Ch 25 The Urinary System Flashcards
What are the primary functions of the kidneys?
- Regulating total water volume and total solute concentration in water
- Regulating ion concentrations in extracellular fluid (ECF)
- Ensuring long-term acid-base balance
- Excreting metabolic wastes, toxins, drugs
- Producing erythropoietin (regulates RBC production) and renin (regulates BP)
- Activating vitamin D
- Carrying out gluconeogenesis, if needed during prolonged fasting
Erythropoietin regulates blood pressure, while renin regulates red blood cell production.
What structures are included in the urinary system?
- Kidneys
- Ureters
- Urinary bladder
- Urethra
The kidneys are the major excretory organs, while the ureters transport urine to the bladder, which serves as a temporary storage reservoir.
What are the three layers of supportive tissue surrounding the kidney?
- Renal fascia (outer layer of dense fibrous connective tissue that anchors the kidneys)
- Perirenal fat capsule (fatty cushion midlayer)
- Fibrous capsule (inner layer that is a transparent capsule that prevents the spread of infection to kidneys)
The renal fascia is a dense fibrous connective tissue, the perirenal fat capsule provides cushioning, and the fibrous capsule prevents infection spread.
What are the three internal regions of the kidney?
- Renal cortex
- Renal medulla
- Renal pelvis
The renal cortex is the superficial region, the renal medulla contains the pyramids, and the renal pelvis is the funnel-shaped area leading to the ureter.
What is the pathway of urine flow in the kidney?
Renal pyramid → minor calyx → major calyx → renal pelvis → ureter
This sequence illustrates how urine is collected and transported out of the kidney.
What is the blood supply path to the kidneys?
Arteriol flow:
Aorta → Renal artery → Segmental artery → Interlobar artery → Arcuate artery → Cortical radiate (interlobular) artery →
Nephron-associated blood vessels:
Afferent arteriole → Glomerulus capillaries → Efferent arteriole → Peritubular capillaries or vasa recta →
Venous flow:
cortical radiate vein → arcuate vein → interlobar vein → renal vein → Inferior vena cava
The kidneys receive about one-fourth (1200 ml) of the cardiac output each minute.
Arteriol and venous flow are opposite to each other except venous flow has no segmental artery
What are the two main parts of a nephron?
- Renal corpuscle
- Renal tubule
Each nephron is responsible for urine formation and consists of these two parts, with the renal corpuscle located in the cortex and the renal tubule extending from the cortex into the medulla and then back into the cortex
What are the components of the renal corpuscle?
- Glomerulus : tuft of capillaries that allows for formation of filtrate, plasma-derived fluid that renal tubules process to form urine (urine precurser)
- Glomerular (Bowman’s) capsule: cup-shaped, hollow struture surrounding the glomerusus
The glomerulus is a tuft of capillaries, while the Bowman’s capsule surrounds it and collects filtrate.
What are the three major parts of the renal tubule?
- Proximal convoluted tubule (PCT)
- Nephron loop
- Distal convoluted tubule (DCT)
The renal tubule processes the filtrate and returns substances to the blood.
What is the function of the proximal convoluted tubule (PCT)?
Reabsorption and secretion
The PCT is lined with cuboidal cells that have microvilli to increase surface area.
What are the two limbs of the nephron loop?
- Descending limb
- Ascending limb
The descending limb is continuous with the proximal tubule, while the ascending limb includes both thick and thin segments.
What is the primary function of the distal convoluted tubule (DCT)?
Secretion
The DCT is characterized by cuboidal cells with few microvilli and is primarily involved in the secretion of substances.
What are the two cell types found in collecting ducts?
- Principal cells
- Intercalated cells
Principal cells maintain water and Na+ balance, while intercalated cells help maintain acid-base balance.
What are the two major groups of nephrons?
- Cortical nephrons
- Juxtamedullary nephrons
Cortical nephrons are primarily located in the cortex, while juxtamedullary nephrons are important for producing concentrated urine.
What is the glomerulus specialized for?
Filtration
The glomerulus is unique as it is fed and drained by arterioles, which allows for high-pressure filtration.
What is the role of peritubular capillaries?
Reclaim filtrate
These capillaries surround the renal tubules and are adapted for absorption of water and solutes.
What is the function of vasa recta?
