2.75 Urine

• Urine contains salts, water and urea.
•  Water and salt particularly affects the composition of the tissue fluid. This is called osmoregulation.
• The removal of urea is part of the process of excretion of metabolic waste.
• The composition of urine varies depends on the condition of each person, both externally and internally. 

2.74 ADH

• Anti-diuretic hormone ( anti-divretic hormone) is produced in a region of the brain known as the hypothalamus. Like all hormones it flows through the blood stream and the target is the kidney.

• The effect of ADH is to control and alter the composition of water which is in blood.
• ADH has the ability to make blood more or less concentrated to keep the tissue fluid isotonic.
• ADH targets the collecting duct and the effect of ADH is that it allows more water to come out of the collecting duct
• We know that water selective reabsorption happens in the collecting duct but ADH can increase the amount of water going into the blood.
• ADH makes the collecting duct walls more porous so that more water can escape from the collecting duct and this water goes back to the blood. 
• The consequence of ADH secretion is that the urine would be more concentrated and have a lower volume.

(credits to daniel)

2.73 Glucose reabsorption

Selective reabsorption means that a molecule will be selected ( glucose) and the reabsorption refers to idea that the glomerulus filtrate will go back to the blood.

• Filtration occurs in the bowman's capsule and the glumerulus filtrate will contain the molecule glucose (and many others e.g. water, salts, amino acids and urea).
• Water is selected back into blood stream at collecting duct where the urine is passed down into the pelvic region.
• At the end of the nephron is urine and normally urine does not contain glucose.
• If we find glucose in the urine it is a condition known as diabetes.
• In the first proximal convoluted tubule glucose is removed and taken back to blood.

2.72 Water re-absorption

• The blood went through ultrafiltration under high pressure in Bowman's capsule and gumerula filtrate ( where this tube contains glucose, water, salts and urea) 
• When the filtration occurs it will filter out too much water and as the filtrate passes along the tubule here. When it reaches the Collecting duct as the filtrate pass through the collecting duct what happens is that water is removed from the filtrate.
• The water is then returned to the blood vessel and will go back to the blood stream.

Selected reabsorption occurs in the collecting duct.

2.71 Ultrafiltration

Nephron carries out the filtration of our blood, which will result into filtered blood and urine.

Urine is composed largely of water, salts (Sodium chloride, etc.) and urea (which contains toxic nitrogen waste of the body) which will going to emerge at the bottom of the tube to the pelvic region.

The first process starts at the bowman's capsule, and the process is called ultrafiltration - the filtration of molecules.

• Blood arrives in the kidney through the blood vessel called afferent arteriole where the blood is under high pressure.
•  Blood vessels then started to branched and became very much slower into twisted parts called glomerulus. 
• The blood then comes out through the blood vessel efferent arteriole in which the diameter of this vessel is smaller and more narrow than the afferent arteriole's. The consequence of narrowed vessels is the increase of blood pressure. 
• The high pressure forces the liquid (plasma) and plasma contains all the substance contained in blood for example water, salts, amino acids, glucose and urea. These are all forced out from the blood into the space, the inside of the bowman's capsule.
• When the plasma is forced into bowman's capsule, we call this filtrate and because it is in the glomerulus we call this glomerula filtrate.
• The blood has been filtered due to high pressure because of the smaller area of the blood vessel.

2.70 Nephron Structure

• Nephron is the functional unit of the kidney. The part that does the filtration and of the composition of blood.
• The aorta brings blood and through the renal artery reaches the kidney 
• The waste which is the urine then goes through the ureter to the bladder.
• The filtered blood exits the renal vein and return to the vena cava. 

If we slice through the kidney we see different colored region, the lighter colored region is called the cotex and the inner, slightly colored region is called the medulla and the lighter colored space is the pelvic region.

•  In this space it is where the urine collects and drains down the ureter.
•  The region of the different color is because the kidney is made up of millions of tubes.
•  The tube starts on the edge of the medulla and moves directly upwards through the medulla and up through the cortex and then will reach a dead-end and is called the bowman's capsule.
• The tubular structure is called the nephron
  
  

In this diagram  is the Nephron structure 

• The tube is made up of twisted section called convoluted tubules and the tube which connects the convoluted tubules into the pelvic region is called the collective duct. 

• The part the dips back into the medulla is called the Loop of Henle

• The Bowman's capsule is the dead end structure in which contains tight knot blood vessels called glomerulus.

• The first twisted section is known as the proximal convoluted tubules (PCT).

• The second twisted section is know as the Distal convoluted tubules (DCT).

It is the arrangement of the nephron which gives us the difference in color between regions in the kidney. There are millions of nephron in a single kidney. 

2.69 Urinary system

In the urinary system 

•  Two kidneys the right and the left each with its own blood supply carrying out the process of filtration, osmoregulation, and excretion. 

• From each kidney there is a tube leading to the bladder which is called the ureter. 

• The urine stored in the bladder travels to outside through the urethra and down through the vagina or the penis.

2.68b Osmoregulation

Osmoreuglation - Osmo refer to Osmosis, regulation refer to control.

We do not want it to be too concentrated ( Hypertonic) and dilute ( Hypotonic) tissue fluid .We want to keep the tissue fluid isotonic (the amount of water into is equal to the output) so that the cell will remain size shape and same function which is achieved by controlling the composition of blood. 


The kidney is the organ which controls the composition of blood. 
Blood circulates through our kidney and excess water or salt is removed and excreted through the ureter here by controlling the content of water and salts in the blood, the kidney can keep the blood and therefore the tissue fluid can be maintained as isotonic which maintains the function of the cells.

2.68a Excretion

To illustrate this 
we show the excretion of urea which contains nitrogen which is toxic to the body -The amino acids are used for growth and excess amino acids needs to b removed

• Blood circulates to the liver and the amino acids are broken down and converted to a molecules which we called urea.
• This re-enters into the blood stream and which then enters both kidneys.
•  The kidneys will filter the urea from the blood and the urea will be added to water to form urine and travel down the ureter to collect in the bladder which is stored there as the form of urine. 
• The filtered blood travels back to the blood stream without any urea.

2.67b Human organs of Excretion

2.67a Excretion in plants

1. Photosynthesis absorb light energy and turn CO2 + H20 -> C6H12o6 + O2 (  where O2 is the Excretion)


2. Aerobic respiration


                       Enzyme            
C6H12O6 + 02 ------------> ATP + Co2 ( excretion) + H20


Plants excrete Oxygen and Carbon Dioxide depending upon the process it is doing.