chapter 25 Flashcards
Functions of The Urinary System
Filter blood
Regulate volume and composition of the blood
Gluconeogenesis during fasting
Produce hormones
Renin (helps regulate blood pressure)
Erythropoietin (stimulates RBC production)
Metabolizes vitamin D from inactive form to active
Kidney Anatomy
Retroperitoneal Bean shaped Right slightly lower than left About the size of a large bar of soap Renal hilum Concave vertical cleft Leads to internal renal sinus Ureter, renal blood vessels, lymphatics and nerves enter here Adrenal glands sit on top
renal fascia
Perirenal fat capsule
fibrous capsule
Renal fascia Dense fibrous connective tissue Anchors kidney and adrenal gland Perirenal fat capsule Surrounds the kidney and cushions it Fibrous capsule Transparent, prevents infections from spreading to the kidney
Nephrons
The structural and functional units of the kidneys Over 1 million in each kidney Form the urine Empty into the collecting tubules Parts glomerulus A ball of capillaries renal tubule glomerular capsule (Bowman’s capsule) Cup shaped end of the renal tubule Has fenestrated endothelium renal corpuscle Glomerulus + Bowman’s capsule Filtrate Solute rich fluid from the blood (no protein) Urine made from this
Bowman’s Capsule Structure
Parietal layer
Simple squamous epithelium
Not involved in forming filtrate
Visceral layer
Clings to the glomerular capillaries
Podicytes
Highly branched modified epithelial cells
Foot processes intertwine and cling to the basement membrane of the glomerulus
Filtrations slits
Spaces between the foot processes
Allow filtrate to enter the capsular space
The rest of the renal tubule…
3 cm long Single layer of polar epithelial cells with basement membrane Three parts Proximal convoluted tubule (PCT) Loop of Henle U-shaped Descending Ascending Distal convoluted tubule Empty into the collecting ducts Run through the medullary pyramids and make them look striped
cortical nephrons
juxtamedullary nephrons
Cortical nephrons 85% Almost entirely in the cortex Part of loop of Henle dips into the outer medulla Juxtamedullary nephrons Concentrate urine Entire loop of Henle is in the medulla
Nephron Capillary Beds
Two capillary beds
Glomerulus
Specialized for filtration
Afferent arteriole and efferent arteriole
Peritubular
Arise from the efferent arteiole
Specialized for reabsorption
Vasa recta for juxtamedullary nephrons
Juxtamedullary Apparatus
Most distal part of the loop of Henle lies along the afferent arteriole (sometimes efferent too) Two important cells types in the JMA Granular cells Aka juxtamedullary cells Sense blood pressure and secrete renin In the arteriole Macula densa Chemoreceptors that sense NaCl in the filtrate
Urine Production
Three steps
glomerular filtration
tubular reabsorption
tubular secretion
Glomerular Filtration
Passive Due to hydrostatic pressure Fluids and small solutes forced out of the glomerulus Amazing filtration membrane Filtration rate=120-125 ml/min
Glomerular Filtrate
Water Ions Sodium, potassium, chloride Nitrogenous waste Urea, uric acid, creatine Organic molecules Glucose, amino acids
Tubular Reabsorption
Two reabsorption pathways
Most of the filtrate is quickly reabsorpted
Must cross the barrier formed by the tubular cells
Two reabsorption pathways
Transcellular (through cells)
Through the luminal and basolateral membranes
Most solutes are reabsorped through this pathway by diffusion or active transport
Paracellular (between cells)
Through tight junctions
Water and some ions use both
Blood Pressure is the driving force of glomerular filtration…what drives reabsorption?
Osmolarity of interstitium is
Blood Pressure is the driving force of glomerular filtration…what drives reabsorption?
Water reabsorption
Osmolarity of interstitium is increased
How-transport sodium into the interstitium
Sodium enables the reabsorption of most everything else
Osmomolarity is total concentration of all solute particles in a solution
Water moves from higher water concentration to lower water concentration
Counter current mechanisms maintain osmotic gradient
Ascending and descending limbs of Loop of Henle interact to maintain
Needed for
Ascending limb Creates the conditions need for the
Actively transports
Highest solute concentration near
Impermeable to
Ascending and descending limbs of Loop of Henle interact to maintain interstitial osmolarity gradient
Needed for urine concentration
Ascending limb
Creates the conditions need for the descending to function
Actively transports NaCl into interstitium
Highest solute concentration near the bottom
Impermeable to water
Tubular secretetion
Reabsorption in reverse Disposes of substances Certain drugs Eliminates undesirable end products that were reabsorped passively i.e. urea Rids excess K+ Controls blood pH
Counter current cont’d
Descending limb Concentrates
Filtrate concentrates to
Descending limb
Concentrates NaCl for ascending limb
Filtrate concentrates to 4X normal body fluid
Vasa Recta
How does the kidney retain the solutes?