Formation of concentrated urine
Vasa recta are associated with juxtamedullary nephrons and run parallel to the nephron loops.
What is the juxtaglomerular complex (JGC)?
A structure involving modified portions of the nephron and arterioles
The JGC regulates the rate of filtrate formation and blood pressure.
What are the three cell populations in the JGC?
- Macula densa
- Granular cells (JG cells)
- Extraglomerular mesangial cells
Each cell type plays a role in sensing NaCl concentration, blood pressure, and signaling.
What is the glomerular filtration rate (GFR)?
Volume of filtrate formed per minute by both kidneys (normal = 120–125 ml/min)
GFR is crucial for kidney function and is influenced by net filtration pressure and surface area.
What are the three processes involved in urine formation?
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
These processes adjust blood composition and produce urine.
What is the main force driving glomerular filtration?
Hydrostatic pressure in glomerular capillaries (HPgc)
HPgc is typically around 55 mm Hg, which is higher than in most capillary beds.
What is the net filtration pressure (NFP)?
Sum of forces promoting and opposing filtrate formation
NFP is calculated as HPgc minus inward pressures, e.g., HPcs and OPgc.
What are the intrinsic controls of GFR?
- Myogenic mechanism
- Tubuloglomerular feedback mechanism
These mechanisms help maintain GFR within a normal range despite fluctuations in blood pressure.
What is the role of the sympathetic nervous system in regulating GFR?
Overrides renal intrinsic controls to increase blood volume and pressure
Under low ECF volume conditions, sympathetic stimulation leads to vasoconstriction and decreased GFR.
What is the renin-angiotensin-aldosterone mechanism?
Main mechanism for increasing blood pressure
Renin is released by granular cells in response to various stimuli, leading to angiotensin II production and increased blood pressure.
What is the effect of adenosine and prostaglandin E2 on renal arterioles?
They act as paracrines affecting renal arterioles
These chemicals are released by renal cells.
What is tubular reabsorption?
A process that reclaims most tubular contents and returns them to blood
It is a selective transepithelial process.
What substances are almost entirely reabsorbed during tubular reabsorption?
- Organic nutrients (glucose and amino acids)
- Water
- Ions
Reabsorption is hormonally regulated and adjusted.
What are the two routes substances can follow during tubular reabsorption?
- Transcellular
- Paracellular
These routes describe how substances move through tubule cells or between them.
Describe the transcellular route in tubular reabsorption.
Solute enters apical membrane, travels through cytosol, exits basolateral membrane, enters blood
This route is essential for the movement of solutes into the bloodstream.
What occurs during tubular reabsorption of sodium?
Na+ is reabsorbed via primary active transport and secondary active transport
Na+-K+ ATPase pumps Na+ into interstitial space.
What is the role of aquaporins in water reabsorption?
Facilitates water reabsorption by osmosis
Aquaporins are present in the proximal convoluted tubule and regulated by ADH in collecting ducts.
What is the transport maximum (Tm)?
The maximum rate of reabsorption for a substance due to the number of carriers available
When carriers are saturated, excess is excreted in urine.
What happens in the proximal convoluted tubule?
Site of most reabsorption; reabsorbs all nutrients, 65% of Na+ and water, many ions, almost all uric acid
It is crucial for reclaiming essential substances.
What is the function of the nephron loop?
Regulates water and solute movement: descending limb allows H2O out, ascending limb allows solutes out
This structure is vital for urine concentration.
What hormones regulate reabsorption in the distal convoluted tubule and collecting duct?
- Antidiuretic hormone (ADH)
- Aldosterone
- Atrial natriuretic peptide
- Parathyroid hormone
These hormones adjust water and ion reabsorption based on body needs.
What is tubular secretion?
The process of moving selected substances from peritubular capillaries into the filtrate
It helps eliminate waste and control blood pH.
What is the normal osmotic concentration maintained by kidneys?
Approximately 300 mOsm
This reflects the number of solute particles in body fluids.
What are the two types of countercurrent mechanisms in the kidneys?
- Countercurrent multiplier
- Countercurrent exchanger
These mechanisms work together to establish and maintain the medullary osmotic gradient.
How does the countercurrent multiplier function?
Involves filtrate flow in opposite directions and differences in permeabilities
It creates an osmotic gradient essential for urine concentration.
What is the impact of dehydration on urine concentration?
