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205 Cards in this Set
- Front
- Back
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Urinary system functions |
Excretion: removal of organic wastes from the body Elimination: discharge of waste products |
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Homeostatic functions of the urinary system |
- regulate blood volume and blood pressure - regulate plasma ion concentrations - help stabilize blood pH - conserve valuable nutrients - assist liver to detoxify poisons |
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How does the urinary system regulate blood volume and blood pressure |
By adjusting water loss and urine releasing erythropoietin and renin |
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How does the urinary system regulate plasma ion concentrations |
Sodium, potassium, and chloride ions (by controlling quantities lost in urine) Calcium level ions (through synthesis of calcitriol) |
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How does the urinary system help stabilize blood pH |
By controlling loss of hydrogen ions and bicarbonate ions in urine |
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How does the urinary system conserve valuable nutrients |
By preventing excretion while excreting organic waste products |
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Organs of the urinary system |
- kidneys: retroperitoneally located organs that excrete urine - urinary tract: organs that eliminate urine (ureters - paired tubes, urinary bladder - muscular sac, urethra - exit tube |
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Urination/micturition |
Process of eliminating urine Contraction of muscular urinary bladder forces urine through urethra and out of the body |
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Kidneys location |
On either side of vertebral column Left kidney lies superior to right kidney Superior surface is capped by adrenal gland |
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How is kidney position maintained |
Overlying peritoneum Contact with visceral organs Supporting connective tissues |
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Measurements of kidney |
10 cm long, 5.5 cm wide, and 3 cm thick Weighs about 150 g |
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How is each kidney protected/stabalized |
By 3 concentric layers if connective tissue (renal capsule, adipose capsule, renal fascia) |
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Renal capsule |
Collagen fibers that cover outer surface of kidneys Stabilizes positions of ureter, renal blood vessels, and nerves |
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Adipose capsule |
Thick layer of adipose tissue Surrounds renal capsule |
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Renal fascia |
A dense fibrous outer layer Anchors kidney to surrounding structures |
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Renal cortex of the kidney |
Superficial portion of kidney in contact with renal capsule Reddish brown granular |
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Renal medulla of kidney |
Contains renal pyramids - 6 to 8 distinct conical or triangular structures; base abuts cortex; tip (renal papilla) projects into renal sinus Also contains renal columns |
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Renal papilla of kidneys |
Ducts discharge urine into minor calyx (cut shaped drain) |
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Major calyx of kidney |
Formed by 4 or 5 minor calyces |
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Renal pelvis of kidney |
Large funnel shaped chamber Consists of 2 or 3 major calyces Fills most of renal sinus Connected to ureter which drains kidneys |
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Renal columns of kidney |
Bands of cortical tissue separate adjacent renal pyramids Extend into medulla |
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Renal sinus of kidney |
Internal cavity within kidney lined by fibrous renal capsule |
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Hilum of kidney |
Point of entry for renal artery and renal nerves Point of exit for renal vein and ureter |
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How much blood goes to the kidneys and where does it come from |
Kidneys recieve 20-25% of total cardiac output 1200 mL of blood flows through kidneys each minute Kidney recieves blood through renal artery |
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What do segmental arteries do |
- recieve blood from renal artery - divide into interlobar arteries - supply blood to arcuate arteries |
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Interlobar arteries go where |
Radiate outward through renal columns between renal pyramids |
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Arcuate arteries are located where |
They arch along the boundary between cortex and medulla of kidney |
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Afferent arterioles |
Branch from each interlobar artery Deliver blood to capillary supplying individual nephrons in the glomerulus |
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Blood flow in the kidneys |
- renal artery - segmental arteries - interlobar arteries - arcuate arteries - interlobar arteries - afferent arterioles - glomerulus (nephrons) - efferent arteriole (nephrons) - peritubular capillaries (nephrons) - venules - interlobar veins - arcuate veins - interlobar veins - renal vein |
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What does sympathetic innervation do |
Adjusts rate of urine formation by changing blood flow and blood pressure at nephron Stimulates release of renin |
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What does renin do |
Restricts losses of water and salt on urine by stimulating reabsorption at nephron |
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The renal nerves |
Innervate kidneys and ureter Enter each kidney at the hilum Follow tributaries of renal arteries to individual nephrons |
