Kidney background Flashcards
Which embryological layer are the kidneys derived from?
Intermediate mesoderm
What is the cortex of the kidney?
Outer layer of kidney
What is the medulla of the kidney?
Inner layer of kidney
What is upper urinary tract?
Kidney and ureters
What is a lower respiratory tract?
Urinary bladder and urethra
What are the kidneys supported by?
Connective tissue
Anterior: renal fascia anterior posterior
Posterior: Fibrous capsule
What is the structural unit of the kidney?
Nephron
What are the majority of kidney nephrons?
Cortical nephrons where glomeruli is located in the cortex
What are the juxtamedullary nephrons?
Glomeruli of the nephron is located in cortex but very close to medulla. Loop of Henle penetrates deep into the medulla and has a greater effect at increasing the conc of the medulla.
What is the innervation of the kidney?
Aorticorenal ganglia- derivative of the coeliac ganglia. Sympathetic nervous system regulates kidney blood flow and renin release
What is the Loop of Henle?
What is the interstitium?
Tissue separating the Loop of Henle and the vasa recta
What is the role of the Bowman’s capsule?
Surrounds the capillary loops of the glomerulus to participate in blood filtration. It creates a urinary space for filtrate to pass through the nephron and enter the PCT.
What is the Bowman’s capsule formed of?
Parietal protective layer formed of simple squamous epithelia. Visceral layer formed of podocytes
What is the role of the parietal layer of the Bowman’s capsule?
Formed of simple squamous epithelia where fluid accumulates.
What is the role of the visceral layer of the Bowman’s capsule?
Composed of podocytes to prevent large molecules leaving the Bowman’s capsule. Podocytes contain glycocalyx to prevent this.
What is the PCT?
Portion of nephron responsible for the reabsorption of Na+, Cl-, K+, glucose, amino acids and urea.
What is the PCT composed of?
Cuboidal epithelia lined with microvilli for absorption and secretion. Rich in mitochondria for energy-dependent ion transfer.
What is the role of the collecting duct?
Reabsorption of water, Na+, Cl- and urea
What are the cells of the collecting duct?
Major cell type are the prinicipal cells for water and sodium balance via Na+/K+ ATPase channels controlled by aldosterone. Intercalated cells are a minor type in the collecting duct.
What are the intercalated cells?
Responsible for acid-base homeostasis via the HCO3-/CL- exchanger and H+ pump in the collecting duct
What is the kidney blood supply?
Afferent arterile is a branch of the renal artery.
Efferent arteriole becomes the vasa recta and peritubular arteries.
What are the vasa recta?
Run parallel to the medulla of the kidney, especially the loop of Henle and DCT
What are the glomerular capillaries?
Anastomosis formed from branches of the afferent arteriole. They are the only capillaries not surrounded by interstital tissue and form a barrier for plasma proteins to enter urine.
What are the features of the glomerular capillaries?
High pressure filtration because vessels are short and wide so there is little resistance. Passive diffusion occurs here via hydrostatic pressure
What type of cell makes up the endothelium of the kidneys?
Fenestrated endothelial cells
What are the peritubular capillaries?
Blood vessels which run alongside the cortex of the kidney
Autoregulation
Adjustment of blood flow to organs depending on immediate requirements. In the kidneys, this is to maintain GFR when BP changes from 80-180
What is GFR?
Amount of blood filtered in the glomerulus
How does arterial blood pressure affect autoregulation of the kidney?
Causes changes in the renal arterial constriction and GFR to prevent renal injury to the glomeruli.
Below 80: BP is low so vasodilation occurs
Above 80: BP increase so vasoconstriction gradually increases
What are the mechanisms of autoregulation?
1)Myogenic mechanism
2)Tuberoglomerular mechanism
What is myogenic mechanism?
Response of smooth muscle mainly in the afferent arterioles and minorly the efferent arterioles for
vasoconstriction: decreased glomerulus blood flow and filtration
vasodilation: increased glomerulus blood flow and filtration
What causes decreased renal blood flow?
Hypertension
-> cholesterol, diabetes, smoking
What is the juxtaglomerular apparatus?
Portion of the DCT close to the glomerulus consisting of macula densa cells. These cells have chemoreceptors for Na+ and Cl- to detect GFR filtration rate.
What is the tuberoglomerular mechanism?
Macula densa of JGA detects Na+ and CL- and releases chemicals to induce changes to the smooth muscle in the glomerular arteries to affect GFR.
