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82 Cards in this Set
- Front
- Back
Urinary System Overview
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• 2 kidneys
• 2 ureters • urinary bladder • urethra |
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What do the kidney's produce?
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urine
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What is the function of the ureter?
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transport urine from kidneys to bladder
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What is the function of the urinary bladder?
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temporary storage for urine
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What is the function of the urethra?
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transports urine from the bladder out of the body
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What are the functions of the the kidney?
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1. filter blood
2. regulate blood volume and blood pressure 3. regulate plasma ion concentrations 4. help stabilize blood pH 5. endocrine function - erythropoietin (EPO) 6. activation of vitamin D |
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What are the regions of the kidney?
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cortex, medulla and renal pelvis (ureter)
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What is the functional unit of the kidney?
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nephron
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Each nephron can be divided into:
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a renal tubule of renal corpuscle
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What is a renal tubule?
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long tubule beginning at the renal corpuscle that's consisted of three regions: proximal convoluted tubule (PCT), Loop of Henle, Distal convoluted tubule (DCT)
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What is a renal corpuscle?
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spherical structure = Bowman's capsule + glomerulus
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The glomerulus is the site of _____
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filtration
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Each nephron empties into the:
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collecting system
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What is the collecting system?
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series of tubes that carry fluid away from the nephron
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What is the collecting duct?
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receives fluid from many nephrons; begins at cortex, descend into medulla
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What is the papillary duct?
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receives fluid from collecting duct - drains into minor calyx
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The regions of the _____ & _____ vary in their structure and function/role in the production of urine
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nephron & collecting system
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What is filtration?
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blood & all of its contents (except proteins & RBCs) are filtered into a nephron
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What is reabsorption?
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H₂O & important ions/nutrients are reabsorbed back into blood
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What is secretion?
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additional "unwanted" solutes, acids, toxins, etc transported further into forming urine
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The renal corpuscle is the production of _____
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filtrate
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What is the Bowman's capsule?
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double layered bag that collects urinary filtrate
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What is the parietal epithelium?
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outer wall; simple squamous epithelium
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What is the visceral epithelium?
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covers glomerular capillaries
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What is the capsular space?
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between parietal & visceral epithelia
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Blood supply to the glomerulus has two locations:
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afferent arteriole & efferent arteriole
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The _____ arteriole brings blood to the glomerulus
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afferent
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The _____ arteriole takes blood away from the glomerulus (after filtration has occurred)
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efferent
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What is the filtration membrane?
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filter that lies between the blood & capsular space
Consists of three layers: • fenestrated endothelium • fused basement membrane • visceral layer of glomerular capsule |
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What are the three layers of the filtration membrane?
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• fenestrated endothelium - of glomerular capillaries
• fused basement membrane • visceral layer of glomerular capsule - podocytes form filtration slits |
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What are the two 2 capillary beds in every nephron?
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glomerulus and peritubular capillaries
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Each glomerulus is:
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• fed by an afferent arteriole
• drained by an efferent arteriole |
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What are peritubular capillary beds?
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low-pressure, porous capillaries adapted for absorption
• arise from efferent arterioles • cling to adjacent renal tubules • empty into renal venous system |
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What is the vasa recta?
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long, straight efferent arterioles connected to peritubular capillaries (15% of nephrons) that follow Loops of Henle into medulla
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Cortical nephrons
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85% of all nephrons
• located in the cortex of the kidney • short loop of Henle • efferent arteriole connects with peritubular capillaries |
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Juxtaglomerular nephrons
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15% of nephrons
• long loops of Henle extend deep into medulla • peritubular capillaries (surround convoluted tubules) connect to vasa recta (long, straight capillaries parallel with loop of Henle) |
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What are the three stages of urine formation?
