GI Theme 3 Flashcards
What is the structure of amylose ?
linear polymer of alpha 1-4 glycosidic links
What is the structure of amylopectin ?
branched polymer with alpha 1-4 and alpha 1-6 glycosidic links
Where can you find alpha amylase ?
pancreatic juice and saliva
What does amylase hydrolyse and what cant it ?
hydrolyses alpha 1-4 links
cant hydrolyse alpha 1-6 links or alpha 1-4 linkks close to terminal branches ?
Starch digestion release what
maltose
maltotriose
alpha limit dextrins
What are alpha limit dextrins?
branched polymers of glucose 5-9 units long
formed due to the inability of amylase to hydrolyse alpha 1-4 links next to branch points
What happens to alpha limit dextrins in the mouth ?
they can be taken up by bacteria and used as an energy source
The length of time food is in the mouth detemrines what ?
how much maltose and maltotriose is released
they are carcinogenic
What carbohydrate digestion takes place in the stomach ?
none- acidic pH inhibits alpha amylase
What carbohydrate digestion takes place in the duodenum ?
pancreatic alpha mylase
digests remaining starch into maltose , maltotriose and alpha limit dextrins
Which is faster salivary alpha amylase or pancreatic alpha amylase ?
pancreatic alpha amylase
What is the role of oligosaccharidases ?
on the brush border
they further digest the maltose, maltotriose and the alpha limit dextrins
Where can you find oligosaccharidases ?
in the duodenum and the jejunum
What does isomalatase (alpha dextrinase) do ?
hydrolyse alpha 1-6 links that amylase csnt
What does maltase do ?
hydrolyse maltose and maltotriose into glucose
What does lactase do ?
hydrolyse lactose into glucose and galactose
What does sucrase do ?
hydrolyse sucrose into glucose and fructose
What are the end products of digestion with oligosaccharidases ?
monosaccahrides- glucose , fructose and galactose which can be absorbed by the duodenum and jejunum
Where does the absorption of monosaccahrides occur ?
duodenum and upper jejunum
How are glucose and galactose actively uptaken ?
by sodium-glucose transporter 1
What type of active transport does the sodium-glucose transporter use ?
secondary active transport
What creates the electrochemical gradient in sodium-glucose active transport ?
Na/K ATPase
basolateral membrane
How do glucose and galactose leave the epithelial cell ?
glucose transporter protein 2
How is the entry of galactose and glucose into the epithelial cell mediated ?
by the presence of sodium in the GI lumen
How does fructose enter and leave the intestinal epithelial cell ?
enters using facilitated diffusion - glucose transporter 5
exits using glucose transporter 2
What is sucrase-isolmaltase deficiency ?
low levels of sucrase and isomaltase in the brush border
intolereane to starch and sucrose
fructose and glucose are tolerated
What is glucose-galactose malabosprtion syndrome ?
mutation in SGLT-1
fructose can be given
What type of transport is SGLT?
secondary active trnasport
symport
What is the type of transport with GLUT proteins ?
facilitated diffusion
uniport
What are alpha limit dextrins hydrolysed by ?
isomaltase
How is pepsinogen converted to pepsin ?
by protons
How much protein does pepsin digest ?
15%
What is pro elastase ?
converted to elastase
digests serine in elastin
What are the peptidases ?
aminopeptidase
dipeptidase
dipetidyl aminopeptidase- cleaves a dipeptide from end of the dipeptide
How can small peptides be further hydrolysed ?
by peptidases in the cytosol
What is present on the apical membrane to provide gradients for peptide transport ?
Na/H transporters
What are the amino acid transport systems on the apical membrane ?
5 dependent on Na - active
2 are facilitated
7 in total
What are the amino acid transport systems on the basolateral membrane ?