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What is the juxtaglomerular apparatus and what does it do |
An endocrine structure that secretes the hormone erythropoietin and enzyme renin |
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How is the juxtaglomerular apparatus formed |
The muscular densa - tall cells with densely clustered nuclei Juxtaglomerular cells - smooth muscle fibers in walk of afferent arteriole |
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How many nephrons are cortical nephrons and where are they located |
85% Located mostly within superficial cortex of kidney |
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In cortical nephrons, how long is the loop of Henle and what do efferent arterioles do |
- Loop of Henle if relatively short and doesn't extend into the medulla - Efferent arterioles deliver blood to a network of peritubular capillaries which surround the entire renal tubule |
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How many nephrons are juxtamedullary nephrons and how long is Loop of Henle |
15% of nephrons Have long loops of Henle that extend deep into medulla |
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Functions of juxtamedullary nephrons and where do peritubular capillaries connect |
Water conservation and forms concentrated urine Peritubular capillaries connect to Vasa recta (long straight capillaries parallel with loop of Henle) |
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What is filtrate, where does it travel, and what does it do |
A tubular fluid in the nephron that travels along tubules and gradually changes composition. These changes carry with activities in each segment if the nephron |
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Where does filtrate empty into |
The collecting system which is a series of tubes that carries tubular fluid away from the nephron |
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Collecting ducts |
Recieve fluid from many nephrons Each collecting duct begins in the cortex, descends into medulla, and carries fluid to papillary duct that drains into a minor calyx |
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What does a nephron consist of |
Renal tubule and renal corpuscle |
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Diameter of renal corpuscle |
150 - 250 microliters in diameter |
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Where is bowmans capsule and what is it |
A cup shaped chamber in the renal corpuscle |
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What is the glomerulus, where is it at, and how does blood move through it? |
A capillary network in the renal corpuscle that consists of 50 intertwining capillaries Blood is delivered via afferent arteriole and leaves via efferent arteriole |
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Where does blood go after leaving the glomerulus of the renal corpuscle |
Flows into peritubular capillaries which drain into small venules and return blood to the venous system |
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What type of capillaries are glomerular capillaries |
Fenestrated. The endothelial contains large diameter pores |
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How does filtration work in the glomerular capillaries |
It is a passive process (only in renal corpuscle) in which blood pressure forces water and small solutes across membrane into capsule space |
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Limitations of glomerular capillaries |
Allows glucose, fatty acids, amino acids, vitamins, and other solutes pass through, however these are reabsorbed in the proximal convoluted tubule (PCT) |
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What is the renal tubule |
Long tubular passageway begins at renal corpuscle |
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What part of the renal tubule are located in the cortex |
Proximal convoluted tubule (PCT) Distal convoluted tubule (DCT) |
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How is the renal tubule seperated |
By the loop of Henle |
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Loop of Henle |
- renal tubule turns towards renal medulla - descending limb: fluid flows toward renal pelvis - ascending limb: fluid flows toward renal cortex |
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3 functions of renal tubule |
- Reabsorb useful organic Murrieta that enter filtrate - Reabsorb more than 90% of water in filtrate - Secrete waste products that failed to enter renal xorpuscke through filtration at glomerulus |
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What is proximal convoluted tubule (PCT) and it's function |
- First segment of the renal tubule - Reabsorbs ions, organic nutrients, vitamins, and water from tubular fluid - Release them into peritubular fluid - Secretes drugs, toxins, and acids |
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What is peritubular fluid |
Interstitial fluid around renal tubule |
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What does each limb of the loop of Henle contain |
Thick and thin segments |
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Thick descending limb |
Has functions similar to PCT Pumps sodium and chloride ions out of tubular fluid |
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Ascending limbs |
Of juxtamedullary nephrons in medulla Create high solute concentrations in peritubular fluid |
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Thin segments of loop of Henle |
Freely permeable to water and not to solutes Water movement helps concentrate tubular fluid |
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The distal convoluted tubule (DCT) |
The third segment if the renal tubule Initial portion passes between afferent and efferent arterioles |
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3 functions of DCT |
- active secretion of ions, acids, drugs, and toxins - selective reabsorption of sodium and calcium ions from tubular fluid - selective reabsorption of water: concentrates tubular fluid |
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Parts of the collecting system |
