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OCR A Biology > Homeostatis ( Year 2 ) > Flashcards

Homeostatis ( Year 2 ) Flashcards

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1
Q

What are the two roles of the kidney?

A

1) Excretion

Filter nitrogenous waste products out of the blood ( especially urea )

2) Osmoregulation

Regulation of the blood water levels ( water balance )

Regulation of pH, regulation of salts in body, homeostasis

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2
Q

What is homeostasis?

A

The maintenance of a dynamic equilibrium within narrow ranges in the body. This is done by monitoring changes in the internal environment. For example, we keep pH, water balance of body fluids and core temp within a narrow range.

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3
Q

How does blood enter the kidney?

A

The kidneys are supplied with blood from the abdominal aorta. This travels through the renal arteries at arterial pressure before it reaches the nephrons.

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4
Q

What 3 components are the kidney made up of?

A

1) Cortex

Dark outer layer
- filtration takes place here
- dense capillary network to take blood from renal artery to the nephrons

2) Medulla
- contains the tubules of nephrons

3) pelvis
- chamber where urine collects before passing out the ureter

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5
Q

Explain the process of ultrafiltration

A

Blood enters the glomerulus through the afferent arteriole from the venal artery. Due to the difference in lumen sizes between the afferent ( wider ) and efferent arteriole ( narrower ), there is a high hydrostatic pressure. This means substances ( liquid ) are forced out of the blood capillaries of the glomerulus into bowman’s capsule. This forms the glomerulus filtrate containing glucose, urea, water, salt ( Na+ and Cl-), amino acids, vitamins and hormones.

Arteriole feeding into the knot of capillaries is wider

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6
Q

What feature of the glomerulus wall filters the blood?

A

It has a basement membrane is made up of a network of collagen fibres and other proteins. It filters out substances that are too large and cannot pass through gaps in the capillary endothelium ( plasma proteins and red blood cells). They cannot be filtered out so they leave through the efferent arteriole.

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7
Q

What feature of Bowman’s capsule filters the blood?

A

The walls of the bowman’s capsule have podocytes that are additional filters. The extensions, called pedicels, wrap around capillaries to make sure any cells, platelets or large plasma proteins that have passed through the endothelium do not get into the tubule itself.

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8
Q

What is the glomerulus filtration rate?

A

The volume of blood that is filtered through the kidney in a given time.

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9
Q

What is the nephrons? What is the function of the nephron?

A

These are long tubules surrounded by capillaries. The function is to remove waste and return most useful, filtered substances back into the blood.

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10
Q

Where are nephrons found?

A

In the medulla

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11
Q

What are the adaptations of the proximal distal convoluted tube?

A

1) microvilli

Wider surface area so increased reabsorption

2) mitochondria

Provides ATP for active transport

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12
Q

What substances are re-absorbed in the PCT? Where is it?

A

All the glucose is re absorbed by active transport ( as it is needed for cellular respiration )

Small substances are re absorbed ( vitamins, hormones, amino acids ) by active transport - SODIUM IONS

Therefore, water leaves by osmosis.

Cl- ions also leave by diffusion.

This is hypotonic to the blood plasma.

80 percent of reabsorption occurs

Cortex

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13
Q

Explain the features of the descending limb of the loop of Henle and what happens here

A

When water enters the descending limb, water leaves the filtrate by osmosis into concentrated tissue fluid of medulla. This is because the walls of the lower part of the Loop of Henle are thin and permeable to water. ( the upper part is impermeable ). Sodium and potassium ions diffuse into the tubules by diffusion. As the conc of the tissue increase through medulla, diffusion gradients maintained. This means the filtrate is hypertonic to the blood and concentrated with ions at the hairpin bend.

No active transport takes place as it is not permeable to sodium and chloride ions.

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14
Q

Explain the features of the ascending limb and what happens here

A

The ascending limb is thicker and impermeable to water so water cannot leave by osmosis.

The first section of the ascending limb is permeable to chloride and sodium ions and they move out of the concentrated filtrate by diffusion into the tissue fluid of the medulla. Sodium ions follow down an electrochemical gradient. In the second section, they are pumped out by active transport. This means the tissue fluid of the medulla becomes concentrated and a high concentration of ions. The filtrate becomes increasingly dilute ( essential for production of urine ). At the top of the ascending limb, the filtrate is isotonic.

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15
Q

What happens in the distal convoluted tubule?

A

The permeability is controlled by the level of ADH. This is where reabsorption is selective to the body’s needs to balance the water, salt and pH of the blood. For eg, if the body lacks salt, sodium ions will be actively transported out of the DCT, with chloride ions following down an electrochemical gradient ( concentrating the medulla ). Water also may leave by osmosis concentrating the urine.

The permeability of the walls also vary with levels of ADH.

