5.1.2 - EXCRETION Flashcards
Define excretion
The removal of waste products from the body
Describe the importance of excretion
- All chemical reactions in our cells make up our metabolism
^— metabolism produces waste products (substances not needed by cells - e.g. carbon dioxide + nitrogenous waste)
^— if they build up, they cause damage to other metabolic reactions (because they are toxic) - Excretion removes these waste products of metabolism (maintains metabolism)
E.g. carbon dioxide is a waste product of respiration + too much in the blood is toxic so the LUNGS remove it (in mammals) - excretory organ
Explain carbon dioxide as a waste product
- Waste product from respiration
^— excreted from the lungs
Explain nitrogenous waste as a waste product
- Urea
- Created from excess amino acids in the diet
- Unlike glucose, excess amino acids cannot be stores
^— this excess in broken down in the liver to ammonia then urea - Urea excretes from the kidneys
MAMMALS: UREA | FISH: AMMONIA | BIRDS: URIC ACID
State the function of the liver
- Glycogen storage
- Detoxification
- Formation of urea
- Contains range of different enzymes that make these processes possible
- very large organ that receives oxygenated blood through hepatic artery + leaves through hepatic vein
- hepatic portal vein supplies liver with blood from digestive system
What are hepatocytes?
- Liver cells
- Many mitochondria
- Large nuclei
- Prominent Golgi apparatus
- High metabolic rate
Describe the function of liver lobules
- Blood is delivered to the lobule through the hepatic portal vein + hepatic artery mixes in sinusoids
- Blood delivered from the hepatic artery is highly oxygenated + this oxygen can mix with blood from hepatic portal vein
What are sinusoids?
Spaces that are surrounded by hepoatocytes
What are Kupffer cells?
- Macrophages within the sinusoids
^— engulf pathogens that may have entered through the blood delivered by the hepatic portal being which came from the digestive system
Describe the functions of individual liver lobule segments
- Hepatocytes produce bile using products from breaking down old blood + blood cells
- Bile is first secreted into spaces called canaliculi, then it passes through the bile ducts to the gall bladder where it is stored
Describe the functions of hepatocytes
- Response to INSULIN, absorb excess glucose from the blood + convert it into glycogen
- Response to GLUCAGON, hepatocytes hydrolyse glycogen back into glucose + release into the blood
What is detoxification?
- The neutralisation + breakdown of unwanted chemicals such as alcohol, drugs, hormones + toxins produces in chemical reactions in teh body
- Many metabolic reactions produce toxins, and the liver contains enzymes to break these down into non-toxic substances
What is the ornithine cycle?
- Urea cycle
- How urea is produced from ammonia, ready to be transported to the kidneys + excreted
- Excess proteins from our diet cannot be stored so are delivered to the liver to be deanimated
What is the kidney responsible for?
- The excretion of nitrogenous waste + osmoregulation
What is osmoregulation?
The process of controlling the water potential of the blood
How is the kidney supplied with blood?
- The renal artery supplies the kidney with blood to be filtered
- The renal vein carries the filtered blood away from the kidney
What are the three layers of the kidneys?
- The cortex
- The medulla
- The pelvis
What is the cortex in the kidney?
Dark outer layer that contains many capillary networks carrying blood from the renal arteries to the nephrons
What is the medulla in the kidney?
Contains the nephrons
What is the pelvis in the kidney?
Where the urine collects before leaving the kidney and travelling to the ureter
Describe the role of the nephron
- We have 2 kidneys made up of millions of nephrons
- Nephrons are structures within the kidney where blood is filtered + useful substances are re absorbed into the blood
- Blood is filtered here to remove waste + selectively reabsorb useful substances back into the blood
Describe the structure of the nephron
- The Bowman’s capsule
- Proximal convoluted tubule (PCT)
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
What occurs at the Bowman’s capsule?
Ultrafiltration
What occurs at the PCT?
Glucose is reabsorbed
What occurs at the Loop of Henle?
Sodium ions are actively transported out of the ascending limb into the medulla to create a low water potential
What occurs at the Distal convoluted tubule?
Water moves out of the descending limb + here by osmosis
What occurs at the collecting duct?
Liquid remaining here forms urine, contains salts, water, urea + others
Describe the process of ultrafiltration
- Blood enters through the afferent arterioles + this splits not a lots of smaller capillaries which make up the glomerulus
- This causes high hydrostatic pressure of the blood
^— water + small molecules (glucose + mineral ions) are forced out of the capillaries + form the glomerulus filtrate - Once the fluid is forced out the capillary, is passes through the basement membrane (made of collagen fibre + protein network)
^— basement membrane + capillary act like a sieve - Bowman’s capsule wall has podocytes | Large protein + blood are too bid to fit through the caps in the capillary endothelium, so remain in the blood (leaves via efferent arterioles)
Describe the process of selective reabsoption
- Occurs in PCT where most of the glomerular filtrate is absorbed back into the blood, leaving urea + excess mineral ions + water behind
- The concentration of sodium ions in the PCT cell is decreased as the sodium ions are actively transported out of the PCT cells into the blood in teh capillaries
- Due to conc. gradient, sodium ions diffuse down the gradient from the lumen of the PCT into the cells lining the PCT - example of co-transport (as proteins which transport sodium ions + carry glucose with it)
- Glucose can then diffuse from the PCT epithelial cell into the bloodstream
Describe the process of the filtrate entering the Loop of Henle
- Filtrate passes into the loop - a sodium + chloride ions diffuse down gradient to enable reabsorption is maintained in the medulla by the loop
-Mitochondria in the walls of the cells provide energy to actively transport sodium + chloride ions out of the ascending limb to the LoH - The accumulation of sodium + chloride ions outside the nephron in the medulla lowers water potential
- Therefore, the water diffuses out by osmosis into the interstitial space + then the blood capillaries (water reabsorbed into blood)
- At the base of ascending limb some sodium + chloride ions are transported out by diffusion as there is now a very dilute solution due to all the water that has moved out
Describe the reabsorption of water at the DCT + collecting duct
- Due to all the sodium + chloride ions being actively transported out of the LoH, when the filtrate reaches the top of the LoH it is very dilute
- The filtrate moves to the DCT + collecting duct - very concentrated
- Even more water diffuses out of the DCT _ collecting duct - what is left is transported to form urine
Briefly describe how the hypothalamus is involved with urine production
Changes in wager potential of blood are detected by osmoreceptors here
Describe the role of the hypothalamus when blood water potential is too low
- Water leaves the osmoreceptors by osmosis + they shrivel
^— stimulates the hypothalamus to produce more of ADH - ADH moves to the posterior pituitary gland + is released into capillaries and blood to kidney
Describe the role of the hypothalamus when blood water potential is too high
- Water enters osmoreceptors by osmosis
^— stimulates the hypothalamus to produce less ADH - ADH moves to the posterior pituitary gland + is released into capillaries and blood to kidney
Explain the function of ADH
- Will bind to complementary receptors that are only located on target cells in the DCT and collecting duct
- When it binds it activates adenyl cyclase to make cAMP
^— activates and enzyme causing vesicles containing aquaporins to fuse with the membrane - As a result, the membrane becomes more permeable to water + more will leave to be reabsorbed back into the blood
What are aquaporins?
Channel proteins that allow water to transport across the membrane
What does ADH stand for?
Antidiuretic hormone
What is the effect ADH on urine?
Causes more water to leave the nephron + be reabsorbed into the blood
^— so urine is more concentrated