- DCT: opens into the collecting system - individual nephrons: drain into a nearby collecting duct - several collecting ducts: converge into a larger papillary duct which Empties into a minor calyx |
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Functions of the collecting system |
- transports tubular fluid from nephron to renal pelvis - adjusts fluid composition - determines final osmotic concentration and volume of urine |
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The 3 organic waste products |
- Urea: most abundant, from amino acid breakdown, about 21 g/day - Creatine: from creatine phosphate used in muscle contraction, 1.8 g/day - Uric acid: waste product from RNA processing |
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How are organic waste products removed |
- dissolved in the bloodstream - eliminated only while dissolved in urine - removal accompanied by water loss |
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Kidney functions |
- to concentrate filtrate by glomerular filtration - usually produce concentrated urine - absorbs and retains valuable materials for use by other tissues (sugars, amino acids) |
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Failure to concentrate filtrate by glomerular filtration leads to |
Fatal dehydration |
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Concentration of concentrated urine |
1200-1400 mOsm/L (4× plasma concentration) |
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Goal of urine production |
- to maintain homeostasis by regulating volume and composition of blood - including excretion of metabolic waste products |
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3 basic processes of urine formation |
Filtration Reabsorption Secretion |
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What does hydrostatic pressure do during filtration and where does this occur |
- it forces water through membrane pores (small solute molecules pass through pores, larger solutes and suspended materials are retained) - occurs across capillary walls as water and dissolved materials are pushed into interstitial fluids - at the renal corpuscle, a specialized membrane restricts all circulating proteins |
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What is reabsorption |
- removal of water and solutes from filtrate and into peritubular fluid - most nutrients/ions the body will reuse - selective process either by simple diffusion or carrier proteins - water done by osmosis |
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Secretion and why is it necessary |
- moment from peritubular fluid to tubular fluid - necessary because filtration is an incomplete process - usually for drug removal |
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What do secretion and reabsorption involve at the kidneys |
Diffusion Osmosis Channel mediated diffusion Carrier mediated transport |
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4 types of carrier mediated transport |
Facilitate diffusion Active transport Cotransport Counter transport |
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Facilitated diffusion (carrier mediated transport) |
Carrier transit that moves without energy - usually movement due to concentration gradient |
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Active transport (carrier mediated transport) |
Uses ATP - goes against a concentration gradient |
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Cotransport (carrier mediated transport) |
2 substrates cross - usually 1 goes down concentration gradient |
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Counter transport (carrier mediated transport) |
- Like cotransport except 2 substrates move in opposite directions - ex. HCO3- and Cl- located in PCT, DCT, and collecting duct |
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5 characteristics of carrier mediated transport |
- a specific substrate binds to carrier proteins and they facilitate movement across the membrane - a given carrier protein usually works in 1 direction only - distribution of carrier proteins varies among portions of the cell surface - the membrane of a single tubular cell which contains many types of carrier protein - carrier proteins, like enzymes, can be saturated, if they are, then max reabsorption occurs but some loss to urine (determines the renal threshold) |
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What is the renal threshold, where does it begin to appear, and how does it vary |
- the plasma concentration at which a specific compound or ion - begins to appear in urine - varies with the substance involved |
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Glucose in the renal threshold |
- approximately 180 mg/dL - if plasma glucose is greater than that, then Tm of tubular cells is exceeded and glucose appears in urine (glycosuria) |
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Amino acids in renal threshold |
- approximately 65 mg/dL - amino acids commonly appear in urine after a protein rich meal (aminoaciduria) |
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Osmolarity |
The osmotic concentration of a solution - total # of solute particles per liter - osmoles per liter (Osm/L) - miliosmoles per liter (mOsm/L) |
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Osmotic concentration of body fluids |
300 mOsm/L |
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How to measure ion concentrations and concentrations of large organic molecules |
Ion concentrations - in milliequivalents per liter (mEq/L) Concentrations of large organic molecules - grams or milligrams per unit volume of solution (g/dL or mg/dL) |
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Where does filtration take place |
Only in the renal corpuscle |
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Where does water and solute reabsorption happen in the renal system |
Primarily along PCT but throught the renal system |
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Where does active secretion take place in the renal system |
Primarily at PCT and DCT |
