Module 2 Lecture 4
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What are the three key processes of urine formation? please LABEL the DIAGRAM
Glomerular filtration, tubular reabsorption and tubular secretion
What is involved in glomerular filtration?
filters the blood –> produces a cell-and protein-free filtrate
What is involved in tubular absorption?
Selectively moves substances from the filtrate back into the blood to reclaim what the body needs –> anything that is not reabsorbed becomes urine
What is involved in tubular secretion?
selectively adds substances from the blood into the filtrate –> anything that is secreted becomes urine
What are some key processes of urine formation?
• the kidney filters about 180 L of blood each day, less than 1% of body weight but consume 20-25% of all oxygen at rest
How is filtrate and urine different?
filtrate is plasma without proteins, while urine contains excess solutes, ions and metabolic waste
Glomerular function in detail (pls label)
Hydrostatic pressure forces fluids & solutes through a membrane, “simple mechanical filters”
What are the 3 layers of the filtration membrane?
• Capillary endothelium • Basement membrane • Podocyte foot processes
What is the outward pressures in the glomerular filtration
Outward pressures • Hydrostatic pressure in glomerular capillaries (glomerular blood pressure forces fluid out of capillary) • Osmotic oncotic/protein pressure in Bowman’s capsule space (this is zero as proteins don’t really enter capsule)
What is the inward pressures in the glomerular filtration
Hydrostatic pressure in Bowman’s capsule space (filtrate in capsule draws fluid into capillary) • Osmotic oncotic/protein pressure in glomerular capillaries (proteins in blood draw fluid into capillary)
What does net filtration pressure favour?
net filtration pressure favours and outward pressure and therefore fluid is forced out of capillary
What is glomerular filtration rate measured in?
Glomerular filtration rate (GFR) is the volume of filtrate formed each minute by the kidneys
What is GFR directly proportional to?
Net filtration pressure • Filtration membrane permeability and total SA for filtration
What is step 2 (tubular r re-absorption)
Reabsorption selectively reclaims tubule contents & returns it to blood
What occurs in tubular re-absorption
• Reabsorption of almost all substances is coupled to active sodium reabsorption – Basolateral membrane: Na+/K+ ATPase pump – Apical membrane: secondary active transport/cotransport carriers or facilitated diffusion – Water reabsorption: aquaporins act as water channels (regulated by ADH in collecting duct)
What occurs in tubular secretion?
Secretion selectively moves substances from blood into filtrate – waste products that ‘escaped’ filtration E.g. H+, excess K+, creatinine, urea, uric acid, certain drugs & metabolites bound to plasma proteins - Urine eventually excretes both filtered (& not reabsorbed) & secreted substances
OVERALL tubular re absorption and secretion? (LABEL)
Each tubule segment is responsible for reabsorbing and/or secreting different solutes • Some are regulated by hormone action • Maintains an osmotic gradient in the medullary interstitial space