16-1

Joke of the Day

16-2

A red blood cell walked into a busy

restaurant.

The hostess asked, "Would you like to sit

at the bar?“

The red cell replied, "No thanks, I'll just

circulate."

16-3

Urinary System and Excretion

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16-4

16-5

EXCRETION – Is the removal of metabolic waste products from the body.

Do NOT confuse this with the elimination of undigested wastes.

Failure to remove these metabolic wastes would result in a build up of toxins in

the body, eventually leading to death. Our focus will be on the URINARY SYSTEM

16-6

Urinary System

Urinary OrgansThe urinary system consists

of the kidneys, ureters,

urinary bladder, and

urethra.

The bean-shaped kidneys

are at the back of the

abdominal wall beneath

the peritoneum, protected

by the lower rib cage.

The renal artery and renal

vein along with ureters

exit the kidney at the

hilum.

16-7

The kidneys produce urine which is conducted by two muscular tubes called ureters to the urinary bladder where it is stored before being released through the urethra.

Two urethral sphincters control the release of urine.

In females, the urethra is 4 cm long; in males, the urethra is 20 cm long and conveys both urine and sperm during ejaculation.

16-8

16-9

The urinary system

16-10

Urination

16-11

Functions of the Urinary SystemExcretion refers to the elimination of metabolic wastes that were cell

metabolites; this is the function of the urinary system.

Kidneys play a role in homeostasis of the blood by excreting metabolic

wastes, and by maintaining the normal water-salt and acid-base

balances of blood.

16-12

Excretion of Metabolic WastesKidneys excrete nitrogenous wastes, including urea, uric acid, and

creatinine.

Urea is a by-product of amino acid metabolism. Deamination of AA’s.

The metabolic breakdown of creatine phosphate in muscles releases creatinine.

Uric acid is produced from breakdown of nucleotides.

Collection of uric acid in joints causes gout.

16-13

Maintenance of Water-Salt BalanceKidneys maintain the water-salt balance of the body which, in turn,

regulates blood pressure.

Salts, such as NaCl, in the blood cause osmosis into the blood; the more salts, the greater the blood volume and also blood pressure.

Kidneys also maintain correct levels of potassium, bicarbonate, and calcium ions in blood.

16-14

Maintenance of Acid-Base BalanceThe kidneys regulate the acid-base balance of the blood.

Kidneys help keep the blood pH within normal limits by excreting hydrogen ions (H+) and reabsorbing bicarbonate ions (HCO3

-) as needed.

Urine usually has a pH of 6 or lower because our diet often contains acidic foods.

16-15

Secretion of HormonesKidneys secrete or activate several hormones:

1) They activate vitamin D to the hormone calcitriol needed for calcium reabsorption during digestion, and

2) They release renin, a substance that leads to the secretion of aldosterone.

16-16

What I just said.. In a

Nutshell…1)Low blood pressure is sensed in the juxtaglomerlar apparatus In the kidneys by

a DECREASE in Na+ will reduce the amount of water in the blood therefore

blood will have a lower pressure

2) The glomerulus releases a hormone RENIN

3)Renin moves to the liver and releases another hormone angiotensinogen ->

angiotensin I

4) Angtiotensin I -> angiotensin II in the lungs; Angiotensin will CONSTRICT blood

vessel therefore increasing blood pressure

4) Angiotensin II also stimulates the adrenal glands on top of the kidneys to

produce the hormone ALDOSTERONE

5) Aldosterone stimulates the REABSORPTION of Na+ in the distal convoluted

tubules; Increasing Na+ also means that WATER and Chloride will follow..

Increasing blood volume

6) An increase in blood volume may trigger the release of hormone ADH (atrial

natruerutic hormone) which INHIBITS the release of ALDOSTERONE, keeping

the body’s water and odium levels at homeostatic levels… this is known as the

NEGATIVE FEEDBACK LOOP

16-17

16-18

Kidney StructureThe kidneys filter wastes from the blood, and thus the renal arteries branch

extensively into smaller arteries and then arterioles inside each kidney.

Many venules unite to form small veins, which merge to become the renal vein.

16-19

There are three regions to a kidney: an outer renal cortex, an inner renal

medulla, and a central space called the renal pelvis.

Microscopically, each contains over one million nephrons.

The nephrons produce urine which flows into a collecting duct; several

collecting ducts merge and drain urine into the renal pelvis.

