Module 5.2 Flashcards
Define excretion.
The removal of metabolic waste from the body.
Define metabolic waste.
Any substance made by metabolism that is toxic or made in excess.
Define metabolism.
The sum total of all cell reactions.
What are the two main types of metabolic waste from the human body?
- Carbon Dioxide
2. Urea
Why is Carbon dioxide produced in the body?
Every living cell in the body produces carbon dioxide as a result of RESPIRATION.
Explain what happens if the Carbon Dioxide levels rise too much? (Hint: H+ ions)
- Excess carbon dioxide dissolves in the plasma
- Once dissolved it combines with water to produce carbonic acid.
- The carbonic acid dissociates to release H+ ions
- The H+ ions lower the pH of the blood plasma and makes it more acidic.
- Proteins in the blood acts as buffers to resist pH changes.
- If the change is small the increased H+ are detected by the respiratory centre in the medulla oblongata of the brain.
- This causes an increase in breathing rate to remove the excess Carbon Dioxide.
Where and why is urea produced?
- Produced in the LIVER
- Removes excess amino acids (excess of amino acids can be toxic to the body)
Where does the hepatic artery come from when entering the liver and what type of blood does it carry?
- Comes from the HEART
- Carries OXYgenated blood
Where does the hepatic portal vein come from when entering the liver and what type of blood does it carry?
- Comes from the INTESTINE
- Carries DEoxygenated blood
Where is bile in the liver get transported to? And what vessel carries bile?
The gall bladder is where the bile is transported.
It is carried via the bile duct.
Where does the hepatic vein go to when leaving the liver?
Goes towards the HEART
What is the liver divided into?
Lobules
What are the vessels in between lobules called?
Inter-lobular vessels
What are the vessels within lobules called?
Intra-lobular vessels
What is the common shape of a liver lobule?
Cylindrical, almost hexagonal-shaped.
What (type of) vessel is the intra-lobular vessel?
(A branch of) Hepatic vein
What types of vessels are located in the interlobular vessel? (3)
- Branch of hepatic portal vein
- Branch of hepatic artery
- Branch of bile duct
What is a sinusoid?
A chamber within the liver lobules where blood from both the hepatic artery and the hepatic portal vein are mixed and pass along.
Give 4 specialised features of hepatocytes.
- Cuboidal in shape
- Many microvilli
- Dense cytoplasm with many organelles (especially ATP)
- Metabolic functions, such as protein synthesis, detoxification, synthesis of cholesterol, etc.
Give 3 specialised features of Kupffer cells.
- They’re specialised macrophages
- Move within sinusoids
- Involved in the breakdown and recycling of red blood cells
Briefly describe how Kupffer cells break down Haemoglobin.
- Haemoglobin is broken down to bilirubin
2. Bilirubin is excreted as part of the bile and faeces (gives faeces that brown pigment)
State 5 functions of the liver.
- Control of blood glucose, amino acids, and lipid levels
- Synthesis of red blood cells in the fetus, bile, plasma proteins, cholesterol
- Storage of vitamins A, D, B12, Iron, glycogen
- Detoxification of alcohol, drugs
- Destruction of red blood cells
Briefly describe how alcohol is detoxified (4).
- Ethanol gets oxidised to ethanal via ethanol dehydrogenase (NAD → NADH)
- Ethanal gets oxidised further to ethanoic acid via ethanal dehydrogenase (NAD → NADH)
- Ethanoic acid is converted to Ethanoate (Acetate)
- The acetate is combined with Coenzyme A to form Acetyl CoA (used in respiration)
How is urea formed? (2)
Deamination: Amino acid gets converted to ammonia and keto acid
Ornithine Cycle: Amino is converted to Urea
State the symbol equation for deamination.
(2) NH2CH(R)COOH + O2 → (2) CO(R)COOH + 2NH3
State the general symbol equation for the conversion of ammonia to urea.
2NH3 + CO2 → CO(NH2)2 + H2O
Briefly describe the ornithine cycle.
- Ammonia and CO2 combine to make citrulline, water is released.
- Ammonia and Citrulline are combined to make Arginine, water is released.
- Arginine is combined with water to make ornithine and release UREA.
What are the 2 main roles of the kidney.
- Filter Urea from the Blood
2. Osmoregulation - Control the amount of water that leaves the body
From top to bottom of the kidney, state the 7 structures of the kidney.
- Capsule
- Cortex
- Nephron tubule
- Medulla
- (Branches of) renal vein, renal artery
- Pelvis
- Ureter
State all the structures in a nephron (renal) tubule (5).
- Glomerulus (with Bowman’s capsule)
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
Define ultrafiltration.
