Week 2 - B - Physiology 3(A) - Starling forces and GFR Flashcards
What is the rate of excretion equal to in the kindeys?
The rate of excretion is equal to = Rate of glomerular filtration (GF) + Rate of tubular secretion (TS) - rate of tubular reabsorption (TR)
What percentage of the cardiac output flows through the kidneys? What percentage of the plasma entering the kidney is filtered into the proximal tubule?
25 % of the cardiac output goes to the kidneys Only 20% of the plasma entering the kidney is filtered, the rest of the 80% is passed into the efferent arteriole
What drains into the glomerulus and what does the glomerular capillaries drain into? Which has a bigger diameter?
Affernet arteriole drains into the glomerular capillaries which drains into the efferent arteriole Afferent arteriole has a greater diameter
The pores found between the endothelial cells of the glomerular capillaries are about 100x bigger than the normal endotherliar pores What are the three filtration barries between the glomerular capillaries and the lumen of the bowman’s capsule? What are the 3 layers collectively known as?
Glomerular capillary endothelium (fenestrated) Basement membrane (basal lamina) Foot process of podocytes with intermittent filtration slits Known as the glomerular membrane
The basement membrane is a plasma protein barrier made up of negative proteins What does it function to repel?
Repels large negative plasma proteins such as albumin
The net filtration pressure is composed of hydrostatic and oncotic pressures What is the balance of the hydrostatic and oncotic pressures known as?
This is known as the Starling Forces
What are the 4 starling forces contributing to the net filtration pressure in the kindeys?
Glomerular capillary blood pressure Bowman’s capsule hydrostatic (fluid) pressure Glomerular capillary oncotic pressure Bowman’s capsule oncotic pressure
What is the most important starling force? What is the pressure of this force?
The glomerular capillary blood pressure (pressure = 55 mmHg)
What does the glomerular capillary blood pressure favour?
It favours the process of filtration in the blood
The efferent arteriole is thinner than the afferent arteriole and therefore there is a backflow of pressure which is why it is important for the glomerular capillary blood pressure to exist There is also a build up of pressure in the bowman’s capsule, what is this known as and what does it cause?
This is the Bowman’s capsule hydrostatic (fluid) pressure which opposes filtration
What is the value of the Bowman’s capsule hydrostatic pressure?
Valued at 15mmHg
What is the other force which opposes filtration known as? What is the value of its pressure?
This is the Glomerular capillary oncotic (colloid osmotic) pressure - 30mmHg
What is the final starling force and what is it value?
This is the Bowman’s capsule oncotic pressure = 0mmHg
What is the oncotic pressure caused by and what does it cause? hence why is the bowman’s capsule oncotic pressure 0?
It is related to the presence of plasma proteins (notibly albumin) and causes the pull of water into the circulatory system (will pull into the the fluid around if there are proteins in the bowman’s capsule) Since there is not meant to be plasma protein in bowmans capsule - the pressure is 0
What can preoteinuria cause due to the decreasing Oncotic pressure to pull fluid (water) into the blood?
The loss of proteins can cause oedema as there is not as strong an oncotic pressure and therefore fluid leaks into adjacent tissues