13. Excretion in humans

Question 1

What is excreted from the body and from where

Answer 1

carbon dioxide is excreted through the lungs
kidneys excrete urea and excess water and ions

Question 2

functions of kidneys, ureters, bladder and urethra

Answer 2

kidneys- filter blood
ureter carry urine from kidney to bladder
bladder- stores urine
urethra- carries urine from bladder to outside

cortex
medulla

Question 3

Process of ultrafiltration

Answer 3

Blood flows into the kidney from the renal artery which divides to form capillaries called glomeruli sitting inside the cup-shaped bowman’s capsule.

The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them. (already at high pressure).

This causes the smaller molecules being carried in blood to be forced out of glomerulus and into bowman’s capsule.

Filtrate - water, urea, glucose, ions.
These substances all continue through nephron. This is ultrafitration

Question 4

Process of reabsorption

Answer 4

All of the glucose, most of the water and some of the ions are taken back into the blood as the fluid flows through nephron. This process is called reabsorption.

glucose- active transport, water-osmosis, ions - diffusion

Blood capillaries come close to nephron, making it easy for these substances to move back into the blood.

Final liquid that flows out of nephron is a solution of urea and salts in water - urine.

It is stored in bladder for a while, before being released from body through urethra. Sphincter muscle relax, urine flows out of the body through urethra

Question 5

Describe deamination

Answer 5

role of the liver- assimilation of amino acids by converting them to proteins.
urea is formed in the liver from excess amino acids.
deamination as the removal of the nitrogen-containing part of amino acids to form urea

Protein taken into the alimentary canal is broken down to amino acids during digestion. The amino acids are absorbed into the blood and taken to liver in hepatic portal vein. Amino acids that are needed are made into proteins or released into the blood to be assimilated by body cells.

Amino acids that are in excess cannot be stored so they are broken down in a process called deamination- the removal of the nitrogen-containing part of amino acids to form area.
Enzymes in liver split up the amino acid molecules, energy is converted to carbohydrates and stored. The rest that contains nitrogen is converted to ammonia which is highly toxic so it’s converted to urea which is less toxic. It dissolves in the blood plasma and is taken to the kidneys to be excreted.

Question 6

Role of glomerulus and nephron

Answer 6

(a) the role of the glomerulus in the filtration from the blood of water, glucose, urea and ions

(b) the role of the nephron in the reabsorption of all of the glucose, some of the ions and most of the water back into the blood

(c) the formation of urine containing urea, excess water and excess ions

Question 7

importance of excretion

Answer 7

Kidneys constantly remove urea from blood ,excreting it in urine as UREA IS TOXIC. if too much builds up in the blood its consequences- cell death, reduces response to insulin leading to diabetes, deposits inside blood vessels