5.1.2 The Liver & Kidney Flashcards
Define excretion
The removal of metabolic waste products from the body
What is egestion?
The removal of undigested food
Define homeostasis
The maintenance of a stable internal environment within a narrow range despite environmental conditions changing
Name metabolic waste products
- Carbon dioxide
- Bile pigments
- Urea
Compare excretion + secretion
Differences
Excretion:Metabolic waste - toxins removed from body not using vesicle
SecretionUseful products - used in cell signalling, targets tissues/organs, released from glands, uses vesicles, remains in body
Similarities
Use ATP
Involved in homeostasis
Products released by cells
Name the 5 main parts of the liver and their function
- Hepatic vein: Dexoygenated blood away from liver
- Hepatic artery: Oxygenated blood from heart
- Hepatic portal vein: Dexoygenated blood rich in digestion products from intestines into liver
- Bile duct: Bile secreted into this duct
- Gall bladder: Bile made in liver stored here
Explain the composition of the liver
Lobes divided into cylindrical lobules to give best contact of blood + hepatocytes (liver cells)
Explain the structure of the liver
- Hepatic artery + hepatic portal vein (inter-lobular vessels) flow through liver cells into hepatic vein (intra-lobular vessel)
- Kupffer cells (macrophages) in sinusoid
- Hepatocytes surround blood vessels
- Bile leaves liver via bile duct
What is bile?
- Greenish-brown alkali fluid
- Aids digestion by breaking down fats into small droplets (emulsification)
- Secreted by liver + stored in gall bladder
- Leaves body in faeces
What is Jaundice and how is it caused?
Causes yellow-orange skin + eyes + white faeces
Bile duct leaving liver blocked, so bile remains in body
What happens to excess proteins/amino acids
- Can’t be stored in body
- Harmful parts converted into urea
- Urea removed from body by kidneys w/ excess water + other substances - forming urine
How is urea formed in the liver?
Process of deamination
- Amine group removed
- Amino Acids + Oxygen = Ammonia + Keto Acids
- Keto acids used in respiration
- Ammonia is highly toxic, so converted to urea in ornithine cycle
Why is deanimation an advantage compared to excreting excess proteins/amino acids?
Keto acids used in respiration to make ATP instead of being wasted
What is the ornithine cycle?
Ammonia + Carbon Dioxide = Urea + Water
- Occurs in cytoplasm of hepatocytes (ATP also required from mitochondria)
What other processes occur in the liver?
- Breakdown of hydrogen peroxide: Hydrogen peroxide = Water + Oxygen
- Carbohydrate metabolism
- Detoxification of alcohol
How is fatty liver (Hepatitis/cirrhosis) caused?
- Too much ethanol in liver to detoxify
- Coenzyme NAD used to breakdown fatty acids for respiration
- Fatty acids build up
How is the liver a detoxifying organ?
- Breaks down harmful substances into the bile or blood
- Liver has good blood supply, so products enter blood easily
- Bile is secreted into intestines - leaving body in faeces
- Faeces therefore contains harmful by-products
Key points about the kidneys
- Two reddish-brown organs
- Attached to back of abdominal cavity
- Surrounded by layer of fat + layer of fibrous tissue
- Involved in excretion + osmoregulation
- Either side of spine just below lowest rib
Describe and explain the structure of the kidney
- Cortex: Dark outer layer where filtering of blood takes place in dense capillary network
- Medulla: Lighter in colour, contains tubules of nephrons + collecting ducts
- Ureter: Carrys urine out
- Blood vessels: Carry blood in + out
Explain the job of the nephron
- Microscopic tubules
- Receive fluid from the blood
- Convert into urine passed into ureter
List the parts of the nephron in order
- Glomerulus
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of henele
- Distal convoluted tubule
- Collecting duct
Give a basic overview of events occurring in the nephron
Glomerulus is a knot of capillaries which increases blood pressure to push fluid out - passing into Bowman’s capsule via ultrafiltration
Useful substances reabsorbed from nephron back into the blood, while excretory products remain: Selective reabsorption
What is the purpose of convolutions in the nephron?
