RENAL SYSTEM

FUNCTION OF THE KIDNEY

FUNCTION OF THE KIDNEY :Formation of urine .

1- Role in homeostasis:Primary function of kidneys is homeostasis such as :

Excretion of waste productsUrea,Uric acid,Creatinine andBilirubin Maintain water balance*conserving water when =decreased *Excreting water when = excess in the body Maintain electrolytes (Na) Especially sodium is in relation to water balance Maintain acid-base balance PH in the blood and body fluid maintained in normal range

FUNCTION OF THE KIDNEY :

2- Hemopoeitic function: secrete erythropoeitin for erythrocytes-secrete thrompopoeitin for thrombocytes3-Endocrine function: erythropoeitin, thrompopoeitin, renin4-Regulation of blood pressure 1. Regulating ECF(extracellular fluid ) volume 2. Renin –angiotensin mechanism 5- Regulation of blood calcium level activate vitamin D necessary for absorption of calcium from intestine to blood.

NEPHRON •It is structural and functional unit of kidney.Types of nephron:1- cortical nephron: in outer cortex2- juxtamedullary nephron: inner cortexEach nephron is formed from:1- renal corpuscle•The function of renal corpuscle is filtration of blood first phase of urine formation2- renal tubule

STRUCTURE OF RENAL CORPUSCLETWO PORTIONS:

1- glomerulus Tuft of capillaries

enclosed by Bowman capsule

These capillaries are disposed between afferent arteriole and efferent arteriole

2- Bowman capsule Is like a funnel with filter

paper Is formed by two layer:1. The inner visceral

layer2. The outer parietal

layer

RENAL TUBULE Is the continuation of Bowman capsule Consists of 3 part :-proximal convoluted tubule (PCT)-loop of Henel: Descending limb, Hairpin bend,

Ascending limb-Distal convoluted tubule (DCT)

JUXTAGLOMERULAR APPARATUS organ situated near glomerulus of each nephrone 3 structures:1 macula densa2 extraglomerular mesangial cell3 juxtaglomerular cells Function :Primary function is secretion of hormonal sub1- secretion of renin2- secretion of other substances (PGs)3- regulation of GBF and GFR

RENIN- ANGIOTENSIN SYSTEM

•Renin released into the blood•Angiotensinogen renin angiotensin I ACE(lung) angiotensin II angiotensinase(RBCs) angiotensin IIIFUNCTIONS OF ANGIOTENSIN II:•Increase blood pressure by vasoconstriction •Stimulate adrenal cortex to secrete aldosterone •Regulate glomerular filtration •Increase water intake by stimulating the thirst center •Increase secretion antidiuretic hormone from hypothalamus

RENAL CIRCULATIONRenal blood vesselsRenal artery from abdominal aorta and enter the kidney through the hilus Regulation of renal blood flow:By Autoregulation.Autoregulation :The ability of an organ to regulate its own blood flowPresent in some vital organs in the body such as brain, heart and kidneys1- Myogenic response2- tubuloglomerular feedback

URINE FORMATIONIntroduction :Urine formation is a blood cleansing function.Normally about 26% of cardiac output enters the kidneys to get rid of unwanted substances Kidneys excrete the unwanted substances in urine Normally about 1 to 1.5 L(1000-1500ml) of urine is formed every dayThe mechanism of urine formation includes three processes :1. Glomerular filtration2. Tubular reabsorption3. Tubular secretion

MECHANISM OF URINE FORMATION

I-Glomerular filteration: DefinitionGlomerular filtration is the process by which the

blood that passes through glomerular capillaries is filtered through the filtration membrane

Filteration membrane:Formed by 3 layer :1. Glomerular capillary membrane2. Basement membrane3. Visceral layer of bowman capsule

Process of glomerular filtration : All substances of plasma even the minute particles are

filtered except plasma proteins due to their large molecular size (ultrafilteration).