Tuberoglomerular mechanism- high Na+ and Cl-
Macula densa releases vasoconstrictor chemical ATP or adenosine to reduce filtration in the glomerulus
Tuberoglomerular mechanism- low Na+ and Cl-
Inhibits ATP release and increases renin release.
RAAS system
Drop in BP induces renin release.
Angiotensinogen is produced from liver, cleaved -> angiotensin 1 by renin.
Angiotensin 1 -> Angiotensin 2 by ACE which occurs in the lungs.
Angiotensin 2 binds to adrenal gland for aldosterone release.
Aldosterone acts on collecting ducts for insertion of aquaporin channels.
How do ion levels increase renin release?
Decrease in Na+ due to reduced reabsorption into blood
or
Increase in K+ due to reduced secretion into kidney
This occurs due to low GFR and BP
How is renal function assessed?
Renal clearance (ml/min) which is the volume of plasma when completely stripped of a substance by the kidney, which is determined by GFR
How to measure renal clearance?
Urinary conc x urine flow rate/ plasma conc in the body
How is filtrate distributed?
Between the ureter and renal vein
Which substances are not absorbed or secreted?
Insulin
What is renal clearance compared to?
Patient’s level of creatinine in the urine which should be lower compared to the blood
What is creatinine?
Waste product from the digestion of muscle and protein. It is majorly filtered and excreted in the urine.
What is renal failure?
Kidneys fail to remove end products of metabolism and regulate pH and electrolyte levels of extracellular fluid.
What is acute renal failure?
Abrupt but reversible onset characterised by: increase in serum creatinine above 26.5
Oliguria: low urine output below 0.5ml/Kg of BW
What is the cause of acute renal failure?
Low BP due to: Hypovolemia, Systemic shock and Heart failure
Obstruction to the ureter
Decreased renal perfusion due to vasoactive mediators such as drugs
What is acute tubular necrosis?
Reduced oxygen and blood flow to the kidneys which can occur when using contrast dyes in X-rays for kidney imaging. This leads to reduced GFR
What is chronic renal failure?
Irreparable kidney damage with GFR less than 60 over 3 months and presence of structural kidney damage
How does chronic renal failure present?
Disturbed acid-base balance
Anaemia due to lower EPO production
Azotemia where there is build up of urea which causes nausea, vomiting and neurological symptoms such as tremor
How does azotemia affect the body?
Excess urea prevents platelet clot formation, leading to bleeding disorders. Skin disorder with uremic frost
How does hypertension affect the kidney?
Hypertension causes narrowing of the glomerulus arteries, reducing blood supply. Macrophages and foam cells infiltrate and cause regression of mesangial cells to mesangiobllasts which secrete ECM and cause renal fibrosis
How does diabetes affect the kidneys?
Excess glucose attaches to endothelial cells of the glomerulus, causing narrowing of the arteries which increases pressure.
What causes glomerulonephritis?
Diabetes
Hypertension
Glomerular disease
Nephritis
Tumours
What is the maintenance range for blood pH?
7.34-7.48
Role of the PCT?
Reabsorption of Na+, K+, CL-, glucose, amino acids and urea
What is the role of the descending limb?
Reabsorption of water into the blood.
What is the role of the ascending limb?
Reabsorption of Na+, K+ and CL-.
What is the role of the DCT?
Reabsorption of Na+, Cl-, Mg2+ and HCO3-.
Where is HCO3- reabsorbed into the bloodstream?
PCT which is Na+ dependent on the HCO3-/NA+ symporter
DCT which is CL- dependent on the HCO3-/CL- exchanger
How is Na+ processed by the kidneys?
Reabsorbed into the bloodstream, leading to hypernatremia
How is K+ processed by the kidney?
Secreted into the kidney in the collecting duct which reduces levels in the blood, causing hypokalemia.
90% is reabsorbed in the PCT and in the ascending limb.
What is the effect of hyperkalemia?
Increase in action potential which causes overactivation of cardiac muscles, leading to MI.
How is Na+ reabsorbed in the PCT?
Enters PCT via the Na+/glucose and amino acid symporter. Glucose enters bloodstream via glucose symporter. Once inside, uses the Na+/K+ ATPase pump to enter the bloodstream
Also enters via Na+/H+ antiporter. H+ allows HCO3- uptake which enters bloodstream via HCO3-/Na+ symporter.
How is Na+ absorbed in the ascending limb of Loop of Henle?
Enters ascending limb via the Na+/CL- symporter to enter bloodstream by Na+/K+ ATPase pump.
How is Na+ absorbed in the DCT?
