Renal 1 Flashcards
Overview of renal functions
- Regulate volume
- Regulate osmolarity
- Regulate pH – (net result of metabolism is acid load)
- Excrete metabolic waste
- Regulate ECF ions
(Na+,Cl-,K+,HCO3-, Ca++, Mg++) - Secrete Hormones
Location of kidney in body + connection to bladder
Diagram of kidney structure
How much blood goes to the kidney per minute and how much urine is produced per minute?
- 1 liter of blood per minute to the kidney
- 1-3 ml of urine produced per minute
Diagram of nephron and flow chart of structures
Flow chart of structures in nephron
Different types of loops of Henle
- Cortical nephrons have smaller loops
- Juxtamedullary ones (depicted in diagram in prev flashcard
What does the loop of Henle allow?
It establishes a vertical osmotic gradient that allows the kidney to very carefully titrate the concentration of urine going out of the body
Big picture of the inputs and outputs of the nephron
How many nephrons does each kidney have?
About 1 million
How are glomerular capillary beds different from other capillary beds?
- The pressure in them is very high (difference in diameter between afferent and efferent arterioles)
How many ml of plasma go in and out of the kidney per minute?
- 500 ml of plasma enters kidney per minute (blood is about half plasma)
- 499 ml of plasma per minute comes out of renal vein
- 1 ml is emptied into the bladder to form urine
How much plasma is filtered out of the glomerular capillary?
~125 ml (between 1/4 and 1/3)
- This is a pretty high filtration rate
- This plasma is filtered into the lumen of the nephrons (outside the body)
- This needs to be recaptured so your body doesn’t lose it
When would you see protein being absorbed into the Bowman’s capsule?
After heavy, intense exercise
How do molecules find their way into urine?
They are either:
- Filtered and not reabsorbed
- Actively secreted along the nephron
Filtration, secretion, and reabsorption in the nephron diagram
First artificial kidney
- Was the first artificial organ
- Contained a set of semi-permeable membranes sitting in a bathtub of isotonic solution (with NaCl)
- Allowed urea to come out of the body
Cross-sectional cut through renal medulla
There are capillaries adjacent to the tubules
Close-up diagram of glomerulus (terms in red show parts where lumen is outside the body)
Afferent arteriole
- Wider diameter than efferent
- Surrounded by smooth muscle
- Empties into glomerular capillary bed
How does a molecule go from the glomerular capillary into the Bownman’s capsule
It has to go through the layer of endothelial cells, some extracellular matrix, and a layer of cells that make up the capsule (podocytes)
Macula densa cells
- Specialized cells that detect the contents of the filtrate going through the arterioles and glomerulus
- They release paracrine factors that regulate what goes on at the front-end of the system
What do glomerular cells release?
Renin
Sympathetic innervation of arterioles
- There is a sympathetic fiber innervating the walls of the afferent arteriole
- Not shown on diagram, but same for efferent
Glomerulus cross-section
Shows:
- Capillaries with endothelial cell nuclei
- Mesangial cells with matrix
EM of glomerulus
Zoomed-in EM of glomerular capillary lumen
Glomerular capillary, basement membrane, and podocytes
___ form the wall of Bownman’s capsule
Podocytes
How does plasma get out of the glomerular capillary lumen?
- It sneaks between the fenestrations in the endothelial cells (these capillary beds are particularly leaky) and podocytes
- Red blood cells do not fit through
- Small proteins could physically squeeze through (but they don’t)
Zoom-in of podocytes (filtration barrier)
- Fenestrations in endothelial cells
- Basement membrane
- Filtration slits in podocytes
- Negative charges and small openings limit movement of negatively charged solutes and large solutes (proteins do not permeate)
Why do small proteins not pass into the Bowman’s capsule?
- The basement membrane (extraceullular matrix) has a combination of proteins that create a charge barrier that repel the movement of proteins through the basement membrane
- Most proteins in solution have a negative charge, and the negative charges of the proteins in the basement membrane repel the other proteins and prevent them from escaping
What escapes into the Bowman’s capsule?
- Everything else that isn’t red blood cells
- Amino acids, sugar, bicarbonate ions, protons, sodium chloride, fatty acids, nutrients, etc.
Key terms
Renal plasma flow considers ___
Hematocrit (not all blood is plasma)
Glomerular filtration rate
The rate at which plasma is filtered into the Bowman’s capsule
Diagram of GFR regulation
- There is a colloid osmotic pressure of 30 mmHG that tends to draw fluid back into the capillary (because of non-permeable proteins)
- Hydrostatic pressure is 55 mHg (very high)
- 15 mmHg of pressure in the fluids filling Bowman’s capsule (filtrate)
- Net filtration pressure is 10 mmHg
- Because there is little resistance, and there is this net filtration pressure, there is a lot of filtration
What factors would affect filtration in the kidneys?
- Anything that would change the concentration of proteins in the plasma
- If there’s a breakdown in the extracellular matrix of the basement membrane, causing proteins to be filtered, this would decrease the pressure drawing water back in, causing an increase in net pressure
- This would increase the urine flow rate
- A drop in arterial blood pressure would decrease net filtration
- A kidney stone (e.g. an excess accumulation of calcium that forms salt crystals) could block off the ureter, causing the filtrate to accumulate in the nephron, increasing pressure in the Bowman’s capsule and greatly decreasing decreasing net filtration
Diagram showing fenestrations in glomerular capillaries
Apical side of cells lining proximal tubule have villi (like a small intestine)
Extra diagram of membrane of glomerular capillary
Resistance, pressure, and flow in capillary bed
Watch lecture at 55:20
Resistors in series
Watch lecture at 59:10
Table of manipulations and effect on GFR
Watch lecture at 1:05:30
What are the categories of regulation of GFR/pressure in glomerular capillaries?
- Sympathetic stimulation
- Autoregulation
- Endocrine (short story)
Sympathetic regulation of GFR
- Moderate to high - constriction of aff and eff arteriole
- Severe – even greater constriction of afferent arteriole
Autoregulation of GFR
- Myogenic Response (Renal baroreceptor-within kidney) (stretch-> ↑[Ca++]in
- Juxtaglomerular Apparatus
Macula Densa Cells
1. Release paracrine factors (afferent arteriole)
- ↑NaCl -> purines (e.g.adenosine) -> constr.
- ↓NaCl -> Nitric Oxide -> dilation
2. Release paracrines that release Renin from Juxtaglomerular Cells. Renin activates hormones in blood (see endocrine)
Endocrine regulation of GFR (short story)
NaCl in distal tubule -> paracrines from macula densa ->renin from juxtaglomerular cells -> Angiotensin II in blood -> constriction of afferent and efferent arteriole (and many other effects throughout body)
Endocrine effects on GFR (RAAS)
Renin-Angiotensin-Aldosterone System (RAAS)
↓Blood Volume -> JGA -> ↑ renin -> ↑ angiotensin II -> ↑aldosterone
Angiotensin II vasoconstricts smooth muscle in blood vessels
(Other effects…many)
Endocrine effects on GFR (ANP)
Atrial Nariuretic Peptide (ANP) (low pressure sensing system)
↑Blood Volume -> ↑ Stretch Atrial Natriuretic Peptide (ANP)
- Vasodilates afferent; vasoconstrict efferent (↑GFR)
(Other effects…)
- ↓reabsorption of NaCl in distal tubule
- ↓release of Renin from JGCs
