5.1.2 Excretion as an example of homeostatic control Flashcards
(75 cards)
1
Q
What is excretion?
A
Excretion is the process of removing metabolic waste from cells to maintain normal metabolism and homeostasis.
2
Q
Why is excretion important?
A
It prevents the build-up of toxic substances (like CO₂ and nitrogenous waste) that can harm cells.
3
Q
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What is the role of the liver in metabolism?
A
The liver carries out chemical reactions that generate waste products and processes substances for excretion.
4
Q
What is detoxification?
A
The liver’s process of breaking down toxins into less harmful substances for excretion.
5
Q
What is deamination and what does it produce?
A
The removal of amine groups from amino acids, producing ammonia and keto acids.
6
Q
What are the Keto acids used for?
A
Either for ATP production or stored as glycogen.
7
Q
How is ammonia converted to a less toxic form?
A
Ammonia combines with CO₂ to form urea in the ornithine cycle.
8
Q
What other substanced are detoxified in the liver?
A
- Alcohol - prevent cell damage
- Hydrogen peroxide - prevent cell damage
- Paracetemol - prevent toxicity to liver and kidneys
- Insulin - helps regulate blood glucose conc.
9
Q
What enzyme breaks down alcohol in the liver?
A
Alcohol dehydrogenase breaks ethanol into ethanal, then to ethanoate.
10
Q
What enzyme breaks down hydrogen peroxide?
A
Catalase splits hydrogen peroxide into water and oxygen.
11
Q
How does the liver lower blood glucose levels?
A
By converting excess glucose into glycogen
12
Q
How are haemoglobin from old erthrocytes broken down?
A
Broken down by hepatocytes (liver cells) into bile pigments.
These are then transported by the bile duct and stores in the gall bladder.
13
Q
What are the four large parts of the liver structure?
A
- Hepatic artery - supplies oxygenated blood.
- Hepatic vein - carries away deoxygenated blood towards the heart.
- Hepatic portal vein - brings nutrient-rich blood from the intestines
- Bile duct - transports bile to the gallbladder
14
Q
Draw a liver lobule.
A
Labelled (branch of) hepatic vein, hepatic artery, hepatic portal vein, kupffercells, sinusoids and hepatocytes.
15
Q
What are sinusoids?
A
Channels that carry mixed blood from the hepatic artery (oxygenated) and hepatic portal vein (products from digestion).
16
Q
What are Kupffer cells and their role?
A
Immune cells that ingest pathogens and other foreign particles.
17
Q
What is the bile canaliculus?
A
A channel that collects bile from hepatocytes and leads to the bile duct.
18
Q
What vessels supply the kidneys with oxygenated blood?
A
Renal arteries
19
Q
How is urine transported from the kidneys to the bladder?
A
Ureter
20
Q
Describe the interal structure of the kidney.
A
- Fibrous capsule - an outer membrane that surround and protects the kidney
- Renal Cortex - outer region, contains Bowman’s capsule, PCT and DCT
- Renal Medulla - inner region, with pyramids that contain loops of Henle and collecting ducts
- Renal Pelvis - collects urine into ureters.
21
Q
Draw the internal structure of a kidney.
A
Labelled renal medulla, renal cortex, renal pelvis, ureter
can do renal artery and renal vein
pyramids
22
Q
What is a nephron?
A
The basic structural and functional unit of the kidney that filters blood and forms urine.
23
Q
What is filtrate?
A
The fluid filtered out of the blood into the nephron at Bowman’s capsule.
24
Q
Describe the three layers that blood has to pass to enter the bowman’s capsule.
A
- Endothelium - has fenestrations (pores), that allow plasma and small solutes to pass but block blood blood cells
- Basement membrane - has collagen fibres that act as a selective filter preventing large molecules from passing
- Epithelium - made of podocytes
25
What happens in the proximal convoluted tubule (**PCT**)?
Reabsorption of useful substances like water, glucose, and salts
Cells have microvilli to increase surface area
26
What is the function of the Loop of Henle?
It creates a high solute gradient in the medulla to help with water reabsorption.
27
What happens in the distal convoluted tubule (**DCT**)?
It refines water balance, influenced by **ADH**, and reabsorbs water.
28
What are the different blood vessels associates with the nephron?
* **Afferent arteriole** - supplies glomerulus with blood
* **Glomerulus** - fluid is forced out of these capillaries into Bowman's capsule through ultrafiltration
* **Efferent arteriole** - smaller diameter than afferent, carries blood away from the glomerulus
* **Capillaries** around PCT, DCT and loop of Henle - absorb salys, glucose and water.
29
What is ultrafiltration?
The process by which small molecules like water, glucose, mineral ions and urea are filtered out of the blood into the Bowman's capsule from glomerular filtrate.