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1. filtration - of H₂O & solutes across filtration membrane
2. reabsorption - removal of H₂O & solutes from filtrate into peritubular fluid 3. secretion - transport of solutes from peritubular fluid into tubular fluid |
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Three processes of urine formation
1. Filtration - solutes travel from _____ to ______ 2. Reabsorption - solutes travel from _____ to _____ 3. Secretion - solutes travel from ______ to _____ |
1. Filtration - solutes travel from _____ to ______
2. Reabsorption - solutes travel from _____ to _____ 3. Secretion - solutes travel from ______ to _____ |
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Filtration
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H₂O & dissolved solutes move out of glomerulus → across filtration membrane → into capsular space
• requires glomerular hydrostatic pressure (BP generated by heart) to force H₂O and solutes through membrane pores ∙ small solute molecules pass through ∙ larger solutes (e.g. proteins, RBCs) can't pass through Filtration → effective and passive • major limitation — in addition to metabolic wastes & excess ions... ∙ glucose, fatty acids, amino acids & vitamins enter capsular space These potentially useful materials are recaptured before the filtrate leaves the kidneys (reabsorption) |
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Glomerular filtration is determined by a balance between:
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1. hydrostatic pressure (fluid pressure)
2. colloid osmotic pressure (of materials in solution) |
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Glomerular hydrostatic pressure (GHP)
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(BP in glomerular capillaries) = 50 mm Hg
(arrows in purple) |
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Capsular hydrostatic pressure (CsHP)
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15 mm Hg (pushes H₂O & solutes out of filtrate)
(arrows in red) |
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Blood colloid osmotic pressure (BCOP)
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25 mm Hg (osmotic pressure due to suspended proteins)
(arrows in teal) |
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Why do we not need to consider the colloid osmotic pressure in the filtrate?
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lack of proteins in filtrate (due to semipermeable membrane) ... BCOP draws H₂O out of filtrate - into plasma
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Net hydrostatic pressure (NHP)
NHP = |
GHP -CsHP
35 mm Hg = 50 mm Hg - 15 mm Hg |
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Filtration pressure (NFP)
NFP = |
NHP - BCOP
10 mm Hg = 35 mm Hg - 25 mm Hg 10 mm Hg = average pressure forcing H₂O & dissolved solutes out of glomerular capillaries into capsular space |
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Typical hydrostatic pressure in the peripheral capillaries is
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35 mm Hg
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Glomerular hydrostatic pressure is
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50 mm Hg
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How is the filtration pressure established/maintained?
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efferent arteriole diameter < afferent arteriole diameter
Therefore high pressures are needed to overcome the resistance |
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Blood pressure in the glomerulus is high because:
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• arterioles are high-resistance vessels (high diameters)
• afferent arterioles have larger diameters than efferent arterioles Fluids and solutes are forced out of the blood throughout the entire length of the glomerulus |
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Glomerular Filtration Rate (GFR)
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amount of filtrate kidneys produce in 1 minute (~ 125 ml/min)
... about 10% of fluid delivered to kidneys - leaves bloodstream & enters capsular space |
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Glomeruli generate about _____ L of filtrate/day but _____% is reabsorbed in renal tubules
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180 L; 99%
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Any factor that alters filtration pressure alters _____.
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GFR
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What are the three levels of GFR regulation?
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1. Autoregulation (local level)
2. Hormonal regulation (initiated by kidneys) 3. Autonomic regulation (by SNS) |
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What level(s) of GFR regulation is under intrinsic control?
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Autoregulation (local level)
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What level(s) of GFR regulation is under extrinsic control?
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Hormonal regulation (initiated by kidneys) and Autonomic regulation (by SNS)
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What is intrinsic control?
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act locally to maintain constant GFR (despite fluctuations in blood pressure or MAP)
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What is extrinsic control?
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aimed at regulating blood pressure (MAP) ... and ultimately GFR (BP drives filtration in the kidneys)
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If we can regulate MAP, Renal BP and/or NFP → can control _____
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GFR
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Autoregulation of Glomerular Filtration Rate (GFR)
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Maintain GFR by changing diameters of afferent arterioles, efferent arterioles & glomerular capillaries
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Autoregulation of Glomerular Filtration Rate (GFR)
If we experience a ↓ in BP do we want to have dilation or constriction of ...... _____ of afferent arteriole _____ of glomerular capillaries _____ of efferent arterioles ... to raise BP to homeostatic levels |
_____ of afferent arteriole
_____ of glomerular capillaries _____ of efferent arterioles |
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Autoregulation of Glomerular Filtration Rate (GFR)
If we experience a ↑ in BP... _____ of afferent arteriole ... to lower BP to homeostatic levels |
_____ of afferent arteriole
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Autoregulation of Glomerular Filtration Rate (GFR)
Under normal conditions, auto regulation maintains nearly _____ GFR |
constant
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Autoregulation of Glomerular Filtration Rate (GFR)
If systemic BP is HIGH → afferent arteriole will be stretched → response: |
Afferent arteriole & glomerular capillary constrict; efferent arteriole dilates → ↓ glomerular hydrostatic pressure → ↓ NFP → ↓ GFR
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Autoregulation of Glomerular Filtration Rate (GFR)
If systemic BP is LOW → |
Afferent arteriole & glomerular capillary dilate; efferent arteriole constricts → ↑ glomerular hydrostatic pressure → ↑ NFP → ↑ GFR
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Hormonal regulation of glomerular filtration rate (GFR) occurs by hormones of the:
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1. renin-angiotensin system
2. natriuretic peptide (ANP and BNP) |
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Renin-Angiotensin System involves the _____.
