Download F214: Communication, Homeostasis and Energy 4.2.1 The Kidney

The Kidney
The Kidney
The Structure of the Kidney
There are three
distinct regions
based on the
distribution of the
different sections of
the nephron. The
human kidney
contains approx. 106
nephrons.
Cortex: Lighter brown colour contains the Malpighian bodies
which are the capsules that contains Bowman's capsule and
a glomerulus at the expanded end of a nephron. There are
also the proximal and distal convoluted tubules and the
upper sections of collecting ducts.
Medulla: The darker, redder region composed of loops of
henle and the lower sections of the collecting ducts. Notice
that it seems to form triangular regions which are called
the pyramids.
Pelvis: This Is a cavity which collects the urine that
emerges from the open ends of the collecting ducts. The
nephrons open on the margin of the pyramids and pelvis. The
white tissue forms a funnel called the ureter which
conducts the urine to the bladder.
The Kidney
This diagram shows
which elements of
the nephron are
present in kidney
cortex and medulla
regions
The Nephron
The capillaries form a knot
called the glomerulus
This is surrounded by the
Bowman’s capsule
Fluid is pushed from the
capillaries into the Bowman’s
capsule by a process called
ultrafiltration
The Bowman’s capsule leads
to the rest of the nephronproximal convoluted tubule,
loop of Henle, distal
convoluted tubule and the
collecting duct
The Nephron
As fluid moves along the
nephron, selective
reabsorption occurs.
Substances are
reabsorbed back into the
tissue fluid and blood
capillaries surrounding the
nephron tubule
The final product is urine
This passes into the pelvis
and down the ureter to
the bladder
The Kidney
Selective Reabsorption
All sugars,
most salts
and some
water is
reabsorbed
Water potential
of the fluid is
decreased by
addition of
salts and
removal of
water
Water potential
increased as salts
are removed by
active transport
Water potential
decreased again
by the removal
of waterensuring that
urine has a low
water potential.
Urine has a
higher
concentration
of solutes than
blood and
tissue fluid
Ultrafiltration
Ultrafiltration
Blood flows from the afferent arteriole, into the
glomerulus, and leaves through the efferent
arteriole, which is narrower, meaning that blood in
the glomerulus is at high pressure
As the blood in the glomerulus is at higher
pressure than in the Bowman’s capsule, fluid from
the blood is pushed into the Bowman’s capsule and
is called glomerular filtrate.
• The barrier between the blood in the capillaries, and the
lumen of the Bowman’s capsule consists of:
Endothelium- having narrow gaps between its cells
that plasma can pass through
•
Basement Membrane- made of a fine mesh of
collagen fibres and glycoproteins which act as a filter to
stop large molecules getting through (most proteins and
all blood cells)
•
Podocytes- epithelial cells of the Bowman’s capsule
containing finger like projections called major processes.
These ensure that there are gaps between the cells
allowing fluid to pass into the lumen of the Bowman’s
capsule
•
Q: What is filtered out of the
blood?
A: Blood plasma which includes
•
•
•
•
•
Water
Amino acids
Glucose
Urea
Inorganic ions (sodium, chloride,
potassium)
What is left in the capillary?
• Blood cells
• Proteins
This makes the blood have a low (very negative)
water potential which ensures some fluid is
retained in the blood
This very low water potential of the blood in
the capillaries helps to reabsorb water at a
later stage (as we shall see!)
Image for Q1a Further Practice
Selective Reabsorption
• Most reabsorption
occurs from the
proximal convoluted
tubule where 85% of
filtrate is reabsorbed
• All glucose and amino
acids, some salts and
some water are
reabsorbed (assuming
healthy working
kidneys)
Selective Reabsorption
• Microvilli on the cell surface membrane of the
tubule provides a large surface area
• Co-transporter proteins in the membrane
transport glucose and amino acids in
association with sodium ions by facilitated
diffusion
• The opposite membrane is folded to increase
surface area and contains sodium-potassium
pumps that pump sodium out and potassium in
• Cell cytoplasm has many mitochondria
indicating that energy is required as ATP
How does Selective Reabsorption Occur?
1.
2.
3.
4.
5.
Sodium ion concentration is reduced as Sodium-potassium
pumps remove sodium ions from the cells lining the proximal
convoluted tubule
Sodium ions transported into the cell with glucose or amino
acids by facilitated diffusion
As concentration rises, they are able to diffuse out of the
opposite side of the cell into the tissue fluid- active transport
may also support this process
from the tissue fluid, they diffuse into the blood and are
carried away
Reabsorption of salts, glucose and amino acids reduces the
water potential in the cells (makes it more negative) and
increases the water potential in the tubule fluid (towards
zero)- this means water will enter the cells from the tubule
fluid and then be reabsorbed into the blood by osmosis
The Kidney
TASK: The Kidney
1. Create a presentation on the kidney…
Success criteria:
Your movie must include:
• Diagrams showing the structure of the
kidney
• Information about the blood vessels and
nephrons
• The stages in Ultrafiltration