Module 11: Renal System 1st Half Flashcards
What is Tonicity? (3)
Hypotonic Solution:
-Lower concentration of solute than compared solution
Isotonic Solution:
-Same concentration of solute than compared solution
Hypertonic Solution:
-Higher concentration of solute than compared solution
What is included in the Renal System? (4 things)
Kidneys
Ureters
Bladder
Urethra
What does the Renal system regulate? (4 things)
1.Water balance
2. Electrolyte levels
3. pH of the blood
4. Long-term regulation of arterial pressure
Basic function of kidneys is to? (3 things)
- Remove nonessential substances (like waste metabolites, excess water, and electrolytes)
- Recover any essential substance (e.g., glucose)
- Kidney is an endocrine gland -> produces hormones or components of hormonal systems (EPO, renin, vitamin D)
Kidney Anatomy: What are the functional units?
Nephrons
-each nephron spans the cortex and medulla
What does the Kidney consist of? (7 things)
-Cortex (outer renal)
-Medulla (middle renal)
-Calyces (collect waste from the collecting ducts of nephrons)
-Renal Pelvis (collects urine and drains into the ureter)
-Ureter (travels into the bladder)
-Renal Artery and Vein
Nephrons function?
To filter the blood, reabsorb essential substances, and excrete nonessential molecules and waste
Vasculature of the Nephron (Blood Travel Path)
-Blood from the renal artery branches into several interlobar arteries that branch into arcuate arteries
-Blood from arcuate arteries flows through interlobular arteries and into the afferent arteriole
-Afferent arteriole gives rise to the glomerulus (where filtration occurs)
-Blood from the glomerulus enters the efferent arteriole
-Blood that enters the peritubular capillaries (network of capillaries surrounding the nephron) drains into the interlobular vein, arcuate vein, interlobar vein and back into the renal vein
What are the processes along the Nephron? (4 things)
Filtration:
-Movement of the fluid through the glomerular capillary due to hydrostatic pressures
Reabsorption:
-Movement of a substance from lumen of the nephron back INTO the blood
Secretion:
-Movement of a substance from the blood INTO the lumen of the nephron
Excretion:
-Removal of a substance from the body
Putting together:
Excretion = Filtration + Secretion - Reabsorption
What is Filtrate?
Is the solution created by filtration. Is composed of: water + all the dissolved solutes in blood (except large proteins)
-Contains same substances as plasma with exception of large proteins and RBCs
What does the Renal Corpuscle consist of?
-Glomerular capsules (Bowman’s capsule): surrounds a very small, high permeable capillary bed called the glomerulus
-Glomerulus
Glomerular Filtration?
Is facilitated by extremely permeable capillaries, which make up the glomerulus, and Starling Forces
What are Podocytes?
Special epithelial cells that surround the capillaries. They have large filtration slits that are formed between pedicles
What are Starling Forces?
Are the physical forces that determine the movement of fluid between capillaries and tissue fluid
Starling Forces in Renal System: (4 things)
- Hydrostatic pressure of Glomerular Capillary (or PGC) is ~60 mmHg, casing filtration of fluid into the glomerular capsule
- Colloid osmotic pressure of Glomerular Capillary (πGC) due to plasma proteins in glomerulus is -32 mmHg, causing reabsorption of fluid into the plasma.
- Hydrostatic pressure of Bowman’s Capsule (or PBC) is -18 mmHg, causing reabsorption of fluid
- Colloid osmotic force of Bowman’s capsule (πBC) causes filtration by presence of proteins in Bowman’s space (pressure = 0 since very few proteins are filtered)
Net Filtration Pressure = 60 + (-32) + (-18) = +10 mmHg out -> Positive number = filtration
What is Glomerular Filtration Rate (GFR)?
Is the volume of fluid that is filtered by the glomerulus during a certain period of time
What is Glomerular Filtration Rate (GFR)?
Is the volume of fluid that is filtered by the glomerulus during a certain period of time
What is Filtered Load? Equation?
The amount of substances filtered by the kidneys per day
Filtered Load = GFR x Plasma Concentration of the Substance
Amount Excreted Equation? (what is urine concentration?)
Amount Excreted = Urine Concentration x Amount of Water Excreted per Day (1.8 L/day)
Urine concentration is the amount of the solute that is excreted per unit volume of urine (g/L)
Amount Reabsorbed Equation?
Amount Reabsorbed = Filtered Load - Amount Excreted
Fraction Excreted Equation?
