Excretion Flashcards
What is excretion?
Process by which toxic waste products of metabolism/substances in excess of requirement are removed from the body
Example of excretion?
Lungs excrete CO2 (waste product) by gas exhale /exhalation
Kidneys produce urine that contains waste product, urea, in solution
Metabolic waste example and how are thye produced?
CO2- from DECARBOXYLATION of respiratory substrates
Nitrogenous waste - ammonia,urea,uric acid
- ammonia from deamination of excess amino acids
Bile pigments - from breakdown of haemoglobin
Urea - ornithine cycle in liver cells
Uric acid - break down of adenine/guanine (purines) in liver
LIVER PRODUCES ALL THESE EXCRETORY SUBSTANCES EXCEPT CO2
Why is excretion important?
Key process in homeostasis
Important in maintaining metabolism - metabolic waste can have bad consequences if accumilates
Effect on body if metabolic waste products accumulate?
CO2 - cell damage if blood pH falls below normal range (acidosis)
Ammonia- increase cytoplasm pH/interfere with metabolic processes (respiration) /receptors for neurotransmitters in brain
Urea - diffuses into cells DECREASING THEIR WP- can burst
URIC ACID: form crystals in joints- cause GOUT (painful form of arthritis)
BILE PIGEMNTS: turn skin yellow - jaundice
Liver external structure?
Good blood supply :
HEPATIC ARTERY - carry OX BLOOD from heart—> liver
(oxygen used for aerobic respiration, fuel metabolic activity in liver cells)
HEPATIC PORTAL VEIN - blood from digestive system —> liver via this vein
(allows liver to absorb/metabolise nutrients absorbed into blood in SI)
HEPATIC VEIN - deoxygenated blood exits liver via this vein /flow back to HEART
What is the liver connected to and what is its role?
Gall bladder
Role:
Store bile - bile contains bile salts (for lipid digestion)/bile pigments
Release bile - into duodenum via bile duct
Internal liver structure?
Liver consist of cells = HEPATOCYTES
Liver cells arranged into LOBULES - each one is supplied with blood by BRANCHES OF HEPATIC ARTERY/HEPATIC PORTAL VEIN
- blood from hepatic artery/portal vein MIXES in each lobule in wide capillaries (SINUSOIDS)
- each lobule connected to branch of HEPATIC VEIN that drains blood away/into main hepatic vein
What is the role of sinusoids?
Blood flowing through sinusoids can exchange substances with nearby hepatocytes
- allows hepatocytes to performs all functions of liver
liver fucntions?
Storage of glycogen
Formation of urea
Detoxification
How does the liver store glycogen?
- Plays a role in GLYCOGENESIS : convert glucose —> glycogen
- glycogen produced from GLYCOGENESIS is stored IN HEPATOCYTES
How does the liver form UREA?
Amino acids in blood transported to liver via hepatic portal vein
Excess amino acids processed in hepatocytes during 2 step process involving :
- deamination
- ornithine cycle
What happens in deamination?
Amino group (NH2) removed from each amino acid , with an extra H+ atom
NH2 + H+ —> NH3 (ammonia)
Part of amino acid remaining after deamination = KETO ACID which can:
Enter Krebs cycle to be respired
Be converted to glucose
Be converted to glycogen/fat for storage
What happens in ORNITHINE CYCLE?
Ornithine cycle - Series of events where ammonia is converted to urea
2NH3 + CO2 —> CO(NH2)2 + H2O
- form urea which diffuses through phospholipid bilayer of hepatocytes/transported to kidneys in blood plasma where its excreted
What is detoxification?
Detoxificaton - breakdown of substances that are not needed or are toxic
- alcohol, hydrogen peroxide,lactate, medicines
How is alcohol detoxified?
Alcohol absorbed in stomach/transported in blood to HEPATOCYTES
Enzyme ALCOHOL DEDHYDROGENASE in hepatocytes converts
ethanol —> ethanal —> other molecules that enter respiration
Why can continuous detoxification cause liver problems?
