Biology HL
Mrs. Ragsdale

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Excretion – removal of waste products from the body leftover from metabolic pathways
 Produce urine
Osmoregulation – control of water balance of the blood, tissue or cytoplasm
 Controls your bloodpressure
 Homeostasis!!
http://www.healthfactshealthtips.com/wpcontent/uploads/2011/09/Kidney-diseases.jpg

Draw and Label
 Renal artery
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Renal vein
Renal pelvis
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Ureter
Cortex
Medulla
Nephron

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Renal Artery – brings blood from the heart
Renal Vein – returns blood to the heart
Pelvis – collects urine
Ureter – carries urine from the kidney to the bladder
Medulla – the middle portion of the kidney
Cortex – the outer portion of the kidney
Nephron – basic structural and functional unit of a kidney

 http://www.biologymad.com/resources/kidne y.swf
 http://bcs.whfreeman.com/thelifewire8e/con tent/cat_040/51040-
01.htm?v=chapter&i=51040.01&s=51000&n=
00040&o =

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Normal human kidney contains 800,000 to 1.5 million nephrons
Nephrons regulate water levels and concentration of soluble substances within the blood
By filtering the blood, the nephrons keep the substances your body needs and excretes the rest as urine
Nephrons eliminate waste, regulate blood volume, blood pressure, pH, electrolyte levels (like Na ⁺ and
K ⁺ ions) and are pretty darn useful to living

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Bowman’s Capsule – the cup shaped formation that holds the glomerulus
Glomerulus – uses ultrafiltration to separate filtrate (pre-urine) from blood
Blood pressure is very high within the glomerulus because the tube taking the blood away is much smaller than the tube leading towards it
The capillaries in the glomerulus are fenestrated meaning that they have many pores

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Blood from the renal artery flows through an afferent arteriole, into the glomerulus, a capillary bed that is situated inside the Bowman’s capsule.
The basement membrane of the Bowman’s capsule has an irregular network of slits, so that much of the fluid from the blood filters into the capsule, leaving behind large proteins and whole cells, which are too big to pass through.
From the Bowman’s capsule, the glomerular filtrate passes into the proximal convoluted tubule.

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Large volume of glomerular filtrate is produced, approx 1 litre every 10 minutes by two kidneys
Proximal convoluted tubule is lined with densely packed microvilli that increase the surface area of the lumen
Majority of re-absorption occurs at this point in the nephron
High quantity of mitochondria in these cells to facilitate the ATP required for active transport of sodium ions out of the tubule
 This causes water to passively flow out of the tubule via osmosis, following the concentration gradient

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Re-absorbed Portion:
 80% of mineral ions, including sodium
 All of the glucose in the filtrate
 80% of water from the filtrate
Filtrate, or the “to be excreted” Portion:
 Urea
 Excess Na and K ions
 Exchange of H ⁺ and carbonate ions – pH maintenance

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Overall purpose of the loop of Henle is to create an area of high solute concentration in the cells and tissue fluid of the medulla
Moves the filtrate between the renal cortex and renal medulla
Ascending limbs are permeable to sodium ions but not to water
 Sodium ions enter filtrate
 Pump sodium ions from filtrate into the medulla by active transport creating a high solute concentration in the medulla
Descending limbs are permeable to water but not to sodium
 As the filtrate flows down into the region of high solute concentration, some water is drawn out via osmosis
 That dilutes the fluid in the medulla slightly
The filtrate that leaves the loop of Henle is more dilute than the fluid entering

Restating Last Slide:
 The loop of Henle descends into the renal medulla.
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 The fluid of the medulla is called the interstitial fluid.
Where the loop of Henle makes its turn, the interstitial fluid is salty. Thus the medulla creates a concentration gradient for the tubular fluid, causing water to move out of the descending limb of the loop of Henle as it approaches the turn.
The fluid left behind (inside the loop of Henle) becomes increasingly salty until it matches the interstitial fluid.
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 At this point, no more water can leave the loop of Henle.
As the tubular fluid moves up the ascending loop of Henle, sodium diffuses out through the thin portion of the loop of Henle and is actively transported out of the thick portion. Water remains behind because the ascending loop of Henle is not permeable to water.

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Osmoregulation – the control of water and solute levels
If water content is too low, the pituitary gland secretes the hormone vasopressin (also called ADH) which makes the cells of the collecting duct produce membrane channels called aquaporins.
 Causes the collecting duct to be more permeable to water – osmosis would draw most of the water out making urine much more concentrated
If water levels are too high, ADH production is inhibited
 Causes aquaporins to be broken down and collecting ducts are much more permeable to water
Water content of the blood is kept within narrow limits
Urine collects in the renal pelvis, down the ureter and into the bladder

Glucose
Urea
Proteins
Content (mg per 100ml of blood)
Blood in Renal
Artery
90
30
740
Urine
0
2000
0
Glomerular
Filtrate
90
30
0
Blood in
Renal Vein
90
24
740
Glucose is often present in the urine of untreated diabetic patients because the glucose concentration of blood rises much higher than the regular 90 mg per 100 ml so the pumps in the proximal convoluted tubule cannot reabsorb all the glucose that is filtered out in the glomerulus