LO8 Flashcards
Function of the urinary system
Main function: eliminate waste
products in the form of urine.
* Maintain body homeostasis.
* Compromised function can
affect the entire body.
* Includes: kidneys, ureters,
bladder & urethra
kidneys
Bean-shaped structures
* Located retroperitoneally (behind
the peritoneal cavity)
* Rt. Kidney slightly lower due to
the location of the liver.
* Adrenal glands lie on top of each
kidney.
* Renal pelvis: beginning of the
collecting system/collects and
transports urine
functions of the kidney
Urine formation
* Excretion of waste products
* Regulation of electrolytes
* Regulation of acid-base balance
* Control of water balance
* Control of blood pressure
* Renal clearance
* Regulation of red blood cell production
* Synthesis of vitamin D to active form
* Secretion of prostaglandins
* Regulations calcium and phosphorus balanc
kidney blood supply
The hilum (concave portion of the kidney):
* Area of entry for the renal artery & ureters
* Area of exit for the renal vein
* The kidneys receive 20-25% of total cardiac output.
* The renal artery divides into smaller vessels afferent arterioles
* Afferent arterioles form a glomerulus
* Glomerulus: capillary bed responsible for glomerular filtration.
* Glomerular Filtration: plasma filtered at the glomerulus into the
kidney tubules
nephrons
Each kidney has 1 million nephrons.
* Responsible for the formation of filtrate that becomes urine.
* If the total number of functioning nephrons is less than 20% of normal, renal
replacement therapy should be considered.
* Two types:
* Cortical nephrons
* Juxtamedullary nephrons
* Made up of two components:
* Filtering element – composed of an enclosed capillary network
(glomerulus)
* Tubule
glomerulus
Network of capillaries.
* Enclosed in a structure called Bowman’s
capsule.
* The glomerular membrane is composed
of three filtering layers.
* This membrane allows filtration of fluid
and small molecules and limits passage
of larger molecules (blood cells &
albumin).
* Pressure changes & permeability of the
membrane facilitate the passage of
fluids and substances from the blood
vessels – filling the space within
Bowman’s capsule
tubular componenent
Responsible for making adjustments in
the filtrate, based on the body’s needs.
* Begins in Bowman’s capsule.
* Filtrate travels into the proximal tubule
loop of Henle distal tubule
cortical or medullary collecting ducts.
* Distal tubular cells (macula densa),
function with adjacent afferent arteriole
and create the juxtaglomerular
apparatus – the site of renin production.
* Renin – hormone involved in the
control of arterial blood pressure.
Essential for functioning of the
glomerulus.
ureters
Long fibromuscular tubes that connect each kidney to the bladder.
* Originate at the lower portion of the renal pelvis and terminate in the trigone
of the bladder wall.
* Urine flows into the renal pelvis and then into the ureters.
* Left ureter is slightly shorter than the right.
* The linking of the ureters (urothelium) prevents reabsorption of urine.
* 3 narrowed areas of each ureter that are prone to obstruction by renal calculi
or stricture:
* Ureteropelvic junction – obstruction here is most serious due to close
proximity to the kidney and the risk of kidney dysfunction
* Ureteral segment near the sacroiliac junction
* Ureterovesical junction
urinary bladder
A muscular, hollow sac located just behind the pubic bone.
* Capacity of the adult bladder is 400-500 mL but can be distended to hold a
larger volume.
* Central hollow area is called the vesicle with two inlets (the ureters) and one
outlet (the urethra)
* Area surrounding the bladder neck is called the ureterovesical junction.
* The angling of the ureterovesical junction prevents backward flow of urine
from the bladder back towards the kidney.
* Contains 4 layers:
* Outermost layer – adventitia, made up of connective tissue
* Smooth muscle layer – detrusor.
* Submucosal layer – loose connective tissue
* Innermost layer – mucosal lining. Impermeable membrane to water and
prevents reabsorption of urine store in the bladder.
* Bladder neck contains bundles of involuntary smooth muscle – internal
sphincter.
* External urinary sphincter – an important portion that helps maintain
continence.
urethra
Arises from the base of the bladder
* Males: passes through the penis.
* Prostate gland lies just below the bladder neck & surrounds the urethra
posteriorly and laterally.
* Females: opens just anterior to the vagina
how is water balance regulated
Water balance is regulated by the kidneys and results in urine formation.
* Formed in the nephrons in a 3-step process:
1. Glomerular Filtration
2. Tubular Reabsorption
3. Tubular Secretion
function of the renal and urinary tract systems
urine formation- Blood flows into the glomerulus from an afferent arteriole and filtration occurs.
