OCR A-level Biology- excretion

What’s excretion

The removal of metabolic waste from the body

What are examples of metabolic waste products

Carbon dioxide, urea, bilirubin

What’s egestion

The removal of undigested food waste

How is most of the carbon dioxide in the lungs transported

In the form of hydrogencarbonate ions

How is carbon dioxide excreted

It diffuses into the blood and combines with water in the presence of carbonic anhydrase to form carbonic acid which then dissociated into hydrogen carbonate ions and hydrogen ions

What does high blood CO2 levels lead to

Respiratory acidosis- a decrease in the pH of the blood

What are the two steps in which amino acids are excreted

Deamination and formation of urea

What happens during deamination

In the liver the amino group is removed forming ammonia and the amino acid combined with oxygen forming a keto acid

What happens during the formation of urea

Ammonia reacts with carbon dioxide forming urea and water

Which cells make up the liver

Hepatocytes

Which two blood vessels transport blood into the liver

The hepatic artery and the hepatic portal vein

Whats the function of the hepatic artery

To transport oxygenated blood from the heart to the liver via the aorta

Whats the function of the hepatic portal vein

To transport blood rich in the products of digestion from the intestines to the liver

Whats the function of the hepatic vein

It transports the products of liver metabolism away from the liver towards the heart

Whats the function of the bile duct

To transport the non-blood related products out of the liver

Which blood vessel transports blood out of the liver

The hepatic vein

What structure is the liver broken down into

Lobules

What structure does blood pass through in the liver

Sinusoids

What are the phagocytes inside sinusoids of the liver called

Kupffer cells

Whats the function of kupffer cells

To destroy worn out red and white blood cells, bacteria and foreign matter from the digestive tract and to break down haemoglobin into bilirubin

Why does bilirubin need to be excreted

It can build up and cause jaundice

Why is ammonia especially toxic

Because it’s highly soluble and so lowers the water potential of cells

In which process is ammonia converted into urea

In the ornithine cycle

How is ethanol broken down in the liver

It’s broken down into ethanal by ethanol dehydrogenase and then is broken down into acetate by ethanal dehydrogenase ton eventually enter the Krebs cycle

Why does liver cirrhosis occur

If large amounts of ethanol are broken down reduced NAD is released if its reduced the NAD cannot oxidise fatty acids leading to them being converted into fat and being deposited in the liver

What connects the kidneys to the bladder

Ureters

Which blood vessel supplies blood to the kidneys

The renal artery

Which blood vessels removes blood from the kidneys

Inferior vena cava

Whats the outer membrane of the kidney called

The capsule

Whats the outer layer of the kidneys called

The cortex

Whats the inner layer of the kidneys called

The medulla

What are the subunits of the kidney called

Nephrons

Whats the function of the glomerulus

Ultrafiltration of the blood

What structure surround the glomerulus

The bowman’s capsule

What occurs in the proximal convoluted tubule and loop of henlee

Selective reabsorption

What occurs in the collecting duct

Water reabsorption into the blood

Which hormone controls water reuptake

ADH

What happens during ultrafiltration

Small molecules are filtered out of the blood and pass into the lumen of nephrons

What are pores between endothelial cells known as

Fenestrations

Whats the first layer of the basement membrane

Endothelium

Whats the second layer of the basement membrane

Podocytes

Whats the function of podocytes

To support the basement membrane and prevent anything large molecules passing through

Why is blood forced out of the glomerulus into the bowman’s capsule

Due to high hydrostatic pressure in glomerular capillaries

What is blood known as when it leaves the glomerulus

Glomerular filtrate

Which substances are reabsorbed out of the convoluted tubule

Glucose, amino acids, vitamins and sodium and chloride ions

How does selective reabsorption occur

Sodium ions are actively transported out of cells into the tissue fluid, glucose or amino acids enter the cells with sodium by facilitated diffusion and then diffuse into the blood capillary

What happens to the water potential of the tubule after selective reabsorption

It increases

What are the stages of reabsorption in the loop of henlee

Sodium ions are actively transported into the interstitial fluid at the ascending limb decreasing the water potential in the tissue fluid, water moves out of the descending limb by osmosis, the water potential of the urine in the collecting duct is higher than the water potential of the tissue fluid so water moves out of the collecting duct into the tissue fluid

