33 (im Going To Jump Of A Bridge) Flashcards
Reabsorption in the nephron: Water - thee important places where water is reabsorbed in the nephron
Proximal convoluted tubule (PCT):
- 67% of filtered load (water) reabsorbed
Descending limb of the nephron loop:
- 25%
Collecting duct:
- 2-8% of filtered load reabsorbed
Excretion:
- < 1- 6% of filtered load is excreted
What kind of absorbtion happens in the first two areas
Bulk (obligatory) water reabsorption
Bulk (obligatory) water reabsorption
- accounts for 92% of total water reabsorption
- not regulated – automatic!!
- leaky epithelia
- trans-and paracellular water reabsorption
Regulated (facultative) water reabsorption
Regulated (facultative) water reabsorption
- accounts for 2-8% of total water reabsorption
- regulated by anti-diuretic Hormone (ADH)
- tight epithelia
- only transcellular reabsorption
Reabsorption in the nephron: Sodium
- 4 important places for reabsortion
Proximal convoluted tubule (PCT):
- 67% of filtered load reabsorbed
Ascending limb of the nephron loop:
- 25% of filtered load reabsorbed
Distal convoluted tubule:
- 5% of filtered load reabsorbed
Collecting duct (CD):
- 2-3% of filtered load reabsorbed
Excretion:
- < 1% of filtered load is excreted
What happens here?
Bulk sodium (Na+) reabsorption
Bulk sodium (Na+) reabsorption
- accounts for 92% of total sodium reabsorption
What happens here?
Regulated sodium (Na+) reabsorption
Regulated sodium (Na+) reabsorption
- accounts for 7-8% of total sodium reabsorption
- regulated by aldosterone (RAAS)
What drives and regulates body water homeostasis?
- Distribution of body water
- Osmolarity/tonicity of solutions
- Changes in blood osmolarity
- Reabsorption of water and sodium in the nephron
- Effects of osmotic changes on the kidney
- Effects of volume changes on the kidney
Reabsorption: Proximal convoluted tubule
- Water reabsorption in the proximal tubule (67% of Na+ the filtered load) is driven by Na+ reabsorption (isosmotic!! - water wants to follow the solute molecule )
- Transporters such as the glucose co-transporter sodium-glucose co-transporter use the sodium gradient to reabsorb solutes (like glucose)
- Glucose and sodium (Na+) are transported through
the proximal tubule cells - the proximal tubule is ‘leaky’ epithelia
- chloride follows via the paracellular pathway
- water follows by the paracellular and transcellular pathways
Nephron loop
Decending is…
Permeable to water (aquaporins)
Nephron loop
Ascending is permeable to
Sodium (ion transporters)
How does reabsorbtion of water from the descending loop work? What pathways?
- The descending loop is leaky epithelium, so water (H 2O) is reabsorbed from the nephron into the peritubular fluid
- via the transcellular pathway: aquaporins
- via paracellular pathway, across the junctions between
cells
How does reabsorbtion of water from the ascending loop work?
The ascending loop reabsorbs Na+ into the peritubular fluid
In Juxtamedullary nephrons: what does the different permeability’s in the nephron loops provide?
The different permeabilities of the descending (water) and ascending (sodium) parts of the JMNs loop allows them to generate a:
- Hyper-Osmotic Medullary Gradient (HOMG)
(Deeper u go in the loop the higher the osmolaroty, same with collecting duct - important for water reabsortion form the collecting duct)
Reabsorption: Distal convoluted tubule and collecting duct
WATER: collecting duct
- Regulated (facultative) water reabsorption
- tight epithelia
- only transcellular reabsorption
- regulated by anti-diuretic hormone (ADH)
Sodium: distal convoluted tubule and collecting duct
- Regulated sodium reabsorption
- regulated by aldosterone (RAAS)
Regulation of body osmolarity - ADH
- TBW changes alter plasma increases due to the gain of water. (ECF) osmolarity
- detected by osmoreceptros in hypothalamus
- stimulates pituitary gland to secrete more/less ADH
- ADH alters permeability of collecting duct cells, so water is retained/ excreted to balance the initial change in TBW
- plamsa osmolarity stable
- cell volume stable
To move anything in or out of cell we need:
- driving force
- a way to move
Reabsorption of water in the nephron: Collecting duct
- what is the driving force - what is the way they can move
- HOMG
- ADH
An increase in iso osmotic fluid
Wont set off
- wont set off osmotic receptor
Regulation of ECF volume – Aldosterone (RAAS) and ANP
Changes in ECF volume:
- an increase in volume : ANP
- a decrease in volume : Aldosterone (RAAS)
Composition of Normal urine:
- Water: 95-98% of urine is water
→1.5 L/day - Creatinine (muscle metabolism)
- Urea (amino acid breakdown)
- Uric acid (purine breakdown)
- H+ (hydrogen ions)
- Na+ (sodium), K+ (potassium)
- Medications (anti-viral, diuretics)
- Toxins
Composition of Pathological urine:
- Glucose (glucosuria, diabetes)
- Protein, especially albumin (proteinuria)
- Blood: red blood cells/erythrocytes (haematuria)
- Haemoglobin (haemoglobinuria)
- White blood cells/leucocytes
- Bacteria (infection)
What can you see - normal urine
Clear, to light or dark amber
What can u taste - normal urine
- pH dependant on diet (4.6 - 8.0)
- “Average” person: pH of 6 - 7.5
- Vegetarians: pH up to 8.0
- High protein diet (e.g. meat eaters): pH as low as 4.6
Smell - normal urine
Unremarkable
What can u see - Pathological urine:
Orange, red, brown, blue/green
Ta s t e - pathological urine
Sweet: Diabetes mellitus
Smell:
Pathological urine:
- “Fruity”: ketones from: fasting, diabetes or chronic alcohol abuse
- “Rotten”: infection (bacteria), tumour
