lecture 25 learning objectives Flashcards
Describe the major functions of the urinary system and which organs are responsible for those functions
The urinary system is responsible for the removal of metabolic waste, regulation of water, electrolyte balance, and blood pressure. Key organs involved are:
Kidneys: Filtration of blood, regulation of electrolyte balance, water balance, and acid-base balance, and secretion of hormones like erythropoietin and renin.
Ureters: Transport urine from the kidneys to the bladder.
Bladder: Stores urine until excretion.
Urethra: Transports urine from the bladder to the exterior of the body.
Identify and describe the anatomic structure of the kidney, including its coverings.
The kidney is a pair of bean-shaped organs located in the retroperitoneal space. The major structural components include:
Renal Capsule: A fibrous outer membrane that protects the kidney.
Renal Cortex: The outer region of the kidney where nephrons are found.
Renal Medulla: The inner portion, consisting of renal pyramids and columns.
Renal Pelvis: The funnel-shaped region that collects urine and directs it into the ureter.
Distinguish histologically between the renal cortex and the renal medulla.
Renal Cortex: Contains the renal corpuscles (Bowman’s capsule and glomerulus) and proximal and distal convoluted tubules. It appears granular under a microscope.
Renal Medulla: Consists of renal pyramids and the loops of Henle. It has a striated appearance due to the parallel arrangement of renal tubules.
Trace the path of blood flow through the kidney, from the renal artery to the renal vein.
o Renal Artery → 2. Segmental Artery → 3. Interlobar Artery → 4. Arcuate Artery → 5. Interlobular Artery → 6. Afferent Arterioles → 7. Glomerulus (Capillaries) → 8. Efferent Arterioles → 9. Peritubular Capillaries/Vasa Recta → 10. Interlobular Vein → 11. Arcuate Vein → 12. Interlobar Vein → 13. Renal Vein.
identify and describe the structure of a typical nephron, including the renal corpuscle (i.e.,glomerular [Bowman’s] capsule, glomerulus) and renal tubule (i.e., proximal convoluted tubule, nephron loop [loop of Henle], distal convoluted tubule).
o Renal Corpuscle: Composed of the glomerulus (capillary tuft) and Bowman’s capsule (encases the glomerulus).
Glomerulus – fenestrated capillary, Bowman’s capsule – surrounds the glomerulus
o Renal Tubule: Includes the proximal convoluted tubule (PCT), nephron loop (Loop of Henle), and distal convoluted tubule (DCT).
Identify and describe the vascular elements associated with the nephron (i.e., afferent and efferent arterioles, glomerulus, peritubular capillaries, vasa recta).
o Afferent Arterioles: Supply blood to the glomerulus.
o Efferent Arterioles: Carry blood away from the glomerulus.
o Peritubular Capillaries: Surround the renal tubules, involved in reabsorption and secretion.
o Vasa Recta: Specialized capillaries that serve the juxtamedullary nephrons, playing a role in maintaining the medullary concentration gradient.
Compare and contrast the anatomic structure of the cortical nephrons and juxtamedullary nephrons.
o Cortical Nephrons: Majority (85%) of nephrons, primarily located in the renal cortex.
o Juxtamedullary Nephrons: Fewer in number but crucial for urine concentration. They have long loops of Henle that extend deep into the medulla.
Trace the flow of filtrate from the renal corpuscle through the collecting duct.
o Filtrate flows from the Bowman’s capsule → proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting duct → papillary duct → renal pelvis.
Describe the three processes that take place in the nephron (i.e., filtration, reabsorption, and secretion) and explain how the integration of these three processes determines the volume and composition of urine.
o Filtration: Occurs in the glomerulus; plasma is filtered into Bowman’s capsule.
fluid from the blood is filtered into the capsular space
o Reabsorption: Occurs mainly in the proximal convoluted tubule, loop of Henle, and distal convoluted tubule, where substances like glucose, ions, and water are reabsorbed into the blood.
it reclaims water and takes things we want back into the blood
o Secretion: Additional wastes are secreted from the blood into the renal tubules, especially in the distal convoluted tubule.
put anything that we don’t need into the nephron tubule (we then urinate it)
Compare and contrast blood plasma, glomerular filtrate, and urine.
o Blood Plasma: The fluid portion of blood containing water, electrolytes, proteins, and nutrients.
o Glomerular Filtrate: The fluid filtered from blood that enters the Bowman’s capsule, similar to plasma but lacks large proteins.
o Urine: The final product, containing waste products (e.g., urea, creatinine) and excess water/electrolytes, after reabsorption and secretion.
where does filtration happen
only in the glomerulus
- filtration will occur across the filtration membrane
- will be done with fenestrated capillaries so that let out water and small solutes
For any solute, explain how renal filtration, reabsorption, and secretion determine the excretion rate of that solute.
o The excretion rate of any solute is determined by the filtration rate (how much is filtered), reabsorption rate (how much is reabsorbed into the blood), and secretion rate (how much is secreted into the filtrate).
what does a podocyte do
Podocytes, specialized cells in the kidney glomerulus, are essential for maintaining the integrity of the kidney filter, and their function is primarily based on their intricate structure, including foot processes
Describe the filtration structures that lie between the lumen of the glomerular capillaries and the capsular (Bowman) space
The filtration barrier consists of:
Fenestrated Endothelium: Allows fluid and small solutes to pass through but prevents blood cells.
