11.3 The kidney and osmoregulation Flashcards
(107 cards)
1
Q
What are the three main forms that animals excrete their nitrogenous waste in?
A
Urea, uric acid and ammonia
2
Q
At the same time that animals excrete their nitrogenous wastes, they control their ___
A
Water and electrolyte balances.
3
Q
Depending on what are animals classified as osmoregulators or osmoconformers?
A
Depending on the strategies used to achieve water balance.
4
Q
What are osmoregulators?
A
- Oganisms that are able to keep or regulate the solute concentration of their body fluids above or below that of their external environment.
- These organisms have the ability to control the osmolarity of their tissues within very narrow limits.
- Changes in their environment generally have no effect on or cause only small fluctuations in their internal solute concentration.
5
Q
Give examples of osmoregulators
A
Examples of osmoregulators include humans and birds.
6
Q
What are osmoconformers?
A
- Marine organisms that actively or passively maintain an internal environment that is isosmotic to their external environment.
- This means that the solute concentration of their body fluid is the same as the solute concentration of the external medium in which the organisms live.
- These organisms cannot regulate the solutes of their body fluids at a concentration that is different from that of the external medium.
7
Q
Give examples of osmoconformers
A
Examples of osmoconformers include sea stars, molluscs, marine crabs, jellyfish and other marine invertebrates.
8
Q
Picture of the jellyfish: an osmoconformer
A
9
Q
The body fluid of a marine organism was analysed and it was found to have the same solute concentration as sea water.
This organism is ___
A
An osmoconformer
10
Q
The type of nitrogenous waste produced and excreted in animals is related to their ___
A
Evolutionary history and habitat
11
Q
Explain how overhydration can happen
A
- Every year some people die of overhydration (excessive intake of water).
- This usually happens during sporting events, such as marathons or triathlons.
- When the normal balance of electrolytes in the body exceeds safe limits by overhydration, for example when sodium levels drop below 135 mmol/L, death may follow.
12
Q
What can cause overhydration (other than drinking too much water)?
A
- Overhydration can also be caused by diseases that encourage water accumulation in the body.
- The consequence of overhydration is the swelling of body cells.
- This creates a very dangerous situation, as swollen cells in the brain lead to intracranial pressure.
13
Q
What can intercranial pressure lead to?
A
- As this pressure increases, the blood flow to the brain can be interrupted, leading to dysfunction in the central nervous system, seizures, coma or even death.
- Additionally, consequences such as nausea and vomiting, changes in mental state (confusion or disorientation), muscle weakness or cramps, as well as unconsciousness may occur.
14
Q
Explain dehydration
A
It occurs when you use or lose more fluid than you take in, and your body doesn’t have enough water and other fluids to carry out its normal functions.
15
Q
What is dehydration caused by?
A
- It can be caused by vigorous exercise (especially in hot weather), intense diarrhoea, vomiting, fever, excessive sweating or by just not taking in enough fluids.
- This may also cause electrolyte imbalance.
16
Q
What happens to your body when you are dehydrated?
A
- When you become dehydrated, your urine becomes darker and your skin will become less elastic, both your heart rate and breathing rate increase, while your blood pressure decreases.
- Dehydration may also affect your ability to sweat and in severe cases may cause brain damage and death.
17
Q
Define osmoregulation
A
The maintenance by an organism of an internal balance between water and dissolved materials, regardless of environmental conditions. It includes the control of the water balance of the blood, tissue or cytoplasm of a living organism.
18
Q
What role do the kidneys play in osmoregulation and excretion?
A
- They filter your blood to rid your body of nitrogenous waste, as well as regulating osmolarity and producing urine.
- Urine leaves the kidney via the ureter.
19
Q
How does urine leave the kidneys?
A
Via the ureter
20
Q
Drawing a kidney for the exam
A
You need to be able to draw and label a diagram of the human kidney
21
Q
Diagram of a human kidney
A
22
Q
What do kidneys regulate?
A
Osmolarity and excretion
23
Q
How do kidneys regulate osmolarity and excretion? (reword?)
