1. Entry slip: What does urine enter after leaving the
bladder?
Lesson 3.4.1- Describe the processes of filtration,
reabsorption and secretion in the nephron.
(pp375-377) of Biology-McGraw-Hill Ryerson)
I. The kidney is composed of three main
structures:
a.Cortex: the outer layer
b.Medulla: the inner layer
c. Pelvis: where urine collects before going
into the Ureters
II. Nephrons:
a.In the cortex and medulla, there are over
1,000,000 tiny filters called nephrons.
i. Like the alveoli in the lungs which are
surrounded by capillaries that bring

2. CO2 to be expired and which take in
O2, nephrons are also surrounded by
capillaries.
ii. These capillaries bring blood that
contains wastes to be excreted such
as:
A.Urea, uric acid and creatinine
B. Excess water
C. Excess minerals such as Na+, Cl-,
K+, HCO3-(basic), H+(acidic) and
Ca2+
b.Each nephron consists of a:
i. Bowman’s capsule:
A. This is like an alveolar sac
surrounded by capillaries, except
that the capsule surrounds the
capillaries. This bundle of
capillaries in the Bowman’s
capsule is called the
“Glomerulus”.

3. B. Blood enters the capsule from
the renal artery
C. 20% of the blood plasma from
the blood passes through the
capillaries’ walls due to blood
pressure. RBC’s and white blood
cells are too large to pass
through.
D. This blood plasma is called
“nephric filtrate” and passes into
the proximal tubule. It contains
nutrients the body wants and
wastes the body wants to get rid
of:
a. Nutrients: water, minerals,
glucose, useful amino acids
b. Wastes: excess water, excess
minerals, urea, uric acid,
creatinine
ii. Proximal tubule:

4. A. “proximal” = closer by, “tubule” =
small tube
B. This tubule takes the nephric
filtrate to the “Loop of Henle”
C. REABSORPTION: While in the
proximal tubule, nutrients that
the body wants begin to be
reabsorbed: they pass back into
the capillaries beside the
proximal tubule.
iii. “Loop of Henle”:
A. Part of this “loop” descends into
the medulla (goes down);
another part ascends back to the
cortex (goes up).
B. FILTRATION: in the descending
loop, some water that the body
wants is filtered out of the
nephrite and sent back into the
capillaries. This happens due to
the high amount of Na+ in the
medulla. (DEMO)

5. C. FILTRATION: in the ascending
loop, some of the minerals that
the body wants are filtered out
and sent back into the capillaries.
D.At the end of this loop, the
nephric filtrate passes into the
distal tubule.
iv. Distal tubule
A.“distal” = farther away, “tubule”
= small tube
B. REABSORPTION: While in this
tubule, more nutrients that the
body wants begin to be
reabsorbed: they pass back into
the capillaries.
C. SECRETION: Substances such as
more creatinine, H+(acid),
penicillin and other drugs are
pulled out of the bloodstream of
the capillaries and secreted into
this tubule containing nephric
filtrate.

6. v. Collecting duct:
A.This liquid can now be called
“urine” and travels through the
collecting duct to the “renal
pelvis”
vi. Renal Pelvis:
A.Holds urine before dumping into
the Ureters.
III.Demos:
a. Youtube search: “Urine Formation” -
RogerOBoston
I. Homework Assignment:
a.None-Take a break!