The kidney substance is composed of about 1 million
functional units, the nephrons, and smaller numbers of collecting tubules. The
nephron consists of tubule closed at one end, with the other end opening into a
collecting tubules. The closed end is indented to form the cup shaped
glomerular capsule (Bowman’s capsule) which encloses a net work of arterial
capillaries, the glomerulus from the glomerular capsule the remainder of the
nephron is described in three part, the proximal convoluted tubule, the loop of
henle and the distal convoluted tubule. The renal artery on entering the kidney
at the hilus divided into smaller arteries.
functional units, the nephrons, and smaller numbers of collecting tubules. The
nephron consists of tubule closed at one end, with the other end opening into a
collecting tubules. The closed end is indented to form the cup shaped
glomerular capsule (Bowman’s capsule) which encloses a net work of arterial
capillaries, the glomerulus from the glomerular capsule the remainder of the
nephron is described in three part, the proximal convoluted tubule, the loop of
henle and the distal convoluted tubule. The renal artery on entering the kidney
at the hilus divided into smaller arteries.
In the cortex, the afferent arteriole enters each
glomerular capsule, then divides into a cluster of capillaries, forming the
glomerulus. The blood vessel, efferent arteriole leads away from the
glomerulus, then breaks into capillaries networks to supply oxygen and nutrient
materials to the remainder of the nephron. The blood pressure in the glomeurlus
is higher than other capillaries because the caliber of the afferent arteriole
is greater than that of the efferent arteriole. The walls of the glomerulus and
the glomerular capsule consist of a single layer of flattered epithelialcells. The
glomerular walls are more permeable than those of other capillaries. The nerve
supply consists of the sympathetic and para-sympathetic nerves.
glomerular capsule, then divides into a cluster of capillaries, forming the
glomerulus. The blood vessel, efferent arteriole leads away from the
glomerulus, then breaks into capillaries networks to supply oxygen and nutrient
materials to the remainder of the nephron. The blood pressure in the glomeurlus
is higher than other capillaries because the caliber of the afferent arteriole
is greater than that of the efferent arteriole. The walls of the glomerulus and
the glomerular capsule consist of a single layer of flattered epithelialcells. The
glomerular walls are more permeable than those of other capillaries. The nerve
supply consists of the sympathetic and para-sympathetic nerves.
Urine formation
Urine formation is a blood cleansing function.
Normally, about 26% of cardiac output enters the kidneys to get rid of unwanted
substances.
Normally, about 26% of cardiac output enters the kidneys to get rid of unwanted
substances.
The kidneys excrete the
unwanted substance along with water as urine. The unwanted substance include
metabolic and products and those substances, with are present in excess
quantities in the body.
unwanted substance along with water as urine. The unwanted substance include
metabolic and products and those substances, with are present in excess
quantities in the body.
About 1-15 litres of urine
is formed every day. The mechanism of urine formation includes several
processes.
is formed every day. The mechanism of urine formation includes several
processes.
First when blood passes
through glomerular capillaries, the plasma is filtered into the Bowman’s
capsule. This process is called glomerular filtration.
through glomerular capillaries, the plasma is filtered into the Bowman’s
capsule. This process is called glomerular filtration.
When the filterate form the
Bowman’s capsule passes through the tubular portion of the nephron, it
undergoes various charges both in quantity and in quality. Many wanted
substances like glucose, amino acids, water and electrolytes are reabsorbed
from the tubules. This process is called tubular reabsorption.
Bowman’s capsule passes through the tubular portion of the nephron, it
undergoes various charges both in quantity and in quality. Many wanted
substances like glucose, amino acids, water and electrolytes are reabsorbed
from the tubules. This process is called tubular reabsorption.