A
- The blood that enters the kidney through the renal artery needs to be filtered.
- The composition of the blood that leaves the kidney is different from the blood that enters the kidney.
- The following compounds are removed: drugs, toxins, nitrogenous waste, excess water, and salts.
- Large proteins remain in the blood.
- Protein found in the urine may indicate infection or disease of the kidney.
24
Q
Explain the difference in the composition of blood entering and leaving the kidney in terms of glucose, oxygen, and carbon dioxide
A
- Glucose – some of the glucose is reabsorbed for metabolic processes, so the glucose concentration in the renal vein is slightly lower than that of the renal artery.
- Oxygen – some of the oxygen is also used in metabolic processes meaning the oxygen concentration is lower in the renal vein than in the renal artery.
- Carbon dioxide – the carbon dioxide concentration is higher in the renal vein than in the renal artery due to the production of carbon dioxide during respiration in the cells of the kidney.
25
What is the kidney responsible for?
Carrying out osmoregulation as well as for removing nitrogenous wastes from the body.
26
What is the primary nitrogenous waste product of humans?
Urea
27
What is the nephron?
The basic functional unit of the kidney.
28
How many nephrons does each kidney have?
About 1 million
29
Describe the structure of the nephron
The nephron is a long tube which starts at the Bowman's capsule and ends at the collecting duct, which drains into the renal pelvis.
30
Annotating the nephron for the exam
You should be able to annotate the following parts on nephron diagrams: glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule and the collecting duct
31
Diagram of two nephrons and intertwining arterioles
32
What are the parts of the nephron?
- Bowman's capsule (is a cup-like sac)
- Glomerulus (is enclosed in the Bowman's capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
- Afferent arteriole
- Efferent arteriole
- Vasa recta
33
What is the function of the Bowman's capsule?
Highly porous wall which collects the filtrate
34
What is the function of the glomerulus?
Knot-like capillary bed where high-pressure filtration takes place
35
What is the function of the proximal convoluted tubule?
Twisted section of the nephron where water, nutrients and salts are reabsorbed back into the blood; contains many mitochondria and microvilli
36
What is the function of the loop of Henle?
Hairpin shaped tube with a descending and ascending limb; water and salt reabsorption takes place here
37
What is the function of the distal convoluted tubule?
Another twisted section of the nephron, where water and salts are reabsorbed back into the blood; also contains many mitochondria and microvilli
38
What is the function of the collecting duct?
A slightly wider tube that carries the filtrate to the renal pelvis
39
What is the function of the afferent arteriole?
Brings blood from the renal artery
40
What is the function of the efferent arteriole?
A narrow blood vessel that restricts blood flow, which helps to generate the pressure needed for filtration
41
What is the function of the vasa recta?
An unbranched capillary shaped like the loop of Henle, with the descending limb bringing blood deep into the medulla
42
In the diagram of the nephron below, what structures are indicated by the letters Y and Z?
Y: Bowman's capsule
Z: Distal convoluted tubule
43
Where does ultrafiltration occur in the nephron?
Bowman's capsule
44
Where are the glomerular capillaries located?
In the Bowman's capsule
45
Diagram showing the overall structure of the Bowman's capsule and the glomerulus
46
What is the glomerulus?
A knot of intertwined capillaries which is enveloped by podocytes.
47
What are podocytes?
These support the capillaries and regulate the filtration process.
48
Describe the structure of podocytes
- Podocytes are the cells of the inner wall of the Bowman’s capsule.
- They have many extensions which fold around the blood capillary forming a network of filtration slits that hold back the blood cells during ultrafiltration with the help of the glomerular basement membrane.
49
Diagram of a podocyte and capillary
50
Describe the structure of the capillaries enveloped by the podocytes and how this is related to their function
- The capillaries have small window-like openings called fenestrations.
- Capillaries are also covered on the outside by a layer of extracellular material known as the basement membrane, which is mainly composed of glycoproteins.
- This is where ultrafiltration takes place; a process that is driven by the high pressure in the capillaries.
