Module 4: Renal PHGY Flashcards

Question

describe hypotonicity + causes

Answer 1

Associated with overhydration, or excess of free H20 Causes Renal Failure (can't produce concentrated urine) Rapid water ingestion (kidneys can't deal with it quick enough) Over secretion of vasopressin (promotes water retention)

Answer 2

Associated with dehydration Causes Insufficient water intake, not drinking enough Diabetes insipidus, vasopressin deficiency Excessive water loss from exercise, vomiting, or diarrhoea

Answer 3

- Has an equal osmolarity to that of normal body fluids - Isotonic fluids are injected into blood plasma within the veins (1/5th of ECF) - When isotonic fluids are injected into the ECF compartments, the ECF volume increases, but the concentration of the ECF remains unchanged (remains isotonic) - There will be no fluid shift between compartments because ECF and ICF are still in osmotic equilibrium (cells would not shrink nor swell) - Isotonic fluid loss, is confined to the ECF, with no corresponding fluid loss from the ICF.

Answer 4

- Hypothalamus, near the vasopressin-secreting cells and thirst centre, there is hypothalamic osmoreceptors (which monitor osmolality of fluid around them) - If osmolality increases, so does vasopressin secretion and thirst - Vasopressin acts on the kidneys to increase water reabsorption Thirst stimulates the intake of water - If it becomes hypotonic, then vasopressin secretion and thirst are not stimulated. - Large losses of ECF volume also impact these pathways (Left atrial volume receptors) monitor pressure of blood in left atrium, they are activated with more than 7% loss of ECF volume and blood pressure, they also stimulate vasopressin and thirst

Answer 5

Filtration: Removes waste products, toxins, and excess ions from the bloodstream. Fluid and Electrolyte Balance: Regulates body fluid volume and composition by reabsorbing water and electrolytes. Excretion of Waste: Eliminates waste products like urea, creatinine, and uric acid through urine. Acid-Base Balance: Maintains pH levels by excreting or retaining hydrogen and bicarbonate ions. Hormone Production: Renin: Regulates blood pressure. Erythropoietin (EPO): Stimulates red blood cell production. Calcitriol (Active Vitamin D): Regulates calcium and phosphate levels. Blood Pressure Regulation: Controls blood volume and vascular resistance to maintain optimal blood pressure.

Answer 6

Renal Corpuscle: Glomerulus: Network of capillaries where blood filtration occurs. Bowman's Capsule: Surrounds the glomerulus, collecting filtrate from blood. Renal Tubule: Proximal Convoluted Tubule (PCT): Initial segment for reabsorption and secretion. Loop of Henle: Descending and ascending limbs involved in water and ion reabsorption. Distal Convoluted Tubule (DCT): Fine-tunes reabsorption and secretion processes. Collecting Duct: Collects tubular fluid from multiple nephrons, regulates water reabsorption.

Answer 7

Filtration: Occurs in the renal corpuscle. Blood pressure forces fluid and solutes from the glomerulus into Bowman's capsule, forming filtrate. Reabsorption: Takes place in the renal tubules. Essential substances like water, ions, and nutrients are reabsorbed from the tubular fluid back into the bloodstream. Proximal Convoluted Tubule (PCT) is a major site for reabsorption. Secretion: Occurs in the renal tubules. Additional substances, such as waste products and excess ions, are actively transported from the bloodstream into the tubular fluid for excretion. Distal Convoluted Tubule (DCT) and collecting ducts are involved in secretion. Concentration: Involves the loop of Henle and collecting ducts. Establishes a concentration gradient in the medulla, allowing for water reabsorption and concentration of urine. Hypothalamus regulates water reabsorption via Antidiuretic Hormone (ADH). Excretion: Final step where urine is excreted from the body. Urine, containing waste products and excess substances, exits the kidneys via the ureters, bladder, and urethra.