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Juxtaglomerular Apparatus (JGA)
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Juxtaglomerular Apparatus (JGA) is an endocrine structure that secretes:
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• hormone erythropoietin (EPO)
-RBC production • enzyme Renin -converts angiotensinogen to angiotensis I |
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Autonomic regulation of Glomerular Filtration Rate (GFR) under normal conditions
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(MAP ~ 80-180 mm Hg)
• SNS - at rest • Autoregulatory mechanisms in control • GFR remains relatively constant |
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Autonomic regulation of Glomerular Filtration Rate (GFR) under extreme stress/emergency
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(acute drop in MAP ~ < 80 mm Hg)
• SNS - activated • Neural mechanisms override autoregulatory control • Blood is shunted to vital organs — decrease in GFR After a crisis passes... Sympathetic control decreases ↓ GFR returns to normal |
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Effect of MAP of GFR
Group Questions 1. Why is the line "flat" between 80-180 mm Hg? 2. If MAP increased to 220 mm Hg what would happen? 3. If MAP decreased to 40 mm Hg what would happen? |
1. Why is the line "flat" between 80-180 mm Hg?
2. If MAP increased to 220 mm Hg what would happen? 3. If MAP decreased to 40 mm Hg what would happen? |
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Reabsorption in the Proximal Convoluted Tubule (PCT)
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• "Mass reabsorption" ~ 70% of filtrate is reabsorbed at PCT
• H₂O, nutrients, ions vitamins, etc returned to blood via peritubular capillaries |
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Epithelial cells of the PCT are specialized for transport:
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• transport proteins (pumps, carriers, channels) in apical & basolateral membranes
• microvilli on apical surface face into lumen of tubule (↑↑ surface area) |
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Primary molecule that drives reabsorption at PCT is
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Na+
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[Na+] = PCT lumen > Tubule cell →
Na+/K+ ATP pump → [Na+] = Peritubular fluid > Peritubular capillaries → |
[Na+] = PCT lumen > Tubule cell → passive diffusion into cell
Na+/K+ ATP pump → active transport into peritubular fluid [Na+] = Peritubular fluid > Peritubular capillaries → passive diffusion into blood |
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Movement of Na+ has 3 important effects:
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(1) creates osmotic gradient → results in water reabsorption called: obligatory water reabsorption ("water follows salt")
(2) Creates an electrical gradient that causes negatively charged ions to "follow along" with Na+ and be reabsorped (3) Diffusion of Na+ into PCT tubule cells releases energy that is "captured" and "used" to pump other nutrients (e.g. glucose, amino acids) into cells or wastes out of cells (e.g. H+) = secondary active transport • nutrients will then diffuse out the other side of PCT tubule cells into the ECF → and then into blood |
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What is the osmotic gradient?
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water "follows" the diffusion and active transport of Na+ via osmosis
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What is the electrical gradient?
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negatively charged ions "follow along" with Na+ to be reabsorped
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What is the secondary active transport?
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movement of Na+ into tubule cells releases energy
• energy is "captured" and "used" to pump other nutrients (e.g. glucose, amino acids) into cells or wastes out of cells (e.g. H+) = secretion |
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Secondary active transport also drives _____ transport
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HCO₃-
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Concept of Transport Maximum
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(Tm)
• Carrier proteins (active and passive) can become saturated (full) ∙ reflects number of carriers in the renal tubules available ∙ when carriers are saturated, excess of that substance is excreted in urine (e.g. diabetes mellitus - high [glucose] in filtrate) |
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Substances are not reabsorbed if they:
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• Lack carriers
• are not lipid soluble • are too large to pass through membrane pores • Urea, creatinine and uric acid are the most important non reabsorbed substances |