1. EXCRETORY SYSTEM

2. WHAT IS EXCRETION?
If you knew there was poison hidden in your house, you would surely do everything possible to find and remove that poison.
If you didn't, you and your family would slowly die.
How would you find and then remove it?
You would probably figure out a system of searching and removing.
That is what the excretory system does!!

3. interesting facts
The Human bladder can stretch to hold about 1.5 cups (400ml) of urine.
All the blood in our body passes through each kidney 400 times every day.
When the bladder is ½ full, our brain tells the bladder to relax and we get the urge to urinate. We can’t control or stop urination until we are 2 years old.
Even if 75% of the nephrons are lost, the kidney will still function. It is possible to live a healthy life with only one kidney.
Normal urine is sterile (germ-free). It is composed of water, salts, and waste products.

4. interesting facts
The kidneys have 1 million little filters which filter 1.3 litres of blood every minute. That is 1,620 litres every day. 
99.9% of the materials passing through the kidneys are reabsorbed back into the blood.
We made approximately 1.5 litres of urine per day.
A traditional medical practice in India is called urine therapy, and they apply urine to the skin or drink it to cure various health problems.
Urine has a lot of urea (waste), and it is a good source of nitrogen for plants. Gardeners often recommend you add 1 cup of urine to 15 cups of water and apply it to pot plants and flower beds to help them grow.

5. interesting facts
The ancient Romans used to bleach their clothes with urine.
People lost at sea or in the desert for a long time often resort to drinking their urine when no rainwater is available. However, this won't prevent you from dying of dehydration, especially if it causes vomiting.
Urine has also been used as an antiseptic. In times of war, when other antiseptics were unavailable, urine, the darker the better, was used on open wounds to kill bacteria.
The yellow colour of urine was once thought to come from gold. Alchemists in the middle ages spent a lot of time trying to extract gold from urine. They were, of course, unsuccessful.

6. FUNCTIONS OF THE EXCRETORY SYSTEM Filters the blood
Removes wastes from the blood
Keeps the amount of water and salts in the blood constant
Helps to regulate Blood Pressure

7. Desiccation
Humans will die if they lose about % of their body water.
The threat of desiccation is the most important problem confronting terrestrial life.
How do we control our loss of water?
Multiple layers of dead, keratinized skin cells
Drink and eat moist foods
Nervous and hormonal mechanisms control thirst
Behaviour: (ie: stay out of intense heat)
Kidneys and other excretory organs help conserve water.

8. Desiccation
Water loss can be considerable: a person in a 38oC temperature will lose 1 Litre of H2O/hour.
We acquire most of our water in our food and drink, and obtain a smaller amount by dehydration synthesis and as a by-product of cellular respiration.
We lose water by urinating, defecating, sweating, and breathing.

9. EXCRETION
The Excretory System is made up of the kidneys, liver, lungs, and skin. Each plays a role in excretion.
Skin: sweat with water, salts, heat and some urea
Lungs: excretes carbon dioxide, water, and heat
Liver: gluconeogenesis – makes urea as a byproduct
Intestines: excretes certain heavy metals
Kidneys: the main excretory organ. Excrete toxins, drugs, wastes (urea…), and water.

10. PARTS OF THE
EXCRETORY SYSTEM

12. #1 Kidney: Bean-shaped 10 cm long Lower, dorsal part of the abdomen
Blood enters the kidney via the renal artery, is cleaned, and leaves the kidney in the renal vein

13. inside the kidney
The kidneys account for less than 1% of the weight of the human body, but they receive about 20% of the blood pumped with each heartbeat.

15. Renal cortex
renal medulla
renal pelvis
Renal pyramid
Ureter

16. #2
KIDNEY
Ureter:
Waste fluid made in the kidney exits through a duct called a ureter.
Moves the urine to the bladder via peristalsis
URETER

17. #3 Bladder: stores the urine
KIDNEY
Bladder: stores the urine
An average bladder can hold a maximum of 1.5 to 2 cups of urine.
When full, the sphincter muscles control the release of urine from the bladder
URETER
BLADDER

18. #4
KIDNEY
Urethra: when the sphincter relaxes, the urethra carries the urine outside the body.
20 cm in males
4 cm in females
Females are more prone to infections of the urinary system.
URETER
BLADDER
URETHRA

21. Homeostasis
The kidneys perform a number of homeostatic functions, as they are the chief regulators of our internal environment:
Regulates blood volume and osmotic balance by excreting or conserving water as the situation demands.
Regulates the ionic balance of the blood by controlling the excretion of inorganic salts (especially sodium).
Regulates Blood pH by excreting excess acids or base
Excretes toxic metabolic by-products such as urea, ammonia, uric acid, and creatine (a product of muscle activity).

