module 4: renal physiology Flashcards
what homeostatic function are the kidneys involved in
reg electrolytes, acid-base control, blood volume control, and regulation of blood pressure
ICF
fluid IN cells, 2/3 of body fluid
ECF
fluid AROUND cells (plasma, interstitial fluid, lymph, transcellular fluid)
1/3 of body fluid
plasma and interstitial fluid are separated by…
blood vessel walls
at the level of the capillaries how does everything in plasma, water, etc exchanged
freely exchanged with the interstitial fluid
the composition of plasma and interstitial fluid are essentially…
identical
what stands in btwn the ICF and ECF, what is not exchanged
the barrier is the plasma membrane that surrounds each cell in the body. ICF contains proteins that do not exchange with the ECF.
how does the barrier between ECF and ICF work
there is an unequal distribution of ions across this barrier. the barrier does not allow passive movement of either ICF or ECF constituents across the plasma membrane, preventing them from equilibrating through the process of diffusion
why is ECF volume regulated
to maintain blood pressure. maintenance of salt balance is important in the long-term regulation of ECF volume.
why is ECF osmolarity
to prevent the swelling or shrinkage of cells
Intracellular Fluid (ICF)
Stores 2/3 of the body water; fluid within the cells
Extracellular Fluid (ECF)
1/3 of body water; plasma (1/5) and interstitial (4/5) fluid
Transcellular Fluid
Water in epithelial-lined spaces; lymph, CSF, negligible amounts
what are compartment barriers
The “major pools” of water are separated by barriers
what are the 2 compartment barriers
Plasma/Interstitial Fluid Barrier
ICF and ECF Barrier
Plasma/Interstitial Fluid Barrier
Separated by the walls of blood vessels except at the capillaries where everything except for proteins are freely exchanged between plasma and interstitial fluid
Plasma/Interstitial Fluid composition (both ECF) are practically the same except for the proteins; changes in one reflect in the other pool because of the capillaries
ICF and ECF Barrier
The plasma membrane surrounding each cell which regulates what goes in and out of the cells; ICF has proteins that ECF does not, there is an uneven ion distribution
Ex., K+ and PO43- is ICF, Na+ and Cl- is ECF; no passive ion movement across for equilibrium
ECF Volume and Osmolarity
Ultimately, overall fluid balance in the body is dependent on regulating the ECF
Components exchanged in the ICF come from ECF water, other constituents
ECF Volume Regulation
Regulated to maintain blood pressure; salt balance also regulates volume
Direct influences on BP by changing plasma volume -> arterial BP is adjusted
ECF Short-Term Control
Minor changes; works with what you have
- Baroreceptor Reflex: Carotid artery/Aortic arch mechanoreceptors detect BP changes and signal ANS; increase total peripheral resistance/cardiac output when low, decreases when high
- Fluid Shifts: Fluids temporarily shift out of the interstitial fluid and into the plasma or vice-versa
ECF Long-Term Control
Larger, input/output changes
- Kidneys: Controls urine output and regulates fluid output
- Thirst Mechanism: Controls fluid input into the diet
ECF Salt Balance
Sodium and anions (Cl- + Bicarb) make up 90% of ECF solutes; water follows salt (osmosis)
Salt Input: Only dependent on dietary salt; we only need to replace 0.5g/day from feces/sweat
Average Canadian input is 3.5g of salt a day
Salt Output: Excess salt (~3.0g dietary) must be eliminated in the kidneys (feces/sweat = 0.5g)
Kidneys have the greatest role in output and control is very precise
ECF Osmolarity
A measure of the concentration of a solute in solution; high = more solute/less water
Water moves down its concentration gradient until osmotic pressure equalizes
This is highly regulated to prevent cell volume changes (swelling/shrinking)
Hypertonic
The solution has a higher solute concentration vs. another solution across a membrane
- Water flows into this solution to equalize solute concentration (less water)
- Water moves from the cells into the ECF (shrinking); has 3 main causes:
1. Diabetes Insipidus: Deficiency in ADH/vasopressin; no water retention
2. Insufficient Water Intake: Not drinking enough water
3. Excess Water Loss: Heavy sweating, extreme exercise, vomiting, diarrhea
Hypotonic
The solution has a lower solute concentration vs. another solution across a membrane
Water flows out from this solution to equalize solute concentration (more water)
Water moves from the ECF into the cells (swelling, burst); impairs cellular function, 3 main:
- Renal Failure: Cannot produce concentrated urine, must filter with dialysis to treat
- Rapid Water Ingestion: More water intake vs. amount kidneys can filter out at a time
- Oversecreted Vasopressin/ADH: Promotes water retention
Isotonic
The solution has equal osmolarity compared to normal body fluids; ex., N/S (NaCl 0.9%)
Injected into blood plasma within veins (1/5 ECF), it is isotonic, so no net fluid shift between ECF and ICF, prevents fluctuations in intracellular volume
No osmotic gradient = no net fluid shift
Water Balance Regulation: Hypothalamic Osmoreceptors
Constant brain monitoring of surrounding fluid osmolarity (plasma)
Increased Osmolarity: High conc., low fluids = Stimulates ADH/Vasopressin release, thirst
Decreased Osmolarity: Low conc., high fluid = Inhibits ADH/Vasopressin, no thirst
Vasopressin: Postpit hormone that acts on kidney tubule to increase water absorption
Thirst: Stimulates the intake of water through drinking
Water Balance Regulation: Left Atrial Volume Receptors
Monitors LA BP; activated during >7% ECF volume/BP loss
Receptors stimulate the hypothalamic ADH/Thirst pathways
Describe an overview of the kidneys
Organs that function to maintain the ECF volume, electrolyte composition, osmolarity
