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Biology > Homeostasis- Kidneys > Flashcards

Homeostasis- Kidneys Flashcards

1
Q

What are the kidneys homeostatic roles?

A

1) Excretion of metabolic waste chemicals
2) Osmoregulation
3) Water balance
4) Blood pH

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2
Q

What are the features of the kidney?

A
  • Two reddish brown, bean shaped organs
  • Located at rear of abdominal cavity
  • Have a very good blood supply
  • Receive blood from paired renal arteries and blood exits into paired renal veins
  • Each kidney attached to a ureter that carries excreted urine to the bladder
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3
Q

Gross anatomy of kidneys:

A

1) CAPSULE
- tough, fibrous covering that is covered by fat to provide protection
2) CORTEX
- dark outer layer
- filtering of blood takes place here
- glomerulus, bowman’s capsule, and convoluted tubules located here, lots of capillaries
3) MEDULLA
- lighter in colour, inner layer
- collecting ducts and Loops of Henle located here
4) PELVIS
- central chamber that the collecting ducts drain into
- connected to ureter

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4
Q

Blood supply to kidneys:

A

1) RENAL ARTERIES
- branch directly from aorta
- carry oxygenated blood to kidneys
2) RENAL VEINS
- drain blood from the kidneys into inferior vena cava

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5
Q

What is a nephron?

A

Microscopic and functional unit of kidney

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6
Q

What components make up the nephron?

A

1) Glomerulus
2) Bowman’s Capsule
3) Proximal Convoluted Tubule
4) Loop of Henle
5) Distal Convoluted Tubule
6) Collecting Duct

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7
Q

What parts of the nephron are located in the Medulla vs Cortex?

A 
CORTEX
-Glomerulus
-Bowman's Capsule
-Proximal Convoluted Tubule
-Distal Convoluted Tubule
MEDULLA
-Loop of Henle
-Collecting Duct
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8
Q

What is ultrafiltration?

A

Filtration on a microscopic scale

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9
Q

How does ultrafiltration occur in Bowman’s Capsule?

A

1) Small molecules and ions are filtered out of the blood and pass into the lumen of Bowman’s Capsule, forming glomerular filtrate
2) Cells that make up capillary walls of glomerulus are leaky because they have fenestrations, so mass flow of plasma occurs
3) Plasma passes through basement membrane that has a filtering function
4) Inner wall of Bowman’s Capsule made from PODOCYTES that have a filtering function because they create filtration slits
This is a triple filter process

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10
Q

How do podocytes have a filtering function?

A
  • Podocytes have extensions called pedicels that wrap around glomerular capillaries
  • Pedicels form filtration slits between them
  • Filtration slits stop blood cells and large plasma proteins, such as albumin leaving the blood plasma
  • Fluid that reaches inside of Bowman’s Capsule contains almost same substances as in blood and at almost the same concentrations
  • Main substances are urea, glucose and salt as Na+ and Cl-
  • Fluid called glomerular filtrate
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11
Q

What are the main functions of the nephrons after Bowman’s Capsule?

A
  • Selective reabsorption
  • Producing urine
  • Osmoregulation
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12
Q

Where does selective reabsorption occur?

A
  • Both convoluted tubules
  • Loop of Henle
  • Collecting Duct
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13
Q

Selective reabsorption in Proximal Convoluted Tubule:

A

1) All glucose, amino acids, vitamins and hormones are selectively reabsorbed by active transport from the glomerular filtrate in the blood
2) A large proportion of sodium ions are selectively reabsorbed by active transport
3) A large proportion of chloride ions are selectively reabsorbed by diffusion
4) A large proportion of water molecules are selectively reabsorbed by osmosis
5) By end of proximal convoluted tubule, 80% of volume of glomerular filtrate has been selectively reabsorbed into the blood

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14
Q

Why is the proximal convoluted tubule longer than the distal?

A

Because majority of the volume of the glomerular filtrate (80%) is selectively reabsorbed into the blood and therefore more time is needed, hence its longer

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15
Q

What are the two function of the Loop of Henle?

A

1) Creates a high concentration gradient of sodium and chloride ions in the tissue fluid that is in between the cells of the medulla
2) Allows mammals to produce urine that is more concentrated than their blood

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16
Q

What are the adaptations of the Loop of Henle?

