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excretion, elimination, homeostatic regulation
Functions of the urinary system
Excretion
Removal of liquid waste from body fluids
Elimination
Discharge of waste products
Homeostatic regulation
Volume and solute concentration of blood
Fibrous capsule
Covers outer surface of entire organ
Perirenal fat
Layer of fat surrounding renal capsule
Renal fascia
Anchors kidney to surrounding structures
Hilum
Point of entry for renal artery and renal nerves
Point of exit for renal vein and ureter
Renal Cortex
Internal anatomy of kidney:
Superficial portion of kidney
Renal medulla
Internal anatomy of kidney:
Made up of renal pyramids and columns
Renal pyramids
6-18 triangular structures in renal medulla
Apex projects into minor calyces
Renal columns
Tissue separating adjacent renal pyramids
Extend from cortex into medulla
Renal Papilla
Ducts that discharge urine into minor calyx
Cup-shaped drain for urine
Major calyx
Formed by 4 or 5 minor calyces
Renal pelvis
Large funnel made of 2 or 3 major calyces
connected to ureter, which drains kidney
20-25%
What percentage of total cardiac output do the kidneys receive?
Renal artery
Kidney receives blood through what?
Segmental arteries
What do renal arteries divide into
Interlobar arteries
What do segmental arteries split into?
These radiate between renal pyramids
Supply blood to arcuate arteries between cortex and medulla
Arcuate arteries
What do interlobar arteries split off into?
Interlobular arteries
These branch off from arcuate arteries, delivering blood to cortex
90% of blood entering the kidneys is in the cortex
Afferent arterioles
Branch off supplying nephrons with blood
Interlobular veins
After blood exits the nephrons, where does it enter?
Nephrons
Structural and functional unit within the kidney
Tubular structures in cortex of each renal lobe where urine production begins
Each kidney contains over 1 million of these
Consists of renal corpuscle and renal tubule
Renal corpuscle
Structure consisting of:
Glomerular capsule
Capsular Space
Glomerulus
Renal tubule
Structure consisting of:
Proximal convoluted tubule (PCT)
Nephron loop
U-shaped tube
Extends partially into medulla
Distal convoluted tubule (DCT)
Cortical nephrons
85% of all nephrons
Located mostly within cortex of kidney
Nephron loop is relatively short
Efferent arteriole delivers blood to peritubular capillaries
Which drain into venules into the renal veins
Juxtamedullary nephrons
15% of nephrons
Nephron loops extend deep into medulla
Peritubular capillaries connect to vasa recta
Plays a role in reabsorption and concentration gradients
Glomerular capsule
Forms outer wall of renal corpuscle
Capsular epithelium
Continuous with visceral epithelium
Encapsulates glomerulus
Separated by capsular space
Connected to proximal convoluted tubules
Glomerulus
Knot of over 50 intertwining capillaries
Blood from afferent arteriole
Blood leaves by efferent arteriole
Podocytes
The epithelium of glomerulus consists of large cells called:
Filtration slits
Exists between adjacent pedicles
Materials must be small enough to pass between these
Passive process
What type of process is glomerular filtration:
Blood pressure forces water and small solutes into capsular space
Proximal convoluted Tubule
First segment of renal tubule
Formed of simple cuboidal cells
Microvilli on apical surfaces (assists in reabsorption)
Absorbs nutrients, ions, water
Release them into peritubular fluid
Peritubular fluid
Interstitial fluid around renal tubules
Nephron loop (loop of henle)
the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule
In between descending limb and ascending limb
Descending limb
This portion of the nephron flows toward renal pelvis
Permeable to water
Water movement helps concentrate tubular fluid
Ascending limb
This portion of the nephron flows toward renal cortex
Pumps sodium and chloride ions out of tubular fluid
Creates high solute concentrations in peritubular fluid
Distal convoluted tubule
Final segment of the renal tubule passes between afferent and efferent arterioles
Epithelial cells lack microvilli
Has three processes
Active secretion of ions, acids, drugs, and toxins
Selective reabsorption of sodium and calcium ions from tubular fluid
Selective reabsorption of water
Concentrates tubular fluid
Juxtaglomerular complex
An endocrine structure that monitors blood volume
Secretes: Hormone erythropoeitin and enzyme renin
Formed by:
Macula densa cells of DCT, near renal corpuscle
Collecting system
DCT opens into the collecting ducts
Several collecting ducts:
Converge into a larger papillary duct
Which empties into a minor calyx
Transports tubular fluid from nephron to renal pelvis
Adjusts fluid composition and pH