5
3 are Na independent - efflux of amino acids into blood
2 are Na dependent - active
How do fat soluble vitamins diffuse ?
diffuse acorss the brush border membrane
Where is vit B12 absorbed ?
ileum
How is B12 found in foods ?
bound to proteins
What happens to b12 in the stomach ?
released and binds to R proteins - high affinity
What is intrinsic factor ?
vitamin b12 binding protein
secreted by gastric parietal cells
binds to B12 with less affinity than R proteins
What degrades the R - protein B12 complexes ?
pacnreatic proteases
What happens to the B12 afte degradation from R proteins ?
binds to IF- resist protease degradation
What happens to the B12 afte degradation from R proteins ?
binds to IF- resist protease degradation
What does the brush border of the ileum contain ?
receptors for B12- IF complexes
What might happen in pancreatic insuffficinecy ?
no degradation from R proteins
B12 deficiency might occur
What is the B12 carrier ?
transcobalamine II
What inhibits gastric emptying locally ?
CCK - lipid present in the duodenum
What emulsifies lipids ?
bile salts and lecithin
What is the purpose of emulsification ?
increase the surface area for water soluble enzymes to act
What are the lipolytic enzymes found in pancreatic juice ?
pancreatic lipase
co-lipase
cholesterol esterase
phospholipase A
How is pancreatic lipase inhibited ?
bile salts bind to fat surface and prevent lipase binding
What does co lipase do ?
displaces bile salts on the fat surface enabling lipase to fucntion
What are the products of triglyceride break down ?
2-monoglyceride
2 x NEFA
What does cholesterol esterase do ?
cleaves a fatty acid from cholesterol esters
What does phospholipase A2 do ?
turns phsopholipids into lypophospholipid and NEFA
What is micelle formation ?
bile salts form micelles with the products of fat digestion
What do the bile salts act as in micell formation ?
surfactant
What is the structure of micelles ?
lipid molecules arranged in a spherical form
Where does absorption of lipids take place ?
in the ileum and the jejunum
What is the unstrirred layer ?
mucus layer
with microvilli between the lumen and the brush border
molecules pass through and become more disorgansied as they approach the apical membrane
What lipid transport occurs at the brush border membrane ?
cholesterol transporter mediates facilitated transport
microvilli membrane fatty acid binding protein transports long chain fatty acids by secondary active transport - Na/K ATPase
What is the role of cytosolic transport membrane ?
transport the products of lipid digestion to the smooth endoplasmic reticulum
What are the cytosolic lipid transport proteins ?
fatty acid binding protein and sterol carrier
What happens to lipids in the smooth endoplasmic reticulum ?
they are esterified again
enter pre chylomicrons
go to golgi
too large to leave across the basement membrane
lacteals - lymphatic capillaries- large enough - empty into the lymph and the the blood by the thoracic duct
Where does absorption of bile salts occur ?
in the terminal ileum
How are conjugated bile salts actively taken up ?
by an Na bile duct co transporter
How do bile salts enter the blood ?
they re enter the portal blood
bound to albumin
return to the liver
How does fructose get from the gut to the blood ?
enters via facilitated diffusion and then leaves bu GLUT 5
What are the brush border peptidases ?
aminopeptidase
dipeptidase
dipeptidyl aminopeptidase
Where does lipid break down occur in the GI tract ?
stomach
duodenum
jejunum
What 2 substances are responsible for emulsification ?
bile salts and lecithin
What is the role of R protein ?
to protect IF from gastric acid
Which compounds predominantly contribute to micelle formation ?
bile salts
What is the mechanism whereby lipids in the duodenum prevent gastric emptying ?
