URINARY SYSTEM

S.S.MOORTHY SEMENCHALAMM.Sc. Comm Health (Occ Health) UKM

B.HSc. Nursing (Aust)Dip Med Sc. (Moh)

Learning objectivesAt the end of the lesson, students will be able to:1.State the main components of urinary system2.Lists the functions of kidney3.State the path of blood flow through the kidney4.State the structure of nephrones5.State and describe 3 main processes in urine formation6.State the compositions of urine7.State the structure and specific functions of ureter,

urinary bladder and urethra8.Discuss the process of micturition

Urinary system consists of:• 2 kidneys ; urine

formation takes place• 2 ureters; carry urine

from kidney to urinary bladder

• 1 urinary bladder; storage of urine

• 1 urethra; carries urine from bladder out from body

Function of the Kidney

1. Eliminates waste products – urea, creatinine etc

2. Regulates blood pressure by secreting renin (juxtaglomerular cells)

3. Maintains water & electrolyte balance

4. Synthesis of prostaglandins & erythropoitein

Structure of kidney

• Retroperitoneal• Superior lumbar region• Right kidney slightly lower

than left• Bean-shaped,

indentation: hilus• Adrenal gland on top

Three layers of supportive tissue

• Renal capsule: fibrous connective tissue that enclosed kidney

• Renal fat pad: adipose tissue around renal capsule; protects kidney from mechanical shock

• Renal fascia: connective tissue that anchor kidney to abdominal wall

Longitudinal section of kidney cortex- outer,

made of bowman’s capsule enclosing glomerulus

medulla- inner, tubules responsible for urine formation

• Within medulla, triangular shaped structures; renal pyramids

• Base: open into cortex

• Apex: point to centre; renal papilla

base apex

• Renal cortex & renal pyramids- form the functional portion of kidney

• Each renal cortex & medulla; is made of 1 million nephrons

• Each nephron is the basic unit of urine formation. When nephrons are damaged they are not replaced

• Urine formed by nephron, drains into large ducts- papillary ducts

• Papillary ducts drain their contents into minor calyces

• Papillary ducts: 8-18 per kidney

• Contents of minor calyces drain into major calyces

• Major calyces: 2-3 per kidney

• From major calyces, urine drains into renal pelvis

• From renal pelvis it drains into the ureters

Route taken by the urine in the kidney after its formation:

Nephrons

Papillary ducts (renal pyramid)

Minor calyx

Major calyx

Renal pelvis

Ureters

Renal medulla ureter urinary bladder urethra

ureterUrinary bladder

urethra

Nephron: The basic functional unit of kidney

• Each kidney made of millions of nephron

• Tubule; closed at one end, other end opening to collecting tubule

NephronClosed-end- indented to form cup-shaped glomerular capsule

(Bowman’s capsule)- enclosed arterial capillaries network (glomerulus)Remainder: i. Proximal convoluted tubule (PCT)ii. Loop of Henleii. Distal convoluted tubule (DCT)

Nephrons: functional units of kidney

Renal artery (at hilum): • from abdominal aorta,

enters renal sinus• Branches to form

afferent arterioles• Supply oxygenated

blood to glomerular capillaries of renal corpuscles

• Efferent arterioles arise from glomerular capillaries & carry blood away from glomeruli

• These gives rise to plexus of capillaries around PCT & DCT

• a.k.a peritubular capillary system

• Join to form renal vein• Renal vein: drains

deoxygenated blood into inferior vena cava

Afferent arteriole - brings blood to the glomerulusEfferent arteriole - brings blood away from the glomerulus

Bowman’s capsule: • externally layered

with squamous epithelium

• Internal viscera: specialized epithelial cells (podocytes)

• Basement membranes: separate endothelial calls of glomerular capillaries & podocytes

• Capillary endothelium

• Basement membrane

• Podocytes* Made of filtrate

membrane; major role in the first step of urine formation

*

The renal corpuscle opens into:• Proximal convulated tubule

(PCT) - lined with microvilli in lumen - cuboidal epithelium - absorption & secretion - opens into nephron loop

• Distal convulated tubule (DCT), further end of the nephron- cuboidal epithelium with fewer microvilli- surrounded by smooth muscles of the space to form juxta glomerular apparatus

PCT, renal corpuscle & DCT: placed in outer kidney cortex

i. nephron loop connect PCT & DCT

ii. collecting tubule receives contents from DCT

iii. squamous epithelium protect the tubules against abrasion

iv. cuboidal epithelium: reabsorption of water & ions in the process of urine formation

v. nephron loop, collecting ducts & DCT placed in medulla

vi. The DCT opens into collecting tubule carrying urine into calyces

•DCT < microvilli than PCT

Urine production:

In nephron• 3 processes

Glomerular Filtration

Tubular Reabsorption

Tubular Secretion

Filtration

• Occurs in Bowman’s capsule by filtrate or hydrostatic pressure from glomerular capillaries

• Due to smaller diameter of efferent arterioles than afferent arterioles

• Pressure exerted by plasma & osmotic pressure in glomerulus (filteration pressure) -forces substances out of glomerulus

• The portion of the plasma entering the nephron is called -Filtrate

• Generally, small molecule: - diameter <40,000 daltons/ 7nM- e.g. water, sugar, ions, aminoacids, ammonia, urea, creatine able to pass through

• Large molecules:- exit into glomerulus- transported through blood into efferent arterioles

Filtration Cont.