Answer 8

Both neural and endocrine inputs

Answer 9

Maintain water balance in the body Maintain body fluid osmolarity Maintain proper plasma volume Help maintain acid-base balance Regulates ECF solutes (NA, K, Cl, Ca, PO4) Excretes wastes of metabolism Excretes foreign compounds ingested Produces erythropoietin Produces renin Activated Vitamin D

Answer 10

Bean shaped organ 10cm in length An adrenal gland on top of the kidney Outside of the kidney is the renal cortex Inner part is renal medulla Renal pelvis is at the core of the kidney (urine empties) Urine channeled to the ureter Functional unit of the kidney is the nephron (blood is filtered to produce urine and reabsorb fluids and molecules

Answer 11

- Glomerulus (ball-like capillary), is where water and solutes are filtered from plasma - Blood enters the kidney via the renal artery, and this subdivides into afferent arterioles (each supplies a nephron) - Leaving the nephron are efferent arterioles, which transport unfiltered blood from the glomerulus (arterial blood enters and leaves with no oxygen extracted) - Capillaries of the nephron, efferent arterioles subdivide into capillaries, the peritubular capillaries deliver oxygen to renal tissues

Answer 12

(Begins with) Bowmans capsule, encircles the glomerulus to collect filtered fluid Fluid then passes into the proximal tubule within the renal cortex Loop of Henle forms a hairpin loop that dips down into the renal medulla The descending limb of loop of Henle travels from the cortex to the medulla back to the cortex Ascending limb of loop of Henle passes through a fork of the afferent and efferent arteries in a region called juxtaglomerular apparatus. Tubule coils again and is called the distal tubule (within the cortex) The distal tubule empties into a collecting duct, which travels deep into the medulla and drains in the renal pelvis

Answer 13

- Cortical Nephrons- lie in the outer layer of the cortex (secretory and regulatory functions) - Juxtamedullary Nephrons - inner layer of cortex (concentration and dilution of urine function) and they form hairpin loops called vasa recta

Answer 14

20% of blood flowing through the glomerular capsule is foltered in Bowmans capsule

Answer 15

As filtrate flows through the tubules, important substances are returned to the peritubular capillaries by the process of tubular reabsorption

Answer 16

Second route for substances in the blood to enter renal tubules Selective transfer of substances from the peritubular capillaries into the tubules (remaining 80%)

Answer 17

Hydrostatic Pressure in Glomerular Capillaries (PGC): Blood pressure within the glomerular capillaries. Forces fluid and solutes out of the blood into Bowman's capsule. Hydrostatic Pressure in Bowman's Capsule (PBS): Pressure exerted by the filtrate in Bowman's capsule. Opposes filtration by pushing fluid back into the capillaries. Osmotic Pressure in Glomerular Capillaries (πGC): Created by proteins (e.g., albumin) in the blood. Draws water back into the capillaries, opposing filtration. Filtration Pressure (Net Filtration Pressure, NFP): NFP = PGC - (PBS + πGC). Represents the overall pressure gradient driving filtration. Positive NFP favors filtration, while negative NFP opposes it.

Answer 18

Intrinsic Regulation: Myogenic Mechanism: Description: Autoregulatory response to changes in blood pressure. Process: Increased blood pressure stretches afferent arterioles, triggering smooth muscle contraction and vasoconstriction to maintain a steady glomerular filtration rate (GFR). Purpose: Protects glomeruli from damage due to excessive pressure. Tubuloglomerular Feedback (TGF): Description: Feedback mechanism involving the juxtaglomerular apparatus. Process: Macula densa cells in the DCT sense changes in tubular fluid composition, particularly NaCl levels. Increased NaCl concentration triggers vasoconstriction of afferent arterioles, reducing GFR. Purpose: Maintains a stable flow of filtrate to prevent electrolyte imbalances. Extrinsic Regulation: Sympathetic Nervous System (SNS): Description: Neural regulation of renal blood flow. Process: Activation of the SNS leads to vasoconstriction of both afferent and efferent arterioles, reducing GFR and renal blood flow. Purpose: Redirects blood flow to vital organs during times of stress or low blood pressure. Hormonal Regulation: Description: Hormones control renal blood flow and GFR. Example: Angiotensin II, released in response to low blood pressure or low sodium levels, constricts arterioles, increasing blood pressure and GFR. Purpose: Maintains blood pressure and fluid balance.

Answer 19

Vital Function: The kidneys play crucial roles in maintaining fluid balance, electrolyte levels, and blood pressure regulation. Adequate renal blood flow is essential for efficient filtration and waste removal. High Metabolic Demand: Despite their small size relative to body weight, the kidneys have high metabolic activity. They require a significant amount of oxygen and nutrients to support filtration, reabsorption, and secretion processes. Filtration Efficiency: Renal blood flow directly affects glomerular filtration rate (GFR), the rate at which blood is filtered by the kidneys. Higher renal blood flow allows for more efficient filtration and waste removal. Regulatory Role: The kidneys play a critical role in regulating blood pressure through mechanisms like the renin-angiotensin-aldosterone system (RAAS). Adequate blood flow ensures proper activation of these regulatory pathways.

