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A level- Biology > Excretion and Kidney > Flashcards

Excretion and Kidney Flashcards

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1
Q

Describe the location of the kidneys in humans and draw and label a diagram to show the human urinary system.

A
  1. They are attached to the back of abdominal cavity.
  2. They are surrounded by a thick protective layer of fat and a layer of fibrous connective tissue
  3. The kidneys are supplied with blood by the renal arteries that branch off from the abdominal aorta.
  4. Blood that has circulated through the kidneys is removed by the renal vein that drains into the inferior vena cava.
  5. From kidney the urine passes down the ureter into the bladder and out the urethra
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2
Q

Name the 3 main areas of the kidney and describe the role of each area.

A
  1. The cortex- dark outer layer. Where the blood is filtered and it has a very dense capillary network carrying the blood from the renal artery to the nephrons.
  2. The medulla- lighter in colour. It contains the tubules of the nephrons that form the pyramids of the kidney and the collecting duct.
  3. The pelvis- is the central chamber where the urine collects before the passing out down the ureter.
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3
Q

Draw and label a diagram to show the internal structure of a kidney.

A

P421

  1. Kidney bean shape
  2. Very outer layer is the capsule
  3. Then Cortex
  4. Then Medulla is the inner layer
  5. In the medulla is nephrons
  6. The inner section in the medulla is the pelvis which have blood vessels on top.
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4
Q

Name the functional unit of the kidney.

A

Nephrons

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5
Q

Draw and label a diagram of a nephron.

A
  1. Glomerulus a bed of capillaries fed by the renal artery - surrounded by Bowman’s capsule
  2. This leads to Proximal convoluted tubule
  3. This goes down to the descending limb of the Loop of Henle (goes thin)
  4. This leads to the Loop of Henle which curves up to the ascending limb of loop of Henle (thicker)
  5. This goes up to the distal convoluted tubule
  6. Joins to the collecting duct which leads to the pelvis of the kidney
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6
Q

Define Bowman’s capsule

A
  1. Cup-shaped structure that contains the glomerulus and is the site of ultrafiltration in the kidney
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7
Q

Define glomerulus

A
  1. A bed of capillaries within the Bowman’s capsule
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8
Q

Define proximal convoluted tubule

A
  1. The first coiled region of nephron after the Bowman’s capsule, found in the cortex of the kidney.
  2. This is where many of the substances needed by the body are reabsorbed into the blood
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9
Q

Define the Loop of Henle

A
  1. A long loop of nephron that creates a steep concentration gradient across the medulla
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10
Q

Define Distal convoluted tubule

A
  1. The second twisted section of the nephron where the permeability of the walls varies in response to ADH levels in the blood
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11
Q

Define collecting duct

A
  1. Final part of the tubule that passes through the renal medulla and the place where hypertonic urine is produced if needed
  2. The permeability of the walls is affected by ADH levels and it is the main site of water balancing
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12
Q

Describe the functions of the kidney

A
  1. Removing waste products from the blood

2. Osmoregulation

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13
Q

Define the term osmoregulation

A

The balancing and control of the water potential of the blood

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14
Q

Label and annotate a photomicrograph of kidney tissue at low and high power to show key histological features.

A

See p422 very hard to describe

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15
Q

Describe the role of the glomerulus

A

Ultrafiltration

  1. The glomerulus is supplied with blood by a relatively wide afferent (incoming) arteriole from the renal artery.
  2. The blood leaves through a narrower efferent arteriole and as a result there is considerable pressure in the capillaries of the glomerulus.
  3. This forces the blood out through the capillary wall-acts as a sieve.
  4. Then the fluid passes through the basement membrane
  5. The basement membrane is a made up of a network of collagen fibres and other proteins- second sieve
  6. Most of the plasma contents can pass through the basement membrane but the blood cells and many proteins are retained in the capillary because of their size. >69000 molecular mass
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16
Q

Describe the role of the Bowman’s capsule

A
  1. The wall of the Bowman’s capsule also involves special cells called podocytes that act as an additional filter.
  2. They have extensions called pedicels that wrap around the capillaries forming slits that make sure any cells, platelets, or large plasma proteins that have managed to get through the epithelial cells and the basement membrane do not get through into the tubule itself.
  3. The volume of blood that is filtered through the kidneys in a given time is known as the glomerular filtration rate.
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17
Q

Define ultrafiltration

A
  1. The process by which blood plasma is filtered through the walls of the Bowman’s capsule under pressure.
18
Q

Define ultrafiltrate

A

The fluid that passes into the tubules of the nephron after having been filtered through the Bowman’s capsule under high pressure.

19
Q

Define podocyte

A

Podocytes are specialised cells in the Bowman’s capsule in the kidneys that wrap around capillaries of the glomerulus.

20
Q

Draw and label a diagram to show the microstructure of the interface between the glomerulus and the Bowman’s capsule.