Via Na+/CL- symporter. Once inside, uses Na+/K+ATPase pump for Na+ to enter bloodstream. CL- enters through channels directly into the bloodstream.
How is Na+ absorbed in the collecting duct?
The Na+/K+ ATPase channel, controlled by aldosterone
Where is the majority of Na+ absorbed?
Majority is absorbed in the PCT, lesser absorbed in the Loop of Henle
How is Mg2+ reabsorbed?
Uptake into the DCT via the paracellular junctions.
How is K+ reabsorbed?
In the PCT via basolateral channels
Tubular maximum for glucose?
Maximum of glucose to be absorbed from plasma.
Where is glucose reabsorbed?
Majority of glucose that enters kidney is reabsorbed in the PCT
What is the transport maximum?
Limit for reabsorption of substances such as glucose. Once this is reached, remaining substances are excreted into the kidneys, leading to glycosuria.
What is an important feature of the ascending limb?
Impermeable to water for reabsorption of Na+, K+ and Cl-.
What is an important feature of the descending limb?
Highly permeable to water; less permeable to solutes.
What is counter current multiplication?
Mechanism for reabsorption of water in the loop of Henle and forming highly concentrated urine. Movement of Na+ and CL- out of ascending limbs induces water to move out of descending limb. This results in a high conc filtrate entering DCT to be excreted.
How is concentrated urine formed?
Ascending limb pumps out Na+, creating a high concentration in the interstitial space. To counteract this, water in the descending limb leaves by osmosis. Na+ then enters the descending limb, creating a high conc in the filtrate of ascending limb which moves lower into the loop of Henle and increases osmolarity of medulla, while low conc filtrate of the descending limb moves out into the DCT. This high conc filtrate will allow more Na+ to be pumped out and the cycle continues until it reaches the maximum conc osmolarity of 1200 msOm
Which part of the kidney is present in the medulla?
Loop of Henle and Collecting duct surrounded by the vasa recta
Which components are involved in the countercurrent mechanism?
Loop of Henle and vasa recta
What is a hypertonic solution?
High conc of solutes and low water conc
What is the countercurrent mechanism?
Na+ is pumped out by the ascending limb and is taken up into the bloodstream of vasa recta to enter the descending limb.
Water is transported from the descending limb to the ascending limb by the vasa recta
Effect of aldosterone
Triggers Na+ and K+ reabsorption in the collecting ducts
Effect of oestrogen in kidney
Enhances Na+ and CL- reabsorption and prevents water loss. When levels drop in menopauseor pregnancy, causes frequent urination.
Effect of progesterone on kidney
Competes with aldosterone and decreases Na+ reabsoprtion in collecting ducts, promoting water loss.
Effect of glucocorticoids on kidney
Enhances tubular reabsorption of Na+ to reduce water loss and promotes increased GFR.
Buffer
Solution such as HCO3- which resists pH change when acid or base is added
What are the buffer systems in the body?
Bicarbonate
Phosphate
Plasma proteins
What controls acid-base balance in the blood?
Bicarbonate, phosphate and proteins
What controls acid-base balance in the kidneys?
Bicarbonate, phosphate and ammonia
What is the phosphate buffer system?
Renal tubular buffer and intracellular buffer. It has H2PO4(-) as a proton donor and HPO4(2-) as proton acceptor.
H2PO4(-) -> H+ and HPO4(-)
What happens when CO2 is excess in the blood?
HCO3- is regenerated
How is HCO3- regenerated when low to combat acidic pH?
From glutamine via the ammonia buffer system
What is the ammonia buffer system?
Glutamine is metabolised to NH4+ and HCO3-. HCO3- is taken up by the peritubular capillary. NH4+ is excreted out into the filtrate and reabsorbed to form NH3+. It is excreted as NH3+ and joins with H+ to form NH4+ and leave via urine
When does H+ secretion into the kidney stop?
When pH falls below 4.5- kidney generates HCO3-
Where is the majority of buffering capacity?
Cells which are metabolically active and produce waste
Extracellular space by bicarbonate ions, lesser by proteins and phosphate buffer system.
Respiratory acidosis
Accumulation of CO2 in the bloodstream
Respiratory alkalosis?
Generally caused by hyperventialtion
Abnormal HCO3-?
Metabolic issue
Metabolic acidosis?
Diabetes mellitus where acidic ketone bodies are generated
Excess protein consumption, increasing levels of amino acids
Diarrhoea: loss of bicarbonate ions
Metabolic alkalosis?
Loss of acid due to vomiting
Eating excess fruits
Ingestion of antacids