Answer 20

Is a network of capillaries located at the beginning of a nephron Blood is filtered across the walls of this capillary networks through the glomerular membranes (which yields its filtrations into Bowmans capsule) The glomerulus receives its blood supply from an afferent arteriole and the glomerular capillaries exit into efferent arterioles The rate at which blood is filtered through all the glomeruli and the measure of its overall function is the glomerular filtration rate (GFR)

Answer 21

The glomerular capillary wall- large pores, albumin can pass through The basement membrane- collagen for structural strength, and glycoproteins to discourage the filtration of small plasma proteins (1% albumin gets through) The inner layer of Bowman's capsule (podocytes) cells that wrap around the capillaries of the glomerulus, and they form a narrow filtration slit between them to allow fluid to pass into Bowman's capsule

Answer 22

- Glomerular Capillary Blood Pressure - Plasma-Colloid Oncotic Pressure - Bowmans Capsule Hydrostatic Pressure

Answer 23

The presence of large proteins in the plasma that cannot be filtered produces an oncotic force that resists the movement of water into Bowmans capsule 30 mmHg*

Answer 24

Pressure of fluid in Bowman's capsule Resists the movement of water oyt of glomerular capillaries 15 mm Hg *

Answer 25

Dependent on filtration pressure, glomerular SA and permability Those factors are also called the filtration coefficient (Kf)

Answer 26

Regulates the diameter of afferent arterioles Constricting the afferent arterioles = decreased glomerular capillary blood pressure Dilating the afferent arterioles = increased glomerular capillary blood pressure

Answer 27

Increased pressure stretches the afferent arteriole walls, they automatically constrict to reduce blood flow, and thus preventing a GFR increase

Answer 28

- Macula densa-sense changes in salt level of the tubular fluid - Increased arterial pressure increases GFR, more fluid will flow through the distal tubule = an increased salt delivery - In response to increased salt, the macula densa will release ATP, degraded to adenosine, which then causes constriction and reduces GFR

Answer 29

Decrease in glomerular capillary blood pressure A decrease in net filtration pressure A decrease in GFR

Answer 30

Increase in glomerular capillary blood pressure Increase in net filtration pressure An increase in GFR

Answer 31

- Extrinsic control, independent of arterial blood pressure - Baroreceptors sense the drop in arterial blood pressure - Kidneys increase sympathetic activity, constricting afferent arterioles, and decreasing GFR, and reducing urine production

Answer 32

Signifies the importance of the kidneys Not for oxygen, but to deliver blood for cleaning Also allows kidneys to maintain tight control of volume and electrolyte concentrations of the body's water pools and eliminate wastes efficiently

Answer 33

Sodium Entry: Sodium ions (Na⁺) enter epithelial cells from the lumen through specific transport proteins like sodium channels or co-transporters. Intracellular Transport: Na⁺ is transported across the epithelial cell via diffusion or active transport mechanisms. Basolateral Exit: Na⁺ exits the cell into the interstitial fluid through sodium-potassium pumps located on the basolateral membrane. Secondary Active Transport: Na⁺ exit creates an electrochemical gradient, driving the co-transport of other solutes into the cell against their concentration gradient. Water Reabsorption: Reabsorption of Na⁺ and co-transported solutes increases interstitial osmolarity, promoting water reabsorption from the lumen into the interstitial space

Answer 34

Hormonal Regulation: Aldosterone: Released by the adrenal glands in response to low sodium levels or high potassium levels in the blood. Stimulates the reabsorption of sodium ions in the distal convoluted tubule (DCT) and collecting ducts by increasing the activity of sodium channels and sodium-potassium pumps on the apical and basolateral membranes of epithelial cells. Atrial Natriuretic Peptide (ANP): Released by the heart in response to high blood pressure or volume. Inhibits the reabsorption of sodium ions in the distal nephron segments, promoting sodium excretion and water loss. Autoregulation: Tubuloglomerular Feedback (TGF): Macula densa cells in the distal convoluted tubule sense changes in sodium chloride concentration in the tubular fluid. Increased sodium chloride concentration triggers vasoconstriction of afferent arterioles, reducing glomerular filtration rate (GFR) and sodium reabsorption to maintain a stable flow of filtrate. Myogenic Mechanism: Smooth muscle cells in the afferent arterioles respond to changes in blood pressure by constricting or dilating to regulate renal blood flow and sodium filtration. Neural Regulation: Sympathetic Nervous System (SNS): Activation of the SNS leads to vasoconstriction of renal blood vessels, reducing renal blood flow and sodium filtration, particularly in response to low blood pressure or acute stress.

