0729- Histology/functional anatomy of nephron- CG Flashcards
Major functions of kidney
- Regulate body fluid volume and osmolarity, electrolyte balance and
acid-base balance.
- Remove metabolic wastes (urea,urobilinogen) and foreign
substances (drugs e.g. penicillin)
- !Endocrinefunctions
Juxtaglomerular cells: !
!Secretion of the enzyme, renin, which cleaves circulating angiotensinogen to release angiotensin I to regulate blood pressure!
Proximal tubules: !
!Hydroxylation of 25-hydroxyvitamin D3 to an active form, 1, 25- dihydroxyvitamin D3 to regulate calcium and phosphorous metabolism!
Interstitial cells and lacis cells (unclear): !
!Secretion of the glycoprotein hormone, erythropoietin, which
enhances the formation of red blood cells.!
Describe functional features of blood supply- wrt distribution and pressure system
- Rich blood supply compared with other organs
Kidneys weigh 0.5% of total body weight,! !but receive 25% of the total cardiac output.
- Distribution of blood in kidney
90% in the cortex (through cortical glomeruli)
10% in the medulla (through juxtamedullary glomeruli)
- High pressure system
!High pressure afferent arterioles (70 mmHg)
!High pressure glomerular capillaries (50 mmHg, other systemic cap. 25)
High pressure efferent arterioles (30 mmHg)
!Low pressure peritubular capillaries (10 mmHg,other systemic cap. 25)
What is the functional and structural unit of the kidney and its components
Nephron, ~2 million in kidney
- each consists of afferent arterioles, glomerular capillaries, efferent arterioles, peritubular capillaries (supply blood to glomeruli) AND VASA RECTA =straight vessels, parallel to loop of henle(not to be confused with vaso vasora)
Plumbing system
Consists of renal corpuscle- filtration (contains bowman’s capsule and glomerulus)
and renal tubule- reabsorption (contain proximal convoluted tubule, loop of henle, distal tubule, collecting duct)
What is the renal lobule? (supplied by interlobular aa)- all nephrons drain into the same collecting duct
What are the 2 types of nephrons
- Cortical (superficial) nephron! (outer- in cortex and outer medulla)
85% of all nephrons!
Short loops of Henle to the border of outer and inner medulla!
Short thin descending limb, No thin ascending limb
!
- Juxtamedullary nephron (outer and inner medulla)
- Account for 15% of all nephrons!
- Corpuscles are located near corticomedullary junction
- Long loops of Henle with thin limbs reaching inner medulla!
- Accompanied by hair-pin shaped vasa recta!
- Establishing osmotic gradients (hypertonicity) in medullary interstitium.
What is a medullary ray? What is a lobule?
In anatomy, the medullary ray (Ferrein’s pyramid) is the middle part of the cortical lobule or renal lobule, consisting of a group of straight tubes to the collecting ducts.
Renal lobule is part of renal lobe- consists of the nephrons grouped around a single medullary ray, and draining into a single collecting duct
Describe the histology of renal corpuscule
renal corpuscle = bowman’s capsule + glomerulus
Bowman’s capsule has 2 layers-
visceral: podocytes, attach to capillaries with pedicles
Parietal- squamous epithelium
Podocytes’ foot processes (pedicles) wrap around individual capillaries- interdigitation with small gaps (filtration slit)
Between the endothelium (fenestrated- interdicular holes ~70nm to make sure RBCs, proteins, etc can’t go through-FIRST FILTER) and podocytes- basement membrane where filtration takes place
Describe the filtration barrier and its histology
- Endothelial cells of capillaries
- Fenestrations, 70nm in diameter
- Only stop blood cells from passing through
- Glomerular basement membrane- IMPORTANT
- 300nm thickness
- Fusion of endothelium basal lamina (BL) and podocyte BL
• One central lamina densa (criss-cross type IV collagen and laminin) - physical barrier!
• Two lamina rara on each side (fibronectin) with negatively charged sites
(glycosaminoglycan) - charge barrier
- Allow molecules < 1kDa passing through freely (water, electrolytes)
- Stop particles > 10nm and proteins > 69kDa (albumin) from crossing (so, glomerular filtrate = plasma - proteins)
- Podocytes (visceral layer of Bowman’s capsule)
- Filtration slit between foot processes (pedicels), 25 nm wide
- Slit diaphragm, 6 nm thick
- Contain actin filaments to contract
What is a mesangial cell? What is it function
Structure:
- Located between capillaries
- Adhere to endothelial cells
- Enveloped by basement membrane
Functions:
- Contract to regulate glomerular blood flow
- Remove molecules trapped in basement membrane
- Support glomerulus- hence not free floating capillaires
What is the juxtaglomerular apparatus and how does it work?
Homeostatic mechanism to increase GFR to normal and release renin when low NaCl detected (and vice versa)
Macula densa = local feedback to compensate, return GFR to normal
- Specialized cells of thick ascending limb contacting its parent glomerulus
- increase the amount of fluid and NaCl at macula densa –> release
paracrine agents (ATP) –> contraction of afferent arterioles –> decrease glomerular filtration rate
juxtaglomerular cells = systemic, renal hypertension
lies just outside bowman’s capsule in afferent arterioles (modified smooth muscle cells), secrete renin (protease enzyme) via granules
Stimulate RAAS to increase BP
Histology and function of proximal and distal tubules, loop of henle
Functionally far away, structurally close together
Proximal convoluted tubule! -reabsorption of the bulk of filtered fluid back into circulation
- Located in renal cortex
- Simple cuboidal epithelium
- Brush border (microvilli)
• Abundant mitochondria near base
Distal convoluted tubule- site for fine control of salt and water reabsorption in response to hormones (ie aldosterone)
• Located in renal cortex
• Simple cuboidal epithelium
• No brush border!
• Abundant mitochondria near base
Loop of Henle- create osmotic gradient in medulla by pumping NaCl into interstitum of the medulla to concentrate urine
- Located mainly in renal medulla
- Cuboidal epithelium (thick limbs)
- Squamous epithelium (thin limbs)
- Wide lumen
Collecting duct ?