Increase surface area for selective reabsoprtion
Describe and explain the changes in water potential in the nephron and how they contribute to reabsorption
Descending limb of loop of Henle: Water potential lowered as water lost by osmosis
Ascending limb of loop of Henle: Water potential increased as salts actively transported out
Collecting duct: Water potential lowered as water removed - urine has high concentration of solutes
Explain how fluid moves in + out of a capillary into tissues
Arterial End
Hydrostatic pressure (from heaty contraction) > oncotic pressure (water moves by osmosis from tissue fluid to blood in capillary), so net flow of fluid out of capillary
Venous end
Oncotic pressure (fluid moved out + pulse lost) > hydrostatic pressure (plasma proteins remain in blood so water potential gradient still large), so net flow into capillary
Explain how high hydrostatic pressure is generated at the glomerulus and how this causes fluid into the Bowman’s capsule
- Blood enters afferent arteriole under high pressure
- Afferent arteriole has wide diameter
- Efferent arteriole has smaller diameter - increaes hydrostatic pressure
- Hydrostatic pressure in glomerulus > Bowman’s capsule - Fluid forced out
Explain the layers of ultrafiltration
Basement membrane (collagen fibres + glycoprotein filters) of glomerulus stop erythrocytes + large molecules (proteins) passing through
Gaps (fenestrations) between endothelial cells of capillary wall allow small substances through (not erythrocytes)
Podocyte cells (Epithelial cells of Bowman’s capsule w/ extensions called pedicels) ensure gaps to allow some substances through ( not cells, platelets or large plasma proteins)
What substances are passed into the bowman’s capsule?
- Water
- Amino acids
- Glucose
- Urea
- Na+
- Cl-
- K+
What can high blood pressure/hypertension cause in ultrafiltration?
Damage capillaries + bowmans capsule, causing proteins to enter filtrate + urine
What could cause blood cells to enter the Bowman’s capsule?
The condition nephritis
What is glomerular filtration rate?
The volume of blood filtered through the kidneys in a given time
How do proteins remaining in the blood after ultrafiltration benefit selective reabsorption?
Lowers blood water potential ensuring water + other substances return later
List similarities between ultrafiltration and tissue fluid formation
- Both occur in capillaries
- Large molecules, proteins, RBCs remain in the blood
- Many molecules (water, sugars, ions) are reabsorbed back into capillaries
- Hydrostatic pressure greater than oncotic pressure
- Neutrophrils can pass through both
List differences between ultrafiltration and tissue fluid formation
Ultrafiltration
- Filtrate enters Bowman’s capsule then PCT
- Molecules not reabsorbed by capillaries form urine
- Blood filtered through 3 layers
- Knot of capillaries
Tissue Fluid Formation
- Tissue fluid enters intercellular space + bathes body cells
- Molelcules not reabsorbed to form tissue fluid enter cells or form lymph
- Blood filtered through 1 layer
- Network of capillaries
Where does reabsorption take place and what gets reabsorbed?
Proximal convoluted tubule
- Glucose + amino acids
- Most water
- Glucose required to form ATP
Describe and explain the structure if the proximal convoluted tubule
Made from cubodial epithelium cells
Many microvilli to increase SA for absorption
Many mitochondria for ATP production
Explain the process of selective reabsorption in the PCT
- Na+ and glucose (Or amino acids) enter cells of proximal convoluted tubule via co-transport proteins
- Water potential of cell lowered - water enters by osmosis down water potential gradient
- Na+ pumped out of cell into blood, K+ go in. Glucose facilitated diffusion into blood capillary (sometimes actively transported into the blood)
- Water potential of blood lowered so water by osmosis down water potential gradient
- Large molecules removed by endocytosis
What is glucose used for in the PCT
In cells for respiration to make ATP for active transport
The water potential at the end of the PCT is isotonic with the blood - what does this mean?
The water potential outside the cell is the same as inside
What is the role of the loop of Henle?
To establish a water potential gradient going down the medulla
What are the 4 rules regarding the loop of Henle?
