BIOL 2420 Lecture Notes - Lecture 2: Peritubular Capillaries, Renal Artery, Renal Vein
26 Apr 2018
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Unit 7 – Lecture 2
The Nephron Is the Functional Unit of the Kidney
Cross section through a kidney
- Shows the interior arranged in two layers
1. Outer cortex
2. Inner medulla
- Layers are formed by organized arrangement of microscopic tubules – nephrons
o About 80% of the nephrons in a kidney are almost completely contained within the
cortex (cortical nephrons)
o About 20% (juxtamedullary nephrons) dip down into the medulla
Nephron is the functional unit of the kidney
- Functional unit – the smallest structure that can perform all the functions of an organ
- Each 1 million nephrons in a kidney is divided into sections
- Each section is closely associated with specialized blood vessels
Vascular Elements of the Kidney
- Blood enters the kidney through the renal artery
o then flows into smaller arteries and into arterioles in the cortex
o Arrangement of blood vessels forms a portal system
▪ One of three portal systems in the body
▪ Portal system:
• composed of two capillary beds in series (one after the other)
Renal portal system
- Blood flows from renal arteries into an afferent arteriole
- Then leads to the first capillary bed (ball-like network known as a glomerulus
- Blood leaving the glomerulus flows into an efferent arteriole
- Then into the second set of capillaries – peritubular capillaries
o In juxtamedullary nephrons, the long peritubular capillaries that dip into the medulla are
vasa recta
- Peritubular capillaries converge to form venules and small veins
o Sending blood out of the kidney through the renal veins
Function of the renal portal system
- Filter fluid out of the blood and into the lumen of the nephron at the glomerular capillaries
- To then resorb fluid from the tubule lumen back into the blood at the peritubular capillaries
- Forces behind fluid movement in the renal system are similar to those that govern filtration of
water and molecules out of systemic capillaries in other tissues
Tubular Elements of the Kidney
Kidney tubule
- A single layer of epithelial cells connected together near their apical surface
o Apical surfaces are folded into microvilli (area increasing folds)
o Basal side of the polarized epithelium rests on basement membrane (basal lamina)
- Cell to cell junctions are mostly tight but some have selective permeability for ions
- Nephron begins with a hollow, ball-like structure, the Bowa’s capsule, surrounds the
glomerulus
o Edotheliu of the gloerulus is fused to the epitheliu of Boa’s apsule so that
fluid filtering out of the capillaries passes directly into the lumen of the tubule
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Document Summary
The nephron is the functional unit of the kidney. Shows the interior arranged in two layers: outer cortex. Layers are formed by organized arrangement of microscopic tubules nephrons. Inner medulla: about 80% of the nephrons in a kidney are almost completely contained within the cortex (cortical nephrons, about 20% (juxtamedullary nephrons) dip down into the medulla. Nephron is the functional unit of the kidney. Functional unit the smallest structure that can perform all the functions of an organ. Each 1 million nephrons in a kidney is divided into sections. Each section is closely associated with specialized blood vessels. Blood flows from renal arteries into an afferent arteriole. Then leads to the first capillary bed (ball-like network known as a glomerulus. Blood leaving the glomerulus flows into an efferent arteriole. Then into the second set of capillaries peritubular capillaries. In juxtamedullary nephrons, the long peritubular capillaries that dip into the medulla are vasa recta.
