Nephron Histology Overview
The nephron is the functional unit of the kidney and renal system. Each adult human kidney typically contains about 750,000 nephrons, though the total number can vary significantly from as few as 250,000 to as many as 2,000,000.
The tubular system can be divided into proximal and distal tubules, which in turn have convoluted and straight portions. The tubules form the loop of Henle.
- Intermediate tubules connect the proximal and distal tubules.
- Running from the cortex of the kidney towards the medulla (descending)
- then turning and running back towards the cortex (ascending)
The glomerulus (renal corpuscle) in humans is the round (~0.2 mm in diameter) blind beginning of the nephron. It is invaginated by a tuft of capillaries at the vascular pole of the glomerulus. The tuft of capillaries and other cells in contact with them form the anatomical glomerulus. Substances which leave the capillaries enter the renal tubule at the urinary pole of the glomerulus.
The anatomical glomerulus is enclosed by two layers of epithelium, Bowman's capsule.
- Cells of the outer or parietal layer of Bowman's capsule form a simple squamous epithelium.
- Cells of the inner layer, podocytes in the visceral layer, are extremely complex in shape. Small foot-like processes (pedicles) of their cytoplasm form a fenestrated epithelium around the fenestrated capillaries of the glomerulus. The openings between the pedicles are called filtration slits. They are spanned by a thin membrane, the filtration slit membrane.
Between the podocytes and the endothelial cells of the capillaries lies a comparatively thick basal lamina, which can be subdivided into an outer lamina rara externa, a middle lamina densa and an inner lamina rara interna. The basal lamina and the slit membranes form the glomerular filtration barrier, which prevents some large molecules from entering the capsular space between the outer and inner epithelial layers of Bowman's capsule.
- Mesangial cells in the glomerulus form the connective tissue that gives structural support to podocytes and vessels.
- Blood pressure is the driving force in the formation of about 125 ml of glomerular filtrate per minute.
- About 124 ml of the glomerular filtrate is reabsorbed in the tubules of the nephron.
- Renal System Histology: Nephron tubule overview | glomerulus structure | vascular and renal poles | Medullary rays | Nephron tubules
- Large Images: medullary rays | glomerulus | distal tubule and collecting duct | proximal and distal tubule | distal and intermediate tubule | medullary ray | glomerulus | proximal tubule | Renal System Development
- bladder exstrophy - A congenital malformation with bladder open to ventral wall of abdomen (between umbilicus and pubic symphysis) and may have other anomolies associated with failure of closure of abdominal wall and bladder (epispadias, pubic bone anomolies).
- blastema - Term used to describe a mass of undifferentiated cells. (More? Wilm's tumour)
- Bowman's capsule - (capsula glomeruli, glomerular capsule) Surrounds the glomerulus within the nephron with a vascular and urinary pole and is the beginning of the tubular component. Named in 1842 after Sir William Bowman (1816 – 1892) an English surgeon and anatomist.
- Brenner hypothesis - a clinical hypothesis that states, individuals with a congenital reduction in nephron number have a much greater likelihood of developing adult hypertension and subsequent renal failure. Developed in the 1980's by Barry Brenner at the Brigham and Women's Hospital, this also fits with the DOHAD hypothesis. (More? PubMed 3063284 | Barry Brenner)
- capillary loop - (C stage) The third stage in nephron development between 25-29 weeks. (stage sequence: V - S - C - M)
- diabetes insipidus - The disorder is related to the hormone antidiuretic hormone (ADH, also called vasopressin) its synthesis, secretion, receptors and signaling pathway. In diabetes insipidus there is an excretion of large amounts (up to 30 litres/day) of a watery urine and an unremitting thirst.
- fenestrated capillary - Specialised capillaries containing circular pores (fenestrae) that penetrate the endothelium, may be closed by a thin diaphragm.