Answer 35

Definition: Tm (Transport Maximum): The maximum rate at which a substance can be reabsorbed by the renal tubules. Represents the saturation point of transporters responsible for reabsorption. Importance: Efficient Reabsorption: Ensures that essential substances like glucose, amino acids, and vitamins are fully reabsorbed from the filtrate into the bloodstream. Prevents Losses: Prevents the loss of valuable nutrients and other solutes in the urine. Maintains Homeostasis: Helps maintain optimal levels of nutrients and other solutes in the body fluids, supporting overall physiological function

Answer 36

Proximal Convoluted Tubule (PCT): Description: Site of major water reabsorption, driven by osmotic forces created by solute reabsorption. Process: Water follows the reabsorption of solutes like sodium, glucose, and amino acids from the tubular fluid into the bloodstream. Descending Limb of the Loop of Henle: Description: Highly permeable to water but not to solutes. Process: Water moves out of the tubular fluid through osmosis into the interstitial space, driven by the increasing osmolarity of the renal medulla. Thin Ascending Limb of the Loop of Henle: Description: Impermeable to water but allows passive transport of solutes. Process: No water reabsorption occurs in this segment, contributing to the concentration gradient in the medulla. Thick Ascending Limb of the Loop of Henle: Description: Impermeable to water but actively transports solutes like sodium, chloride, and potassium out of the tubular fluid. Process: Creates a dilute tubular fluid, contributing to the osmotic gradient in the medulla. Distal Convoluted Tubule (DCT) and Collecting Ducts**: Description: Water reabsorption occurs under the influence of antidiuretic hormone (ADH). Process: ADH increases the permeability of the tubular epithelium to water, allowing water to move out of the tubular fluid and into the interstitial space, following the osmotic gradient established by solute reabsorption.

Answer 37

Processes by which water and other necessary solutes are returned to the plasma, while allowing waste products to remain in the filtrate 1. Reabsorption begins with either active or passive movement of substances from the tubule into the interstitial space 2. Reabsorption then continues with passive movement of substances from the interstitial space back into the bloodstream

Answer 38

Water-mostly reabsorbed Sodium-mostly reabsorbed Urea-half reabsorbed Phenol-none reabsorbed

Answer 39

- The tubule is composed of a single layer of epithelial cells - Epithelial cells that are in contact with the tubule lumen is the luminal membrane, and the area of the epithelial cells that are in contact with the tubule lumen is the luminal membrane - Epithelial cells that are in contact with the interstitial fluid is the basolateral membrane - Transepithelial transport is defined as the movement of solutes across an epithelial cell layer throughout the cell - Tight junctions between them (substance must move through the cell into the interstitial space

Answer 40

Steps : 1. Substance moves across luminal membrane 2. Substance passes through cytosol 3. Substance moves across basolateral membrane 4. Substance diffuses through interstitial fluid 5. Substance crosses capillary wall to enter plasma

Answer 41

The proximal tubule - 76% reabsorbed Na+ (needed for reabsorption of glucose, amino acids, water, Cl, and urea( The ascending limb of the loop of Henle - 25% reabsorbed (Na and Cl are essential for concentration or dilution of urine) The distal and collecting tubules - 8% (hormonal control and plays a key role in regulating ECF volume and secretion of both K and H

Answer 42

- Active and passive for Na - Movement of Na across basolateral membranes is active transport with Na K ATPase pump - 80% of energy needs from kidney is for this

Answer 43

- Luminal membrane transport - Na crosses by a cotransporter in the proximal tubule that also moves glucose and amino acids - These nutrients are transferred by secondary active transport (they use the gradient concentration of Na established by the K-Na pump to be transported against their concentration gradient along with Na - In the collecting duct, Na passively enters the epithelial cell