CCK
what are anciliary organs of digestion
pancreas, gallbladder and liver
how long is the human gut
5m long
how is the sa increased in the human gut
folds and microvilli in the SI
outline the journey through the gut
Oesophagus Pyloric sphincter and stomach Upper small intestine Lower small intestine Caecum Colon Rectum
what are the GI Tract Disorders
Physical (blockages/strictures/ fat deposition)
Functional (nerve-peristalsis/muscle)
Environmental insult (infections, toxins, DNA mutations)
Immune-related ( defence becomes attack)
Unknown aetiology
All may have metabolic implications
what disorder affect the whole length of the GI tract
GI cancers
Crohns disease
what disorders move down the GI tract
oesophagus:
- Dysphagia (difficulty swallowing)
Oesophageal stricture/tumours
Oesophageal varices (liver disease)
Oesophageal reflux/indigestion
Barret’s oesophagus
what is dysphagia
oropharygeal
- neuromuscular disorders or stroke
- cant close trachea
- choking
- aspiration pneumonia
- anxiety, anorexia
- dehydration
how can dysphagia be managed
soft diet
pureed diet
thickened fluids
PEG- feeding tube, long term feeding
what happens in dysphagia
food can go to lungs
what is oesophageal stricture
food sticking after swallowing caused by - achalasia -astrictures -present with dysphagia
how can oesophageal stricture be treated
dietery management
surgical
what is Gastroesophogeal Reflux Disease (GORD)
Reflux of gastric contents through lower oesophageal sphincte
what is Chronic: GORD
potential progression to Barret’s Oesophagus/cancer
what can GORD be aggrevated by
Spicy and fatty foods, tomatoes, onion, garlic
Caffeine and alcohol, carbonate drinks
Obesity and pregnancy
what is Laryngo-pharyngeal Reflux (LPR)
refluxate that travels above the upper oesophageal sphincter
is LPR physiological
no
How is GORD linked to erosive tooth wear
Intrinsic acids from the stomach can travel to the mouth and can damage enamel and dentin
how is erosive tooth wear managed in those with GORD
dental treatment & PPI therapy
what is hiatus hernia
stomach protrudes up to chest cavity
what is dyspepsia
discomfort in upper abdomen thta is food related
what is the cause of dyspepsia
peptic ulcer (by bacterial infection- helicobacter pylori)
what is the treatment for peptic ulcers
single 14 dyacourse combinatin therapy leading to healing
why are 2 antibiotics needed to treat peptic ulcers
h pylori can be antibiotic resistant
what is perniciuos anaemia
automimmune destrcution of gastric parietal cells that produce IF
what happens to rbc in pernicious aneamia
large
what are the symptoms of pernicuous anaemia
extreme fatigue shortness of breath pins and needles muscle weakness mood swings memory
how is pernicuous anaemia treated
vit b injection every 3 mnths
what are the oral symptoms of B12 deficiency
atrophic glossitis (sore and red beefy tongue)
mouth ulcers
angualr chleiltis
what is coeliac disease
autoimmune resposne to gluten and gliadin proteins
- wheat, rye, barley. oats
what happens in coeliac disease
damage to villi which affects absorption of nutrients
what are the complication in coeliac disease
anaemia
osteoporosis
neurological conditions
increased risk of small bowel cancer and intestinal lymphoma
how is coelaic disease managed
complete avoidance of gluten
gluten free breads
iron calcium and folate supplement
what crohns disease
inflammatory disease
what causes crohns disease
genetics
inapropirate immune response to commensal bacteria
environmental trigger
where can crohns disease occur
any where in gi tract from mouth to anus
what are the symptoms of crohns disease
Abdominal pain Diarrhoea Nausea and vomiting Fatigue Weight loss fistule- 2 parts of SI join anal fissures
Crohn’s Disease Complications
Inflammation Strictures/blockages Abscesses Fistulae- 2 parts of SI join Anal fissures Bacterial Overgrowth Toxic megacolon
what are treatments for crohns disease
Steroids Antibiotics Liquid diet Supplementary nutrition Surgeries (multiple
what are the oral symptoms of crohns disease
mouth sores
ulcers
swellings
gum problems
what are the oral symptoms of crohns disease
mouth sores
ulcers
swellings
gum problems
what are the disorders moving down the gi tract (large intestine)
diverticular disease
irritable bowel disease
what is diverticular disease
pockets created in teh lining trapping food and waste
what is diverticular disease caused by
thickening of msucle in colon casuing extra pressure
how is diverticular disease treated
fibre in diet
what is IBS
disorder of the motor activity whole bower but mostly colon
how can IBS be managed
low FODMAP
how is IBS diagnosed
when all other caused are ruled out
what is the microbiome
role of bacteria in periodontitis
role in digestion, vit production, immune function
what does the gut microbiome have implications for
obesity
cancers
mental health
autism?
