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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 2 | LIVER. PANCREAS.

LIVER. PANCREAS.

LIVER (LV)
Microscopically LV is composed of 500.000 HEPATIC LOBULES.
CLASSICAL hepatic LOBULE – is hexagon-shaped block of tissues. It contains: a) central vein, b) radially arranged hepaticPLATES, c) SINUSOIDAL capillaries (between 2 plates), d) bile canaliculi (between 2 hepatocytes). Hepatic PLATE –is groop of anastomosing hepatocytes with thickness in 1 cell.
BOUNDARIES between neighboring lobules presented by: A) only portal triades (in HUMAN liver), B) thick layers of loose connective tiss. (in PIG liver).
Portal triade is:1) interlobular artery, 2) interlobular vein, 3) interlobular bile duct
HEPATOCYTE - is epithelium, forming liver PARENCHYME. It has 1-2 nuclei and abundance of rER and sER. Funct.: 1) synthesis and secretion of blood plasma proteins (on rER) – albumins, fibrinogen, 2) On sER 2 reactions happen: a) synthesis of glycogen from uptaken glucose, leading to decreasing of blood glucose level, b) glycogenolysis and secretion of glucose into blood. 3) On sER synthesis of lipoprotein particles happens. 4) On sER synthesis of pigment bilirubin and bile salts and following it secretion into bile canaliculus. 5) On sER synthesis of  low toxic urea from toxic NH3.
Wall of SINUSOIDAL capillary has 4 types of NONparenchymal cells: 1)50% -endothelial cells (simp. squam. epith.). Rest 3 types are STAR-shaped cells: 2) Kupffer cells (hepatic MACROPHAGES). Funct.:phagocytosis. 3) Stellate cells (or fat storing cells, Ito cells).. Funct.: a) vit. A storage, b) after stimulation by alcohol it secrete too much collagen and promotes CIRRHOSIS development. 4) Pit cells (NK cells=Natural Killers). Funct.: elimination of cancer cells.
Bile CANALICULUS does not have proper wall and formed by plasma membrane of 2 neighboring hepatocytes.

PANCREAS. (PC).

Connective tissue capsule covers the PC; septae extend from capsule and divide PC on the LOBULES. Lobule is composed of 2 portions of parenchyma (it is epithelium):
1) exocrine parenchyma and 2) endocrine parenchyma
EXOCRINE parenchyma (97% in lobule) presented by tubuloacinar serous exocrine gland. It is composed of 3 components: a) pancreatic ACINUS (it is secretory portion), b) intercalated duct, c) intralobular duct. ACINUS is spherical sacculus, composed of 8-12 acinar cells and a few centroacinar cells.
Each acinar cell is pyramid-shaped. Nucleus is in basal domain. Apical domain contains secretory ZYMOGEN granules. Funct.: secretion of digestive proenzymes ((trypsinogen, inactive amylase, inactive lipase) into duct system. Activation happens ONLY in duodenum lumen (trypsinogen becomes by active trypsin).
ENDOCRINE parenchyma (3% in lobule) presented by Langerhans islets. Each islet is: A) association of 3000 pancreatic endocrine cells and B) fenestrated capillaries.
Endocrine cells in islet are classified on 5 types:
1) 70% B-cells. It secrete hormone INSULIN. Insulin reduces blood glucose level (HYPOglycemia action) and prevents diabetes mellitus.
(deficiency of insulin leads to HYPERglycemia).
2) 20% A-cells. It secrete hormone GLUCAGON. It increases blood glucose level (HYPERglycemia action).
3) D-cells. It secrete hormone somatostatin.
4) D1-cells. It secrete hormone VIP.
5) PP-cells. It secrete hormone “pancreatic polypeptide”
Embryonic origin for parechymal epithelium (hepatocytes, acinar cells, endocrine cells) – is ENDODERM of foregut.
Куратор темы – доцент В.В. Бондаренко.
 
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