Physio Renal 1

Physiology

What are the functions of the kidneys

• Regulation of: electrolyte, osmolarity, acid-base balance

• Excretion of foreign substances and metabolism

• Produces hormones (Eg. Erythropoietin)

Renal functional anatomy

• Cortex (outer portion)

• Medulla (inner portion)

• Renal Corpuscle (Glomerus and Bowman’s capsule)

• Loop pf henle

• Collecting duct

• Nephron (Functional unit)

• Blood vessels

• Lymphatics

• Nerves

This tubule reaches up to medullary portion and is impiortant for concentrating and diluting ability of the kidney

Juxtamedullary nephrons

This is the site where urine formation occurs

Nephron

Glomerular capillaries enclosed within the Bowman’s capsule

Renal corpuscle

Proximal to bowman’s capsule

Proximal convoluted tubule

Appears as hairpin loop consisting of ascending and descending loop

Loop of henle

What are the two ascending loop

• Thin ascending loop

• Thick ascending loop

Responsible for filtering out toxic substances, secreting substances back into urine, and reabsoring substances back into the blood

Blood flow

Cardiac output:

1. Cortex

2. Medulla

Cortex > Medulla

Blood flow pathway

Aorta - Renal artery - afferent arteriole - glomerular capillaries - efferent arteriole - peritubular capillaries

Surrounds the tubules and is the second capillary system. Important for tubular reabsorption and secretion processes

S

Glomerular capillariesn enclosed within the Bowman’s capsule

Renal Corpuscle

Visceral layer ofn the Bowman’s capsule

Podocytes

Space between visceral and parietal layers

Bowman’s space

Filtration

1. Large surface area

2. smaller surface area

Large surface area (Dilated) > small surface area (constricted)

Function of mesangial cells

• Structural support for capillaries

• Secrete extracellular matrix

• Secrete prostaglandins, cytokines

• Phagocytic activity

Filtration barrier is composed of

• Podocyte foot processes

• Glomerular basement membrane

• Capillary endothelium

Fenestrated and Contains negatively charged glycoproteins

Capillary endothelium

Identify one’s that are permeable to capillary endothelium

• RBC

• WBC

• Platelets

• Sodium

• Urea

• Glucose

• anions

• cations

• RBC (unpermeable)

• WBC (unpermeable)

• Platelets (unpermeable)

• Sodium (permeable)

• Urea (permeable)

• Glucose (permeable)

• anions (unpermeable)

• cations (permeable)

Porous matrix of njegatively charged glycoproteins and is MAIN CHARGE-SELECTIVE FILTER

Glomerular Basement membrane

Long-fingerlike processes that interdigitate to coverthe GBM. It is size-selective filter

foot processes of the podocytes

Fluid found within Bowman’s space that contains substances which have passed through kidney’s filtration process

Ultrafiltrate

Filterability

1. > 42A

2. 18-42 A

3. < 18 A

1. > 42A (not filtered)

2. 18-42 A (Varying filterability)

3. < 18 A (freely filtered if polycationic or neutral)

Filterability

1. Water

2. Sodium

3. Glucose

4. Inulin

5. Myoglobin

6. Albumin

1. Water (1)

2. Sodium (1)

3. Glucose (1)

4. Inulin (1)

5. Myoglobin (0.75)

6. Albumin (0.005)

Rationale:

Filterability of 1: Substance is filtered as freely as water

As it approaches zero filterability decreases

Comes from muscle hence should not be seen in signifgseen n sigificant amounts in urine

Myoglobin

Its negative charge causes it to be repelled

Albumin

Glomerular filtration wherein antibodies attack GBM and loses its glomerular filtration barrier negative charges hence filtration of anionic proteins between 18 and 42 A increases

Proteinuria/Albuminuria

Marker of kidney disease

• Usually glomerular disease

• Strenous exercise

• Endothelial problems

• GBM problems

• Foot processes

Characterizes by too much albumin in urine

Nephrotic syndrome

Measure kidney function and filtering ability of the glomerulus, and is the theoretical basis for measuring GFR and RPF

Renal clearance

True/False

A 24 hour urin sample and serum creatinine is used for clearance

True

A certain value that estimates how good your kidneys are in terms of filtration

Aggregate index of kidney function

Kidney health

1. High value of AIK

2. Low value of AIK

High value of AIK > Low value of AIK

Substance used for the GFR

• Stable plasma concentration

• Freely Filtered

• Not reabsorbed

• Not secretedn

• Not metabolized or produced by the kidney

• Does not alter GFR

Gold standard for the substance used for GFR

Inulin

Rationale:

• Not readily available

• Natural soluble fiber

Alternative and most used clinically substance

Creatinine

Formula of creatinine clearance to measure GFR

cuv/P

Creatinine

• Higher muscle mass vs lower muscle mass

• Male vs female

• Younger vs older

• Caucasians and africans vs asians

• Higher muscle mass > lower muscle mass

• Male > Female

• Younger > older

• Caucasians and africans > asians

Indication of very low GFR <60

• decrease of filtration

• Kidney disease or failure

Indication of very high GFR > 140

• Hyperfiltrating kidney

• Pressure within glomerulus is very high

Factors that increase GFR

• PGC

• πBS

Factors that decrease GFR

• PBS

• πGC

Glomerular capillary hydrostatic pressure, and is the main driving force of GFR

PGC

Bowman’s space oncotic pressure and is the pulling pressure exerted by albumin. It is equally zero in healthy in individuals

πBS

VR

1. KF

2. GFR

A.

Rationale:

• Increase in KF increases GFR

• Increase KF Increase permeability

• Increase KF Increase SA

• Increase KF Increase Kidney filtration

Afferent arteriolar Resistance Vasodilation

• ↓ Resistance

• ↑ PGC

• ↑ GFR

• ↑ RBF

Rationale:

• Afferent arteriole is dilated

• Efferent Arteriole is Constricted

• Afferent favors filtration while efferent favors reabsorption

Afferent arteriolar Resistance Vasoconstriction

• ↑ Resistance

• ↓ PGC

• ↓ GFR

• ↓ RBF

Afferent vasoconstriction favors reabsorption