Excretion Flashcards
What 3 products can be excreted?
- Carbon dioxide
- Nitrogen-containing compounds e.g. Urea
- others e.g. bile pigments found in faeces
What is Excretion?
The removal of metabolic waste from the body
What is metabolic waste?
A substance produced in excess by the metabolic processes in the cells, it may become toxic
Carbon dioxide’s 3 fact profile
○ Harmful in excess (disturb pH balance)
○ Carried in blood buffer system
○ Removed by lungs
Nitrogenous wastes 3 fact file
○ Excess amino acids deaminated in liver
○ Converted into ammonia then urea
○ Urea excreted in urine by kidney
What kind of blood does the hepatic artery carry?
Oxygenated blood
What kind of blood does the hepatic portal vein?
Deoxygenated blood
What else, other than deoxygenated blood, does the hepatic portal vein carry?
Products of digestion
Through what does blood exit the Liver?
Via the hepatic vein
Where does oxygenated and deoxygenated mix?
In the Sinusoids
What are cells of the Liver called?
Hepatocytes
How are hepatocytes structured?
Cuboidal with microvilli
What are Kupffer cells?
Specialised macrophages in sinusoids
What do Kupffer cells do?
Break down old RBC’s into Bilirubin
Describe the process of Deamination
Amino acids —> Keto acids + Ammonia
Summarise the ornithine cycle
- Ammonia + CO2 —> Urea
- Urea is excreted by the kidney
How is sugar stored in the liver?
In the form of Glycogen. It forms granules in the cytoplasm of the hepatocytes
What two enzymes do liver cells contain that render toxic molecules less toxic?
Catalase and Cytochrome P450
What does the enzyme catalase do to make toxic molecules less toxic?
It turns hydrogen peroxide to oxygen and water
What is the ‘Nephron’ part of the Kidney?
The functional unit
What does the Nephron do?
Filters waste from the blood
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, which leads to the ureter
What is the function of the Bowman’s capsule/
Ultrafiltration
What is the function of the Proximal Convoluted Tubule?
Selective reabsorption including glucose reabsorption
What is the function of the Loop of Henle?
Water reabsorption
What is the function of the Distal Convoluted Tubule?
Osmoregulation
Name the 4 Blood vessels in the Kidney
- Glomerulus
- Afferent arteriole
- Efferent arteriole
- Peritubular capillaries
What happens in the Proximal Convoluted Tubule (PCT)?
- Reabsorption of salts, glucose and H2O
- 85% of water reabsorbed here
What happens in the descending limb?
- Salts added; water removed
- Water potential increases
What happens in the ascending limb?
- Salts removed (active)
- Water potential increases
What happens in the collecting duct?
- Water removed; Water potential decreases
Fluid from the capillaries in the glomerulus is pushed into the Bowman’s capsule by what process?
Ultrafiltration
What acts as the filter in Ultrafiltration?
The barrier between the blood in the capillary and the lumen of the Bowman’s capsule
What are the three layers of the filter in Ultrafiltration?
- The endothelium of the capillary
- The basement membrane
- Epithelial cells of the Bowman’s capsule
Outline the 4 steps of Ultrafiltration
- Blood enters glomerulus via afferent arteriole
- Afferent diameter bigger than Efferent diameter
- Therefore blood is under high pressure
- Small solutes enter Bowman’s capsule
Which layer of the Ultrafiltration filter keeps most proteins held in the capillaries of the Glomerulus
The basement membranes’ fine mesh of Collagen fibres and Glycoproteins
What is the name of epithelial cells of the Bowman’s capsule?
Podocytes
How do Podocytes have a specialised shape?
- They’ve many finger-like projections (major-processes)
- On each one there are minor processes that hold the cells away from the endothelium of the capillary
- Ensure there are gaps between the cells
- So fluid from Glomerulus can pass between cells into lumen of Bowman’s Capsule
The Bowman’s capsule leads into the rest of the tubule after Ultrafiltration, which is composed of what 3 parts?
- Proximal Convoluted Tubule
- Loop of Henle
- Distal Convoluted Tubule
The cells lining which part of the Kidney are specialised to achieve (selective) reabsorption?
The cells lining the Proximal Convoluted Tubule
Give three ways that the cells lining the PCT are specialised to achieve selective reabsorption
- cell surface membrane in contact with tubule fluid is highly folded into microvilli - High SA for absorption
- Cell surface membrane also contains special cotransporter proteins that transport glucose/AAs
- Cell cytoplasm has many Mitochondria
Outline the 5 step process of selective reabsorption
- Sodium actively pumped out of cells lining tubule into blood
- Glucose/AAs co-transported into cells with sodium from tubule
- Diffuse into blood
- Water follows into cell by osmosis
- Glucose/AAs diffuse into the blood
Outline water reabsorption in the Loop of Henle
- In descending limb, water potential falls
- In ascending limb, water potential increases
- Overall effect is increase in water potential
What happens in the descending limb of the loop of henle during water reabsorption there?
