IGCSE Biology 0610. Chapter 13 Excretion in Humans

IGCSE Biology 0610 Chapter 13

1. Chapter 13. Excretory System Secondary 3

2. Urine Of every litre of blood processed, the kidneys filter out about one millilitre of waste liquid, or urine. Urine is produced at the rate of one drop per minute, or one to two litres per day. Urine consists of approximately: 95 per cent water five per cent urea small amounts of salts and other substances a small amount of bile (which gives urine its yellow colour )

3. a protein rich diet will result in more urea being present in the urine (urea is formed when excess amino acids are deaminated in the liver)   Taking in more liquids or water rich food increases water potential of the urine  A high intake of salty foods will result in excess salts being excreted in urine  A person with diabetes excretes large amounts of glucose in his/her urine .

4. Urine color

5. Urinary System All reactions in the body require watery surroundings in order to occur That fluid must be closely regulated to ensure that the solution is not too salty or not salty enough The urinary system helps to keep that balance.

6. Urinary System Kidneys are bean shaped Excretes waste and maintains homeostasis Kidney  ureter  bladder  urethra Kidneys - Process urine and regulate amount of water in the body  Ureters - Transports processed urine to bladder, narrow muscular tract Bladder - Storage, muscular sac which can expand and contract Uretha - Excreted out, narrow tube leading outside the body

7. Kidney remove wastes from the blood, form urine

8. Kidney structure Nephrons - Microscopic filters  - Millions present - Tissues (modifiable)  - Filters waste and water from the blood  Glomerulus  - Clump of capillaries present at the end of each nephron  - Network of coiled tubes  - Blood re-absorbs water if needed after waste is filtered (homeostasis &  ADH hormone) 

9. Nephron The kidney is made up of repeating units called nephrons These help maintain fluid balances

10. Nephron Structure

11. Urine Formation Occurs in nephron 3 Steps Filtration Reabsorption Secretion

12. Urine Formation: Filtration Movement of water and solutes from the capillaries into the glomerular capsule

13. Urine Formation: Filtration Glomerular filtration rate (GFR): total amount of water filtered per unit of time

14. Urine Formation: Reabsorption Movement of useful substances (water, salts, glucose) back into the capillaries.

15. Urine Formation: Reabsorption Filtrate from glomerular capsule flows into the renal tubule. Substances are reabsorbed into the surrounding capillaries.

16. Urine Formation: Reabsorption Sodium is actively pumped out of the epithelial cells of the renal tubule and diffuses into capillaries.

17. Urine Formation: Reabsorption The increased sodium in the interstitial space creates high osmotic pressure, which draws water out of the tubule by osmosis.

18. Urine Formation: Secretion At the same time that the “good” substances are being reabsorbed, wastes (urea) still in the blood are actively secreted from the capillaries.

19. Ureters transfer urine from the kidneys to the bladder

20. Bladder store urine until it is released by the body

21. Urethra carry urine from bladder to outside of the body

22. Kidney Failure Common causes of kidney failure:  - High blood pressure  - Diabetes  - Alcohol abuse  - Severe accidents that physically damage the kidney  - Complications from undergoing major surgeries  Patients with kidney failure may get a kidney transplant, but if not available, will undergo dialysis.  A dialysis machine mimics the functions of a kidney and helps to clean the patient's blood from metabolic waste products and toxins.  The patient needs to undergo dialysis 2-3 times a week, with each sessions lasting 3-5 hours. 

23. Dialysis Dialysis Process:  1. Unfiltered blood   is drawn from the vein in patient's arm and is pumped through the tubing in the dialysis machine  2. The tubing is bathed in a specially controlled fluid (walls of tubing are partially permeable). the blood flows in the  opposite direction  to dialysis fluid, allowing  exchange  to occur between the two where a  concentration gradient  exists 3. Small molecules, such as urea and metabolic waste diffuse out of the tubing into the dialysis fluid. Blood cells, platelets and other large molecules remain in the tubing.  4. The filtered blood is returned to a vein in the patients arm.  Dialysis fluid contains: a  glucose  concentration similar to a normal level in blood a concentration of  salts  similar to a normal level in blood no  urea

24. Urinary tract infection Common infections that happen when bacteria, often from the skin or rectum, enter the urethra, and infect the urinary tract. The infections can affect several parts of the urinary tract, but the most common type is a  bladder infection  (cystitis).

25. Lungs and skin Sweat glands in the skin serve as excretory function due to urea and water released in perspiration Lungs release carbon dioxide Failed breathing can kill

26. liver Urea which is from broken protein compounds are from urea Liver converts part of the hemoglobin molecule from old red blood cell to bile. Abnormal liver causes jaundice

27. The Role of the Liver Many digested food molecules absorbed into the blood in the small intestine are carried to the liver for  assimilation  (when food molecules are converted to other molecules that the body needs) These include amino acids, which are used to build proteins such as  fibrinogen , a protein found in blood plasma that is important in blood clotting

28. Deamination Excess amino acids  absorbed in the blood that are not needed to make proteins  cannot be stored , so they are broken down in a process called  deamination Enzymes in the liver split up the amino acid molecules The part of the molecule which contains  carbon  is turned into  glycogen  and stored The other part, which contains  nitrogen , is turned into  ammonia , which is highly toxic, and so is immediately converted into  urea , which is less toxic The urea dissolves in the blood and is taken to the  kidney  to be excreted A small amount is also excreted in  sweat

29. Deamination In deamination, the nitrogen-containing amino group is removed and converted into ammonia and then urea to be excreted