Renal System Flashcards
Main functions of the kidneys
Extract fluid from blood via filtration
Change composition of fluid by retaining substances and returning to blood or tissues
Excretion of waste or foreign substances
Regulate blood pH, erythrocyte production, hormone production and blood glucose levels
Three layers of the external kidney anatomy
Renal capsule
Adipose capsule
Renal fascia
Renal capsule
Connective tissue
Physical barrier to protect against trauma
Maintains kidney shape
Adipose capsule
Fatty connective tissue
Padding and physical protection
Maintains kidney position
Renal fascia
Connective tissue
Anchors kidneys to surrounding structures
Describe a lobe
Between 8 - 12 in humans
Contains a medullary pyramid, the overarching cortex and 2 halves of a renal column on either side
3 things you would find in the renal cortex
Cortical blood vessels
Part of nephrons
Lobule intersections
Interlobar
Between lobes
Interlobular
Between lobules
Peritubular capillaries of the cortex
Connect glomerulus to ascending and descending vasa recta
Ureter
Connects urinary bladder and renal pelvis
Papillary ducts
Found at bottom of medullary pyramid next to renal pelvis
Nephron
Starts in renal cortex, threads through medullary pyramid where collecting ducts of nephron feed into papillary ducts
Minor calyx
Connects bottom of renal columns to renal pelvis between medullary pyramids and papillary ducts
Major calyx
Large area of renal pelvis that connects minor calyces to blood supply
Peritubular capillaries of the medulla
Connect ascending and descending vasa recta
Ascending vasa recta
Run alongside descending loop of Henle
Venous, low oxygen levels
Connected to descending vasa recta by peritubular capillaries of the medulla
Descending vasa recta
Run alongside ascending loop of Henle
Arterial, high oxygen levels
Connected to ascending vasa recta by peritubular capillaries of the medulla
Glomerulus
Endothelium
Little ball of capillaries in the nephron
Accepts blood from afferent arterioles and pushes it into efferent arterioles and proximal convoluted tubule of nephron
Afferent renal arteriole
Accepts blood from interlobular artery and feeds it into glomerulus
Efferent renal arteriole
Accepts blood from glomerulus and transports it into descending vasa recta and peritubular capillaries of the cortex
Parenchyma
Functional portion of the kidney
Contains 1 million nephrons
Renal corpuscle
Glomerulus and Bowmans capsule
Summarise the basic structure of a nephron
Glomerulus Proximal convoluted tubule Thick descending loop of Henle Thin descending loop of Henle Thin ascending loop of Henle Thick ascending loop of Henle Distal convoluted tubule Collecting duct Papillary duct
Bowmans capsule
Epithelium
Visceral podocytes
Parietal simple squamous epithelium forms the outer wall of the capsule
3 parts of the filtration membrane
Fenestrations
Basal lamina
Slit membrane
Fenestrations
Pores
Prevents filtration of blood cells but allows all components of blood plasma to pass
Basal lamina
Fusion of podocyte basement membrane and endothelium basement membrane
Prevents filtration of large proteins
Slit membrane
Between pedicels
Prevents filtration of medium sized proteins
Osmolarity
A measure of the effective gradient for water assuming all osmotic solute is completely impermeant
Number of dissolved particles
Tonicity
Tendency of a solution to resist expansion of intracellular volume
Concentration of solute + permeability
Isosmotic
Same number of dissolved particles per unit regardless of how much water would flow across a given membrane
Isotonic
No water movement across a given membrane would occur regardless of how many particles are dissolved
Describe the fluid in the body of a 70kg male
Water makes up 60% of males, about 42L
Intracellular fluid makes up 2/3 of the bodys fluids, about 28L
Extracellular fluid makes up the other 1/3, about 14L
20% of ECF is blood plasma, 80% interstitial fluid
2.8L plasma, 5L blood
4 reasons to maintain osmolarity
Membrane potential
Electrical activity
Muscle contraction
Nutrient uptake
Sources of water gain
Metabolic water (8%) Ingested foods (28%) Ingested liquids (64%)
Sources of water loss
GI tract (4%)
Lungs (12%)
Skin (24%)
Kidneys (60%)
Ions with a higher concentration in the ECF than ICF
Sodium
Calcium
Chlorine
Ions with a higher concentration in the ICF than ECF
Potassium
3 processes of urine formation
Glomerulus filtration
Tubular reabsorption
Tubular secretion
The filtration equation
Excretion of substance X = Filtered - reabsorbed + secreted
Substances of little excretion
Water
Sodium ions
Substance not excreted at all
Glucose
Substance completely excreted
Creatinine
Describe the equation NFP = GBHP - CHP - BCOP
Net filtration pressure = glomerular blood hydrostatic pressure - capsular hydrostatic pressure - blood colloid osmotic pressure
Glomerular blood hydrostatic pressure drives fluid out of the glomerulus, a force that is opposed by both capsular hydrostatic pressure and blood colloid osmotic pressure resulting in a net filtration pressure
NFP
Net filtration pressure
Determines how much water and small dissolved solutes leave the blood
About 10 mmHg
GBHP
Glomerular blood hydrostatic pressure
Mechanical pressure between afferent and efferent arterioles within glomerulus
Drives plasma filtrate from glomerular capillaries into capsular space
About 50 mmHg
CHP
Capsular hydrostatic pressure
Pressure exerted on plasma filtrate by elastic recoil of glomerular capsule
About 15 mmHg
BCOP
Blood colloid osmotic pressure
Osmotic force of proteins left in the plasma pulling the water from the plasma filtrate into the glomerulus
About 25 mmHg
Describe how glomerular pressure is regulated
Vasoconstriction of afferent arterioles decreases glomerular pressure by restricting oncoming flow
Vasoconstriction of efferent arterioles increases glomerular pressure by restricting outgoing flow
Glomerular filtration rate
