1
Q
What is the concept of water balance
A
ECF extra cellular fluid
* FLuid that surrounds the cells
* Includes, plasma, intersitial fluid
* trabscellular fluid such as CSF
* is a 1/3 of all body fluid
ICF
* Fluid within the cells and is 2/3 total body fluid
2
Q
What are the barriers between the Plasma and the Intersitialfluid
A
- seperated by blood vessel walls
- At capillary levels, water and everything else in the plasma except proteins can exchange w/ ICF
- compositions are the same
- Any change in one compartment is reflected in the other
3
Q
What are the barriers between the ICF and the ECF
A
- Barrier is the plasma membrane
- ICF has proteins that do not exchange with the ECF
- Unequal distribution of ions across this barrier
- COncentration of K isgrater in the ICF while concentration of NA is greater in the ECF
- Barrier does not allow passive movement of ICF or ECF constituents
- PReventing them from equilibriumn by diffusion
4
Q
What is the ECF volume and osmolarity
A
- Exhcnage of materials and water between the ICF and external world dependnt on the ECF
- Even cells that tightly regulate their own ICF can be said that the overral control of the fluid bapance is dependent upon regulaying the ECF
**ECF Volume ** - closely regulated to maintain BP
- Maintainace of salt balance is important for the loing term regulatyion of the ECF volume
ECF osmolarity
* CLosely regulated prevents the swelling or shrinkage of cells
5
Q
Control of ECF volume
A
- ECF volume directly influences blood plasma pressure by changing plasma volume
- Increasing ECF volume will increase plasma volume nadt hus increase the BP
- There are mechanisms that control tehse factors
6
Q
WHat are the shrot term control factors of the ECF volume
A
Baroreceptor reflex
* mehcanoreceptors in the carotid artery and the aortic areas
* Detect changes in Arterial BP though the ANS on heart and blood vessels
* When pressure falls too low cardiac output and the pheripheral resistance will increase to raise BP
* When Bp rises above normal, both decrease to reduce blood pressure
FLuid shifts
* Decrease in plasma volume can temp be compensated by a shift in fluids out of the ICF and into the plasma
* Oppoiste is also trie
* Increase in plasma volkume can cause fluid to shift to the Intersiotial compartment
7
Q
WHat are the long term factors that affect the control of ECF volume
A
** Fluid input/output**
* short term are temporary and only account for minor changes
* Long term is the primary function of the kidneys
* regulation of blood pressure
* Kidneys control fluid oputput and input
* Kidney is critical for long term regulation of BP
8
Q
How is salt controlled
A
- Na and anions account ofr 90% of ECF solutes
- when salt is transported across a membrane
- water follows because of osmosis
- This is used to control salt levels
9
Q
How is salt input controlled
A
- Poor becuase dependent on dietary salt
- necessary on a daily basiss to replace salt lost in feces and sweat
- more salt and physical actiovites will require more
10
Q
How is salt output controlled
A
- Eliminated through the kidneys
- 3 paythways to eliminate salt
- Feces
- sweat
- kidneys
11
Q
What is hypotonicity
A
- Associated with overhydration
- excess free H2O has 3 major causes
Renal failure - patient unable to produce cincentrated urine
Rapid water ingestion
* Occurs in healthy individuals if they drink water volumes in excess of what the kidneys can deal with in a timely manner
Over secretion of vasopressin
* Promotes water retention
12
Q
What is the regulation of water balance
A
- Within the hypothalamus, near the vasopressin secreting cells and the thirst centers
- Are hypothalamic osmoreceptors which constantly monitor osmolarity of the fluid surrounding them
- In order to counteract and fluctuations in water balance
- Hypothalamic osmoreceptors monitor osmolarity in the fluid surrounding them
- As osmolarity increases both vasopressin secretion and thirst are stimed
- vasopressin acts on the kidneys increase wtaer retension
- thirst stims intake of water
- if fluids in osmoreceptors are hypotonic, water loss is promoted by not secreting vasopressin and thirst
- large losses in ECF volume impact these pathways
- left atrium as artial receptors which monitor pressiure of the blood in the left atrium