A

1) Descending limb is permeable to water but relatively impermeable to sodium and chloride ions
2) Ascending limb is permeable to sodium and chloride ions but relatively impermeable to water
This means that as loop descends into the medulla, the tissue fluid becomes more salty (lower water potential)
3) Blood vessels that surround loop have a blood flow that is in the opposite direction to the filtrate flow in both limb, allowing counter-current exchange

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17
Q

Hypertonic definition:

A

A solution outside the cell with a lower water potential compared to the inside of the cell

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18
Q

Isotonic definition:

A

A solution outside the cells with the same water potential as the solution inside the cell

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19
Q

Hypotonic definition:

A

A solution outside the cell with a higher water potential compared to the inside of the cell

20
Q

Ascending Limb of the Loop of Henle:

A
  • In lower part of ascending limb, sodium and chloride ions move from the filtrate into the tissue fluid of the medulla by diffusion
  • In the upper part of the ascending limb, sodium and chloride ions are pumped from the filtrate into the tissue fluid of the medulla by active transport
  • Ascending limb is impermeable to water, so water cannot move from filtrate into tissue fluid by osmosis
  • A high concentration and a concentration gradient of sodium and chloride ions is produced in the tissue fluid of the medulla
  • Dilute filtrate is produced at the top of the ascending limb as is hypotonic to the blood plasma
21
Q

Descending Limb of the Loop of Henle:

A
  • Filtrate entering descending limb is isotonic to the blood plasma
  • Water moves out of the filtrate into the tissue fluid around the medulla cells by diffusion
  • Happens because ascending limb has created a high concentration of sodium and chloride ions in medulla’s tissue fluid
  • Water in tissue fluid then diffused back into the blood plasma in the vasa recta
  • Descending limb impermeable to sodium and chloride ions so that they do not diffuse back into the filtrate
  • Filtrate at the bend is hypertonic to blood plasma
22
Q

Selective reabsorption in Distal Convoluted Tubule:

A

1) Water balance of blood plasma regulated in distal convoluted tubule
2) Dilute filtrate produced at top of ascending limb of Loop of Henle
3) Filtrate has lower water potential than blood plasma
4) Water permeability of cells that make up distal convoluted tubule controlled by ADH
5) More or less water leaves filtrate and enters blood plasma by diffusion
6) If blood plasma has too little sodium and chloride ions then they are pumped by active transport into tissue fluid so that they diffuse into blood
7) Blood pH also regulated here

23
Q

Selective reabsorption in the Collecting Duct:

A

1) Main part of creating volume and concentration of urine happens here
2) As urine flows through collecting duct, water leaves urine and moves into tissue fluid of medulla by diffusion, then back into blood plasma
3) This produces urine that is either:
- Hypertonic (concentrated) when body needs to reduce water loss
- Hypotonic (dilute) when body needs to increase water loss
4) Permeability of walls to water controlled by ADH

24
Q

What is the vasa recta?

A
  • Straight arterioles and straight venules of the kidney
  • Capillaries connect the arteriole to the venule
  • Lie parallel to the loop of Henle
  • Counter current flow arrangement so substances can diffuse into blood plasma
25
Q

Why is counter current flow important in nephron?

A

Overcomes the problem of maximum rate of transport

26
Q

What does ADH control?

A

Increases permeability of collecting duct wall to water, which affects amount of water in the urine and hence the concentration of the urine

27
Q

Mechanism of ADH:

A

1) Osmoreceptors in hypothalamus detect concentration of inorganic ions in blood
2) ADH released into blood by posterior pituitary gland when water potential of blood is too low
3) ADH binds to receptors in plasma membrane of cells of the walls of the collecting duct
4) Receptor protein activates enzyme that produces cAMP
5) Vesicle of AQUAPORINS present in cell
6) Cascade of enzyme reactions cause vesicles to fuse with apical sides of cells
7) Aquaporins embedded in plasma membrane and allow increased amounts of water to move by osmosis from urine into the blood vessels of vasa recta
8) More ADH in blood= More aquaporins embedded in plasma membrane=More water out of urine=More conc. and smaller volume of urine
9) When ADH blood levels fall, aquaporins removed from plasma membrane and returned to vesicles

28
Q

How do monoclonal antibody pregnancy tests work?

