The Renal System Flashcards
What are the functions of the kidneys?
-maintenance of homeostasis and formation of urine
-excretion of waste products and toxins
-regulation of electrolyte balance
-regulation of fluid balance
-regulation of acid: base balance
-produce renin- control blood pressure
-produce erythropoietin
-metabolism of vitamin D
What is the nephron?
This is the microscopic functional unit of the kidney.
What does a nephron consist of?
-glomerulus
-bowmans (glomerular capsule)
-proximal convoluted tubule
-nephron loop (loop of henle)
-distal convoluted tubule
-collecting duct
What are the 3 processes for the formation of urine?
Filtration, reabsorption and secretion.
What does the afferent arteriole do?
Takes plasma into the glomerulus (for filtration).
What does the efferent arteriole do?
Takes the molecules that can’t be filtered back into the plasma.
What are the 3 stages of filtration?
-Pores (fenestrations)
-filtration membrane
-podocytes (more pore like)
What is the stage of the pores for filtration?
Only small molecules can fit through the pores, larger molecules are sent back into the plasma.
What is the stage of the filtration membrane?
This membrane has a negative charge so anything other molecule with a negative charge will be sent back to the plasma as repelled (such as plasma protein).
What is the stage of the podocytes?
Any molecule that is big that managed to get through the first 2 stages are caught here and sent back into the plasma.
Why is filtration a selective process?
Only want certain molecules in the urine (keep the important ones in the body)
Where does filtration take place?
The glomerulus.
What is the glomerular filtration rate (GFR)?
The rate at which the kidney/ nephron filters the blood.
Where does the filtrate pass through?
The proximal convoluted tubule.
What does filtrate contain?
Everything except red and white blood cells, platelets and large proteins (albumin).
How many litres of urine is produced per day?
180 Litres.
What is net filtration pressure?
Sum of forces of:
-out (hydrostatic pressure in glomerular capillaries, efferent arteriole narrower than afferent)
-in (pressure in capsular space, colloid osmotic pressure in capillaries)
What value should the net outward force be?
10 mmHg.
How to calculate net filtration pressure?
Outward pressures- inward pressures.
What happens if the value of NFP shifts from 10mmHg?
The glomerulus has to adapt.
How does the glomerulus decrease pressure to shift NFP value?
If pressure is higher, afferent arteriole constricts so less blood enters and therefore reduces pressure.
How does the glomerulus increase pressure to shift NFP value?
If pressure is lower, afferent arteriole can dilate and also efferent can constrict so less blood leaves the glomerulus to increase pressure.
What is the meaning of tubular reabsorption?
Return of useful substances and water from the filtrate back into the blood.
What are some substances that are reabsorbed?
Na+, water, some ions and nutrients through osmosis, diffusion and facilitated diffusion.
What is Transport Maximum?
The maximum amount of a substance that can be reabsorbed (eg if glucose exceeds its Tm, it is lost in the urine).
Where does reabsorption occur?
The proximal convoluted tubule.
What influence does aldosterone have on reabsorption?
Influences in distal convoluted tubule (movement of Na+ and water).
What influence does ADH have on reabsorption?
ADH affects the permeability of the collecting duct to water for example (reabsorb water to increase water loss).
What is meant by tubular secretion?
Active removal of unwanted substances/ wastes from the blood into the filtrate.
Where does tubular secretion occur?
All along the tubule (PCT mainly for K+, also in DCT for exchange for Na+).
Why is tubular secretion important?
Important for regulating K+ and pH.
What is the chemical composition of urine?
Water (95%), urea, Na+, K+, phosphate and sulphate, creatinine, uric acid.
Where does creatinine come from?
From metabolism in muscle tissue.
Where does uric acid come from?
From metabolism of nucleic acids.
What is osmolality?
Number of solute particles in 1kg of water.
What is osmolarity?
Number of solute particles in 1 litre of water.
What is the vasa recta?
These are small vessels that maintain plasma concentration (highly permeable to water and solutes).
In the nephron loop, is ascending or descending side more permeable to water?
Descending.
In the nephron loop, is the ascending or descending more permeable to sodium?
Ascending.
What is the function of the vasa recta?
-preserve the gradient
-able to reabsorb water and solutes into general circulation without undoing osmotic gradient.
What is the function of the ADH hormone in the kidneys?
-affects permeability of the collecting duct
-ADH secretion from posterior pituitary is increased or decreased in response to osmolality (hypothalamus detects change, stimulates pituitary gland to release ADH to increase reabsorption and decrease urine production).
What is the ideal value of osmolality?
300mosmol.
What happens with an increase in ADH?
There is greater reabsorption- therefore less urine.
What happens with a decrease in ADH?
There is less reabsorption therefore more urine (don’t want to dilute plasma).
Which system is involved in blood pressure control?
RAAS.
What is released in result of low pressure?
Renin.
What is process after the release of renin to increase blood pressure?
-renin converts angiotensinogen into angiotensin 1 (inactive)
-angiotensin 1 converted to angiotensin 2 by ACE.
What does angiotensin 2 cause?
-vasoconstriction of blood vessels
-release of aldosterone (sodium and water retention)
-influences ADH release.
What happens to K+ levels when Na+ levels are increased (retained)?
K+ levels decrease (inhibitor)- more is secreted.
How is acid base balance regulated?
Depends on the amount of H+ released and present in the blood.
How is H+ produced?
A result of metabolism.
What is the pH if more H+ in blood?
Lower pH (more acidic).
What is the pH if more OH- in blood?
Higher pH (more alkaline).
What is the process for H+ and HCO3- being eliminated?
These join to form H2CO3 which dissociate to CO2 and water (breathes out).
What are the three mechanisms to maintain acid base balance?
-Buffers (acts as sponge to soak up H+ or OH-)- also insulin captures H+
-Respiratory system/lungs (H+ increase, RR increases and more H+ breathed out as CO2)
-Renal system (if pH falls, H+ secreted into urine, H+ combines with buffer, excreted into urine).
What is the function of erythropoietin?
This is produced by the kidneys (stimulated by hypoxaemia), stimulates bone marrow to produce RBC.
Hb principal carrier of O2 to cells of body.
How is levels of calcium controlled?
Through release of parathyroid hormone (PTH).
What happens if Ca2+ is low?
PTH released, increased calcium reabsorption from kidneys, releases calcium from bones to maintain plasma calcium.
What is the function of active vitamin D?
The kidneys convert vitamin D to the active form, stimulates reabsorption of calcium to maintain calcium levels.
What is calcium needed for?
-strong bones and teeth
-normal transmission of nerve impulse
-normal muscle contraction
-blood clotting.