Answer 44

- Granular cells detect a drop in blood pressure, secretes renin - Granular cells innervated by the sympathetic nervous system will release renin when sympathetic activity increases - Macula densa cells are sensitive to Na, and a decrease in luminal Na triggers secretion of renin

Answer 45

- Renin acts like an enzyme and converts angiotensin into angiotensin I - Circulating angiotensin I passes through the lungs, it is converted to angiotensin II by the enzyme angiotensin converting enzyme (ACE) - Angiotensin II stimulates the adrenal cortex, and the release of aldosterone - Aldosterone increases Na reabsorption in the distal and collecting tubules

Answer 46

- Under the influence of aldosterone, tubular epithelial cells increase the insertion of Na channels in the luminal membrane and Na K ATPase carriers in the basolateral membrane - This makes a greater flow of Na out of tubular fluid - This enhanced Na retention increases water retention - Water follows Na

Answer 47

- Opposite of aldosterone - Reduces Na load - Reduces blood pressure Actions 1. Inhibits Na reabsorption in the distal tubules (more Na excreted in urine) 2. Inhibits renin and aldosterone secretion 3. Dilates the afferent arterioles and increases GFR (more salt and water filtered= more salt and water excreted)

Answer 48

A limited number of carrier proteins in a membrane Limit to how much substance can be absorbed Tubular or transport maximum ™ For any substance, if its concentration in the tubular fluid exceeds Tm, then the excess will be secreted in the urine Plasma concentration at which Tm is exceeded is called the renal threshold

Answer 49

Kidneys regulate phosphate plasma concentration Renal threshold for phosphate is the same as normal plasma concentration of phosphate Phosphate and calcium are hormonal regulation

Answer 50

Not regulated by kidneys Have a Tm for reabsorption Urine usually does not have glucose because kidneys reabsorb it Proximal tubule can only reabsorb a limited amount of glucose, if it gets over this then glucose appears in urine

Answer 51

- Water is passively reabsorbed as it follows sodium - Water flows through water channels called aquaporins (proximal tubule are controlled by osmosis) (distal tubule are controlled by vasopressin so not always open) - Chloride is not directly regulated by kidneys, moves between epithelial cells, and goes down electrochemical gradient, following the amount of Na reabsorption (amount of chloride is determined by amount of sodium) - Urea is a waste product of protein, renal failure=less urea is excreted so it accumulates in plasma

Answer 52

Hydrogen Ion Secretion: Description: Process of actively transporting hydrogen ions (H⁺) from the blood into the renal tubular fluid. Location: Primarily occurs in the proximal tubule and collecting ducts. Process: H⁺ ions are secreted across the tubular epithelium into the tubular fluid via hydrogen pumps, primarily in exchange for sodium ions (Na⁺) or bicarbonate ions (HCO₃⁻). Purpose: Helps regulate blood pH by eliminating excess acid from the body. Potassium Ion Secretion: Description: Process of actively transporting potassium ions (K⁺) from the blood into the renal tubular fluid. Location: Occurs primarily in the distal tubule and collecting ducts. Process: K⁺ ions are secreted across the tubular epithelium into the tubular fluid via potassium pumps, typically in exchange for sodium ions (Na⁺). Purpose: Regulates potassium balance in the body, ensuring optimal cellular function and electrical activity.

Answer 53

xic Waste Removal: Description: Organic anions and cations include metabolites, drugs, and toxins that need to be eliminated from the body. Importance: Secretion of these substances into the renal tubular fluid facilitates their removal from the bloodstream, preventing accumulation and potential toxicity. Renal Excretion of Drugs: Description: Many drugs and their metabolites are organic compounds that require renal excretion to be eliminated from the body. Importance: Secretion of these substances ensures effective clearance of drugs and metabolites, optimizing therapeutic outcomes and preventing adverse effects. Regulation of Body Homeostasis: Description: Organic anions and cations include endogenous substances like hormones, neurotransmitters, and metabolites involved in various physiological processes. Importance: Proper secretion of these substances helps regulate body homeostasis by controlling their levels in the bloodstream, ensuring optimal physiological function. Maintenance of Acid-Base Balance: Description: Organic anions like citrate and cations like ammonia are involved in buffering systems that help maintain acid-base balance in the body. Importance: Secretion of these compounds contributes to the regulation of blood pH, preventing acidosis or alkalosis.