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What are the loops of Henle and what do they do |
Long loops of juxtamedullary nephrons and collecting system Regulate final volume and solute concentration of urine |
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3 components of glomerular membrane |
Capillary endothelium Lamina densa Filtration slits |
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What does glomerular filtration involve and what type of capillaries |
Involves passage across a filtration membrane (capillary endothelium) Has fenestrated capillaries |
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Fenestrated capillaries |
Have pores 60-100 nm in diameter Prevent passage of blood cells Allow diffusion of solutes, including plasma proteins |
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Lamina densa of glomerular membrane |
More selective Allows diffusion of only small plasma proteins, nutrients, and ions |
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Filtration slits of glomerular membrane |
Finest filters Have gaps only 6-9 nm wide Prevent passage of most small plasma proteins |
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What two filtration pressures create a balance that governs glomerular filtration |
Hydrostatic pressure (fluid pressure) Colloid osmotic pressure (of materials in the solution) On either side of capillary walls |
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What is Glomerular hydrostatic pressure (GHP) and what does it tend to do |
Blood pressure in glomerular capillaries Tends to push water and solute molecules out of the plasma into the filtrate |
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Is GHP higher or lower than capillary pressures in systemic circuit and why |
Significantly higher due to arrangement of vessels at glomerulus (50 mmHg) |
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Where does blood leaving the glomerular capillaries flow |
Into arteriole with diameter smaller than an afferent arteriole |
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What do efferent glomerular arterioles do |
Produces resistance and requires relatively high pressures to force blood into it |
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What does capsular hydrostatic pressure (CsHP) oppose and what does it do |
Opposes glomerular hydrostatic pressure Pushes water and solutes out of filtrate into plasma |
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What does CsHP result from and what is the average |
Results from resistance to flow along nephron and conducting system Averages about 15 mmHg |
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Net hydrostatic pressure (NHP) |
The difference between GHP and CsHP 50 - 15 = about 35 mmHg |
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Colloid osmotic pressure |
Of a solution is the osmotic pressure resulting from the presence of suspended proteins |
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Blood colloid oncotic pressure |
Tends to draw water out if filtrate into plasma Opposes filtration Averages 25 mmHg |
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Filtration pressure (FP) |
The average pressure forcing water and dissolved material out if glomerular capillaries into capsular spaces |
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What is FP at the glomerulus the difference between |
Net hydrostatic pressure (NHP) - colloid osmotic pressure across glomerular capillaries 35 - 25 = 10 mmHg |
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Glomerular filtration rate (GFR) and it's average |
The amount of filtrate kidneys produce each minute Averages 125 ml/min in males and 115 ml/min in females |
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How much of cardiac output to kidneys is reabsorbed by the GFR |
20-25% of cardiac output to kidneys (1200 ml/min) |
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How much fluid is delivered to the kidneys |
10% It leaves the bloodstream, enters capsular spaces, 99% is reabsorbed to help prevent dehydration |
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How much filtrate do the glomeruli generate per day |
180 L/day |
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How often is all the blood filtered |
Every 40 minutes |
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What does GFR depend on |
Filtration pressure |
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Anything that alters FP also alters what |
GFR |
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What would a drop in renal blood pressure of 20% do |
Change it from 50 to 40 mmHg and FP would cease because it would be 0 |
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What is FP sensitive to |
Changes in blood pressure such as hemorrhaging, shock, and dehydration Could lead to renal failure |
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3 levels of GFR control |
Autoregulation (local level) Hormonal regulation (initiated by kidneys) Autonomic regulation (by sympathetic division of ANS) |
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Why does GHP need to be maintained |
To maintain FP and in turn, maintain GFR |
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What does autoregulation do and how |
Maintains GFR despite changes in local blood pressure and blood flow by changing diameters of afferent arteriole, efferent arterioles, and glomerular capillaries |
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What does reduced blood flow or glomerular blood pressure trigger in autoregulation |
Dilation of afferent arterioles and glonerular arterioles Constriction of efferent arterioles Elevates blood flow and glomerular pressure |
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What does a rise in renal blood pressure cause in autoregulation |
It stretches the walls of afferent arterioled Causes smooth muscle cells to contract Constrict afferent arterioles Decreases glomerular blood flow |
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Where do hormonal regulation hormones come from |
Renin-angiotensin system Natriueretic peptides (ANP and BNP) |
