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The Kidney

Kidney Functions-:

-Excretion of Metabolic Waste Products:

 Urea (from protein metabolism(

 Uric acid (from nucleic acid metabolism(

 Creatinine (from muscle metabolism(

 Bilirubin (from hemoglobin metabolism(

-Excretion of Foreign Chemicals:

Pesticides , Food additives , Toxin and Drugs.

-Secretion Metabolism and Excretion of Hormones:

-Hormones produced in the kidney:

 -Renal erythropoetic factor

 -1,25dihydroxycholecalciferol (Vitamin D(

 -Renin

 -Hormones metabolized and excreted by the kidney:

-Most peptide hormones (e.g., insulin, angiotensin II, etc(.

 

Kidney Function Test:-It’s a test measuring the Bilirubin , Creatinine ,

Uric acid and Urea level and it reflect the

wellness of the kidney (within the normal

average. (

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And the most important one is the erythropoietin factor.……

Because of this most of whom complaining of renal failure have

anemia because there is low production of Erythropoetin.

Regulation of acid-base balance (in addition to respiratory system) :

-Excretion acids ( kidneys are the only means of excreting non-volatile acids )

-Regulation body fluid buffers (e.g. bicarbonate(

Regulation of water and electrolytes balances:

• Sodium and Water 

• Potassium

• Hydrogen Ions

• Calcium, Phosphate, Magnesium

Regulation of arterial pressure:

Endocrine Organ

• renin-angiotensin system

• prostaglandins

• kallikrein-kinin system

Control of Extracellular Fluid Volume

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 SO to sum up here are the main functions of the kidneys :

• Excretion of metabolic waste products: urea, creatinine, bilirubin, hydrogen

• Excretion of foreign chemicals: drugs, toxins, pesticides, food additives

• Secretion, metabolism, and excretion of hormones

- renal erythropoetic factor 

- 1,25 dihydroxycholecalciferol (Vitamin D)

- Renin

• Regulation of acid-base balance

• Gluconeogenesis: glucose synthesis from amino acids

• Control of arterial pressure

• Regulation of water & electrolyte excretion

-Now in order of you to understand the kidney work you should now a little about

its anatomy : (doctor indicate that he will not ask us about this but its really helping to

now this)

At level of kidney we have :

abdominal aorta >> renal artery >>

segmental artery >> interlobar arteries >

> Arcuate arteries >> interlobular arterioles

At level of  Nephron

 (functional unit of the kidney):

Interlobular arterioles >> afferent arteriole >>

glomerulus ( bowman's capsule) and here happen

the filtration (We have 3 layers glomerulus( a network of capillaries ) :1-Epithelium of the glomerulus2-Basement membrane (highly negative charge)3-Endothelium (Wall of bowman's capsule) .the filtrate should cross these three layers .>> efferent arteriole >>network pretubular capillary (it’s the only place

where the arteriole com from capillary )

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And these functions are acomplished by a sereis of processes like :

Filtration ….. reabsorption …. Secretion …. Excertion of urine .About 180 L of blood are filtered through the kidneys daily , 178.5 L arereabsorbed and 1.5 L are excreted as urine. so most of the filtered fluid isreabsorbed again .

the reabsorption process is important because we have 3L of plazma in our bodies

which is filtered 60 times aday so without this process all the plazma will be gone with

the urine . the kidneys get its arterial supply by the renal artery which isa branch of theabdominal aorta.

 The functional unit of the kidney is the Nephron which is composed of 

Bowman's capsule , proximal tubule, loop of Henle ( ascending anddescending) , distal tubule & collecting duct . in Bowman's capsulethere's anetwork of capillaries (all from the afferent branch of renal artery)From the other side of the capillaries of the glomerulus there is theefferentarteriole and from the efferent arteriole we get the Peritubular capillarieswhich are involved in the processes reabsorption and secretion

( PS: the reabsorption and the secretion happened between thepretubular capillaries and the tubules …..Filtration occurs betweenthe glomerulus and Bowman's capsule )

- Every one must have minimal urine output which is 500 ml why ?

to dissolve soled toxin

If there is no intake of water the patent will die because we have to excrete the

minimal amount which come from the plasma that has 90% content of water

20% of the blood that enters the kidney by the afferentarteriole is filteredthe rest of the blood continue to the efferent arteriole thenat thepretubular capillaries there will be either reabsorption of the materials that

the body needs (like amino acids , electrolytes , water ..) orsecretion.

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SO :

 Filtration: somewhat variable, not selective (except for proteins),averages 20% of renal plasma flow

Proteinsare not filtered Because:1- they have high molecular weight (large in size)2- they are negatively charged and the basement membrane of theBowman's capsule is also negative . ( so there will be a repelbetween the basement membrane and the proteins )- In some cases we might have some proteins with low M.W but It'samount in urine shouldn't be higher than 150 mg daily.

- The presence of proteins in urine (known as Proteinuria) indicatesthat we

have a problem in the kidney.Its occurs between the glomerulus and the bowman’s capsule .Reabsorption: highly variable and selective, most electrolytes (e.g.Na+, K+, Cl-) and nutritional substances (e.g. glucose) are almostcompletely reabsorbed; most waste products (e.g. urea) poorlyreabsorbed

Secretion: variable; important for rapidly excreting some waste

products (e.g. H+), foreign substances (including drugs), and toxins.

- Renal Handling of Water and Solutes :

Filtration Reabsorption

Excretion

Water(liters/day)

180 179 1

Sodium(mmol/day)

25560 25410 150

Glucose 180 180 0

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(gm/day)Creatinine(gm/day)

1.8 o 1.8

 Notioce here that the glucose is fully reabsorbed . if we fined glucose in the urine

( excertion for glucose was more than 0 ) this means that we have glucose urea or 

hyperglycemisa which happens in diapetas maletus .Creatinine is a toxic material so all of the filtered creatinine will be excreted

Filtration depend on the molecular size & its charge

Sorry 4 any mistake done by : Mohammad Owesat