chapter 4- Epithelium

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epithelium

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(a) basement membrane (TEM) The dense basal lamina (BL) has thin clear zones on each side, is anchored to a thicker, more diffuse reticular lamina (RL) which contains collagen III reticular fibers.
Hemidesmosomes (H) bind the basal surface of the epithelial cell (C) to the basal lamina. (X54,000)

(b) Laminin, a major glycoprotein within basal laminae, identifies the basement membranes of the stratified epithelium (E) and the simple epithelium lining a small blood vessel (V)
Laminin also occurs in the external laminae surrounding nerves (N) and muscle (M) fibers, seen here in cross-section.

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Image: (a) basement membrane (TEM) The dense basal lamina (BL) has thin clear zones on each side, is anchored to a thicker, more diffuse reticular lamina (RL) which contains collagen III reticular fibers.
Hemidesmosomes (H) bind the basal surface of the epithelial cell (C) to the basal lamina. (X54,000)

(b) Laminin, a major glycoprotein within basal laminae, identifies the basement membranes of the stratified epithelium (E) and the simple epithelium lining a small blood vessel (V)
Laminin also occurs in the external laminae surrounding nerves (N) and muscle (M) fibers, seen here in cross-section.

apical side

facing the sheet's free surface

basal side

facing a basement membrane and underlying connective tissue.

transcytosis

pinocytosis of material at the apical (free) side and exocytosis at the basolateral side (or vice versa) [transcellular transport- i.e. this both processes happen]

epithelial cell MA

MEDICAL APPLICATION
-Both benign and malignant tumors can arise from most types of epithelial cells. (malignant are carcinomas)
-Malignant tumors derived from glandular epithelial tissue=adenocarcinomas.
-Adenocarcinomas are the most common tumors in adults after age 45

epithelial cell MA

MEDICAL APPLICATION

-Some epithelial cells are prone to abnormal growth or dysplasia, can progress to precancerous growth (neoplasia)

-Early neoplastic growth is often reversible and does not always result in cancer.

metaplasia (MA)

-one type of epithelial tissue undergoes transformation into another type.
-Process is reversible, happens under abnormal conditions.
-In heavy cigarette smokers, the ciliated pseudostratified epithelium lining the bronchi can be transformed into stratified squamous epithelium.

Type IV collagen

in basal lamina

Type III collagen

in the reticular lamina

Type VII collagen

anchors reticular lamina to the basal lamina

(holds everything together, regulatory)

Laminin

-large glycoproteins that attach to integrins at the cells' basal surface
-project through the network of type IV collagen.

Nidogen

-short, rod-like protein cross -links laminin to the collagen network -helps determine the porosity of the basal lamina

perlecan

a proteoglycan, cross-links laminin to the collagen network and help determine the porosity of the basal lamina

basment membrane

-a thin extracellular layer of specialized proteins
-two parts: a basal lamina and reticular lamina.
-always lies at the interface of epithelial cells and connective tissue.
-Nutrients for epithelial cells must diffuse across the basement membrane.
-Nerve fibers normally penetrate this structure, but small blood capillaries (being epithelial themselves) normally never enter epithelia.

This section of kidney shows basement membranes (arrows) of epithelia which form structures within the large, round renal glomerulus and its surrounding tubules.
In kidney glomeruli the basement membrane has a supporting function and a highly developed role as a filter that is key to renal function.

chapter 4- Epithelium

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