- Activated when there is a greater than 7% loss in ECF volume and blood pressure
- Once activated, they also stim the hypothalamic pathway
13
Q
What is a basic overview of the kidneys
A
- controlled by neural and endocrine inputs
- Primary function is to maintain ECF volume, electrolyte and osmolarity
- In the presence of excess water or of a particular electrolyte
- Kidneys increase their elimination when there is a deficienty of water or solute
- Kidneys cannot actively correct this
- can can further reduce their elimination
14
Q
WHat are the functions of the kidney
A
- Maintain water balance
- maintain fluid osmolarity
- Maintain proper plasma volume
- Help maintain acid-base balance
- Regulate ECF solutes such as Na, K, Cl, Ca, P and others
- excrete wastes of metabolism
- Excrete foreign compounds ingested
- Produce erthorpotein
- Produce renin
- Activate vitamin D
15
Q
WHat is the structure of the kidneys
A
- Outside is the renal cortex
- Inside in the renal medulla
- Inner core of each kidney is the renal pelvis where urine emptoes and is channeled to the ureter
- Functional unit of the kidney is the nephron
- More than 1 mil of them
16
Q
WHat is the nephron
A
- Has 2 components
- Vascular supplies blood to the nephron
- Tubular carrier filtrate throughout the nephron
17
Q
WHat is the vascular component of the kidneys
A
- Major part is the glomerulus - ball like capillary which water bad solutes are filtered through the plasma
- blood enters kidney from renal artery
- it then subdivides into many small afferent arteriol;es which supply a nephron
- Leaving the nephraon are the efferent arterioles which transport unfiltered blood from the glomerulus
- Capillaries of the nepgron are differeny in the arterial blood
- Enters then leave with no O2 extracted
- Instead efferent arteries subdivide into capillaries in the pertubular capillaries that deliver O2 to renal tissues
18
Q
What are the tubular components of the kidney
A
- Filtered blood enters the tube formed by a sungle layer of epithelia cells
- Trabsports urine to the renal pelvis
- Tehcnically a continous tube
- Dvided based on differences in struicture and function
- Begins with the bowmans capsule which encircules the glomerules to collect fluid filtered from the glomerular capillaries
- Fluid passes into the proximal tubule within the rebal corttex
- Highly coiled in length
- Next is the loop of henle.
- This is a hairpin which dups into the medulla
- Desecnding limb of the loop of henle travels from the cortex to the medulla while the ascending travels from the medulla back to the cortex
- Ascending limb passes through the fork of the afferent and efferent arteries in a region called the juxtaglomerular apparatus
- Then coils into the distal tubule
- the ntmpties into the duct which travels deep into the medulla and drains in the renal pelvvis
19
Q
What are the 2 types of nephrons
A
- Cortical
- Juxtaglomerular
20
Q
What are cortical nephrons
A
- Glomeruli of this type of nephron are on the outer layer of the cortex
- 80% of all nephrons are cortical and primarily serve the secretory regulatory functions
- Their loop of henle slihhyly dips into the medulla
- The pertubular capillaries from this type of nephron wrap around the short loops of henle
21
Q
WHat is a juxtamedullary nephron
A
Found in the inner layer of the cortex
Responsible for concentration and dillution of urine from the pertubular capillaries
They form loops of vasculature called vasa recta that are in close proximity to the long loops of henle
22
Q
WHat are the 3 basic renal processes
A
Glomerular filtration
* 20% of all blood that flows through the glomerular capillaries is filtered into the bowmans
* This plasma giltrate is normally protein free
* Does contain the same solutes as the plasma
* 125mL of glomerular filtrate is formed every minute
Tubular reabsorption
* FIltrate flows through the tubules
* Substances are returned to the pertubular capillaries by the process of tubular reabsorption
* 180L of plasma filtered each day 178,5mL are reabsorbed
Tubular secretion
* Second route for substances in the blood to enter the renal tubules
* Selectibe yransfer of substances from the pertubular capillaries into the tubules
* 20% of the plasma is filyered in the glomerulo
* This route allows the excretion of selectyed substances from the remanining 80% of the the plasma