* The filtered fluid (filtrate) enters the renal tubules.
* Normally – about 20% of the blood passing through the glomeruli is filtered into the
nephron, amounting to about 180 L/day of filtrate.
* Filtrate consists of water, electrolytes, and small molecules.
* Efficient filtration depends on adequate blood flow through the afferent arteriole,
maintaining a consistent pressure through the glomerulus (hydrostatic pressure).
* Factors affecting hydrostatic pressure – hypotension, decreased oncotic pressure in the
blood, increased pressure in the renal tubules due to obstruction.
tubular reabsorption and tubular secretion
Second and third step of urine formation occurring in the renal tubules.
* Tubular reabsorption: substances move from the filtrate back into the peritubular
capillaries or vasa recta
* Tubular secretion: substances move from the peritubular capillaries or vasa recta
into tubular filtrate.
* Helps with the elimination of potassium, hydrogen ions, ammonia, uric acid, some
drugs, and other waste products
* 99% of the 180 L of filtrate produced each day is reabsorbed into the bloodstream
resulting in 1-2 L of urine each day.
* Reabsorption mostly occurs in the proximal tubule
* Reabsorption & secretion involve passive and active transport – may require the use of
energy
osmolarity and osmolality
Osmolarity refers to the ratio of solute to water.
* The regulation of salt and water is paramount for control of the
extracellular volume and serum/urine osmolarity.
* Degree of dilution or concentration of the urine is also measured in terms of
osmolality – number of particles dissolved per kilogram of solution.
regulation of water excretion
High fluid intake = a large volume of dilute urine is excreted and conversely
a low fluid intake = small volume of concentrated urine is excreted.
* A person normally ingests 1-2 L of fluid per day.
* 900 mL of ingested fluid is lost through the skin and lungs (insensible loss),
50 mL through sweat, and 200 mL through feces.
* Daily weight measurements are a reliable way to determine overall fluid
status. 1 kg = approx. 1 L.
antidiuretic hormone
Also known as vasopressin.
* Secreted by the posterior portion of the pituitary gland in response to
changes in osmolality of the blood.
* Decreased water intake = increased blood osmolality = stimulation of ADH
release.
* ADH acts on the kidney increase reabsorption of water and thereby
returning the osmolality of the blood to normal.
* Increased water intake = secretion of ADH is supressed and less water is
reabsorbed = increased urine volume (diuresis).
* A dilute urine with a fixed specific gravity or osmolality indicates an
inability to concentrate and dilute the urine common early sign of kidney
disease
regulation of electrolyte excretion
With normal kidney function, the volume of electrolytes excreted per day =
the amount ingested.
* Regulation of sodium volume excreted depends on aldosterone – a
hormone excreted from the adrenal cortex.
* Increased aldosterone in the blood less sodium excreted in the urine.
* Release of aldosterone is controlled by Angiotensin II which in turn is
controlled by Renin.
* This complex system is activated when the pressure in the renal arterioles
falls below normal levels:
* Shock
* Dehydration
* Decreased sodium chloride
* Activation of this complex system = retention of water and intravascular
volume = increased pressure to maintain glomerular filtration.
regulation of acid base balance
Normal pH is 7.35-7.45 & must be maintained for optimal physiological
function.
* The kidneys perform two major functions to maintain this balance:
* Reabsorb and return any bicarbonate from the urinary filtrate to the body’s circulation.
* Excrete acid in the urine
autoregulation of blood pressure
Specialized vessels of the kidney – vasa recta – constantly monitor blood
pressure as blood passes through the kidney.
* Decrease in blood pressure is detected juxtaglomerular cells (macula
densa cells) secrete Renin.
* Renin converts angiotensinogen angiotensin I angiotensin II, a
powerful vasoconstrictor.
* Vasoconstriction increases blood pressure.
* Adrenal cortex secretes aldosterone = increase in blood pressure.
* Vasa recta recognize the increased blood pressure and supress the
secretion of renin.
* Failure of this feedback mechanism is one of the primary causes of
hypertension
renal clearance
Refers to the ability of the kidneys to clear solutes from the plasma.
* Primary test for renal clearance – 24 hour urine collection.
* Depends on several factors:
* Speed of filtration across the glomerulus
* Amount of the substance that is reabsorbed along the tubules
* Among of the substance that is secreted into the tubules.
vitamin d synthesis
The kidneys are responsible for the final conversion of vitamin D to its
active form
excretion of waste products
The kidneys eliminate the body’s metabolic waste products.
* Major waste product is urea. Other excreted waste products include:
creatinine, phosphates, sulphates, and uric acid.
* The kidneys are the primary mechanism for excreting drug metabolites
