1. The Kidney

2.  Define excretion
Excretion is the removal from the body of the waste products of metabolic activities

3. Osmoregulation Key Factors
Osmoregulation maintain an osmotic potential of their body fluids that is different from the environment.
Organisms living in fresh water have to eliminate the excess water that flows in by osmosis
Organism living in salt water have to conserve water and eliminate salt
All of this is controlled by feedback systems (hemeostatic mechanisms).

4. Osmoconformers
Organisms that allow their body fluid osmotic potential to mirror the environmental osmotic pressure
They do this by using active transport to maintain specific ion concentration in their tissue fluid at concentration different from environment.
Examples: Marine fish

5. Osmoregulation and excretion
Osmoregulation = maintaining correct fluid level in the body
Ways in which organisms regulate
The Malpighian tubule system in insects
The kidney in mammals
Metabolic pathways produce waste product that could be toxic to an organism
Urea (breaks down weak non-covalent bonds in protein leading to denaturation.
Excretion is the removal of waste product
The kidneys in mammals

6. Malpighian Tubules
Blind ending outgrowths from the gut and are surrounded by the insects blood in the body cavity
They perform both osmoregulation and excretion
Uric acid is synthesized by insect tissues and release in soluble form into the blood
This is transported to the Malpighian tubules
The low pH in the lumen of the tubule causes precipitation of the uric acid
Active transport creates an osmotic gradient where water is reabsorbed and uric acid is released as waste.

8. 11.3.2 Draw and label a diagram of the kidney
IP Physiology
Anatomy: pgs

9. 11.3.3  Annotate a diagram of a glomerulus and associated nephron to show the function of each part
The nephron is the functional unit of the kidney and includes:
Afferent arteriole:  Brings blood to the nephron to be filtered
Efferent arteriole:  Removes blood from nephron (minus filtered components)
Glomerulus:  Capillary tuft where filtration occurs
Bowman's Capsule:  First part of nephron where filtrate is collected
Proximal Convoluted Tubule:  Where selective reabsorption occurs
Loop of Henle:  Important for establishing a salt gradient in the medulla  
Distal Convoluted Tubule:  Final site of selective reabsorption
Collecting Duct:  Feeds into ureter and is where osmoregulation occurs
Vasa Recta:  Blood network that reabsorbs components from the filtrate

14.  Explain the process of ultrafiltration, including blood pressure, fenestrated blood capillaries and basement membrane [ip phys – glomerular filtration]
Ultrafiltration occurs when hydrostatic pressure forces blood through a semi-permeable membrane, separating blood cells and large proteins from the remainder of the serum (filtrate)
Ultrafiltration occurs between the glomerulus and the Bowman's capsule and requires two things to form the filtrate:
Hydrostatic Pressure
Basement membrane

15. Hydrostatic Pressure
The glomerulus increases blood pressure by forming narrow branches (which also increases surface area for filtration)
This pressure is maintained by a narrow efferent arteriole (relative to the afferent arteriole), which restricts the outflow of blood, keeping pressure high
The net pressure gradient in the glomerulus forces blood into the capsule space

16. Basement Membrane
The basement membrane is a fine mesh that restricts the passage of blood cells and proteins - it is the sole filtration barrier
Blood can exit the glomerulus directly through pores as the capillaries are fenestrated
The filtrate can enter the Bowman's capsule directly because the podocytes that surround the glomerulus contain filtration slits between their pedicels
The basement membrane lies between the glomerulus and Bowman's capsule

18. Untrafiltration

19. 11.3.5 Define osmoregulation [ ip phys – filtration pg 8]
Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism

20.  Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport [IP phys.]
The proximal convoluted tubule extends from the Bowman's capsule and is where most selective reabsorption in the nephron occurs
All glucose, amino acids, vitamins and hormones are reabsorbed here, along with most (~80%) of the mineral ions and water
The proximal convoluted tubule has a microvilli cell lining to increase the surface area for the absorption of materials from the filtrate
There are also a large number of mitochondria in these cells, as reabsorption from the filtrate involves active transport
IP Phys: Early filtration