23
Q
WHat is the glomerulus
A
- Network of cpaillaries located at the begnning of a nephron
- Blood is fultered acorss the walls of this capillaru through the glomerular membrane
- Yield filtrate into the bowmans capsule
- Filtrtae enters the renal tubule of the nephron
- Recieves its blood supply from the afferent arteriole and the glomerular capilalries exit into efferent arterioles
- Rate of blood is filtered through the glomruli
- The measure of all renal functions is the glomerular filtrate rate GFR
24
Q
What is glomerular filtration
A
Glomerular capillary wall
* single layuer of endothelial cells
* Large pores make it 100x more permeable to fluids and solutes than regular capillaries
* Pores are of such size that large plasma proteins cannot pass but small ones like albumin can
Basement membrane
* Layer contains no cells
* COllagen layer which provides strength
* GLycoproteins discourage the filtratetion of small plasma proteins
* Glycoproteins are negatively charged
* They repel any proteins that do get through capillary walls
* 1% of filtered albumin will pass the capsule
Inner layer of bowmans capsule
* Layer composed of podocytes
* Form narrow filtration slits between them
* allow fluid to pass into the bowmans capsule
25
WHat are the forces that regulate GFR
**GLomerular capillary blood pressure**
* pressure exerted by blood in the glomerular capillaries
* Regular capillaries have a pressure of 18mmHg
* GLomerular capillaries average 55mHg
* Due to afferent arteriole diameter being larger tnan the diameter of the efferent arterioles
* Increase resistance to blood leaving the glomerular capillaries
* Also prevents glomerula capillary pressure from decreasing along their length further favouyring filtration
**Plasma colloid oncotic pressure**
* PResence of large poroteins in the plasma tha tcannot be filtered produce and oncotic force that resists the movement of water into the bowmans
* The plasma colloid oncotic pressure is about 30mmHg
**Bowmans capsule hydrostatic presusre**
* Pressure of the fluid in the bowmans
* Resist movement of water out of the glomerula capillaries
* HAs a hydrostatic pressure of 15mmHg
26
WHat is the GFR
* Filtration coefficent (Kf)
* Kf x filtration pressure = GFR
27
what are controlled changes in GFR
* look at onenote
28
WHat is autoregulation
* Changes in GFR are directly proportional to capilalry blood pressure
* autoregulatory mechanisms are in palce to prevent sudden swings in GFR
29
What is myogenic activity in autoregulation
* Increased pressure streches the afferent arterioles
* AUto constric tto reduce blood flow to the glomerular
* This prevents increase in GFR
* opposite is also true
* BP decreases, afferent arterioles will dillate to increase flow and prevemnty a decrease in GFR
* Constriction of blood vessels is called vasocontriction
* Vasodillation is the dillation of them
30
What is tuboglomerular feedback
* Jucxtaglomerular appratus is the area of distal tubult that passes through region where afferent and efferent arterioles meet
* combination of tubular and vascular cells
* Specialized tubualr cells in this are are collectively called the macula densa
* Sense changes in salt level of the tubular fluid
* IF increase in arterial pressure that increases the GFR
* more fluid than normal will flow through the distal tubule
* Also means there is an increased salt delivery
* In response to the macula dense releases ATO
* degreated DEnosine
* This acts on teh afferent arteruoles to cayse constriction and reduce GFR
* opposite is also true
31
What is the sympathetic control of the GFR
* under intrinsic and extrinsic control
* independent of fluctations of blood
* COntrolled by sympathetic nervous system
* Use heamoraage as an example - sudden loss of blood volume
* FOllowed by a drop in arterial pressure
* This is sense by baroreceptors
* initiates responses to normalize blood pressure
* Kidney level increased sympatyhetic activity would constrict the afferent arterioles
* Decreases glomerular capilary pressure
* Decreasing GFR and reducing urine production
* This is mechanisms which depleyted plasma vokumes can be corrected
32
33
What are the kidneys and the cardiac output
* 20% of plasma enters the kidneys and becomes glomerular filtrate
* means 125mL/min
