Urinary SystemYousaf khanLecturer in Renal Dialysis TechnologyIPMS- KMU

Introduction Excretion: is the process by which the unwanted

substances and metabolic wastes are eliminated from the body.

GIT: excrete food residues in the form of fees. Some bacteria and toxic substance also are excreted through feces.

Lung: remove CO2 and water vapor. Skin: excess water, salt and waste. Its also remove

heat from the body. Liver : bile pigment, heavy metals , drugs, toxin,

bacteria, etc. through bile.

Urinary SystemRenal system includes: A pair of kidneys Ureters Urinary bladder Urethra

Kidneys produce the urine. Ureters transport the urine to urinary bladder. Urinary bladder stores the urine until it is voided (emptied). Urine is voided from bladder through urethra

Anatomy of Kidneys Paired Retroperitoneal Partially protected by the 11th and 12th ribs Right slightly lower due to liver Surrounded by renal capsule Adipose capsule

FUNCTIONS OF KIDNEY Kidneys perform several vital functions besides

formation of urine. By excreting urine, kidneys play the principal role in homeostasis.

ROLE IN HOMEOSTASIS Excretion of Waste Products Urea (end product of amino acid metabolism) Uric acid (end product of nucleic acid metabolism) Creatinine (end product of metabolism in muscles) Bilirubin (end product of hemoglobin degradation) Products of metabolism of other substances

Maintenance of Water Balance Maintenance of Electrolyte Balance Maintenance of Acid–Base Balance

FUNCTIONS OF KIDNEYHemopoietic function Erythropoietin Thrombopoietin

Endocrine function Erythropoietin Thrombopoietin Renin I,25-dihydroxycholecalciferol (calcitriol) Prostaglandins.

Regulation of Blood calcium level Activating 1,25-dihydroxycholecalciferol into vitamin

D.

Regulation of Blood Pressure i. By regulating the volume of extracellular fluidii. Through renin-angiotensin mechanism.

Structure of KidneyOuter Cortex Dark and granular in appearance and contains renal corpuscles and convoluted tubules.

Inner Medulla Contains tubular and vascular structures arranged in

parallel radial lines. 8 to 18 medullary pyramids.

Renal Sinus Upper expanded part of ureter called renal pelvis Subdivisions of pelvis: 2 or 3 major calyces and about 8

minor calyces Branches of nerves, arteries and tributaries of veins Loose connective tissues and fat

Structure of Kidney

Nephron Structural and functional unit of kidney Each kidney consist of 1 to 1.3 million of nephrons Nephron start decreasing after about 45 to 50 years

of age at the rate of 0.8% to 1%

Each nephron is formed by two parts Renal corpuscle Tubular portion

RENAL CORPUSCLE Renal corpuscle is a spheroidal and slightly flattened

structure with a diameter of about 200 μ. Function of the renal corpuscle is the filtration of

blood which forms the first phase of urine formation

Type of NephronCortical Nephron Short size nephron Present in cortex Hairpin bend penetrates only up to outer zone of

medulla In human kidney 85% nephron are cortical nephron. Peritubular capillaries

Juxtamedullary Nephron Long in size 15% Corpuscles in cortex and tubular segment in medulla Vasa recta Mainly the concentration of urine and also formation of

urine

Glomerulus Tuft of capillaries enclosed by bowman capsule Afferent and efferent arteriole Vascular system is purely arterial Single layer of endothelial cell Attached to basement membrane. Filtration pores and diameter of each pores is 0.1 u.

Bowman Capsule: Capsular structure Form by two layers ( inner visceral layers and outer parietal

layer) Functional anatomy of Bowman capsule resembles a funnel

with filter paper. Diameter of Bowman capsule is 200u. Flattened epithelial cells Each cell is connected with basement membrane by

cytoplasmic extension of epithelial cells called pedicles. Epithelial cells with pedicles are called podocytes

STRUCTURE OF RENAL CORPUSCLE

Tubular portion of nephron Proximal convoluted tubule Loop of Henle Distal convoluted tubule.

