Lecture 11 (2) : renal histology, function & circulation Flashcards
Describe the structure of renal corpuscle
- capillaries - called the glomerulus - increase SA for filtration
- glomerulus surrounded by epithelium layer called Bowman’s capsule
- internal layer of capsule = visceral & external = parietal
- between each layer is the capsular space which receives filtered fluid that through capillary wall & visceral layer
What is the difference between the vascular pole & urinary/ tubular pole?
- Vascular pole - where the afferent arteriole enters and efferent arteriole leaves
- Urinary / tubular -where the proximal convoluted tubule begins
What are podocytes?
- cells present that make up the visceral the epithelial lining of the bowman’s capsule
What are podocytes primary and secondary processes?
- Podocytes have primary processes which wrap around the glomerular capillaries. The trabeculae in turn have secondary processes called pedicels
- pedicels make the thin gaps called filtration slits
What are filtration slits?
- the spaces between pedicels on the glomerular basement membrane through which water, glucose and amino acids move through as they become glomerular filtrate
What is the filtrate called during the glomerular filtration process?
- glomerular filtrate
What are the 3 layers of the glomerular filtration barrier?
- endothelium of the glomerular capillaries which contain fenestrations ( lets everything through except blood cells)
- basement membrane - (what the endothelial cells sit on) - a matrix of negatively charged glycoproteins which prevent the filtration of large proteins
- Podocytes - pedicels -Filtration slits - key selectively barrier in filtration, lets molecules based on their size and charge
What is the function of the glomerular basement membrane?
- it is a selective macromolecular barrier that acts as a physical (not cellular) filter/barrier against negatively charged particles and large macromolecules eg proteins
Why are filtration slits the key selectively barrier in the filtration barrier of the bowman’s capsule?
- they are important as they prevent large blood proteins and blood cells from moving into the bowman’s capsule
What does GFR stand for?
- Glomerular filtration rate - the total amount of filtrate formed by all renal corpuscles in both kidneys per min
- can be used to diagnose if patient has kidney impairment
- typically 125ml/min or 180L per day ( note most of this is reabsorbed - 124ml/min)
By what 3 processes does regulation of the plasma concentration occur?
- Filtration - renus corpuscle
- reabsorption
- secretion
What is the composition of the glomerular filtrate?
- chemical composition similar to blood plasma except it contains little protein because macromolecules dont readily cross the glomerular filter
What is the difference between hydrostatic pressure (p) and oncotic pressure in the capillaries?
- in the capillaries, hydrostatic pressure increases filtration by pushing fluid and solute out of the capillaries
- capillary oncotic pressure pulls fluid into the capillaries and
How might GFR be altered?
- Through constriction and or dilation of the afferent and efferent arterioles - hormonal & neural input
- constriction (narrowing) of afferent arterioles causes decreased - hydrostatic pressure in the glomerular capillaries (reduction of blood available for filtration), GFR decreases
- constriction of efferent arterioles causes increased hydrostatic pressure
What does it mean if NFP is a positive value?
- The net fluid movement is OUT of the capillaries
What does it mean if NFP is a negative value?
- The net fluid movement is INTO the capillaries
What is hydrostatic pressure?
hydrostatic pressure = pressure exerted or transmitted by fluid PUSHING
- hydrostatic pressure difference across capillary wall or bowmans capsule that favors filtration
What is oncotic pressure
- form of oncotic pressure exerted by plasma proteins eg non filtered albumins or globulins in the blood vessels draw fluid into the vascular system PULLING
- the protein conc difference across the wall that creates an osmotic force that opposes filtration
Why does hydrostatic pressure decrease only slightly along the length of glomerular capillaries?
- Due to the presence of another set of arterioles - efferent arterioles which offer resistance to blood flow ( smooth muscle in arteriole)
- branching of glomerular capillaries
Why does oncotic pressure increase along the length of glomerular capillaries?
- due to its large loss of fluid into bowman’s capsule
- impermeability of filtration barrier to larger blood proteins
PLASMA PROTEIN CONC INCREASES
Why is there a fall in blood pressure from arteries to capillaries?
- there is a lower resistance to blood flow in capillaries - therefore a small decrease occurs before blood enters the glomerular capillaries
Describe a summary of the estimated forces involved in glomerular filtration
- glomerular capillary hydrostatic pressure (Pcap)
- Pcap decreases slightly along length of glomerular capillaries - due to large increase in cross sectional area & resistance to flow by efferent arterioles located after glomerular capillaries
- oncotic capillary pressure increases along length of capillaries as plasma protein conc rises
Where does net filtration occur ?
- across glomerular capillaries
What is the major driving force for filtration?
- the hydrostatic pressure of the glomerulus - which forces fluid out of capillary
- This is opposed by hydrostatic forces of the bowmans capsule and the oncotic pressure of the glomerular capillary protein
What is net filtration pressure NFP?
- NFP= the pressures favoring filtration minus the pressures opposing filtration
- ie hydrostatic pressure of glomerulus minus - hydrostatic pressure of the bowman’s capsule minus - oncotic pressure of the glomerular capillary protein
What is GFR determined by?
- the net filtration pressure NFP, the surface area available for filtration and also permeability of glomeruli
Why does the surface area and permeability of the glomerular capillaries tend to be greater than that of other capillaries?
- due to the presence of fenestrations and extensive branching and looping
What is the difference between glomerular capillaries & peritubular capillaries?
- glomerular capillaries arise after the afferent arteriole and the peritubular capillaries arise after the efferent arteriole