* Total blood flow to kidneys must be 5x125 or 625ml/minute
* 55% of whole blood is filterable plasma
* adjust renal blood flow to 1140ml/minute
* total cardiac output equals around 5000mL
* calculate kidneys recieved around 22% of total cardiac output
* This far exceeds what would be expected based on tissue size
* kidney weight is only 1% of total body weight
34
WHat is tubular reabsorption
* GLomerular filtrate that enters tubules is identical to plasma
* Exception of plasma proteins
* No slectivity to glomerular filtration
* Tubular reabsorption includes the processes water and other solutes are retruned to the plasma
* Allowing waste products to remain i nfiltrate
* Reabsorption begins weather passive or active movement of substances
* from tubule to intersitial spaces
* Continues iwth passive movement of substances from the intersitial space back to the blood stream
35
What are the fates of various susbtances filtered by the kidneys
* Tubular reabsorption is highly seletcive and variable
* tubules have high rebasorptive abilities needed for the body
* it has a low reabsortive capacity for substances that are not needed
* water and solutes are critical for maintaining homeostasis, theur tubular reabsorption is high
* General trend can be seen in the chart comparing percentages of reabsorbed substances
36
What is transepitheilal transport
* tubule composed of a single layer of epithelial cells
* They are in contact with the tubule lumen
* They are called luminal membrane
* cells with the intersitual fluid are **basolateral membrane**
* Transepithelial transported is the movement of solutes across the epithelail layer through the cell
* Membranes from, neighboring epithelial cells are not in contact
* Other than where tight junctions connect them
* SUbstances that enter an epithelila cell cannot transport it to a neighbouring cell
* substances must move through the cell into the intersitial space
37
Steps on transepithelial transport
Substances cross luminal membrane
substances must pass through cytosol
Substances cross basolateral membrane
Diffuse through intersitial fluid
Cross the cpaillary wall to enter the plasma
38
WHat is the location of rebasorption of Na
* 99.5% of all Na is reabsorbed
* Na can be reabsorbed to various extents
* Along the entire tubules
* Na is rebabsorbed in so many places, it is critical to the reabsorpotion of other substances
**Proximal tubule**
* 76% Na here in the segment of the nephron is needed fpr yje reabsorption of glucose
* amino acids, water, Cl, and urea
**Ascending limb and loop of henle**
* Absorbs 25% of the total reabsorbed Na
* Na along with Cl are seential to concentrate or dillute
* urine depening on what the body needs
**Distal and collecting tubules**
* Collectively reabsorb 8% of Na
* Na reabsorptopm is under hormonal control
* plasma plays a key role in regulating eCF volume and secretion of K and H
39
How is Na Actively transported in the kidneys
* Reabsorption is active and passive
* Na moves passively acorss the luminal membrane
* Movement of NA across the basolateral membrane is active transport involbing NaK ATPase pump
* Large colume of Na that is reabsorebd accounts for 80% of energy needs by kidneys
* Actively transporting Na into the intersitial fluid, it helps keep the cyotsol Na concentration low to allow for the passive diffuision across the luminal membrane
40
What is the passive transport of NA
* Passive transport of Na across the luminal membrane varies throughout the various segments of the tubules
* Proximal tubule
* Na crosses by a cotransporter carrier that simultanouesly moves organic nutrients such as glucose and amino acids
* These nutrients are transffered by secondary active transport
* They are concentrtaion gradients of Na established by NA K ATPase pumps to bet ransported against their concentration gradient
* Along with the passive transport of NA
* They collecting duct NA passively enters the epithelial cells through the NA channel
41
WHat is the hormonal regulation of NA
* In proximal tubule and loop of henle, constant percentage of Na is reabsorbed regardless of the total amount of NA within the body fluids
* In the distal tubule, however the reabsorbtion of a small percentage is filytered NA is subject to hormonal control
* ReninAngiotensin-aldosterone system within the Juxtaglomerular appratus
