Renal System Flashcards
Urinary system components
- two kidneys
- two ureters
- a bladder
- a urethra
Kidney anatomy
- Retroperitoneal organ
- Covered by thin fibrous capsule
- Outer renal cortex (darker due to blood suppy) and an inner renal medulla
- Concave medial border (hilum) – structures entering and exiting
- Renal artery comes from abdominal aorta (L1/2)
Functions of the kidney
- Regulation of the balance between water & electrolytes (inorganic ions) and the acid-base balance.
- Excretion of metabolic wastes along with excess water and electrolytes in urine.
- Excretion of many bioactive substances, including many drugs.
- Secretion of renin, enzyme/hormone important for regulation of blood pressure.
- Secretion of erythropoietin, hormone that stimulates erythrocyte production in red marrow when the blood O2 level is low.
- Conversion of the steroid prohormone vitamin D, initially produced in the skin, to the active form (1,25-dihydroxyvitamin D3 or calcitriol).
Divisions of a nephron
- Renal corpuscle, an initial dilated part comprised of capsule of bowman and glomerulus, always in cortex.
- Proximal tubule, a long-convoluted part, located in cortex, with a shorter straight part that enters the medulla.
- Loop of Henle, in the medulla, with a thin descending and a thin ascending limb.
- Distal tubule, consisting of a thick straight part ascending from the loop of Henle back into the cortex and a convoluted part completely in the cortex.
- Connecting tubule, a short minor part linking the nephron to collecting ducts where reabsorption of water takes place.
Uriniferous tubule epithelial types
= nephron + collecting duct
PCT – Simple cuboidal (with microvilli), darker than DCT
DCT – Simple cuboidal (wider lumen/no microvilli)
Thick Loop – Simple cuboidal
Thin Loop – Simple squamous
Collecting tubule – Simple cuboidal to columnar
Types of nephrons
- Cortical nephrons - located in the upper cortex of the kidney
- Juxtamedullary nephrons - situated near the junction of the cortex and medulla of the kidney, have long loops of Henle
What is the renal corpuscle and what epithelium is present?
= glomerular capillaries + Bowman capsule
- 2 layers of capsule.
- Afferent and efferent arterioles (vascular pole).
- Presence of podocytes (modified epithelial cells) in visceral layer – assist in filtration.
- Change in epithelium from corpuscle to tubule.
- Epithelium in parietal layers is simple squamous. Epithelium changes to cuboidal in PCT. DCT is also simple cuboidal epithelium.
What is the glomerular filter and where does filtration take place?
Filtration barrier (between blood in glomerular capillary and space of Bowman’s capsule/BC).
Filtration occurs in these 3 parts:
1. Fenestrated endothelium of glomerular capillary.
2. Thick, fused basal laminae of the podocytes (visceral layer of BC) and the glomerular endothelial cells (restricts large proteins).
3. Slit diaphragms (pink arrow) between pedicels (secondary processes) of visceral layer of epithelium (restricts small proteins).
Cross section of renal corpuscle
- PCT – Stained darker than DCT
- Lumen of DCT is wider than PCT
- Nucleus is more prominent in DCT than PCT
- CD – cells are more columnar than DCT and PCT (cuboidal)
- Water reabsorption takes place in CD under the influence of ADH
Summary of renal corpuscle
PL – parietal layer of BC
CS – capsular space
G - Glomerulus
Visceral layer of BC you can’t see as it is fused to glomerular endothelial cells
Between PCT and DCT, which one has wider lumen?
MD – macula densa
What is the juxtaglomerular apparatus composed of?
- Macula Densa cells - Cluster of modified cells in the wall of DCT adjacent to the juxtaglomerular cells. They monitor sodium concentration.
- Juxtaglomerular cells - Modified smooth muscle cells in wall of an afferent arteriole. They release renin to regulate blood pressure.
Blood pressure regulation (RAAS)
Renin–Angiotensin–Aldosterone System.
1. Renin secreted by the juxtaglomerular apparatus (JGA) catalyses the production of angiotensin I from its inactive precursor, angiotensinoagen (protein).
2. Angiotensin I is then converted in the lung into the active octapeptide angiotensin II, which stimulates the release of aldosterone from the adrenal cortex.
3. Aldosterone mediates the absorption of sodium and water from the glomerular filtrate at the distal tubule.
4. Decreased arterial pressure leads to increased autonomic stimulation to the JGA as a result of baroreceptor function, including local baroreceptors in the afferent arteriole.
5. This causes the JG cells to release renin, an aspartyl protease, into the blood. There renin cleaves the plasma protein angiotensinogen into the inactive decapeptide angiotensin I.
6. Angiotensin-converting enzyme (ACE) on lung capillaries clips this further to angiotensin II, a potent vasoconstrictor that directly raises systemic blood pressure and stimulates the adrenals to secrete aldosterone.
7. Aldosterone promotes Na+ and water reabsorption in the distal convoluted and connecting tubules, which raises blood volume to help increase blood pressure.
8. The return of normal blood pressure turns off secretion of renin by JG cells.
Renal cortex vs kidney medulla
Ureter anatomy and histology
- The ureters are muscular tubes that carry urine from the kidneys to the bladder. Urine is transported from the pelvicalyceal system as a bolus, propelled by peristaltic action of the ureteric wall. The wall of the ureter contains two layers of smooth muscle, arranged as an inner elongated spiral but traditionally known as the longitudinal layer and an outer tight spiral traditionally described as the circular layer Another outer longitudinal layer is present in the lower third of the ureter.
- The lumen of the ureter is lined by transitional epithelium ( urothelium ) which is thrown up into folds in the relaxed state, allowing the ureter to dilate during the passage of a bolus of urine. Beneath the epithelium is a broad collagenous lamina propria, the collagen fibres of which are stained greenish-blue in this preparation. Surrounding the muscular wall is a loose collagenous adventitia containing blood vessels, lymphatics and nerves.
What is the epithelium type in the urinary bladder?
Lined by a transitional epithelium (specialized to provide for distension of the organ); a thick muscular wall contains three interlacing layers of smooth muscle.
Summary of renal tubules