- glomerulus - The capillary network (tuft) within Bowman's capsule of the nephron enters at the vascular pole (afferent and efferent arteriole).
- hydronephrosis - (congenital hydronephrosis, Greek, hydro = water) A kidney abnormality due to partial or complete obstruction at the pelvi-ureteric junction. This leads to a grossly dilated renal pelvis causing extensive renal damage before birth.
- hyperplastic rests - In kidney development, embryonic blastema cells can persist and proliferate to form a pool of cells, which under either genetic or epigenetic influence can then change to become a neoplastic rest. Normally the majority of nephrogenic rests either regress or become dormant.
- juxtaglomerular cells - Cells located at the vascular pole that secrete renin and form a part of the juxtaglomerular complex.
- loop of Henle - Nephron region spanning from the proximal convoluted tubule to the distal convoluted tubule. Named after Named after Friedrich Gustav Jakob Henle (1809–1885) a German anatomist.
- macula densa - Columnar cell cluster appearing as a dense row of cell nuclei where the straight portion of the distal tubule contacts the glomerulus. Region also in close contact with the efferent and afferent arterioles of the glomerulus and involved in sodium chloride regulation. (More? image)
- maturation stage - (M stage) The forth stage in nephron development in infants aged 1-6 months. (stage sequence: V - S - C - M)
- mesangial cells - Cells in the nephron glomerulus that form the connective tissue giving structural support to podocytes and vessels.
- mesonephros - The second temporary stage of kidney development (pro-, meso-, meta-). The intermediate mesonephros develops and disappears with the exception of its duct, the mesonephric duct, which will form the male reproductive duct system. In males, the mesonephric tubules go on to form the ducts of the testis. In females, these degenerate. A few mesonephric tubules remain as efferent ductules in the male and vestigial remnants in the female.
- mesonephric duct - (= Wollfian duct) An early developing urogenital duct running the length of the embryo that will differentiate and form the male reproductive duct system. In females this duct degenerates (some remnants may remain associated in broad ligament).
- metanephros - The adult kidney, third stage of mammalian kidney (pro-, meso-, meta-) development within the intermediate mesoderm.
- metanephric cap - (metanephric blastema) The intermediate mesoderm which surrounds the ureteric bud and will contribute most of the adult nephron.
- multicystic kidney - There is no functional kidney tissue present in the kidney and it is replaced by a multilocular cyst. This is non-familial and is produced by atresia of a ureter and is always unilateral.
- neoplastic rest - In kidney development, a neoplastic rest can develop under either genetic or epigenetic influence from a hyperplastic rest, originating from an embryonic blastema cell. Normally the majority of nephrogenic rests either regress or become dormant.
- nephrogenic rest - Used to describe the embryonic blastema cells which persist and under either genetic or epigenetic can change to become a neoplastic rest. These neoplastic rests can develop postnatally as a benign form (adenomatous rest) or a malignant Wilm's tumour form. The rests are further characterised by the time of generation leading to different anatomical kidney locations: early intralobar nephrogenic rests (within the renal lobe) and late pelilobar nephrogenic rests (periphery of the renal lobe)
- nephron - (Greek, nephros = kidney) The functional unit of the adult kidney.
- nephros - (Greek, nephros = kidney) Term used to describe features associated with the kidney. (pronephros, mesonephros, metanephros, nephric, nephron, nephroblastoma).
- parietal layer - Cells of the outer of Bowman's capsule that form a simple squamous epithelium. The inner layer is the visceral layer.
- podocyte - (visceral epithelial cell) kidney glomerulus cell forming the main component of the glomerular filtration barrier. (glomerular podocyte) Kidney epithelial cell type in the nephron (kidney functional unit) located in the glomerulus. Podocytes form the visceral layer of Bowman's capsule and are at the filtration barrier between capillary blood and the nephron tubular system and function to ultrafiltrate blood, and support glomerular capillary pressures. The differentiation of podocytes involves the formation of cellular foot processes and then the slit membrane. (More? image)
- podocyte specific proteins - podocalyxin, glomerular epithelial protein-1, podocin, nephrin, synaptopodin, and alpha-actinin-4), podocyte synthesized proteins (vascular endothelial growth factor and novH), transcription factors (WT1 and PAX2).
