Hormones & Excretion (kidney) Flashcards
1
Q
what is the definition of homeostasis?
A
The maintenance of a constant internal environment within normal set limits despite external changes.
2
Q
what examples are there of internal conditions which must be kept constant?
A
- blood pressure
- blood glucose concentration
- body temperature
- blood salt concentration
- carbon dioxide concentration
3
Q
To maintain a constant internal environment what must occur?
A
- detecting a change (receptor)
- signal changes to other cells (nerves/hormones)
- respond to change (effector)
4
Q
what order does homeostasis act in?
A
stimulus - receptor - cell signalling - effector - response
5
Q
what is negative feedback?
A
A process that responds to changes in the environment by returning the internal environment back to its steady state
6
Q
what does positive feedback lead to?
A
usually harmful and WILL NOT lead to homeostasis
7
Q
what is the order for negative feedback?
A
optimum condition - change away from optimum - receptor detects change - cell signalling to effector - effector reacts to reverse change - return to optimum condition
8
Q
what is the order for positive feedback?
A
optimum condition- change away from optimum - receptor detects change - cell signalling to effector - effector reacts to increase change - change away from optimum
9
Q
what is glucose used for? and what is the normal blood glucose level?
A
- Glucose is the main respiratory substrate for all cells (and the only one for brain cells)
- Normal blood glucose level is 80 – 120mg per 100cm3
10
Q
what happens if there is too much blood glucose in the body?
A
lowers water potential of blood which causes dehydration
11
Q
what happens if there is too little blood glucose in the body?
A
cell deprived of energy and die
12
Q
what are the sources of blood glucose?
A
- directly from the diet
- breakdown of glycogen stores in the muscle & liver
- produce new glucose from glycerol and amino acids.
13
Q
what is glycogenolysis?
A
Breakdown of glycogen stores in the muscle & liver
14
Q
what is gluconeogenesis?
A
Produce new glucose from glycerol and amino acids
15
Q
what are the endocrine glands and what do they do?
A
Endocrine glands are ductless glands that secrete hormones directly into the blood.
16
Q
what is the endocrine gland found in the pancreas?
A
group of cells called the islet of langerhans
17
Q
what does the islet of langerhans do?
A
secretes hormones which control blood glucose levels by negative feedback
18
Q
what is a hormone?
A
A hormone is a regulating chemical produced by an endocrine gland and is carried in the blood to the cells/tissues/organs on which it acts – target cells
19
Q
what does a hormone bind to?
A
it binds to receptors on the surface of target cells
20
Q
what are the following characteristics of hormones?
A
- small molecules
- effective in small concentrations
- transported in the blood
- produced by endocrine glands
- short lifespan
- often proteins but can be steroids
21
Q
what type of cell do the islets of lanerghans contain?
A
- a cells which secrete the hormone glucagon.
- b cells which secrete the hormone insulin
22
Q
what does insulin do?
A
decreases the blood glucose concentration
23
Q
what does glucagon do?
A
increase the blood glucose concentration
24
Q
what happens when the blood glucose level is high?
A
a cells stop secreting glucagon, B cells start to secrete insulin
25
how does insulin lower blood glucose concentration?
- Increases absorption of glucose from blood into cells
- Increases rate of respiration of glucose
- Increases the rate at which glucose is converted to glycogen in the liver and muscles - glycogenesis
- Increases rate of conversion of glucose to fat
26
what happens when blood glucose level is low?
- b cells stop secreting insulin, a cells start to secrete glucagon
27
how does glucagon increase blood glucose concentrations?
Increases glycogenolysis
- Increases respiration of fatty acids instead of glucose
- Increases gluconeogenesis
- Glucagon only affects liver cells as they are the only cells that have receptors which will bind to glucagon
28
what is the reaction for glycogenolysis?
glycogen --> glucose
29
what is the reaction for gluconeogenesis?
amino acids/glycerol ---> glucose
30
what is excretion?
The removal of unwanted toxic waste products from metabolism
31
what is excreted?
any substance produced in excess during metabolic reactions
32
what are two products produced in very large quantities?
- carbon dioxide
- nitrogenous compound called urea
33
how is nitrogenous waste products produced?
from the break down of:
- proteins
- nucleic acids
34
how soluble is:
- ammonia
- urea
- uric acid
ammonia - very soluble
urea - fairly soluble
uric acid - almost insoluble
35
how toxic is:
- ammonia
- urea
- uric acid
ammonia - very toxic
urea - fairly toxic
uric acid - not very toxic
36
what excretes ammonia?
freshwater fish
37
what excretes urea?
mammals
38
what excretes uric acid?
birds
39
where is urea produced and why is it produced?
produced in the liver from excess amino acids.