Determines final solute concentration and volume of urine
filtration membrane
Glomerular filtration involves a passage across a __________
There are three components of this membrane
Capillary endothelium
Dense layer
Filtration slits
Produces filtrate similar to blood plasma
Capillary endothelium
Component of filtration membrane:
Fenestrated capillaries
Prevents passage of blood cells, but allow diffusion
Dense layer
Component of filtration membrane:
Allows diffusion of small proteins, nutrients, and ions
Filtration slits
Component of filtration membrane:
Finest filters
Prevent passage of most small plasma proteins
Hydrostatic pressures (fluid pressure), colloid osmotic pressure (ion pressure)
Glomerular filtration is governed by the balance between:
Glomerular hydrostatic pressure
Pushes water and solutes out of blood through filtration membrane
Efferent arterioles have a smaller diameter than afferent
Produces resistance inside and pressure inside glomerular capillaries
Averages 50mm Hg
Capsular hydrostatic pressure
Opposes glomerular hydrostatic pressure
Pushes water and solutes from filtrate back into the blood
Produces from left over filtrate within the glomerular
Net hydrostatic pressure
Difference between glomerular and capsular hydrostatic pressures (35mm Hg)
Colloid osmotic pressure
Pressure resulting from the presence of suspended proteins
Draw water out of filtrate and into blood
Opposing filtration
Averages 25 mm Hg
Net filtration pressure
All the pressures moving water and dissolved materials
Hydrostatic and colloid osmotic pressure across glomerular capillaries
Glomerular filtration rate
Amount of filtrate kidneys produce each minute
Averages 125 mL/min
10% of fluid delivered to kidneys leaves bloodstream and enters capsular spaces
Glomeruli generate about 180 liters of filtrate per day
Autoregulation
Regulation of glomerular filtration:
At the local level
Maintains glomerular filtration rate despite changes in blood pressure or flow
Reduced blood flow or glomerular blood pressure triggers:
Dilation of afferent arteriole and glomerular capillaries
Rise in renal blood pressure
Stretches walls of afferent arterioles
Causing arterioles to constrict
Decreases glomerular blood flow
Autonomic regulation
Regulation of glomerular filtration:
Sympathetic nervous system
Mostly consists of sympathetic fibers
Activation constricts afferent arterioles
Decreases glomerular filtration rate
Slows filtrate production
May be opposed by autoregulation at local level
Natriuretic peptides
Released by the heart due to increased blood volume or pressure
Trigger dilation of afferent arterioles and constriction of efferent arterioles
Elevate glomerular pressures and increase GFR
Oppose secretion of aldosterone
Decrease sodium retention
Renin angiotensin aldosterone system
Main mechanism for increasing blood pressure
Increases blood volume and pressure thereby increasing GFR
Angiotensin II
Vasoconstricts the arterioles and precapillary sphincters
Elevating glomerular pressures and filtration rates
Stimulates secretion of Aldosterone by adrenal cortex
Accelerates sodium reabsorption
Stimulates thirst
Releases ADH
Increases sympathetic motor tone
Proximal convoluted tubule
These are the functions of what structure:
Reabsorption of organic nutrients
99% reabsorbed via cotransport and facilitated diffusion
Active reabsorption of ions
Reabsorption of water
Passive reabsorption of ions
Secretion
Countercurrent multiplication
Exchange between parallel segments of nephron loop
Refers to exchange between tubular fluids moving in opposite directions
Descending limb flows toward renal pelvis
Ascending limb flows toward cortex
Effect of exchange increases as movement of fluid continues
Nephron loop
What reabsorbs the ½ of water and 2/3 of sodium and chloride ions remaining through the process of countercurrent multiplication and exchange
Descending limb
Which limb of the nephron loop is permeable to water and mostly impermeable to solutes
Ascending limb
Which limb of the nephron loop is mostly impermeable to water and solutes
contains active transport mechanisms for sodium and chloride ions
10-15%
What percent of initial filtrate volume reaches the DCT
tubular cells
What actively transports sodium and chloride ions out of tubular fluid at the distal convoluted tubule
distal portions contain ion pumps
Reabsorb tubular sodium ions in exchange for potassium ion
Aldosterone
This is produced by the adrenal cortex, which reduces sodium list in urine
controls ion pumps and channels for sodium
Parathyroid hormone and calcitriol
Circulating levels of these hormones regulate calcium ion reabsorption at the DCT
Water reabsorption
