Renal System Development 10th week ~12 weeks

Development of Three Nephric Systems Cervical Nephrotomes & Mesonephroi Upper thoracic region to the third lumbar region

Development of Three Nephric Systems Cervical Nephrotomes & Mesonephroi 6-10weeks-func >10-regress. Mesonephric ducts in females regress and in males they persist to form parts of male genital duct system. Renal Corpuscle: Glomerulus & Bowman’s capsule Mesonephric excretory unit: Renal corpuscle & Nephric tubule 26 Days ~22 days

Development of Three Nephric Systems. Mesonephroi & Metanephroi Regress to the 1st three lumbar levels Mesonephric duct forming Sacral Region Reciprocal induction ~22 days

Collecting Duct System of the Metanephroi Sequence of bifurcations.

Sequence of bifurcations ~22 days

Sequence of bifurcations. 11 additional generations of bifurcations--> 1-3 mil branches. ~22 days 32nd Week 8 months

Nephron Development Contains neural crest derived neurons. They play a role in nephron induction. The neurons regulate blood flow and secretory function. 9th week ~22 days

Nephron Development 10weeks+-->func: gl. filtrate to urine, but main func to produce amniotic fl. 10th week

Definitive Kidney Architecture Minor calyx Major calyx Pelvis Contains the nephrons. Contains the loops of Henle and collecting ducts . 5th-15th weeks Renal Pyramid (inner medulla)

Kidneys ascend from a sacral to lumbar location ~22 days

Movement of the Kidneys ~22 days Figure 8-6

Anomalies during kidney ascent Inferior mesenteric artery ~22 days

The remainder of the urinary tract develops from the hingut endoderm Cloacal expansion and partition 4th week Female Male Vestibule of Penile vagina urethra Membranous membranous urethra & prostatic urethra 6th week

Exstrophy of the mesonephric ducts and ureteric buds. 4-6 weeks * * * * * * * * -Endoderm grows over trigone -Splanchnopleuric mesoderm associated with the hindgut forms the smooth muscle of the bladder wall.

Ureteric bud or metanephros induction defects Renal agenesis A. Defects in the inductive interaction between the ureteric bud and metanephric blastema may cause renal agenesis. B. Bilateral renal agenesis results in death. Unilateral renal agenesis results in hypertrophic kidney. C. 75% of the cases involving renal agenesis occur in males. D. Bilateral renal agenesis can also result in oligohydramnios, causing Potter’s syndrome (deformed limbs and facial defects. E. Unilateral renal agenesis is usually associated with heart defects and constrictions of the gastrointestinal tract.

Genital System Development 4-6 weeks ~12 weeks

The genital and urinary systems develop in close conjunction Primitive sex cord & Paramesonephric duct development (mullerian) Third thoracic segment caudally to the posterior wall of the urogenital sinus 5-6 weeks

Virtually identical male and female genital systems. 6th week At this point the sex cords have both a cortical and medullary region. After the 6th week these regions pursue different fates in the male and female.

Basis of sex differentiation Autosomes and Sex Chromosomes 1. There is a total complement of 46 chromosomes, 22 pairs consist of matching homologous chromosomes called autosomes. The 23rd pair are called the sex chromosomes because they determine the sex of the individual. 2. XX individuals are genetically female. XY individuals are genetically male. Subsequent phases of sexual development are controlled by both the sex chromosome genes and by the hormones and factors encoded by the autosomes. 3. The sex-determining region of the Y chromosome (SRY) encodes a transcription factor that controls the choice between the male and female developmental paths.

Basis of sex differentiation Autosomes and Sex Chromosomes 4. Male development is triggered when SRY is expressed in the sex cords during the indifferent phase. 5. Thus the male pathway is actively induced.

Figure 10-13

Male genital (internal) Development Sertoli cell differentiation in the medullary sex cords ~7th week

Male genital (internal) Development Anti-Mullerian hormone (AMH) secretion by Sertoli cells (reminant of cranial end of mesonephric duct) ~8-12th week Sertoli Cells Ductuli efferentes (reminant of inferior mesonephric tubules)

Male genital (internal) Development Differentiation of the mesonephric ducts of the male ~10th-12th week

Male genital (internal) Development Differentiation of the accessory glands of the male urethra ~10th-12th weeks

Female genital (internal) development Absence of a Y chromosome

Female genital (internal) development Absence of AMH in the female embryo

Female genital (internal) development Absence of AMH in the female embryo

Female genital (internal) development Absence of AMH in the female embryo

External genitalia development Male and Female external genitalia develop from the same primordia or urethral fold External genitalia is similar in male and female embryos through the 12th week.

External genitalia development. Male external genitalia. 12 weeks 14 weeks

External genitalia development Female external genitalia 7th week 3rd month

The gubernaculum controls the descent of the testes and ovaries The descent of the testes

The gubernaculum controls the descent of the testes and ovaries The descent of the testes

The gubernaculum controls the descent of the testes and ovaries The descent of the testes

The gubernaculum controls the descent of the testes and ovarie The descent of the ovaries

Abnormal dev of the genital system Testicular Feminization Syndrome--> the androgen receptors are abnormal or lacking, resulting in the formation of a blind-ending vagina (Male genotype, Female external phenotype, no ovaries). Since the testes are still present and AMH is produced, the paramesonephric ducts regress (Thus no superior vagina, uterus, or fallopian tubes).

Abnormal dev of the genital system True hermaphrodites--> have both ovarian and testicular tissue. The gonads are usually a composite ovotestes containing both seminiferous tubules and follicles. Or an individual may have an ovary on one side and a testes on the other side. Most true hermaphrodites are reared as males since a phallus is usually present at birth.