22. Nitrogen Wastes
Nitrogen wastes are a by-product of protein metabolism. When proteins are turned into glucose during gluconeogenesis, ammonia is made.
Because ammonia is very toxic and must be diluted as it travels around the body, however, terrestrial animals usually need to conserve water.
What do we do? The liver converts the ammonia to urea, which is then transported to the kidneys, where it is concentrated and excreted out of the body as urine. This takes a lot of energy.

23. NEPHRON
The functional unit of the kidney is the NEPHRON, which consists of a renal tubule and its associated blood vessels.
Each kidney contains approximately 1 million nephrons, which represents approximately 80km of tubules.

24. Water, urea, salts, and other small molecules in the blood flow from the capillaries into the renal tubules, where the fluid is now called FILTRATE.
The epithelial cells that line the renal tubule adds and removes things from the filtrate to eventually form URINE.
From the 1100 to 2000L of blood that flows through the human kidneys each day, the nephron processes about 180L of filtrate, but excretes only ~1.5L of urine.
The rest of the filtrate, including ~99% of the water, is reabsorbed into the blood.
NEPHRON

28. NEPHRON STRUCTURE 1 4 2 5 3

29. NEPHRON STRUCTURE
1. Bowman’s Capsule: this cup shaped receptacle is the blind end of the renal tubule, which receives filtrate from the blood. It encloses a ball of capillaries called the glomerulus.
blood
filtrate

30. NEPHRON STRUCTURE
2. The proximal convoluted tubule (PCT): most of the important things (nutrients, water, salt…) are reabsorbed from the PCT.
nutrients
water
salt

31. NEPHRON STRUCTURE
3. The ascending and descending loop of Henle: a lot of salt and water are reabsorbed from Loop of Henle.
water
salt
salt
water

32. NEPHRON STRUCTURE
4. The distal convoluted tubule (DCT): the blood dumps things it wants to get rid of into the DCT so it can be removed in the urine.
drugs
acids

33. NEPHRON STRUCTURE
5. The collecting duct collects filtrate from many tubules and pass the urine into the renal pelvis. Water and urea are also reabsorbed here.
water
urea

35. NEPHRON CAPILLARIES 2 3 1 4 5

36. NEPHRON CAPILLARIES
1. Afferent Arteriole: this arteriole enters the bowman’s capsule from the renal artery .
Renal artery
Renal vein

37. NEPHRON CAPILLARIES
2. Glomerulus: the capillaries of the glomerulus are porous and very twisted up. They sit within the Bowman’s capsule.
Renal artery
Renal vein

38. Bowman’s Capsule

40. NEPHRON CAPILLARIES
3. Efferent Arteriole: this arteriole leaves the bowman’s capsule. The blood is very hypertonic as most of the plasma has left the blood. The blood carries RBC, WBC, platelets and blood proteins.
Renal artery
Renal vein

41. NEPHRON CAPILLARIES
4. Peritubular Capillaires: these are the capillaries that surround the Proximal and Distal convoluted tubules.
Renal artery
Renal vein

42. NEPHRON CAPILLARIES
5. Vasa Recta: these are the capillaries that surround the Loop of Henle.
Renal artery
Renal vein

43. 1 2 3
The Nephron has 4 main functions: 4

44. The Job of the Nephron
1. Pressure Filtration: the blood pressure forces water and solutes through the pores of the glomerulus into the Bowman’s capsule.
The holes in the glomerulus are small, so they are permeable to water and small solutes, but not to blood cells or blood proteins.
The filtrate contains a mixture of solutes such as salts, nutrients, water and other small molecules.
At this point, the concentration of substances in the blood plasma is equal to that of the filtrate.