40
where does the urea go once it has been produced in the liver?
to the kidneys in the blood plasma
41
where does the urea go once its in the blood plasma?
it is removed from the blood dissolved in water and excreted as urine
42
what is deamination?
The process by which urea is made from excess amino acids
43
how does deamination work?
the amino acid group from amino acids is removed and with the addition of another hydrogen is turned into ammonia.
44
how is urea made from ammonia?
ammonia combines with carbon dioxide to produce urea which is less soluble and less toxic in a metabolic process.
45
what is the ornithine process?
combination of urea and carbon dioxide
46
Why are excess amino acids not excreted?
Contain almost as much energy as carbohydrates – would be wasteful
47
What happens to the rest of the amino acid after the amine group has been removed?
Remaining keto acid used in respiration to release its energy or converted to carbohydrate/fat for storage
48
Ammonia and uric acid are nitrogenous waste products. Ammonia is very soluble and toxic and uric acid is almost insoluble, not very toxic and light. Explain why ammonia can be excreted by fish and uric acid by birds.
Ammonia excreted by fish as they live in water so this dilutes the ammonia as it is excreted
Uric acid produced by birds is light. Also as it is fairly non toxic, this means it can build up in eggs without damaging developing embryo
49
how much does the kidney weigh and what is the length?
11cm long and weights 150g
50
how many kidneys do mammals have, where are they and what are they surrounded by?
Mammals have 2 kidneys one on either side of the spinal cord. They are usually surrounded by fat protection
51
what does the renal vein do?
returns blood to the heart via the vena cava
52
what is the fibrous capsule in the kidney?
protective outer membrane
53
what is the cortex in the kidney?
outer region containing Bowman's capsule and convoluted tubules
54
what is the medulla in the kidneys?
inner region made of the loops of hence and collecting ducts
55
what is the renal pelvis in the kidneys?
collects urine and funnels it to the ureter
56
what is the ureter in the kidneys?
tube that carries urine to the bladder
57
what is the nephron in the kindeys?
basic structure and functional units of the kidney
58
what is the renal artery in the kidneys?
Supplies kidney with oxygenated blood from the aorta
59
what is the renal (bowman's capsule)?
- this is the start of the nephron and is cup shaped
- found on the cortex of the kidney
- contains a mass of blood capillaries called the glomerulus
- lined by specialised cells called podocytes
60
what are the podocytes?
Cells with finger-like projections that line the renal capsule and have gaps between them. They have an important role in filtering small molecules out of the blood
61
what is the proximal convoluted tubule?
- a twisted region of the nephron found after the renal capsule in the cortex
- surrounded by a network of capillaries
- Walls are made of cuboidal epithelial cells with microvilli to increase the surface area
62
what is the loop of hence?
- Long hairpin loop found after the proximal convoluted tubule that extends into the medulla (descending loop) and back up to the cortex (ascending loop)
- Surrounded by a dense network of capillaries
62
what is the distal convoluted tubule?
- Twisted region of the nephron found after the loop of Henle in the cortex of the kidney
- Surrounded by a dense network of capillaries
- The distal convoluted tubule then joins a collecting duct
63
what is the collecting duct?
- extends from the cortex into the medulla
- connected to many distal convoluted tubules
- carries urine to the pelvis
64
what brings blood to the nephron from the renal artery?
the afferent arteriole
65
what does the afferent arteriole do next?
It then splits to form a network of capillaries called the glomerulus.
66
what do the glomerulus do next?
These capillaries then recombine to form the efferent arteriole which takes blood away from the renal capsule to the dense network of capillaries that surround the proximal convoluted tubule , loop of Henle and distal convoluted tubule
67
what do the capillaries eventually do to the nephron?
The capillaries eventually merge together and return blood from the nephron to the renal vein
68
what is difference between the afferent arteriole and efferent arteriole?
the afferent arteriole has a wider diameter
69
why does the afferent arteriole have a wider diameter?
makes sure the blood pressure inside the glomerulus is high which is important in the process of ultrafiltration
70
what is the role of the kidney?
- Regulate the composition of the blood
- Maintain water volume
- Remove urea
- Maintain mineral ion concentration
71
what are the two process to make urine?
- ultrafiltration
- selective reabsorption
72
what is ultrafiltration?
Small molecules (including urea) are filtered out of the blood into the renal/Bowman’s capsule.
