5.1.1-5.1.2~ Homeostasis, communication and excretion as an example of homeostatic control

Define excretion?

• the removal of unwanted products of metabolism

Why is it important that metabolic waste products are removed from the body?

• many of the metabolic waste products are toxic so if they build up they will cause damage to the body

Define egestion?

• the removal of waste which cannot be digested

State the 3 main metabolic waste products in mammals?

• carbon dioxide, bile pigments, nitrogen waste products (urea)

In what process is CO2 a waste product in?

• one of the waste products of cellular respiration which is exerted from the lungs

What are bile pigments formed from?

• formed from the breakdown of haemoglobin from old red blood cells in the liver

• They colour the faeces

Where are nitrogenous waste products (urea) formed from?

• formed from the breakdown of excess amino acids by the liver

State the 2 important roles of the liver?

• excretion

• Energy storage

State 3 alternative toxic substances which the liver removes?

• alocohol

• Paracetamol

• Insulin

State the 3 main blood vessels which the liver contains?

• hepatic artery- carries oxygenated blood to the liver

• hepatic vein- carries deoxygenated blood from the liver

• Hepatic portal vein- carries blood form the intestines and other parts of the digestive system to the liver

What is blood carried from the hepatic portal vein rich in?

• products of digestion; glucose and amino acids

What can liver cells also be known as?

• hepatocytes

What features of hepatocytes show they are metabolically active?

• Large nuclei, prominent Golgi apparatus, and many mitochondria.

Where does blood from the hepatic artery and hepatic portal vein mix?

• In spaces called sinusoids.

What surrounds the sinusoids?

• hepatocytes

Why is mixing blood in the sinusoids important?

• It increases oxygen content of blood from the hepatic portal vein, supplying hepatocytes with enough oxygen.

What specialised macrophages are found in the liver sinusoids?

• Kupffer cells.

What is the function of Kupffer cells?

• They ingest foreign particles and help protect against disease.

What do hepatocytes secrete and where does it go ?

• They secrete bile into canaliculi then into bile ductules, which take it to the gall bladder

What hormone stimulates hepatocytes to store glucose as glycogen?

• Insulin.

What hormone stimulates hepatocytes to convert glycogen to glucose?

• Glucagon.

Define deamination?

• The removal of an amino group from an amino acid.

What toxic substance is first produced during deamination?

• ammonia

State the process by which ammonia is made safe?

• It is converted into urea via the ornithine cycle.

Where does the ornithoses cycle take place?

• in hepatocytes in the liver

Which organ excretes urea?

• the kidneys

What happens to the remainder of an amino acid after deamination?

• It enters respiration or is converted into lipids for

Which enzyme in hepatocytes breaks down hydrogen peroxide?

• catalase

What does catalase convert hydrogen peroxide into?

• oxygen and water

Which enzyme breaks down ethanol in the liver?

• Alcohol dehydrogenase.

What is ethanol converted into during detoxification?

• Ethanal, then ethanoate.

What can ethanoate be used for in the body?

• Enters kerbs cycle to produce ATP

State the 2 important roles the kidneys play in the body?

• excretion

• Osmoregulation

State the millions of structures which kidneys are made up of?

• nephrons

State the role of the nephrons?

• filter blood, some filtered material returns to the blood

Why is blood filtration important?

• it removes urea and maintains water and ion balance

State the name of the tubules which urine passes out kidneys?

• ureters

What is the sterile liquid produced by kidney tubules called?

• urine

What is the cortex of a kidney?

• The dark outer layer where blood filtration occurs and where a dense capillary network carries blood from the renal artery to nephrons.

What does the medulla contain?

• the tubules of the nephrons forming renal pyramids

What is the pelvis of a kidney?

• the central chamber where urine is collected before passing out through the ureter

What is the bowman’s capsule?

• A cup-shaped structure containing the glomerulus (a tangle of capillaries) where ultrafiltration occurs.

What is the proximal convoluted tubule?

• The first coiled tubule after Bowman’s capsule, located in the cortex.

What is the main function of the PCT?

• Selective reabsorption of useful substances such as glucose, amino acids, ions, and most water back into the blood.

What happens in the descending limb of the Loop of Henle?

• it is permeable to water so water leaves the filtrate by osmosis

What happens in the ascending limb of the Loop of Henle?

• It is impermeable to water; ions (Na⁺ and Cl⁻) are actively transported o

What hormone acts on the DCT and how?

• DH (antidiuretic hormone) increases permeability of the walls to water, affecting reabsorption.

What is the collecting duct?

• A tube that carries urine from the DCT through the medulla to the pelvis of the

How does ADH affect the collecting

• ADH increases the permeability of the duct’s walls to water to regulate final urine concentration.

Where does ultrafiltration occur?

• n the Bowman’s capsule / glomerulus.

What causes ultrafiltration?

• High hydrostatic pressure in the glomerulus forcing small molecules out of the blood.

Define osmoregulation?

• the control of water content of the body to match the water requirements

What is the amount of water lost in urine controlled by?

• ADH

What is ADHproduced by and what is it secreted into?

• produced by the hypothalamus

• Secreted into the posterior pituitary gland