Renal physiology 25 Volume and Osmolality of Extracellular and - - PowerPoint PPT Presentation

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Renal physiology 25 Volume and Osmolality of Extracellular and - - PowerPoint PPT Presentation

May 04, 2023 272 likes •1.08k views

By: Dr. Foadoddini Department of Physiology & Pharmacology Birjand University of Medical Sciences Body fluids and Renal physiology 25 Volume and Osmolality of Extracellular and Intracellular Fluids in Abnormal States Pc Edema C Kf

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Body fluids and

Renal physiology

By: Dr. Foadoddini

Department of Physiology & Pharmacology Birjand University of Medical Sciences

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25

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Volume and Osmolality of Extracellular and Intracellular Fluids in Abnormal States

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Fluids in the "Potential Spaces" of the Body

Edema

Pc Kf πC

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Safety factor

Low compliance in IF 3 mmHg "Washdown“

  • f IF Protein

7mmHg Lymph Flow 7mmHg Safety Factors That Normally Prevent Edema

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26

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Blood Supply to the Kidneys

  • Blood travels from afferent arteriole to capillaries in the nephron called glomerulus
  • Blood leaves the nephron via the efferent arteriole
  • Blood travels from efferent arteriole to peritubular capillaries and vasa recta
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Internal Anatomy

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  • Blood is filtered in

the nephrons

  • The cortex of each

kidney contains ± 1,2 million nephrons

  • The nephron

consists of a renal corpuscle and a renal tubule

  • The renal tubule

consists of the convoluted tubule and the loop of Henle

  • The main filter of the

nephron is glomerulus which is located within the Bowman's capsule

Function of the Kidney

  • Terminology
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Micturation

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Bowman’s capsules - with glomerulus

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The filtration barrier - podocytes

fenestrated endothelium fenestrated endothelium primary process podocyte cell body secondary process (pedicel) filtration slit basal lamina podocyte pedicel filtration slit basal lamina

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Detailed structure of the filtration system

Capillary Capillary Basement membrane Basement membrane Fenestrations Fenestrations Podocyte process Capillary BM Endoth cell nucleus Endoth cell nucleus E F

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The filtration barrier - pedicels Bowman’s space capillary

pedicel filtration slit

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Control of Kf

  • Mesangial cells have contractile properties, influence capillary

filtration by closing some of the capillaries – effects surface area

  • Podocytes change size of filtration slits
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GLOMERULAR FILTRATION

The first step in the formation of urine is the production of a plasma ultrafiltrate. The ultrafiltrate is cell and protein-free and the concentration of small solutes are

the same as in plasma.

The filtration barrier restricts movement of solutes on a basis of size and charge.

Molecules < 1.8 nm freely filtered; >3.6 nm not filtered Cations are more readily filtered than anions for the same molecular radius. Serum albumin has a radius if about 3.5 nm but its negative charge prevents its filtration In many disease processes the negative charge on the filtration barrier is lost so that proteins are more readily filtered - a condition called proteinuria The glomerular filtration rate (GFR) is about 125 ml/min in a normal adult

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10mmHg

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Glomerular hydrostatic pressure, PGC, is high and relatively constant ≈45 mmHg. This is offset by a pressure in Bowman’s capsule PBC ≈10 mm Hg Net filtrative force is: ≈ 35 mm Hg PGC-PBC

40 30 20 10 mm Hg

  • aff. art eff. art.

THE GLOMERULUS - THE STARLING EQUILIBRIUM The glomerulus is unusual with respect to most capillary beds.

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Glomerular hydrostatic pressure, PGC, is high and constant ≈45 mmHg. This is offset by a pressure in Bowman’s capsule PBC ≈10mmHg Net filtrative force is:≈ 35 mm Hg

Osmotic pressure, ΠGS, ≈25 mm Hg. Due to the large net filtration of fluid ΠGS increases along the capillary to 35 mm Hg to achieve a balance of forces. PGC-PBC

40 30 20 10 mm Hg

Net filtration force ΠGS THE GLOMERULUS - THE STARLING EQUILIBRIUM

  • aff. art eff. art.
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FILTRATION FRACTION Filtration fraction is an important expression of the extent of glomerular filtration. It is the ratio: Filtration fraction = Glomerular filtration rate Renal plasma flow It is the fraction of renal plasma flow that is filtered at the glomerulus

RPF 750 ml/min GFR 125 ml/min Renal blood flow 1250 ml/min

Efferent Arteriole 625 ml/min

Urine 1 ml/min

124 ml/min

renal vein glomerulus tubule

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Thus, in this example filtration fraction is: 125 750 ≈ 0.17 GFR and RPF can be measured separately using clearance methods Glomerular filtration rate (GFR) is about: 125 ml/min Renal blood flow is about: 1250 ml/min Renal plasma flow (RPF) is about: 750 ml/min FILTRATION FRACTION an example Remember: plasma volume is about 60% of total blood volume

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RENAL BLOOD FLOW (RBF) Renal blood flow is ≈1.25 l/min -i.e. about 25% of the cardiac output This is a very large flow relative to the weight of the kidneys (≈350 g) Renal blood flow GFR 0 100 200 Arterial blood pressure, mm Hg 1.5 1.0 0.5 Flow, l/min

RBF determines GFR RBF also modifies solute and water

reabsorption and delivers nutrients to nephron cells.

Renal blood flow is autoregulated

between 90 and 180 mm Hg by varying renal vascular resistance (RVR)

i.e. the resistances of the interlobular

artery, afferent arteriole and efferent arteriole

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RENAL BLOOD FLOW - AUTOREGULATION Two hypotheses have been proposed to explain autoregulation 1. Myogenic hypothesis When arterial pressure increases the renal afferent arteriole is stretched Autoregulation effectively uncouples renal function from arterial blood pressure and ensures that fluid and solute excretion is constant. Increase of arterial pressure Flow increases Remember: Flow α 1 r4

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RENAL BLOOD FLOW - AUTOREGULATION

  • 1. Myogenic hypothesis

When arterial pressure increases the renal afferent arteriole is stretched Vascular smooth muscle responds by contracting thus increasing resistance Increase of arterial pressure Increase of vascular tone Flow increases Flow returns to normal

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RENAL BLOOD FLOW - AUTOREGULATION

  • 2. Tubuloglomerular feedback

Alteration of tubular flow (or a factor in the filtrate) is sensed by the macula densa of the juxtaglomerular apparatus (JGA) and produces a signal that alters GFR. It is unclear what is the factor (NaCl reabsorption?) or the nature of the signal (renin?).

  • 4. ↑Ra

↓GFR

  • 1. ↑GFR
  • 2. ↑filtrate

3.signal from JGA

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27: Tubular Processing of the Glomerular Filtrate

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10mmHg

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First Defense line: TGF GFR regulation Second Defanse line: GTB Reabsorption regulation

ΔP ΔUO

AgII

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Use of Clearance Methods to Quantify Kidney Function

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C = U * V/ P

GFR = Cinulin FF= GFR / RPF RPF= CPAH