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28. The retroperitoneum. Development of body cavities. The histology of the parathyroid gland.

28 Dec

28. The retroperitoneum. Development of body cavities. The histology of the parathyroid gland.

Retroperitoneal Space

The retro peritoneal space is seperated into the 3 compartments by the renal fasica. This fascial covering is like a tent that is closed susuperiorly and open inferiorly.

Ant Chamber = b/w peritoneum and renal fascia, has all secondary retroperitoneal organs

  • asc colon
  • desc colon
  • duodenum (except sup hor part)
  • pancreas (except tail, sometimes)
  • Br. of sup mesenteric a, celiac trunk, sup/inf mesenteric v, portal v, common bile duct

Middle Chamber = w/in renal fasica, has primary retroperitoneal organs.

  • kidneys
  • suprarenal glands
  • ureters
  • Ab aorta + branches
  • IVC + branches
  • Thoracic duct
  • Cisterna Chyli

Post Chamber = b/w renal fascia and transverse fascia(post ab wall)

  • asc lumbar v (becomes azygos v, once crosses diaphragm into thoracic cavity)
  • Greater/Lesser splanchnic n
  • SNS trunk
  • Subcostal n.
  • Lumbar plexus + branches
  • Ilioinguinal n.
  • Inohypogastric n
  • Obturator n
  • Genitofemoral n
  • Gonadal a/v

The histology of the parathyroid gland.
Slide 35: Parathyroid glands * H&E
General Info:
generally have 4 parathyroid glands
2 sup/2 inf
sit on posterior surface of thyroid gland

With naked eye: small, pale, round specimen

  • connect to thyroid via CT capsule
  • CT trabeculae extend from capsule –> substance of the gland
  • CT trabeculae w/ a/v  that make capillaries
  • cells of parathyroid gland arranged into clumps, surrounded by capillaries
  • Structure of gland: islands of adipose tissue in stroma & rich in a/v
    cells form zigzag cells cords

2 main cells types:
Chief Cells

  • most numerous
  • differentiate during embryonic development
  • pale stained nucleus
  • round and pale, slightly acidophilic cytoplasm
  • cytoplasm contains:
    • lipofuchsin vesicles
    • lipid droplets
    • large accumulation of glycogen
    • membrane limited vescicle = store PTH

Functions:
produce Parathryoid hormone

  • maintain proper calcium levels in EC body fluid
  • raises calcium level on blood
  • opposite action as calcitonin (prod by parafollicular cells in thyroid glands)
  • NOTE – release of PTH depends primarily on Ca levels in blood, not on PTH

PTH stimulates:

  1. Bone resorption
    1. -stimulates activity & increases the proliferation of osteoclasts in bones
    2. increases osteolytic activities, release of more calcium into blood stream
  2. Kidney tubule re-absorption of Ca2+ -distal convoluted tubules inc both resorption of Ca from glomerular filtrate,
  3. Urinary PO4 excretion –  and elimates of PO4, Na, K+ ions into urine, dec Po4 conc in blood, CSF
  4. Kidney activation of Vit D3 – causes kidneys to form calcitrol, active form of Vit D
  5. Intestinal action – increases Ca absorption from GI tract/bloodstream

Oxyphil Cells

  • larger than chief cells w/ smaller nucleus
  • less numerous than chief cells
  • more scattered than chief cells
  • acidophilic cytoplasm, smaller dark stained nuclei
  • function unclear, inc in # w/ age
  • differentiate @ puberty
  • found singly or clusters

*Embryo:
develop from endodermal cells derived from 3rd & 4th pharyngeal arches
inf – 3rd
sup – 4th
Cheif cells are active in regulating fetal Ca2+ metabolism
Oxyphil cells differentiate @ puberty

Embryology: Development of body cavities.

From intraembryonic mesoderm –> 3 portions:
paraaxial mesoderm
intermediate mesoderm
lat plate mesoderm

lat plate mesoderm splits into somatic/ splanchnic mesoderm
splanchnic mesoderm is continuous w/ wall of yolk sac

somatic and splanchnic mesoderm border the intraembryonic cavity
@ 1st intra/extra embryonic cavity are connected, after embryo folds (cephalo-caudally, laterally)
this splits intraembryonic region into thoracic & ab region

Serous membranes:
splanchnic mesoderm – forms visceral layer of mesothelium (pleura, pericardium, peritoneum)
somatic mesoderm – forms parietal layer
Both layers become continous @ ventral and dorsal mesentery

  • ventral = is all along gut tube, mesoderm band from caudal end of foregut –> end of hindgut
  • dorsal = from caudal end of foregut –> upper duodenum (from thinning of mesoderm of septum transversum)

Seperation of cavities:

Separation of cavities – done  by the formation of lungs/diaphragm

1. Development of Lungs:

  • Septum transversum – mesoderm plate b/w thoracic cavity & yolk sac
    • makes 2 pericardioperitoneal canals on either side of foregut
    • Lungs grow & expand to form
    • pleuropericardial folds –> from small ridges on primitive thoracic cavity
    • mesoderm of body wall divides into
      • 1. definitive wall of thorax
      • 2. pleuropericardial membranes – contain  common cardinal v & phrenic n
        • After sinus venosus & heart  change position, they move to midline & fuse w/ each other and root of lung —>
        • this divides the thoracic cavity into the definitive pleural/pericardial cavities

2. Diaphragm of Lungs:

Made from 4 structures:

  1. Septum transversum
  2. 2 pleuroperitoneal membranes –> expand med/ant to fuse w/ mesentery of esophagus, & septum transversum
  3. Musc of lat/dorsal body wall
  4. Mesentery of esophagus (makes the crura of diaphragm)