physio4,5.ppt

Anatomy of the Urinary System
Kidneys
(urine formation)
Lower Urinary Tract
 Ureters (2) transports urine
to the urinary bladder
 Bladder (1)
Temporally stores urine prior to
elimination
 Urethra (1)
(conducts urine to exterior)

Cortex
Glomeruli
Medulla
Renal tubules
Ureter
Takes urine to bladder
Blood carried to the kidney
by the renal artery and taken
away by the renal vein.
Cortex
Medulla
Renal artery
Renal vein
Renal pelvis
Ureter
Renal hilum

Each KIDNEY consists of 1 million NEPHRONS
Nephron is the structural and functional unit of the kidney
Their number about one million in each kidney
Each nephron consists of a:
 GLOMERULUS (found in cortex)
forms a protein-free filtrate from blood
 TUBULE (found in medulla)
processes the filtrate to form urine
Each TUBULE consists of several segments:
 Proximal tubule
 Loop of Henle
 Distal Tubule
 Collecting Ducts.

Functional Unit of the Kidney is the NEPHRON
 Glomerulus
 Proximal Tubule
 Loop of Henle
 Distal Tubule
 Collecting Duct

Kidney Functions
1. Filter
2. Regulation
3. Excretion
4. Regulation of arterial blood pressure
5. Regulation of red blood cells production
6. Regulation of vitamin D production
7. Gluconeogenesis

Kidney Functions
1) Filter 200 liters of blood daily, allowing toxins,
metabolic wastes, and excess ions to leave the body in
urine,
2) Regulation
of water and electrolyte balance: Maintain the proper balance
between water and salts, and acids and bases,
3) Excretion of bioactive substances (hormones and many
foreign substances, especially drugs) that affects body
function , urea and creatine
9

Kidney Functions
4) Regulation of arterial blood pressure: by
production of renin – angiotensin system
Controlling sodium and water retention
5) Regulation of red blood cells production:
erythropoietin hormone to stimulate RBC production
by bone marrow,
10

Kidney Functions
6) Regulation of vitamin D production :
25, cholecalciferol will be activated in the kidneys to 1,25
dihydrocholecalciferol D3
7) Gluconeogenesis:
during prolonged fasting .
glucose can be synthesized in the liver and kidneys.
11

 Layers of Tissue Supporting the Kidney
 Renal capsule – fibrous capsule that prevents kidney infection
 Adipose capsule – fatty mass that cushions the kidney and helps
attach it to the body wall
 Renal fascia – outer layer of dense fibrous connective tissue that
anchors the kidney
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Tissue Supporting the Kidney

REGULATION
OF
RENAL BLOOD FLOW
(renin-angiotensin system)

Regulation of blood pressure by renin-angiotensin

SECRETION OF HORMONES
Juxtaglomerular apparatus secretes two
hormones:
1. Renin
2. Prostaglandin
Juxtaglomerular apparatus

1. Renin
Juxtaglomerular cells secrete renin.
Along with angiotensins, renin forms the renin-angiotensin
system,
which is a hormone system that plays an important role in
the maintenance of blood pressure.
Stimulants for renin secretion
Secretion of renin is stimulated by four factors:
i. Fall in arterial blood pressure
ii. Reduction in the ECF (extracellular fluid) volume
iii. Increased sympathetic activity
iv. Decreased load of sodium and chloride in macula densa.

Actions of Angiotensins
Angiotensin I is physiologically inactive and serves only as the
precursor of angiotensin II.
Angiotensin II is the most active form. Its actions are:
 Angiotensin II increases arterial blood pressure by directly
acting on the blood vessels and causing vasoconstriction. It
is a potent constrictor of arterioles.
 It increases blood pressure indirectly by increasing the
release of noradrenaline from postganglionic sympathetic
fibers. Noradrenaline is a general vasoconstrictor.

INTRODUCTION
Urine formation is a blood cleansing
function. Kidneys excrete the unwanted
substances along with water from the blood
as urine. Normal urinary output is 1 L/day to
1.5 L/day.
A. Glomerular filtration
B. Tubular reabsorption
C. Tubular secretion

GLOMERULAR FILTRATION
Glomerular filtration is the process by
which the blood is filtered while passing
through the glomerular capillaries by
filtration membrane.
It is the first process of urine formation.
The structure of filtration membrane is
well suited for filtration.

Ultrafiltration
Glomerular filtration is called
ultrafiltration because even the minute
particles are filtered.
But, the plasma proteins are not filtered
due to their large molecular size. The
protein molecules are larger than the slit
pores present in the endothelium of
capillaries.
Thus, the glomerular filtrate contains all
the substances present in plasma except
the plasma proteins.

GLOMERULAR FILTRATION RATE
Glomerular filtration rate (GFR) is defined as
the total quantity of filtrate formed in all the
nephrons of both the kidneys in the given
unit of time.
Normal GFR is 125 mL/minute or
about 180 L/day.

FILTRATION FRACTION
 Filtration 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.

INTRODUCTION
Tubular reabsorption is the process by
which water and other substances are
transported from renal tubules back to
the blood.
Large quantity of water (more than
99%), electrolytes and other
substances are reabsorbed by the
tubular epithelial cells.

ROUTES OF REABSORPTION
Reabsorption of substances from tubular
lumen into the peritubular capillary
occurs by two routes:
1. Transcellular route
2. Paracellular route

SITE OF REABSORPTION
1.Substances Reabsorbed from Proximal Convoluted
Tubule
Substances reabsorbed from proximal convoluted
tubule are glucose, amino acids, sodium, potassium,
calcium, bicarbonates, chlorides, phosphates, urea,
uric acid and water.
2. Substances Reabsorbed from Loop of Henle
Substances reabsorbed from loop of Henle are
sodium and chloride.
3. Substances Reabsorbed from Distal Convoluted
Tubule
Sodium, calcium, bicarbonate and water are
reabsorbed from distal convoluted tubule.

REGULATION OF TUBULAR
REABSORPTION
Tubular reabsorption is regulated by
three factors:
1. Glomerulo-tubular balance
2. Hormonal factors
3. Nervous factors

Tubular secretion is the process by which the
substances are transported from blood into
renal tubules. It is also called tubular excretion.

SUMMARY OF URINE FORMATION
1. Glomerular filtration
Plasma is filtered in glomeruli and the
substances reach the renal tubules along with
water as filtrate.
2. Tubular Reabsorption
The 99% of filtrate is reabsorbed in different
segments of renal tubules.
3. Tubular Secretion
Some substances are transported from blood
into the renal tubule.

INTRODUCTION
Micturition is a process by which urine is
voided from the urinary bladder. It is a reflex
process. However, in grown up children and
adults, it can be controlled voluntarily to some
extent.

URINARY BLADDER & URETHRA
Urinary bladder
 is a triangular hollow organ located in lower abdomen.
 It consists of a body and neck.
 Wall of the bladder is formed by smooth muscle.
detrusor muscle
Bladder is opened in urethra from where urine is
excreted out from the body.

URETHRAL SPHINCTERS
There are two urethral sphincters in
urinary tract:
1. Internal urethral sphincter
2. External urethral sphincter.

NERVE SUPPLY TO URINARY
BLADDER AND SPHINCTERS

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