Basement Membrane: A gel-like structure that restricts large proteins.
Podocytes: Cells with foot processes that further restrict large molecules from passing through.
Define glomerular filtration rate (GFR) and explain the role of blood pressure, capsule fluid pressure, and colloid osmotic (oncotic) pressure in determining GFR.
GFR is the volume of filtrate produced by the kidneys per minute (usually 125 mL/min).
o Influenced by:
Blood pressure: Higher pressure increases GFR.
Capsular Fluid Pressure: Higher pressure decreases GFR.
Colloid Osmotic Pressure: Higher osmotic pressure in the blood (due to proteins) reduces GFR.
Describe factors that can change blood pressure, capsule fluid pressure, and colloid osmotic (oncotic) pressure and thereby change glomerular filtration rate (GFR).
o Blood pressure: Increased blood pressure raises GFR.
o Capsule Fluid Pressure: Increased pressure in the capsule reduces GFR.
o Colloid Osmotic Pressure: An increase in plasma proteins raises osmotic pressure and decreases GFR.
Identify the location, structures and cells of the juxtaglomerular complex and discuss its significance.
The juxtaglomerular complex (JGC) is located at the junction of the distal convoluted tubule and the afferent arteriole. It includes:
Macula densa: Cells in the distal tubule that sense sodium levels and regulate GFR.
Juxtaglomerular cells: Secrete renin in response to low blood pressure or sodium levels.
Explain the role of the juxtaglomerular Complex in tubuloglomerular feedback.
The juxtaglomerular complex plays a key role in tubuloglomerular feedback:
When the macula densa detects low sodium concentration in the distal tubule, it signals the juxtaglomerular cells to release renin, triggering the renin-angiotensin-aldosterone system (RAAS), which increases blood pressure and GFR.
- Net filtration pressure = pressure out - pressure in
o Hydrostatic pressure
o Osmotic pressure
- Glomerular Filtration rate (125 mL/min)
o How much is being filtered through the nephrons
intrinsic versus extrinsic GFR factors
Intrinsic
o Myogenic: controlling muscles to control pressure
o Tubuloglomerular feedback: increase GFR = less NaCl reabsorption
Macula densa senses NaCl levels → releases vasoconstrictors (reduce blood flow)
Extrinsic
o RAAS
Juxtaglomerular cells release renin (increase BP)
Macula densa gives the signal to the juxtaglomerular cells
o Nervous system
Sympathetic nervous system release NE → constricting → higher BP
tubular reabsorption
Tubular Reabsorption
Direction of Solute Movement: Movement of solutes from the filtrate (inside the nephron) back into the bloodstream (peritubular capillaries).
Key Locations:
Proximal convoluted tubule (PCT): Most reabsorption occurs here (e.g., glucose, amino acids, Na+).
Loop of Henle: Water is reabsorbed in the descending limb, while Na+ is reabsorbed in the ascending limb.
Distal convoluted tubule (DCT) & Collecting duct: Reabsorption of Na+, water, and other ions like calcium and chloride occurs.
Process Involved: Active transport (e.g., Na+/K+ pump), facilitated diffusion, osmosis.
what is reabsorption
- Mostly happen in PCT, some in DCT
- We use the peritubular capillaries surrounding the area to bring back reabsorbed nutrients and fluids back to circulation
- Vasa recta surrounds the nephron loop
- We also use ATP
- Our nephrons can only reabsorb at certain point (Transport Maximum)
o Any excess goes to urine
tubular secretion
Direction of Solute Movement: Movement of substances from the blood (peritubular capillaries) into the filtrate (nephron tubules).
Key Locations:
Proximal convoluted tubule (PCT): Secretion of substances like H+, drugs, and urea.
Distal convoluted tubule (DCT): Secretion of K+ and H+ in exchange for Na+ (regulated by aldosterone).
Process Involved: Active transport, countertransport (e.g., Na+/H+ exchange), facilitated diffusion.
in secretion where are things lost
Everything that’s lost in urine
o Certain drugs that bind to plasma proteins
o Urea-nitrogenous waste
o Excess K+
o Creatinine
o H+ or HCO3
o Diuretics: those that enhance urine output
Alcohol, caffeine, lasix (furosemide)
Describe specific mechanisms of transepithelial transport that occur in different parts of the nephron (e.g., active transport, osmosis, facilitated diffusion, electrochemical gradients).
Active Transport
Example: Na+/K+ pump in the PCT and DCT, actively pumping Na+ out of the cells and K+ into cells.
Facilitated Diffusion
Example: Glucose reabsorption in the PCT via GLUT transporters. No energy required, but transport proteins are needed.
Osmosis
Example: Water reabsorption in the PCT and descending limb of the loop of Henle. Water moves through aquaporins in response to osmotic gradients.
Electrochemical Gradients
Example: Na+ movement across the nephron creates electrochemical gradients that enable transport of other ions (Cl-, K+).