A

p424

  1. To the left is capillary with blood plasma and endothelial cells with gaps between.
  2. Then there is the basement membrane
  3. Then there is the podocytes
  4. Then there is the Bowman’s capsule which contains the filtrate
21
Q

Compare the composition of the blood in the capillaries and the ultrafiltrate in the Bowman’s capsule

A
  1. The filtrate which enters the capsule contains glucose, salt, urea and many other substances in the same concentrations as they are in the blood plasma.
  2. The process is so efficient that up to 20% of water and solutes are removed from the plasma as it passes through the glomerulus.
22
Q

Define selective reabsorption

A
  1. The reabsorption of selected substances needed by the body in the kidney tubules
23
Q

What substances are reabsorbed in the proximal convoluted tubule

A
  1. All of the glucose- by active transport
  2. All amino acids- by active transport
  3. All vitamins- by active transport
  4. All hormones - by active transport
  5. All mineral ions- by active transport
  6. 85% water follows by osmosis
  7. 85% sodium chloride
24
Q

Describe the role of the proximal convoluted tubule

A
  1. In the proximal convoluted tubule all of the glucose, amino acids, vitamins, and hormones are moved from the filtrate back into the blood by active transport
  2. Around 85% of the sodium chloride and water is reabsorbed as well
  3. The sodium ions are moved by active transport while the chloride ions and water follow passively down the concentration gradients.
  4. Once the substances have been removed from the nephron, they diffuse into the extensive capillary network which surrounds the tubules down steep concentration gradients.
  5. These are maintained by the constant flow of blood through the capillaries.
  6. The filtrate reaching the loop of Henle at the end of the proximal convoluted tubule is isotonic with the tissue fluid surrounding the tubule and isotonic with the blood.
25
Q

Explain how the cells of the proximal convoluted tubule are adapted for their function.

A
  1. They are covered with microvilli, greatly increasing the surface area over which substances can be reabsorbed
  2. They have many mitochondria to provide the ATP needed in active transport systems
26
Q

Describe the role of the loop of Henle

A
  1. Enables mammals to produce urine more concentrated than their own blood
  2. Different areas of the loop have different permeabilities to water- central to the way it functions
  3. It acts as a countercurrent multiplier using energy to produce concentration gradients that result in the movement of substances such as water from one area to another.
  4. Cells use ATP to transport ions using active transport and this produces a diffusion gradient in the medulla.
  5. The changes that take place in the descending limp of the loop of Henle depend on the high concentration of sodium and chloride ions in the tissue fluid of the medulla that are the result of events in the ascending limb of the loop.
27
Q

Describe the what happens in the descending limb of the loop of Henle

A
  1. The descending limb leads from the proximal convoluted tubule- region where water moves out of the filtrate down the concentration gradient.
  2. The upper part is impermeable to water and runs down into the medulla
  3. The concentration of the sodium and chloride ions in the tissue fluid of the medulla is high as a result of the a lot being moving out of the ascending limb of the loop of Henle by active transport.
  4. The filtrate entering the descending limb of the loop of Henle is isotonic with the blood.
  5. As it travels down the limb, water passes out of the loop into the tissue fluid by osmosis down a concentration gradient.
  6. It then moves down a concentration gradient into the blood of the surrounding capillaries
  7. The descending limb is not permeable to sodium and chloride ions, and no active transport takes place in the descending limb
  8. The fluid that reaches the hairpin bend is very concentrated and hypertonic to the blood in the capillaries
28
Q

Describe the what happens in the ascending limb of the loop of Henle

A
  1. The first section of the ascending limb of the loop of Henle is very permeable to sodium and chloride ions and they move out of the concentrated solution by diffusion down a concentration gradient.
  2. In the second section of the ascending limb, sodium and chloride ions are actively pumped out into the medulla tissue fluid against a concentration gradient.
  3. This produces a very high sodium and chloride ion concentration in the medulla tissue.
  4. The ascending limb of the loop of Henle is impermeable to water, so water cannot follow the chloride and sodium ions down a concentration gradient.
  5. This means the fluid left in the ascending limb becomes increasingly dilute, while the tissue fluid of the medulla develops the very high concentration of ions that is essential for the kidney to produce the urine that is more concentrated than the blood
  6. By the time the dilute fluid reaches the top of the ascending limb it is hypotonic to the blood again and it then enters the distal convoluted tubule and collecting duct
29
Q

Describe the roles of the distal convoluted tubule and explain how it can perform these roles.

A
  1. Balancing the water needs of the body takes place in the distal convoluted tubule and the collecting duct.
  2. These are the area where the permeability of the walls of the tubules varies with the levels of ADH
  3. The cells lining the distal convoluted tubule also have many mitochondria so they are adapted to carry out active transport.
  4. If the blood lacks salt, sodium ions will be actively pumped out of the distal convoluted tubule with chloride ions following down an electrochemical gradient.
  5. Water can also leave the distal tubule, concentrating the urine, if the walls of the tubule are permeable in response to ADH.
  6. The distal convoluted tubule also plays a role in balancing the pH of the blood
30
Q

Describe the roles of the collecting duct and explain how it can perform these roles.