Fraction Excreted = (Amount Excreted / Filtered Load) x 100%
Reabsorption and Secretion involve a number of transport mechanisms which are: (5 ways)
- Active Transport
- Secondary Active Transport
- Facilitated Diffusion
- Simple Diffusion
- Osmosis
Reabsorption: 99% of substances filtered in the glomerulus are reabsorbed back into circulation via 2 transport routes:
- Paracellular Transport
- Transcellular Transport
Paracellular Transport
Tubular cells are joined together by tight junctions -> do NOT allow substances to cross between cells
Along the nephron, tight junctions vary and can be leaky. Some substances can diffuse between tubular cells by paracellular transport
Paracellular transport is non-regulated (without hormone control)
Transcellular Transport
Other substances are transported across tubular cell membranes from the lumen into the cell, then into the interstitial fluid and into the blood. This is transcellular transport
Can be regulated (increased or decreased) by hormones, but in most cases, they are non-regulated and occur without hormonal control
Reabsorption: Na+/K+ Pump
Is an active transport mechanism (requires ATP to move 3 Na+ OUT and 2 K+ INTO cell)
It establishes a concentration gradient for both ions across the cell membrane (HIGH conc. of Na+ outside, HIGH conc. of K+ inside)
This pump can power other transport mechanisms by secondary active transport
Secondary Active Transport
Uses the Na+ conc. gradient from the Na+/K+ pump
As Na+ moves into cell down conc. gradient, other substances will either move in with Na+ or move out in exchange with incoming Na+
Secondary Active Transporters include: (2 things)
- Na+/Glucose co-transporter
-is located on the luminal side of the tubule cells
-As each Na+ diffuses into the cells, 1 glucose molecule is carried with it - Na/H+ exchanger
-moves 1 H+ out of the cell for every Na+ that diffuses in
-located on the luminal side of the cells
What is Secretion?
Process which kidneys remove unwanted substances from the blood into the lumen of the nephron
Is generally hormonally regulated, but in some cases, can occur without hormonal control (non-regulated)
Most substances that are secreted are eventually excreted in urine
Secreted substances include H+ and K+
-relies on the Na+/K+ pump
What happens in the Proximal Convoluted Tubule? And how?
Reabsorption of Na+, Glucose, and Amino Acids
It reabsorbs ~66% of total filtrate
Due to Na+ conc. gradient (from Na+/K+ pump) Na+ can be reabsorbed into tubule cells by:
1.Simple Diffusion
2.Na+/Glucose co-transporter
3.Na/H+ Exchanger
Amino acids are reabsorbed by Na+/Amino Acid co-transporter -> similar to Na+/glucose
What is Diabetes Mellitus?
Nephron unable to reabsorb all glucose due to lack of insulin
-Glucose conc. builds up
-Large quantities of glucose are filtered by the glomerulus, and Na+/glucose co-transporter can’t reabsorb all of it
-Thus, SATURATION of glucose transporters in proximal tubule
-Some glucose will be excreted in the urine
Proximal Convoluted Tubule: Reabsorption of Water
Once Na+, glucose and amino acids are reabsorbed, the filtrate will have a LOWER solute conc. (and HIGHER water conc.) compared to cell and interstitial fluid
With this osmotic gradient + special water channels (aquaporins), water will move down conc. gradient by osmosis
Water is reabsorbed by paracellular and transcellular transport across the cells
IMPORTANT: water reabsorption happens ONLY AFTER solutes have been reabsorbed (particularly Na+)
Proximal Convoluted Tubule: K+ and Cl- Reabsorption
Solvent Drag:
-reabsorption of K+ (solute) with movement of water (solvent)
-when water is reabsorbed by osmosis, it carries some dissolved filtrate with it (e.g., K+)
Simple Diffusion:
-as water is reabsorbed, K+ conc. in filtrate becomes more concentrated
-K+ conc. gradient increases and K+ can move into interstitial space via simple diffusion
Cl- ions are reabsorbed in the proximal tubule by transcellular transport
Reabsorption of Filtrate Back into Circulation: Process?
Materials (Na+, glucose, and water) first leave the cells and enter interstitial space
Na+ leaves the tubule cells by the active Na+/K+ pump
Glucose and amino acids are transported across basal membrane of the tubule cells by specific facilitated diffusion transporters (K+ and Cl- are already in the interstitial fluid by paracellular transport)
Once in interstitial fluid, water and all substances are reabsorbed into circulation (peritubular capillaries) by Starling Forces
Net Filtration Pressure: Equation?
Net filtration pressure (NFP) = glomerular blood hydrostatic pressure (GBHP) – [capsular hydrostatic pressure (CHP) + blood colloid osmotic pressure (BCOP)
NOTE: After reabsorption of solutes & water:
The concentration of filtrate leaving proximal convoluted tubule will NOT be much different than when it entered (only a volume difference)
Means that the same proportion of water & solutes are being reabsorbed in the proximal convoluted tubule