Metabolism of ethanol generates ATP
- so hepatocytes wont metabolise as much fat as usual/store the fat —> FATTY LIVER
- stored fat reduces ability of hepatocytes to carry out other functions/lead to cirrhosis - SCARRING OF LIVER
What are the two main functions of the kidneys?
- As an osmoregulatory organ, they regulate the water content of the blood vital for maintaining blood pressure.
- As an excretory organ, they excrete toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts).
What does the renal artery/vein do?
Artery: Carries oxygenated blood (containing urea and salts) to the kidneys
Veins :Carries deoxygenated blood (that has had urea and excess salts removed) away from the kidneys.
What is the role of the ureter?
Carries urine from the kidneys to the bladder.
What surrounds the kidney?
tough outer layer - the fibrous capsule.
What are the three main areas of the kidney?
- Cortex (contains glomerulus, Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule of the nephrons).
- Medulla (contains the loop of Henle and collecting duct of the nephrons).
- Renal pelvis (where the ureter joins the kidney).
What is a nephron?
The functional unit of the kidney, responsible for the formation of urine.
What does the afferent arteriole and efferent arteriole do?
Afferent: Carry blood from renal artery into glomerulus - THICKER DIAMETER
Efferent: carry blood from capillaries in glomerulus to capillaries close to rest of nephron - THINNER DIAMETER
- this blood will eventually go into renal vein
Process of ultrafiltration?
Location : Bowman’s Capsule
Afferent arteriole has larger diameter than efferent arteriole —> leads to HIGH BLOOD PRESSURE IN GLOMERULUS
- HIGH pressure causes small molecules in blood to be forced out the capillaries in glomerulus into BOWMAN’S CAPSULE —> forms GLOMERULAR FILTRATE
What are the capillaries in glomerulus and Bowman’s capsule separated by?
Endothelium of capillary: each endothelial cell has many membrane-lined holes
Basement membrane : made up f network of collagen/glycoproteins
Epithelium of Bowman’s capsule: epithelial cells with tiny projections with gaps in between them, called PODOCYTES
What are the main substances in the glomerular filtrate?
Amino aids, water, glucose, urea, inorganic ions (Na+, K+, Cl-)
What substances should not be in the glomerular filtrate?
RBCS/WBCS/platelets - too large to pass through holes in capillary endothelial cells
Proteins- basement membrane stops them as they’re too large
Factors effecting WP in glomerulus/Bowman’s capsule ?
PRESSURE: afferent wider than efferent —> blood pressure high in glomerular capillaries close
- raises WP of blood plasma in capilaries above WP of filtrate in Bowman’s capsule
WATER MOVES FROM blood plasma —> bowman’s capsule
SOLUTE CONC: solute conc in plasma in glomerular capillaries > Bowmna’s capsule , as proteins STAY IN BLOOD PLASMA , so…
WP of blood plasma < filtrate
Water moves from BOWMAN’S CAPSULE —> capillaries
EFFECT OF PRESSURE GRAD OUTWEIGHS EFFECT OF SOLUTE GRAD
What is selective reabsorbtion?
When Substances in glomerular filtrate are reabsorbed into blood
- most happens in PROXIMAL CONVOLUTED TUBULE
Water/salts reabsorbed via LOOP OF HENLE/collecting duct
Adaptation of the PCT that aids reabsorption?
Many microvilli present on luminal membrane (CSM facing the lumen) —> INCREASE SA for reabsorption
Many co-transporter proteins in luminal membrane —> each co transporter, transports a specific solute across luminal membrane
Many mitochondria- provide energy for Na+/K+ pump in basal membrane of cells
Cells packed tightly together - no fluid can pass between cells ( all substances reabsorbed must pass through cells)
Process of selective reabsorption ?
- Basal membranes of PCT epithelial cells — closest to the blood capillaries
- Na-K pumps in the basal membranes actively transport Na+ out of epithelial cells into blood/carried away
- Lowers conc of Na+ in epithelial cells so causes Na in filtrate to diffuse DOWN CONC GRAD into LUMINAL MEMBRANE of epithelial cell —> epithelial cell by CO TRANSPORTER PROTEINS (transports a sodium ion and glucose/amino acid )
- Once in epithelial cell, these solutes diffuse down their conc grad —> BLOOD**
- Movement of solutes to surrounding tissues, lowers tissues’ water potential - water moves out FILTRATE by osmosis
Urea diffuses out PCT filtrate down conc grad (eventually enter blood capillaries to be carried away)
Process of osmoregulation?