This filtrate then flows along the nephrons
73
what do the gaps between the endothelial cells lining mean?
Gaps (more/larger) between endothelial cells lining the glomerulus capillaries and gaps between the podocytes allow molecules to leave the blood.
74
what do the gaps do?
These gaps reduce resistance to movement
75
what is a negative to the basement membrane?
However, the basement membrane will only allow molecules with a mass less than 69 000 kDa across into the lumen of the renal/Bowman’s capsule so it acts as a filter.
76
what are the purpose of the podocytes?
This allows molecules to pass through the gaps into the lumen rather than through the cells themselves which reduces the resistance to movement.
77
what is the glomerular filtrate rate?
The glomerular filtrate rate is the rate of movement of fluid from the blood in the glomerulus into the renal capsule
It is usually 125cm3min-1
78
What makes the glomerular filtration rate so fast?
water potential
- Water moves from an area of higher y to lower water potential y
hydrostatic pressure
- Higher hydrostatic pressure (in glomerulus) forces blood plasma out through the pores in the capillaries
solute concentration in capillaries
- This will decrease water potential
79
why is there a high hydrostatic pressure in the glomerulus?
There is a high hydrostatic pressure in the glomerulus because the lumen of the afferent arteriole is wider than the lumen of the efferent arteriole.
This means the water potential in the glomerulus is higher than the renal capsule.
80
Why can’t plasma proteins leave the blood in the glomerulus?
plasma proteins are too large to leave the blood in the glomerulus then this means the glomerulus has a higher solute concentration than the renal capsule (which acts to lower the water potential in the glomerulus)
81
What effect will this have on the water potential in the glomerulus?
Overall the hydrostatic pressure outweighs the solute concentration so the water potential in the glomerulus is higher than the renal capsule so water moves by osmosis from the blood in the glomerulus into the renal capsule.
82
what is selective reabsorption?
- Many substances in the filtrate need to be kept in the body so are reabsorbed back into the blood as the filtrate passes through the nephron
- As only certain molecules are reabsorbed the process is called selective reabsorption
- Most reabsorption takes place in the proximal convoluted tubule
83
what are reabsorbed into the blood in the PCT?
All glucose
Amino acids
Vitamins
Na+
Cl-
65% water absorption
50% urea
84
The cells of the wall of the proximal convoluted tubule have a low sodium ion (Na+) concentration.
Explain what happens to these Na+
Na+ moves into cells lining PCT by facilitated diffusion
85
2. Why do cells lining the walls of the proximal convoluted tubule have lots of mitochondria?
active transport is needed, so energy needed from mitochondria. site of aerobic respiration
86
Explain how Na+ from the filtrate in the lumen of proximal convoluted tubule diffuse into cells of the
wall of the proximal convoluted tubule. What else is transported with Na+.
active transport.
Glucose and amino acids cotransported
87
what is the function of the loop of henle?
- Create a high concentration of Na + and Cl- in the tissue fluid of the medulla
- Allows water to be reabsorbed from the descending limb and from the collecting duct which makes urine more concentrated
88
what is the descending limb of the loop of henle permeable to?
Descending limb permeable to both sodium ions and water
89
what is the ascending limb of the loop of henle permeable to?
Ascending limb permeable to sodium ions and impermeable to water
90
what is actively transported out of the ascending limb in the loop of henle and what does It do?
Na+ and Cl- are actively transported out of the ascending limb
This gives the tissue fluid of the medulla a lower water potential
91
what movesout of the descending limb in the loop of henle and what does It do?
Water moves out of the descending limb by osmosis (and passes into surrounding blood capillaries)
This increases the conc of Na+ and Cl- inside the descending limb
92
what is increased in the descending limb of the loop of Henle and why?
Na+ and Cl- conc inside the descending limb is further increased as they diffuse into the descending limb from medulla tissue fluid
93
what does the loop of Henle act as?
The loop acts as a counter current multiplier – fluid runs in opposite directions in the loop of Henle to increase the exchange of materials
94
how does water leave the Loop of Henle?
Water also leaves the collecting duct by osmosis which further concentrates the urine
95
what is the counter-current mechanism?
- The 2 limbs enables the maximum concentration to be built up inside and outside the loop – always a lower water potential in the tissue fluid of the medulla for the whole length of the LoH
- The longer the loop of Henle, the more concentrated the fluid inside becomes.
96
what is the role of the kidneys in osmoregulation and where does it occur?
Water is reabsorbed in the following parts of the kidney:
- Proximal Convoluted Tubule
- Loop of Henle
- Distal Convoluted Tubule
- Collecting Duct
97
what is osmoregulation?
