The urinary system Flashcards
The urinary system is
one of the human body’s waste disposal units
* It carries out filtration and excretion
* Composed of the kidneys, ureters, bladder and urethra
* Helps to remove potentially harmful waste substances e.g. urea and alcohol
what is The kidneys
- Bean shaped organs about 11cm long
- Located against the back muscles in the upper abdominal area
- The right kidney sits a bit lower that the left kidney to
accommodate the size of the liver
Blood flow through the kidneys
- Blood flows into the kidneys through the renal artery
- Blood exits the kidneys through the renal vein
- The kidneys receive 20% to 25% of the cardiac output (about 1.0 to 1.1 litres per minute)
- Total blood volume is filtered every 40 minutes
what is the Cortex of the kedney
Outer granular region
what is the Medulla of the kidney
Inner striated region Subdivided into renal pyramids and columns
what is Renal Pelvis
-Central collecting cavity
- A funnel shaped cavity which connects the medulla to the ureter
what is Hilum
Concave centre of the kidney The point at which blood
vessels, lymphatic vessels, nerves and the ureter enter
the organ
Micturition function
- When 200ml collects in the bladder, the stretching stimulates the autonomic nerve ending in the bladder
- The walls contract
- The internal sphincter relaxes when the walls contract
- Urine empties in the urethra
function of Renal pelvis
Collects urine from the tubules in the medulla and
passes it to the ureter
the ureter function
Transport urine from the kidneys to the bladder
Bladder function
- Sac like organ in the pelvic cavity
- A reservoir for urine
Urethra function
Has an external sphincter which is voluntarily controlled by the CNS
Each kidney contains about a million very fine tubes
called ———–
called nephrons
* Each has its own blood supply
what is the The nephron
About 3cm in length composed of five functional regions:
1-The malpighian body
2- Proximal convoluted tubule
3- Descending and ascending limbs of the loop of Henle
4- Distal convoluted tubule
5- Collecting duct
The Malpighian body - ultrafiltration
- Adapted for the process of ultrafiltration
- The afferent arteriole is wider than the efferent arteriole
-Blood in the glomerulus is at high pressure - Capillary walls are permeable to water (fenestrae) and other substances
- Pressure pushes the fluid into the Bowman’s capsule
- Blood cells and most blood proteins are unable to pass through
- Volume of filtrate produced by both kidneys each minute = 115(W)−125(M) ml
- Averages 180 L/day males, 150L/day females
The proximal convoluted tubule - reabsorption
- The longest section of the nephron
- The wall is one cell thick
- Cells are packed with mitochondria
- The cell membrane in contact with the filtrate has a ‘brush border’ of microvilli, increasing the surface area
for uptake. - Most (65%) of the filtrate (salt and water) is reabsorbed here
Loop of Henle - reabsorption
- Fluid entering loop of Henle is isotonic to extracellular fluids
- A descending limb
- permeable to water
- no active transport
- An ascending limb
- impermeable to water
- Thick segment lined with Na+-K+ pumps
- Pumping of ions out of thick segment of ascending limb
creates osmotic gradient in interstitial fluid of the medulla
Distal convoluted tubule - reabsorption
- Cells of the distal convoluted tubule walls look identical to those of the proximal convoluted tube
- Selective reabsorption of ions, typically Ca2+, Mg2+,K+ and especially Na+ , occurs here
- Aldosterone from the cortex of the adrenal gland maintains a constant level of blood Na+
- Aldosterone acts directly on the kidney to decrease the rate of Na+ excretion (with accompanying retention of water), and to increase the rate of K + excretion.
Collecting duct – water regulation
- The permeability of the walls of the collecting duct to water is variable
- Impermeable to NaCl
- The permeability is controlled by antidiuretic hormone (ADH) secreted by the pituitary
Collection of fluid in the pelvic calyces
1-Each renal pyramid drains into a minor calyx
2-Minor calyces drain into major calyces
3-Major calyces drain into the renal pelvis
4-Urine empties into the ureter
Urine composition
Only 1% of the liquid filtered into the Bowman’s capsule is actually excreted as urine
* About 1.5l (minimum 0.5l)
* Composed of
- 96% water
- 2% urea
- 2% other substances
- Ammonia, sodium, potassium, phosphates,
chlorides, sulphates, excess vitamins
* Salts are excreted to maintain the correct balance of fluids and electrolytes
* Bilirubin gives the urine its colour
* Normal urine is acidic but may vary with diet
Kidney stones (renal lithiasis/nephrolithiasis)
- Hard deposits made of minerals and salts that form inside the kidneys
- Often form when the urine becomes concentrated allowing minerals to crystallize and stick together
- May cause a urinary infection if lodged in the urinary tract
- Symptoms include blood in the urine, severe pain in the groin or side, vomiting and nausea
Diabetes insipidus symptoms
-Impaired ADH production by the pituitary gland
-Large amounts of dilute urine
-Excessive thirst
-Amount of urine can be nearly 20 litres/day
-Urine does not contain glucose
Urinary tract infections
- A bacterial infection that affects any part of the urinary tract
- Most involve the bladder and urethra
- Women are at a greater risk of developing a UTI
- Symptoms may include a burning sensation when urinating, pelvic pain and a strong smelling urine
Cystitis
- An inflammation of the bladder
- Very common in women partly due to a shorter urethra
- Generally caused by a urinary tract infection
Kidney polycystic disease
- An inherited disorder
- Clusters of cysts develop primarily in the kidneys
- Kidneys enlarge and lose function over time
- Cysts may also develop in the liver and elsewhere
- May cause severe complications e.g. kidney failure
Duplicated ureters
(Duplex kidney)
- Two ureters from a single kidney
- Can drain independently into the bladder or connect and drain as a single ureter
- Can occur in one or both kidneys
- Most common renal abnormality
- Occurs in approximately 1% of the population
- May result in urine reflux
