Slides from a virtual session on human excretory system.

1. Excretion and
Interaction of SystemsBiology by
Mr. Lakhani
https://www.linkedin.com/in/karimmlakhani/

2. These non-essential substances, if accumulates, causes harm to the body.
These include
Function: Regulate composition and volume of body fluids
Therefore, the product that emerges – excreta, waste, non-essential for the body
Excretory System
• Mostly nitrogenous compounds such as
• Ammonia – NH3(Can you share the chemical formula?)
• Urea CO(NH2)2 (Ammonia converts to Urea in liver)
• Half of the Urea produced is excreted in Urine
• Uric Acid
• Less produced in mammals including humans, excreted through Urine
• Most birds produce Uric acids

3. Digestive System – Loss of pigments, water, salt, lipid, etc.
Skin – perspiration causes loss of water, salts and some amount of Urea
Lungs – Loss of CO2 and other gases through breathing
Excretion happens through various body organs
then we may intuitively think of
Feces ≠ Excretion
Excretory System = Urinary System

4. Excretory System Organs
• Two Kidneys
• Kidneys are protected by large cushion of fat and partially by rib cage
• Ureters
• About 28 cm long
• Moves urine into bladder to peristaltic movement
• https://www.youtube.com/watch?v=kVjeNZA5pi4
• Urinary Bladder
• Can hold about 600 ml urine
• Drainage is controlled by two sphincters
• Inner ring of sphincter is involuntary
• Outer ring of sphincter is voluntary which we learn control with in
childhood

5. Excretory System Organs
• Urethra
• Male
• Urethra – about 20 cm in length
• Merges with Vas Deferens, a part of
reproductive system forming a single
passageway
• Vas = Vessel, Deferens = Carrying away
Vessel that carries away (in this case
sperms away from testicles)
• Female
• Urethra – about 4 cm in length
• Reproductive and Urinary tracts are
separate

6. Excretory System Organs
• Kidneys
• Ureters
• Urinary Bladder
• Urethra
Urination – How is it caused?
• When bladder is half full, sensory reception in the
wall of bladder send signal to spinal cord
• This results in contraction of inner sphincter
(remember involuntary) by brain
• Urge to urinate – can be controlled for a shorter
while by outer sphincter
How is urine formed? We will see in late slides.

7. Structure of Kidney
• Renal = related to Kidney/of Kidney
• Three parts
Renal Pelvis
• Pelvis = Basin
• Opens into Ureter
Renal Medulla
• Medulla = Pith, marrow, essence, middle
Renal Cortex
• Bark, outer layer (do not confuse with ‘core’)
Medulla and Cortex hold the most important units responsible for filtration – Nephrons
About 1 million Nephrons in each kidney. Size = 0.5 cm when extended lengthwise.

8. Structure of Nephron
• Each Nephron consists of three parts.
Filter
•Bowman’s capsule (because Mr. Bowman)
•Glomerulus – its walls act as filter. Network of capillaries.
Glomerulus = little ball
Tube
•Proximal Tubule – closer to bowman’s capsule, hence
proximal
•Distal Tubule – distant to bowman’s capsule, hence distal
•Loop of Henle (because Mr. Henle) – Descending and
Ascending
Duct
•Collects urine and directs to renal pelvis
All Nephrons works simultaneously to filter blood. Renal Artery from aorta branches and
enter each kidney. Filtered blood then gets into vein which further joins to inferior vana cava.
Bowman’s capsule + glomerulus = Renal Corpuscle
Corpuscle = small body, many together make a larger body

9. Structure of Nephron
• Each Nephron consists of three parts.
Filter
•Bowman’s capsule (because Mr. Bowman)
•Glomerulus – its walls act as filter. Network of capillaries.
Glomerulus = little ball
Tube
•Proximal Tubule – closer to bowman’s capsule, hence
proximal
•Distal Tubule – distant to bowman’s capsule, hence distal
•Loop of Henle (because Mr. Henle) – Descending and
Ascending
Duct
•Collects urine and directs to renal pelvis
All Nephrons works simultaneously to filter blood. Renal Artery from aorta branches and
enter each kidney. Filtered blood then gets into vein which further joins to inferior vana cava.
Bowman’s capsule + glomerulus = Renal Corpuscle
Corpuscle = small body, many together make a larger body
Did you notice what components of Nephrons are embedded in which parts of kidneys?

