into the tubule lumen any wastes that didn’t pass into the filtrate at the glomerulus
Transport maximum (Tm)
The concentration at saturation for any substance
Reflects the number of available carrier proteins in the renal tubules
Normally, carrier proteins involved in tubular reabsorption seldom become saturated
Renal threshold
The plasma concentration at which a specific substance or ion begins to appear in the urine
Osmotic concentration/osmolarity
The total number of solute particles in each litre
Osmotic concentration of body fluids
300 mOsm/L
Ion concentrations
Measured in milliequivalents
PCT reabsorption and secretion
- Reabsorption of organic nutrients
- Active reabsorption of ions
- Reabsorption of water
- Passive reabsorption of ions
- Secretion
Reabsorption along the nephron loop
Sodium and chloride ions and water
DCT reabsorption and secretion
Reabsorption of sodium and chloride ions and water
Secretion of hydrogen, ammonium ions and creatinine, drugs and toxins
Collecting system reabsorption and secretion
Sodium, bicarbonate ion and urea reabsorption
Secretes bicarbonate ions and pumps hydrogen ions into the pertibular fluid if pH rises
Countercurrent multiplication
Exchange of substances between descending thin and ascending thick limbs of the nephron loop
Tubular fluid in the descending limb flows toward the renal pelvis while tubular fluid in the ascending limb flows toward the cortex
Functions of the countercurrent multiplication
- Efficient reabsorption of solutes and water before the tubular fluid reaches the DCT and collecting system
- Establishment of a concentration gradient in the peritubular fluid that permits the passive reabsorption of water from the tubular fluid in the collecting system
Countercurrent multiplication
- NA+ and Cl- ions are pumped into thick ascending limb and into peritubular fluid
- Osmotic concentration is increased in the peritubular fluid around the descending thin limb
- This creates a small concentration difference between the tubular fluid and peritubular fluid in the renal medulla
- Osmotic flow of water out of the descending thin limb and into the peritubular fluid
- Highly concentrated tubular fluid in the thick ascending limb speeds up the transport of sodium and chloride ions into the peritubular fluid
Medullary osmotic gradient
Concentration gradient created in the peritubular fluid of the medulla
Na+-K+/2Cl- transporter
Carrier that performs active transport at the apical surface of the TAL
Which limb of the nephron loop is impermeable to water?
Ascending limb of the nephron loop
What does the volume of water lost in urine depend on?
How much of the remaining water in the tubular fluid is reabsorbed along the DCT and collecting system
ADH
Causes aquaporins to be inserted into the apical plasma membrane, enhancing the rate of osmotic water movement
ADH level rises
DCT and collecting system become more permeable to water, the amount of water reabsorbed increases
Why does the concentration of urine never exceed that of the medulla
Because the concentrating mechanism relies on osmosis
ANP
Stimulates the production of a large volume of dilute urine
Countercurrent exchange
Solutes and water reabsorbed in the medulla returning to the bloodstream without disrupting the medullary osmotic gradient
The concentration gradient in the renal medulla encourages osmotic flow of water out of the tubular fluid. As water is lost by osmosis and the volume of the tubular fluid increases, the urea concentration increases
Urinalysis
Chemical and physical analysis of a urine sample
Creatinine clearance
Compares creatinine level in urine with. creatinine level in the blood by estimating GFR
BUN
Measures the amount of urea in blood
Pyelogram
Image of the urinary system
Ureters
Pair of muscular tubes that extend from kidneys to the urinary bladder
Layers of the ureters
- Inner mucosa
- Middle muscular layer
- Outer connective tissue layer
Median umbilical ligament
Extends from anterior, superior border towards the navel
Lateral umbilical ligaments
Pass along the sides of the bladder to the navel
Rugae
Folds of the mucosa lining the urinary bladder that disappear as the bladder fills
Trigone
Triangular smooth area bounded by the opening of the ureters and the entrance of the urethra
Acts as a funnel
Neck of the urinary bladder
Area surrounding the urethral opening
Internal urethral sphincter
Involuntary control over discharge of urine
Layers of the urinary bladder
Mucosa, submucosa and muscular
Detrusor
Muscle of the urinary bladder
Male urethra
Prostatic, membranous and spongy
External urethral sphincter
Muscular band in both sexes
Voluntary control
Urine storage reflex
Occurs by spinal reflexes and the pontine storage centre in pons
Afferent impulses from stretch receptors in the urinary bladder stimulate sympathetic outflow to the detrusor and internal urethral sphincter
Pontine storage centre inhibits urination by decreasing parasympathetic activity and increasing somatic motor nerve activity at the external urethral sphincter
Urine voiding reflex
Occurs by spinal reflexes and the pontine micturition centre
Afferent impulses from stretch receptors in the urinary bladder stimulate interneurons that relay sensations to the pontine micturition centre. The centre initiates sacral spinal reflexes that
- Stimulate increased parasympathetic activity
- Decrease sympathetic activity
- Decrease efferent somatic motor nerve activity
