The main functions of the kidney and basic nephron processes Flashcards
why do we need kidneys?
to control what is in our blood and how much blood we have
our cells produce waste products:
- from metabolism
- from breaking down old cell parts
the kidneys remove these from the blood
we consume things that can affect the function of our body
- drugs/medications
- toxins
the kidneys remove these from the blood
the balance of:
- water
- ions
- pH
by controlling water and sodium the kidneys control the osmolarity and volume of body water
what are the major functions of the kidney?
endocrine functions:
- erythropoietin
- activation of vit D into calcitriol
- renin secretion (RAAS)
metabolic functions:
- glucogneogenesis
pH regulation
water homeostasis:
- ECF osmolarity, blood pressure
Salit/ion homeostasis:
- Na+, K+, blood pressure
Re-absorption of nutrients:
- amino acids, glucose
Excretion of medications, toxins and metabolites
- aspirin, lignocaine, urea, uric acid
describe the endocrine functions of the kidney
Erythropoietin (EPO)
- low blood oxygen levels are detected by the kidneys
- the kidneys release EPO, and EPO stimulates the bone marrow to produce more RBCs
Chronic kidney/renal failure:
- the kidneys cannot make enough EPO
- reduced red blood cell production
- anaemia: low blood oxygen levels
describe the metabolic functions of the kidney
gluconeogenesis
- during fasting, or when out body is under stress: the kidneys make glucose (from lactate)
- which is good because glucose is used to make ATP
describe the pH of the kidney
pH = -log(H+)
The more H+ ions there are the lower the pH = more acidic
The fewer H+ ions there are the higher the pH = more basic/alkaline
Blood pH normal range: 7.35-7.45
Blood pH <7.35: acidosis
- too much acid
- OR too little base
Blood pH >7.45: alkalosis
- too little acid
- OR too much base
Urine pH normal range: 4.6 - 8
- we put all the stuff we don’t want form the blood into the urine to keep the blood pH maintained
describe the pH regulation functions of the kidney
CO2 + H2O <–> carbonic acid <–> bicarbonate + H+
Two main sources of acid in the body:
- acids coming from metabolism, food and drink: direct sources of H+ (non-volatile acids)
- carbon dioxide form metabolism
The pH of the blood is controlled by:
- lungs: exhalation of carbon dioxide
- kidneys: by reabsorption and secretion of bicarbonate and hydrogen ions
describe the salt/ion homeostasis functions of the kidney
potassium (K+) concentration is vital for many processes
All cells:
- the rising membrane potential is based on K+ gradient (inside/outside) of cells
Neurons and cardiomyocytes:
- action potentials, rhythm generation in pacemaker cells, contractility, signalling
Kidneys secrete potassium, to maintain potassium balance. So if you suffer from kidney failure it can lead to hyperkalemia (death)
- kidneys cannot secrete enough potassium. potassium builds up in the blood and can cause arrhythmias
describe the excretion of medicines functions of the kidney
lidocaine is a commonly used local anaesthetic
- excreted by the kidneys after metabolism in the liver due to its fat soluble (lipophilic) nature
- metabolism in liver turns it into a hydrophilic molecule so we can then excrete it
aspirin is a common pain killer:
- can be excreted directly by the kidneys due to its high water solubility (hydrophilic)
medications are filtered and secreted by the kidneys to be excreted form the body in the urine
describe the body water balance functions of the kidney and the volumes and composition in the body
- total body water remains relatively constant
- intake and loss of water must balance
- urine output is adjusted to maintain balance
TBW: males (60%), females (55%)
ECF: 33% of TBW, ICF: 67% of TBW
Plasma: 20% of ECF, Interstitial fluid: 80% of ECF
volume of fluid in the body water compartments can change due to: how much water is in the body and the osmolarity of the body water compartments (water moves to where the osmolarity is highest)
- why does this matter??
- increase in plasma: increase in BP
- decrease in plasma: decrease in BP
- increase in ICF: swelling of cells
- decrease in ICF: shrinking of cells
describe osmolarity
osmolarity: the total number of solute molecules in a solution
NaCl:
concentration = 145mmol/L NaCl
osmolarity = 145mmol/L Na+ + 145mmol/L Cl- = 290mosmol/L
Glucose:
concentration = 285mmol/L glucose
osmolarity = 285mosmol/L glucose
Natural osmolarity:
- extracellular fluid (including plasma): 275-300mosmol/L
- intracellular fluid: 275-300mosmol/L
define isosmotic and how changes in the amount of water in the ECF change the osmolarity
isosmotic:
- same amount of solute molecules per litre
- same osmolarity
ECF = 275-300mosmol/L
ICF = 275-300mosmol/L
A change in the amount of water in the ECF changes the osmolarity
Hyposmotic: increase in water
- less solute molecules per litre
- decrease in ECF/plasma osmolarity
Hyperosmotic: decrease in water (dehydration)
- more solute molecules per litre
- increase in ECF/plasma osmolarity
describe how changes in osmolarity and volume in the isosmotic fluid change things
YOU ALWAYS GAIN OR LOSE FROM EXTRACELLULAR FLUID FIRST!
Changes in osmolarity:
Loss of water ONLY, water loss from ECF:
- ECF osmolarity increases, so water moved from ICF to ECF until osmolarity of each is balanced
- loss of water from BOTH ECF and ICF, so cells shrink
Gain of water ONLY, water gain to the ECF:
- water chain into the ECF, ECF osmolarity decreases and water moves from the ECF to the ICF until the osmolarity of each is balanced
- gain of water to BOTH ECF and ICF, so cells swell
Loss of isosmotic fluid (water and ions) from the ECF:
- the osmolarity of the CFS an the ICF are the same
- no NET water movement, decreases in ECF volume ONLY
Gain of isosmotic fluid (water and ions) into the ECF:
- the osmolarity of the ECF and ICF are the same
- no NET water movement, increase in the ECF volume ONLY
describe the basic function of the nephron, filtration
Filtration:
- occurs in the renal corpuscle/glomerulus
- movement of plasma from the glomerular capillaries (blood) into the glomerular capsule (nephron)
Most substances in plasma are freely-filtered:
- exception: large proteins (eg. albumin) and substances bound to proteins
- water and solutes are filters at a constant rate at the renal corpuscle (glomerulus)
Creates a plasma-like filtrate of the blood (only plasma like because everything is the same EXCEPT no large proteins)
describe the basic function of the nephron, secretion
Section:
- movement of solutes from the peritubular capillaries (blood) into the tubular fluid (nephron)
- removed additional substances (waste products) from the blood by secreting them into tubular fluid so that are excreted in the urine (eg. metabolites, medications and toxins)
proximal convoluted tube:
- secretion of metabolites, medications and toxins
describe the basic function of the nephron, reabsorption
Reabsorption:
- movement of solutes from the tubular fluid (nephron) into the peritubular capillaries (blood)
- return useful substances to the blood so they are NOT excreted in the urine
Proximal convoluted tube:
- bulk reabsorption of ions (sodium), water and nutrients (glucose)
Nephron loop:
- bulk reabsorption of ions (sodium), water
Distal tubule and collecting duct:
- fine-tuning reabsorption of ions (sodium) and water
