Histology Flashcards
functions of the kidney
Excretory: as the blood passes thru the kidney, an ultrafiltrate is produced. excess water and ions, some drugs, toxins and metabolic breakdowns products (urea,creatinine) are excreted in the urine
Homeostatic: regulating and maintaing extracellular fluid volume and composition by selective secretion and reabsorption of water, ions, and other compounds. Maintenance of acid base balance by generation of bicarbonate and selective secretion of H ions
Endocrine: monitoring the O2 carrying capacity of the blood via Erythropoietin, regulating blood pressure thru RAAS
the nephron: structural and functional unit of the kidney
Components: renal corpuscle, renal tubule (the epithelial lined tubule that varies in size, shape and function along its length
Function: a filtrate and a fluid modifier (recycle/secrete) the kidney produces an ultrafiltrate of the blood, but recylcles many components that are in the filtrate, other coponents are added to the filtrate as it goes thru the tubular system
Macroscopic structure: cortex, medulla, and lobe
The cortex is granular in appearance and homogeneous in consistency. Linear arrays of tubules extending into the cortex are called medullary rays
The medulla has a striated appearance and consists of 6-18 renal pyramids. the apex or the tip of a renal pyramid is called a renal papilla
A kidney lobe consists of a renal pyramid and its surrounding cortex.
Macroscopic structure: lobule and capsule
A kidney lobule consists of a medullary ray and the cortical tissue (nephrons) on either side. The tubules of these nephrons connect with the collecting ducts within the medullary rays
The Capsule consists of mainly fibrous CT and surrounds the kidney. the parenchyma is not subdivided by septa
vasculature of the kidney
The kidneys receive 20-25% of the total cardiac output/minute. Total blood volume of the body passes thrue the kidneys every 4-5 minutes
125 ml of fluid is extracted from the blood each minute as filtrate (124 of which is REABd in the kidney tubules), 1 m l is excreted
Renal aa-> lobar A–> interlobar a–> acruate a–> afferent arteriole
Microvasculature
2 capillary systems:
Gomerulus (between the afferent and efferent arteriole
Efferent arteriole–> Tubular plexus (supplies tubules of the cortical nephrons)–> vasa recta (long capillary loops supplying tubules of juxtamedullary nephrons–> venules
Renal intersitium: the space between the tubules
Interstitial (stromal) tissue is found in the renal cortex and medulla (stroma is finer in cortex)
Interstitium components: interstitial connective tissue, interstitial cells (fibroblasts) in cortex and medulla
Renal corpuscle has 4 components
Glomerulus, visceral layer of the renal capsule (Bowmans), Parietal layer of renal capsule, mesangium
Corpuscle small body is a spherical, double-layered sac (renal capsule) that surrounds a network of capillaries (glomerulus- ball of thread)
It has avascular pole where arterioles enter and exit and a urinary pole that is continuous with the proximal convoluted tuble
Renal corpuscles are found only in the kidney CORTEX
glomerulus and bowmans capsul
The glomerulus: a network of capillary loops supplied and drained by an arteriole, the afferent (supplying arteriole is larger in diameter than the efferent (draining) arteriole. This size creates a pressure differential that drives glomerular filtration
Bowman’s capsul: a double-layered epithelial sac surrounding the glomerulus, the outer parietal layer is a simple squamous epithelium. The visceral layer is also simple epithelium is coomposed of podocytes
The space between the 2 epithelial layer is called the urinary space and is continuous with the proximal tubule. the glomerular filtrate enters this space
Glomerular filtration barrier (filtration membrane of the kidney)
Capillary endothelium- discontinuous big pores. Pores are freely permeable to water and solutes (<7 kD) lumen surface has a negative charge (coated with glycocalyx
Basement membrane is the primary barrier that prevents protein from entering the glomerular filtrate
Podocytes with foot processes make basement membrane
Glomerular mesangium
intraglomerular mesangial cells (specialized pericyte/smooth muscle cells),
Functions: physical support, regulation of glomerular blood flow (contracts in response to Angiotensin), resorption of basement membrane
ECM contains fibronectin and collagen, cells and ECM that abut the inner surface of the glomerular basement membrane
proximal tubule
Proximal convoluted tubule: begins at the urinary pole and located in the cortex, (Glucose, Amino acids, proteins REAB thru facilitated transport), Cuboidal/columnar cells with granular cytoplasm and basal nuclei, apical brush border w/ glycocalyx obscures the lumen, numberous mitochondria at base of cell provide energy for transport, complex lateral interdigitation between epithelial cells make lateral cell membranes indistinguishable
Straight portion: also thick descending limb of henle (cuboidal epithelium)
Loop of henle (intermediate tubule)
4 parts: 1) straight portion of the proximal tubule (thick descending limb), 2) thin descending, 3) thin ascending limbs, 4) straight portion of the distal tubule (thick ascending limb)
Located in medulla, length determined by the location of its renal corpuscle with respect to the corticomedularry junction. Cortical nephrons (located external to the juxtamedullary zone, have short loops that only have descending thin limbs. Juxtamedullary nephrons are long looped and have ascending and descending thin limbs
Thick potions of the loop are lined with cuboidal epithelial but the thin segments are lined with simple squamous epithelium
Thin descending limb is permeable to water
Cell membranes in the ascending thin limb are interdigitated– water impermeable
Tubular-interstitium vascular interaction
Provides a mechanism for modifying and concentrating urine
Components: collecting ducts, loops of henle, vasa recta
Countercurrent Multiplier: urine concentration thru differential resorption of water, yields hypotonic fluid in the distal tubule because the ascending limb of the loop of henle is impermeable to water, while the descending limb is somewhat water permeable
Countercurrent exchanger: maintians osmotic gradient established by countercurrent multiplier, accomplished because the arterioles around the descending limp of the loop have continuous endothelium and the venules around the ascending limb of the loop have fenesterated endothelium
Distal tubule
Straight portion (thick ascending limb)- lined with cuboidal epithelium, scant microvilli, efficient tight junctions, lateral and basal membrane interdigitations, abundant mitochondria, impermeable to water (NaCl is REAB, H is secreted