A

1) Stick dipped into urine
2) HCG-specific antibodies bound to pink beads carried up. If there is any HCG present, it binds to the antibodies and is also carried up
3) If stick is working, a pink line always appears in the control region. HCG-specific antibody bound to pink is carried upwards and captured by antibody specific to it, which was immobilised here
4) If urine contains HCG, it binds to the pink HCG-specific antibody and is carried upwards. When this meets immobilised HCG-specific antibody it is bound and a pink line appears for a positive test

29
Q

What can urine be used for?

A

Diagnosis and drugs testing

30
Q

What are the main causes of kidney failure?

A

1) Type 2 diabetes
2) Hypertension (high blood pressure)
3) Infection of kidney that leads to structural changes to kidney
4) Genetic condition

31
Q

Differences between acute and chronic kidney failure:

A

1) ACUTE
fast development, short acting, more easily treated, recover quicker
2) CHRONIC
slower development, longer acting, less easily treated, slower or no recovery

32
Q

What are the symptoms of kidney failure?

A 
KIDNEY INFECTION
-Protein in urine
-Blood in urine
BOTH KIDNEY FAILURE
-Pain and stiffness in joints
-Hypertension (lead to stroke/death)
-Anaemia (kidneys produce hormone stimulate erythrocyte production)
-Loss of electrolyte balance (lead to death)
-Increased urea conc. in blood (death)
33
Q

What is the Glomerular Filtration Rate?

A
  • Used to measure the extent of kidney disease or failure
  • Measure indirectly by a blood test measuring the concentration of creatine in the blood
  • Creatine breakdown product of creating phosphate which is excreted by kidneys
  • If there is a high concentration then kidneys aren’t removing it properly from the blood
34
Q

How can kidney failure be treated?

A
  • Renal dialysis is a treatment for kidney failure
  • Two types of dialysis
    1) HAEMODIALYSIS
    2) PERITONEAL DIALYSIS
  • Kidney transplant longer term solution to kidney disease or failure
35
Q

What is haemodialysis?

A
  • Blood from patient’s artery passed through very small tubes made from a partially permeable membrane (dialysis membrane)
  • On outside of membrane, dialysis fluid and blood flow in opposite directions to allow counter current exchange
  • Dialysis fluid has water potential and concentration of ions and glucose isotonic to patient’s blood
  • No urea so there is a steep concentration gradient for it to diffuse out of patient’s blood into dialysis fluid
36
Q

What is peritoneal dialysis?

A
  • Catheter inserted into peritoneum cavity
  • Dialysis fluid passed in and left there
  • Takes several hours for exchange to occur
  • Dialysis fluid then drained off through catheter
37
Q

Advantages of haemodialysis:

A
  • Counter current flow
  • Large surface area
  • Mimicks kidney
  • Fluid constantly refreshed
38
Q

Disadvantages of haemodialysis:

A

-Bed bound for hours, several times a week

39
Q

Advantages of peritoneal dialysis:

A
  • Don’t need to go into hospital as much

- Live a more ‘normal’ life

40
Q

Disadvantages of peritoneal dialysis:

A
  • Fluid never refreshed
  • Small surface area
  • No counter current flow
41
Q

Advantages of kidney transplant:

A
  • Live a normal life
  • Cheaper than long term dialysis
  • Last around 9 to 10 years, or even longer
42
Q

Disadvantages of kidney transplant:

A
  • Risk of rejection
  • Have to take immunosuppressants
  • Long waiting list
43
Q

Histology of Bowman’s Capsule:

A
  • Glomerulus at centre of Bowman’s capsule (tangle of capillaries)
  • Bowman’s space in between Bowman’s capsule and glomerulus
44
Q

Histology of Proximal Convoluted Tubule:

A
  • Cuboidal epithelial cells line tubules
  • Cells are large so not every nucleus will be visible
  • Cells have apical brush border of microvilli to increase surface area
45
Q

Histology of Loop of Henle:

A
  • Lower end of ascending limb is very thin and lined by simple squamous epithelium
  • Upper end of ascending limb is thick and lined by simple cuboidal epithelium
  • Centre of descending limb darker
  • Collecting duct circular
46
Q

Histology of Distal Convoluted Tubule:

A
  • Smaller and more lightly stained
  • More nuclei apparent in cross section
  • Lack a brush border
  • Much less space occupied by it
47
Q

Histology of Collecting Ducts:

A

-Prominent lateral borders of epithelial cells

Biology (33 decks)

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