Lecture 60 - Control of Excretion Flashcards
What compounds does the body excrete as waste?
H+
Creatinine
Urea
Where is sodium and water found?
Extracellular fluid:
- plasma
- interstitial fluid
Where do H+ come from?
What do we have to do to them?
Metabolism
They must be excreted, otherwise we become acidotic.
Must be maintained and pH 7.4
What is creatinine?
By product of muscle metabolism
What is blood made from?
Plasma
How much blood must be filtered to make 2 litres of blood?
200 L
What is the blood flow to the kidney, in terms of cardiac output?
25%
Which compounds are concentrated in the urine?
K+
PO4 (phosphate)
Urea
Creatinine
Which things aren’t present in the urine?
HCO3
Albumin
Glucose
What is HCO3 used in the body?
Buffer in the blood
What is the role of Albumin in the blood?
- Osmotic active substance: maintains colloid osmotic pressure
- Binds other compounds in the blood
What other proteins in the blood must not be lost?
Immunoglobulins
Fibrinogen
Draw the nephron
Slide 5
Name the structures of the nephron
Bowman's Capsule, Glomerulus Proximal convoluted tubule (PCT) Loop of Henle: - descending limb - ascending limb Distal convoluted tubule (DCT) Collecting duct
Where is the DCT?
Why is this important?
Near the glomerulus
The cells near the glomerulus release hormones that affect the DCTs secretion and reabsorption
Describe what happens in the glomerulus
Blood comes in via afferent arteriole
Filtration in the capillary
Remaining blood leaves by efferent arteriole
What is stuff reabsorbed back into?
Peritubular capillaries
What is reabsorbed in the PCT?
Water
salt
Where is reabsorption occuring?
PCT
Loops of Henle
DCT
Collecting duct
Where is secretion occuring?
PCT
DCT
Collecting duct
Describe what happens to water in the kidneys
Vast majority is reabsorbed
What happens to Na+ in the kidneys
Vast majority is reabsorbed
What happens to K+ in the kidneys
Secreted
Describe what happens to creatinine in the kidneys
100% filtered
None reabsorbed
Describe what happens to urea in the kidneys?
50% of what is filtered is reabsorbed
What do arterioles have that capillaries don’t?
Arterioles have smooth muscle in their wall
Thus, they can constrict and relax
Describe the structure of the Bowman’s capsule
- Capsular epithelium
- Glomerular capillaries
- Podocytes
- Lumen of Bowman’s Capsule
What is the role of podocytes?
Control what is and isn’t filtered from the blood
Forms filtration slits
What is GFR?
Glomerular filtration rate
Volume of plasma filtered by the glomerulus per unit time?
What is the filtration fraction?
Portion of blood going through glomerulus that is filtered
20%
In a clinical setting, how do we measure kidney function
Measure GFR
Measure creatinine function
What is the most important force that affects GFR?
Hydrostatic pressure in the glomerular capillary
What does oncotic in the glomerulus do?
Opposes filtration
However, hydrostatic pressure is very strong, so it overcomes this.
What is oncotic pressure in the Bowman’s capsule?
Should be zero, because no albumin can get out into the Bowman’s capsule
What is net filtration pressure?
What affects this pressure?
10 mmHg
Glomerular hydrostatic pressure
Glomerular colloid osmotic pressure
Bowman’s capsule fluid pressure
Does colloid osmotic pressure in the glomerular capillary change?
Yes
It increases along the glomerular capillary
Because water is being removed
