3.7 Homeostasis and the kidney Flashcards
(66 cards)
1
Q
What is homeostasis?
A
The maintenance of a constant internal environment
2
Q
What is the internal environment?
A
Includes tissue fluids that bathe cells, supplying nutrients and removing wastes and maintaining glucose concentration, pH, core temperature and solute potential.
3
Q
How can the body be protected by changes in the external environment?
A
by keeping the body fluids at a constant and optimum level protects cells from changes in the external environments.
4
Q
What do I mean when I say the body is kept at a dynamic equilibrium?
A
constant changes occur but a set point is resumed. Homeostasis is the ability to return to that set point.
5
Q
What controls homeostatic responses and how?
A
The endocrine system controls homeostatic responses, with hormones operating by negative feedback.
6
Q
What is negative feedback?
A
A change in the system produces a second change, which reverses the first change.
7
Q
What are the stages in which negative feedback occurs?
A
- Set point (normal state)
2.Input (change to normal state)
3.Receptor (measures the change)
4.Co-ordinator (stores info and used to co-ordinate the effector)
5.Effectors (bring about changes to the system that reverse effect of the input)
6.Output (corrective procedures)
7.Set point (back to normal)
8
Q
what are examples of effectors?
A
muscles and glands
9
Q
Give 2 examples of negative feedback:
A
- If glucose concentration in the plasma increases above a set point, insulin is secreted, reducing the glucose concentration by converting it to glycogen and increasing the rate at which is is respired. If the level falls below the set point, glucagon is secreted, which results in glycogen being converted to glucose.
- If the body’s core temperature falls below the set point, increased respiration generates heat, and constriction of superficial blood vessels allows the body to retain it. if the temp rises above the set point, superficial blood vessels dilate, and heat radiates from the body, reducing its temperature.
10
Q
What is positive feedback?
A
where an effector increases a change i.e movement away from norm causes a further movement away from the norm.
11
Q
Give two examples of postitive feedback:
A
- Oxytocin stimulates the contraction of the uterus at the end of a pregnancy. The contractions stimulate the production of more oxytocin, which increases the contractions.
- When skin is cut, the platelets cut cause a clot, they also send out signalling molecules that attract more platelets forming more clots.
12
Q
What is excretion?
A
removal of wastes made by the body
13
Q
what is excreted in the urine?
A
Urea - amino acid breakdown
Creatinine - muscle tissue breakdown
Uric acid - Nucleic acid breakdown
14
Q
What is excreted in expired air?
A
- CO2
- Water
this happens in respiration
15
Q
what is excreted through the skin?
A
Sweat containing urea
16
Q
What is excreted in faeces?
A
Bile pigments due to haemoglobin breakdown
17
Q
what are the kidneys two main functions?
A
- Excretion - the removal of nitrogenous metabolic waste from the body
- Osmoregulation - the control of the water potential of the body’s fluids (plasma, tissue fluid, lymph) by regulating the water content, and thus the solute concentration.
18
Q
what is osmoregulation?
A
The control of the water potential of the body’s fluids by the regulation of the water content of the body.
19
Q
What is deamination:
A
The removal of an amine group from a molecule. Excess amino acids are deaminated in the liver, and the amine group is converted to urea.
20
Q
What is the structure of the kidney?
A
a tough renal capsule covers each kidney. Each kidney receives blood from a renal artery and returns blood to the general circulation in a renal vein. The blood from the renal artery is filtered in the outer layer, the cortex, at the bowmans or renal capsules. The medulla contains the loop of Henle and the collecting ducts that carry urine to the pelvis. The pelvis empties urine into the ureter and a ureter from each kidney carries urine to the bladder.
21
Q
What are the tube like structures called that you see when observing a kidney under a microscope?
A
Nephrons, there are many to increase SF for exchange
22
Q
What is the route of filtrate in the nephron?
A
The filtrate is made by blood in the glomerulus from the afferent arteriole filtering into the bowman’s capsule, then moving down into the proximal convoluted tubule where selective reabsorption occurs and then travels into the medulla down the loop of Henle where osmoregulation occurs and then back up into the cortex where the the distal convoluted tubule is and then back down into the medulla down the collecting duct and then down to the pelvis and down the ureter to the bladder.
23
Q
Describe the image of this kidney cortex.
A
24
Q
Where does ultrafiltration take place?
A
The Bowman’s Capsule
25
How does the blood first arrive for Ultrafiltration?
Blood arrives in the capillaries of the glomerulus from the AFFERENT ARTERIOLE.
26
Why is the blood pressure high in the afferent arteriole?
- The hearts contraction increases the pressure of arterial blood
- The afferent arterial has a wider diameter than the efferent arteriole
27
How and where does the ultrafiltration happen?
The blood entering the glomerulus is separated from space inside the Bowman's Capsule, called the Bowman's space via three layers;
- The wall of the capillary is a single layer of endothelium cells with pores called FENESTRAE.