- pronephros - (Greek, pro = before) The first temporary stage of kidney development (pro-, meso-, meta-). This forms the kidney of primitive fish and lower vertebrates. Kidney development occurs within the intermediate mesoderm interacting with endoderm. In humans, this very rudimentary kidney forms very early at the level of the neck. It is rapidly replaced by the mesonephros, intermediate stage kidney, differentiating in mesoderm beneath.
- proteinuria - The abnormal presence of protein in the urine and an indicator of diesease including diabetic kidney disease (DKD, diabetic nephropathy).
- proximal tubule - Portion of the nephron duct between Bowman's capsule to the loop of Henle, divided into the proximal convoluted tubule (PCT) and the proximal straight tubule (PST).
- renal - (Latin, renes = kidney) Term used in relation to the kidney and associated structures (renal pelvis, renal artery)
- S-shaped body - (S stage) The second stage in nephron development between 20-24 weeks. (stage sequence: V - S - C - M)
- transitional epithelium - (urothelium) Histological term to describe the epithelium lining the ureters and urinary bladder. (More? image)
- trigone - refers to the urinary bladder triangular region formed by the two ureters and the urethra.
- ureter - The two ureters are hollow tubes that link the kidney and the bladder and carry urine. They develop from the ureteric bud and are lined by a transitional epithelium with an outer muscular wall.
- urethra - The single muscular tube that links and carries urine from the bladder to the exterior. In humans, the urethral length differs between the sexes (male longer, female shorter).
- vascular pole - The side of nephron Bowman's capsule where the afferent arteriole and efferent arteriole enter the glomerulus. image
- visceral layer - Cells (podocytes) of the inner of Bowman's capsule that form extremely complex shapes. Cytoplasm form a fenestrated epithelium around the fenestrated capillaries of the glomerulus. The outer layer is the parietal layer.
- vesicle stage - (V stage) The first stage in nephron development between 13-19 weeks. (stage sequence: V - S - C - M)
- urinary - Term used to describe all components of the kidney system including the bladder, ureters and urethra.
- urinary pole - The side of nephron Bowman's capsule where the proximal convoluted tubule starts. image
- urine - Term used to describe the liquid waste produced by the kidney, stored in the bladder and excreted from teh body through the urethra.
- urorectal septum - (URS) The structure which develops to separate the cloaca (common urogenital sinus) into an anterior urinary part and a posterior rectal part.
- Wilms' tumour - A form of kidney/renal cancer (nephroblastoma) named after Dr Max Wilms who first described the tumor. This childhood kidney cancer is caused by the inactivation of a tumour suppressor gene (BRCA2) or Wilms tumor-1 gene (Wt1) and is one of the most common solid tumors of childhood, occurring in 1 in 10,000 children and accounting for 8% of childhood cancers. Wt1 also required at early stages of gonadal development. (More? OMIM - Wilm's tumour | Dr Max Wilms)
- Wilms' tumor 1-associating protein - (WTAP) protein expressed in extraembryonic tissues and required for the formation of embryonic mesoderm and endoderm.
- Wolffian duct - (= mesonephric duct, preferred terminology), runs from the mesonephros to cloaca, differentiates to form the male vas deferens and in the female regresses. Named after Caspar Friedrich Wolff (1733-1794), a German scientist and early embryology researcher and is said to have established the doctrine of germ layers. (More? Caspar Friedrich Wolff)
Links: Histology | Histology Stains | Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes. See also the page Histology Stains.
Cite this page: Hill, M.A. (2019, February 18) Embryology Nephron histology.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Nephron_histology.jpg
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