10. Urine Formation (Function of Nephron)
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
Reabsorption in collecting duct

11. Urine Formation (Function of Nephron)
Glomerular Filtration
• Blood enters glomerulus through renal artery
• Glomerular capillaries have pores in their walls causing filtration.
• Pores > water, ions – hence get filtered
• Pores < RBC, important protein – hence they stay in blood
• The resulting fluid is called FILTRATE
• Filtration depends on two factors
• Permeability of Capillaries
• Blood Pressure
• (Blood pressure in glomerular capillaries = 4 * regular capillaries)

12. Urine Formation (Function of Nephron)
Glomerular Filtration
• Approximately 1600 – 2000 liters of blood pass through Kidneys
• About 180 liters of glomerular filtrate is produced per day
• Composition of glomerular filtrate is similar to plasma (except proteins)
Composition Plasma Filtrate
Protein 44.4 g/l 0 g/l
Na+ 3 g/l 3 g/l
CL- 3.5 g/l 3.5 g/l
Glucose 1 g/l 1 g/l
Urea 0.3 g/l 0.3 g/l

13. Urine Formation (Function of Nephron)
• About 65% of filtrate
gets reabsorbed
through three ways –
• Active transport:
Na+ and Ca2+
• Passive transport:
Cl- and HCO3-
• Osmosis: Water
Tubular Reabsorption

14. Urine Formation (Function of Nephron)
• DL: moves towards medullar region
which is SALTIER than cortex
• Hence, medulla has more
concentration than cortex. So, water
moves out into interstitial fluid
which is taken up by capillaries with
minimal solutes.
• DL is more permeable to water than
ions and urea.
• Filtrate gets more concentrated
Tubular Reabsorption

15. Urine Formation (Function of Nephron)
• AL: Impermeable to water but slightly
permeable to ions. AL is thicker than DL
• Na+ and Ca2+ get actively reabsorbed
• Cl- and HCO3- ions follow passively through
attraction
• Again, these ions diffuse into interstitial fluid
first and then taken up by capillaries
• 2/3 of Na+ ions get reabsorbed
• Na+ removal – helps maintain salty
environment of medulla
• And makes filtrate less concentrated for
the cortex region
Tubular Reabsorption

16. Urine Formation (Function of Nephron)
• Na+ transport – hormone
controlled
• K+ is actively secreted
• H+ is actively secreted to
maintain pH
• Substances that are not part
of body normally are secreted.
E.g. Penicillin and other drugs
Tubular Secretion (Distal Tubule)

17. Urine Formation (Function of Nephron)
• As ions are actively transported in blood
(remember in the previous process), the
concentration of blood increases
compared to urine. Thus, Water again gets
absorbed through osmosis.
• Water absorption is hormone controlled.
Thus, if needed, permeability of water can
be reduced or increased.
• Urine becomes 4 times more
concentrated
• 1% of initial volume gets filtered which
excretes as Urine.
Reabsorption in collecting duct

18. Maintaining Excretory System
Why Excretory System?
• To remove waste
• What is a waste for a healthy human body?
• Substances which are harmful to body and
which are not required by the body (excess and
which may not be visibly harmful)
• Think of things which are not required by the
body – water, ions
We drink water, where does it go?
Water gets added right away to blood from digestive
tract.
How much blood can our body handle normally? -
about 5 liters, do you recall from circulatory system.

19. Maintaining Excretory System
Volume of blood increases
• Think of a tank of 5 liters. When you force more water
into the tank, what happens to its wall
• Pressure increases: This pressure is seen on heart as
there is more volume to pump and hence on blood
vessels
Now think of ions –
Increased ion concentration in blood increases
concentration of blood. What impact would it have?
• The normal pH balance will get disturbed
• Positive and negative ions cause action potential for
nervous system to work. Remember our heart is
controlled by nervous system. The imbalance will have
adverse effect.

20. Maintaining Excretory System
ADH (anti-diuretic Hormone)
• Osmoreceptors in Hypothalamus get activated when
osmotic pressure in kidney increases
• When does osmotic pressure in kidney increase. When
blood passing through kidney is concentrated, water in
urine exerts pressure on nephron walls to enter into
blood.
• Osmoreceptors send signal to pituitary gland to release
ADH (Dia = through, Uretic = Urine: Promoting Urine)
• ADH travels to kidney through blood and increases
permeability of distal tubule and increases water
absorption.
• When blood concentration is too low, Osmoreceptors
prevent ADH. Thus, increase urine volume

21. Maintaining Excretory System
ADH (anti-diuretic Hormone)
• Lack of ADH/ADH inactivity is called Diabetes insipidus
(Insipid = ’Tasteless’)
• 4-8 liters of urine per day, intense thirst, dehydration
and ion imbalance are symptoms
• Treatment: synthetic ADH
• Diuretic examples: Ethanol (Alcohol) and Caffeine

22. Maintaining Excretory System
Aldosterone
• Another hormone that regulates ions
• Na+ active transport into blood
• K+ secretion into distal tubule
Maintaining pH
• Normal blood pH = 7.4, why maintaining blood pH is
important?
• Happens through three mechanisms
• Acid-Base buffer system
• Breathing
• Kidneys