About 125 mL per minute so about 180 L per day
Similar solute concentration to plasmin - lacks proteins, heavy compounds and blood cells
Kept relatively constant
Urine output directly proportional to renal pressure
3 types of GFR regulation
Renal autoregulation
Neural regulation
Hormone regulation
2 types of renal autoregulation
Myogenic mechanism
Tubuloglomerular feedback
2 types of renal hormone regulation
Angiontensin II
Atrial natriuretic peptide
Describe how the myogenic mechanism regulates GFR
Blood pressure increases causing stretching of smooth muscle fibres in afferent arteriole walls
Stretched smooth muscle fibres contract, narrowing afferent arteriole lumens and decreasing GFR
Describe how tubuloglomerular feedback regulates GFR
High systemic blood pressure causes rapid delivery of sodium and chloride to macula densa cells
Juxtaglomerular apparatus decreases release of nitric oxide causing vasoconstriction of afferent arterioles and decreasing GFR
Describe how neural mechanisms regulate GFR
Renal sympathetic nerve activity increases causing norepinephrine release
Renin released and alpha receptors activated causing constriction of afferent arterioles and decreasing GFR
Describe how angiotensin II regulates GFR
Decreased blood volume or blood pressure increases angiotensin II production
ANG II causes afferent and efferent arteriole constriction and decreasing GFR
Describe how atrial natriuretic peptide regulates GFR
Atrial stretching causes ANP release
ANP relaxes mesangial cells in glomerulus which increases capillary surface area available for filtration and increases GFR
Reabsorption in the proximal convoluted tubule
Site of largest amount of solute and water reabsorption from filtered fluid
60% glomerular filtrate, NaCl, water
100% glucose
Also amino acids, organic nutrients and some HCO3 reabsorbed
Sodium movement by symporters and antiporters
Sodium actively pumped out, glucose uses already set up sodium gradient to be transported out via symporter
Brush border increases surface area
Reabsorption in the descending loop of Henle
Mainly water reabsorbed by osmosis as interstitial fluid in renal medulla is 2 - 4 x more concentrated than glomerular filtrate
Low permeability to ions and urea
Very concentrated filtrate at the bottom of loop due to lots of water being removed but no other solutes
Reabsorption in the ascending loop of Henle
Sodium, potassium and chlorine actively absorbed
Virtually impermeable to water so no more gets reabsorbed and tubular content becomes more dilute
Osmolarity about 100 mOmol/L
Reabsorption in the late distal convoluted tubule and collecting duct
Additional reabsorption of NaCl
Water requires ADH in this section to be reabsorbed. In absence of ADH a very dilute urine is produced
Location of dilute urine
Cortical nephrons
Location of concentrated urine
Juxtamedullary nephrons
Describe the negative feedback loop of GFR regulation
Increased GFR
Increased tubular flow rate
Increased tubular sodium, chlorine and water content sensed
Juxtaglomerular apparatus commences intracellular signalling
Afferent arteriole vasoconstriction
Decreased GFR
Describe how ADH acts on urine concentration
Osmoreceptors in hypothalamus detect changes in osmolarity
ADH precursor synthesised in hypothalamus and stored in posterior pituitary
Osmolarity increases, ADH released from posterior pituitary into blood
ADH binds membrane receptor on the last part of the convoluted distal tubule and the collecting duct
cAMP is activated
ADH stimulates aquaporin-2 containing vesicles into apical membrane of collecting duct epithelium allowing water to move freely into the cell
Basolateral membrane always relatively permeable to water allowing water to be reabsorbed by osmosis into the blood
Describe how osmoreceptors work
Cell shrinkage due to hypertonic solution opens stretch inhibited cation channels
Sodium enters and triggers a cell action potential
Plasma osmolarity increases causing ADH increase and thirst sensation is triggered by osmoreceptors
3 ways angiotensin II affects renal physiology
Vasoconstriction of afferent arterioles causing decreased GFR
Small direct effect on reabsorption in proximal convoluted tubule
Stimulates release of aldosterone from adrenal cortex
3 renin stimulators
Decreased NaCl in distal tubule
Decreased perfusion pressure by granular cells
Increased renal sympathetic nerve activity
How macula densa cells respond to decreased NaCl
Increase prostaglandins
Summary of the renin-angiotensin-aldosterone system
Angiontensinogen converts renin to angiotensin I
Angiotensin converting enzyme converts angiotensin I to angiotensin II
Angiotensin II acts on the adrenal cortex to increase aldosterone
Aldosterone increases transcription of sodium/potassium/ATPase pumps in the distal tubule and collecting ducts
ACE inhibitors
Heart failure treatment
Kidneys normally try to increase renin and angiotensin II to increase blood volume. In heart failure, atria and ventricles hypertrophy causing increased blood volume and putting more strain on the heart
ACE inhibitors stop the conversion of ANG I to ANG II, decreasing blood volume and relieving some pressure on the heart
Describe how increased salt intake results in decreased blood volume
Increased salt intake means increased plasma concentrations of Na+ and Cl- resulting in increased osmosis of water from ICF to interstitial fluid to plasma resulting in increased blood volume
Increased blood volume can increase atrial stretching resulting in atrial natriuretic peptide and decrease release of renin and therefore formation on ANG II and aldosterone
Decreased ANG II causes increased GFR and both decreased aldosterone and increased GFR causes reduced reabsorption of NaCl by kidneys
Reduced NaCl reabsorption causes increased loss of Na+ and Cl- in urine which also causes increased water loss in urine and therefore decreased blood volume
