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To enable students

1. To define the ultrafiltration process

2. To describe the factors needed for ultrafiltration

3. To understand factors affecting glomerular filtration rate(GFR)


Students will cover the basic function of renal capsule in ultrafiltration process which marks the first region of nephron, a structural and functional unit of kidney. 

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Definition of Ultrafiltration


filtration under pressure
•all substance RFM < 68 000        

.plasma less large proteins and blood cells


The Kidney and Nephron

Overview of how the nephrons in the kidney filter blood and reabsorb water and other molecules.

Describe ultrafiltration in the Bowman's capsule and the composition of the glomerular filtrate.

1. Nephron - carries out the filtration of blood --> filtered blood (clean)
                                                                            --> Urine (waste)
2. Urine is composed of: Water, Salts, and Urea (nitrogen waste - toxic) 

3. Bowman's Capsule: where ultra-filtration begins.
a) Blood arrives in the kidney in the Afferent arteriole - at high pressure - (with a wide blood vessel).
b) Blood passes through the Glomerulus and pases out the Efferent arteriole - (with a narrow blood vessel.)
c) Blood pressure increases in the Glomerulus.
d) High pressure forces the plasma (liquid in blood - water, salts, amino acids, glucose and urea) out of the blood vessel into the inside of the Bowman's Capsule - This is called "Glomerula Filtrate."

Looking at how the urine is actually formed:

- Begins in the Bowman's capsule and is known as ultrafiltration - the filtration of mollecules. Explained using the larger diagram.

- Filtration of blood begins with blood arriving in the Kidney, in the Nephron in the Afferent Arteriole. This blood is under high pressure and as it comes in, and it starts to branch and become much much smaller. This twisted smaller structure is known as the glomerulas.

- The next part to notice is the blood coming out of the Bowman's capsule by the Efferent Arteriole. We should notice that the diameter of this blood vessel in which the blood leaves the Bowman's capsule, is much smaller than the Afferent Arteriole which leads the blood into the Bowman's capsule. Because of the smaller tube, this means the blood pressure increases, and it has a very high pressure. So the glomerulas function is to increase the pressure of the blood. So while the blood is in the glomerulas it is of a very high pressure.

- The consequence of this is that the high pressured blood forces the liquid within blood (plasma - contains components dissolved in blood (salts, water, amino acids, glucose and urea) which forces them out of the blood vessel.

- The high pressure of blood in these twisted tubes, forces the plasma into the space surrounding the glomerulas which is the inside of the Bowman's capsule. When this happens we call this Glomerula filtrate.

- So the blood has been filtered by pressure, due to the restricted space in the blood vessel at the twisted point, which forces the plasma into the Bowman's capsule. The cleaner blood then continues on to do it's job and the plasma travels down the Bowman's capsule and begins it's journey till excretion