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16
Q

Explain what happens in the collecting duct

A

This passes through the concentrated tissue fluid of the renal medulla. If walls are permeable, water moves out by osmosis into concentrated tissue fluid ( urine is MORE concentrated ). The level of sodium ions increase from the medulla to the pelvis. More water will move from filtrate of high WP to tissue fluid of low WP down WP gradient by osmosis.

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17
Q

Why does a camel have a longer loop of Henle?

A

It is longer so it has a larger surface area. This means the filtrate spends more time travelling through it so more sodium ions and water can be reabsorbed.

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18
Q

What happens once the filtrate leaves the nephron?

A

It becomes urine as it flows out of the kidneys, along the ureters into the bladder to be stored.

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19
Q

What are the functions of the kidney? ( excluding cellular respiration )

A

Layer of fat to protect against mechanical damage
Good blood supply to maintain a steep diffusion gradient
Different sized blood vessels going in and out of the glomerulus to give high blood pressure for ultrafiltration

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20
Q

List the 5 substances that should be in the glomerulus filtrate

A
  • water
  • urea
  • glucose
  • amino acids
  • mineral ions

( Vitamins and hormones )

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21
Q

How can a kidney infection result in protein in the urine?

A

There may be damage to the podocytes which means proteins get through the kidney tubules. They are not reabsorbed in the tubules so they will end up in the urine.

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22
Q

What factors could affect the levels of urea?

A
  • the level of excercise
  • the amount of protein consumed
  • blood pressure levels
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23
Q

Why is the concentration of urea constant?

A

The urea is always being removed from the blood by the kidneys

24
Q

What type of cells make up most the liver?

A

Hepatocytes (I.e liver cells ) that carry out most homeostatic functions

25
Q

What is the basic structural and functional unit of the liver?

A

Lobules / lobes

26
Q

What is excretion? Give examples of substances excreted

A

The removal of toxic waste products of metabolism from the body and substances in excess

Important in maintaining homeostasis

Examples of substances are carbon dioxide and nitrogenous ( nitrogen containing ) waste. Carbon dioxide is a waste product of respiration and can be toxic and may cause damage if too much is in the blood. Therefore, it can be removed in the body through excretory organs ( lungs in mammals or gills in fish ).

27
Q

What are the main metabolic waste products of the body? How are they formed and their effects?

A
  • Carbon dioxide

This has been excreted from the lungs in cellular respiration through the decarboxylation of respiratory substances in mitochondria

Effects :

Acidosis ( when drop in pH ) which causes damage to cells

  • Nitrogenous waste product urea

This is formed by the breakdown of excess amino acids by the liver

Effects :

Bursting and expands as urea diffuses into cells, lowers WP, therefore cells absorb water by osmosis

  • Bile pigments

These are the breakdown of haem groups of heamoglobin of old RBC of the liver forming bilirubin. It is excreted in the bile from the liver via the gall bladder and bile duct.

Effects :

Accumulate in skin and cause yellowing of skin ( jaundice )

28
Q

What are the adaptations of hepatocytes?

A

1) large nuclei

Active DNA transcription

2) lots of Golgi

Protein repacking and modifying

3) lots of mitochondria

High production of ATP needed for cell reactions

29
Q

What is the function of the hepatic artery?

A

This brings oxygenated blood to the liver. It is a thick wall and narrow lumen as it carries blood under high pressure ( away from the hard ). This allows respiration to take place, providing lots of energy.

30
Q

What is the function of the hepatic portal vein?

A

To carry deoxygenated blood containing products of digestion and cell metabolism from the intestines ( duodenum and ileum ) to the liver

Ingested harmful substances are FILTERED and broken down straight away

31
Q

Where is the hepatic vein? What does it do?

A

This is opposite the hepatic portal vein where it drains the blood.

This takes deoxygenated blood away from the liver, taking the products of metabolism away back to the heart.

32
Q

What are Kupffer cells?

A

These are the resident macrophages that engulf and digest foreign pathogens, foreign cells and debris arriving from the digestive tract. Also breaks down old and worn out RBC and WBC, Therefore, this will not be transported in the blood.

Haemoglobin is broken down into bilirubin ( bile pigment ) which is excreted in faeces

33
Q

What is the canaliculi? What happens in the canaliculi and the bile duct

A

The canaliculi are tubes that connect the bile duct to the central vein. It is surrounded by hepatocytes. Hepatocytes secrete bile into the canaliculi when blood breaks down (i.e heamoglobin breaks down ). Bile is drained into the canaliculi, then drains into the bile ductules which take it to the gall bladder for storage.

34
Q

What is the sinusoid?

A

The hepatic artery and hepatic portal vein is connected to the central vein by sinusoid. This is a space where the oxygenated blood from the HA and deoxygenated blood from the HPA combine and mix. This provides oxygen and raw materials for the hepatocytes needs. Thus, cells can process and function.

35
Q

What does the hepatic vein do?

