Physiology 3120 Lecture Notes - Lecture 2: Macula Densa, Juxtaglomerular Apparatus, Basal Lamina

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Renal Physiology
Lecture 2
Renal Corpuscle
Function of Corpuscle: filter blood and produce filtrate
o 1st part of nephron
o Filtrate is processed by the rest of nephron
Structure of Corpuscle:
o Bowman’s Capsule: flattened epithelial cells (simple squamous)
o Capsular space: where fluid will filter into
o Glomeruli: Leaky/fenestrated capillary bed
o Podocytes: finger-like cells that are continuous with capsule and lines the
glomerulus to prevents some substance from filtering out
o Juxtaglomerular apparatus: sits right beside glomerulus
Part of the nephron tubule that twists back
Last part of ascending limb of loop of Henle passes in bw and touches
the efferent and afferent arteriole
Multiple things junctioning together to form this apparatus
Macula Densa: part of tube
Detect sodium and chloride (chemoreceptors)
Have primary cilia: (allow them to detect fluid flow; how fast
it’s flowing
Provides info to cells around them
Juxtaglomerular cells (granular cells): compose a part of the
afferent arteriole
Respond to the signals from macula densa cells
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Barriers to Filtration
Endothelial cells: of glomerulus are fenestrated
o Things can flow through these pores
Podocytes: a component of Bowman’s capsule & wrap around glomerulus
o Things can flow in between podocytes (diaphragm slits)
Basal lamina: adheres glomerulus to the podocytes
o Provides adhesive function & barrier to filtration
o Things can flow through lamina
o Composed of collagen, negatively charged glycoproteins (acts like a sieve)
Filtered Material: fluid/molecules that have passed through pores, basal lamina,
and in bw podocytes
Molecules that can pass:
o Ions (- and +); negative glycoproteins does not inhibit negative ions
o Water
o Glucose (small molecule)
o Amino acids
o Hydrophilic metabolites
Molecules that can’t pass: things you shouldn’t see in urine
o Proteins (most are too large & -vely charged); mostly inhibited by basal
lamina
o RBC and WBC’s
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Clinical Note: Urinalysis
Specific gravity: indicates hydration
o Really hydrated low gravity value
o Dehydrated high gravity value (increased solutes in blood)
Ketone: can indicate ketoacidosis (if lots)
o Should NOT be found in urine
o Production is caused by uncontrolled diabetes mellitus diabetics will break
down fats instead, making these ketones
Bilirubin: indicates intestinal or liver problem
o Should NOT be in urine
o Normally excreted through bile duct system in intestines
Glucose: indicates problem in kidney function
o should NOT be in urine
o Despite the fact it is easily filtered should be 100% reabsorbed
Overall health of the body can be quickly assessed by measuring
components of urine
Test strips with colorimetric reactions have been developed to
indicate substances in the urine
Urinalysis
Leukocytes: Indicates some kind of infection
Nitrite: indicates bacterial infection
o Nitrate (typically found in urine) is metabolized by
bacteria to form nitrite
Urobilinogen: indicates liver function problem (too high/low)
o Normal metabolite from Hb
Protein: indicates problem with filtration (carrying too much
protein in your blood)
o Should be repelled by basal lamina
pH: indicates acidity/basicity of blood
o Urine will try to compensate by excreting excess
bicarbonate or H+ ions
Hb: indicates RBCs are breaking down faster than they should
o Small so can get through but lots is a problem
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