What is CT proper? Embroynic CT? Adult CT?

Specialized CT?

Adult CT

•CT proper: loose (areolar) and dense CT (reg/irreg)

•Specialized CT: Reticular and Adipose and Mesenchyme

Embryonic CT

•mesenchyme

•mucous

Describe the histoloogy of white fat -- cell types, ECM, functions

• cells are spherical in shape filled with a single large lipid droplet made of triglycerides
• unilocular* – meaning that each cell contains a single fat droplet
• the cytoplasm and nucleus are crowded to the
periphery of the cell

• during tissue preparation, the fat is dissolved out of the cell; what remains is a rim of cytoplasm and nucleus, giving a signet ring appearance

• the cell contains a Golgi apparatus, mitochondria,
poorly developed rER, and free polyribosomes
• the cells are separated by a basal lamina
• the cells are associated with thin partitions of CT
containing vessels, nerves, fibroblasts, macrophages
and reticular fibers

Functions:

• lipid storage and mobilization

– fat can originate from three sources:

» dietary fats transported as chylomicrons
» triglycerides synthesized by liver and transported as VLDL
» can be synthesized locally from free fatty acids and glycerol

• endocrine function
– secretes leptin – a 16 kD polypeptide involved with satiety

– NOTE: releases cytokines, termed “adipokines”: obesity is associated with chronic inflammation

[image]

Describe the histology of brown fat -- cell types, ECM, functions

• many small lipid droplets (multilocular)
• cells are polygonal, smaller than white fat cells, with a spherical central nucleus, many mitochondria (heat)
• tissue lobulated by CT partitions – has epithelial
appearance
• cells receive direct sympathetic innervation

• brown fat is relatively abundant in infants
• recently, it has been shown that adults contain brown
fat deposits in the neck and chest regions

• function: heat production by nonshivering thermogenesis[image]

Give an explanation of how fat is metabolized in both white and brown fat.

White: Norepinehrine -> hormone-sensitive lipase -> metabolizes trigyclerides->diffuse to capillary (albumin)

                                  -> diffuse to liver (glycerol)

(+) glucagon and growth hormone

(-) insulin

Brown: Norepinehrine -> hormone-sensitive lipase -> metabolizes trigyclerides->FA fast metabolized (heat)

                                  -> diffuse to liver (glycerol)

                                  ->diffuse to capillary (albumin)

Explain the endocrine function of fat cells.

Endocrine:

– secretes leptin – a 16 kD polypeptide involved w/ satiety

– releases cytokines, termed “adipokines”: obesity is associated with chronic inflammation

Explain the histogenesis of fat tissues.

White: mesenchymal -> lipoblasts* (while accumulating fat) -> unilocular adipocyte

*WAT: lipoblasts may resemble fibroblasts early on

Brown: mesenchyme (earlier than white)-> lipoblasts** -> multilocular adipocyte

**BAT: lipoblasts may resemble epithelium prior to accumulating fat

Give a description of the basic types of embryonic CT and CT proper. Include cell and fiber types and composition of ground substance; give examples of locations of these various CT: loose (areolar) CT

Description:

• support tissue when under mild pressure or low friction
• flexible, well vascularized

Components:
– fibroblasts, macrophages, etc.
– collagen, reticular and elastic fibers
– abundant ground substance
– vessels, nerves

Examples:
– supports epithelia
– surrounds blood and lymph vessels
– surrounds muscles and nerve fibers
– papillary layer of dermis; hypodermis
– peritoneal and pleural linings
– glands and mucous membranes

[image]

Give a description of the basic types of embryonic CT and CT proper. Include cell and fiber types and composition of ground substance; give examples of locations of these various CT: dense CT

Description:

• offers greater resistance and protection
• same components as loose CT, with less cells and ground substance and more fibers
• less flexible, more resistant to pressure and friction

Components (same as loose CT):
– fibroblasts, macrophages, etc.
– collagen, reticular and elastic fibers
– abundant ground substance
– vessels, nerves

Examples:

– dense irregular CT: collagen fibers arranged in bundles with random orientation (not parallel)
» resistance from stress in all directions
» often associated with loose CT

– dense regular CT: collagen fibers arranged in
bundles with parallel orientation
» greater resistance to traction

» cytoplasm of fibroblasts not seen in tissue sections
» some ligaments (e.g. ligamentum flavum) also contain elastic fibers

» found in tendons and ligaments

NOTE: tendons are poorly vascularized and heal slowly
– tendons surrounded by sheath of dense irregular CT = “investing fascia”
– some tendons are surrounded by a tendon sheath
lined by synovial tissue

[image]

Give a description of the basic types of embryonic CT and CT proper. Include cell and fiber types and composition of ground substance; give examples of locations of these various CT: reticular

Description: specialized CT

• reticular cells (specialized fibroblasts) secrete ECM
• fibers form meshwork in hematopoietic & lymphoid
tissues

– provide sponge-like environment allowing free movement of fluid and cells

• MPS (mononuclear phagocyte system) cells present

Composition

formed of heavily glycosylated type III collagen fibers

Give a description of the basic types of embryonic CT and CT proper. Include cell and fiber types and composition of ground substance; give examples of locations of these various CT: mesenchyme

Description: specialized (embryonic)

• embryonic CT formed of undifferentiated cells
• cells are characterized by oval nuclei with prominent
nucleoli; many thin cytoplasmic processes
• abundant ground substance, sparse fibers
• develops primarily from mesoderm
• gives rise to a number of other types of CT cells[image]

Give a description of the basic types of embryonic CT and CT proper. Include cell and fiber types and composition of ground substance; give examples of locations of these various CT: mucous CT

• found primarily in the umbilical cord, where it is called “Wharton’s jelly”

• abundant ground substance rich in hyaluronan

[image]