* Granular cells secrete renin into blood
* granular cells detect a drop in BP and secrete Renin
* Granular cells are innervated by the sympathetic nervous system, release renin when sympathetic activity increases
* Macula densa cells in the tubular portion of the juxtaglomerular appratus are sentive to the NA and when there is a decrease in Luminal NA. The macula Densa cells trigger the grabular cells to secrete them
42
What is NA and Renin's relation
**Renin**
* When secreted acts like an enxyme to convert angiotensin into angiotensin I
**Angiotensin converting enzyme**
* 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 to release aldosterone
**Aldosterone**
* Causes increase in NA reabsorption in the distal and collecting tubules
43
WHat is atrial natur uetic peptide ANP
* Another homrone involved in regulation of Na
* actions are opposite of aldosterone
* ANP released Na and blood pressire when blood volume increases
* Or an increase in venous return, stretch receptors in the left atrium, aortic arch, and carotid sinus tim the release of ANP
**3 main actions**
* Inhibuts Na reabsorption in the dustal tubule so there is more Na excreted in urine
* inhibits renin and aldosterone secretion
* Dillates the afferent arteroles and increases GFr, as more salt and water are filteres, more salt and water are excreted
44
What are the atcively reabsorbed susbtances
* Any substance that is actigvely reabsorbed will bind to s epcific carrier protein in the plasma
* Limited number of protein carriers in the membrane
* **This is called the tubular transport maximum**
* if concentration of the tubular fluid exceeds its Tmax, excesds will be excreted in the urine plasma concentration at which the Tm exceeded is calledt he renal trheshold
* Plasma concnetrated of many substances is reguklated by the kidneys
* carrier mediated limitation an example is phosphate
* som substances like glucose habe a Tm but their plasma concentration are not regulated by the kidneys
45
What is the realtionship of phosphate and the kidneys
* Renal threshold for phosphate is the same as normal plasma concnetration of phosphate
* diets are rich in phosphate
* after eating there is a rise in phosphate
* increases the filtered load of the phosphate
* since max reabsorbtopn is the same as the plasme phosphate concentration, All phosphate above the normla plasma concnetration is excreted in the urine
* Restores plamsa phosphate concentration to normal
* Reabsorpton of Phosphate and Ca are under homronal control
* Hormone can alter renal thresholds and mediatet heir reabsorption to match the bodys needs
46
WHat ist he relationship of glucose and the kdiney
* Not regulated by the kidney
* small enough to be freely filterable
* plasma concnetration of 100mg per 100ml of plasma
* concentration in the bowmans is the same as the plasma given normal GFR
47
What is the relationship of Water
* Passively reabsorbed all along the tubule
* as it follows sodium
* proximal tubule 65% 117L day
* loop of henle 15%
* distal and collecting tubules 20%
* porportion collected by the distal and collecting is dependant on the hydration state of the body
* water flowst hrough aquaporins
* proximal tubule always open for flow of water by osmosis
* Distal tubulr are under control of vasopressin so they are not always open
* sodium alone doesnt produce osmotic driving force
* Plasma colloid ontic pressure of the pertubular capillaries also produce strong osmotic drive for water
48
What is the realtionship of the kidneys and chlorde
* Majority of chloride does not undergo transepothelial transport
* rather is leaves tubular fluid by moving between the epithelial cells
* goes down the electrochmical graident
* following the amount of Na reabsorption
* Amount of chloride reabsorbed is determined by the amount of sodium reabsorbed
49
What is the relationship of kidneys and urea
* Waste products from breakdown of proteins
* large amounts of urea is reabsorbed
* concentration of urea at beggining of the proximal tubule is the same as the plasma concentration of urea so there is no net diffusion
* as fluid moves through prixmal tubule volume is reduced by 1/3 as water is reabsorbed
* tubular concentration of urea increases 3 fold
* as it is passibely reabsorbed