1: Deeper in the medulla = lower water potential
2: Descending limb is impermeable to outward movement of ions but permeable to the movement of water
3: Ascending limb is permeable to ions but impermeable to water
4: Collecting duct is permeable to water but impermeable to ions
How much fluid is selectively reabsorbed in the PCT?
85%
What happens in the ascending limb of the loop of Henle?
First section - Na+ & Cl- ions diffuse out down concentration gradients
Second section - Na+ & Cl- ions actively transported out into Medulla
Higher water potential in filtrate - more dilute
Ions can diffuse into descending limb
What happens in the descending limb of the loop of Henle?
Water lost from filtrate by osmosis as water moves from higher water potential in filtrate to lower water potential in tissue fluid in Medulla
(Goes into blood)
What happens at the bottom of the ascending limb?
Ion concentration slightly higher than Medulla so ions diffuse out
Explain the composition of the fluid that reaches the hairpin bend
Very concentrated + hypertonic to blood in capillaries
What happens in the collecting duct?
Water lost from filtrate by osmosis as it descends into medulla (low water potential)
Water moves from high to low water potential
Small amount of urea moves out too
What does the two limbs of the nephron running next to each other cause?
Fluid flows in opposite directions
Descending + ascending limbs exchange substances through tissue fluid
Explain counter-current exchange in the Nephron
Ensures that ions in tissue don’t leak away in the blood to be transported out of kidneys
This is called Hair pin counter current multiplier
Why does water potential become lower as fluid descends deeper into the medulla?
Water is lost by osmosis to surrounding tissue fluid
Sodium + chloride ions diffuse into filtrate from surrounding tissue fluid
Why does water potential become higher as fluid ascends back towards cortex?
At base of tubule, sodium + chloride ions diffuse out of tubule into tissue fluid
Higher up the tubule sodium + chloride ions actively transported out of filtrate into tissue fluid
Walls of ascending limb are impermeable to water so this can’t leave the tubule
Explain the loop of Henle in desert animals
- More Na+ & Cl- ions actively transported out of longer ascending limb
- Lowering medulla water potential
- More water moves out from filtrate in descending limb by osmosis down water potential gradient
- Deeper in medulla water potential is even lower
- More water leaves collecting duct through aquaporins - so reabsorbed by blood
- Urine has lower water potential
- Urine is more concentrated + less volume
What are the roles of the Distal convoluted tubule?
- If the body lacks salt, Na+ ions actively transported out of distal convoluted tubule with chloride ions
- If ADH released, walls become more permable to water, so it leaves
- Balances the pH of the blood
How is water gained and lost in the body?
Gained
- Food + drink
- Metabolism e.g. respiration
Lost
- Water vapour from breathing
- Sweat
- Urine
- FaecesH
Explain the process of osmoregulation
Controlled by ADH
Released by Pituitary gland in the brain
Targets collecting ducts
ADH changes permeability of collecting duct
How does the pituitary gland regulate ADH Concentration?
Blood flows through hypothalamus - water potential monitored
1. Neurosecretory cells in hypothalamus produced ADH down their axons
2. ADH passed down axon + stored in posterior pituitary until action potential causes release into the blood
3. If water potential drops, osmoreceptors in hypothalamus lose water + shrink - causing ADH to be released from posterior pituitary ekks
4. ADH binds to complimentary specific shaped receptors on plasma membrane of collecting duct
Explain how ADG causes more water to be reabsorbed from the collecting duct
- ADH binding to specific shaped receptors on plasma membrane of DCT cells activates series of enzyme controlled reactions via secondary messenger cAMP
- Vesicles formed with water permeable channels (aquaporins)
- Vesicles fuse with membrane of collecting duct making it permeable to water
- Membrane of collecting duct has more aquaporins so water moves into tissue fluid of medulla + into blood by osmosis
How do aquaporins only allow passage of water?
- Ions too large to pass through the channel
- Shape of ion not complimentary to aquaporin
- Positive charge of aquaporin repels positively charged ions
What will eventually happen to ADH?