A

It removes the deoxygenated blood carrying products of detoxification ( eg urea ) away from the liver

36
Q

What are the 3 functions of the liver?

A

1) Carbohydrate metabolism ( i.e the storage of glycogen )
2) Formation of urea through the deamination of excess amino acids
3) Detoxification

37
Q

What other function does the liver have?

A

The hepatocytes make bile which emulsifies fats ( larger oil droplets into smaller oil droplets to maximise lipase action )

38
Q

How does the homeostatic function of carbohydrate metabolism work?

A

When blood glucose conc rise, there is a rise in insulin levels. Hepatocytes respond to insulin by converting glucose to glycogen. ( it binds to receptors )

When blood glucose levels are low, increase in glucagon - converts glycogen back into glucose to be released into the bloodstream

The glucose can be transported as a product of digestion in the HPV, or through the hepatic artery from the pancreas to the sinusoids.

39
Q

How does the homeostatic function of deamination work?

A

The removal of the amine group from excess amino acids. This combines with an extra hydrogen atom to form ammonia which is very soluble and toxic substance. This is then converted to urea which is less toxic in the ornithine cycle ( by combining with Co2 ). This is removed from the liver through the hepatic venule into the blood. The kidneys then filter the blood and remove the urea in urine.

40
Q

What happens to the rest of the amino acid once the conversion to urea takes place?

A

Remainder of the amino acid becomes pyravate, a substrate used in respiration for ATP production.

So it is used for cellular respiration.

Or, it is converted to a carbohydrate and stored as glycogen.

41
Q

How does the homeostatic function of detoxification work?

A

The breakdown of substances that are toxic or not needed. ( eg alcohols, drugs )

Eg :

When we intake alcohol, this affects liver cells ( hepatocytes ) and is absorbed and concentrated in the liver. It contains the enzymes alcohol dehydrogenase which converts ethanol to ethanal, then into ethanoate which can then be converted into fatty acids. This is used for storage and respiration.

42
Q

Why does drinking cause a build up of fatty tissue?

A

Ethanol is detoxified in the liver therefore ethanoate is produced. This feeds into the pathway synthesising fatty acids and so one’s lipids. This means lots of fat builds up in the hepatocytes when we consume lots of alcohol due to detoxification

43
Q

Give an example of detoxification in the liver other than Ad

A

Catalyse in the hepatocytes

This converts hydrogen peroxide into oxygen and water.

44
Q

Why can the liver recover fast if a person stops drinking alcohols?

A

Hepatocytes can divide rapidly, and the liver is a fast growing organ. Therefore if an organ is damaged, it can regenerate over a few months.

45
Q

What is cirrhosis? What can cause this?

A

This is when normal liver tissue is replaced with fibrous scar tissue. This blocks blood flow to the liver.

Caused by excess alcohol

46
Q

What is the effects of a damaged liver?

A

Weight loss - cannot break down excess amino acids and use them, cannot produce bile which breaks down fats

Tiredness and weakness - inability to make urea which will affect kidney and retain fluid

Affect on brain and behaviour due to lack of balance of proteins and other chemicals

47
Q

Describe the structure of a single lobule

A

It has a central vein in the middle that connects to the hepatic vein. It also has the 3 branches ( HV, HPA and bike duct).

48
Q

Where does blood run to in a lobule?

A

Blood runs to the central vein. The central veins from all lobules connect to form the hepatic vein.

49
Q

Why can we not store excess amino acids?

A

Amine groups of amino acids contain nitrogen. Nitrogenous substances cannot be stored in the body. Therefore, they must be used by the body ( eg to make proteins ) or broken down and excreted.

50
Q

What are the functions of the excretory organs?

A

Lungs - CO2 breathed out

Liver - bilirubin from haemoglobin breakdown is passed into bile, and excess amino acids to urea

Skin - sweat contains urea, Uric acid and ammonia

51
Q

Deamination and formation of urea equations

A

Amino acid + oxygen ———> keto acid + ammonia

Ammonia + carbon dioxide ———> urea + water

52
Q

What are the functions of hepatocytes?

A
  • protein synthesis
  • transformation / storage of carbohydrates ( in liver )
  • synthesis of cholesterol and bile salts
  • detoxification
53
Q

Why do multicellular organisms need good communication systems?

A

They need to coordinate different organs, so they need a good communication system that covers the whole body, allows rapid and specific communication, and enables short term and long term responses.

54
Q

Where are the kidneys found?

A

Below the rib cage at the back

55
Q

What effect does being metabolic activity on excretion?

A

Mammals are active so they have high metabolic rates. This means it produces large amounts of metabolic waste.

56
Q

How are bile pigments formed? What is the effect if it accumulates in the body?

A

The breaking down of haem group of haemoglobin in liver cells

Bile pigments accumulate in the skin causing jaundice ( yellowing )

OCR A Biology (9 decks)

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