Excretory system

Question 1

Organs that Process and Remove Wastes

Answer 1

Lungs: Excrete CO2 (produced during cellular respiration) during exhalation, water.
Sweat Glands: (sweat) water, salts, urea and lactic acid.
Alimentary Canal: bile pigments (from RBC’s)
Kidneys: (main excretory organ) To rid the body of wastes, especially nitrogenous wastes such as urea, uric acid and creatinine. To balance water, salt and pH levels.
Liver: processes many substances so they can be excreted.

Question 2

Liver

Answer 2

-Does not excrete anything but processes many substances so that they can be excreted.
-The liver converts excess protein into urea for excretion (by deamination).
-Detoxifies alcohol and many other drugs
-Deactivates many hormones and converts them into a form that can be excreted by the kidneys
-Breaks down haemoglobin from dead red blood cells to produce bile pigments (passed out of body with feaces)

Question 3

Deamination

Answer 3

Deamination is the removal of an amine group from a molecule

Question 4

The amino group to urea

Answer 4

The amino group is removed from the amino acids and is converted by the liver cells to ammonia.

Ammonia is then converted to urea (less toxic)

Urea is excreted via the kidneys in urine, and also in sweat.

The remaining part of the amino acidis converted to a carbohydrate and is then broken down and releases energy, water and carbon dioxide.

Question 5

Sweat glands

Answer 5

Sweat glands secrete about 500 ml of water per day. Sweat glands are located in the lower layers of the skin. A duct carries the sweat to a hair follicle or to the skin surface that opens up to a pore. Cells surrounding the glands are able to contract and squeeze the sweat to the skin surface.

Question 6

Sweat

Answer 6

Dissolved in the water are sodium chloride, lactic acid and urea and are excreted by the skin. Some drugs are also excreted here.

Question 7

Kidneys main roles and prosesses

Answer 7

Maintain the concentration of materials in the blood
Removes toxic wastes such as urea, uric acid and creatinine. They achieve these outcomes by filtering the blood as it passes through the kidneys, Waste substances are removed by the processes of glomerular filtration and tubular secretion, Useful substances are returned to the body by the process of selective reabsorption.

Question 8

Parts of the kidney

Answer 8

Renal capsule – encloses kidney.
Renal cortex – outer part of kidney
Renal medulla – Inner part of kidney
Renal pelvis – Cavity of kidney that collects urine before it passes to ureter
Renal hilum – lies on concave surface of kidney and is where the vessels enter and leave.
Renal pyramids – in medulla and are separated by renal columns where blood vessels lie

Question 9

The nephron

Answer 9

The functional unit of the kidneys is the nephron. Each kidney contains approx 1.2 million nephrons.

Question 10

The renal corpuscle function and made up of

Answer 10

Filtration takes place in the renal corpuscle. the renal corpuscle consists of the glomerular capsule and a knot of arteriole capillaries – the glomerulus.

Question 11

Podocytes

Answer 11

Lining the glomerular capsule are specialized cells called podocytes. These cells have finger-like extensions that wrap around the capillaries of the glomerulus. The spaces between the “fingers” are filtration slits.

Question 12

Glomerular Filtration

Answer 12

Head of the nephron is the Glomerular Capsule and has a selectively, semi permeable membrane.

Pressure in the Glomerulus is very high.- Due to wide diameter of afferent arteriole and narrow diameter of efferent arteriole. This increases resistance to the flow of blood and forces the blood fluid out of the glomerulus into the GC due to high pressure.

The whole process of blood fluids leaving is called FILTRATION. About 20% of plasma is filtered. Total Filtrate is about 125mL per minute = 180 L a day but most is reabsorbed. 1% leaves the body as urine.

Question 13

Filtrate

Answer 13

The filtrate is made up of water, glucose, salts, urea, uric acid, ions, creatinine, hormones, lactic acid, and other toxins. NO blood (RBC, WBC) or plasma proteins leave the blood. They are essential as antibodies and for blood clotting. They are also TOO BIG to enter the semi permeable membrane.

Question 14

Reabsorption

Answer 14

(Substances moving from the tubule back into the bloodstream – peritubular capillaries)

Cells of the renal tubule allow water, glucose, amino acids, sodium, potassium calcium chloride and bicarbonate to be reabsorbed. Some urea too.

Large Surface Area allows this to happen due to long length of nephron tube and also large number of nephrons in each kidney.

Water reabsorption is regulated depending on the body’s water needs. active process under hormonal control and is called FACULTATIVE REABSORPTION.

Question 15

The proximal tubule

Answer 15

Microvilli line the proximal tubule and create a brush border, which greatly increases the surface area for reabsorption.

Question 16

Tubular Secretion

Answer 16

Tubular secretion adds substances to the filtrate (in the tubule) from the blood usually in DCT. Substances eg potassium, hydrogen ions, creatinine, drugs – penicillin.

Question 17

The formation of urine is maximised by the structure of the kidney, particularly the nephron, as follows

Answer 17

1. Glomerular capsule surrounds glomerulus, collecting filtrated fluid.
2. There are only 2 cells for the filtrate to pass through – one cell capillary wall, one cell glomerular capsule wall.
3. Large volume of blood passes through each kidney, Continual flow maintains the concentration gradient.
4. Afferent arteriole has larger diameter than efferent arteriole. Results in higher blood pressure to increase fluid filtered out of blood.
5. Large surface area for reabsorption and secretion as each tubule has 2 sets of convolutions and a long loop.