- Water lost out of tubule
- Sodium/chloride diffuse out
What happens in the ascending limb of the loop of henle during water reabsorption there?
- Wall of ascending limb impermeable to water
- Sodium/Chloride actively transported out
- Urine becomes more dilute
What is meant by the countercurrent multiplier system?
- Its the name of the arrangement of the Loop of Henle system
- Close arrangement of the ascending and descending limb
What is the role of the countercurrent multiplier system?
To increase the efficiency of transfer of mineral ions in ascending limb to the descending limb, in order to create water potential gradient seen in the Medulla
What does the countercurrent multiplier system do? (what sequence happens because of it)
Sodium ion pumped out of ascending limb draws water out of the descending limb
What does the collecting duct do?
- The fluid flowing in contains lots of water
- So it carries fluid back down the collecting duct to the pelvis
Describe the change in the concentration of Glucose in the tubule fluid as the fluid passes along the Nephron and the collecting duct
Glucose decreases in concentration as it is selectively reabsorbed from the proximal convoluted tubule
Describe the change in the concentration of Sodium ions in the tubule fluid as the fluid passes along the Nephron and the collecting duct
- Sodium ions diffuse into the descending limb of the Loop of Henle, causing the concentration to rise.
- They’re then ACTIVELY pumped OUT of the ascending limb so concentration decreases
Describe the change in concentration of Urea in the tubule fluid as the fluid passes along the nephron and the collecting duct
Urea concentration rises as water is withdrawn from the tubule. Urea is also actively moved into the tubule
Describe the increase in the concentration of the minerals Sodium and potassium in the tubule fluid as the fluid passes along the nephron (the distal convoluted tubule part) and the collecting duct
- Even though sodium ions are removed from the tubule (in the ascending limb of the Loop of Henle) their conc rises in DCT and collecting duct as water is removed
- Potassium ions conc increases too, as water is removed. It increases further than Sodium because it’s also actively transported into the tubule. (to be removed in urine)
85% of the fluid is reabsorbed where in the Nephron?
Proximal Convoluted tubule
What happens/is the purpose of the distal convoluted tubule? (i.e. what happens here?)
Active transport is used to adjust the concentrations of several mineral ions
What is Antidiuretic hormone? (ADH)
A hormone that controls the permeability of collecting duct walls
What is an Osmoreceptor?
A sensory receptor that detects changes in water potential
How do the kidneys alter the volume of urine produced?
By altering the permeability of the collecting ducts
How do the cells in the walls of the collecting duct respond to levels of Antidiuretic hormone in the blood?
- Cells in the walls have membrane-bound receptors for ADH
- ADH binds to these receptors and causes a chain of enzyme controlled reactions inside the cell
How do the enzyme controlled reactions stimulated by ADH actually cause the membrane to become more permeable?
Vesicles containing water permeable
channels fuse with the cell surface membrane, making the walls less permeable to water, and more water can be reabsorbed
What happens if ADH levels in the blood fall?
- The cell surface membrane folds inwards to create new vesicles that remove water channels from the membrane. - The walls are now less permeable to water, so it passes down the collecting duct to form a greater volume of urine
Where are Osmoreceptor’s found?
The Hypothalamus
Where is ADH stored in/released from?
The Posterior Pituitary
What produces ADH?
The Hypothalamus
How is the release of ADH controlled?
By a negative feedback system
Once the water potential of the water rises back up again, what happens to the ADH?
ADH is broken down, so ADH in the blood is broken down and the collecting ducts receive less stimulation
What is Glomerular Filtration rate?
The rate at which fluid enters the Nephrons
What are monoclonal antibodies?
Antibodies made from one type of cell - They are specific to one complementary molecule
What are 4 causes of Kidney failure?
- Diabetes
- Heart disease
- Hypertension
- Infection
What are the two main treatments for Kidney failure?
Transplant and (Renal) Dialysis
Name the two types of Renal Dialysis
Haemodialysis and Peritoneal Dialysis
What is a benefit of Peritoneal dialysis over Haemodialysis?
Can be done at home or work, whilst walking around rather than at a clinic 2-3 times a week. Does need a carefully monitored diet though.
Name three advantages of a Kidney transplant
- Freedom from time-consuming dialysis
- Feeling physically fitter
- Improved quality of life (can travel)
Name three disadvantages of Kidney transplant
- Need to take immunosuppressants + their side effects
- It’s major surgery under general anaesthetic
- Need for regular checks for signs/possibility of rejection
Name four substances that the urine can be tested for?
- Glucose (Diabetes diagnosis)
- Anabolic steroids (In sports)
- hCG (In pregnancy testing)
- Alcohol and recreational drugs
What is hCG?
A small protein released in early pregnancy
How does a pregnancy test detecting hCG work?
- hCG detectable in urine
2. Receptors bind to colour-activating enzymes in a line
Briefly describe the process of Gas chromatography/Mass spectrometry to test a urine sample e.g. for anabolic steroids
- Sample vaporised in gas solvent
2. Absorbed into lining and analysed using chromatogram