What are the functions of the kidney ?
Excretion
Homeostasis
Hormone production
What does the kidney excrete ?
foreign substances and products of metabolsim
urea
creatinine
hormones and drugs
What does the kidney regulate in homeostasis ?
ECF volume blood pressure osmolarity ion levels- calcium and potassium regulation of pH
What hormones does the kidney produce ?
renin
Urine produced by the kidney travels where ?
out of the kidney via the ureter and into the bladder where it is expelled by the urethra
Where does the renal vein drain back into ?
inferior vena cava
What are the 2 types of nephrons ?
cortical- Superficial cortical and the midcortical
juxtamedullary- penetrate deeply into the medulla and surrounded by the vase recta
where is the loop of henle longer
in the juxtameduallry nephrons therefore th urine id more cocnentrated
What is the glomerulus ?
a cluster of blood vessels
water and solutes flter from the blood into the renal tubule through the glomerulus
What is the glomerulus bounded by ?
the afferent and the efferent arterioles
What is the purpose of the afferrent and the efferent arterioles ?
they contain smooth muscle which contracts to increase blood pressure
What is the nephron surrounded by ?
the peritubular capillaries
What happens in the renal corpuscle ?
the production of filtrate
What happens in the loop of henle ?
urinary concnetration
What happens in the distal tubule ?
control of water and Na balance
What happens in the collecting duct ?
control of water and sodium balacne
What is the average glomerular filtration rate (GFR) ?
125mL a min
180 L a day
What does the filter cocnsit of ?
fenestrated endothelium
collagen basement membrane
epithelium of bowmans capsule which has podocyte filtration slits
How does the filter restrict solute movement ?
based on size and charge
What is the first step in the production of urine ?
production of ultrafiltrate - contains no cellulr elements or proteins (RBCs and albumin)
The concentrations of solutes in the ultrafiltrate is similar to ?
the plasma
What is filtered out of the plasma ?
all plasma constituents except for RBCs and serum albumin
What is proteinuria ?
the presence of proteins in the urine as they are more readily filtered
What is haematuria ?
the presence of RBCs in the urine
What are the 3 pressures that determine the overall net pressure in the bowmans capsule ?
outwards- hydrostatic pressure in glomerular capillaries
inwards
- colloid osmotic pressure
- hydrostatic pressure in the bowman’s capsule
what does autoregulation of the GFR do?
Maintains Renal Blood Flow (RBF) & GFR within narrow limits despite Blood Pressure fluctuations
What are the 2 mechanisms of autoregulation of the GFR ?
myogenic response
tubuloglomerular feedback
What is the myogenic response ?
arterial pressure increases the renal afferent arteriole is stretched and flow increases
vascular smooth muscle responds by contracting and thus increasing resistance
flow returns to normal
Where is the loop of henle situated between ?
the afferent and the efferent arterioles
What is communication between the tubules and the arterioles mediated by ?
macula densa- plaque of epithelial cells in loop of henle adjacent to the arterioles in the tubules- they sense flow rate
granular cells
granular cells (juxtaglomerular cells) in afferent ateriole which secrete renin)
What happens if there is an increase in GFR ?
flow through the tubule increases
flow past the macula dense increases
paracrine are sent from the macula densa to the afferent arterioles
the afferent atriole contricts and the efferent atriole pressure increased
hydrostatic pressure in thhe glomerulus decreased
GFR decreases
what happens to GFR when the afferent atreriole constricts
decreases
what happens to GFR when efferent ateriole constricts
increased
How can we measure GFR ?
by using a substance that isnt excreted or absorbed into the tubules
What is inulin ?
a polymer of glucose that is not indogeneous
What is GFR and what is it measured in ?
rate of filtrate production
ml/min
What is the equation for GFR ?
Amount filtered=Amount excreted
Pinulin x GFR=V x Uinulin
What are the units for the plasma and the urine concentrations of the inulin ?
mg/ml
What is the unit for the rate of urine production ?
ml/min
What are the requirements for a substance to be able to measure GFR ?
must be freely filtered at the glomerulus
must not be abosrorbed or secreted into the nephron
Must not be subject to metabolsim or produced by the kidney
Must not alter the GFR
What are suitable substances for the measurement of GFR ?