- The fenestrations in the capillary wall allow blood to flow out, however, the basement membrane acts like a sieve during the ultrafiltration process and stops the blood cells and large proteins.
- Thus, white and red blood cells cannot pass through, but small proteins, salts and nutrients can.
51
Why is there unusually high capillary pressure (podocyte)?
- The unusually high capillary pressure (that allows ultrafiltration to occur) is the result of the short, large diameter afferent arterioles conveying blood at high arterial pressure directly to the glomerular capillaries.
- The smaller diameter of the efferent arterioles leaving the glomerulus also helps maintain the pressure by restricting the outflow of blood.
52
Table showing the composition of the blood that enters the glomerulus and the filtrate that flows, via the Bowman's capsule, into the proximal convoluted tubule
53
What causes the transfer of fluid from the glomerulus to the Bowman's capsule?
High blood pressure in the capillaries of the glomerulus
54
Where does ultrafiltration take place in the nephron?
-Glomerulus
-Ultrafiltration takes place in the glomerulus of the nephron as small molecules move from the blood into the Bowman's capsule. Ultrafiltration is facilitated by the high pressure of blood in the glomerulus, the fenestrated nature of capillaries, the basement membrane and the podocytes of the Bowman's capsule.
55
From the Bowman's capsule, the glomerular filtrate flows into the ___
Proximal convoluted tubule.
56
What is the main function of the nephron?
To reabsorb all the important salts and nutrients (such as glucose) that have been filtered out of the plasma.
57
Where does the bulk of all the reabsorption in the kidney take place?
- In the proximal convoluted tubule immediately after the filtrate has left the Bowman's capsule.
- Most of the water in the filtrate is also recovered.
58
Which substances in the filtrate are the only ones that are reabsorbed by active transport?
Out of all the dissolved substances present in the filtrate, only useful substances are reabsorbed by active transport.
59
How are cells of the proximal convoluted tubule adapted for their function?
They have large numbers of mitochondria to provide energy for active transport.
60
The tubule structure has evolved to maximize ___
Reabsorption.
61
Diagram of the proximal convoluted tubule and the reabsorption process
62
Selective reabsorption in the proximal convoluted tubule
Selective reabsorption is the second of the three processes by which blood is filtered and urine is formed
- It involves the reuptake of useful substances from the filtrate and occurs in the convoluted tubules (proximal and distal)
- The majority of selective reabsorption occurs in the proximal convoluted tubule, which extends from the Bowman’s capsule
The proximal convoluted tubule has a microvilli cell lining to increase the surface area for material absorption from the filtrate
- The tubule is a single cell thick and connected by tight junctions, which function to create a thin tubular surface with no gaps
There are also a large number of mitochondria within these tubule cells, as reabsorption involves active transport
- Substances are actively transported across the apical membrane (membrane of tubule cells facing the tubular lumen)
- Substances then passively diffuse across the basolateral membrane (membrane of tubule cells facing the blood)
The tubules reabsorb all glucose, amino acids, vitamins and hormones, along with most of the mineral ions (~80%) and water
- Mineral ions and vitamins are actively transported by protein pumps and carrier proteins respectively
- Glucose and amino acids are co-transported across the apical membrane with sodium (symport)
- Water follows the movement of the mineral ions passively via osmosis
63
What and how much of it is reabsorbed by the end of the proximal convoluted tubule?
By the end of the proximal convoluted tubule, approximately 80% of all the water, glucose and mineral ions have been reabsorbed.
64
What is the main function of the proximal convoluted tubule?
Reabsorbing most of the glucose, mineral ions, and water
65
How are the cells of the proximal convoluted tubule adapted to their function?
They possess microvilli and large numbers of mitochondria
66
Explain the countercurrent system in the loop of Henle
- The loop of Henle makes use of a countercurrent system to achieve maximum reabsorption of water and sodium ions.
- In the descending limb of the loop of Henle, water moves out into the medullary interstitial fluid by osmosis before being reabsorbed into the vasa recta.
- But, because this descending loop is impermeable to sodium ions, the concentration of the filtrate increases as water is lost.
67
What are vasa recta and what is taken into them?