Question 18

Composition of urine

Answer 18

-clear, transparent fluid. It normally has an amber color. (due to bile pigments)
-collected in the bladder and eliminated through the urethra in a process called micturition/urination or voiding.
-Volume produced decreases during sleep and exercise.
-95% water and 5% other solutes, ions and other metabolic wastes.

Question 19

Uric acid

Answer 19

produced by metabolism of purines. (purines come from breakdown of nucleic acids when cells die. Eg of purines are adenine and guanine. Purines are also present in foods)

Question 20

Creatinine

Answer 20

produced in muscle from the breakdown of creatinine phosphate.

Question 21

Factors affecting urine production

Answer 21

-Amount of food and drink consumed
-Drugs such as alcohol and caffeine
-Osmotic pressure (is the amount of salt relative to the amount of water in the blood.)
-Level of perspiration: amount of exercise, humidity level, environmental temperature
- generally an increase in sweat causes a decrease in urine volume.
- High protein diet: Increase in both urea production and volume of urine.

Question 22

Kidney stones

Answer 22

Kidney stones are formed from solid crystals that build up inside the kidneys.
- urine is too concentrated
-Small crystals pass down ureter and out urethra -> Crystals can combine to form stones ->Large stones may get stuck in the ureter/bladder or urethra = pain.
- Smaller stones may pass with aid of fluids/pain relief/muscle relaxants.

Question 23

Kidney failure

Answer 23

Most Kidney diseases affect glomeruli and filtration, therefore can’t filter the blood. ie excess protein + RBC in filtrate and then urine.

If excess proteins are lost in urine = blood protein levels fall + fluid accumulates in the tissues = hand/feet/face swelling.

To have healthy kidneys, healthy weight, don’t smoke, drink water, alcohol in moderation, don’t use performance enhancing drugs

Kidney Failure usually occurs over years and kidneys lose ability to excrete wastes and control level of fluid in body. Treatment – Dialysis or transplant.

Question 24

Dialysis

Answer 24

Removing wastes from blood once kidneys fail.
Two types of dialysis: Peritoneal dialysis and Haemodialysis.

Question 25

Peritoneal Dialysis

Answer 25

A soft plastic tubule is placed in your bely, a sterile cleansing fluid is put into your belly which filters your blood.

Occurs inside the body using the peritoneum as a membrane across which waste can be removed -> A catheter is inserted through the abdomen wall. Wastes then diffuse out of blood into the fluid in the abdominal cavity due to concn difference (Useful substances stay in blood as no concn difference). After a period of time abdominal fluid is drained out through catheter to remove all fluid.
- happens once a day.

Question 26

Haemodialysis

Answer 26

Hemodialysis is a procedure where a dialysis machine and a special filter called an artificial kidney, or a dialyzer, are used to clean your blood. To get your blood into the dialyzer, the doctor needs to make an access, or entrance, into your blood vessels.

Fluid concentration is similar to blood except it contains no wastes -> Due to the concentration differences wastes diffuse out of blood into the fluid.

-takes about 4-5 hrs a day 3 times a week.

Question 27

Liver Disease

Answer 27

When liver is not able to function effectively, it can’t process toxins ready for elimination.

Liver disease can be caused by infection, autoimmune problems, genetic disorders, cancer and lifestyle factors eg fatty diet, excessive alcohol.

Symptoms are due to build-up of toxins that would normally be eliminated. abdominal pain and swelling, swelling in legs and feet, nausea or vomiting

Question 28

Collecting ducts

Answer 28

Active reabsorption of water, depending on the body’s water needs

Question 29

Distal convoluted tubule

Answer 29

Active reabsorption of sodium ions
Active reabsorption of water, depending on the body’s water needs
secretion of hydrogen and potassium ion, creatine and certain drugs such as penicillin

Question 30

Proximal convolutes tubule and loop of henle

Answer 30

Passive reabsorption of potassium, chloride and bicarbonate ions
Active reabsorption of glucose and sodium
passive reabsorption of water by osmosis

Question 31

Renal corpsicle

Answer 31

A renal corpuscle is the blood-filtering component of the nephron of the kidney. It consists of a glomerulus - a tuft of capillaries composed of endothelial cells, and a glomerular capsule known as Bowman’s capsule.

Filtration of blood from capillaries of glomerulus, and the formation of filtrate in the glomerulus.

Question 32

efferent arteriole

Answer 32

Capillaries eventually unite to form another arteriole – efferent arteriole, which passes out the renal corpuscle. After leaving the renal corpuscle, efferent arteriole breaks up into a second capillary network – peritubular capillaries – which surround the PCT, loop of Henle, DCT and collecting duct.

Question 33

Urine through the collecting ducts to the exterior

Answer 33

Water and other substances not reabsorbed drain into collecting ducts and then into renal pelvis.

From the pelvis, urine drains into the 2 ureters, (25-30cm) and then is pushed by muscular contraction into the urinary bladder. (urine stored here) Urine then exits the bladder via the urethra to the exterior of the body.

Question 34

Renal arteries

Answer 34

Blood enters the kidney via renal arteries. Kidney receives about a quarter of the blood from the heart. About 1.2 L blood pass through the two kidneys every minute.

Renal artery divides into small arteries and arterioles inside the kidney. Renal corpuscle is supplied by an arteriole (afferent arteriole) – forms a knot of capillaries- glomerulus. Glomerulus sits inside the glomerular capsule.

Question 35

The movement through the kidney

Answer 35

Leading away from glomerular capsule is the renal tubule (5 cm long) into the Proximal convoluted tubule (PCT), loop of Henle (descending limb, hairpin loop, ascending limb) Distal convoluted tubule (DCT) and then collecting duct. Renal pelvis channels fluid from the collecting ducts into the ureter.