Lecture 35 Flashcards
How is basement membrane of glomerulus is re-generated
Basement membrane is continuously re-generated by podocytes and by
endothelial cells
H and E: DCT and PCT
Renal cortex has distal convoluted tubule and proximal convoluted tubule surrounding the renal corpuscles
DCT has well defined lumen with a smooth
border and the ep cells are cuboidal. Larger lumen and more cells per SA compared to PCT. Cytoplasm stains lighter in comparison to PCT
PCT has narrower lumen. Lumen is fuzzy with stuff inside.
PCT is longer than DCT, so you see more PCT cross section
H and E: Thin segment of loop of henle and collecting duct
Medulla has thin segment of loop of henle and collecting duct
Thin segment of loop of henle has squamous ep. Straight segment of loop of henle has no cell borders
Straight segment of loop of henle similar to the tubule from which they originate from. For example, the descending straight segment looks like PCT. The ascending straight segment of loop of henle looks like DCT.
Collecting ducts are the largest tubules in the medulla and can be distinguished from other tubules by the visible cell border. Collecting duct has larger lumen and has cuboidal to low columnar ep.
Collecting duct function is to remove water from urine, regulate how much water you pee out and recover water. There are lots of ion and water channels (aquaporins) in the cell membrane, and these things pick up stain, allowing us to see cell borders
Function of diff parts of the nephron
Proximal convoluted tubule
- Re-absorption of nutrients, vitamins amino acids, glucose, small proteins, cations
Descending limb of thin loop of Henle
- Water follows passively and concentrates the urine in the nephron.
- removal of water driven by resorption of sodium chloride
Ascending limb of thin loop of Henle
- Sodium Chloride is re-absorbed into the interstitium by active transport, creating a gradient in the medulla.
- therefore, sodium chloride conc outside of the tubule is higher than inside the tubule.
- to equilibriate this conc diff, water will
passively flow out of the descending loop of henle
- Aldosterone regulates how much sodium chloride is resorbed in the ascending part of the loop of henle but also in the DCT
Distal Convoluted Tubule
- Aldosterone dependent
Collecting duct
- Permeability for Water is ADH- dependent
- As filtrate enters collecting duct, we control
volume. Don’t want to lose too much water if you are in dry climate or just in case for accidents, so we can control how much water is removed from urine. This is under hormonal control called anti-diuretic hormone aka vasopressin
Juxtaglomerular apparatus
Afferent arteriole brings blood into glomerulus and efferent arteriole drains glomerulus
DCT contacts vascular pole of nephron and has macula densa (very dark b/c cells packed closer, so lots of nuclei) that measure how much sodium chloride remain in DCT.
If nephron not happy with balance of water and sodium chloride, this info is sent from macula densa to modified smooth muscle cells surrounding the afferent arteriole called juxtaglomerular cells. There are also some extraglomerular mesangial cells involved in this info relay.
In response, justaglomerular cells (near sympathetic nerve fiber) will produce or shut down renin production. Justaglomerular cells make renin, which is an enzyme that systemically regulates a whole bunch of things
Renin-angiotensin-aldosterone system
Kidney operates as a big organ that is also involved in systemically involved in regulating blood volume and blood pressure
Kidney receives:
- ADH from brain
- Aldosterone from adrenal cortex located on top of kidney
- increased SYN
- decreased pressure
- decreased Na+ delivery to distal tubule
Which results in 2 pathways:
1. Kidney causes Na+ and H2O retention, which increases blood volume + cardiac output, which increases arterial pressure
- Kidney causes renin release, which interacts with angiotensinogen to make AI, which then combines with ACE to make AII. Then from AII, it increases SVR, which then increases arterial pressure. But AII can also cause brain to make ADH and kidney to make aldosterone. Causing the loop to start again
Renin, AI, AII
Renin is enzyme. If renin is high, it breaks down angiotensinogen (made by liver) to angiotensin I or AI. AI flows through circulatory system, including our lungs
Lung endothelial cells and capillaries have enzyme on surface called ACE (angiotensin converting enzyme). As AI hits ACE, the ACE cleaves off aa from AI to convert it to angiotensin II or AII
AII, ADH and aldosterone functions
- AII is highly active molecule that does lots of things
- It is vasoconstrictor acting on smooth muscle cells, so systemic vascular resistance goes up (and subsequently arterial pressure goes up)
- It binds to receptors and cells in adrenal cortex. In cortex, there are cells that make aldosterone hormone (acts on DCT and ascending limb of loop of henle) to increase resorption of sodium chloride.
- All is used to maintain BP and blood volume.
- In the brain, the pituitary gland has cells that make ADH (anti diuretic hormone aka vasopressin). ADH increases activity of aquaporin in collecting duct to resorb and retain lots of water from the filtrate.
PCT function and structure
PCT resorbs useful material via their brush border (microvilli increase SA for resorption
from filtrate) (makes PCT lumen look fuzzy) on apical end. They need to pass material to capillaries located in the surrounding vasculature. Basal infoldings on basal end that contact the basement membrane allows the highly fenestrated capillaries to receive material from PCT.
Lots of mitochondria in PCT cytoplasm, so lots of transport happens across ep
Overall: Abundant microvilli, mitochondria, and basal infoldings facilitate the transport of water, peptides and glucose
List of nephron tubules in the renal medulla
Nephron tubules run in parallel in medulla.
Thin loops of henle, thick descending tubules, thick ascending tubules, collecting ducts and capillaries run parallel and side by side. Vasa recta are capillaries. Lots of exchange of water and electrolytes occur here.
H and E: thick segment of loop of Henle
Either looks like PCT or DCT.
Look like simple cuboidal ep, no borders b/w
individual cells.
No need to distinguish b/w descending or ascending loop of henle
H and E: thin segment of loop of Henle
Squamous ep, nuclei protrude into lumen, thin cytoplasm b/w cells.
H and E: collecting tubule
Has cell border
Papillary duct of Bellini
Collecting tubules merge into larger ducts called ducts of bellini that collect urine from all diff lobes from kidney and pass it on into the calyx (part of the ureter that is lined
by transitional ep)
Papillary ducts of Bellini have a columnar epithelium and open at the tips of renal papillae; has relatively defined lumen
All these larger ducts open up at renal papillae and deliver the content into the ureter
Ureter
Urine leaves the renal medulla at the renal papillae and travels to the Urinary Bladder through the Ureter
Ureter connects to kidney and collects the filtrate and it receives diff volumes of material at diff times. It needs to adapt to pressure (hydrostatic pressure).
Ureter has:
- transition epithelium, which allows adaptation to hydrostatic pressure
- inner longitudinal smooth muscle spiral
- outer circular smooth muscle spiral
- lumen forms a star shaped circumference
Empty bladder vs full bladder
Hydrostatic pressure goes up and bladder fills. The ep flattens, so you have lower heigh tof cells and surface ep cells flatten out. This
is full bladder
These cells make special proteins called uroplakins. Uroplakins are integrated into the apical plasma membrane and are
sandwiched b/w 2 lipid leaflets of the plasma membrane, forming large islands of uroplakins. The islands or plaques of uroplakins hook onto and are bound to the cytoskeleton.
If bladder is empty, plaques are not on cell surface but integrated into apical cytoplasm
As the cells spread out due to full bladder,
uroplakins are released onto the cell surface. This allows you to change SA without spending too much energy.
Full bladder: uroplakins go to top
Empty bladder: uroplakins go back down
