Urinary System Flashcards
What does the urinary system do and what are the components?
Components
- 2 kidneys
- 2 ureters
- urinary bladder
- urethra
Functions to…
- form urine and eliminate it
- process of urine formation assists in maintaining normal composition, volume, and pH of both blood and tissue fluid
What is the function of the kidneys?
Form urine to excrete:
- Waste products of cellular processes (urea, creatinine, and ammonia)
-Remnants from medications and foods we consume
The process regulates…
- BLOOD VOLUME by excretion or conservation of water
- The ELECTROLYTE CONTENT OF BLOOD via excretion or conservation of minerals
- The ACID BASE BALANCE OF THE BLOOD via excretion or conservation of ions such as H+ or HCO3 ions
- All of the above factors w/in Extracellular fluids
Where are the kidneys located?
Located in retroperitoneal space on either side of spine
- Upper portions of kidneys rest on lower surface of diaphragm
- Partially enclosed and protected by lower rib cage - Left kidney slightly higher than right
- Embedded in adipose tissue
- Provides cushioning
- Covered by renal fascia (fibrous CT)
- Holds kidneys in place and provides support
What is the hilus of the kidneys and what does it contain?
Located medially on kidneys
Site for entry for renal artery and exit for renal vein and ureter
Renal artery: branches off abdominal aorta
Renal vein: return blood to IVC
Ureter: carries urine from kidney to bladder
What are the layers of the kidneys?
Outer tissue layer: renal cortex
-> Comprised of renal corpuscles and convoluted tubules
Inner tissue layer: renal medulla
-> Comprised of loops of Henle and collecting tubules
-> Consists of wedge shaped regions called renal pyramids
- Tip of each pyramid is its apex or papilla
Medial area: renal pelvis
-> Cavity formed by the expansion of the ureter w/in kidney at the hilus
-> Calyces: funnel-shaped extensions of renal pelvis
- Enclose the papillae of renal pyramids
- Urine flows from renal pyramids -> calyces -> renal pelvis -> ureter
Blood vessels of the Kidney
- Blood flow through kidneys is essential in urine formation (blood plasma contributes to urine)
- 2 set of capillaries
-> provides 2 sites of fluid and solute exchange - Exchanges taking place b/w nephrons and capillaries will form urine from blood plasma
What happens in the Renal Corpuscle?
Consists of glomerulus surrounded by Bowman’s capsule
Glomerulus: capillary network ARISING from AFFERENT arteriole and EMPTYING into EFFERENT arteriole
-> diameter of efferent arteriole is smaller than afferent arteriole
- High BP in glomerulus (compared to other systemic capillaries)
Bowman’s capsule (glomerular capsule): expanded end of renal tubule
- Encloses the glomerulus
- Inner layer: made of podocytes with projections to glomerular capillaries
-> creates pores making the layer very permeable
- Outer layer: no pores and is NOT permeable
- Space btwn inner and outer layers contains renal filtrate that becomes urine
What happens in the Renal Tubule?
Continuation of Bowman’s capsule
Consists of…
- Proximal convoluted tubule
- Loop of Henle (aka loop of the nephron)
- Distal convoluted tubule
- Surrounded by peritubular capillaries receiving materials reabsorbed by renal tubules
- Distal convoluted tubules from several nephrons empty into a collecting tubule
- Several collecting tubules unite to form a papillary duct that empties urine into a calyx of the renal pyramid
What is the first step of Urine Formation?
Glomerular filtration
- Filtration is selective based on molecule size
-> Renal filtrate is similar to blood plasma (but less protein and no blood cells)
-> Waste products, some nutrients and minerals dissolved in plasma pass into renal filtrate
- BP of glomeruli is high compared to Bowman’s capsule
-> BP forces plasma, dissolved substances, and small proteins out of glomeruli and into Bowman’s capsules
-Creates renal filtrate
What is Glomerular filtration rate (GFR)?
- Amount of renal filtrate formed by the kidneys in 1 minute*
Avg 100-125 mL per minute
- Change in blood flow through kidneys alters GFR
-> INCREASED blood flow INCREASES GFR
-> INCREASES filtrate and urinary output
-> DECREASED blood flow DECREASES GFR
-> DECREASES amount of filtrate and urinary output
What is the 2nd step of urine formation?
Tubular reabsorption
- Renal tubules into peritubular capillaries (components of renal filtrate are reabsorbed back into blood via peritubular capillaries)
- Most renal filtrate is kept in the body
-> ~99% of filtrate is reabsorbed back into blood via peritubular capillaries
-> ~ 1% of the filtrate enters the renal pelvis as urine - Most reabsorption and secretion take place in PROXIMAL CONVOLUTED TUBULES
> Cells have microvilli to increase surface area - Distal convoluted tubules and collecting tubules are also sites for reabsorption of water
What are the mechanisms of tubular reabsorption?
Active transport
- Used to transport most materials from the filtrate to blood
-> Glucose, amino acids, vitamins, and POSITIVE IONS (+)
- Threshold level of reabsorption (limited amount tubules can remove from filtrate)
-> Exceeding the threshold causes substance to be excreted in urine
Passive transport
- Various NEGATIVE IONS (-) reabsorb into blood following POSITIVE IONS (+) due to attraction of opposite charges
Osmosis
- Reabsorption of water follows that of minerals, esp SODIUM IONS (where sodium is, water is)
Pinocytosis
- Small proteins transported back into blood
What is the 3rd step of urine formation?