30
Describe the ultrafiltration process
1. Blood enters the glomerulus through the **afferent** arteriole.
2. Blood leaves the glomerulus via the **efferent** arteriole, maintaing **high hydrostatic pressure**.
3. This high pressure **forces** molecules out of the blood through fenestrations in the **endothelium**.
4. The molecules then move through **basement membrane**, **selective filter** that blocks large molecules and blood cells.
5. The molecules then move through the **epithelium** (which has podocytes).
6. The filtered fluid then collects in Bowman's capsule.
31
Which substances are found in the glomerular filtrate?
Water, salts, glucose and urea.
32
Which substances remain in the blood?
Blood cells, platlets and proteins.
33
What is glomerular filtration rate (GFR)?
The volume of filtrate formed per minute - a measurment of kidney filtration efficiency.
34
What is the main function of the proximal convoluted tubule (PCT)?
To **reabsorb useful substances** like glucose, amino acids, ions, and water from the filtrate back into the blood.
35
What are some key adaptations of epithelial cells in the PCT?
* Microvilli - increase SA for reabsorption
* Basal infoldings - increase SA for reabsorption
* Numerous mitochondria - provide ATP for active transport
* Co-transport proteins in plasma membrane - allow co-transport of substances from filtrate into epithelial/capillary.
36
Describe **Selective Reabsorption**.
1. **Na⁺** ions are **actively transported** out of PCT epithelial cells into the blood.
2. This creates a low Na⁺ concentration inside the cells.
3. Na⁺ moves from filtrate into cells via **co-transport** with glucose or amino acids.
4. Glucose and amino acids then diffuse into blood capillaries.
5. As solutes are reabsorbed, the **osmotic gradient** causes water to follow into the capillaries.
37
What is the role of the distal convoluted tubule (DCT)?
To make **final adjustments** to the filtrate by reabsorbing water and ions and regulating **blood pH**.
38
How is the DCT adapted for its function?
It has microvilli and mitochondria for active transport
It is also regulated by hormones (ADH) to adjust permeability.
39
Where is the loop of Henle located?
It starts in the renal cortex and descends into the renal medulla
40
What are the two limbs of the loop of Henle?
The descending limb and the ascending limb.
41
What are some features of the descending limb in the loop of Henle?
Narrow, highly **permeable to water** but **impermeable to ions**.
42
What are some features of the ascending limb in the loop of Henle?
Wider (than descending), **impermeable to water** but **permeable to ions**.
43
What is the primary function of the loop of Henle?
To **decrease** the **water potential** in the medulla via active transport of ions into the intersitial (tissue) fluid .
44
Describe water reabsorption in the loop of Henle.
1. The descending limb is **permeable to water** but impermeable to ions, so water leaves the filtrate by osmosis into the surrounding **interstitial fluid** in the medulla.
2. As water exits the filtrate, it becomes more concentrated, reaching its lowest water potential at the **bottom** of the loop.
3. Water that exits the filtrate is then **reabsorbed** into the blood via nearby capillaries.
4. The ascending limb is impermeable to water but permeable to **Na⁺** and **Cl⁻**.
5. Na⁺ and Cl⁻ diffuse out of the filtrate in the lower ascending limb, **further lowering** the water potential in the surrounding interstitial fluid.
6. This creates a **high ion concentration** in the medulla interstitial fluid, making the water potential even lower.
7. In the upper ascending limb, Na⁺ and Cl⁻ are **actively transported** out, continuing to build the concentration gradient in the surrounding tissue.
45
Why does the ascending limb use active transport near the **top**?
Because the ion concentration in the filtrate decreases as it ascends, so diffusion is no longer sufficient.
46
What is the role of the collecting duct in water reabsorption?
Water is drawn out even more by osmosis due to the low water potential in the medulla, set up by the loop of Henle.
47
What is a **countercurrent multiplier**?
A system where fluid flows in opposite directions
Enhances the salt gradient for more efficient water reabsorption.
48
How is the countercurrent multipler set up?
1. As filtrate moves **down** the collecting duct, it **loses water**, decreasing its water potential.
2. However, due to the **pumping of ions out** of the ascending limb of the loop of Henle, especially deeper in the medulla, the water potential of the surrounding tissues in the **medulla is even lower than in the collecting duct**.
3. This allows water to **continue to move out** of filtrate down the whole length of the collecting duct.
49
What is **osmoregulation**?
The homeostatic control of the water potential of the blood.
50
Where is antidiuretic hormone (ADH) produced and stored?
Produced in the **hypothalamus** and stored in the **posterior pituitary gland**.
51
What structures in the kidney is influenced by ADH?
DCT and Collecting duct
52
How does ADH increase water reabsorption?
ADH binds to **receptors** on cell surface
Triggering **cAMP** to insert **aquaporins** into the cell membrane
Allowing water to move into surrounding intersitial fluid and be reabsrobed into blood vessels.
53
What type of feedback system controls ADH release?
Negative feedback
54
Where are the osmoreceptors that detect blood water potential?
In the hypothalamus
55
Describe the mechanism of ADH action.