The filtered fluid is called glomerular filtrate The glomerular filtrate contain all the substance of

plasma except the Plasma proteins Glomerular filtration rate (GFR)Total quantity of filtrate formed in all nephrons of both

kidneys in the given unit of time The normal (GFR) (125mL/min)or (180 L/ day) Filteration fraction: Is the fraction (portion) of the renal plasma which

becomes the filtrate It is the ratio between renal plasma flow and glomerular

filtration rate It is expressed in percentage = GFR/RPF X 100

FACTORS AFFECTING GFR1-renal blood flow (RBF): It is the most important factor for glomerular filtration 2-Tubuloglomerular feedback: Is the mechanism that regulate GFR3-Glomerular capillary pressure:Pressure exerted by blood in glomerular capillary4-Colloidal osmotic pressure:Pressure exerted by plasma protein in the glomeruli5-Hydrostatic pressure in bowman capsule:Pressure exerted by filterate in Bowman capsule6-Constriction of afferent & efferent arteriole: The Constriction of afferent arteriole reduces the blood

flow to the glomerular capillary . If efferent arteriole is constricted, the GFR increases

because of stagnation of blood in the capillaries.

7-Systemic arterial pressure: 8-Sympathetic stimulation: afferent & efferent arteriole are supplied by

sympathetic nerves. Strong sympathetic stimulation cause

sever constriction of the blood vessels9-Surface area of capillary membrane:10-Permeability of capillary membrane:11-Hormonal: • increase GFR by vasodilatation: prostaglandin

(PGE2)• decrease GFR by vasoconstriction: (Angiotensin II)

II- TUBULAR REABSORPTION Definition

Tubular reabsorption is the process by which water and other substances are transported from renal tubules back to the blood .

Selective reabsorption • Essential substances such as glucose , amino acids and

vitamins . • Substances like metabolic waste products are excreted

through urine. Mechanism:

2 -passive reabsorption 1- active reabsorption

o Is the movement of molecules along the electrochemical gradient . o does not need energy .o substances reabsorbed urea, water

o Is the movement of molecules against the electrochemical gradient .o it needs energy (ATP)o substances reabsorbed sodium, calcium ,potassium

Regulation of tubular reabsorption:1-Glomerulotubular balanceIs the balance between the filtration and reabsorption of

solutes and water in kidney.2-Hormonal factorWhich regulate GFR. Aldosterone Angiotensin ll Antidiuretic hormone 3-nervous factor Activation of sympathetic nervous system increase the

tubular reabsorption Transport maximum (Tm) value: The rate at which a substance is reabsorbed from the

renal tubule. 375mg/min for males 300mg/ min for females

Reabsorption of important substances: sodium: 99% reabsorbed water: from proximal convoluted tubule (PCT): obligatory water

reabsortption from distal convoluted tubule and collecting duct (DCT):

facultative water reabsorption glucose: Is completely reabsorbed in the proximal convoluted tubule Renal threshold for glucose:Is 180mg/dl in venous blood .When blood level for glucose reaches 180 mg/dL, glucose

is not reabsorbed completely and appear in urine. bicarbonate :mostly in proximal tubule in the form of CO2

III- TUBULAR SECRETION

• Is the process by which the substance are transported from blood into renal tubules

Substances secreted in renal tubules :

PotassiumAmmoniaHydrogen ions

CONCENTRATION & DILUTION OF

URINE

CONCENTRATION OF URINE Osmolarity of glomerular filtrate is same as

that of plasma and it is 300 mOsm/L. Normally urine is concentrated and its

osmolarity is 4 times more than that of plasma 1200 mOsm/L.

Depends on two factors: Water content in the body. Antiduiretic hormone .

When the water content in body decreases kidney retains water and excretes concentrated urine

Formation of concentrated bySecretion of ADH

FORMATION OF DILUTE URINE

If water content in the body is more , kidney excretes excess water making the urine dilute .

ADH increases the water reabsorption from renal tubule and collecting duct resulting in concentration of urine .

