EXAM 3: SEC 3/Kidneys Flashcards Preview

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Flashcards in EXAM 3: SEC 3/Kidneys Deck (64):

Function of the kidneys

- regulation of water, inorganic ion balance, and acid-base balance (in corp with lungs)
- removal of metabolic waste products and foreign chemicals from the blood and their excretion in urine
- gluconeogensis


Production of hormones/enzymes

- erythropotetin which controls erythrocyet production
- renin, enzyme that controls formation of angiotensin and influences blood pressure and sodium balance
- 1, 25 - dihydroxyvitamin D influences calcium balance


Urinary components

- ureters, bladder, urethra


main function of ureters

- transport urine from kidneys to bladder


main function of bladder

-stores urine until voided from body



- carry urine from bladder to the outside of the body



- structural and function units of kidneys
- each kidney has over 1 million
- each consists of a glomerulus (tuft of capillaries) and a renal tubule
- tubule forms cup around glomerulus called glomerular/Bowman's capsule


Juxtaglomerular Cells

- in arteriole wall the granular cells (JG) are enlarged smooth muscle cells that have secretory granules which contain the hormone renin
- JG cells are mechanoreceptors (sense BP) in afferent arteriole


Macula Densa

- group of tall, closely-packed cells that are adjacent to JG cells
- macula densa cells are chemoreceptors that respond to changes in NaCl content of filtrate


Juxtaglomerular Apparatus

- JG cells and Macula densa work in tandem and are critical regulators of blood pressure


Gross Anatomy

- paired kidneys form a filtrate of the blood that is modified by reabsorption and secretion ; urine designated for excretion moves along ureters to bladder


Renal cortex

- the outer layer of kidney and is site of glomerular filtration, as well as convulated tubules


Renal Medulla

- inner part of kidney and is located along longer loops of Henle
- drainage of the collecting ducts into renal pelvis and ureter



- capillaries of glomerulus are fenestrated, which allows large amounts of solute-rich fluid to pass - there shouldn't be lots of protein in urine!
- inner layer contains highly modified branching epithelial cells called podocytes
- contains smooth muscle like cell = glomerular mesangial cell



- terminate in foot processes which surround the basement membrane of glomerulus
- the clefts between the foot processes are called filtration slits = where filtrate enters capsular space


Glomerular Mesangial Cell

- help regulate blood flow in glomerulus by contraction and engulf macromolecules that get hung up during filtration


Juxtamedullary nephrons overview

- long loop henle
- involved in concentration of urine
- found at border between cortex and medulla
- about 15% of all nephrons are in this category


Cortical nephrons overview

- most nephrons fall in this category
- short loop of henle


Basic renal processes for sodium and water

- sodium reabsorption is active process occurring in all tubular segments except descending limb of loop of henle
- water reabsorption is by diffusion and is dependent upon sodium reabsorption
- water moves through aquaporin channels. pressure of awuaporin varies throughout the tubule segments
- highly expressed in proximal nephron
- absent in collecting ducts unless anti-diuretic hormone ADH active


Concentration of urine concentrations and volume

- kidneys maintain plasma osmolarity at 300 mOsm
- it does this through countercurrent mechanisms (fluid in one tube flows oppositely of adjoining tube)


Why countercurrent works

- descending loop of henle is relatively impermeable to solutes and freely permeable to water
- ascending limb is permeable to solutes, not water
- urea recycling contributes to medullary osmotic gradient


Dilute Urine

- urine is normally diluted as moves through the ascending limb of loop of Henle
- to secrete dilute urine, DCT and collecting duct cells secrete substances and then kidney just leaves it alone
- osmolarity as low as 70 mOsm


Glucose concentration/secretion

- the reabsorption of many organic substances such as glucose is accomplished with transport proteins
- when concentration exceeds the capacity of the transporters, the excess is excreted in the urine


Capillaries Associated with Nephrons

- nephrons are associated with 2 sets of capillaries
- glomerular
- pertibular


Glomerular capillaries

- specialized for filtration
- only capillaries in body that are fed and drained by an arteriole (afferent and efferent)
- this allows the blood pressure in the capillary bed to be very high and it foreces fluid and solute out of blood into glomerular capsule


Pertibular capillaries

- most of the filtrate is reabsorbed in renal tubule cells and returns to blood though pertibular capillaries


Basic Renal Process

- glomerular filtration
- tubular secretion
- tubular reabsorption


Glomerular Filtration

- glomerular filtration is passive process where hydrostatic pressures force the fluids and solute through a membrane. moves fluid from glomerular capillaries and into bowmans capsule
- the glomeruli in kidney are much more efficient filter than other capillary beds in the body because large SA and permeable to water and solutes
- during filtration, important to keep plasma proteins in plasma to maintain osmotic pressure
- if see blood cells or protein in urine then theres a problem with filtration membrane (untreated = renal disease)


Net Flomerular filtration pressure

P(GC) = P(BS) = piGC


glomerular filtration

- refers to the movements of fluid and solutes from glomerular capillaries into bowmans space


tubular secretion

- refers to the secretion of solutes from the pertibular capillaries into the tubules


Tubular reabsorption

- begins as soon as filtrate enters the tubular cells
- paracellular transport occurs between cells (even though they have tight junctions) and is seen mainly with ions
- transport can be active (requires ATP) or passive (no ATP)
- moves substrances from pertibular capillaries into tubular lumen


sodium reabsorption

- Na+ is most abundant cation in filtrate
- Na+ reabsorption is almost always active transport
- active pumping of Na+ generates an electrochemical gradient that couples to passive entrance of other substances via co-transporters


