Download Urinary system

Histology
Lec-10-
Ass. Lec.
Wafaa H. M. Alhashimy
Dentistry College
Second Stage
Urinary system
The kidneys are The kidney has a bean-shaped structure that serve several essential
regulatory roless in the urinary system and also serve homeostatic functions such as
the regulation of electrolytes, maintenance of acid–base balance, and regulation of
blood pressure (via maintaining salt and water balance). They serve the body as a
natural filter of the blood, and remove wastes which are diverted to the urinary
bladder. In producing urine, the kidneys excrete wastes such as urea and ammonium,
and they are also responsible for the reabsorption of water, glucose, and amino acids.
The kidneys also produce hormones including calcitriol, erythropoietin, and the
enzyme renin.
Each kidney is covered by a dense irregular connective tissue capsule . a sagittal
section through the kidney shows a darker , outer cortex and a lighter , inner medulla ,
which consists of numerous cone – shaped renal pyramids . the base of each pyramid
faces the cortex and forms the cortico medullary boundary. the round apex of each
pyramid extends downward to the renal pelvis to form the renal papilla . a portion of
the cortex also extends on each side of the renal pyramids to form the renal columns .
Located at the rear of the abdominal cavity in the retroperitoneum, There are two, one
on each side of the spine.The asymmetry within the abdominal cavity caused by the
liver typically results in the right kidney being slightly lower than the left, the kidneys
receive blood from the paired renal arteries, and drain into the paired renal veins. Each
kidney excretes urine into a ureter, itself a paired structure that empties into the
urinary bladder.The kidney is approximately 11–14 cm in length, 6 cm wide and 4 cm
thick.
The tip, or papilla, of each pyramid empties urine into a minor calyx; minor calyces
empty into major calyces, and major calyces empty into the renal pelvis, which
becomes the ureter.
Nephron is the basic structural and functional unit of the kidney. Its chief function is
to regulate the concentration of water and soluble substances like sodium salts by
filtering the blood, reabsorbing what is needed and excreting the rest as urine. A
nephron eliminates wastes from the body, regulates blood volume and blood pressure,
controls levels of electrolytes and metabolites, and regulates blood pH. Its functions
are vital to life and are regulated by the endocrine system by hormones such as
antidiuretic hormone, aldosterone, parathyroid hormone and important hormone for
erythrocyte synthesis called Erythropoeitin . In humans, a normal kidney contains 1.3
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million nephrons. Each nephron is composed of renal corpuscle an initial filtering
component filters out solutes from the blood, Composed of a glomerulus and the
Bowman's capsule
-The glomerulus is a capillary tuft that receives its blood supply from an afferent
arteriole of the renal circulation. The glomerular blood pressure provides the driving
force for water and solutes to be filtered out of the blood and into the space made by
Bowman's capsule.
-The Bowman's capsule, also called the glomerular capsule, surrounds the glomerulus.
It is composed of epithelial cells . The inner or visceral layer of capsule consist of
unique and highly modified branching epithelial cells called podocytes, and a parietal
outer layer composed of a single layer of flat cells consist of simple squamous
epithelium. Fluids from blood in the glomerulus are filtered through the visceral layer
of podocytes, and the resulting glomerular filtrate is further processed along the
nephron to form urine.
The renal tubule is the portion of the nephron containing the tubular fluid filtered
through the glomerulus. After passing through the renal tubule, the filtrate continues to
the collecting duct system . The components of the renal tubule are: renal tubule a
specialized for reabsorption and secretion .
-Proximal
convoluted tubule (lies in cortex and lined by simple cuboidal epithelium
with brushed borders which help to increase the area of absorption greatly.)
-Loop
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of Henle (hair-pin like U-shaped and lies in medulla)
This has a thick descending portion (pars recta), a thin descending portion, a
thin ascending portion, and a thick ascending portion.
The lumen is made up of simple squamous epithelium.
This part of the nephron is hard to tell apart from adjacent capillaries, except
that there are no red blood cells in the lumen.Distal convoluted tubule has a
different structure and function to that of the proximal convoluted tubule. Cells
lining the tubule have numerous mitochondria to produce enough energy (ATP)
for active transport to take place. When aldosterone is present.
Collecting tubules and Collecting ducts are not part of the nephron.
The epithelium of these tubules consist of cuboidal or columnar cells. They empty into
collecting ducts that are easy to recognise, because they have large lumens, with pale
staining columnar epithelium.Collecting tubules have two main functions:
1. resorb water in response to the hormone vasopressin.
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2. resorb sodium in response to the hormone aldosterone.
Juxtaglomerular apparatus
The juxtaglomerular apparatus is a specialized region of the nephron it is found
between the vascular pole of the renal corpuscle and the returning Distal Convoluted
Tubule of the same nephron, responsible for production and secretion of the enzyme
renin, involved in the renin-angiotensin system. This apparatus occurs near the site of
contact between the thick ascending limb and the afferent arteriole.
It contains three components: the macula densa, juxtaglomerular cells, and
extraglomerular mesangial cells .
Macula Densa Cells
are columnar epithelium thickening of the distal tubule. The macula densa senses any
increase in the sodium chloride concentration in the distal tubule of the kidney.
Arterial Blood Supply of kidney
1. Renal arteries, branches of the abdominal aorta, supply the kidney
2. Interlobar arteries are found between renal pyramids and branch to form arcuate
arteries found at the junction of cortex and medulla.
3. Interlobar arteries between cortical lobules.
4. Afferent arterioles supply blood to capillaries of the glomerulus.
5. Efferent arterioles exit the glomerulus
6. Peritubular capillaries are supply proximal and distal tubules.
7. Vasa Recta are capillaries fed up by efferent arterioles of juxtamedullary nephron
found parallel to long loops of Henle in the medulla.
Urine leaves the medullary collecting ducts through the renal papillae, emptying into
the renal calyces, the renal pelvis, and finally into the urinary bladder via the ureter.
Ureter
The ureter extends from the renal pelvis to the urinary bladder. In the adult, the
ureters are usually 25–30 cm . The lumen of the ureter is lined with a transitional
epithelium, and its lamina properiacontains smooth muscle arranged in bundles.
Smooth muscle contraction affects peristalsis, which forces urine toward the urinary.
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The bladder is finally emptied through the urethra. Initially, the urethra is lined by a
transitional epithelium . The lamina propria contains loose connective tissue. Smooth
muscle cells in the muscularis are mainly oriented longitudinally.
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