Module 5: Excretion

Question 1

What is excretion

Answer 1

The removal of metabolic waste (any substance produced in excess by cells that may become toxic) from the body

Question 2

Importance of excretion

Answer 2

Build up of products from metabolism can alter pH which interfere with cellular processes. Some act as enzyme inhibitors and reduce activity of enzymes

Question 3

Structure of mammalian liver

Answer 3

Made up of numerous lobules which are packed with hepatocytes. The liver is supplied with blood flowing in from the hepatic artery (bringing oxygen) and the hepatic portal vein (bringing blood from the gut).

Blood flows through the sinusoids which contain kupffer cells which breakdown and recycle old red blood cells. As blood flows thorough sinusoids, the hepatocytes take in what they need from it and shed their waste into it.

Question 4

Function of Mammalian liver

Answer 4

Storage of glycogen which can be broken down and released as glucose
Detoxification of alcohol- broken down by ethanol dehydrogenase into ethanal
Formation of urea from the deamination of amino acids

Question 5

Structure of Kidneys

Answer 5

Supplied with blood from renal artery and blood is drained by renal vein.
Outer region is cortex, inner region is medulla and centre is pelvis which leads to ureter where urine passes through.

Made up of millions of nephrons which starts in the cortex at the Bowman’s Capsule. Coiled tubule which passes through cortex, forms a loop down into the medulla and back into the cortex before joining a collecting duct that passes back down into medulla

Renal artery splits to form many afferent arterioles which each leads to the glomerulus. Blood from the glomerulus continues into an efferent arteriole which carries blood to more capillaries which eventually flow to the renal vein

Question 6

Process of ultrafiltration

Answer 6

1. Blood flows into the glomerulus with a high hydrostatic pressure via the afferent arteriole which is wider than the efferent arteriole. Difference in diameters ensures that the blood in capillaries of the glomerulus maintains a higher pressure than the blood in the Bowman’s capsule
2. Pressure difference forces small molecules such as glucose, water and amino acids out of the glomerulus and into the lumen of bowman capsule. Proteins and blood cells left in the capillary

Question 7

Process of selective reabsorption

Answer 7

1.As fluid moves along the nephron, Sodium-Potassium pumps move sodium ions from the cells lining the PCT into the tissue fluid
2. Sodium ions then diffuse back into the cell, along with glucose or amino acids, via co-transporter proteins
3. As the glucose and amino acid concentrations rise indies the cell, these substances diffuse out of the opposite side of the cell into the tissue fluid
4.Reabsorption of salts, glucose and amino acids reduce the water potential in cells and increases it in the tubule fluid
Water will enter cells

Question 8

Osmoregulation process (decrease in water potential)

Answer 8

1. Change detected by osmoreceptors
2. More ADH is release from posterior pituitary gland
3. Collecting duct walls more permeable
4. More water reabsorbed into blood

Question 9

ADH mechanism

Answer 9

1. ADH detected by cell surface receptors
2. Enzyme-controlled reactions
3. Vesicles containing aqauporins fuse to membrane
4. More water can be reabsorbed

Question 10

Problems from Kidney failure

Answer 10

Unable to regulate levels of water and electrolytes in the body or remove waste- leads to rapid death

Question 11

Haemodialysis

Answer 11

Blood from an artery is passed into a machine and dialysed
Heparin added to avoid clotting
Performed at a clinic three times a week

Question 12

Peritoneal Dialysis

Answer 12

Uses filter in the abdominal membrane and uses a permanent tube implanted in the abdomen
Dialysis solution fills space between organs and membrane and solution drained after several hours
Patient able to walk around and can be carried out at home