This occurs when osmotic concentration of peritubular fluid exceeds that of tubular fluid
Obligatory water reabsorption
Water movement that cannot be prevented
usually recovers 85% of filtrate produced
Facultative water reabsorption
Controls volume of water reabsorbed along DCT and collecting system
15% of filtrate volume
segments are relatively impermeable to water
except in presence of ADH
Antidiuretic hormone
Hormone that causes special aquaporins to appear in apical cell membranes
increases rate of osmotic water movement
Higher levels increase:
Number of water channels and water permeability of DCT and collecting system
Without this water is not reabsorbed
Vasa recta
Returns solutes and water reabsorbed in medulla to circulation without disrupting the concentration gradient
Solute Concentration increases as blood descends into medulla
Involves solute absorption and water loss
Blood flowing toward cortex:
Gradually decreases with solute concentration of peritubular fluid
Involves solute diffusion and osmosis
Solutes absorbed in descending portion don’t diffuse out in ascending portion
More water moves into ascending portion than is moved out of descending portion
Carries water and solutes out of medulla
Balances solute reabsorption and osmosis in medulla
Renal clearance
Volume of plasma the kidneys removes a particular substance from in a minute
Used to estimate glomerular filtration rate
C = UV/P
Cloudiness
What indicates infection in urine
clear, yellow color
What is the composition of normal urine
urobilin
What gives urine a yellow color (pigment)
4.5-8.0
What is the pH range of urine
Ureters
Pair of muscular tubes
Begin at renal pelvis
attached to posterior abdominal wall
penetrate posterior wall of the urinary bladder
Ureteral openings
Slit-like rather than rounded
helps prevent backflow when urinary bladder contracts
Inner mucosa, muscularis layer, adventitia
What are the 3 layers of ureter
Inner mucosa
Layer of the ureter:
Transitional epithelium and lamina propria
Muscularis layer
Layer of the ureter:
Longitudinal and circular bands of smooth muscle
peristaltic contractions force urine toward urinary bladder every 30 seconds
Adventitia
Layer of the ureter:
Outer connective tissue layer
Continuous with fibrous renal capsule of the kidney
Urinary bladder
Hollow, muscular organ
temporary reservoir for urine storage
Full bladder can contain 1 liter of urine
Peritoneal folds
Several of these stabilize and maintain bladder position
Ligamentous bands
Anchor urinary bladder to pelvic and pubic bone
Trigone
Triangular area formed by:
Openings of ureters and the entrance to urethra
Internal urethral sphincter
Acts as a funnel
Mucosa, submucosa, muscularis, adventitia
What are the 4 layers of urinary bladder
Urethra
Thin walled muscular tube that drains the urinary bladder
extends from urinary bladder to the exterior of the body
External urethral sphincter
Circular band of skeletal muscle
Voluntary control and acts as a valve
Voluntary relaxation permits micturition
Male urehtra
From urinary bladder to tip of penis
Regions of the male urethra
Prostatic urethra passes through prostate gland
Membranous urethra short segment that leaves pelvic cavity
Spongy urethra from pelvic cavity to external urethral orifice
Epithelial mucous glands form tubules that extend into lamina propria
Lamina propria anchor urethra to surrounding structures
Female urethra
Short
Extends from bladder to vestibule between labia
Lamina propria contains extensive network of veins
Complex is surrounded by concentric layers of smooth muscle
Volume greater than 500 mL
What triggers urination reflex
Efferent fibers
In pelvic nerves:
Stimulate neurons in wall of bladder
stimulates detrusor muscle contraction
Cerebral cortex
Allows for voluntary relaxation of external urethral sphincter
somatic muscles
causes relaxation of internal urethral sphincter
Hypernatremia
High levels of sodium
Dehydration, excessive intravenous NaCl
Thirst, confusion, lethargy progressing to coma, neuromuscular issues
Hyponatremia
Low levels of sodium
Solute loss, water retention
Neurological dysfunction, decrease in blood volume and pressure
Hyperkalemia
High levels of potassium
Renal failure, aldosterone deficit, severe tissue injury
Nausea, vomiting, cardiac arrhythmia, skeletal muscle weakness
Hypokalemia
Low levels of potassium
Inadequate dietary intake, excessive vomiting or diarrhea
Cardiac arrhytmia, metabolic alkalosis, mental confusion
Hypercalcemia
High levels of calcium
Hyperparathyroidism, renal disease
Decreased neuromuscular excitability, skeletal muscle weakness, kidney stones
Hypocalcemia
Low levels of calcium
Burn victims, hypoparathyroidism
Increased neuromuscular excitability, skeletal muscle cramps, convulsions