Excretion Flashcards
define excretion
process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body
examples of waste produces
carbon dioxide from lungs / urine made in kidneys
Nitrogenous waste (ammonia, urea and uric acid)
Bile pigments (produced during the breakdown of haemoglobin)
source of metabolic waste + effect on body if allowed to accumulate
carbon dioxide
source of metabolic waste + effect on body if allowed to accumulate
ammonia
source of metabolic waste + effect on body if allowed to accumulate
urea
source of metabolic waste + effect on body if allowed to accumulate
bile pigments
source of metabolic waste + effect on body if allowed to accumulate
uric acid
where is the liver
below diaphragm
how much blood is received by the liver
rich blood supply – 1dm3 of blood per minute
describe the blood flow through the liver
receives oxygenated blood from the heart via the hepatic artery -
receives deoxygenated blood from the digestive system via the hepatic portal vein
deoxygenated blood leaves the liver via hepatic vein
what is the purpose of the hepatic portal vein
allows the liver to absorb/metabolise nutrients from small intestine / digestion
what is connected to the liver
the gall bladder via the bile duct
what is stored in the gall bladder + its purpose
bile salts (that help to digest fats) a
bile pigments (a waste product from the breakdown of haemoglobin)
all make up bile
where does the bile go after being stored in the gall bladder
bile is then released into the duodenum via the bile duct
how many lobules does the liver have and how are they separated
4
separated from each other by connective tissue
what is a hepatocyte
The main liver cells which are highly metabolically active which divide and replicate
describe the appearance of a hepatocyte
uniform in appearance
large nuclei
prominent golgi apparatus
describe the internal structure of the liver
liver has lobes (right, left) + lobules with hepatocytes arranged radially.
Blood from hepatic artery and portal vein mixes in sinusoids.
Bile canaliculi collect bile, which flows through ducts to the common hepatic duct.
Connective tissue provides structural support.
Central veins drain blood at the lobule center - hepatic vein
gallbladder stores concentrated bile.
what are sinusoids
Spaces between hepatocytes where blood from the hepatic artery and portal vein mixes to increase the oxygen content
allowing to remain active.
what are kupffer cells
Like macrophages,
ingest foreign particles to protect the liver from disease.
Found in sinusoids.
what ar Canaliculi
Spaces in the liver where bile is secreted
from the canaliculi, the bile drains into ductules which transport it to the gall bladder
what is the hepatic artery
Artery which supplies oxygenated blood
what is the hepatic portal vein
Vein which supplies blood rich with digestive products for metabolism.
what is the hepatic vein
Vein which removes deoxygenated blood.
what is the gall bladder
A sac in which bile is stored before being released into the small intestine.
what is the falciform ligmanet
Ligament which separates the left and right lobes of the liver.
what is the portal triad
Between each hepatocyte is a triad of portal veins, arteries and bile ducts
drain into or out of the central vein of a hepatocyte to transfer substances via diffusion
how are sinusoids adapted for exchange
Walls more porous then capillaries
No basement membrane
Wider – slowing blood down
All so in close contact with surrounding hepatocytes
state the functions of the liver - 8
storage of glycogen
formation of urea
deamination
transamination
detoxification
synthesis of phospholipids
bile production
metabolism of RBC’s
what is transamination
Conversion of one amino acid into an other
what does bile consists of
water
electrolytes (bile salts / bicarbonate)
phospholipids
bile pigments – biliverdin + bilirubin
whats the purpose of bile
emulsify large fat globules into smaller droplets
has bicarbonate – neutralises stomach
how does the liver metabolise red blood cells
Broken into haem + globin
Haem– broken into biliverdin
Biliverdin reduced into bilirubin
Becomes water soluble in hepatocytes
Excreted into bile
what is glycogenesis
make glycogen from glucose
where does glycogenesis occur
in the liver and muscles
what is glycogenolysis
breakdown of glycogen into glucose molecules
where does glycogenesis occur
liver and muscles
what is gluconeogenesis
synthesis of glucose from non-carbohydrate precursors
such as amino acids and glycerol
where does gluconeogenesis occur
liver
2 stages of forming urea
deamination
ornithine cycle
how are amino acids deaminated
The amino group (-NH2) of an amino acid is removed, together with an extra hydrogen atom
These combine to form ammonia (NH3)
forms ammonium ions (NH₄⁺) in the cytoplasm
remaining keto acid
purpose of the keto acid after deamination
enter krebs cycle
converted to glucose / glycogen
why is the ornithine cycle important
Ammonia – very toxic / very soluble – dangerous when accumulates
Must be converted into urea
describe the ornithine cycle
what is the overall equation for the ornithine cycle
what happens to the urea formed
diffuses through the phospholipid bilayer of the membranes of the hepatocytes
then transported to the kidneys dissolved in the blood plasma
examples of things detoxified in the liver