Answer 54

- Involves the movement of substances from the peritubular capillaries to the tubule lumen, for removal of substances - Substances that undergo tubular secretion: Hydrogen ions, potassium ions, organic anion and cations

Answer 55

Secreted in the proximal, distal and collecting ducts Too much H+ in plasma = secretion Low H+ in plasma = decreases tubular secretion of H+ Renal H+ regulates the acid-base balance

Answer 56

Tubular reabsorption and secretion Kidneys regulate plasma K levels K+ ion secretion in the distal tubule is an active process dependent upon Na - K - ATPase pump

Answer 57

Increasing secretion-adding more organic ions to tubular fluid can increase the organic ion excreted Excrete poorly soluble organic ions Removal of foreign compounds

Answer 58

A rise in plasma K+ = release of aldosterone Aldosterone increases Na reabsorption, secreting more K H+ secretion effects it

Answer 59

Definition: Plasma clearance refers to the volume of plasma that is completely cleared of a substance by the kidneys per unit of time. Process: It measures the efficiency of the kidneys in removing a specific substance from the bloodstream. Clearance is determined by the rate at which the substance is filtered by the glomeruli, reabsorbed from the tubular fluid, and secreted into the tubular fluid. Calculation: Clearance (C) is calculated using the formula: C = (U x V) / P, where: C = clearance, U = urinary concentration of the substance, V = urine flow rate (volume of urine produced per unit of time), P = plasma concentration of the substance. Importance: Plasma clearance provides valuable information about kidney function and the rate at which a substance is eliminated from the body. It is used clinically to assess renal function, monitor the progression of kidney diseases, and adjust drug dosages based on renal clearance rates.

Answer 60

The vertical osmotic gradient in the renal medulla is crucial for concentrating urine and conserving water. It is generated by countercurrent exchange mechanisms in the loop of Henle and maintained by the vasa recta. This gradient allows the kidneys to regulate urine concentration and maintain fluid balance, making it essential for overall kidney function and homeostasis.

Answer 61

The loop of Henle is essential for generating the osmotic gradient necessary for water reabsorption and urine concentration. Its unique structure, with a descending limb permeable to water and an ascending limb actively transporting solutes, facilitates the establishment and maintenance of the osmotic gradient. Dysfunction of the loop of Henle can lead to impaired kidney function and electrolyte imbalances, highlighting its critical role in renal physiology.

Answer 62

Countercurrent exchange is a physiological process essential for efficient urine concentration in the kidneys. By creating and maintaining osmotic gradients through countercurrent flow, it maximizes water reabsorption and facilitates electrolyte balance, contributing to overall renal function and fluid homeostasis.

Answer 63

The micturition reflex is an involuntary neurological process that coordinates bladder contraction and sphincter relaxation to facilitate urination. Initiated by bladder distension, the reflex arc involves sensory input, spinal cord processing, and efferent motor output to ensure controlled voiding. Dysfunction of this reflex can lead to urinary issues and is associated with various neurological conditions.

Answer 64

Substances have been cleaned from the plasma (any substance as the volume of plasma cleared of that substance by the kidneys per minute Plasma clearance expresses the effectiveness of the kidneys to remove a substance from internal fluids Types 1. Substances that are filtered, not absorbed (insulin) 2. Substances that are filtered and reabsorbed (glucose) 3. Substances that are filtered and secreted (hydrogen)

Answer 65

Concentrate urine occurs because there is a vertical osmotic gradient in the interstitial fluid of the medulla

Answer 66

the loop of Henle only dips slightly into the medulla

Answer 67

the loop of Henle dips all the way down to the renal pelvis. the vasa recta of these nephrons also goes all the way to the renal pelvis. flow in the loop of Henle and the vasa recta goes in opposite directions in what is called countercurrent flow

Answer 68

1. Fluid leaves Bowman's capsule and enters proximal tubule (strong osmotic reabsorption drive) 2. Isotonic tubular fluid 965% of filtrate volume absorbed at proximal tubule) 3. Loop of Henle, additional 15% of filtered water is reabsorbed

