Urinary system

1.

Urine formation

2.

Lesson objectives
To explain the mechanisms of filtration
and urine formation

3.

Lets think!
How is urine formed?

4.

What are kidneys?
Kidneys are a pair of bean-shaped organs
which are part of urinary system.

5.

The Job of the Urinary System:
It is responsible for cleaning the
blood by removing metabolic
wastes, excess solutes, and excess
water and excreting them as urine.
Besides removing urea, it also
removes excess salts or glucose, the
remnants of drugs, and excess water
and keeps homeostasis.

6.

Functions of the
kidneys
filters blood
makes urine.

7.

Kidney structure
Kidneys have two parts : outer cortex and
inner medulla

8.

Nephrons
Each kidney
consists of
millions of
nephrons.
Nephrons are
the
fundamental
units of the
kidney.

9.

Nephron structure
Glomerulus
Bowman’s capsule
Convoluted tubules:
proximal and distal
A loop of Henle
Collecting duct

10.

Renal artery and renal vein
Renal artery bring blood to kidneys
Renal vein takes the cleaned blood away
from the kidneys

11.

Steps of urine formation:
Filtration
2) Reabsorption
3) Secretion
1)

12.

Filtration

13.

Filtration
It takes place in glomerulus and Bowman’s
capsule

14.

A closer look to the glomerulus and
Bowman’s capsule
Each glomerulus is formed by network of capillaries that is branch of renal
arteriole.
Renal arteriole through which blood flows into glomerulus is called as
afferent arteriole.
Arteriole through which blood leaves glomerulus is called as efferent
arteriole.
Glomerulus has only one cell thick walls with many pores, so some
materials can leave glomerulus and pass into Bowman’s capsule.
Bowman’s capsule is cup-shaped structure that surround glomerulus. It has
very thin walls with only one cell-thick.
Afferent
arteriole
Efferent
arteriole

15.

Filtration process
Blood pass from afferent arteriole
into glomerulus.
Glomerulus has high blood pressure
which forces small materials of
plasma, such as ions, urea, amino
acids, salts, glucose, water etc to
pass into Bowman’s capsule
So blood is filtered through the
glomerulus, allowing small
substances to pass into Bowman’s
capsule, but large materials such as
blood cells and proteins remain in
blood.
The fluid that enters Bowman’s
capsule then renal proximal tubules
is called filtrate.
filtrate

16.

Reabsorption

17.

Reabsorption
It takes place in renal tubules (convoluted
tubules: proximal and distal, loop of Henle)

18.

A closer look into renal tubules
Renal tubules:
proximal tubule, loop
of Henle, distal tubule
is covered by network
of capillaries.
Loop of Henle is Ushaped and has two
segments: descending
limb and ascending
limb

19.

20.

Process of reabsorption
As the filtrate flows through the
renal tubule , most of water and
nutrients are reabsorbed into the
blood.
Water and chloride ions are
transported passively.
Glucose, amino acids and sodium
ions are transported by active
transport.
As descending loop is permeable for
water it is reabsorbed into blood.
And filtrate becomes very
concentrated.
As ascending loop is impermeable for
water because of gradient salts pass
into blood by diffusion.

21.

Secretion

22.

Secretion
It takes place into
renal tubule.
Substances
including H+,
potassium, uric
acid and
ammonium enter
the tubules from
blood.
The concentrated
fluid that remains
is called urine.

23.

What is Urine?
Urine is a liquid waste that is 95% water.
The remainder consists of:
Urea (majority) and uric acid
Ammonia
Hormones
Dead blood cells
Proteins, salts, and minerals
Various Toxins.

24.

What happens to urine?
Urine flows into collecting duct
and then into pelvis.
Further it passes into ureters
that lead to urinary bladder.
Urinary bladder store urine
temporary.
Urine leaves bladder and body
through urethra. It is called as
urination.

25.

Let’s do the activity on p. 85

26.

Homework
Read p. 84-85
Answer to literacy questions on p 85.
New words