* each pass through the nephron onlu 40-50% of the plasma urea is filtered and excreted from the body
* blood-urea mewasued as blood urea nitron BUN has historically been used as a measure of renal failure
* renal failure, less urea excreted so it accumulates in the plasma and can be clinically measured
50
What is the kidneys H and ion secretion
* secreted in proximal , distal, and collecting tubules
* Extent depends on the acidity of the plasma
* Too mich H present
* More H undergoes Tubular secreteion
* Plasma H is low
* Tubular secreetion of H decreases
* Renal H secretion plauys a key role in the regulation of acid-base balance
51
What is K and ion secretion
* Undergo tubular reabsorpotion and secretion
* is freely filtered at glomerulu
* actively reabsorbed in proximal
* Majority of K is reabsorbed un unregulated fashion
* Secretion is variable and subject to regulation
* If plasma concentration is elevatedm K is actively secreyed in distal and collecting tubiules
* Kidneys are activbely involved in regulating plasma K levels
* Active process dependent on Na K ATPase pump
* Na concentration gradient maintained by pumping Na out across the basolateral membrane in exhcnage for K
* since most of the K was reabsorbed in the proximal tubules
* Makes concentration graident such that J moves down its graident and passes through K channels in the luminal membrane into the tubular fluid
52
# at
How is K controlled and secreted
**Na and K**
* rise in plasma K stims release of aldosterone from adrenal cotex
* this increases Na reabsorption
* More K is secreted
* stimuli such as decreased plasma N, decreased ECF volume or arterial BP and stim abnormal K secretion to the extend thatK depeletion occurs
**Effects on H secretion**
* acid-base status
* Na K ATPase pump on basolateral membrane of the distal section of the nephron can sub H for K
* Limited number of pumos
* Decrease the rate at which other is transported
* Plasma is too acidic
* H move into the interistial space
* Passively mobe into the tubular fluid
* COnsequence is that less K is secreted and it can lead to high levels of K
53
What is the secretion of anions and cations
**Increasing Excretion **
* add more organic ions to the tubular fluid
* Increase the amount of organic ion excreted compared to GFR
* Important in blood-borne chemical messengers
* Norepinephrine
* Histamine
* Prstogladins
* reduce or limit bio activity
**Excrete poorly soluble organic ions**
* Many organic ions are not very soluble, they are hydrophobic
* Circulate within plasma bound to carriers
* Large proteins arent filtered
* Fraction that isnt carrier bound can enter the glomerulus filtrate
* secretion further removes small, unbound fraction of organic ions
* which causes more unloading
* Organic ions highly bound to carrier proteins can be excreted
**Removal of freign compounds**
* Endogenous organic ions
* Foreign organic ions such as food additives, drugs, pesticides
* need to be removed from the body
* Kidney routinely removes these compounds
* No regulatory mechanism in plase to increase their removal if neccessary
54
WHat is plasma clearance
* Urine produced in a day is 1mL/min 1.5L/day
* Concentrations of waste products and other substances thata re to be excreted in urone
* substances that have a been cleaned is called plasma clearnace
* Defined for any substance as the volume of plasma cleared of the substance by the kidneys per minutes
* Unit of plasma cleared is plasmaM
* amount of substance plasma clearance expresses the effectiveness of the kidneyts to remove a substance from the internal fluid
55
What are the types of plasma clearance
* Substance filtered and not reabsorbed
* Flitered, secreted, not reabsorbed
* filtered and reabsorbed
56
What is filtered and not reabsorbed
* Neither absorbed or secreted
* Inulin, exogenous carbos found in onions
* Plasma cleareance is used to estimate GFR
* All filtrate is cleared of inulin, volume of plasma cleared per minute of inulin equals the volume of plasma filtered per minute
57
What is filtered and reasborbed
* plasma clearance must be less than GFR
* glucose
* urea is partially reabsorbed
* Only half gets filtered
58
59
WHat is filtered, secreted, not reasbroebd
* plasma clearance will be greater than the GFR
* Hydrogen Ion tubular secretion
* Secreted H top be the amount of H in 25mL of the plasma
