INTRODUCTION. Several organs system Produce urine and excrete it from the body Maintenance of homeostasis. Components. two kidneys, produce urine; two ureters, carry urine to single urinary bladder for storage; urethra, passes urine out through the external urethral orifice. 1 Kidney functions 1. Removal of organic wastes. Urea, uric acid, creatinine, and bilirubin. 2. Regulation of ions Excrete sodium, potassium, calcium, magnesium, sulfate, and phosphate ions. 3. Regulation of the acid-base balance of the body. Control the loss of hydrogen (H + ), bicarbonate (HCO 3- ), and ammonium (NH 4+ ) ions produce an acid or alkaline urine 2
Kidney functions 4. Regulation of RBC production. Release erythropoietin; stimulates RBCs production 5. Regulation of blood pressure. Regulate fluid volume of the Produce the enzyme renin part of the renin-angiotensinaldosterone mechanism. Regulates blood pressure and water retention. 6. Limited control of blood glucose and blood amino acid concentration. Excrete excess amounts of glucose and amino acids from the blood. 7. Elimination of toxic substances. Eliminate pollutants, food additives, drugs, or other foreign chemicals 3 Gross anatomy of the kidneys 1. Appearance. bean-shaped, dark red organs Female: 115 to 155 g ; male: 125 to 175 g 2. Location Posterior (retroperitoneal) abdominal wall. 3. Connective tissue coverings. Three layers of CT. a. Renal fascia; outer Maintains position of the organ. b. Adipose capsule Fat layer c. Fibrous (renal) capsule smooth membrane; directly covers the kidney. 4
Internal structure of the kidney 1. Hilus (hilum) depression; medial surface +IDNEY SINUS 2. Renal sinus (ILUS space near the hilus. attachment site for the ureter, the renal artery and vein, nerves, and lymphatic vessels. CAPSULE PELVIS CORTEX ARTERY MEDULLA VEIN -EDULLARY RAYS NEPHRONS 3. Renal pelvis PYRAMID expanded proximal end of the ureter. Formed by two to four major calyces COLUMNS Each major calyx branches can form (~ 12) minor calyces. 5RETER ¹2AO -AJOR CALYX -INOR CALYX 5 4. Renal parenchyma surrounds the renal sinus. Two parts inner medulla and outer cortex. +IDNEY SINUS a. Medulla (ILUS Renal pyramids Tip of each pyramid, the papilla, extends into a minor calyx. CAPSULE PELVIS CORTEX ARTERY MEDULLA VEIN b. Cortex -EDULLARY RAYS NEPHRONS tubules and blood vessels of nephrons. PYRAMID renal columns consist of collecting tubules; drain into collecting ducts. COLUMNS 5. Kidney lobes subdivide the kidney. 5RETER ¹2AO -AJOR CALYX Consists of a renal pyramid, the adjacent renal columns, and the overlying cortical tissue. 6 -INOR CALYX
The structure of the nephron Each kidney; ~1 to 4 million nephrons; urine- forming units. Each nephron has a vascular (capillary) component and a tubular component. 1. Renal corpuscle a. Consists of the glomerulus and Bowman's capsule. b. Located in the renal cortex c. Performs filtration of blood plasma (1) Renal corpuscle made of Glomerulus; tuft of capillaries, Bowman's capsule a double walled, epithelial membrane surrounds glomerulus (2) Visceral layer of Bowman's capsule is the internal layer of epithelium. Podocytes (foot-like cells ); modified epithelial cells surround the glomerular capillaries. 7 8
Podocytes have several long processes adhere to the outer surface of a glomerular capillary Each has secondary foot processes or pedicels ("little feet ). Pedicels interdigitate with adjacent pedicels. 9 10
Filtration slits (slit pores) Narrow spaces between pedicels ~25 nm wide. Covered by a thin membrane regulates the movements of some molecules Glomerular filtration barrier Tissue barrier that separates the blood in the glomerular capillaries from the space in Bowman's capsule. Consists of capillary endothelium basement membrane (basal lamina) of the capillary filtration slits 11 12
Parietal layer of Bowman's capsule Periphery of the renal corpuscle Simple squamous epithelium At vascular pole of the renal corpuscle Larger afferent arteriole enters the glomerulus Narrower efferent arteriole exits Difference in diameter causes an increase in BP within these arterioles. At the urinary pole of the renal corpuscle filtrate drains into the proximal convoluted tubule. 13 14
Proximal convoluted tubule (PCT) ~ 15 mm in length; highly coiled. Lumenal surface of the PCT cuboidal epithelial cells with abundant microvilli (brush border) increase surface area. Very delicate; usually disintegrates during slide-preparation brush border is no longer intact fragments of the brush border tend to occlude the lumen. 15 16
Proximal convoluted tubule (PCT) PCT is mostly in the cortex Convoluted means having a very winding path. Cells of the PCT are very metabolically active have a brush border for absorption at this high rate cytoplasm very eosinophilic more than any cells of the rest of the nephron. PCT's--they are the most abundant component of the cortex 17 PCT leads into the thin (t) descending limb of the loop of Henle dips down into the medulla, forms a sharp hairpin turn (the loop), and returns as the thick (H) ascending limb of the loop of Henle. i. Thin: simple squamous ii. Thick; simple cuboidal Epithelial cells of both stain lightly to moderately with eosin squamous cells stain more lightly than the cuboidal cells; Neither type has a brush border. Loop of Henle leads to the DCT Distal convoluted tubule 18
19 Distal convoluted tubule (DCT) Highly coiled, ~ 5 mm in length Last part of the nephron. Wall; simple cuboidal epithelium Less metabolically active than the PCT no brush border light eosinophilic cytoplasm Restricted to the cortex. DCT is shorter than PCT Less convoluted and abundant than PCT cortex 20
Along its path, the DCT establishes contact with the wall of the afferent arteriole. Contains modified cells; macula densa. Functions as a chemoreceptor Stimulated by a decrease in sodium ions. 21 Wall of the afferent arteriole next to the macula densa contains modified smooth muscle cells called juxtaglomerular cells. These cells are stimulated by a decrease in BP to produce renin. Juxtaglomerular apparatus (GA) = macula densa, + juxtaglomerular cells important in BP regulation 22
GA has several functions If [Na+] in the DCT is very high; suggest inadequate Na+ reabsorption from the PCT Danger of excessive Na+ loss from the body Responds by constriction of the afferent arteriole BP in the glomerular capillaries falls; filtration rate decreases. DCT supplies the Collecting tubule (CT) CT is a short and straight Connecting to collecting duct Uncommon in sections of cortex 23 Collecting duct (CD) Collecting tubules and ducts. Each collecting tubule descends in the cortex drains an increasing number of DCTS. CTs join and form larger, straight CDs which drain the urine into minor calyces. Columnar epithelium. CD is important for final nephron H 2O reabsorption 24
25 Histological appearance of zones of the medullary pyramid Outer zone Most common: thick portion of LH; Less common: thin portion of LH, CD, capillaries Rare: DCT. 26
Histological appearance of zones of the medullary pyramid, as seen in cross-section: Inner zone: Composed of CD's, thin portions of LH's, and capillaries. 27