1. ADH attaches to **receptors** on the surface of cells in the DCT and collecting duct.
2. This triggers the activation of **cAMP**, a second messenger, which initiates a **cascade of reactions** that cause **vesicles** containing **aquaporins** to **fuse** with the cell-surface membrane.
3. Water moves through aquaporins by **osmosis** from the DCT and collecting duct into the surrounding interstitial space.
4. Water is then reabsorbed into the surrounding blood vessels.
56
Explain how the body responds to a **decrease** in blood water potential.
1. The water content of the blood **drops**, lowering its water potential.
2. This change is detected by **osmoreceptors** in the hypothalamus.
2. The **posterior** pituitary gland is stimulated to release **more ADH** into the bloodstream.
3. ADH **increases the permeability** of the distal convoluted tubule (DCT) and collecting duct to water by stimulating the **insertion of aquaporins** into their membranes.
4. More water is reabsorbed into the blood by osmosis from the filtrate.
5. A small volume of highly concentrated urine is produced, and less water is lost from the body.
6. Blood water potential rises, returning towards the normal range - negative feedback inhibits further ADH release.
57
Explain how the body responds to a **increase** in blood water potential.
1. The water content of the blood** increases**, so its water potential rises.
2. Osmoreceptors in the hypothalamus detect this increase.
3. The posterior pituitary gland will release **less ADH** into the bloodstream.
4. This mean, fewer ADH molecules bind to receptors on the cells lining the **DCT** and **collecting duct** in the kidney.
5. As a result, **fewer aquaporin** channels are inserted into the membranes of these cells.
6. This makes the DCT and collecting duct less permeable to water, so less water is reabsorbed into the blood.
7. More water remains in the filtrate, leading to the production of a large volume of dilute urine, allowing the body to restore normal blood water potential.
58
What can glucose in urine indicate?
Diabetes
59
What might high creatinine levels in urine suggest?
Kidney or muscle damage
60
What can blood or protein in urine indicate?
Kidney disorders
61
What hormone does a pregnancy test detect?
hcG
62
How do monoclonal antibodies help in pregnancy tests?
They bind to hCG, forming a coloured complex that indicates pregnancy.
63
How do pregnancy tests work if someone is pregnant?
1. The wick of the test is soaked in urine - will contain hcG
2. Mobile **monoclonal antibodies** attached to coloured beads **bind to hCG** to form an **antibody-hCG complex**.
3. Urine carries this complex to a window with **immobilised** monoclonal antibodies that only bind to the antibody-hCG complex.
4. This creates a coloured line/symbol indicating pregnancy.
5. Other immobilised antibodies bind to mobile antibodies with or without hCG, forming a **control** line to confirm the test is working.
64
What types of drugs can be detected in urine?
Anabolic steroids
Recreational drugs
65
How do urine drug tests work?
The presence of steroids is detected via **gas chromatography** by measuring the time taken for the urine sample to pass the column compared to the time taken for a steroid to pass through.
66
What can cause kidney failure?
Kidney infections - lead to inflammation and swelling in the kidneys
High blood pressure - damages the glomeruli capillaries, so proteins and blood leak into urine.
67
What are the consequences of kidney failure?
* Build-up of toxic waste (e.g., urea) - can poison cells
* Fluid retention and swelling
* Ion imbalance - leading to brittle bones, loss of electrolyte balance or osmotic imbalances
* Anaemia
* Death if untreated
68
What are the two types of dialysis?
Haemodialysis
Peritoneal dialysis
69
How does haemodialysis work?
Blood is removed from the body and passed through a machine with **dialysis fluid** in **countercurrent** flow across a **partially permeable** membrane.
Dialysis fluid contains normal plasma levels of glucose and mineral ions and no urea.
**Blood thinners** (heparin) are used to prevent clotting.
70
How does peritoneal dialysis work?
Dialysis fluid is inserted into the **abdominal cavity**, where exchange occurs across the **peritoneal membrane**.
Fluid must be regularly drained and replaced.
71
What are the advantages and disadvantages of **Haemodialysis**?
Advantage:
Lower risk of infection
Disadvantage:
Requires specialist equipment, must be done at hospital or medical centre, patient must be immobile during treatment
72
What are the advantages and disadvantages of **peritoneal dialysis**?
Advantages:
No need for specialist equipment, can be done at home, patient can be mobile during treatment, no risk of rejection.
Disadvantages:
Risk of infection, required more frequently (fluid must be regularly changed)
73
What is the best long-term treatment for kidney failure?
Kidney Transplant
74
What are the advantages of kidney transplants?
No need for regular dialysis sessions
No need for dietary monitoring
Generally improves quality of life
Prevents the build-up of waste products between dialysis sessions that can cause long-term body damage.
75
What are the disadvantages of kidney transplants?
Risk of organ rejection so patient must take immunosuppressant drugs
Shortage of donor kidneys, dialysis is readily available
Involves major surgery with associated risks