* GFR rate of 125mL/min we can calculate the plasma clearance of H to be 150ml/min
60
Explain the kidneys are urine concentratation
* concentrating urine requires osmosis
* ECF osmolarity depends on the relative amount of water compared to solute
* water moves by osmosis
* Concentrated urine osmotically draws water from surrounding tissues
* Ability to concentrate urine occurs because there is a **Vertical osmotic graident in the indertisitial fluid and medulla**
* normal osmolarity id 300MOsm/L
* The ICF is 300
* as you move from the cortex to the renal pelvis the osmolarity increases to 1200
* allows the kidneys to produce urine in ranges from 300 to 1200
61
Describe the steps in the medullary vertical osmotic gradient
* Follow flow of filtrate through the juxtaglomerular nephron
* Soon as fluid leaves the bowmans
* Enters proximal tububle
* STrong drive for osmotic reabsorption of Na
* water follows NA
-
* End of proximal tubule
* due to Na reabsorption
* 65% of filtrate B has be reabsorbed
* Somolarity in the tubular fluid at this point is 300
* or isotonic to other bodily fluids
-
* Additional 15% filtered water will be reabsorbed
* maintenance of vertical osmotic gradient
* descending and scending limbs of the loops of are distinct in their function
* Ascending limbs are impermeable to water
* In this case water does no follow NA
* descending limbs are hhighly permeable to water
* they do not reabsorb NA
62
What are the mechanisms of countercurrent multiplication
* Descening and asencing limbs are in close proximity
* To establish vertical graideny, process occurs bc filtrate is constantly flowing
* Starts at the medulla without graident
63
What are the steps of countercurrent multiplication
**Fluid movement 1 **
* Proximal tubule enters the descenfing loop of henle
* 300m)sm/L
* Descending limb allows Na and water to pass
* Since it is isotonic to the intersitial space, there is no net movement
**Step 2**
* Close proximity of ascending limb
* Actively reabsorbs Na but not water
* Na moves to intersitial
* Na can move until the fluid is 200 more concentrated than the ascending limb entering the distal tubule
* Tubular fluid is 400 because Na and water move acorss the descending limb
* osmolarity of initial part of descending limb equilibrates
* The intersitial fluid so the tubular fluid in the descending limb is now 400
**Step 3**
* as new fluid enters into the descending loop of henle
* FLuid shifts forward
* now 300 entering the descening limb
* pushing 400 fluid deeper into the medulla
* Fluid moves around the ascending limb
* Na is reabsorbed until an osmotic difference
* is again established
* No longer gave a 300 different between the descending and ascending limb fluids
**Step 4**
* ascending limbs transports Na out
* water continues to passively leave the descending limb until 200 different between the descending and ascending limb is established
* Concentration of each tubular fluid in the descending limb is gradullay increase to remain isotinic to intersitial fluid
* fluid in ascending limb is graduallyu decreasing to maintain the 200 difference
**Step 5**
* as fresh 300 fluid enters the descending loop
* all fluid moves forward
* disrupting concentration graident at all vertical levels until it equilibrates
**STep 6**
* Fresh filtrate enters
* osolarity of the interitusla fluid increases
* Osmoalrluity of the ascending loop fluid decreases to maintain 200 Difference
**Step 7**
* Equilibrium is achieved such that even 300 filtrate entering the descending limb
* Vertical osmotic graident that results in the tubular fluid being 1200 as it enters the ascending limb
* Tubular fluid is 100 as it enters the distal tubule
* Maximum osmolarity if 4x grater than the normal osmolarity of body fluids
* Osmolarity leaving the ascending limb is 1/3 of normal osmolarity
64
What is the purpose of countercurrent multiplication
* seems pointless
* isotonic fluid enters the loop becomes progressively more concentrated
* as it flows down the limb
* Only to become progressivlye more dillyte as it flows up the ascending limb
* Establishes a graident in the medullary
* Allows collecting ducts to both form more concentrated and more dilluted urine than normal bodily fluids
* Allows for overall volume of urine to be significantly reduced