Alcohol
Artificial chemicals – paracetamol
Lactic acid
Hormones e.g insulin
Hydrogen peroxide
where does detoxification of alcohol occur
occurs in surface of SER
explain how the detoxification of alcohol occurs
- ethanol is oxidised into ethanal by ethanol dehydrogenase
- hydrogen lost reduces NAD into NADH
- ethanal is oxidised into ethanoate by ethanal dehydrogenase
- hydrogen lost reduces NAD into NADH
what happens to the ethanoate produced from the detoxification of alcohol
ethanoate added to CoA to form acetyl CoA = used in krebs cycle
how can excessive alcohol intake lead to cirrhosis
NAD is used to detoxify alcohol instead of breaking down fatty acids, which are stored as lipids in hepatocytes.
stored fat reduces the ability of the hepatocytes to carry out their functions
eventually lead to severe problems = scarring (fibrosis) of the liver
what is lactate
end product of anaerobic respiration
lactate is metabolised by the liver - what is it converted into
pyruvate
label the liver cells
words to describe the kidney
osmoregulatory
excretory
describe the flow of blood / urine in the kidney
oxygenated blood enters kidney via afferent arteriole from renal vein
passes through the nephron
leaves via efferent arteriole + renal vein
ureter carries urine from the collecting ducts to the bladder
urethra releases urine outside of body
describe the structure of the kidney
surrounded by capsule
has three main areas - cortex / medulla / renal pelvis
functional unit - nephron
describe the cortex
what does it contain / its colour + why
contains glomerulus / bowman’s capsule / PCR / DCT
dark layer
very dense capillary network carrying blood from renal artery to nephrons
describe the medulla
what does it contain / its colour + why
lighter
loop of Henle + collecting ducts
what is the renal pelvis
where the ureter joins kidney
label this diagram of the kidney
describe blood flow through nephron
each glomerulus supplied with blood from afferent arteriole
carries blood from renal artery + leaves through efferent arteriole
then through rest of nephron and then into renal vein
what is the GFR of humans
125 ml per minute = 180L per day
how much urine do humans produce a day
1.5 L per day
what is the glomerulus
knot of arterioles / capillaries in the nephron
why is the glomerulus high pressure
afferent arteriole wider than efferent arteriole
state how is the blood ultrafiltrated
through the 3 part fliter
what are the parts of the 3 part filter
Endothelium of capillary
Basement membrane
epithelium of bowman’s capsule
how does the endothelium of a capillary act as a filter
fenestrated
perforated by thousands of tiny membrane-lined circular holes
how does the basement membrane act as a filter
negatively charged to repel solutes
e.g – plasma proteins may get through endothelium of capillaries but repelled
how does the epithelium of the bowman’s capsule act as a filter
podocytes – specialised cells
pedicels - foot-like extensions from surface of cell + wrap around capillaries
Fit loosely together leaving filtration slits – 25nm wide
Filtered fluids pass through slits
what are the main substances in glomerular filtrate
amino acids, water, glucose, urea and inorganic ions (mainly Na+, K+ and Cl-)
NOT RBC / WBC / platelets
how is the proximal convoluted tubule adapted for selective reabsorption
microvilli - increases SA
many co-transporter proteins - transport specific solute across
many mitochondria - provide energy for sodium potassium pump
cells tightly packed together - no fluid can pass between cells
what is the basal membrane
part of PCT epithelial cell closest to capillaries
what is the luminal membrane
part of PCT epithelial cell closest to lumen of PCT
how does selective reabsorption occur in the PCT
Sodium-potassium pumps – actively pump sodium ions out of epithelial cell through into capillaries
These ions carried away
Lowers concentration of sodium ions inside epithelial cells
Different ions diffuse down conc gradient from filtrate into PCT epithelial cells – like transpiration stream
BUT – ions – cant diffuse freely – co-transporter proteins on membrane = bring amino acids / glucose into epithelial cells
inside the epithelial cells = solutes diffuse down their conc gradients = using transport proteins in the basal membranes into the blood
molecules reabsorbed from filtrate to blood in PCT
ALL glucose
Amino acids / vitamins / inorganic ions / urea
water
where does water reabsorption occur
along entirety of nephron but mainly DCT / loop of Henle / collecting ducts
whats the purpose of the loop of henle
allows us to produce urine more concentrated than blood
whats the main feature of the loop of henle
counter current system
what is the ascending limb permeable / impermeable to
permeable to ions BUT impermeable to water
what is the descending limb permeable / impermeable to
impermeable to ions – no active transport
permeable to water
describe selective reabsorption in the loop of henle
filtrate entering descending from PCT – isotonic with blood
top of the ascending limb = sodium ions are actively pumped into the medulla/ capillaries
bottom of ascending limb = ions leave via diffusion
lowers the water potential of the medulla
water moves out of the nephron by osmosis from the descending limb
As water moves out of the nephron = filtrate becomes more concentrated.