The filtering of molecules from the blood by at a molecular level (anything less than 69000 Daltons) under pressure
Using keywords such as hydrostatic pressure, briefly explain the process of ultrafiltration (5)
- Blood flows into the glomerulus via the afferent arteriole and leaves by the efferent arteriole
- The afferent arteriole has a wider lumen than the efferent arteriole
- This creates a bottleneck effect in the glomerulus (network of capillaries)
- This generates a high hydrostatic pressure inside the glomerulus compared to the lumen of the Bowman’s capsule.
- As the hydrostatic pressure is high, small molecules are squeezed out of the blood and into the Bowman’s capsule.
State the three key components of the specialised exchange surface between the glomerulus and the Bowman’s capsule that it enables ultrafiltration.
- ENDOTHELIUM OF CAPILLARIES
- BASEMENT MEMBRANE
- EPITHELIAL CELLS OF BOWMAN’S CAPSULE (PODOCYTES)
Explain how the endothelium of capillaries is adapted to enable ultrafiltration.
Contains gaps/pores between endothelial cells to allow blood plasma/dissolved substances to pass out of capillary.
Explain how the basement membrane is adapted to enable ultrafiltration.
A mesh of collagen fibres, prevents molecules greater than 69000 Daltons to enter (most proteins remain in glomerulus capillaries)
Explain how epithelial cells (podocytes) are adapted to enable ultrafiltration.
Contains finger-like projections called major processes; and gaps called foot/minor processes which allow fluid from glomerulus blood to enter Bowman’s space (hydrostatic pressure)
State 5 things that the glomerular filtrate contains.
- Water
- Glucose
- Inorganic mineral ions (Na+/Cl-)
- Amino Acids
- Urea
What are the 2 things left in the blood during glomerular filtration?
- Red blood cells
2. Large proteins
Explain how fluid is able to be retained in the capillaries
Because the blood is left with a very low water potential
What is selective reabsorption?
The reabsorption of useful molecules back into the blood.
Where does selective reabsorption take place?
At the PCT (Proximal Convoluted Tubule)
What does the PCT have that is an adaptation to maximise selective reabsorption?
- A BRUSH BORDER: cells that line it have a folded membrane which generate microvilli, so a higher S.A.
Briefly explain the process of selective reabsorption (4).
- Na+ actively pumped into the blood from the cells lining the PCT (REQUIRES ATP)
- Concentration of Na+ in cells fall, creating a concentration gradient.
- Na+ diffuse back through a cotransporter protein; carries glucose/amino acids at the same time.
- Water follows into the cell by osmosis.
What is the aim/function of the Loop of Henle.
To reduce the volume of urine without changing its concentration.
What is the name of the system that the Loop of Henle uses?
HAIRPIN COUNTERCURRENT MULTIPLIER SYSTEM
a dynamic system, creates different levels of water potential down the Loop
What is the overall effect of the Loop of Henle?
Reduces the water potential of the medulla
Briefly describe how the Loop of Henle works (7)
- Na+ / Cl- actively pumped OUT of the THICK ascending limb.
- The water potential is reduced in the medulla
- Water moves out of the THIN descending limb
- This concentrates the fluid in the Loop of Henle
- Na+ and Cl- start to DIFFUSE (passive) out of the THIN ascending limb
- So as a result, there’s an increasing concentration of solutes down the medulla (reduces W.P.), allows Water to move out of the collecting duct (important)
- But ultimately, the body can regulate how much is H2O is reabsorbed by adjusting the permeability of collecting duct to water.
Why do kangaroo rats (desert) have longer Loops of Henle than beavers (wet)?
The longer the Loop of Henle, the more concentrated the interstitial fluid. Therefore, the more water can be absorbed back into the blood. (so kangaroo rats can conserve as much water as possible)
What adaptation/feature do the collecting duct walls have that enable osmoregulation to occur?
The walls of the collecting duct can be modified to change the PERMEABILITY to water.
e.g. If water needs to be conserved, the walls can be made more permeable to allow water to be reabsorbed, producing CONCENTRATED urine.
Explain all the steps in osmoregulation.
- The water potential (wp) of the blood is monitored by osmoreceptors in the hypothalamus of the brain.
- When the wp of the blood is very low, the osmoreceptors shrink and stimulate neurosecretory cells in the hypothalamus.
- These produce and release anti-diuretic hormone (ADH) which flows down the axon to the posterior pituitary gland where it is stored until needed.
- When the neurosecretory glands are stimulated they send action potentials down their axons and cause the release of ADH into the blood.
- ADH enters the capillaries running through the posterior pituitary gland. It is transported around the body and acts on the cells of the collecting ducts.
- When it binds to the receptors, it causes a chain of enzyme-controlled reactions. The end-result is the insertion of vesicles containing water-permeable channels (aquaporins) which are fused into the membranes of the collecting duct wall cells. (so more permeable to water).
- More water is reabsorbed by osmosis into blood.
- Less urine, with a lower water potential, is released.
- Less ADH is released when the wp in the blood rises again.
- ADH is slowly broken down and the collecting ducts receive less stimulus.
