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Biology > 5.1.2 - EXCRETION > Flashcards

5.1.2 - EXCRETION Flashcards

1
Q

Define excretion

A

The removal of waste products from the body

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2
Q

Describe the importance of excretion

A
  • 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

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3
Q

Explain carbon dioxide as a waste product

A
  • Waste product from respiration
    ^— excreted from the lungs
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4
Q

Explain nitrogenous waste as a waste product

A
  • 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

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5
Q

State the function of the liver

A
  • 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
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6
Q

What are hepatocytes?

A
  • Liver cells
  • Many mitochondria
  • Large nuclei
  • Prominent Golgi apparatus
  • High metabolic rate
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7
Q

Describe the function of liver lobules

A
  • 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
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8
Q

What are sinusoids?

A

Spaces that are surrounded by hepoatocytes

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9
Q

What are Kupffer cells?

A
  • 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
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10
Q

Describe the functions of individual liver lobule segments

A
  • 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
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11
Q

Describe the functions of hepatocytes

A
  • 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
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12
Q

What is detoxification?

A
  • 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
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13
Q

What is the ornithine cycle?

A
  • 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
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14
Q

What is the kidney responsible for?

A
  • The excretion of nitrogenous waste + osmoregulation
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15
Q

What is osmoregulation?

A

The process of controlling the water potential of the blood

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16
Q

How is the kidney supplied with blood?

A
  • The renal artery supplies the kidney with blood to be filtered
  • The renal vein carries the filtered blood away from the kidney
17
Q

What are the three layers of the kidneys?

A
  • The cortex
  • The medulla
  • The pelvis
18
Q

What is the cortex in the kidney?

A

Dark outer layer that contains many capillary networks carrying blood from the renal arteries to the nephrons

19
Q

What is the medulla in the kidney?

A

Contains the nephrons

20
Q

What is the pelvis in the kidney?

A

Where the urine collects before leaving the kidney and travelling to the ureter

21
Q

Describe the role of the nephron

A
  • 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
22
Q

Describe the structure of the nephron

A
  • The Bowman’s capsule
  • Proximal convoluted tubule (PCT)
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
23
Q

What occurs at the Bowman’s capsule?

A

Ultrafiltration

24
Q

What occurs at the PCT?

A

Glucose is reabsorbed

25
Q

What occurs at the Loop of Henle?

A

Sodium ions are actively transported out of the ascending limb into the medulla to create a low water potential

26
Q

What occurs at the Distal convoluted tubule?

A

Water moves out of the descending limb + here by osmosis

27
Q

What occurs at the collecting duct?

A

Liquid remaining here forms urine, contains salts, water, urea + others

28
Q

Describe the process of ultrafiltration

A
  • 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)
29
Q

Describe the process of selective reabsoption

A
  • 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
30
Q

Describe the process of the filtrate entering the Loop of Henle

A
  • 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
31
Q

Describe the reabsorption of water at the DCT + collecting duct

A
  • 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
32
Q

Briefly describe how the hypothalamus is involved with urine production

A

Changes in wager potential of blood are detected by osmoreceptors here

33
Q

Describe the role of the hypothalamus when blood water potential is too low

A
  • 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
34
Q

Describe the role of the hypothalamus when blood water potential is too high

A
  • 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
35
Q

Explain the function of ADH

A
  • 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
36
Q

What are aquaporins?

A

Channel proteins that allow water to transport across the membrane

37
Q

What does ADH stand for?

A

Antidiuretic hormone

38
Q

What is the effect ADH on urine?

A

Causes more water to leave the nephron + be reabsorbed into the blood
^— so urine is more concentrated

Biology (26 decks)

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