Creatinine and Inulin
What is creatinine ?
product of skeletal muscle metabolism
Amount produced is proportional to the muscle mass
constantly produced therefore constantly excreted
What is the need for the GFR ?
allows us to assess the perfomrance of the kidney
see any signs of kidney disease
analyse the way the kidney handles solute
What is the clearance rate ?
mls of plasma totally cleared of a given solutein 1 minute
What is the equation for clearance rate ?
Px x Cx=Ux x V
If there is no reabsorption no secretion what is the relationship of the CR and the GFR ?
GFR=CR
eg. inulin
f there is total reabsorption and no secretion what is the relationship of the GFR and the CR ?
CR= 0
If there is net absorption what is the relationship between the GFR and the CR ?
Cx
If there is net secretion what is the relationship between the GFR and the CR ?
CR>GFR
What affect does diabetes have on the urine ?
Excess plasma glucose means that more glucose is filtered out of the blood- not all of this can be reabsorbed therefore theire is glucose in the urine
increased osmolarity in the tubule meas that fluid is drawn in - triggers the thirst response and more urine is produced
What are the anatomical features of the kidney ?
renal artery renal vein urteter renal medulla and the renal cortex papilla
Is the cortex or the medulla more densely supplied by the renal artery ?
cortex
How is urine concentrated ?
More water abosorption through the CD as it is permeable to water
increases the concentration inside the tubule and urine is hyperosmotic
Where is ADH produced ?
in the supraoptic and paraventricular nuclei of the thalamus
Where is ADH released from ?
posterior pituitary gland
What stimulates ADH release ?
increased plasma osmolarity
decreased blood pressure and blood volume
What are the actions of ADH ?
increases permeability of the CD
increases urea permeability of the CD
increases NaCl resbsorption in the TAL
What is the net effect of ADH ?
increases water absorption
What are changes in osmolarity detected by ?
osmoreceptors in the hypothalamus
Where do the osmoreceptors of the hypothalamus send a message to ?
posterior pituitary to release ADH
If there is an increase in plasma osmolarity ?
ADH secretion increases
How is ADH destroyed ?
liver and the kidneys
What is the cellular mechanism by which ADH increases water absorption ?
ADH binds to receptors on the basolateral membrane
stimulates the production cyclic AMP from ATP by adenylyl cyclase
activates protein kinse
insertion of AQP2 channels on the CD membrane - apical cell membrane
water permability increases and water is taken into the blood
If ADH is present what is the condition of urine ?
ADH increases water reabsorption from the CD therefore the urine is hyperosmotic
What happens if ADH is absent ?
there is no stimulation of the downstream aquaporin production therefore no water reabsorption and the urine is dilute
What is the the role of the supraoptic and paraventricular nuclei of the hypothalamus ?
stimulate ADH secretion from the posterior pituitary
What happens if there is a decreased ECF osmolarity ?
ADH release is supressed
thirst response is supressed
CD not permeable
What is the effect of ANP on ADH ?
ANP inhibits ADH
What is the affect of alcohol on ADH ?
alcohol inhibits ADH
What is the effect of nicotine on ADH ?
nicotie promotes ADH
What is the main role of aldosterone ?
Aldosterone is the main hormone regualting sodiium balance
Where is aldosterone released from ?
Zona Glomerulosa of the adrenal cortex
What stimulates aldosterone ?
hyperkalaemia
low blood pressure
angiotensin II in the RAS
What are the actions of aldosterone ?
increase potassium secretion into the DT and the CD
Increases sodium reabsorption in the DT and the CD
leads to increased blood volume and pressure
What is the cellular mechanism of aldosterone action ?
Aldosterone binds to receptors in the cytoplasm
initiates transcription of sodium channels
number of sodium channels on apical surface increases
increased sodium uptake
sodium goes through the basolateral membrane into the blood and inreases blood pressure
What are the 3 stimuli of aldosterone ?