A
  1. The collecting duct passes down the through the concentration tissue fluid of the renal medulla.
  2. This is the main site where the concentration and volume of the urine produced is determined.
  3. Water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the renal medulla. As a result the urine becomes more concentrated
  4. The level of sodium ions in the surrounding fluid increases through the medulla from the cortex to the pelvis.
  5. This means water can be removed from the collecting duct all the way along its length, producing very hypertonic urine when the body needs to conserve water.
  6. The permeability of the collecting duct to water is controlled by the of ADH, which determines how much or little water is reabsorbed.
31
Q

Define the term “osmotic stress” and describe 5 factors that could put the body under osmotic stress.

A

Osmotic shock or osmotic stress is a sudden change in the solute concentration around a cell, causing a rapid change in the movement of water across its cell membrane.

  1. Eating a salty meal
  2. Drinking large volumes of liquid
  3. Exercising hard
  4. Running a fever
  5. Visiting a very hot climate
32
Q

State 3 ways in which the body gains water and 4 ways in which water is lost from the body.

A 
Gains water
1. Respiration in cells
2. Food
3. Drink
Water losses
1. Exhaled air
2. Faeces
3. Sweat
4. Urine
33
Q

State the main way (from the ways water can be gained by, or lost from, the body) the body can adjust its water balance.

A
  1. The amount of water lost in the urine is controlled by ADH in a negative feedback system
  2. ADH is produced by the hypothalamus and secreted into the posterior pituitary gland, where it is stored
  3. ADH increases the permeability of the distal convoluted tubule, and the collecting duct to water
34
Q

State the full name and the abbreviation of the hormone that controls the amount of water lost in urine, where it is produced and where it is stored

A
  1. ADH- Anti-diuretic hormone
  2. Produced- hypothalamus
  3. Stored- Posterior pituitary gland
35
Q

Describe what causes ADH to be released from the posterior pituitary gland.

A
  1. When osmoreceptors detect changes in water potential of the blood
36
Q

How does ADH start the process of osmoregulation

A
  1. ADH is released from the pituitary gland and carried in the blood to the cells of the collecting duct where it has its effect
  2. The hormone does not cross the membrane of the tubule cells- it binds to receptors on the cell membrane and triggers the formation of cycling AMP (cAMP) as a second messenger inside the cell
37
Q

Following the release of ADH, what effect does cAMP have in osmoregulation

A

cAMP sets of a cascade of events

  1. Vesicles in the cells lining the collecting duct fuse with the cell surface membrane on the side of the cell in contact with the tissue fluid of the medulla
  2. The membranes of these vesicles contain protein- based water channels (aquaporins) and when they are inserted into the cell surface membrane, they make it permeable to water
  3. This provides a route for water to move out of the tubule cells into the tissue fluid of the medulla and the blood capillaries.
38
Q

How does ADH affect the water retained or lost by the body

A

More ADH
1. The more ADH that is released, the more water channels are inserted into the membranes of the tubule cells.
2. This makes it easy for more water to leave the tubules by diffusion resulting in the formation of a small amount of very concentrated urine.
Less ADH
1. When ADH levels fall the reverse happens
2. Levels of cAMP fall, then the water channels are removed from the tubule cell membranes and enclosed in vesicles again.
3. The collecting duct becomes impermeable to water once more, so no water can leave.
4. This results in the production of large amounts of very dilute urine and maintains the water potential of the blood and tissue fluid.

39
Q

How does the negative feedback loop respond when water is in short supply

A

p429

  1. Osmoreceptors in the hypothalamus of the brain are sensitive to the concentration of inorganic ions in the blood and are linked to the release of ADH
  2. The concentration of inorganic ions in the blood rises and the water potential of the blood and tissue fluid becomes more negative
  3. This is detected by osmoreceptors in the hypothalamus.
  4. They send nerve impulses to the posterior pituitary which in turn releases stored ADH into the blood.
  5. The ADH is picked up by receptors in the cells of the collecting duct and increases the permeability of the tubules to water
  6. Water leaves the filtrate in the tubules and passes into the blood in the surrounding capillary network .
  7. A small volume of concentrated urine is produced
40
Q

How does the negative feedback loop respond when there is an excess of water

A
  1. When large amounts of liquid are taken in, the blood becomes more dilute and its water potential becomes less negative.
  2. Again, the change is detected by the osmoreceptors of the hypothalamus
  3. Nerve impulses to the posterior pituitary are reduced or stopped and so the release of ADH by the pituitary is inhibited
  4. Very little re absorption of water can take place because the walls of the collecting remain impermeable to water
  5. In this way the concentration of the blood is maintained- and large amounts of dilute urine are produced.

A level- Biology (46 decks)

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