- The basement membrane is made up of collagen and glycoproteins. It is a molecular filter and acts as sieve (selective barrier), between the blood and the nephron.
- The wall of the Bowman's capsule is made of squamous epithelial cells called podocytes ( go more in detail in their own card)
28
what are podocytes structure and function?
Podocytes are squamous epithelial cells that make up the wall of the Bowman's capsule. Podocytes contain PEDICELS that wrap around a capillary, pulling it closer to the basement membrane. The gaps between the pedicels are called filtration slits.
29
What is the definition of Ultrafiltration and how does this occur in the nephron?
The definition of ultrafiltration is filtration under high pressure. It occurs in the nephron as the high pressure in the capillaries of the glomerulus forces solutes and water through the fenestrae of the capillaries, through the basement membrane and through the filtration slits between the pedicels.
30
What is forced into the bowman's capsule and thus makes up the glomerular filtrate?
- water
- glucose
- salts (sodium etc)
- urea
- amino acids
31
What remains in blood and cannot make it through the basement membrane and why?
Blood cells, platelets and large proteins such as antibodies remain in the blood as they are too large to pass through (>68,000)
32
Has the blood flowing through the efferent arteriole got a high or low water potential and why?
The blood that flows into the efferent arteriole has a low water potential as much water has been lost and there is a high protein concentration remaining.
33
What is the glomerular filtration rate? And how is it determined?
The rate at which fluid passes from the blood in the glomerular capillaries into the bowman's capsule is called the glomerular filtration rate. It is determined via the different water potentials between the two areas.
34
What equation is used to work out the filtration rate?
Blood volume entering the kidneys x - volume of filtrate produced per minute y = blood volume leaving glomerulus per minute z
%filtered =y/x multiplied by 100
35
What is the definition of selective reabsorption?
The uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream.
36
Why is selective reabsorption necessary?
The glomerular filtrate contains wastes that the body needs to eliminate, but also useful molecules and ions, including glucose, amino acids, sodium ions and chloride ions. Selective reabsorption is the process of by which useful products are reabsorbed back into the blood.
37
Describe briefly the proximal convoluted tubule and what occurs there:
The PCT is the longest and widest part of the nephron. It carries the filtrate away from the bowmans capsule. The blood in the capillaries around the PCT reabsorbs all the glucose and amino acids, some of the urea and most of the water, sodium and chloride ions from the filtrate in the PCT.
38
Describe the structure of the proximal convoluted tubule:
- Large surface area due to how long it is and there are a million nephrons in the kidney
- Cuboidal epithelial cells in its walls. Their surface area is increased by microvilli, about 1 um long, facing the lumen, and invaginations called basal channels in in the surface facing the basement membrane and the capillary.
- Many mitochondrian for active transport.
- A close association with capillaries.
- Tight junctions between the cells of the proximal convoluted tubule epithelium.
39
During selective reabsorption in the proximal convoluted tubule, how are salts reabsorbed back into the blood?
around 70% of salts in the filtrate are reabsorbed back into the blood. Some reabsorption is passive although most is done via active transport by membrane pumps.
40
During selective reabsorption in the proximal convoluted tubule, how are glucose and amino acids reabsorbed back into the blood?
All the glucose and amino acids are reabsorbed via co-transport with sodium ions. A glucose molecule and two sodium ions bind to a transporter protein in the cuboidal epithelial cell membrane. They enter the cell by facilitated diffusion, dissociate from the transporter and diffuse across. Sodium ions are pumped into the capillary ; glucose moves in by facilitated diffusion into the cell, carrying in the glucose.
41
During selective reabsorption in the proximal convoluted tubule, how are water molecules reabsorbed?
About 90% of the water in the glomerular filtrate is reabsorbed to the blood passively, by osmosis, as reabsorbed ions lower the water potential of the blood.
42
During selective reabsorption in the proximal convoluted tubule, how is urea and small proteins reabsorbed?
About 50% of urea and small proteins are reabsorbed back into the blood via diffusion. So much water has been lost in the filtrate that the concentration of urea and small proteins have become high in the filtrate creating a steep gradient that they diffuse down and back into the blood.
43
What could be the reasons for loss of glucose in the urine?
- The pancreas secretes too little insulin (type 1 diabetes)
- Insulin receptors in the surface membrane of livers are damaged thus their response to insulin is reduced (type 2 diabetes)
44
In terms of absorption of water, what is the difference between the PCT and the loop of henle, and the DCT and collecting duct?
The PCT and loop of Henle usually always reabsorb the same amount of water, whereas the DCT and collecting duct will reabsorb depending on the circumstance. E.g more reabsorbed if dehydrated in the DCT and collecting duct
45
How is the walls of the ascending limb of the loop of Henle adapted?
Thick walls that contain mitochondria for active transport of sodium ions and chloride ions into the tissue fluid of the medulla. Also the wall is impermeable to water to keep the tissue fluid salty and thus allowing water molecules to flow out of the descending limb via osmosis.