Increased potassium
Decreased blood pressure
Decreased flow past the macula densa
What is the inhibitor of aldosterone release ?
Increased plasma osmolarity
What are the 3 components of the juxtaglomerular apparatus ?
Juxtglomerular cells
macula densa
extraglomerualr mesangial cells
Where do the extraglomerular mesangial cells sit ?
between the TAL and the afferent arteriole
What is the mode of activity in resposne to Sympathetic activity of the heart ?
high HR
to return to normal the wall tension in the afferent arterioles decreases
sodium delivery to the macula densa decreases
low blood volume
What does angiotensin II do to renin ?
it acts as a negative feedback loop and stops renin release
What is ANP ?
anti-natriuretic peptide
Where is ANP produced from ?
atria when stretched
What is the effect of ANP ?
increases water and sodium excretion
What affect does ANP have on the adrenal cortex ?
it stops aldosterone release
What affect does ANP have on the kidney ?
stops renin
increases GFR
inhibis sodium chloride and water reabsorption
What is the affect of aldosterone on the hypothalamus ?
stops ADH release from posterior pituitary
What is secreted into the proximal tubule ?
urea and creatinine
What is reabsorbed in the proximal tubule ?
Glucose
proteins
aminaoacids
lactate
What is reabsorbed from the descending limb ?
water
What is secreted into the loop of henle ?
urea
What is absorbed from the ascending limb ?
sodium and chloride
What is absorbed from the distal tubule ?
ions
What is secreted into the distal tubule ?
protons
ammonium ions
What is reabsorped from the collecting duct ?
water
urea
What percentage of water and solutes of the filtrate are reabsorbed into the PCT ?
70%
What is the average GFR
125 ml/min
what are the three layer of glomerular filter
Collagen basement membrane
fenestrated enothelium
epithelium of bowmans capsule with podocyte slits
How does the macula dens work ?
increased flow past the macual densa paracrine released from the macula densa and acts on the affferent arteriole increases resistance reduces hydrostatic pressure GFR reduces
What is the normal blood osmolarity ?
290 mOsmoles
What is the affect of nicotine on ADH production ?
stimulates ADH
What are the channels that Aldosterone promotes ?
ENACC channels
Na/K pump
What is reabsorbed i the proximal convuluted tubule ?
70% water and solutes
What is present on the apical surface of PCT ?
microvilli
What are the functions of the PCT ?
Reabsorption of the bulk of filtered NaCl
Reabsorption of glucsoe,amino acids
Secretion or organic molecules
pH homeostasis
What is the form of Na+ transport on the apical membrane ?
Na transport acorss the apical membrane is mediated by glucose and amino acids in secondary active transport
counter exchange of Na/H exchanger
What is the form of Na transport in the basolateral membrane ?
Na is rmeoved by the Na/K ATPase on the basolateral membrnae
this is followed by chloride and water by a paracellualr route
What happens in the descending limb of the loop of henle ?
Water moves out
NaCl stays
What happens in the ascending limb of the loop of henle ?
Water stays
NaCl moves out
What are the mechanisms of Sodium transport in the loop of henle ?
Na/Cl/L transporter
Na/H transporter - allows the acidification of urine
Na/K ATPase on the basolateral membrane
What happens in the DCT ?
NaCl moves out the blood and H20 stays
What are the mechanisms of Na transport in the DCT ?
NaCl moves into the blood
NaCl transporter and Na?K ATPase on the basolateral membrane
What happens in the collecting duct
NaCl movement
what are the 2 types of cells in the collecting duct
principle and intercalated cells
what can block Na+/K+/2Cl transport in the loop of henle
loop diuretics
what can block Na/Cl cotransporters in the DCT
thiazide Diuretics
what do principal cells do
regulate ion balance based on expression of channels on the apical membrane
What are examples of the action of principal cells ?
aldosterone increases ENac Channels on the apical membrane
ADH increases aquaporins on the CD membrane
What are the actions of intercalated cells ?
Acid/base homeostasis
What are the two types of intercalated cells ?