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What does autonomic regulation of GFR consist of |
Mostly sympathetic postganglionic fibers |
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What does sympathetic activation do to autonomic regulation of GFR |
Constrict afferent arterioles Decreases GFR Slows filtrate production |
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What can oppose changes in blood flow to kidneys due to sympathetic stimulation |
Autoregulation at local level |
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What 3 triggers cause the juxtaglomerular apparatus (JGA) release renin (renin-angiotensin system) |
- decline in blood pressure at glomerulus due to decrease in blood volume - stimulation of juxtaglomerular cells by sympathetic innervation due to decline in osmotic concentration of tubular fluid at macula densa - decrease in osmotic concentration of tubular fluid |
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Overall effect of angiotensin II (the mother of all dehydration hormones) |
- increase in systemic blood volume and pressure - restoration of normal GFR - constricts efferent arterioles of nephron (increasing GFR) - stimulates reabsorption of sodium ions and water at PCT - stimulates adrenal gland to release aldosterone |
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What does aldosterone do |
Causes Na+ reabsorption in the DCT and the collecting system |
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What does angiotensin II do in peripheral capillary beds |
- causes brief, powerful vasoconstriction of arterioles and precapillary sphincters - elevating arterial pressures throughout the body (less volume of space, higher pressure) |
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What does angiotensin do in the CNS |
- stimulates thirst - triggers release if antidiuretic hormone (ADH) - increases sympathetic motor tone |
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What does ADH stimulate |
The reabsorption of water in distal portion of DCT and collecting system |
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What does increasing sympathetic motor tone do |
Mobilizes the venous reserve Increasing cardiac output Stimulating peripheral vasoconstrictiin |
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Natriuretic peptides and where they are released |
Atrial natriuretic peptide (ANP) released by the atria Brain natriuretic peptide (BNP) released by the ventricles |
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What do ANP and BNP do |
Make you pee |
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When are ANP and BNP released by the heart |
In response to stretching walls due to increased blood volume or blood pressure |
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What do natriuretic peptides trigger and what do they decrease |
- trigger dilation of afferent arterioles and constriction of efferent arterioles - elevates glomerular pressures and increases GFR - decrease tubular reabsorption of sodium ions (increases urine production, decreases blood volume and pressure) |
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What does increased blood volume do to GHP, and in turn GFR |
Increases GHP, increasing FP, and then increasing GFR Automatically increases GFR to promote fluid loss Hormonal factors further increase GFR accelerating fluid loss in urine |
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What do reabsorption and secretion do |
Reabsorption - recovers useful materials from filtrate Secretion - ejects waste products, toxins, and other undesirable solutes |
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Where do reabsorption and secretion occur |
In every segment of the nephron except the renal corpuscle |
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How much filtrate is excreted as urine, and what is obligatory water loss |
1% of daily filtrate excreted as urine 400 mL minimum for obligatory water loss |
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5 functions of the PCT |
- reabsorption of organic nutrients - active reabsorption of ions - reabsorption of water - passive reabsorption of ions - secretion |
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How much filtrate does PCT reabsorb and where does it go |
Normally PCT cells reabsorb 60-70% of filtrate produced in renal corpuscle Reabsorbed materials enter peritubular fluid and diffuse into peritubular capillaries |
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Why is sodium ion reabsorption important and how do ions enter tubular cells |
Important in every PCT process Ions enter tubular cells by - diffusion through leak channels - sodium linked cotransport of glucose - countertransport for hydrogen ions - Na+/K+ pump |
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Loop of Henle reabsorbs what from tubular fluid and how |
Reabsorbs about 1/2 of water and 2/3 of sodium and chloride ions remaining in tubular fluid by process of countercurrent multiplication |
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What is countercurrent multiplication |
The exchange that occurs between 2 parallel segments of the loop of Henle (thin descending and thick ascending limbs) |
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How are the limbs of the loop of Henle serperated and what is different between the two |
Serperated only by peritubular fluid and they have very different permeability characteristics |
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How much filtrate does loop of Henle reabsorb |
20% |
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Thin descending limb |
Juxtamedullary nephron Permeable to water Osmosis to Vasa recta (not in tissue) Relatively impermeable to solutes Tubular fluid reaches high osmolality |
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Thick ascending limb |
Relatively impermeable to water and solutes Active transport at apical surface (moves Na+, K+, and Cl- out of tubular fluid into peritubular fluid of medulla) Uses carrier proteins (Na+, K+, Cl- transporter by ATP) Each cycle of pump carries ions into tubular cell (1 Na+, 1 K+, 2 Cl-) |