Osmoreceptors detect decrease in WP of blood, nerve impulses sent along sensory neurones —> POSTERIOR PITUITARY GLAND
Impulses stimulate Posterior pituitary to release ANTIDIURETIC HORMONE (ADH)
- cause kidney to reabsorb more water - reduce loss of water in urine
How does ADH work in the kidneys?
Reabsorption occurs as filtrate passes though collecting ducts
*ADH causes luminal membranes of collecting duct cells to become MORE PERMEABLE to water
This is done by: increasing no. AQUAPORINS (water permeable channels) in luminal membranes of collecting duct
How does ADH increase the no. AQUAPORINS in luminal membranes, therefore increase membrane permeability?
1.Collecting duct cells contain vesicles - their membranes contain many AQUAPORINS
2. ADH binds to receptor proteins, activating signalling cascade leading to PHOSPHORYLATION of aquaporin molecules
3. This activates AQUAPORINS, causing the vesicles (containing AQUAPORINS) to fuse with luminal membranes of collecting duct cells —> INCREASES PERMEABILITY
Why does ADH cause small vol of CONCENTRATED urine to be produced?
As Filtrate in nephron travels along collecting duct (high WP)
Water moves from duct —>through the aquaporins —>into tissue fluid/blood plasma in medulla (low WP)
- so filtrate is losing water - becomes more concentrated
SMALL VOL OF CONC URINE
Which molecules are reabsorbed from the PCT in selective reabsorption?
All glucose (no glucose should be in urine)
Amino acids, vitamin, inorganic ions
Urea - conc of urea in filtrate higher than in capillaries so diffused from filtrate to blood
This movement of these solutes from PCT into capillaries INCREASE WATER POTENTIAL of filtrate/ decrease WP of blood
- create steep WP and are water to move into blood by osmosis
Why does kidney failure occur?
Blood loss in accident
High BP
Diabetes
Overuse of certain drugs (e.g aspirin)
Problems that arise from kidney failure?
Urea, water, salts and various toxins retained, not excreted
Less blood is filtered by the glomerulus, causing the glomerular filtration rate (GFR) to decrease
- leads to a build-up of toxins in the blood
the electrolyte balance in the blood is disrupted (the concentrations of ions and charged compounds are not maintained)
Importance of the balance of electrolytes?
Excess K+ in blood —> abdominal cramps, tiredness, muscle weakness, paralysis
Frequency of impulse from SAN in heart decrease—> arrrhythmia /cardiac arrest
Balance of sodium it’s important as has role in neuromuscular function, fluid balance, acid/base balance
Build up of sodium —> disorientation, muscle spasms, high BP and weakness
Why is kidney failure fatal and the treatments ?
Will be build up of toxic wastes In body which is fatal if not removed
2 treatments;
Renal Dialysis (haemodialysis)- toxic, metabolic waste products/excess substances removed from blood by diffusion via dialysis membrane
Kidney transplant - one kidney transplanted
What is haeomodialysis?
Needs regular treatment in hospital/homr using HAEMODIALYSER (acts as artificial kidney)
Partially permeable dialysis membrane separate patent’s blood from dialysis fluid (DIALYSATE)
Diasylate constants substances needed In blood (glucose and Na+ ions) in the right concs
- diasylate continually refreshed so conc grads are maintained
What substances are in diasylate and their quantities ?
Contains:
Glucose conc equal to normal blood sugar level —> prevents net movement of glucose
Salt conc similar to ideal blood conc —> movement of salt will only occur if there is an imbalance (blood salt conc is too high/low)
No urea - allows urea to diffuse down conc grad from blood into diasylate /disposed of
Why does blood flow in opposite direction to diasylate ? What reduced risk of blood clots?
Create conc grad - ensure all urea is removed from blood
Drug, HEPARIN , added to blood —> anticoagulant (blood thinner) prevents blood clots
Disadvantage of renal dialysis?