- Blood capillaries that run parallel to the loop of Henle are known as vasa recta.
- Water and ions absorbed from the loop of Henle are taken into the vasa recta.
68
Explain how the ascending limb (loop of Henle) works
- The ascending limb is impermeable to water but permeable to Na +.
- Na + moves out of the filtrate into the interstitial fluid of the medulla.
- The salt remains near the loop of Henle (it is not immediately removed by the blood) and helps to maintain a concentration gradient in the medulla.
- The ultimate absorption of Na + from the interstitial fluid into the vasa recta occurs by active transport.
- The fluid which leaves the loop of Henle is less concentrated than the tissue fluid around it.
69
Osmolarity in the loop of Henle
- Body fluids, such as plasma and interstitial fluids, have an osmolarity of around 300 milliosmoles (mOsm).
- However, as Na + is pumped out of the ascending loop of Henle, the interstitial fluid in the medulla becomes hypertonic, with osmolarity values reaching up to 1200 mOsm.
- This facilitates the reabsorption of water in the descending limb of the loop of Henle.
70
The loop of Henle maintains ___ conditions in the ___.
Hypertonic
Medulla
71
Diagram showing the loop of Henle
72
Why do some animals have longer loops of Henle?
- Some animals living in the desert have longer loops of Henle because this allows for more water reabsorption.
- The length of the loop of Henle is positively correlated with the need for water conservation in animals.
- A consequence of this adaptation is that the medulla in the kidneys of those animals, for example, a gerbil, is much thicker to accommodate the longer loop of Henle.
73
What is the difference between the descending and ascending loop of Henle?
Descending loop of Henle: permeable to water, impermeable to Na +.
Ascending loop of Henle: impermeable to water, permeable to Na +.
74
What is the function of ADH?
Antidiuretic hormone (or ADH, sometimes referred to as vasopressin) regulates water reabsorption in the collecting duct and the distal convoluted tubule.
75
What is ADH secreted by?
By the pituitary gland.
76
What is the function of osmoreceptors in the hypothalamus?
They monitor the solute concentration (and thus indirectly the water concentration) in the blood.
77
What happens if the solute concentration is too high in the blood (i.e not enough water)?
The pituitary secretes ADH, which travels through the bloodstream to the collecting ducts and the distal convoluted tubule.
78
What structures does ADH increase the permeability of and what effect does this have?
- ADH increases the permeability of the collecting ducts and the distal convoluted tubule to water, therefore more water can be reabsorbed and the solute concentration will decrease.
- This, in turn, will make the urine more concentrated and darker in color.
- Once the situation returns to normal, ADH secretion will stop.
- This is an example of control by negative feedback.
79
Diagram summarizing the actions of ADH
80
How does ADH increase the permeability to water?
- By acting on receptors in the membrane of cells in the collecting tubules.
- The binding of ADH to these receptors initiates a series of events that causes aquaporin to move to the surface membrane.
- The aquaporin then allows water molecules to pass through.
81
What are aquaporins?
- Membrane proteins.
- They initiate a series of events that causes vesicles with aquaporins to fuse with the surface membrane.
- The aquaporin then allows water molecules to pass through.
82
What happens to ADH when the blood solute concentration (osmolarity) is back to normal?
- ADH secretion stops and the water channels are removed from the membrane and reform as vesicles.
- The collecting duct is then impermeable to water and the filtrate flowing through it is lost as urine without further water absorption.
83
Diagram of aquaporin insertion in the apical membrane of collecting duct cells
84
When does increased ADH secretion occur?
When sweating-induced dehydration increases plasma osmolarity.
ADH secretion is the result of the osmoreceptors detecting a high solute/low water concentration in the blood. ADH will increase the permeability of the collecting duct and the distal convoluted tubule, thus increasing the reabsorption of water and restoring water balance.
85
Which nephron structure is acted upon by antidiuretic hormone?
Collecting duct
86
What can cause kidney failure?
Diabetes and hypertension (high blood pressure) are primary causes of kidney failure, but untreated urinary tract infections can also lead to kidney problems.