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What do sodium and chloride pumps do and what does this cause |
Elevate osmotic concentration in peritubular fluid around thin descending limb Which causes osmotic flow of water - out of descending limb into peritubular fluid, increasing solute concentration in thin descending limb - concentrated fluid arrives in thick ascending limb - accelerates Na+ and Cl- transports into peritubular fluid of medulla |
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How are potassium ions pumped and removed abs where do they diffuse |
Pumped into peritubular fluid by cotransport carriers Removed from peritubular fluid by sodium potassium leak channels Diffuse back into lumen of tubule through potassium leak channels |
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Regional differences in Na+ and Cl- |
More Na and Cl are pumped into medulla at the start of the thick ascending limb than near the cortex |
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Regional difference in ion transport rate |
Causes concentration gradient within medulla Normal maximum solute concentration of peritubular fluid near turn of loop of Henle (1200 mOsm/L) |
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Concentration gradient of the medulla |
2/3 (750 mOsm/L) from Na+ and Cl- pumped out of ascending limb Remainder from urea |
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What does countercurrent refer to |
The exchange between tubular fluid moving in opposite directions - fluid in descending limb flows towards renal pelvis - fluid in ascending limb flows towards cortex |
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What does countercurrent multiplication refer to |
The effect of exchange Increases as movement of fluid continues |
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2 benefits of countercurrent multiplication |
Efficiently reabsorbs water and solutes (before tubular fluid reaches DCT and collecting system) Establishes concentration gradient (that permits passive reabsorption of water from tubular fluid in collecting system) |
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What does the Vasa recta do |
Carries water and solute out of medulla to general circulation without disturbing the concentration gradient Balances solute reabsorption and osmosis in medulla |
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Tubular fluid arrives at DCT with what osmotic concentration |
100 mOsm/L - only 1/3 concentration of peritubular flutist of renal cortex - only recieves about 15-20% of initial volume |
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Rate of ion transport across thick ascending limb is proportional to |
Ion concentrations in tubular fluid |
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What happens to electrolytes and organic wastes in tubular fluid at DCT |
No longer resemble blood plasma |
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What do tubular cells at the DCT do |
Actively transport Na+ abs Cl- out of tubular fluid along distal portions (contain ion pumps, reabsorb tubular Na+ in exchange for K+) Selective reabsorption or secretions, primarily asking DCT, makes final adjustments in solute composition and volume of tubular fluid |
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K+ and H+ secretion at DCT |
H+ and K+ secretion rises or falls - tubular cells exchange Na+ in tibial fluids for excess K+ in body fluids - H+ is associated with reabsorption of sodium - countertransport - carbonic anhydrase facilitates NCO3- to diffuse into bloodstream (buffer changes in plasma pH) |
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What does hydrogen ions secretion do |
Acidifies tubular fluid Elevates blood pH Accelerates when blood pH falls |
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When do lactic acidosis and ketoacidosis develop |
Lactic acidosis (elevated blood pH) - develops after exhaustive muscle activity Ketoacidosis (elevated blood pH) - develops in starvation or diabetes mellitus |
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What is the response to acidosis |
- PCT and DCT deaminate amino acids - ammonium ions are pumped into tubular fluid - bicarbonate ions enter bloodstream through peritubular fluid |
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What happens what the PCT and DCT deaminate amino acids |
It ties up H+ ions and yields ammonium ions (NH4+) and HCO3- |
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What is alkalosis and how is it caused |
Abnormally high blood pH that can be caused by prolonged aldosterone stimulation which stimulates secretion |
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Hormones of reabsorption |
Antidiuretic hormone (ADH) Aldosterone Natriuretic peptides (ANP and BNP) Parathyroid hormone and calcitriol |
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What does aldosterone do in reabsorption |
Stimulated synthesis and use of Na+ pimps and channels (DCT and collecting duct) to reduce Na+ lost in urine |
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How is hypokalemia produced |
By prolonged aldosterone stimulation, dangerously reduced plasma concentrations |
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What do natriuretic peptides (ANP and BNP) oppose |
Oppose secretion of aldosterone |
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What do parathyroid hormone and calcitriol regulate |
Regulate Ca2+ reabsorption at the DCT |
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How are urine volume and osmotic concentration regulated and where/how is water reabsorbed |
Regulated through control of water reabsorption Water is reabsorbed by osmosis in the PCT and descending limb of the Loop of Henle |
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What is obligatory water reabsorption and how much filtrate does it recover |
Water movement that cannot be prevented Usually recovers 85% of filtrate produced |
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What does facultative water reabsorption control and what % of filtrate |
