Histology of the Kidney and Urinary Tract Flashcards
What are the 3 functions of the kidney?
Excretory: as blood passes through th ekidney an ultrafiltrate is produced. excess water and ions, some drugs, toxins and metabolic breakdown products
Homeostatic: regulating and maintaining extracellular fluid volume and composition by selective secretion and re-absorption of water, ions (Na, K, H, Ca/PO4) and other compounds. Maintenance of acid-base balance by generation of bicarb and selective secretion of H ions
Endocrine: monitorng the CO2 carrying capcity of the blood via erythropoietin, regulaitng blood pressure through the renin-angiotensin system
What is the structural and functional unit of the kidney? What are its components?
The nephron
- components:
- renal corpuscle (where blood enters the nephron)
- renal tubule (an epithelial lined Tubule that varies in size shape and funciton along its length
- function: a filter and fluid modifier (recycle/secrete)
- the kidney produces and ultrafiltrate of the blood, but it recylces many components that are in the filtrate. other compunds are added to the filtrate as it goes through the tubular system
Describe the appearance of the cortex
Linear arrays of tubules extending into the cortex are called ________
Describe the appearacne of the medulla
what is the apex of the medulla called?
the cortex is granular in appearance and homogenous in consistency. linear 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 tip of a renal pyramid is called renal papilla
what is a kidney lobe?
a kidney lobe is a macroscopic subdivision consisting of a renal pyramid and its surrounding cortex. in adult kidneys, the loabr strucutre is usually indistinct externally as well as internally
What is a kidney lobule?
a kidney lobule is a microscopic subdivision consisting of a medullary ray and the cortical tissue (primarily nephrons) on either side. the tubules of these nephrons connect with the collecting ducts within the medullary rays
What is the capsule of the kidney?
mainly fibrous connective tissue surrounding the kidney. the parenchyma is not subdivided by septa
the total blood volume of the body passes through the kidneys every ________. How much fluid is extracted from the blood as filtrate and how much is excreted as urine?
4-5 minutes
125 ml of fluid is exxtracted from the blood each minute as filtrate (180L/day)
but 124 ml is reabsorbed back into the kidney tubules and 1 ml is excreted as urine
what is the order of arterial supply to the kidney?
renal artery
lobar artery
interlobar
arcuate
afferent arterioel
what are the 2 capillary systems in the microvsaculature of the kidney
glomerulus:
- afferent arteriole to glomerulus to efferent arteriole
THEN EITHER
tubular plexus: supplies tubules of the cortical nephrons
or vasa recta: long capillary loops supplying tubules of juxtamedullary nephrons
WHat is the space between the tubules called and what are its components?
Renal interstitium
- interstitial (stromal) tissue is found in the renal cortex nd medulla (stroma is finer in cortex)
- interstitium components:
- interstitial connective tissue
- interstitial cellls (fibroblasts) in cortex and medulla
what are the 4 components of the renal corpuscle?
glomerulus
visceral layer of the renal capsule (bowman’s capsule)
parietal layer of the renal capsule
mesangium
What is the renal corpuscle and what does it surround? describe its structure. where are they found?
the renal corpuscle: (small body) is a spherical, double layered sac that surround a network of capillaries called the glomerulus (ball of thread)
it has a vascular pole where the arteries enter and exit and a urinary pole that is continuous with the proximal convoluted tubule
what is the glomerulus? what drives glomerular filtration?
a network fo capillary loops supplied and drained by an arteriole
the afferent (supply) arteriole is larger in diameter thatn the efferent (draining) arteriole. this size difference creates a pressure differential that drive glomerular filtration
What is Bowman’s capsul? what kind of tissue is it made up of?
- a double layered epithelial sac surrounding the glomerulus
- the outer or parietal layer is a simple squamous epithelium
- the visceral layer is also a simple epithelium composed of cells called podocytes
- the space between the 2 epithleial layers is called the urinary space and is continuous with the proximal tubule. the glomerular filtrate enters this space
What 3 things make up the glomerular filtration barrier/ filtration membrane of the kdiney?
- capillary endothelium: discontinous contianing 70-100nm pores. the pores are freely permeable to water and solutes < 6-8kD and moderately permeable to molecules 8-16kD. The luminal surface has a negative charge because it is coated with a glycocalyx consisting of negatively charged proteoglycan molecules (free to water and solutes, and small solutes)
- basement membrane: is the primary barrier that prevents protein from entering the glomerular filtrate
- podocytes: with foot processes make the basement membrane
- there are also filtration slits
what is the function of the glomerular mesangium? WHat makes up the glomerular mesangium?
Functions: physical support, regulation of glomerular blood flow
Glomerular mesangium: cells and ECM that abut the inner surface of the glomerular basmeent membrane. ECM contains fibronectin and collagen and specialized pericyte/smooth muscle cells
What is proximal tubule? what happens there? what type of tissue? where is it?
- Convoluted PortionL begins at the urinary pole and is located in the cortex
- glucose, amino acids, proteins are reabsorbd through facitialted transport
- cuboidal columnar cells with granular cytoplasm and basal nuclei
- apical brush border with glycocalyx obscures lumen
- lysoosmes and apical vessicles
- numerous mitochondria at base of cell provide energy for transport
- complex lateral interdigitations between epithelial cells make ateral cell membrans indistinguishable
- Straight portion: also called the thick
what kind of tissue if the straight portion aka the thick descending limb of henle?
cuboidal epithelium
What are the 4 parts of the loop of henle (intermediate tubule)? Where is is located?
- straight portion of the proximal tubules (thick desceding limb)
- thin descending limb
- thin ascending limb
- straight potion of the distal tubule (thick ascending limb)
located within the medulla
How is the length of the loop of henle determined? what are the 2 kinds of nephron and how does this relate? What kind of tissue makes up the different segemnts?
the length is deterined by the lcoation of its renal corpuscle with respect to the cortiomedullary juction
- Cortical Nephron: located external to the juxtamedullary zone, have short loops that have only a Descending Thin Limb ( no thin ascending limb bc is short)
- Juxtamedullary Nephrons are long looped and have ascending and descending thin limbs
thick portions of the loop are lined with cuboidal epithelium, but the thin segements are lined with simple squamous
Describe the permeability of water through out the loop of henle
thin descending limb is permeable to water
ascedning limb is impermeable. cell membraned in the ascending thin limb between epithelial cells are interdigitated, resulting in water impermeability
What does the tubular-interstitium-vascular interaction provide a mechanism for? what are the components?
provides a mechanism for modifying and concentrating urine
components: collecting ducts, loops of henle, vasa recta
What is the countercurent multipler and what is the countercurrent exchanger?
-
Countercurrent multiplier:
- urine concentration through differential resportion of water
- yields hypotonic fluid in the distal tubule becasue the ascending limb of hte lop of henle is impermeable to water, while the descending lim is somewhat permeable
-
Countercurrent Exchager:
- maintains osmotic gradietn established by countercurrent multiplier
- accomplished becuase the arterioles around the desceinding limb of the loop have continous endotheium and the venules around the ascending limb of the loop have fenestrated endothelium
What kind of tissue is the straight portion of the distal tubule lined with? what ions are absorbed and secreted here? Describe general characteristics.
aka the thick ascending limb
- lined with cuboidal epithelium
- scant microvili, efficient tight junctions
- lateral and basal membrane interdigitations
- abundant mitochondria
- impermeable to water
- Na, Cl resorbed
- H ions secreted
