the renal system Flashcards
what is the renal systems main job
- what is meant by an integrative system
- the major homeostatic control point for controlling H2O and Na+ reabsorption
- works with CVS and lymphatic system to help body maintain water balance.
4 functions
Removal of metabolic waste from blood and excreted in urine, eg. Urea, creatinine
Regulate h2o and electrolyte balance
Production of hormones and enzymes
Gluconeogenesis during prolonged fasting
structure of renal system
- basic structures
- blood flow
- what happens to the filtrate at the CD
- number of lobes each consists of an outer renal cortex and an inner renal medulla, nephrons flow between these sections
- renal artery, afferent arteriole, glomerular capillary, efferent arteriole, renal vein,
- CD deposits urine in renal pelvis, which leads to ureter connecting kidney to bladder
nephron
- what do they do, how many are there
- what makes up each nephron
- what tubule surrounds the glomerulus
- are functional units of the kidney for filtration. Each kidney has over 1 million.
- a renal corpuscle, which contains the glomerulus (which is a tuft of capillaries) and a renal tubule (PCT,LOH, DCT)
- bowman’s capsule
process of ultrafiltration at glomerulus
+ what is and isnt filtered
- Afferent arterial inflow into plexus (wider than efferent so creates high pressure forcing more molecules out of blood down pressure difference)
- Glomerulus plexus very porous and has podocytes (so lots of filtering/fluid moves out)
- Forms ultra-filtrate in Bowmans capsule
- Filtered- na+, glucose, amino acids, urea
Not filtered- RBC, large proteins (if they are, glomerulus is damaged- common with diabetes and hypertension, if untreat will lead to renal disease and failure)
what happens in the proximal convoluted tubule (2)
- role of parathyroid hormone
- Bulk reabsorption of solutes, eg. Na+ glucose, aa’s (by AT) and water (by diffusion)
into cells lining lumen then into surrounding blood vessels - Secretion of solutes (except k+) and organic acids (by AT)
- inhibits phosphate ion reabsorption
loop of henle
- where in the kidney is it
- what happens in each limb
- From cortex to medulla then back into cortex
- Bulk reabsorption of water via osmosis down water potential gradient in descending limb.
In ascending limb (impermeable to water) NaCl actively transported out, creating hyperosmolarity of medulla
distal convoluted tubule and cortical collecting duct
- where is it and what is filtrate like when enters
- what is reabsorbed
- what does aldosterone stimulate
- what does parathyroid hormone stim
- Back into cortex and Filtrate more concentrated as water has left
- Some Sodium chloride reabsorbed, but Most of what body needs has been reabsorbed
- na+ reabsorption and K+ secretion
- calcium ion reabsorption
cortical and medullary collecting duct
- what does it do
- what hormone affects permeability of the cd epithelial cells to water
- extra product reabsorbed
- Reabsorbs water by osmosis as it runs through hyperosmotic medulla back past LOH
- Anti diuretic/vasopressin hormones
- reabsorbtion of urea
summary of division of labour
- where is majority of reabsorption
- where is fine tuning of reabsorption and secretion
- pct and loh
- distal segments determining final amounts excreted
handling within the kidney
- how does a substance get into urine to be excreted
- what happens to a substance once its in the tubule
- what does this mean (calc)
- what happens to a foreign substance
- what happens if substance is retained but regulated within homeostatic range
- what happens if substance must be retained
- by glomerular filtration and/or tubular secretion
- its excreted or reabsorbed
- Amount excreted= Amount filtered + Amount secreted - amount reabsorbed
- completely removed, by filtering and Tubule secretion, 0 reabsorbed
- most retained and reabsorbed and some excreted
- completely reabsorbed
glomerular filtration (GFR)
- what is GFR
- whats a healthy GFR
- what does a lower than normal GFR indicate
- 4 factors affecting GFR
- how much of the plasma volume does the kidney filter a day
- amount of blood filtered by the glomeruli each minute.
- around 125ml/min
- a loss of functioning nephrons
- Capillary permeability
- Surface area of the capillary bed
- vasodilation/ constriction of arterioles around (constrict AA / dilate EA= reduced GFR)(dilate AA/constrict EA= increased GFR)
- Starlings forces - Hydrostatic pressure that drives fluid out of the capillaries VS Osmotic forces within the capillaries (caused by protein conc difference across wall), which oppose the exit of fluid.
