(5.2) Excretion as an example of homeostatic control Flashcards
What is the metabolic function of the liver?
- controls blood glucose, amino acids and lipid levels
- synthesis of bile, plasma proteins and cholesterol
- synthesis of red blood cells within a fetus
- storage of vitamins A,D and B12
- storage of iron and glycogen
- detoxification of drugs and alcohol
- breakdown of hormones
- destruction of red blood cells
What are destroyed red blood cells turned into?
forms bilirubin which creates bile
How is hydrogen peroxide detoxified?
- done by the enzyme catalase
- is converted to oxygen and water
- turnover of 5 million per second
How are drugs detoxified?
- done by the enzyme cytochrome p450
- breakdown of recreational drugs e.g. cocaine
- cytochrome p450 is also used in other metabolic reactions e.g. electron transport during respiration
How is alcohol detoxified?
ethanol —> ethanal —> ethanoate acid —> acetyl CoA (for respiration)
How is ethanol turned into ethanal?
- by ethanol dehydrogenase
- removes 2 hydrogen ions which then creates reduced NAD
How is ethanal turned into ethanoate acid?
- ethanal dehydrogenase
- removes 2 hydrogen ions which then creates reduced NAD
What does the detoxification of alcohol mean?
- Due to the removal of hydrogen ions from ethanol and ethanal, the krebs cycle cannot take place
- Fatty acids within the krebs cycle are converted back to lipids and stored in the hepatocytes
- causes an enlarged liver and conditions such as cirrhosis
How is urea formed?
amino acids —> ammonia and keto acid —> urea
How are amino acids turned into ammonia and keto acid?
- addition of oxygen
- deamination
Describe deamination
- removes amino acids by adding oxygen
- creates ammonia and keto acid
- keto acid is converted into pyruvate and enters the link reaction or enters directly at the krebs cycle
- ammonia is immediately converted into urea as it is very soluble and highly toxic
Describe the 2 problems with ammonia
- very soluble
- toxic
Why is ammonia being highly soluble an issue?
Interferes with osmosis
Describe the ornithine cycle
- ammonia is combine with CO2 to produce urea
- ammonia and CO2 combine with the amino acid ornithine to produce citrulline
- citrulline is converted to arginine by more addition of ammonia
- arginine is then re-converted to ornithine by the removal of urea
What is the outer region of the kidney called?
The cortex
What is the inner region of the kidney called?
The medulla
What is the centre of the kidney called?
The pelvis
What is the role of the kidney?
Remove waste products from the blood and produce urine
Where does the urine go after it has been produced in the Kidney?
Passes out of the kidney through the ureter and is stored in the bladder
What are the majority of tubules called in kidneys?
Nephrons
How many nephrons are there in each kidney?
1 million
Describe the journey/shape of nephrons
- starts in the cortex at the bowman’s capsule
- remainder of nephron coiled in a tubule that passes through the cortex forming a loop down into the medulla and back into the cortex
- then joins the collecting duct which passes back down into the medulla
What is the bowman’s capsule?
A cup-shaped structure where selective reabsorption takes place
What are the three layers of the barrier within the bowman’s capsule?
- The endothelium of the capillary
- The basement membrane
- The epithelial cells of the bowman’s capsule
Describe the endothelium of the capillary
- Has narrow gaps between the cells
- cells also contain pores (fenestrations)
What is the purpose of the gaps between cells within the endothelium of the capillary?
Allows blood plasma and substances dissolved in it to pass out of the capillary
Describe the basement membrane
- fine mesh of collagen fibres and glycoproteins
-acts as filter to prevent the passage of molecules with a relative molecular mass greater than 69,000 - means most proteins are held in the capillaries of the glomerulus
Describe the epithelial cells of the Bowman’s capsule
- called podocytes
- have a specialised shapes
- many finger like projections (called major processes)
- major processes there are minor processes - hold the cells away from the endothelium of the capillary
- ensures gaps between the cells
- fluid from the blood can pass between the gaps into the lumen of the bowman’s capsule
Why is there a high hydrostatic pressure within the glomerulus?
The afferent arterioles have a larger diameter than efferent arteriole meaning there is more blood flowing into the glomerulus than out
What does the high hydrostatic pressure within the glomerulus cause?
Causes small parts of the blood to be passes out of the glomerulus e.g. water, amino acids, glucose, urea and inorganic mineral ions
What happens to the small parts of the blood passed into the glomerulus?
They are passed into the lumen after going through the three different membranes within the glomerulus - the endothelium of the capillary, the basement membrane and the epithelial of the bowman’s capsule
Why does some water move back into the blood during ultrafiltration?
There is a low oncotic pressure - the high water potential in the bowman’s capsule and low water potential in the glomerulus causes the water to move by osmosis back into the glomerulus
Describe the process of selective reabsorption
- sodium is moved out of the cells lining the tubule by active transport via a sodium potassium ion pump
- Concentration of sodium ions in the cytoplasm decreases creating a concentration gradient with the tubule fluid
- Sodium ions co-transport amino acids or glucose as they diffuse into a cell via a co-transport protein within the plasma membrane
- water moves into the cell by osmosis
How do substances from the blood move to the tissue fluid and blood?
They move by facilitated diffusion however if there is an equilibrium then they will be moved by active transport - this causes water to follow by osmosis
How are small proteins reabsorbed into the blood?
Endocytosis
What are the adaptations of the proximal convoluted tubule for selective reabsorption?
- folded to create microvilli and increase surface area for reabsorption (closer to the tubule fluid)
- special co-transport proteins in the membrane to transport glucose and amino acids
- the membrane is in contact with tissue fluid for small diffusion distances
- cytoplasm of the cells have many mitochondria as ATP is needed for active transport of sodium ions
Describe what happens within the loop of henle
- sodium and chloride ions move out of the ascending limb by active transport
- this lowers the water potential in surrounding tissue fluid
- this means water will leave the descending limb by osmosis
- Sodium and chloride ions diffuse out the descending limb by facilitated diffusion
- This is then repeated lower down the descending limb
- By the bottom of the descending limb, the tubule fluid is extremely concentrated (lower water potential)
- This means that at the bottom of the ascending limb, sodium and chloride ions are moved out by facilitated diffusion
- Once equilibrium is reached, more chloride ions are moved out by active transport (process is repeated)
What does a longer loop of henle mean?
More sodium and chloride ions are pumped out of the ascending limb into the medulla meaning a build up of a concentration gradient
What is active transport used for in the loop of henle?
Used at the distal convoluted tubule to adjust concentrations of various mineral ions
Define osmoregulation
Control of water potential in the body
Why is it important to control water balance?
Prevents water entering and leaving cells and causing lysis or crenation
When does the body conserve more water?
on a hot day
When does the body conserve less water?
On a cold day