48. Blood plasma in glomerulus Filtrate in Bowman’s Capsule
The Job of the Nephron
Blood plasma in glomerulus
Filtrate in Bowman’s Capsule
salts, nutrients (glucose, fatty acids, glycerol, nucleotides, amino acids), water, hormones, antibodies, water soluble vitamins, penicillin and other drugs, histamines, nitrogenous wastes (urea, uric acid…) and other small molecules.
salts, nutrients (glucose, fatty acids, glycerol, nucleotides, amino acids), water, hormones, antibodies, water soluble vitamins, penicillin and other drugs, histamines, nitrogenous wastes (urea, uric acid…) and other small molecules.

49. Composition of Plasma, and Glomerular Filtrate
Urea
0.03
Glucose
0.10
Amino acids
0.05
Water
52.0
Salts (ie: Na+, Cl-)
0.9
Protein
8.0
None
RBC, WBC, Platelets
Lots

50. The Job of the Nephron
Selective Reabsorption: since filtration is nonselective, the body MUST make sure that the important molecules are returned to the blood plasma as soon as possible.
Nearly all of the nutrients (esp. sugar), salts and water are reabsorbed.
This happens at the PCT and it is a very selective process. There are a lot of mitochondria in the cells of the PCT.
Why? This costs ENERGY!!

51. WHAT IS REABSORBED? : 70% of the water, and 75% of the salts, glucose, amino acids, and other nutrients move back into the blood.
The positive sodium ions are actively transported into the interstitial fluid and the negative chlorine ions follow passively, and finally, water follows by osmosis.
The glucose, amino acids, and other nutrients are actively transported into the blood.
Lots of ATP required!! 

52. OSMOREGULATION
Recall that osmosis is the movement of water (from [High] to [Low])across a selectively permeable membrane.
This movement occurs whenever two solutions separated by a membrane differ in total solute concentration or osmolarity.  
The osmolarity of human blood is ~300 mosm/L.

53. When two solutions differ:
The one with the greater concentration of solutes (salt, urea) is HYPEROSMOTIC
The one with the more dilute (watery) solution is HYPOOSMOTIC
Remember:
Water always moves towards a hyperosmotic environment. SALT SUCKS!!
Hyperosmotic
Hypo-osmotic
Hyperosmotic
Changes in the body fluids are controlled by a variety of regulatory mechanisms, usually involving negative feedback.
The control of water gain/loss is called OSMOREGULATION.

54. The Job of the Nephron
Water Reabsorption: water reabsorption occurs mainly at the loop of henle and in the collecting duct.
The nephron pumps out salt and urea in these areas to make the blood and medulla extremely hyperosmotic.
Water then moves back in to the blood by osmosis.

55. Counter Current Exchange
It is important to note that the blood in the vasa recta moves in the OPPOSITE DIRECTION that the filtrate is moving.
This allows the nephron to create a hyperosmotic environment around the descending loop of henle.
So we’ll talk about the ascending Loop of Henle 1st.

56. The ASCENDING LOOP OF HENLE:
This part of the loop of henle is NOT PERMEABLE to water, but the salt can move.
So, the NaCl passively and actively moves out of the tubule and into the blood and the medulla of the kidney.
This creates a very HYPERTONIC solution in the blood.
As the filtrate moves towards the DCT, most of the salt has left and the filtrate becomes more and more dilute.

57. The DESCENDING LOOP OF HENLE:
The loop of henle continues the reabsorption of water as the filtrate moves from the cortex and down into the concentrated medulla.
The epithelium of this portion of the renal tubule is permeable to water, but not very permeable to salt and other solutes.
Lots of WATER moves into the HYPERTONIC blood (created at the ascending loop) by osmosis as it follows the salt.
As a result of this great loss of water, the filtrate becomes more and more concentrated.

59. The COLLECTING DUCT:
Water is also reabsorbed here.
The epithelium of this duct is permeable to water and urea.
As the duct moves down into the VERY HYPERTONIC medulla, the filtrate loses more and more water by osmosis as it moves back into the blood.
This loss of water concentrates the urea in the filtrate, and because there is so much UREA in the collecting duct, some of it diffuses down its concentration gradient and back into the blood and medulla.

60. The kidney is made up of two sections: the cortex and the medulla
The kidney is made up of two sections: the cortex and the medulla. The medulla is HYPEROSMOTIC as it has high concentrations of the solutes NaCl and urea.
renal medulla
HYPERTONIC
renal cortex

62. The Job of the Nephron
Secretion: if the blood still needs to rid itself of other ions and waste products (hydrogen ions, ammonia, potassium ions), it will secrete them into the Distal Convoluted Tubule (DCT).
This is a very selective process that involves both active and passive transport. Lots of mitochondria in the DCT too! ATP required!!!