Table No. 49.2

Processes of Urine Formation Glomerular filtration Tubular reabsorption Tubular secretion

Glomerular filtration: Blood is filtered while passing through the glomerular

capillaries by filtration membrane. First process of urine formation.

Filtration Membrane: Filtration membrane is formed by three layers: Glomerular capillary membrane Basement membrane Visceral layer of Bowman capsule.

Pressures determining filtrationGlomerular Capillary Pressure Pressure exerted by the blood in glomerular capillaries. It is about 60 mmHg and, varies between 45 and 70 mm

Hg.

Colloidal Osmotic Pressure Pressure exerted by plasma proteins in the glomeruli These proteins develop the colloidal osmotic pressure,

which is about 25 mm Hg.

Hydrostatic Pressure in Bowman Capsule Pressure exerted by the filtrate in Bowman capsule. It is about 15 mm Hg.

Net filtration pressure = GP – (Cp + Hp)Net filtration pressure = 60 – (25 + 15) = 20 mm Hg

TUBULAR REABSORPTION Process by which water and other substances are

transported from renal tubules back to the blood. When the glomerular filtrate flows through the tubular

portion of nephron, both quantitative and qualitative changes occur.

Large quantity of water (more than 99%), electrolytes and other substances are reabsorbed by the tubular epithelial cells.

The Reabsorbed substances move into the interstitial fluid of renal medulla. And, from here, the substances move into the blood in peritubular capillaries.

Since the substances are taken back into the blood from the glomerular filtrate, the entire process is called tubular reabsorption.

SLECTIVE REABSORPTION

MECHANISM OF REABSORPTIONActive Reabsorption Substances reabsorbed actively Sodium, calcium, potassium, phosphates, sulfates, bicarbonates,

glucose, amino acids, ascorbic acid, uric acid and ketone bodies.

Passive Reabsorption Substances reabsorbed passively Chloride, urea and water

ROUTES OF REABSORPTION Trancelluar route Paracellular route.

SITE OF REABSORPTION Substances Reabsorbed from DCT Sodium, calcium, bicarbonate and water are reabsorbed from

distal convoluted tubule.

Substances Reabsorbed from PCTGlucose, amino acids, sodium, potassium,calcium, bicarbonates, chlorides, phosphates, urea, uric acid and water.

Substances Reabsorbed from Loop of HenleSodium and chloride.

TUBULAR SECRETION Main goals: To filter out any waste that may have re-entered the

blood stream during tubular reabsorption. To maintain blood pH homeostasis This step requires active transport.

So waste moves from the: peritubular capillary interstial space distal convoluted tubule

Common substances that must be filtered in this step are:1. Wastes that moved back into the blood passively by

accident.2. Artificial materials that didn’t go into the Bowman’s

capsule during glomerular filtration (penicillin)3. Excess ions the body needs to get rid of to adjust the

blood pH.

Tubular secretion:

Tubule cell

NEPHRON TUBULE

URINE FILTRATEH2O, urea, creatinine, few other wastes

blood

Distal Convoluted Tubule

Nephron tubule

capillary

To collecting tubule

creatinine ureaH+pennicillin

pesticide

rbcCapillary cell

Glomerular

filtratio

n

bloodFiltered

solutes

Tubula

r

Reabs

orptio

n

cortex

Outer medulla

H2O

Active transportPassive transport

H2O

NaCl

NaCl

NaCl

NaCl

H2O

H2O

H2O

H2O

H2O

H2O

Loop of Henle

Urine

conc

entra

tion

Distal convoluted tubule

Tubular

secretion

WastesH+ ions

Final Urine concentration and regulation of electrolytes at the Collecting tubuleCompletes 2 main goals here:1. Adjusts blood pH and salt homeostasis 2. Maintains water homeostasis.

Adjusting blood pH and salt homeostasis continues: K+, H+ and HCO3

- ions that were collected in the distal convoluted tubule can be either stay in the urine for excretion or reabsorbed by the blood if the body needs them.