Fluid that reaches bend = very conc + hypertonic to blood
causes sodium ions to move out of the nephron at the bottom of the ascending limb down conc gradient by diffusion
lowers the water potential of the medulla even further, causing water to move out of the DCT. + collecting duct by osmosis.
Water that has moved into the medulla eventually moves into the capillary.
Sodium ions move back into the loop of Henle – conc gradient = increases conc of loop of Henle = cycle repeats
quickly summarise selective reabsorption in loop of henle
Sodium ions out of ascending
Lowers water potential in medulla
Water out of descending
Lowers water potential in filtrate
So more sodium ions out of ascending
Lowers water potential in medulla even further
Water moved out of DCT // collecting ducts
what happens to the DCT if water potential is too high
ions actively pumped out DCT down electrochemical gradient
Balances pH
how is water gained + lost
Gained – food / drink / metabolism
Lost – urine / sweat / water vapour / faeces
how does the body detect a fall in water potential
Osmoreceptors = hypothalamus – monitor water potential
When too low = cells lose water by osmosis + shrink = stimulating neurosecretory cells
Cell body of neurosecretory cells = make ADH and is stored in pituitary glands
When needed = action potentials sent down + pituitary gland release ADH
where is ADH made + stored
Made in hypothalamus + stored / released from pituitary
what is the overall effect of ADH
Causes luminal membranes to be more permeable
how does ADH make the
Collecting ducts have vesicles = with aquaporins in membranes
ADH molecules bind to receptor proteins
Activates cAMP as secondary messenger
leads to phosphorylation of aquaporin molecules
vesicles (with aquaporin containing membranes) fuse with luminal membrane
Increases permeability of membrane to water
More ADH = more channels
how does water leave the collecting duct
water molecules move from the collecting duct (high water potential)
through the aquaporins
into the tissue fluid and blood plasma in the medulla (low water potential)
effects of kidney failure
Urea / water / salts / toxins retained not excreted
Less blood filtered by glomerulus = GFR decreases
leads to build up of toxins in blood
Electrolyte balance disrupted
whats the significance of electrolyte balance being disrupted due to kidney failure
Excess k+ interferes with the resting membrane potential of cells
Elevated k+ cause depolarization of cardiac cell membranes
normal cardiac action potential is disrupted = leading to arrhythmias
what is creatinine
metabolic waste product from breakdown of muscle tissue
what is GFR
amount of blood filtered per unit of time by the kidney’s glomerulus into the Bowman’s capsule
relationship between creatinine and GFR
if impaired kidney – level of creatine in blood increases
as GFR decreases, blood creatinine rise – inversely relationship
state two treatments for kidney failure
renal dialysis
kidney transplant
what is dialysis + whats its purpose
separation of small + large molecules using partially permeable membrane
toxins / metabolic waste removed from the blood by diffusion
two types of dialysis
haemodialysis
peritoneal dialysis
what is in the dialysate + relative concentrations for haemodialysis
electrolyte / pH / glucose balance – 2.5% balance similar to blood
no waste products / NO UREA
describe the process of haemodialysis
connected to machine via fistula
heparin + citrate added
blood flows through machine with partially permeable membrane
in machine – counter current
no net movement of glucose
ion content in dialysate same as blood -movement only occurs where there is an imbalance
net movement of urea out of blood
dialysate continuously refreshed to maintain conc gradient
why is heparin added to blood in heamodialysis
it is an anticoagulant (blood thinner) = prevents the formation of blood clots
why is citrate added to blood in heamodialysis
prevent calcium-mediated clotting
describe the counter current system in heamodialysis and why is it significant
Blood and dialysate flow in opposite directions through adjacent tubes