The control of the water content of the fluids in the body
98
Water Reabsorption in the Distal Convoluted Tubule
- First part behaves in the same way as the loop of Henle
- Second part behaves in the same way as the collecting duct – which will be the focus of this powerpoint
99
Water Reabsorption in the Collecting Duct
- Homeostatic mechanism which uses a negative feedback mechanism
- Receptors monitors water potential of the blood
- Effector does something to return to the water potential to within normal set limits
100
what does dehydration mean?
Dehydration means the water potential of your blood is too low so more water is reabsorbed into the blood so the urine is more concentrated
101
what happens if there is a lot of water in the blood?
When there is a lot of water in the blood, less is reabsorbed and your urine is more dilute
102
how is osmoregulation controlled?
- Osmoreceptors in the hypothalamus of the brain detect low water potential of blood
- This stimulates neurosecretory cells in the hypothalamus to release a hormone called ADH (antidiuretic hormone)
- ADH moves to the posterior pituitary gland and is released into the blood
103
how is water content controlled?
ADH binds to receptors in the plasma membrane of cells lining the collecting duct
This activates a phosphorylase enzyme which causes vesicles containing water permeable channels (aquaporins) to fuse with the plasma membrane
This makes the cells lining the collecting duct more permeable to water
Water moves out of the collecting duct by osmosis down a water potential gradient into blood vessels
This makes the urine more concentrated
As the water content/potential returns to normal set limits ADH release is switched off
104
how is water content controlled - summary?
Dehydration
|
ADH release
|
Increased water reabsorption in collecting duct
|
Concentrated urine
105
what is the stimulus in negative feedback - osmoregulation?
water potential of blood
106
what is the receptor in negative feedback - osmoregulation?
osmoreceptors in hypothalamus of brain
107
what is the effector in negative feedback - osmoregulation?
pituitary gland
108
what is kinder dialysis?
- When the kidneys do not function properly, dialysis must be performed artificially. Without this artificial kidney dialysis, toxic wastes build up in the blood and tissues, and cannot be filtered out by the failing kidneys.
- Carbon dioxide and urea (a waste product from protein metabolism), must be removed from the blood or they will accumulate and interfere with normal metabolic processes.
109
what does dialysis work on?
works on the principle of diffusion of solutes across semi permeable membrane.
Blood flows by one side of this, and a dialysis solution or fluid flows by the opposite side. Smaller solutes pass through the membrane
110
the concentration of undesired solutes are high in the blood...
but low or absent in the dialysissolution and constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this side of the membrane. The dialysis solution has levels of minerals like sodium and chlorine that are similar to their natural concentration in healthy blood.
111
what is removed in dialysis?
waste products and excess ions pass from the blood and into the dialysis fluid
112
what is haemodialysis?
MOST COMMON
A dialysis machine and fluid is used as seen in the previous slides.
Patient is fitted with a fistula and blood flows from this to dialysis machine.
Blood returns via a vein to patient
113
what is peritoneal dialysis?
COMMON
Takes advantage of the peritoneum membrane surrounding the intestine being a natural semi-permeable membrane.
Dialysis fluid is introduced to the abdominal cavity, where waste products transfer through the peritoneum membrane into the fluid, thus doing the work normally done by the kidneys. On draining the abdomen, the waste is removed
114
Why does the dialysate flow in the opposite direction to the blood?
Maintain a high concentration gradient across the whole length
115
Why is a large surface area needed?
Increase the rate of diffusion
116
Explain why the dialysing solution is constantly being replaced rather than being recirculated?
To maintain a steep concentration gradient to be able to continually remove waste products by diffusion from the blood
117
Explain why ions such as potassium and sodium, and small molecules such as glucose, do not diffuse rapidly from the blood?
They are present in the dialysis solution at the SAME concentration as in the blood so NO concentration gradient exists so they do NOT diffuse out of the blood
118
Outline how a kidney machine functions as a replacement kidney in case of kidney failure.
- fistula/shunt fitted
- patients blood flows over a filter
- cellulose/detail of filter/size
- dialysate flows opposite side of filter
- cross current/dialysate circulating
- detail of dialysate content
- e.g. identical to blood plasma but no urea, less water
- urea/water diffuses through membrane into dialysate
frequency/number of times a week
118
Why does the urea pass from the blood into the dialysing fluid?
There is a higher concentration of urea in the blood and a lower concentration of urea in the dialysis fluid so urea diffuses DOWN its concentration gradient from the patient’s blood and into the dialysis solution