21. Once materials have been actively reabsorbed into the tubule cells, they can passively diffuse into the bloodstream (along the concentration gradient)
Mineral ions and vitamins are actively transported via protein pumps or carrier proteins
Glucose is actively transported across the membrane in symport with sodium
Water follows the movement of the ions passively (via osmosis)

24.  Explain the roles of the loop of Henle, medulla, collecting duct and ADH (vasopressin) in maintaining the water balance of the blood
Creating a Salt Gradient in the Medulla
The function of the loop of Henle is to create a salt bath concentration in the fluid surrounding the tubule
The descending limb of the loop of Henle is permeable to water, but impermeable to salts. As Water is moving into the interstitial it is being reabsorbed into the vasa recta (capillaries).
The ascending limb of the loop of Henle is permeable to salts, but impermeable to water
This means that as the loop descends into the medulla, the interstitial fluid becomes more salty (and less salty as it ascends into the cortex)
As the vasa recta blood network that surrounds the loop flows in the opposite direction (counter-current exchange), this further multiplies the effect

25. Collecting Ducts Osmoregulation
As the collecting duct passes through the medulla it drains into the ureter, the hypertonic solution of the deep medulla will draw water by osmosis
Antidiuretic hormone (ADH or vasopressin) is a hormone released from the posterior pituitary in response to dehydration (detected by hypothalamus)
ADH increases the permeability of the collecting duct to water, allowing more water to be reabsorbed by osmosis (via the production of aquaporins)
This means less water remains in the filtrate and the urine becomes more concentrated
When the individual is suitably rehydrated, ADH levels will decrease and less water will be reabsorbed from the collecting ducts.
This is an example of a negative feedback system.

27.  Explain the difference in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine
Proteins:
Proteins will be present in blood plasma, but not present in glomerular filtrate or urine
This is because proteins cannot pass across the basement membrane during ultrafiltration and thus cannot form part of the filtrate

28. Glucose:
Glucose will be present in blood plasma and glomerular filtrate, but not present in urine (normally)
This is because the glucose is selectively reabsorbed in the proximal convoluted tubule
It is reabsorbed from the filtrate into the blood by active transport (symport with Na+ ions)

29. Urea:
Urea will be present in blood plasma, glomerular filtrate and urine
Only about 50% of urea is reabsorbed (some urea is reabsorbed to help regulate the medullary osmolarity gradient)
Because water is reabsorbed from the filtrate (by osmosis, due to the hyper tonicity of the medulla), urea becomes more concentrated in urine
The concentration of urea in the urine will depend on the amount of water in the urine

30. 11.3.9  Explain the presence of glucose in the urine of untreated diabetic patients
The urine of non-diabetic patients should contain no glucose as it is selectively reabsorbed from the filtrate in the proximal convoluted tubule
Diabetics have higher levels of blood glucose due to either a lack of insulin secretion (type I) or insensitivity to insulin secretions (type II)
Because of this, not all of the glucose in diabetics is reabsorbed into the blood (protein pumps in tubule wall become saturated)
This results in the presence of glucose in the urine of untreated diabetics, which can be detected using test strips

31. If you were going to design a nephron for a dessert animal what could you do to increase the reabsorption of water?
Recall, the loop of Henley creates an osmotic gradient in the medulla of the kidney
The longer the loop the greater the concentration gradient
Longer collecting ducts and increase in ADH.

32. Kidney Failure: The kidney tubules fail to filter enough blood
Treatment:
Hemodialysis
Transplants

33. Evolution and excretion of nitrogenous waste
Metabolism of proteins and NA create ammonia as a waste.
Ammonia is highly toxic
Early animals (aquatic invertebrates, amphibian tadpoles, croc) used ammonia as an excretory molecule.
As animals moved on land they evolved mechanism to maintain water but rid the toxic effects of ammonia
Mammals, most amphibian adults, cartilaginous fish) create urea.
Insects, birds and reptiles excrete uric acid.