Some unwanted substance are
secreted into the tubule from peritubular blood vessels. This process is called
tubular secretion
secreted into the tubule from peritubular blood vessels. This process is called
tubular secretion
Thus, the urine formation
includes three processes
includes three processes
i. Glomerular filtration
ii. Tubular reabsorption
iii. Tubular secretion
Function of the Kidney
The kidney forms urine which passes through the
ureters to the bladder for excretion. There are three phases in the formation
of urine (1) simple filtration (2) selective re-absorption (3) Secretion
ureters to the bladder for excretion. There are three phases in the formation
of urine (1) simple filtration (2) selective re-absorption (3) Secretion
1. Simple Filtration
Filtration takes place through the semi-permeable
walls of the glomerulus and glomerular capsule. Water and a large number of
molecules pass through; blood cells, plasma protein and large molecules are
unable to filter through. Filtration is assisted by the difference between the
blood pressure in the glomerulus and the pressure of the filtration in the
glumerular capsule, and because of the caliber of the efferent arteriole is
less than that of the afferent arteriole, capillary hydrostatic pressure of
about 70mm Hg in the glomerulus is opposed by osmotic pressure of blood 5 mm Hg
in the glumerular capsule.
walls of the glomerulus and glomerular capsule. Water and a large number of
molecules pass through; blood cells, plasma protein and large molecules are
unable to filter through. Filtration is assisted by the difference between the
blood pressure in the glomerulus and the pressure of the filtration in the
glumerular capsule, and because of the caliber of the efferent arteriole is
less than that of the afferent arteriole, capillary hydrostatic pressure of
about 70mm Hg in the glomerulus is opposed by osmotic pressure of blood 5 mm Hg
in the glumerular capsule.
2. Selective Re-absorption
Is the process by which the composition and volume of
the glomerular filtrate are altered during its passage through the convoluted
tubules the loop of Henle and the collecting tubules. This is to reabsorb those
filtrate constituents needed by the body to maintain fluid and electrolyte
balance; in some cases re-absorption is regulated by hormones.
the glomerular filtrate are altered during its passage through the convoluted
tubules the loop of Henle and the collecting tubules. This is to reabsorb those
filtrate constituents needed by the body to maintain fluid and electrolyte
balance; in some cases re-absorption is regulated by hormones.
·
Parathryroid from the parathyroid glands and
calcitonin from the thyroid gland together regulate re-absorption of calcium
and phosphate.
Parathryroid from the parathyroid glands and
calcitonin from the thyroid gland together regulate re-absorption of calcium
and phosphate.
·
Anti diuretic hormone from the posterior lobe of
the pituitary gland affects the permeability of the distal convoluted tubules
and collecting tubules regulating water reabsorption.
Anti diuretic hormone from the posterior lobe of
the pituitary gland affects the permeability of the distal convoluted tubules
and collecting tubules regulating water reabsorption.
·
Aldosterone, secreted by the cortex of the
adrenal gland influences reabsorption of sodium and excretion of potassium.
Waste products such as urea and uric acid, are reabsorbed only to a slight
extent.
Aldosterone, secreted by the cortex of the
adrenal gland influences reabsorption of sodium and excretion of potassium.
Waste products such as urea and uric acid, are reabsorbed only to a slight
extent.
2. Secretion
Substances not required and foreign materials e.g.
drugs not required and foreign materials e.g. drugs, may not be cleared from
the blood by filtration because of the short time in the glomerulus. Such
substances are cleared by secretion into the convoluted tubules and passed from
the body in the urine.
drugs not required and foreign materials e.g. drugs, may not be cleared from
the blood by filtration because of the short time in the glomerulus. Such
substances are cleared by secretion into the convoluted tubules and passed from
the body in the urine.
Composition of Urine
Water 96%
Urea 2% Urine
is amber in colour due to the
is amber in colour due to the
Urine acid presence
of urobilin, a bile pigment.
of urobilin, a bile pigment.
Creatinine Specific
gravity
gravity
Ammonia. between
1020 and 1030 with acidic
1020 and 1030 with acidic
Potassuim reaction.
Adult passes 1000ml to
Adult passes 1000ml to
Chlorides 1500ml
per day. This depend
per day. This depend
Phosphates on
fluid intake.
fluid intake.
Sulphates
Ureter:
The ureters are the tubes that allow the passage of
urine from the kidney to the bladder. They are about 25 – 30cm length and about
3mm in diameter. The ureter is continuous with the renal pelvis. It passes down
ward into the posterior way of the bladder.
urine from the kidney to the bladder. They are about 25 – 30cm length and about
3mm in diameter. The ureter is continuous with the renal pelvis. It passes down
ward into the posterior way of the bladder.
