1. Kidney: Anatomic basis Flashcards
What is the primary function of the kidney?
- Maintainance of homeostasis: Isovolemia, isosmosis, isoionia, isohydria
- Conservation of essential substances (water, electrolytes, glucose, aminoacids)
- Participation in acid-base balance
- Participation in cardiovascular regulation (especially through Angiotensin 2 synthesis)
- Elimination of exogenous and endogenous organic components (protein-metabolic endproducts, toxins, medicines)
- Hormone production (direct or indirect): 1-25-OH-D3; erythropoietin; PGE2; T3
Anatomic basis of the cattle
- There´s no renal pelvis
- Pyramids lead to amaller or larger calynx which open directly to the urether
- Adipose tissue around renal sinus serves as shock-absorber
Anatomic basis of the dog and cat
- Have no papillae
Anatomic basis of the horse
- No papillae
- Have recessus terminalis
Picture of kidney
Nephron
It is the functional unit of the kidney.
Capable of urine formation by itself.
Each kidney consists of one million nephrons.
- Malpighi-body – Bowmans capsule, glomerulus
- Tubular system – Procimal tubule, henle loop, distal tubule, collecting tubule, finally urine flows to the renal-pelvis, through papillae.
- Incomplete nephron – I.e. at aglomerular fishes or in birds.
- Some of the nephrons lack Henle loop (reptilian-type nephrons).
- Others have loop of Henle (mammalian-type nephrons)
- Junxatamedullary 15%, Cortical 85 %.
Tubular system
- Proximal tubule: PCT proximal convoluted, PST proximal straight tubule
- Hele loop: decending thin limb (DLT), Ascending thin limb (ATL), thick ascending limb (TAL)
- Distal tubule: distal convoluted tubule (DCT), distal connective tubule (CNT)
- Collecting duct: cortical collecting duct (CCD), Medullary collecting duct (MCD)
- Finally urine flows to the renal-pelvis, through the papillae.
Glomerulus/Bowman´s Capsule
20% of plasma is filtrated.
Anatomic basis of glomerular filtration, three layers:
- Fenestrated endothelium
- Glomerular basement membrane (GBM)
- Outermost epithelial podocyte process with their interconnecting slit diaphragms.
- Glomerular filtration barrier behaves as a size-selective filter that restricts the passage of plasma macromolecules based on their size, shape and charge.
- Negatively charged molecules are filtered in smaller amounts than neutral molecules of comparable size and the traversal of positively charged molecules is actually facilitated
Podocytes
They are cells in the bowman´s capsule in the kidney that wrap around capillaries of the glomerulus. They have foot projections that wraps around the capillaries and leave slits, called slit diaphragm, between them.
Slit diaphragm
It has a zipper-like structure with pores localized between the foot processes of the podocyte, and is the ultimate barrier for proteins of the size of albumin. The slit diaphragm is considered to be a rigid structure with a fairly constant width, but it can increase with intraglomerular pressure indicating that the slit diaphragm is partially elastic.
Kidney circulation/portal circulation
The kidney has two capillary beds arranged in series. The glomerular capillaries which are under high pressure for filtering (non-real capillaries). The peritubular capillaries which are situated around the tubule and are at low pressure (real capillaries).
Circulation of the medullary zone
- The vasa recta is a portion of the peritubular capillary system which enters the medulla where the solute concentration in the interstitium is high. It acts with the loop of Henle to concentrate the urine by a complex mechanism of counter current exchange.
- If the vasa recta did not exist, the high concentration of solutes in the medullary interstitium would be washed out.
- Length of vasa recta is 100x (40mm) larger than normal capillaries.