Has neural/endocrine (hormonal) inputs for control
Increases and reduces elimination in excess of water or electrolytes
Cannot actively correct a deficiency (can correct surplus); just slow down elimination
describe the structure of the kidneys
- ~10cm bean-shaped organs, each has an adrenal gland on top
- Has outer renal cortex (with nephrons), and inner renal medulla (renal pyramids, tubules)
- Inner core has a renal pelvis that channels urine into ureter towards the bladder
- Nephron: Functional unit of the kidney; filters blood, reabsorbs fluids/molecules, makes urine
~1,000,000 per healthy kidney
Kidney Major Functions
- Water Balance: Plasma volume regulation
- Body Fluid Osmolarity: Keeps the fluid isotonic to prevent fluid shifts
- Solutes: Regulates ECF solutes (Na+, K+, Cl-, Ca2+, PO43-); Acid-Base Balance
- Excretion: Metabolic waste excretion, ingested foreign compounds
- Hormonal: Produces erythropoietin (EPO), renin, vitamin D
What are the 6 vascular parts of the nephron
The portion that supplies blood to the nephron
1. Renal Artery: The artery through which blood enters the kidneys and further subdivides into:
2. Afferent Arteriole: Brings the blood into the nephron to the glomerulus (1:1 supply)
3. Glomerulus: A ball-like capillary that filters out solutes and water (plasma) from the blood
About 20% of blood is filtered and enters the renal tubules for filtrate concentration
Remaining 80% is not fully “filtered” until it leaves via renal vein
No gas exchange occurs at this capillary; arterial blood stays oxygenated
4. Efferent Arterioles: Arteriole that carries unfiltered blood (80%) from the glomerulus into the secondary capillary beds for further tubular exchange between the blood/filtrate
5. Peritubular Capillaries: Secondary capillary bed; gas exchange occurs, supplies oxygen to the renal tissues for perfusion
6. Renal Vein: Returns filtered blood back to the heart
the tubular component of the nephron
Carries the filtrate throughout the nephron until the renal pelvis as a continuous tube separated into several segments with distinct structures and functions
1. Bowman’s Capsule: Encircles the glomerulus; collects the fluid filtered from its capillaries
2. Proximal (Convoluted) Tubule: Highly coiled tube within the renal cortex after the capsule
3. Loop of Henle: Forms a hairpin loop that dips down into the renal medulla
Descending Loop: Travels from the cortex to the medulla
Ascending Loop: Travels from the medulla to the cortex, passes through the juxtaglomerular apparatus, a fork between afferent/efferent arterioles
4. Distal (Convoluted) Tubule: Another highly coiled tube within the renal cortex after the loop
5. Collecting Duct: A long duct that collects filtrate from nephron tubules, draining into pelvis
6. Renal Pelvis: Area in the kidney core that channels urine into the ureters to the bladder
what are the 2 nephron types
- cortical nephrons
- juxtamedullary nephrons
Cortical Nephrons
Glomeruli are in the outer cortical layers; about 80% of nephrons
- Serves secretory and regulatory functions
- Loops of Henle are short, only have slight medullary dips; peritubular capillaries wrap around it
Juxtamedullary Nephrons
Glomeruli are in the inner cortical layers; about 20% of nephrons
- Responsible for concentrating and diluting urine (via countercurrent exchange)
- Long loops of Henle deep in the medulla for urine concentration
- Peritubular capillaries form vasa recta hairpin loops close to the long loops for exchange
Glomerular Filtration (GF)
Only about 20% of blood flowing through the glomerulus is filtered into the capsule; protein-free but has all plasma solutes
The rest of the blood exits via the efferent arteriole and filtered by tubular secretion (80%)
Glomerular Filtration Rate (GFR)
Normally about 125mL formed per minute (125mL/min)
Tubular Reabsorption (TR)
Filtrate flowing through the tubules has many important substances returned to the capillaries through reabsorption
Also uses selective transfer of substances by mediator proteins
Tubular Secretion (TS)
Secondary route for blood substances to enter renal tubules
Allows for the selective transfer of substances from the capillaries to the tubules
This is where the remaining 80% of plasma contents are excreted from the blood
glomerulus
Capillary network at the nephron start; blood filters across its walls, through the membrane to form filtrate in Bowman’s Capsule to enter the tubules
Receives blood supply from afferent arterioles, exits via efferent arterioles
Glomerular Filtration Rate
The rate at which blood is filtered through all glomeruli
- Measures overall renal function; approximately 125mL/min men, 115mL/min women
Glomerular Filtration
The plasma passes through three layers making up the glomerular membrane
Glomerular Capillary Wall
Single layer of endothelial cells, but pores are large, 100x more permeable to fluids/solutes vs. normal capillaries
Everything except large plasma proteins (ex., Hb) pass; small proteins (ex., albumin) do
Basement Membrane
No cells; collagen network that provides structural strength, negatively charged glycoproteins that repel, discourage small protein filtration (albumin is negative)
Only 1% of filtered albumin actually passes into the capsule
Inner Layer of Bowman’s Capsule/Podocytes
Cells that wrap around the glomerular capillaries; forms narrow filtration slits that allow fluid to pass between, into Bowman’s capsule
Glomerular Capillary Blood Pressure
Pressure exerted by the blood in the glomerular capillaries
About 55mmHg (outwards), compared to 18mmHg in normal capillaries
Afferent arterioles = LARGE diameter vs. efferent, there is more resistance to blood leaving the glomerular capillaries as pressure is constant along its length (like big water, small hose)