Alpha and beta
What is the role of alpha intercalated cells ?
excrete protons into the urine and reabsorb bicarbonate into the blood
What channels does the alpha intercalated cells use ?
secrete protons by the H ATPase and H/K exchanger
Cl/HCO3 exchanger on the basolateral membrane
What is the role of beta intercalated cells ?
they excrete bicarbonate and reabsorb protons into the blood
What channels do the beta intercalated cells use ?
Cl/HCO3 exchanger
H ATPase
What happens after a high water load ?
water must be excreted in excess - dilute urine that is hyposmotic to the plasma
What is the normal plasma osmolarity ?
290 mOsml
What happens after a water restriction ?
water msut be retained
hyperosmotic urine to the plasma is produced
How is excretion of a dilute or concentrated urine achieved ?
by the countercurrent mechanism
What acts as the countercurrent multiplier ?
loop of henle
What acts as the countercurrnent exchanger ?
vasa recta
What does countercurrent flow mean ?
2 parallel limbs with fluid moving in opposite directions
What is the osmolarity of the PCT compared to the interstitial fluid ?
isotonic
What happens in the ascending limb of the loop of henle and what is the consequence
solutes move into the interstitium
increases the osmolarity of the interstitium
What happens in the descending limb of the loop of henle ?
fluid becomes more concentrated as water move out to equilibrate the interstitium
What happens as more fluid enters the loop of henle ?
more concentrated fluid is formed in the descending limb and enters the ascending limb
a gradient forms from top to bottom in the interstitium
What is the condition of the fluid at the bottom of the loop of henle ?
Hypertonic as water had moved out
What is the condition of the fluid at the DCT ?
hypotonic as solute has moved out
What are the vasa recta ?
long extensions of the peritubular capilaaries
run parallel to the loop of henle in juxtamedulalry nephrons
What are the functions of the vasa recta ?
water and solutes are reabsorbed by the vasa recta
provides o2 to the medulla
What happens in the descending vasa recta ?
solutes move into the VR down their conc gradient
water moves out the VR
What happens in the ascending vasa recta ?
water moves into the VR
Solutes move out the VR
What is the role of urea ?
important for maintaining medullary concentration gradient
What are the 3 mechanisms of pH control ?
buffers
respiratory control
renal control
What happens if the metabolic rate increases ?
co2 increases - equilibrium pushed to the right
increased protons cant be buffered by bicarbonate but can be buffered by non bicarb buffers such as Hb
bicarb is much higher now and can buffer protons from non resp sources
what is the consequence of increased protons in metabolism being released from organic acids ?
bicarbonate can act as a buffer
How is respiratory control of pH carried out ?
high levels of co2 signalled by the carotid and aortic peripheral chemoreceptors and they go to the respiratory centre and signal an increased VR
How is pH controlled in acidosis ?
H is high in the interstitial space reacts with bicarbonate to make co2 and water which dissociates into protons and bicarbonate and the protons are excreted by a H/K ATPase
alpha intercalated cells
How is pH controlled in alkalosis ?
beta intercalalted cells
carbon dioxide and water in the cell are reacted into protons and bicarbonate and the cl/HC03 exchanger excretes bicarbonate into the urine
What does contraction of the afferent arteriole lead to ?
reduces renal blood flow and reduces GFR and hydrostatic pressure
What does contraction of the efferent arteriole lead to ?
reduces RBF
increases hydrostatic pressire and increases GFR
What does dilation of the afferent arteriole lead to ?
increases RBF and increases GFR and hydrostatic pressure
What does dilation of the efferent arteriole lead to ?
increases RBF but decreases hydrostatic pressure and GFR
What does the macula densa do if therie is increases GFR ?
increased NaCl in the distal tubule
macual densa sense an increased flow
release paracrine that act on afferent arterioles
increases ressitance of the afferent arteriole and therefore reduce plasma flow
What are renal arterioles innervated by ?
sympathetic neurones
What are he sympathetic neurones activated in response to
fear
pain
response to fall in blood pressure
What does the sympathetic inenrvation cause ?
constriction of renal blood arterioles