* allows the body to conserve salt and water
65
Whatis vasopressin controlled water reabsorption
* Vasopressin or antiduretic hormone released in responseto water deficit
* once released travels to kidneys and acts on distal tubular cells
* Increase number of aquaporin molecules
* Increases amount of water reabsorbed into epithelial cells
* water passively moves into the intersitial fluid and plasma
* Vasopressin has no actions on the proximal tubule or loop of henle
* 80% of water is reabsorbed
* Increse water reabsoirption iun the distal and collecting tubules
66
What is the regulation of water
* tubular fluid entering the distal is 100
* ICF and renal cortex is 300
* gets higher approaching 1200
* as it plunges to the renal pelvis
* water wants to leave the tubular fluid due to osmosis can only do so with vasopressin
67
What happens in a deficit of water
* Vasopressin released
* increase aquaporin channels
68
WHat happens in excess of water
* body fluid osmolarity below 300
* tubular fluid in the diustal is still 100
* When fluoids are so hypertonmic that vasopressin secretion is completely supressed
* prevents the insertion of aquaporins
* So no water is reabsorebd
* In this manner
* Urine with osmoalrity of 100 can be produced with a V of 25ml/min
69
What is counter current exchange with vasa recta
* this is the blood supply to the medulla
* associated with ascending and descending loops of henle
* highly permeable to to NaCl and H2O
* blood flow of the vasa recta is opposute to the counter current to fluid flow through the loop of henle
* Travel through the medulla where the intersitial fluid osmolarity can be 1200
70
What effects does counetrcurrent exchange have with vasa recta
* efferent arterioles leave the renal cortex. Osmoalrity is 300 Isotonic to intertisial
* Descending loop moves towards the renal pelvis
* Plasma remain isotinic to the suyrrounding intersitial fluid by reabsorbing Na
* Bottom of the loop plasma osmolarity is 1200
* Blood flows up the ascending linmb
* opposite occurs wuith water being reabsorbved and Na leaving
* to keep plasma isotinic
* vasa recta re enters the cortex its osmolarity back to 300 again istonic to ICF
71
Explain water reabsorption
* tubular segments permeable to water, solute reabsortopn always leads to water reabsorption due to osmosis
* Opposite is also true
* Excreteion of solute accompanied by water
* Excess unreabsorbed solute in the tubukar fluid
* exerts osmotic influence to retain excessive water in the tubule
* Thisi s called osmotic diresis
* Uncreases Urinary secretion
72
What is osmotic diuresis
* Increased excreteion of both water and excess un-reabsorbed solute
* seen in diabetics with glucose level high enough that all filtered glucose is reabsorbed
* Excess glucose in tubules attracts water and increases urine production
* This is why diabetes is always peeing
73
What does the bladder do
* Smooth muscles with specialized epithelial linning
* capable of expanding to increase storage
* Highly innervated by the parasympathetic
* Stim causes bladder contractions
* exit through urethra is guarded by interal urethral spinchter and external urethral spinchter
74
What is the interanl urethral spinchter
* Under involuntary control
* part of bladder wall
* not a trude spinchter when yhe bladder relaxes
* closes the outlet to the urethra
75
What does the external urethral spinchter do
* Encircles the urethra and is supported by the pelvic diaphragm
* Kept closed by constant tonic firing of motor neurons
* Comprised of skeletal muscle
* can be under voluntary control
76
What is the matruotion relfex
* bladder normally holds 250-400mL
* internal pressure truggers the reflex
* stretching activates afferent fibers the spinal cord to activate the parasympathetic system to stim the contraction of the external spinchter
* no other mechanism tha texists to open it
* In infants they have no volunatry control so once their bladder fills up they release it
77
What is the voluntary control of the maturition relfex
* can be overiffden by voluntary control
* signals from the cortex override this
* can only continue for so long
* as urine prodcution is constant and eventually the pressure activation reflex will become stronger than the voluntary control and it will force it to empty
PHGY216
flashcards
Decks in class (6)
# Cards