23. Maintaining Excretory System
Acid-Base buffer system:
• pH= -log [H+] concentration
• Look at the below reaction
H+ + HCO3
- <=> H2CO3 <=> H2O + CO2
• If you add H+ to the system, the reaction will move towards
right hand side.
• So, if blood is too acidic, H+ is excreted and HCO3
- is
reabsorbed. If blood is too basic, H+ is not excreted and HCO3
-
is not reabsorbed.
Breathing
• Breathing aids increased loss of CO2
Kidneys
• Loss of H+ and HCO3- is regulated to increase or decrease pH
Urine is acidic: hence, H+ usually excreted

24. Chemical composition of Urine determines one’s health.
However, not the case every time –
• More Glucose in urine when you have sugary meals
• More protein when you had a rigorous work out
• More Ketone-acids when you fast or carbs deprived

25. Disorders
• Urinary Tract Infections
• Kidney Stones
Urinary Tract Infections
• Cystitis: Bacterial/Viral infection in bladder
• Urethritis: If infection in Urethra
• Women are more prone to infection because of proximity of
openings
• Painful burning sensation while urinating, need to urinate
frequently, bloody/brown urine, chills, fever, nausea and vomiting
are some symptoms
• Severe infections can lead to permanent damage or kidney failure
• Treatment: antibiotic, surgery in serious condition
• Precautions: Drinking lots of water, maintaining hygiene

26. Disorders
• Urinary Tract Infections
• Kidney Stones
Kidney stones
• Happens when there is excess of Calcium
• 85% of stones are made of calcium compounds
• Causes: Recurring urinary tract infection, insufficient water
consumption and low physical activity
• Treatment: Depends on the size of stones
• Most pass through urine on their own
• Medications can help break crystals depending on size
• If stones smaller than 20mm in diameter, Ultrasound shock
waves can break stones = Lithotripsy
• Surgery for larger stones

27. Renal insufficiency
Renal insufficiency = kidney unable to maintain homeostasis
due to nephron damage
• Causes: Infection, high blood pressure, diabetes mellitus,
trauma on the lower back, constant vibration from
machinery, poisoning of heavy metals like mercury, lead or
solvent such as paint thinners, atherosclerosis (reduction
of blood flow to kidneys), blockage of tubules
• Nephrons can regenerate. If some damaged, other
nephrons can compensate
• Humans can live with 1/3rd of kidney. Even 75% of
nephrons are damaged, humans can live. But urine
output will be insufficient for maintaining homeostasis.
• Treatment: Kidney transplant or dialysis

28. Dialysis
Two types
• Hemodialysis
• Blood is passed through semipermeable membrane
from artery of a person’s arm and then sent into vein
• Artery and vein are joined – called FISTULA for longer
term access (Fistula = tubular, pipe)
• Use of Heparin = anticoagulant (discovered by Gorden
Murray in 1946)
• Peritoneal dialysis
• Uses lining of intestine as filter
• Dialysate is introduced into abdomen using a Catheter
(flexible tube, Catheter = impel, letting down, throw)
and blood continues to get filtered
• Later Dialysate is extracted

29. Dialysis
• Peritoneal dialysis - types
• CPD: Continuous Peritoneal Dialysis
• Dialysate is introduced in abdomen. Hence, dialysis
continues
• CAPD: Continuous Ambulatory Peritoneal Dialysis
• Can be done at home, school or clean environment
• 3-5 dialysate exchange required per day
• APD: Automated Peritoneal Dialysis
• Machine performs dialysis
• Usually done at night as requires about 12 hours
Dialysis is still not a permanent solution. Permanent solution
occurs through Kidney transplant

30. Kidney Transplant
• Canadian Data
• 14 donors per million
• About 75% are waiting for kidney
• Kidney Transplant surgery = Laparoscopy
• Making three small incisions in abdomen and
minimum invasive
Types of Donors
Cadaveric (Dead) Live
Live donors can
donate kidney, part
of liver and lungs

31. Kidney Transplant
• Success rate of Transplant
• Genetic makeup needs to match for transplant
• Live donor (98%) > Cadaveric donor (95%)
• To ensure successful transplant, anti-rejection drugs are
used
• Remember immune system = it attacks foreign tissues
• Hence, anti-rejection drug = immune suppressants –
suppresses T cells
• Rejection of new organ may lead to failure of the
transplanted or other indigenous organs
• Anti-rejection drug is given before treatment so that
body is ready for transplant and greater chances of
acceptance

32. Maintaining Healthy
Kidneys

33. Excretory
System
Coronary
System
• Increase in blood pressure leads
to increased reabsorption of
water in kidney and vice versa
• Chronic increase in blood
pressure leads -> increased
pressure on nephron, damaging
nephrons
• Increased Blood Pressure and
Nephron Damage are known at
a very later stage.
Kidney – Coronary Connection
Treatment: Physical exercise -> release of Nitric oxide on the inner walls of blood vessels -> reduction of plaques
-> maintaining of heart and kidneys

34. Metabonics
• Metabolites
• NMR: Nuclear Magnetic Resonance Spectroscopy