46
Describe how the water potential changes from the beginning to the end of the loop of Henle:
At the beginning the water potential is very high as the filtrate is mostly made up of water, thus the water moves out of the filtrate via osmosis going down the descending limb. As we go down the descending limb water is lost thus the filtrate becomes more concentrated and water potential is lowering. At the bottom/the hairpin the water potential in the filtrate is at its lowest. This is why the walls of the ascending limb is impermeable to water as otherwise water would move in to the filtrate from the tissue fluid in the medulla. But then due to the active transport of sodium and chloride ions out of the ascending limb, the water potential increases as you go up the ascending limb.
47
Where does water go after osmosing into the tissue fluid in the medulla?
It goes into the VASA RECTA (capillaries surrounding the loop of Henle) via osmosis
48
What is the mechanism of the loop of Henle called and describe it briefly:
It is called the counter-current multiplier.
Because flow of the two limbs in opposite directions (counter-current) and the concentration of solutes is increased (multiplied)
49
Using the structure of the negative feedback cycle, write the cycle in terms of the release of ADH when excess salt is consumed:
1. Set point - Normal water potential
2. Input - salt consumed
3. Receptor - hypothalamus
4. Co-ordinator - hypothalamus
5. Effector - posterior pituitary gland
6. Output - ADH released
7. Water potential rises back to set point
50
What is the antidiuretic hormone (ADH)?
Hormone produced in the hypothalamus and secreted via the posterior pituitary gland. It increases permeability of the cells of the distal convoluted tubule and collecting duct walls to water, increasing water reabsorption.
51
What does ADH do when it is released?
- Increases the permeability of the walls of the distal convoluted tubule and the collecting duct to water.
- More water is reabsorbed from there into the region of high solute concentration, low water potential in the medulla.
- More water is reabsorbed from the medulla into the blood in the vasa recta.
- The water potential of the blood is then restored to normal.
- The then small volume of urine produced is very concentrated.
52
What are aquaporins? spell it
Aquaporins are intrinsic membrane proteins with a pore through which water molecules move.
53
What is the mechanism/route of ADH once its released?
- ADH binds to membrane receptors
- Adenyl cyclase catalyses the production of cyclic AMP, the second messenger.
- Vesicles containing the aquaporins in the cytoplasm move and fuse with the cell membrane.
- Aquaporins are now incorporated into the membrane.
- Water molecules then move in single file through the pores of the aquaporins, down the gradient.
54
What are the most common causes of kidney failure?
- Diabetes can lead to a condition called glomerulosclerosis
- High blood pressure can damage the capillaries and prevent ultrafiltration
- Auto immune disease
- infection
crushing injuries like a car crash
55
What are different ways of treating kidney failure?
- Dietary restriction
- Drugs to reduce blood pressure
- dialysis
- transplantation
56
What occurs in haemodialysis?
Blood is taken from the artery, usually in arm, and run through thousands of long, narrow fibres made of selectively permeable dialysis tubing. The fibres are surrounded by dialysis fluid. The pores of the tubing let molecules in solution out into the dialysis fluid, but not large proteins, blood cells or platelets. The blood and dialysis fluid run through the machine in opposite directions, enhancing diffusion out of the blood via a counter current mechanism. The blood is then returned to a vein. HEPARIN is added to the blood to thin it and stop it clotting. There is a sensor in the dialysis fluid that detects haemoglobin that would diffuse through if red blood cells were damaged.
57
What is transamination?
An enzyme-catalysed reaction that transfers an amino group to an alpha-keto acid, making an amino acid.
58
What is the system of plants making amino acids?
Plant cells combine ammonium ions with alpha-keto glutarate, making the amino acid glutamate; glutamate is converted to any other amino acid by transamination of other alpha-keto acids.
59
Why are plants more efficient than animals at transamination?
As plants synthesise only the amino acids and proteins that they need, so they do not need to excrete nitrogen-containing molecules.
Animals eat protein, and make the molecules they need from its constituent amino acids, they cannot store any the do not need so the excess is deaminated into urea and secreted.
60
What are the three different ways excess amino acids are excreted via different types of animals?
- aquatic organisms excrete ammonia
- birds reptiles and insects excrete uric acid
- mammals urea
61
What are the two types of nephrons called?
- Cortical nephrons (cortex)
- Juxtamedullary nephrons (medulla)
62
What organisms usually have a cortical nephron?
Humans, beavers and muskrats- low chance of being dehydrated
63
What organisms usually have a juxtamedullary nephron?
Australian hopping mice - dry habitat
64
what is the difference between the two types of nephrons?
Juxtamedullary has its glomerulus in the closer to the cortex's boundary with the medulla and has a long loop of henle that goes deep into the medulla.
The cortical nephrons have their glomerulus in the outer cortex and a short loop of henle that just penetrates the medulla.
65
What is metabolic water?
Water produced from the oxidation of food reserves- the kangaroo rat relies entirely on metabolic water.
66
What are behavioural characteristics of desert animals?
Remain underground during the day, living in burrows, which are cool and humid, reducing water loss by evaporation.