Net filtration pressure (NFP)= ∆hydro - ∆osmotic - produce 180 L/day (125 ml/min)(Plasma volume ~3 L total so kidney’s filter the entire PV ~ 60x per day!)
2 ways GFR is regulated
- Myogenic autoregulation- The smooth muscle in the arteriolar walls responds to stretch by contracting, limits extent of increased arteriolar pressure, therefore GFR
- Tubulo-glomerular feedback- 1. If GFR rises, more NaCl delivered to the macula densa cells, resulting in vasoconstriction of the afferent arteriole that decreases GFR.
2. If GFR falls, less NaCl to macula densa cells resulting in increased GFR due to vasoconstriction of the efferent and vasodilation of afferent arteriole.
tubular secretion
- examples of substances that are secreted
- why is it important (4)
- hydrogen ion, potassium, and organic anions
1. disposing of drugs and drug metabolites.
2. eliminating undesired substances (urea and uric acid).
3. removing excess K+.
4. controlling blood pH.
tubular reabsorbtion-
- when does it begin
- how does it occur
- what processes does it occur by
- Begins when filtrate enters the tubule cells.
- Paracellular transport occurs through tight gaps between epithelial cells.
- Transport can be active (requires ATP) or passive (no ATP)
renal clearance
- what is renal clearance
- calculation
- what is required of a substance to estimate the rate of GFR at the glomerulus
- what 2 substances can we use to determine RC
- is amount of a substance filtered per minute, divided by its plasma concentration.
- RC=(U*V)/P
U=concentration of the substance in the urine (mg/mL) V=flow rate of urine formation (mL/min) P=concentration of substance in the plasma (mg/mL) - If the substance is freely filtered and not reabsorbed or secreted
- inulin and creatinine
filtration fraction
- what is the filtration fraction
- how to calculate
- what is a normal filtration fraction value
- The proportion of the plasma that enters the kidneys that is filtered at the glomerulus entering the renal tubules
- GFR/renal plasma flow (RPF)
- typically 0.16-0.2 (around 20% of blood entering is filtered)
fluid compartments of the body
- how much of our BW is water
- where is the water located
- makes up approx 60%
- 2/3 within cells (intracellular fluid)
- 1/3 outside cells (extracellular fluid- plasma and interstitial fluid)
total body balance of sodium
- how do we gain sodium, what is normal intake
- how do we lose it
- why must we balance it
- from food, intakes ranges from 0.05-25 g/day
- Lose sodium by sweat, faces, urine
- Must keep sodium balance equal as it determines extracellular fluid (ECF) volume. Ecf volume increases - we reabsorb less sodium and water reabsorption decreases.
total body balance of water
- how do we gain water, what is normal intake
- how do we lose it
- what happens when plasma osmolarity changes
- process when osmolarity increases (dehydration)
- from ingestion of fluid, foot metabolism, intake can range from 0.4-25l/day
- Lose water from breathing, sweat, faces, urine
- cells will either lose or gain fluid
- neurons in the hypothalamus- Release (ADH) that increases water reabsorption by the kidneys and Increase thirst. Vice versa if it decreases
what ensures intake=output
urinary output varying between 0.4 and 25 L/day
basic renal processes for sodium and water
- where does sodium reabsorption occur and what type of process is it
- how does water reabsorption occur and what is it mainly dependent on
- relationship between water reabsorption and sodium reabsorption
- an active process in tubular segments except descending limb of LOH and medullary CD
- by diffusion through aquaporins in proximal nephron and CD (only present with ADH in CD) and is dependent on sodium levels
- Sodium reabsorption creates osmotic difference across tubule which drives passive water reabsorption through epithelial cells into interstitial fluid
aquaporins and ADH
- function of aquaporins
- what does ADH do
- how does water enter body from CD cells
- how is ADH release regulated
- to increase water reabsorption from tubules
- uses cAMP systems causing vesicles to insert of AQP2 channels in luminal membrane, increasing passive diffusion/flow of water into the cell
- through AQP3 and AQP4 which are always present
- released from posterior pituitary gland which receives input from osmoreceptors (primarily) and baroreceptors
osmoreceptor control of ADH secretion
- what happens when more water is ingested
- reduces body fluid osmolarity (diluting blood with more water), reduces firing by hypothalamic osmoreceptors, so less ADH secreted by PPG, so tubular permeability low and less water reabsorbed so more water excreted (more dilute urine)
