lecture 31 - kidney, nephron & urine physiology Flashcards
What are the 7 key fucntions of the kidneys?
Endocrine functions ,metabolic functions, blood filtration, water homeostasis, salt/ion homeostasis, nutrient reabsorption, medicine, toxin & metabolite excretion
What is the key endocrine function of the kidney?
Detect low blood oxygen levels and release EPO (erythropoietin) to stimulate the kidneys to produce more red blood cells
What is the endocrine issue created in kidney failure?
Kidneys cannot make sufficient EPO leading to anaemia - low blood oxygen levels
What is the key metabolic function of the kidneys?
Gluconeogenesis
How do the kidneys perform gluconeogenesis?
They can make glucose from lactate during times of fasting or stress
What is the kidney’s role in pH regulation?
Ensures the blood pH remains within a small range by controlling the concentration of bicarbonate and hydrogen ions in the blood
What is the main buffer in the blood?
Bicarbonate (HCO3-)
What are the 2 organs that control blood [HCO3-]?
The lungs and the kidneys
How does HCO3- act as a buffer?
Reacts with H+ to form carbonic acid which forms CO2 and water in 2 equilibrium reactions
How do the lungs regulate [HCO3-]?
The exhale CO2, which decreases [CO2] driving the equilibrium reaction to form carbonic acid and then bicarbonate
How do the kidneys regulate [HCO3-]?
By reabsorbing bicarbonate or secreting H+
What is the resting membrane potential of cells dependent on?
Primarily the K+ gradient across the membrane (and Na+concentration)
How do the kidneys balance [K+]?
By secreting potassium to maintain balance
What is the resulting condition when the kidneys cannot maintain K+ homeostasis due to kidney failure?
Hyperkalemia - failure to excrete potassium leads to elevated levels
What are the 2 types of drugs, classified by their solubility?
Lipophilic and hydrophilic
What are lipophilic drugs?
Fat soluble drugs that are metabolised in the liver
Where are lipophilic drugs metabolised then excreted?
Metabolised in the liver then excreted by the kidneys
What type of drug is lidocaine?
A lipophilic drug used as a painkiller
How are hydrophilic drugs and toxins metabolised/excreted?
No need to be metabolised as they can be excreted directly by the kidneys due to their high water solubility
What are the 3 basic functions of the nephron?
Filtration, reabsorption, secretion
What is the product of filtration in the kidneys?
A plasma-like filtrate of the blood
Why is filtrate in the kidneys referred to as ‘plasma-like’?
Has similar concentrations of key solutes, has no red blood cells. However, lacks plasma proteins
Where does secretion occur in the nephrons?
Secretion from peritubular capillary blood into the tubular fluid of the nephrons
Where does filtration occur in the kidneys?
The glomerulus
What key substance cannot be filtered at the golmerulus?
Proteins, e.g. albumin, and substances bound to proteins, such as lipid soluble substances
What is secreted in the proximal tubule?
metabolites, medications, and toxins
What is the equation for the amount of a substance in the urine?
[urine] = filtered - absorbed + secreted
Where in the nephron is sodium reabsorbed?
Most parts of the tubule
What proportion of sodium ions are reabsorbed in the nephron?
Almost all of it
Where is glucose reabsorbed in the nephron?
100% of glucose reabsorbed in proximal tubule
What is the breakdown product of muscle metabolism that is found in urine?
Creatinine
What is the product of amino acid breakdown that is found in urine?
Urea
What is the product of purine breakdown that is found in urine?
Uric acid
Why are H+ ions found in urine?
Excreted to regulate blood pH
Why are Na+ and K+ found in urine?
To balance blood and cellular concentrations of these ions
What is the condition in which the urine contains glucose?
Glucosuria
What is the condition in which the urine contains protein, particularly albumin?
proteinuria
What is the condition in which the urine contains red blood cells?
Haematuria
What is the condition in which the urine contains haemoglobin?
haemoglobinuria
What is osmolarity?
A measure of the number of solute molecule in a solution. If a substance is ionic, the sum of all of the ions it dissociates into
What is an isosmotic solution?
Solution with the same osmolarity as the reference solution
What is a hypoosmotic solution?
Solution with lower osmolarity than the reference solution
What is a hyperosmotic solution?
Solution that has higher osmolarity than the reference solution
What is tonicity?
The effect a solution has on cell volume due to the net/overall movement of water
What occurs if a cell is hypotonic?
Net movement of water into cell - swelling
What occurs if a cell is hypertonic?
Net movement of water out of cells - shrinking
What occurs if a cell is isotonic?
Movement of water into and out of cells is equal so no net movement and cell volume is constant
