Transcript F214: Communication, Homeostasis and Energy 4.2.1 The Kidney

F214: Communication, Homeostasis and Energy
4.2.1 The Kidney
• describe, with the aid of diagrams and
photographs, the histology and gross structure
of the kidney;
• describe, with the aid of diagrams and
photographs, the detailed structure of a
nephron and its associated blood vessels;
The Structure of the Kidney
Task
• You are going to complete a kidney dissection
and explore the structure of the kidney. You
will need a dissection kit and a copy of
Cambridge Biology 2 p47.
• Read the instructions on the sheet provided
and complete the activities.
The photograph is of a large pig
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.
Task
• Now that you have dissected the kidney, use
the textbooks to make any drawings or notes
that you feel you need to be able to describe
the structure of a kidney
• Ensure that you include the structure of
nephrons and any associated blood vessels
Basic Kidney Structure
In a longitudinal section of the
kidney, we can see:
• outer region called the cortex,
surrounded by the capsule
• inner region called the medulla
• the pelvis in the centre leading to
the ureter
The Nephron
The bulk of the kidney
consists of tiny tubules
called nephrons- about a
million in each kidney
The Nephron
Each nephron starts in the
cortex.
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 nephron- proximal
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
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
decreased again
by the removal of
water- ensuring
that urine has a
low water
potential. Urine
has a higher
concentration of
solutes than blood
and tissue fluid
Water potential
increased as
salts are
removed by
active transport
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
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 molecules with a relative molecular mass of 69000 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
What is filtered out of the blood?
• 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
The very low water potential of the blood in the
capillaries helps to reabsorb water at a later stage
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
Specialised for 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?
• 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
1. Create a movie 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