How does the loop of henlee act as a countercurrent multiplier

Because solutions travel down the nephron in two directions the concentration of ions in the tissue fluid is increased

Whats the permeability of the descending limb of the loop of henlee

It’s permeable to water

Whats the permeability of the ascending limb of the loop of henlee

It’s impermeable to water

Whats the function of the distal convoluted tubule

To pump sodium ions out of the nephron into the blood

How can more water be reabsorbed in the loop of henlee

A longer loop

Where are osmoreceptors found

In the hypothalamus

Which type of receptors monitor water concentration

Osmoreceptors

Which gland and where in the gland stores and secretes ADH

The posterior lobe of the pituitary gland

What happens if osmoreceptors detect an increase in water potential

Less ADH is secreted which decreases the permeability of the collecting ducts

What happens is osmoreceptors detect a decrease in water potential

The pituitary gland secreted more ADH which increases the permeability of the collecting duct

Describe the chain of events that occur when ADH is released

ADH acts as a first messenger and binds to cell surface receptors activating a G-protein which then activates adenyl cyclase which converts ATP top cyclic AMP which acts as a second messenger and activates kinase proteins which then cause vesicles contains aquaporins to fuse with the cell membrane

What does ADH act as

A first messenger

What does ADH activate when it binds to cell surface receptors

G-proteins

What do G-proteins activate

Adenyl cyclase

What does adenyl cyclase trigger

The conversion of ATP to cyclic AMP

What does cyclic AMP acts as

The second messenger

What does cyclic AMP do

Activate kinase proteins

What do kinase proteins cause

Vesicles containing aquaporins to fuse with the cell membrane

Which arteriole is wider

Then afferent arteriole

Which arteriole is narrower

The efferent arteriole

What are some causes of kidney failure

Type 2 diabetes, hypertension and infection

Whats acute kidney failure

Fast developing, short acting and easily treatable kidney failure

Whats chronic kidney failure

Slower developing, longer acting and less easily treatable kidney failure

What are two options for treating kidney failure

Dialysis or a kidney transplant

What happens during haemodialysis

Blood from the patients vein is passed through small tubes made from a partially permeable membrane, dialysis fluid is pumped in flowing in the opposite direction to the blood allowing urea to diffuse out of the blood into the dialysis fluid

What does the dialysis fluid contain

The same concentration of ions, glucose and water potential as the blood but a lower concentration of urea

What’s peritoneal dialysis

Dialysis that occurs within a patients abdomen

How does peritoneal dialysis work

A catheter is inserted into the abdomen and dialysis fluid pumped in, left and then drained out

What hormone is found in the urine of pregnant women

HCG

How does a pregnancy test work

Urine passes up the stick and if HCG is present it attaches to free monoclonal antibodies with coloured dye on the end they then reach immobilised monoclonal antibodies which can form a HCG-antibody complex if HCG is present in the urine if it is they bind and the coloured dye on the free antibodies form a line, then further up the stick there are immobilised antibodies complimentary to the free antibodies as a control

Why is there a second line on pregnancy tests

To act as a control and indicate that a test is functional

What does 2 lines on a pregnancy test indicate

That a person is pregnant

What does one line at the top of a pregnancy test indicate

That a person isn’t pregnant

What does one line at the bottom of a pregnancy test mean

That the test is faulty

What problems arise from kidney failure

Unbalanced electrolyte levels, build up of urea, high blood pressure

What effect does kidney failure have on glomerular filtrate rate

Decreases GFR

What builds up if the kidneys aren’t working properly

Creatine

What are limitations of dialysis

It can be very long and must be repeated often, patients must restrict their diets

What dietary changes would need to be made if you were on dialysis

Low protein and low salt intake

What is a difference between dialysis and ultrafiltration

There’s no active transport in haemodialysis just diffusion

What are limitations of kidney transplants

Immunosuppressants have to be taken for life, there’s a risk of rejection, requires you to find a donor

How can urine be used to test for anabolic steroids

Anabolic steroids are broken down into specific byproducts and urine tests can indicate whether these are present or not