creates a concentration gradient along the entire length of the dialyser
maximises the concentration difference between the blood and the dialysate,
efficient diffusion of solutes across the semipermeable membrane
whats the significance of having ion / glucose present in the dialysate in the same concentrations as that in the blood
glucose conc same as blood – no net movement out of blood
ion same as blood – movement only occurs where there is an imbalance = if the blood is too low in salts, they will diffuse into the blood; if the blood is too high in salts, they will diffuse out of the blood
disadvantages of heamodialysis
in hospital – closely monitored
performed three times a week
vascular access / fistula needed – complications can arise based off this surgery
limited mobility in sessions
blood pressure complications due to rapid removal of fluid
what is the peritoneum
a thin membrane that lines the walls of the abdominal cavity and covers the organs within it
describe the process of peritoneal dialysis
catheter surgically inserted into the patient’s abdomen
One end of the catheter remains outside the body
patient introduces the dialysis solution into the abdominal cavity through the catheter
peritoneum acts as a natural partially permeable membrane.
Waste products - urea /creatinine - diffuse from the blood vessels in the peritoneum into the dialysis solution
Osmosis occurs - excess fluid in the blood also moves into the dialysis solution as conc gradient of solutes.
what is the dwell period
in peritoneal dialysis the dialysis solution remains in the abdominal cavity for a specified period
during which the exchange of waste products and fluids occurs.
advantages of peritoneal dialysis
Home-based
No vascular access – less risk of infection
Continuous therapy – more stable waste / more gradual removal – less fluctuations in blood pressure
disadvantages of peritoneal dialysis
- Less efficient than haemodialysis
(lower surface area for exchange– less diffusion + slower blood flow rate)
risk of infection – peritonitis
damage peritoneal membrane
replace every few hours
advantages of kidney transplant
improves quality of life
no need to control diet so religiously
no more dialysis
disadvantages of kidney transplant
risk of rejection can be reduced NOT ELIMINATED by tissue typing – matching blood antigens
immunosuppressants – any surgery with general anaesthetic is high risk
limited donor organs
should there be glucose in the urine
no
all glucose in GF should be reabsorbed in PCT
what do proteins in urine indicate
blood pressure too high
kidney infection
damage to the 3 part filtrate
state how is urine used to test for pregnancy
site of developing placenta produces human chorionic gonadotrophin - hCG
excreted in urine
whats the main feature of pregnancy tests
contain monoclonal antibodies – specific to HCG
what are monoclonal antibodies
antibodies from a single clone of cells + target specific cells
how are monoclonal antibodies made
mouse injected with hCG to make antibody
B cells that make antibody are fused with myeloma cell
Clone of millions are hybridoma cells
Monoclonal antibodies collected + purified
describe the process of how pregnancy tests work
Wick soaked in urine
mobile monoclonal antibodies that have small coloured beads
Only bind to hCG
Forms hCG-antibody complex with coloured beads
Urine reaches first window
Immobilised monoclonal antibodies arranged in line only bind to hCG-antibody complex
Coloured pattern if pregnant
Second window – line of immobilised monoclonal antibodies in pattern that only bind to mobile antibodies - don’t have to be bound to hCG
Coloured line forms regardless if test is positive
what is rennin + what is its effects
enzyme produced + secreted by kidney
vasoconstriction
increased ADH
increased aldosterone
activates thirst response
what is Erythropoietin
secreted by kidney when low oxygen
travels to to bone marrow
results in the production of more RBC
what does raised Erythropoietin levels show
cancer uses up 02 / chronic lung disease
kidney think lack of 02 in body
so more epo released