When the volume of body fluid increases or the osmolarity of body fluid decreases ,ADH secretion stops so water reabsorption from renal tubules dose not take place

Leads to excretion of large amount of water urine

making the urine dilute

ROLE OF ADH The final concentrated of urine is achieved by

ADH Normally the distal convoluted tubule and the

collecting duct are not permeable to water . In the prescence of ADH distal convoluted

tubule and the collecting duct become permeable to water resulting reabsorption

The water reabsorption induced by ADH is called facultative reabsorption of water .

ROLE OF KIDNEY IN ACID-BASE BALANCE

Kidneys play important role in maintenance of acid-base balance by:

excreting hydrogen ions retaining bicarbonate ions. Normally urine is acidic in nature with pH of 4.5

to 6 The metabolic activities in the body produce lot

of acids (with hydrogen ions) which threaten to push the body towards acidosis .

Kidney prevent this by excreting hydrogen ions and conserving bicarbonate ions.

MICTURITION Definition Is a process by which urine is voided from the

urinary bladder it is a reflex process

FILLING OF URINARY BLADDER: A reasonable volume of urine can be stored in

urinary bladder without any discomfort and without much increase in pressure inside the bladder

It is due to the adaptation of detrusor muscle The relationship between the volume of urine and

pressure in urinary bladder is studied by cystometrogram

CYSTOMETROGRAMDefintion : Cystometrogram is the graphical registration of

pressure change in urinary bladder in relation to volume of urine collected in it .

MICTURITION REFLEX

It is the reflex by which Micturition occurs

This reflex is elicited by the stimulation of stretch

receptors situated on the wall of urinary bladder and

urethra.

When about 300 to 400ml of urine is collected in the

bladder the pressure inside the bladder increases

This stretches the wall of bladder resulting in

stimulation of stretch receptors and generation of

sensory impulses .

THANK YOU

MCQ

CHOOSE THE CORRECT ANSWER:1- kidney function concerned with homeostasis such as: Maintenence of water balance Maintenence of electrolyte balance Maintenence of acid-base balance All of the above2- The hormones secreted by the kidney: Erythropoietin Thrombopoietin Rennin All of the above3- the function of renal corpuscle: Secretion of hormones Regulattion of blood pressure Filtration of blood None of the above4- The hormone which is secreted by juxtaglomerular apparatus is: Renin Antidiuretic hormone Aldosterone hormone calcitonin

5- Hormones which regulate GFR are: Aldosterone Angiotensin II Antidiuretic hormone All of the above6- the important role of renin-angiotensin system is: Maintenance of water balance Maintenance of body temperature Maintenance of electrolyte balance Maintenance of blood pressure7- the pressure exerted by plasma proteins in the glomeruli is called: Glomerular capillary pressure Colloidal osmotic pressure Hydrostatic pressure in Bowman`s capsule Systemic blood pressure8- Important substances for reabsorption are: Water Glucose Sodium All of the above

9- the most important factor affecting GFR is: Tubuloglomerular feedback Renal blood flow Constriction of afferent arteriole Sympathetic stimulation10- mechanism of tubular reabsorption: By active reabsorption By passive reabsorption By endocytosis A and b11- substances secreted in different segments of renal tubules are: Potassuim Ammonia Hydrogen ions All of the above12- the final concentration of urine is achieved by: ADH Aldosterone Angiotensin I parothormone

13- kidney regulate acid-base balance by: Excrete hydrogen ions Retaining bicarbonate ions Retaining hydrogen ions A and b Fill in the bLank: The structural and functional unit of kidney is ………………… which is

formed by two parts:1- …………… 2-……………… Nephrons are classified into two types:1-…………… 2-………………. Kidney secrete …………….. which important for erythropoiesis and

………………. for production of thrompocytes. The mechanism of urine formation includes three processes: 1-……….……………………2-…..………………….. 3-………………………… Renal blood flow is regulated by ………………….. which involve two

mechanisms:1-…………………………………… 2-……………………………….. Glomerular filteration rate(GFR) is defined as …………………… .

……………..Normal GFR is ……………………. The final concentration of urine is achieved by …………………..

homrone kidney maintains acid-base balance by………………………

and…………………