Produces small volume of concentrated urine with maximal ADH release
Urine can reach ~1200 mOsm in severe dehydration.
What are diuretics?
Chemicals that enhance urinary output
Examples include ADH inhibitors and Na+ reabsorption inhibitors.
What is renal clearance?
Volume of plasma kidneys can clear of a particular substance in a given time
It is used to determine GFR and assess kidney function.
What is the typical chemical composition of urine?
- 95% water
- 5% solutes (urea, uric acid, creatinine)
Abnormal concentrations may indicate pathology.
What indicates a cloudy appearance in urine?
May indicate urinary tract infection
Normal urine is typically clear.
What is the typical pH range of urine?
Approximately 4.5 to 8.0
Diet and conditions can influence urinary pH.
What are the physical characteristics of the bladder?
Distensible, collapses when empty, expands during filling
A moderately full bladder can hold ~500 ml.
What is the role of the ureters?
Transport urine from kidneys to bladder
They prevent backflow of urine as bladder pressure increases.
What is micturition?
The act of urination or voiding
It involves the muscular tube (urethra) draining the urinary bladder.
What is the renal medulla composed of?
Medullary (renal) pyramids that are made up of:
1. Papilla - tip of pyramid that points internally
2. renal columns - separate renal pyramids
These make up lobes which are the medullary pyramid and its surrounding cortical tissue. There about 8 lobes per kidney
What is the renal pelvis made up of?
Minor calyces that collect urine from pyramidal papillae and funnel it to major calyces which empty urine into the renal pelvis
There are about 2 to 3 major calyces and each one has multiple minor calyces that funnel into them. From the renal pelvis the urine goes to the uterer.
What is the nerve supply to the kidneys?
via autonomic fibers from renal plexus
Function of nephrons
- Recover needed chemicals
- Secrete unneeded chemicas into filtrate →collecting duct → renal pelvis
We have about 1 million nephrons per kidney
Glomerular (Bowman’s) capsule consists of two layers:
- Parietal layer: simple squamous epithelium for structure
- Visceral layer: clings to glomerular capillaries and contains podocytes. Contain foot processes that cling to basement membrate with filtration slits between the foot processes that allow filtrate to pass into capsular space.
HP gc
Hydrostatic pressure in glomerular capillaries. This is the chief force pushing water and solutes out of blood and thus is usually high around 55 mm Hg (vs 26 mm Hg in most capillary beds)
essentially glomerular blood pressure
HP cs
Hydrostatic pressure in capsular space. Filtrate pressure in capsule of around 15 mm Hg. This is an inward force that works to inhibit filtrate formation
OP gc
Colloid osmostic pressure in capillaries. The pull of proteins in blood. This creates pressure from proteins in blood pulling water into the vessels. Around 30 mm Hg. Force inhibiting filtrate formation
NFP
Net filtration pressure. This is the sum of forces for filtrate formation.
HP gc - HP cs +OP gc = NFP
55 mm Hg - 15 mm Hg + 30 mm Hg = 10 mm Hg of outward force to create filtrate
The main controllable factor determing GFR (glomerular filtration rate)
GFR
Golmerular filtration rate
volume of filtrate formed per minute by both kidneys
Normal= 120 to 125
Directly proportional to :
* NFP in which the primary pressure is the HP gc (Primary variabe in GFR
* Total surface area available for filtration which is controled by the glomerular mesangial cells contration
* Filtration membrate permeability
Extrinsic controls
Nervous system and endocrine system
Goal is to maintain systemic BP
Increased GFR > Increased urine output > Decreased blood volume > Lowers
Intrinsic Controls
Renal autoregulation to maintain a constant GFR in kidney
Two types of renal autoregulation:
* Myogenic mechanism
* Tubuloglomeru
Myogenic mechanism
When stretched (increased BP), the local smooth muscle contracts to restrict blood flow from the afferent arterioles and into the glomerulus. This lowers the HPgc to maintain the NFP and GFR and thus protects the glomeruli from being damaged by high BP.
▲BP →▼afferent diameter→▼HP gc →normal NFP and GFR
▼BP →▲afferent diameter →▲HP gc → normal NFP and GFR
Tubuloglomerular Feedback Mechanism
Directed by macula densa cells in the JGC that responds to NaCl concentration in the ascending limb