87
What are the two options for kidney failure treatment?
Once the kidney stops functioning or has a very limited capacity for cleansing the blood, two options are available: kidney dialysis (also called hemodialysis) or a kidney transplant.
88
How does hemodialysis (kidney dialysis) work?
It is a process that uses an artificial membrane known as dialysis tubing (found within the dialyser) to remove wastes, such as urea, from the blood as well as to restore the proper balance of electrolytes in the blood and eliminate extra fluid from the body.
89
Describe the structure of the kidney dialyzer
- It is made up of two parts, one for your blood and one for a washing fluid called dialysate.
- The dialysis tube is a thin membrane that separates these two parts.
90
What is kept in the blood and what is removed during hemodialysis?
- Blood cells, protein and other important molecules remain in your blood because they are too big to pass through the membrane.
- Smaller waste products in the blood, such as urea, creatinine, potassium and extra fluid, pass through the membrane and are washed away in the dialysate.
91
Diagram of a kidney dialysis machine
92
Why are kidney transplants a difficult option for treatment of kidney failure?
- The alternative, unfortunately only available in richer nations to a select group of patients, is a kidney transplant.
- Aside from finding a suitable donor, the danger of tissue rejection remains.
- In any case, recipients of a kidney transplant need to take immunosuppressant drugs for the rest of their lives.
93
What can urine analysis be used for?
- To detect drug abuse, kidney failure or diabetes.
| - When athletes are tested for drug abuse, test kits using monoclonal antibody techniques are used.
94
Picture of a commercial drug-testing kit for certain opiates using urine analysis
95
How can urine analysis be used to test kidney function?
- Any deviation from the normal values can be detected using a simple test kit requiring strips that are dipped into urine.
- This particular kit tests for the presence of cells and a range of compounds.
- Each indicates a particular disorder of the kidney.
96
Give examples of what urine analysis results could show about kidney function
- For example, too much glucose would indicate that the patient may have diabetes.
- The presence of blood or leucocytes may indicate an infection or a kidney tumor.
- If your urine contains too much protein, the ultrafiltration process may be failing, which could be an indication of advanced and prolonged hypertension.
97
What can microscopic analysis of urine samples be used for?
- It can be used to reveal the presence of certain blood cells.
- Erythrocytes in the urine can indicate a severe infection or a tumor.
98
What is the presence of leucocytes in the urine most likely to be an indication of?
A urinary tract or kidney infection
99
After carrying out a urinary test, it was found that a person has excessive levels of glucose in her urine.
Name the disease that she is likely to suffer from.
Diabetes
100
Give an overview of the excretion of nitrogenous waste in insects
- Just like other animals, insects metabolize proteins and produce nitrogenous waste that needs to be excreted.
- All arthropods (phylum to which the insects belong) have hemolymph, a fluid that combines characteristics of blood and interstitial fluid.
- Their internal organs are bathed in this hemolymph.
101
What is hemolymph?
A fluid that combines characteristics of blood and interstitial fluid.
102
What structures do insects lack and how do they make up for this?
- Insects lack a closed circulatory system and a kidney, or other organ that could cleanse the circulating hemolymph.
- Instead, insects rely on tubules that branch off from their hind gut.
- These form the Malpighian tubule system, which consists of branching tubules extending from the alimentary canal.
- The tubules absorb solutes, water, and waste from the surrounding hemolymph.
103
What is the function of the Malpighian tubule system in insects?
It carries out osmoregulation and removal of nitrogenous wastes.
104
Diagram of the Malpighian tubules and their connection to the gut within an insect's body
105
Explain how reabsorption and excretion happen in insects
- The hind gut reabsorbs most of the water and mineral salts.
- Insects convert ammonia into uric acid, which is insoluble in water and is excreted as semisolid in their feces.
- The formation of uric acid instead of urea is a successful adaptation to water conservation in a terrestrial environment because less water is lost during its excretion.
106
The osmoregulatory/excretory system of an insect is based on the operation of ___
Malpighian tubules
107
In insects, nitrogenous wastes are mainly excreted in the form of ___
Uric acid