- controls volume of water reabsorbed along DCT and collecting system - 15% of filtrate volume (27 L/day) - segments are relatively impermeable to water (except in presence of ADH) |
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What are the 2 methods water and solute loss is regulated in the collecting system |
- aldosterone: controls sodium ion pumps, actions are opposed by natriuretic peptides - ADH: controls permeability to water and is suppressed by natriuretic peptides |
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What does ADH do |
- a hormone that causes special water channels to appear (in apical cell membranes) - increases rate of osmotic water movement |
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What does higher levels of ADH increase |
Number of water channels and water permeability of DCT and collecting system |
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What happens without ADH |
Water is not reabsorbed and all fluid reaching the DCT is lost in urine, producing large amounts of dilute urine |
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What is the osmotic concentration of tubular fluid arriving at DCT, in the presence of ADH in cortex, and in the minor calyx |
Tubular fluid arriving at DCT: 100 mOsm/L In presence of ADH: 300 mOsm/L In minor calyx: 1200 mOsm/L |
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What does the hypothalamus do |
Continuously secretes low levels of ADH so DCT and collecting system are always permeable to water |
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At normal ADH levels, how much does the collecting system reabsorb |
16.8 L/day (9.3% of filtrate) |
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What does the collecting system reabsorb |
Sodium ion, bicarbonate, urea |
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What does the collecting system secrete and what does this control |
Hydrogen or bicarbonate ions Controls body fluid pH |
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How much urine does a healthy adult produce |
1200 mL/day (0.6% of filtrate) with an osmotic concentration of 800-100 mOsm/L |
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What is diuresis and what does diuretic therapy reduce |
The elimination of unusually large volumes of urine Therapy helps reduce blood volume, blood pressure, extracellular fluid volume |
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Movement of filtrate through the body |
Glomerulus, PCT, PCT and descending limb, thick ascending limb, DCT and collecting ducts, Vasa recta |
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How is filtrate composed at the glomerulus |
Filtrate produced at renal corpuscle has the same composition as blood plasma without plasma proteins |
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What happens to filtrate at the PCT |
Active removal of ions and organic substrates - produces osmotic water flow out of tubular fluid - reduces volume of filtrate - keeps solutions inside and outside tubule isotonic |
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What happens to filtrate at the PCT and descending limb |
Water moves into peritubular fluids, leaving highly concentrated tubular fluid Reduction in volume occurs by obligatory water reabsorption |
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What happens to filtrate at the thick ascending limb |
Tubular cells actively transport Na+ and Cl- out of tubule Urea becomes higher proportion of total osmotic concentration |
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What happens to filtrate at the DCT and collecting ducts |
Final adjustments in composition if tubular fluid Osmotic concentration is adjusted through active transport (reabsorption/secretion) Final adjustments in volume and osmotic concentration of tubular fluid Exposure to ADH determines Final urine concentration |
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What happens to filtrate at the Vasa recta |
Absorbs sokutes and water reabsorbed by loop of Henle and the ducts Maintains concentration of gradient of medulla |
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Where does urine transport, storage, and elimination take place |
In the urinary tract (ureters, urinary bladder, urethra) |
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Peristaltic contractions |
Begins at the renal pelvis, sweep along ureter, and force urine toward urinary bladder every 30 seconds |
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What is the urinary bladder and how much fluid can it contain |
A hollow, muscular organ that functions as a temporary reservoir for urine storage Full bladder can contain 1 liter of urine |
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Where is the urethra |
Extends from the neck of urinary bladder to the exterior of the body |
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What is the external urethral sphincter |
A circular band of skeletal muscle that acts as a valve and is under voluntary control |
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Micturition reflex |
Coordinates the process of urination |
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What happens as the bladder fills with urine |
Stretch receptors in the urinary bladder stimulate sensory fibers in pelvic nerve Increases with urinary volume Any volume > 500 mL triggers micturition reflex |
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3 problems with micturition reflex |
- sphincter muscles lose tone - control of micturition can be lost U - urinary retention may develop in males if enlarge prostate gland compresses the urethra and restricts urine flow |
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What happens when sphincter muscles lose tone and why can this happen |
Leads to incontinence (inability to control urination voluntarily) and may be caused by trauma to internal or external urethral sphincter |
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3 ways micturition control can be lost |
Stroke Alzheimers CHS problems affecting cerebral cortex/hypothalamus |