16-20

E

F

G

H

I

J

L

K

16-21

Blood flow through kidney

1. Renal artery

2. Afferent arterioles

3. Glomerular capillaries

4. Efferent arterioles

5. Pertublar capillaries

6. Renal vein

Flow of Urine

1. Glomerulus

2. Bowmans Capsule

3. Proximal Convoluted tubule

4. Loop of Henle

5. Distal Convoluted Tubule

6. Collecting Duct

7. Calyx

8. Renal Pelvis

9. Ureter

10.Urinary Bladder

11.Urethra

16-22

Maintaining Water-Salt BalanceThe kidneys maintain the water-salt balance of the blood within normal

limits.

By doing so, they also maintain blood volume and blood pressure.

Most of the water and salt (NaCl) present in the filtrate is reabsorbed

across the wall of the proximal convoluted tubule.

Approximately 65-70% of Na+ ions are

reabsorbed at the Proximal Convoluted

tubule.

Approximately 25 -30% of Na + is

reabsorbed along the Ascending Limb

of the Loop Of Henle

The remaining 0 -10% of Na + ions are

regulated at the Distal Convoluted

Tubule, based on what hormone levels

are signalling these cells.

65%

25%

0-10%

16-23

16-24

Reabsorption of WaterSalt passively diffuses out of the lower portion of the ascending limb of

the loop; the upper thick portion actively extrudes salt into the tissue of the outer renal medulla.

Water is reabsorbed by osmosis from all parts of the tubule.

The ascending limb of loop of the nephron establishes an osmotic gradient that draws water from the descending limb of the nephron and the collecting duct.

16-25

The permeability of the collecting duct is under the control of antidiuretic hormone (ADH). Remember the H = Affect on H20

Diuresis is an increase in urine flow and antidiuresis is a decrease.

When ADH is present, more water is reabsorbed, blood volume and blood pressure rise, and there is a decreased amount of urine.

If there is insufficient water intake, the posterior pituitary releases ADH, causing more water to be reabsorbed with a decreased urine output.

16-26

ADH is actually made in the

Hypothalamus and then sent to the

Posterior Pituitary for storage and

release.

16-27

Reabsorption of SaltKidneys regulate salt balance by controlling excretion and reabsorption

of ions.

Two hormones, Aldosterone and Atrial Natriuretic Hormone (ANH), control the kidneys’ reabsorption of sodium (Na).

ALDOSTERONE = Affect on Na+ reabsorption. Works on the cells of the

Distal Convoluted Tubule to Increase their ability to actively transport Na+

ions back into the blood. This regulates the last 0-10% Na+ ion

reabsorption. Blood Volume will go up so to will Blood Pressure.

Aldosterone is produced by the Adrenal Glands.

Effects Of Renin – Brings up BP

16-28

16-29

A.N.H. = Atrial Natriuretic Hormone – Sensors in the atria can detect when Blood

Pressure is getting dangerously high. Then A.N.H. is secreted into blood. This

A.N.H. will inhibit the effect of Aldosterone on the nephron cells, so less Na+ is

actively reabsorbed. As a result, more Na+ will stay in filtrate (urine) causing

more H2O to stay in urine, so you pee more and blood volume is reduced and

Blood Pressure goes down.

“Natriuresis” takes place = Peeing Out More Sodium, water will follow.

16-30

Reabsorption of salt increases blood volume and pressure because more water is also reabsorbed.

ANH is secreted by the atria of the heart when cardiac cells are stretched by increased blood volume.

ANH inhibits secretion of renin; the resulting excretion of sodium also causes excretion of water and blood volume drops.

16-31

DiureticsDiuretics are chemicals that lower blood pressure by increasing urine

output.

Alcohol inhibits secretion of ADH; dehydration after drinking may contribute to the effects of a hangover.

Caffeine increases the glomerular filtration rate and decreases tubular reabsorption of sodium.

Diuretic drugs inhibit active transport of Na+ so a decrease in water reabsorption follows.

A.D.HAlcohol inhibits the

secretion of ADH

from the Pituitary

Gland. Reduced ADH

will cause collecting

duct cells to become

less permeable to

water.

Maintaining Acid-Base BalanceKidneys rid the body of acidic and basic substances.

If the blood is acidic, hydrogen ions (H+) are excreted and bicarbonate ions (HCO3-

) are reabsorbed.

If the blood is basic, H+ are not excreted and HCO3- are not reabsorbed.

Breathing also ties up H+ when carbon dioxide is exhaled.

16-33

Acid-base balanceWhen would you want to increase HCO3- ion reabsorption into blood?

When would you want to decrease H+ Excretion during Tubular

Secretion?

16-34

16-35