Urinary system
Renal InterstitiumFormed of protein, glycosaminoglycans, collagen fibers, lipid droplets, basal like materials, variable number of interstitial cells.
Interstitial cells are of two types:
1. Stellate:
Irregular shape stellate in shape.
Cytoplasmic processes surround the loop of Henle & the medullary capillaries.
Cytoplasm contain mitochondria, RER, lysosomes, lipid droplets.
2. Spindle shaped:
contain abundance RER.
Resemble fibroblasts
Importance of Interstitium:
1. Salt & water homeostasis.
2. Synthesis of prostaglandin.
JUXTA GLOMERULAR APPARATUS
Is formed at the site of the contact between the distal convoluted tubules with the afferent arterioles & to a lesser extent with the efferent arter. Changes occur in the lining epithelium of the distal convoluted tubules. The cells become columnar &their nuclei are closely packed together. The Golgi apparatus in the basal region. They are called Macula densa. (due to close proximity of the nuclei). Their function is not clear.Changes also occur in the tunica media of the afferent arteriole consist of modification of the muscle cells into cells called Epithelioid cells or juxta glomerular cells (JG) cells. Internal elastic membrane in the area of contact disappear. JG cells: under E\ M
1. Have rounded nuclei.
2. Are highly specialized myo- epithelial cells.
3. Contain contractile filaments.
4. Neuro endocrine granules.
Two types of granules are seen by E\M .
1.Type I:
Irregular in shape, they are precursor for granules type 2.
2. Type 2:
Larger, spherical, uniform.
Are mature renin secreting granules.
Function of JG_cell:
It secretes Renin which circulate in the blood & act on angiotensinogen which is produced in the liver & change it into angiotensin type 1 & then change it into angiotensin type 2 by the enzyme secreted from the lung. Angiotensin type 2 act on the adrenal cortex stimulate it to secret aldosterone which cause reabsorption of Na & water from the wall of the dist. conv. tubu. thereby maintain plasma volume & blood pressure.
Secretion of erythropoietin (ESH); i.e. erythrocyte stimulating hormone which stimulate the synthesis of RBC.
Extra mesangial cell LACIS cell:
Lies in the base of the triangular area formed by the afferent &efferent arterioles with the dist. Conv. tubu. (which form the base of the triangle) LACIS cell have processes forming a network in a cellular matrix of the basement membrane like materials. Its function is unknown. so, the JG apparatus is formed of:1. JG cells.
2. Macula densa.
3. LACIS cells.
Renal pelvis & Ureters:
The wall of the renal pelvis & ureters consist of three layers: an inner mucosa, a middle muscular, & an outer fibrous layer. The mucosa of the ureter is lined by transitional epithelium which varies in thickness depending on the state of distension of the ureter. In collapsed state, the basal layers are cuboidal or columnar. The superficial layer consists of large cuboidal cells with lighter cytoplasm, often containing 2 or more nuclei. A basement membrane is not seen with L\ M but a Basel lamina & lamina reticularis, diffuse lymphatic tissue occur in the lamina propria. occasionally the lymphatic tissue takes the form of small lymphatic nodules. The muscular layer formed of the inner longitudinal & the outer circular. In the lower part of the ureter a discontinuous outer longitudinal is added. the fibrous layer is present as loosely arranged connective tissue which contains many large blood vessels.The urinary bladder:
The wall of the bladder is similar in structure to those of the ureter. The mucous membrane is thrown into folds according to the degree of distension of the organ. Epithelium is transitional; the surface cells have 2 or more nuclei. The shape of the cells & the number of the layers change according to the state of the bladder.
In moderately distended bladder; the superficial cells become flatter& the entire thinner than in the contracted organ. the number of the entire epithelium is 2 - 3 cells in thickness.
In contracted bladder; the surface epithelium are rounded bulge into the lumen containing 1 or more nuclei. the thickness is 5- 6 layers.
Urethra:
It is a tube which carries the urine from the bladder to the exterior. In the male the sperms are also pass through it during ejaculation. In the female the urethra is exclusively a urinary organ. A male urethra consist of 3 parts :1. Prostatic part: lined with transitional epithelium; the prostate is situated very close to the initial part of the urethra pass through it the ejaculatory ducts which open into it lies posterior part of the prostatic urethra .
2.Membranous part: 1 cm in length & lined with pseudostratified columnar epithelium. Surrounding this part, a sphincter formed of striated muscle called external sphincter of the urethra which adds further closing pressure to that exerted by involuntary urethral sphincter formed by a continuation of the internal longitudinal muscle of the bladder.
3. The bulbous or pendulous part: located in the corpus spongiosum distally the pendulous urethra dilate to form the navicular fossa. Glands of Littre are mucus glands found along the entire length of the urethra mostly the pendulous part. The secretary portions of these glands are lined with the same epithelium of the urethra.
The female urethra is a tube of 4-5 cm, lined with stratified squamous epithelium with areas of pseudostratified columnar epithelium. The middle part of the female urethra is surrounded by external striated voluntary sphincter.