Tubular Reabsorption:• The filtrate leaves

Bowman’s capsule & flow through proximal tubule, nephron loop & DCT

• Substances needed in filtrate are reabsorbed back into blood- to maintain fluid & electrolyte, pH

• Active transport

• These include water, important amino acids, nutrients, hormones etc.

a. Water is reabsorbed by osmosis in PCT

b. Amino acids, ions(Na+) are reabsorbed by active transport in the PCT

c. limit to glucose reabsorbtion: up to 100 mg/100ml, then all is reabsorbed (no glucose in urine)

d. above 150 mg/100ml glucose, then glucose present in urine

e. active ion reabsoption: sodium, potassium, calcium, magnesium,bicarbonate,

phosphate, and sulfate ions actively resorbed (selective reabsorption)

f. The small volume of filterate forming a part of urine are urea, creatine, toxic substances and K+.

Secretion

• Substances that is not required & foreign material (e.g. drugs); secreted into tubules to be excreted out from body (in urine)

• Tubular secretion: secrete H+ to maintain homeostasis of blood pH

• Ammonia is secreted by the epithelial cells of nephron and secreted into lumen of nephron by passive transport.

• Substances that are toxic to body include drugs, hydrogen ions, K+ ions are secreted into PCT, DCT by active transport.

• Though the filtrate that enters the proximal convoluted tubule is 180 lts,

• only 1% is ultimately removed as urine and• 99% is reabsorbed along the different regions of

the nephron

Urine composition

• Colour: clear - Light yellow (presence of urobilin)

• Normal volume 1 to 1.5L/day• pH ≈ 6 (4.5-8) but mostly acidic• Normal specific gravity- 1.003 to 1.040

Major nitrogen-containing wastes

a. Urea: most abundant organic waste product (21g/day), d/t breakdown of amino acids

b. Uric acid: results from breakdown of nucleic acids (0.5g/day)

c. Creatinine: generated in muscle tissue from breakdown of creatine phosphate (1.8g/day: amount depend on muscle mass)

d. Ammonia salt: small amount filtered into Bowman’s capsule

Water balance & urine output

• Regulation of urine formation – regulates homeostasis of fluids in the body

• Hormones:i. Antidiuretic hormone (ADH)ii. Aldosteroneiii. Antinatriuretic hormone (ANH)

a. When water concentration is low……….Aldosterone released

Stimulates gene expression of those proteins that involved in Na+ active transport

Na+ ion concentration in blood (K+ eliminate)

Water reabsorbed & conserved

i. Maintain water levels in blood

ii. Maintain blood pressure

Urine formation

b. When water concentration is high………Release of aldosterone is inhibited

Stopping gene expression of those proteins that involved in Na+ active transport

Na+ ion concentration in blood (reduce ion Na+ uptake)

Water excretion increases

i. Maintain water levels in blood

ii. Maintain blood pressure

Urine formation

Ureters• Tubes; convey urine from

kidney to urinary bladder• Continuous with renal

pelvis; passes obliquely through the posterior wall of bladder

• Urine accumulates – pressure in bladder – ureters compressed – opening occluded- to prevent urine reflux back

Ureters: structure & function

• 3 layers of tissue:i. fibrous tissue – outer coveringii. muscular layer – middleiii. Mucosa – inner, transitional epithelium

• Function: propel urine from kidney into bladder by peristaltic contraction of the smooth muscle

Urinary bladder• Reservoir for urine• Situated in pelvic cavity – size & position

vary depends on the amount of urine contain• Structure:

- pear-shaped – oval (filled with urine)- 3 surface: anterior, superior & posterior (base)- opens into urethra at the lowest point (neck)- have folds/ rugae- 3 orifices; form trigone (2: posterior wall – opening of ureters & 1: lower – origin of urethra)

Urinary bladder: structure & function

• 3 layers of bladder walli. outer: loose connective tissue (blood, lymph

vessels & nerves)ii. middle: smooth muscle & elastic tissue;

dextrusor muscleiii. inner: mucosa, transitional epithelium

Urethra

• Urethra opens to out side by external sphincter made of skeletal muscles.

• ♂ - opens into penis• ♀ - opens into vestibule in vagina.• By parasympathetic stimulation , muscles of

bladder expel urine.

Male urethra

• 18-20cm long• 2 curvatures – s-

shaped• Extend from internal

urethral orifice at the neck of bladder to external urethral orrifice at tip of penis

Female Urethra

• Narrow membranous about 4cm long

• Extend from internal to external urethral orifice directly in front of the vaginal opening

• Place behind the symphysis pubis in the anterior wall of vagina

MICTURITION

• The reflex center for urination is present in the spinal cord

• Reflex center respond to stretch receptors of urinary bladder

• Initiates urge to urinate

• Process of urination requiresi. relaxation of external urethral sphincter,ii. contraction detrusor muscles iii. the muscles of abdominal wall and pelvis

• Detrusor is a smooth muscle under parasympathic control

• Where as • Muscles of abdomen and pelvis and

external urethral sphincter are skeletal muscles under voluntary control

Muscle involved in micturition

Thank you….

Questions please!!