- Hydrolysed by protease enzymes in hepatocytes in liver into amino acids
- Amino acids can’t be stored - so used for protein synthesis or deanimation
- Removal of amine group then ornithine cycle to form urea which is removed by kidneys in ultrafiltration
Explain the two negative feedback loops if water potential increases too high or too low
Too high
1. Osmoreceptos in hypothalamus cause less ADH to be released from posterior pituitary
2. Collecting duct wall less permeable so less water absorbed into blood/more urine
Too low
1. Osmoreceptos in hypothalamus cause more ADH to be released from posterior pituitary
2. Collecting duct wall more permeable so more water absorbed into blood/less urine
What causes kidney failure?
Can be acute (Sudden within days/weeks) or chronic (over many years)
Tends to occur due to swollen or inflammed glomeruli due to:
- Diabetes mellitus (type 1 + 2)
- Hypertension (high blood pressure damages basement membrane)
- Infection (Structure of podocytes + tubules destroyed/damaged)
- Genetic conditions (Polycystic kidney disease - tissue fills with fluid filled cysts)
What can be found in urine during kidney infections and failure?
Infections
- Proteins as basement membrane
- Blood cells in urine
Failure
- Excess ions in blood
- Urea increase in blood
- Water in blood)
Homoeostasis fails - can result in death
Explain problems caued by kidney failure
- Tiredness (Decreased Erythropoietin)
- Stiffness in joints (Abnormal proteins
- Increased risk of heart attack (Excess water)
- Weakend bones (Ca/P imbalance)
- Poisoned cells (Excess urea)
Explain key aspects of GFR
Glomerular filtration rate (cm3/min or cm3/min-1)
Rate at which blood is filtered (used to indicate kidney function)
Blood test measures level of creatinine in blood - indirect measure of filtration rate
If levels of creatinine increase: Sign kidneys not working properly
Decreases with age + men generally have more creatinine than women
Advantages + disadvantages of using creatinine to measure GFR
Advantages
- Produced at a constant rate per day
- Freely filtered at glomerulus
Disadvantages
- Estimate of GFR
- 10% secreted by tubules
Describe and explain two ways of kidney failure treatment
Haemodialysis (renal)
Blood taken from vessel and passed through dialysis machine where it passes next to partially permeable membrane
Other side contains fluid with correct concentration of substances so diffusion can occur
3 x week for several hours
Kidney transplant
Human tissue carries special genetic marker (Human leukocyte antigen (HLA)
Ideally should receive transplant from someone with idential/similar HLA tissue type
Requires same blood group as recipient
Explain key aspects of haemodialysis
- Blood passes the filter in the opposite direction as dialysis fluid - maintaining concentration gradient for diffusion
- Water molecules diffuse across membrane by osmosis
- Excess urea + mineral ions leave blood, however glucose + some ions stay
- Blood leaves artery + anticoagulant drug (prevents clotting) released to prevent clots in machine (stopped towards end of treatment to allow clotting in body)
- Blood pumped to maintain pressure
- Air detectors used to stop air bubbles entering blood - can be fatal
- Clean blood enters the vein
Explain the advantages + disadvantages of kidney transplants
Advantages
- No time consuing dialysis
- Diet not restricted
- Fells better
- Able to travel
- No longer chronically ill
Disadvantages
- Need immunosuppresant drugs for life (may cause side effects: infections)
- Major surgery
- Risk of infection
- Frequent rejection checks
What could happen if a person’s HLA is not similar to their kidney transplant?
Bodies immune system identifies kidney as non self
Antigen variation causes rejection
What and why is urine tested?
- Glucose in urine: symptom of type 1+2 diabetes
- Creatine in urine: sign of muscle damage
- hCG found in urine of mother: Pregnancy tests
- LH : Testing for ovulation
- Performance enhancing drugs: Used to cheat in sports
What are monoclonal antibodies and how are they made (for hCG)?
Antibodies formed from a single clone of cells produced to target particular cells or chemicals in the body
1. Mouse injected with hCG to make required antibody
2. B cells that make antibody removed from spleen of mouse (these cells don’t divide)
3. B cells fused with myeloma cell which divide rapidly
4. Hybridoma formed - reproduces rapidly
5. Hybridoma produces desired antibody, which are collected, purified and used