Tubular secretion (peritubular capillaries -> renal tubules)
- Components of blood in peritubular capillaries are secreted into renal filtrate in renal tubules)
- Substances actively secreted from blood in peritubular capillaries into the filtrate in renal tubules
-> Waste products (ammonia, creatinine, etc)
-> Removal and excretion of excess H+ ions from blood
- Walls of collecting tubules have proton pumps in membranes
- Pumps can secrete H+ ions into renal filtrate against a very high concentration gradient
- Helps maintain normal pH of blood (H+ regulates pH, increase H+ acidic pH)
How does Antidiuretic hormone (ADH) (posterior pituitary) influence the kidneys?
Increases reabsorption of water from filtrate to blood
Decreases urinary output
How does Parathyroid hormone (PTH) (parathyroid glands) influence the kidneys?
Increases reabsorption of Calcium ions from filtrate to the blood and excretion of phosphate ions into filtrate
Does not directly influence urinary output
How does Aldosterone (adrenal cortex) influence the kidneys?
-Increases reabsorption of Sodium ions from the filtrate to the blood and excretion of Potassium ions into the filtrate
-> Water is reabsorbed following the reabsorption of sodium
Decreases urinary output
How does Atrial natriuretic peptide (ANP) (atria of heart) influence the kidneys?
Decreases reabsorption of Sodium ions
-> More sodium and water are eliminated in urine
Increases urinary output
What are other kidney functions?
- Renin secretion: secreted by juxtaglomerular cells in walls of Afferent arterioles
-> Decreased BP stimulates the kidneys to secrete renin - Erythropoietin secretion: secreted when blood oxygen level decreases
-> Stimulates and increased rate of RBC production - Activation of vitamin D: Converts vitamin D to vitamin D3 (calcitriol)
-> Calcitriol is most active form of vitamin D
- Increases absorption of calcium and phosphate in small intestine
Describe the Renin secretion mechanism
- Low BP is detected by the kidneys
- Angiotensinogen turns into Angiotensin I (renin turns angiontensinogen into angiotensin I, which is secreted by the juxtaglomerular cells)
- Angiotensin I turns into Angiotensin II (ACE turns Angiotensin I into Angiotensin II, from the lungs)
-> Angiotensin II causes VASOCONSTRICTION - Vasoconstriction stimulates the release of Aldosterone from the adrenal cortex
-> Aldosterone causes Sodium retention making water follow the sodium, Potassium is being secreted
-> causes an INCREASED BP and DECREASED URINARY OUTPUT
How is Urine eliminated?
Ureters, bladder, and urethra
- Responsible for periodic elimination of urine
- Each ureter extends from kidney hilus to the lower, posterior side of bladder
- Smooth muscle in wall of ureter contracts in waves to move urine toward bladder
- As the bladder fills, it expands
-> Compresses lower ends of ureters to prevent backflow of urine
What makes up the Bladder?
Bladder: muscular sac below peritoneum and behind the pubic bones
- Inferior to the uterus in females
- Superior to the prostate gland in males
Reservoir for accumulating urine and contracts to eliminate urine
-Muscosa layer: transitional epithelium
- Rugae: folds in the mucosa that allow for expansion
-Trigone: on floor of bladder; triangular area w/out rugae and doesn’t expand
-Detrusor muscle: smooth muscle layer of bladder wall
- Forms hollow sphere and volume decreases when detrusor contracts
- Detrusor fibers form internal urethral sphincter at entry to urethra (involuntary muscle)
What does the Urethra do?
Carries urine from the bladder to the exterior
-> External urethral sphincter comprised of skeletal muscle (voluntary control)
What is the Micturition Reflex?
Mediated by stretch reflex
- Spinal cord reflex with ability to exert some voluntary control over it
- Reflex stimulus = stretching of detrusor muscle
- Bladder holds up to 800mL of urine, but reflex is activated btwn 200-400mL
- Stretching generates sensory impulses to SACRAL SPINAL CORD
- Motor impulses return via PNS to detrusor muscle, causing contraction
-> Simultaneously, internal urethral sphincter relaxes - If external urethral sphincter is voluntarily relaxed, urine flows into urethra, and bladder empties
- Can prevent urination by voluntary contraction of external urethral sphincter
- UP TO A POINT
What are the characteristics of Normal Urine?
Amount
- 1-2 L per 24hrs
- Depends on fluid intake and water loss through skin and GI tract
Color
- Straw or amber; darker means more concentrated
- Should be clear, not cloudy
pH
- Avg: 6.0
- Range 4.6-8.0
- Diet affects urine pH
Components
- 95% water
- 5% salts and waste products
Nitrogenous wastes
- Urea: from amino acid metabolism
- Creatinine: from muscle metabolism
- Uric acid: from nucleic acid metabolism
Specific gravity: measure of the concentration
- Normal range: 1.010-1.025
- Lower the value, the more dilute the urine