Heavy restriction on patient’s life—> many trips to hospital /treatment takes 3 hrs
Control diet - minimise urea production/salt intake
Disadvantage of kidney transplant?
Donors wont have same antigens on cell surface —> immune response to new kidney
(Tissue typing can reduce risk of rejection)
- need immunosuppressant drugs Forrest of their life —> have long term side effects/patient vulnerable to infection
Lack of donors
Advantage of transplant rather than dialysis?
More freedom - less restrictive
Dialysis is expensive so REDUCED COST
Transplant is LONG TERM SOLUTION , dialysis is FOR LIMITED TIME
What do urine tests show?
Test for glucose:
No glucose should be present in urine - should all be reabsorbed by PCT
If present: something wrong with homeostatic control of glucose , in particular functioning of insulin
Test for ketones:
Ketones (acetone/acetoacetate) produced by metabolism by people with diabetes
- if present in urine —> person has diabetes
Test for proteins:
If present in urine, HIGH BP /kidney infection/ something wrong with blood filtration mechanism
Test for nitrate ions:
If positive —> bacteria infection in urinary tract
How do pregnancy tests work?
Pregnancy test needs a URINE SAMPLE
Pregnancy tests contain monoclonal antibody that are specific to hormone, hCG (human chorionic gonadotropin)
- hCG secreted by early embryo
These monoclonal antibodies originate from clone of B LYMPHOCYTE cells that all produce antibody specific to hCG -> minimise chance of false test result
Test for anabolic steroids?
Use URINE SAMPLE
- detected in urine via gas chromatography/mass spectrometry
Anabolic steroids rapidly build muscle mass by stimulating protein synthesis
Loop of Henle structure?
Consists of:
descending limb - descends into medulla (narrow/high permeable to water)
Ascending limb- ascends back into cortex (wider and impermeable to water/permeable to ions)
Water reabsorption in the loop of henle?
- Na+ and Cl- actively transported out TOP OF ASCENDING LIMB because water potential increases UP THE ASCENDING LIMB - lowers WP of medulla
- Duu to lower WP in medulla, descending limb’s walls PERMEABLE TO WATER so water leaves filtrate by osmosis —> interstitial space (FILTRATE MORE CONC)
- Water that is lost is re absorbed into blood in surroundings capillaries by osmosis + carried away
ions - Na+ and Cl- diffuse out filtrate —> interstitial space, at BOTTOM of ascending limb, further LOWERING WP of medulla
Overall creates WP gradient in interstitial space , with HIGHEST WP in cortex and increasingly LOWER WP deeper into medulla - MORE WATER CAN BE REABSORBED by collecting duct
Role of loop of henle?
Lower the WP of the medulla, so water can move from collecting duct into medulla BY OSMOSIS
And water can then be reabsorbed back into blood —> produce low volume of CONCENTRATES URINE
Wat happens when filtrate enters collecting duct?
Water from the filtrate moves into INTERSTITIAL SPACE and into SURROUNDING CAPILLARIES by osmosis + carried away
- water continues to exit filtrate as it moves through collecting duct, even deep in medulla when MOST WATER HAS ALREADY BEEN LOST
This is because of the low WP of interstitial space established by loop of henle
Urine leaving collecting duct has LOW WP, as most water re absorbed into blood
How is the countercurrent multiplier set up?
Loop of henle operates as a countercurrent system (ASCENDING limb and one DESCENDING LIMB (move in opposite directions)
Filtrate moves down COLLECTING DUCT , it loses water, DECREASING water potential
BUT , due to pumping of ions out ASCENDING LIMB OF LOOP OF HENLE, especially deeper in medulla, WP OF surrounding tissues of medulla is even lower than collecting duct
Allows water to continue to move out filtrate down whole length of collecting duct
- ensure concentrated urine produced
What is peritoneal dialysis?
Dialysis fluid put through a tube that passes from outside of patient’s abdomen , into their abdominal cavity
Waste products diffuse out patient’s blood into dialysis fluid ACROSS PERITONEUM (membrane lining of abdominal cavity)
- carried out several times a day or overnight
Risk of infection around site of tube