63. REVIEW OF NEPHRON: http://www.youtube.com/watch?v=glu0dzK4dbU

65. Urea 0.03 1.8 50% Glucose 0.10 None 100% Amino acids 0.05 Water 52.0
Composition of Plasma, Glomerular Filtrate, and Urine (g/100 ml of fluid).
Plasma
Filtrate
Final Urine
% Reclaimed
Urea
0.03
1.8
50%
Glucose
0.10
None
100%
Amino acids
0.05
Water
52.0
1.0
99%
Salts (ie: Na+, Cl-)
0.9
<
99.5%
Protein
8.0
RBC, WBC, Platelets
Lots

66. When the Blood is Acidic
If the blood is ACIDIC, 2 things will happen:
The bicarbonate ions are actively transported back into the blood. The HCO3- is an important buffer which will join with H+ to remove it from the solution.
The blood will also secrete hydrogen ions into the filtrate so we will pee it out.
HCO3- H+

69. Hormone control of Water & Salt Reabsorption
If you are dehydrated, the kidneys can excrete a small, concentrated volume of urine and reabsorb the majority of water from the filtrate. You will have very little dark yellow urine.
If you have consumed an excessive amount of fluid, the kidneys can excrete a large, dilute volume of urine, with very little water being reabsorbed from the filtrate. You will have lots of pale yellow urine.
How do we maintain the proper amount of water in our bodies? It is controlled homeostatically with 2 hormones.

70. Hormone control of Water & Salt Reabsorption
FIRST HORMONE: ANTIDIURETIC HORMONE (ADH)
This hormone controls water reabsorption with a negative feedback cycle.
The hypothalamus makes ADH and it is stored and released from the posterior pituitary gland.
It is released in response to an increase in the osmolarity of the blood (very concentrated blood) when you are dehydrated (inadequate intake of water).

71. dehydrated

72. Hormone control of Water & Salt Reabsorption
When you have low blood volume (high osmolarity), the osmoreceptor cells in the hypothalamus triggers the posterior pituitary to release ADH.
ADH increases the permeability of the DCT and collecting ducts to water.
This causes more water to be reabsorbed and ultimately increases blood volume (amount of blood).
At the same time, the removal of water from the filtrate increases the concentration of the urine. You urinate less and it will be dark yellow.

74. Hormone control of Water & Salt Reabsorption
When you have high blood volume and low osmolarity, sensors in the heart signal the hypothalamus to cause a reduction of the amounts of ADH in the blood.
This decreases the amount of water that is reabsorbed into the blood, and large quantities of a more dilute urine are produced.
This is a negative feedback cycle, because as the osmolarity of the blood is reduced (blood volume increases) less ADH will be secreted.

75.  Alcohol can perturb water balance by inhibiting the release of ADH, causing excessive loss of water in the urine and dehydrating the body.
This leads to the symptoms of a hangover. Which is why you should always drink a lot of water when drinking alcohol. This keeps you hydrated.

76. Hormone control of Water & Salt Reabsorption
Second Hormone: ALDOSTERONE
There is tissue surrounding the afferent arteriole called the juxtaglomerular apparatus (JGA) which measures Blood Pressure.
When the BP drops, or if the [Na+ ] in the blood is too low (due to diarrhea, a severe injury…), the JGA releases an enzyme called RENIN.
The liver makes a protein called ANGIOTENSIN which is always circulating around the blood.
RENIN activates angiotensin.

78. Hormone control of Water & Salt Reabsorption
The active form of ANGIOTENSIN does two things:
It stimulates the adrenal gland to release the hormone ALDOSTERONE.
Aldosterone tells the DCT to reabsorb lots of Na+, and water follows the sodium by osmosis. This increases the amount of water in the blood, which increases the BP.
It also causes VASOCONTRICTION of the arterioles, which also raises blood pressure.

79. Low BLOOD PRESSURE

81. Why are the kidneys so concerned with the BLOOD PRESSURE?
Low blood pressure is bad because there is not enough pressure to filter the blood properly. This makes the kidneys less efficient at ridding the body of drugs and toxins.
High blood pressure is bad because the glomerulus can burst and then we would see blood and blood proteins in the urine.