Tubular secretion important for:

- disposing of drugs and drug metabolites
- eliminating undesired substrances or end products that have reabsorped via passive processes (urea and uric acid)
- removing excess K+
- controlling blood pH


metabolism by the tubule

- renal tubule cells can synthesize glucose during fasting and add it to the blood, and they can catabolize many organic compounds


regulation of membrane channels and transporters

- regulation of reabsorption and/or secretion of many substances is achieved by regulating the activity or concentrations of the appropriate transport proteins in response to hormones and paracrnie/autocrine factors


Division of labor in tubules

- majority of reabsorption is by proximal tubule and loop of henle
- extensive reabsorption by proximal tubule and henle's loop ensures that the masses of solutes and volume of water entering tubular segments beyond henle's loop are small
- distal segments do fine-tuning for most substances, determining final amounts excreted in urine by adjusting their rates of reabsorption and in a few cases secretion


renal clearance (RC)

- this is the volume of plasma cleared of a substance in one minute (ml/min)
- creatine can be used but is less accurate, it is freely filtered but also secreted in small amounts



- RC = renal clearance
- U = concentration of the substance in urine
- V = flow rate of urine formation
- P = concentration of substance in the plasma



- urine is formed in renal tubules then travels through calyxes until drains into renal pelvis
- fluid chains from renal pelvis to ureter, leading to urinary bladder
- bladder stores urine until excreted from body by micturition reflex
- micturition is initiated by a nervous reflex which causes the smooth muscle of bladder walls to contract and expel urine
- goes through 2 sphincters
1) internal urethral sphincter (smooth muscle)
2) external urethral sphincter (skeletal muscle)



- involuntary release of urine
- most common types are stress incontinence from sneezing, coughing or exercise, and urge incontinence associated with desire to urinate
- more common in women
- meds can often help 'stress'
- severe cases may require surgery
- can be treated with drugs but often have side effects
- irritation to bladder or urethra can cause 'urge'



- because filtered but not reabsorbed, or secreted, can be used to estimate glomerular filtration on rate



- product of muscle metabolism and produced daily
- gets into nephrons via glomerular filtration
- 10-15% lost in urine a day
- NOT reabsorbed once gets into nephron


if GFR decreases in kidney disease

plasma creatine increases


Concentrated Urine

- ADH uses cAMP systems to cause the insertion of aquaporins into the membranes of the principle cells of collecting ducts
- if water flows out of collecting ducts to be absorbed by the body
- urine can reach 1200 mOsm


Glomerular Filtration Rate

- volume of filtration formed each minute
- affected by volume of surface available, filtration membrane permeability and NFP, blood pressure/blood flow to glomerular capillaries
- directly proportional to NFP. in absence of regulation, increase in systemic blood pressure means increase GFR


Renal regulation of calcium and phsophate

- calcium reabsorption increase by parathyroid hormone
- phosphate reabsorption decreases by parathyroid hormone


glomerulus/bowmans capsule job

- forms ultrafiltrate of plasma


proximal tubule job

- bulk reabsorption of solutes and water, secretion of solutes (except K+) and organic acids/bases and secretion of urea


descending limb job

- bulk reabsorption of water


ascending limb job

- bulk reabsorption of NaCl


distal tubule and cortical collecting ducts job

- fine tuning of the reabsorption / secretion of small quantity of solute remaining


Cortical and medullary collecting ducts job

- fine-tuning of water reabsorption and reabsorption of urea



- substances that promote loss of Na+ and water
- alcohol inhibits release of ADH
- osmotic diuretics --> high glucose loads in urine
- loop diuretics are most powerful diuretics because inhibit formation of medullar gradient
- hydrochlorithiazide acts on the distal collecting ducts
- spironolactone is an aldosterone receptor antagonist known as K+ sparing diuretic. acts because K+ in urine is from aldosterone-driven active tubular secretion into the late DCT and collecting ducts


Buffering of Hydrogen Ions in body

- major extracellular buffer = CO2 / HCO3- system
- major intracellular buffer = phosphate and proteins


Integration of Homeostatic controls

- kidneys and respiratory system work together to regulate hydrogen ion concentrations


Renal Mechanisms

- the kidneys eliminate or replenish hydrogen ions from the body by altering plasma bicarbonate concentration


Responses to Acidosis

- H+ is secreted to reabsorb all filtered HCO3-
- still more H+ secreted, contributing to new HCO3- to the plasma as H+ excreted bound to nonbicarbonate urinary buffers such as HPO4-
- tubular glutamine metabolism and ammonium excretion are enhanced, also contributing new HCO3- ion than usual added
*overall result: move new HCO3- ion than usual added to blood, and plasma bicarbonate increases, compensating for acidosis


Responses to Alkalosis

- overall result: plasma bicarbonate concentration decreases thereby compensating for alkalosis. urine is alkaline > 7.4


Kidney disease

- diseases affecting kidneys = bacterial infections, hypertension, and diabetes
- end stage renal disease is one of the leading causes of death in the world and the leading cause of needed renal transplants


Clinical issues with kidneys

- severe cases when kidney swells, abscessess for and pelvis fills with pus. can result in irrepairable damage
- antibiotics are used to treat this condition
- renal failure and anuria can result from any situation where nephrons cease to function, including acute nephritis, transfusion reactions, and crash injuries



- abnormally low urine output (less than 50ml/day)
- may indicate that glomerular blood pressure is too low to cause filtration


if issue affects entire kidney



infection of renal pelvis that occurs via bacteria