1. Urinary System

2. Our Goals This Section....
Identify and explain the functions of each of the following:
kidney
ureter
urethra
urinary bladder
renal cortex
renal medulla
renal pelvis
nephron
Identify and explain the functions of the following components of the nephron:
glomerulus
Bowman’s capsule
afferent and efferent arterioles
peritubular capillary network
proximal and distal convoluted tubules
collecting duct
loop of Henle

3. Wastes Excretion Main wastes: carbon dioxide and ammonia
Ammonia comes from the digestion of amino acids
Ammonia goes to liver and is converted to UREA
Digestion of nucleic acids produce URIC ACID
Must be secreted so they don’t become toxic
Some wastes and water are excreted when you exhale
Water is also excreted in sweat
Kidneys are the primary organ of waste excretion – they take urea, uric acid, excess H+, water soluble vitamins, etc from the blood and excrete as urine

4. Urinary System

5. Kidneys Renal arteries deliver blood to kidneys to “clean it”
Blood leaves the kidneys via the renal vein
Nephrons
Functional unit of the kidney
Remove wastes
Make Urine
Millions/kidney
Urine collects in the pelvic region of the kidney where peristalsis moves it to the ureters and then the urinary bladder

7. Nephron

8. Nephron Tubules All the same pattern
Start in the cortex of the kidneys with the Bowman’s capsule
Then loop down into the renal medulla
Bowman’s capsule →proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting duct

9. Blood Flood Renal Artery Afferent Arterioles Glomerulus
Efferent Arterioles
Peritubular Capillaries
Venule
Renal Vein

10. Remember Our Goals Today....
Identify and explain the functions of each of the following:
kidney
ureter
urethra
urinary bladder
renal cortex
renal medulla
renal pelvis
nephron
Identify and explain the functions of the following components of the nephron:
glomerulus
Bowman’s capsule
afferent and efferent arterioles
peritubular capillary network
proximal and distal convoluted tubules
collecting duct
loop of Henle

11. Our Goals Today...
Describe the production of urine with reference to the following terms:
pressure filtration
selective reabsorption
reabsorption of water following an osmotic gradient
tubular excretion
metabolic waste (e.g., nitrogenous waste, urea, ammonia)
Describe how the kidneys maintain blood pH
Compare urea and glucose content of blood in the renal artery with that of the renal vein
Identify the source glands for antidiuretic hormone (ADH) and aldosterone
Describe how the hypothalamus, posterior pituitary, ADH, and the nephron achieve homeostasis of water levels in the blood
Describe how the adrenal cortex, aldosterone, and the nephron achieve homeostasis of water and sodium levels in the blood

12. Urine Formation
Interaction between the tubules of nephrons and the blood capillaries
Modified version of blood capillary fluid exchange
There are 3 stages of urine formation
Pressure Filtration
Selective Reabsorption
Tubular Secretion

13. Pressure Filtration
Blood slows down when it enters the cortex (enters the capillaries of the glomerulus)
Structure allows blood pressure to force small parts of the blood plasma into the spaces surrounding the glomerulus
Bowman’s capsules cup around each glomerulus
Substances removed from blood are forced into the beginning of the nephron tubules by constant blood pressure

15. Pressure Filtration Fluid entering tubules is called FILTRATE
Large components like blood cells and globulins are too big therefore stay in the blood
Creates an osmotic gradient between the blood and extracellular fluid

16. Selective Reabsorption
Filtrate contains useful materials that the body needs (eg. Glucose, amino acids, nutrients, etc.)
Cells in the proximal convoluted tubule have CARRIER PROTEINS designed to pump these materials back into the peritubular capillaries
Requires ATP
Some Na+, Cl- and water are reabsorbed
Na+ is pumped out of filtrate
Cl- and water follow passively into the blood plasma

17. Selective Reabsorption
As the filtrate moves through the nephron it makes 3 passes between the cortex and the medulla before entering the renal pelvis
Filtrate goes from the proximal convoluted tubule to the descending loop of Henle
Here the tubule is permeable to water but not Na+
The extracellular region of this part of the tubule has a high solute concentration – therefore water moves out of the tubule and into blood (osmosis)
Filtrate is now very “salty”

18. Selective Reabsorption
Permeability of the ascending loop of Henle is different
permeable to Na+ and not permeable to water
Na+ diffuses out of the tubule (concentration gradient)
When the filtrate gets closer to the cortex diffusion lessens so ATP is used to remove more Na+ from the filtrate
Once at the distal convoluted tubule in the cortex the filtrate is iso-osmotic to the extracellular fluids

19. Tubular Secretion
Substances that are excess in the blood are pumped out of the peritubular capillaries around the distal convoluted tubule (enter filtrate)
Substances: penicillin, histamines, vitamins
In the distal tubule pH of the blood is also adjusted – absorption of H+ or HCO3-

21. Final Phase of Urine Formation
Collecting duct moves the filtrate through the medulla one last time
Filtrate is subjected to the increasing concentration gradient of the extracellular fluids
Extracellular fluid in the medulla is hypertonic to the filtrate
Water is withdrawn as the filtrate as moves into the renal pelvis

22. Final Phase of Urine Formation
~99% of water in the filtrate is reabsorbed when urine is produced
Throughout the tubule urea is reabsorbed in very small amounts because of its low threshold level
However some urea will diffuse out of the collecting duct into the medulla (contributes to the high solute concentration around the loop of Henle)
It will re-enter the tubule along the ascending loop of Henle
Urine is what remains in the tubule

23. Composition of Urine
Mainly water even though most of the water has been reabsorbed
Urea – low threshold in blood therefore stays in the nephron during urine formation

24. Glucose
Blood has a high threshold level in the plasma so most of it is reabsorbed from the nephron
Requires ATP and transport proteins in the tubules
Liver removes excess glucose and stores it as glycogen
Diabetes is a malfunction in this system – higher glucose concentration in the blood causes glucose to be excreted in the urine (less water is reabsorbed)
Abnormal amounts of urine can be a symptom of diabetes
Diuretic versus Antidiuretic

25. Regulation of Urine Formation
Antidiuretic Hormone (ADH) is secreted by the posterior pituitary gland when blood volume is low
ADH causes more water to be reabsorbed in the collecting duct
This increases blood volume (& blood pressure)
Alcohol is a diuretic because it inhibits ADH
Causes increased urine production
Excessive consumption leads to dehydration

27. Aldosterone
If the blood pressure drops the regulation of urine is in danger
Aldosterone is released from the adrenal cortex
Increases the amount of Na+ absorption in the distal convoluted tubule
This in turn leads causes more water to be absorbed restoring the blood pressure

28. Remember Our Goals Today...
Describe the production of urine with reference to the following terms:
pressure filtration
selective reabsorption
reabsorption of water following an osmotic gradient
tubular excretion
metabolic waste (e.g., nitrogenous waste, urea, ammonia)
Describe how the kidneys maintain blood pH
Compare urea and glucose content of blood in the renal artery with that of the renal vein
Identify the source glands for antidiuretic hormone (ADH) and aldosterone
Describe how the hypothalamus, posterior pituitary, ADH, and the nephron achieve homeostasis of water levels in the blood
Describe how the adrenal cortex, aldosterone, and the nephron achieve homeostasis of water and sodium levels in the blood