Structure
The ureters consist of three layers of tissue.
1. Outer covering of fibrous
tissue, continuous with the fibrous capsule of the kidney
tissue, continuous with the fibrous capsule of the kidney
2. Middle muscular layer
consist of interlacing smooth muscle fibres that form a functional unit
spiralling round the ureter, some in
clockwise and some in anti-clockwise direction and an addition outer
longitudinal layer in lower third.
consist of interlacing smooth muscle fibres that form a functional unit
spiralling round the ureter, some in
clockwise and some in anti-clockwise direction and an addition outer
longitudinal layer in lower third.
3. Inner layer, the mucosa,
composed of transition epithelium.
composed of transition epithelium.
Function
Propelsion of urine from the kidney into the bladder
through peristaltic contraction of the smooth muscle layer.
through peristaltic contraction of the smooth muscle layer.
Bladder:
The bladder is a reservoir for urine it lies in the
pelvic cavity and its size and position vary, depending on the volume of the
urine it contains. When distended, it rises into the abdomen cavity.
pelvic cavity and its size and position vary, depending on the volume of the
urine it contains. When distended, it rises into the abdomen cavity.
Structure
The bladder is roughly pear shaped, but more oval as
it fills with urine. Posterior, it surround the uterus in female and the rectum
in male.
it fills with urine. Posterior, it surround the uterus in female and the rectum
in male.
The bladder wall is composed of three layers.
i.Outer layer of loose
connective tissue
connective tissue
ii.Middle layer, consist of
mass of interfacing smooth muscle fibres and elastic tissue lossely arranges in
three layers. This is called the detruosor muscle and when it contracts,
empties the bladder.
mass of interfacing smooth muscle fibres and elastic tissue lossely arranges in
three layers. This is called the detruosor muscle and when it contracts,
empties the bladder.
iii.Mucosa, composed of
transitional epithelium.
transitional epithelium.
Urethra:
The urethra is a canal extending from the neck of the
bladder to the exterior, at the external urethral orifice. It is longer in male
than in female. The male urethra is associated with urinary and reproductive
system.
bladder to the exterior, at the external urethral orifice. It is longer in male
than in female. The male urethra is associated with urinary and reproductive
system.
Structure
It is composed of three layers of tissue
i.
The muscle layer, is continuous with the
bladder, made of elastic tissue and smooth muscle fibre.
The muscle layer, is continuous with the
bladder, made of elastic tissue and smooth muscle fibre.
ii.
The submucosa is a spongy layer containing blood
vessels and nerves.
The submucosa is a spongy layer containing blood
vessels and nerves.
iii.
Mucosa is continuous with that of the bladder in
the upper part of the urethra. The lower part consist of stratified.
Mucosa is continuous with that of the bladder in
the upper part of the urethra. The lower part consist of stratified.
Squamous epithelium, continuous externally with the
skin of the vulva.
skin of the vulva.
Urinary bladder
Is the reservoir for urine. It lies in the pelvic
cavity and its size and position vary depending on amount of urine it contains.
cavity and its size and position vary depending on amount of urine it contains.
Micturition
Micturition: Is the process by which the urinary
bladder empties when it becomes filled.
This involves two main steps:
bladder empties when it becomes filled.
This involves two main steps:
1. The bladder fills
progressively until the tension in its walls rises above a threshold level,
which then elicits the second step;
progressively until the tension in its walls rises above a threshold level,
which then elicits the second step;
2. A nervous reflex called
micturition reflex occurs that empties the bladder or, if this fails, at least
causes a conscious desire to urinate. Although the micturition reflex is an
autonomic spinal cord reflex. It can also be inhibited or facilitated by
centers in the cerebral cortex of brain stem.
micturition reflex occurs that empties the bladder or, if this fails, at least
causes a conscious desire to urinate. Although the micturition reflex is an
autonomic spinal cord reflex. It can also be inhibited or facilitated by
centers in the cerebral cortex of brain stem.