Page 78 - Atlas of Histology with Functional Correlations

blood.

CELLULAR ORGANELLES

Each cell cytoplasm contains numerous organelles, each of which performs a

specialized metabolic function that is essential for maintaining cellular
homeostasis and cell life. A membrane similar to the cell membrane surrounds
such cytoplasmic organelles as nucleus, mitochondria, endoplasmic reticulum,
Golgi apparatus or Golgi complex, lysosomes, and peroxisomes. Organelles that

are not surrounded by membranes include ribosomes, basal bodies, centrioles,
and centrosomes.

Mitochondria

Mitochondria are round, oval, or elongated structures whose variability and
number depend on cell function. Each mitochondrion (singular) consists of an
outer and inner membrane. The inner membrane exhibits numerous folds called

cristae, which contain respiratory chain enzymes that produce the energy
molecule adenosine triphosphate (ATP). In protein-secreting cells, these
cristae project into the interior of the mitochondria as shelves. In steroid-
secreting cells, such as the adrenal cortex or interstitial cells in the testes, the
mitochondria cristae are tubular and contain enzymes for steroidogenesis

(production of steroid hormones).

FUNCTIONAL CORRELATIONS 2.1 ■

Mitochondria

Mitochondria produce most of the high-energy molecule adenosine

triphosphate (ATP) in cells and are, therefore, considered the powerhouses
of the cells. The cristae in the mitochondria increase the surface area of the
inner membrane. The cristae contain most of the respiratory chain enzymes
as well as ATP synthetase, which is responsible for cell respiration
(oxidative phosphorylation) and production of cell ATP. ATP is the chemical

energy responsible for various metabolic cell activities.

The number of mitochondria in a given cell is directly related to the
cell’s energy needs. Thus, cardiac or skeletal muscle cells with continuous

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