How does the kidney retain the solutes?
They would be absorbed by normal capillaries but are not by the vasa recta, why?
They function as circulatory counter current exchangers
Loops deliver nutrients and oxygen
Then form hairpin loops to go from increasing osmolarity back to decreasing.
Urine
Color and transparency
Yellow due to
-Pigment by product of
Pink, brown
Cloudy
Color and transparency Clear, pale to deep yellow Yellow due to urochrome Pigment by product of hemoglobin destruction Pink, brown may be due to eating certain foods may be due to presence of bile pigments or blood Certain meds or vitamins Cloudy may indicate urinary tract infection
odor
Odor Fresh usually has little smell Develops an ammonia odor due to bacteria Some drugs and foods alter odor i.e. asparagus, brocholi Some diseases affect odor i.e. diabetes mellitus fruity smell
pH
Acidic
Alkaline-
pH Usually about 6 Health and diet can affect pH Range 4.5-8 normal Acidic- due to high protein diet Alkaline- due to vegetarian diet
urine Compostion
95% water
Next is urea
other nitrogenous waste
Uric acid, creatine
Solutes (in order of normal concentration most to least)
Na+, K+, PO43-, SO42-, creatine, uric acid, Ca2+, Mg2+, HCO3-
Ureters
Slender tubes that carry urine from the kidneys to the urinary bladder
Urinary Bladder
Collapsible muscular sac Temporarily stores urine Retroperitoneal Trigone Outlined by the three openings, area where infections “sit” Ureters enter inferiorly So a full bladder closes them off, prevents back flow Urethra exits inferiorly Detrusor muscle Rugae
How much can a bladder hold???
Very distensible!
Holds about 500 ml of urine when moderately full
Can hold about twice that much (800-1000 ml)
Can burst if over extended
Due to blockage, you cannot hold it long enough to burst your bladder, your body won’t let you
Urethra
Thin walled muscular tube Drains urine from the bladder Internal urethral sphincter At bladder-urethral junction Involuntary Prevents leaking when not voiding Contracts open and relaxes closed (weird right?) External urethral sphincter Surrounds the urethra as it passes through the urogenital diaphram Voluntary Works with the levator ani
Now to gender differences
Female 3-4 cm Bound to anterior vaginal wall External urethral orifice Anterior to vaginal opening Posterior to the clitoris
Male 20 cm Three regions Prostatic urethra 2.5 cm Within the prostate Membranous urethra Through urogenital diaphram 2 cm from prostate to the beginning of penis Spongy urethra 15 cm Passes through the penis and opens at the external urethral orifice at the penis tip Carries semen and urine
Micturition 3 thing must happen to allow micturition The detrusor muscle must The internal urethral sphincter must The external urethral sphincter must
AKA urination, voiding
The act of emptying the urinary bladder
3 thing must happen to allow micturition
The detrusor muscle must contract (open)
Involuntary
The internal urethral sphincter must open (relax)
Involuntary
The external urethral sphincter must open (relax)
Voluntary
In general low bladder volumes inhibit micturition and high volumes stimulate
Where most of the tubular reabsorption occurs so the fluid becomes more concentrated
Proximal convoluted tubule
Where the filtrate is formed
glomerulus
Blood vessels that receive the products being reabsorbed in the kidneys
pertitubal capillaries
Drains the distal convoluted tubule
collecting duct
Passive movement of water out of the tubule
descending limp of Nephron loop
Blood vessel that enters the glomerulus
afferent arteriole
Blood vessel that exits (drains) the glomerulus (unique!)
efferent arteriole
Establishes the medullary osmotic gradient
nephron loop
The structural and functional unit of the kidney
nephron
Bowman’s capsule plus glomerulus
renal corpuscle
Regulates systemic blood pressure by controlling filtrations rate and producing renin (granular cells) when the blood pressure drops
juxtaglomerular complex