Answer 69

- Descending and ascending limbs are in close proximity, and so important interactions occur between them to establish the vertical osmotic gradient - Filtrate is constantly flowing - Fluid from the proximal tubule enters the descending loop of Henle (300 mOsm/L) and the interstitial space is also 300 mOsm/L = both isotonic and no net movement - Na moves into the interstitial space until it is 200 mOsm/L more concentrated than the ascending limb (tubular fluid is 200 mOsm/L and the interstitial fluid is 400 mOsm/L - As new fluid moves into the descending loop of Henle, fluid shifts so we have 300 mOsm/L (pushing the 400 mOsm/L fluid deeper into the medulla - While the ascending limb is still transporting Na out, water continues to passively leave the descending limb until 200 mOSM/L difference - A fresh 300 mOsm/L enters the descending loop, stopping the vertical gradient until it re equilibriates - Again, fresh filtrate enters,, and the osmolarity of the interstitial fluid increases, and the osmolarity of the ascending loop decreases to maintain 200 mOsm/L difference - Eventually, equilibrium is achieved and even the (300 mOsm/L) filtrate, the vertical osmotic gradient results in it being 1200 mOsm/L as it enters the ascending limb, and the tubular fluid is at 100 mOsm/L as it enters the distal tubule

Answer 70

The isotonic fluid that enters the loop becomes progressively more concentrated as it flows down the descending limb, only to become more dilute as it flows up the descending limb

Answer 71

Allows the collecting ducts to both form more concentrated and more dilute urine than normal bodily fluids Allows the overall volume of urine to be significantly reduced (conserves both salt and water)

Answer 72

Vasopressin (antidiuretic hormone) released from the posterior pituitary gland is released in response to a water deficit (Hypertonic ECF) It's release is inhibited when the ECF is hypotonic Once released into circulation, it travels to the kidneys where it acts on distal tubular cells to increase the number of aquaporin molecules in the luminal membrane (increases amount of water reabsorbed into the epithelial cells) Once inside the epithelial cells, water passively moves into the interstitial fluid and plasma (only works is proximal and distal tubules)

Answer 73

Tubular fluid entering the distal tubule is around 100 mOsm/L Interstitial fluid of the renal cortex is 300 mOsm/L, and gets higher approaching 1200 mOsm/L These gradients mean that water wants to leave the tubular fluid due to osmosis, but can only do so in the presence of vasopressin Deficit of water-dehydration = vasopressin hormone, increasing aquaporin channels in the distal and collecting ducts Excess of water- body fluid osmolarity below 300 mOsm/L, so hypotonic that vasopressin is supressed, this prevents the insertion of aquaporins in the luminal membrane

Answer 74

Ensures tubular fluid is always hypotonic to interstitial fluid

Answer 75

- vasa recta (blood supply to the renal medulla) 1. as efferent arteriolar blood leaves the renal cortex, its osmolarity is 300 mOsm/L, isotonic to the interstitial fluid 2. as the descending loop moves towards the renal pelvis, the plasma remains isotonic to the surrounding interstitial fluid by reabsorbing Na+ and water leaving. 3. At the bottom of the loop, the plasma osmolarity is 1200 mOsm/L 4. As the blood flows up the ascending limb, the opposite occurs with water being reabsorbed and Na+ leaving, to keep the plasma isotonic with the different levels of the medulla 5. as the vasa recta re-enters the cortex its osmolarity is back to 300 mOsm/L, again isotonic to the interstitial fluid

Answer 76

Tubular segments permeable to water, solute reabsorption always leads to water reabsorption due to osmosis Osmotic diuresis (increased secretion of both water and excess un-reabsorbed solute Excess glucose in tubules attract water and increase urine production, as seen with diabetics Water diuresis (an increases excretion of water when there is little to no change in the excretion of solutes) (alcohol consumption because vasopressin is suppressed)

Answer 77

- The bladder is composed of smooth muscle and can expand to increase storage (parasympathetic nervous system = bladder contraction) - Urethra is the exit, guarded by an internal urethral sphincter and external - Internal=voluntary control (relaxed bladder=closed) - External=closed constant, tonic firing motor neurons (Voluntary control by deliberately tightening)

Answer 78

Micturition is the process of bladder emptying and is governed by 2 mechanisms Micturition reflex- adult bladder holds 250-400 mL before the internal pressure on the bladder wall initiates the micturition reflex (this stretch activates afferent fibres to the spinal cord where interneurons activate the parasympathetic system) (bladder contraction and relaxation of external sphincter) Voluntary Control- micturition can be overrode by voluntary control, learning the perception of bladder filling prior to the activation of the reflex, voluntary excitatory signals from the cerebral cortex can override this reflex.