Human Physiology, 14th edition (2016)

Cell Structure and Genetic Control 51

3.1 PLASMA MEMBRANE AND

ASSOCIATED STRUCTURES

The cell is the basic unit of structure and function in the

body. Many of the functions of cells are performed by par-

ticular subcellular structures known as organelles. The

plasma (cell) membrane allows selective communication

between the intracellular and extracellular compartments

and aids cellular movement.

Cells look so small and simple when viewed with the ordinary

(light) microscope that it is difficult to think of each one as a living

entity unto itself. Equally amazing is the fact that the physiology

of our organs and systems derives from the complex functions

of the cells of which they are composed. Complexity of function

demands complexity of structure, even at the sub-cellular level.

As the basic functional unit of the body, each cell is a

highly organized molecular factory. Cells come in a wide

variety of shapes and sizes. This great diversity, which is also

apparent in the subcellular structures within different cells,

reflects the diversity of function of different cells in the body.

All cells, however, share certain characteristics; for example,

they are all surrounded by a plasma membrane, and most of

them possess the structures listed in table 3.1. Thus, although

no single cell can be considered “typical,” the general structure

of cells can be indicated by a single illustration ( fig. 3.1 ).

George, who is 28 years old, complains of pain in his hips

and knees, and he has a swollen abdomen. Upon exten-

sive medical examination, he is found to have hepato-

megaly (an enlarged liver) and splenomegaly (an enlarged

spleen). He thinks his enlarged liver might be due to his

abuse of alcohol and drugs.

Some of the new terms and concepts you will

encounter include:

• Lysosomes and lysosomal storage diseases


• Rough and smooth endoplasmic reticulum

Clinical Investigation^ LEARNING OUTCOMES

After studying this section, you should be able to:

1. Describe the structure of the plasma membrane,
   cilia, and flagella.


2. Describe amoeboid movement, phagocytosis,
   pinocytosis, receptor-mediated endocytosis, and
   exocytosis.

Figure 3.1 A generalized

human cell showing the

principal organelles. Because

most cells of the body are highly

specialized, they have structures

that differ from those shown

here.

Chromatin

Lysosome

Mitochondrion

Nuclear envelope

Golgi complex

Plasma membrane

Microtubule

Cytoplasm

(cytosol)

Ribosome

Agranular
endoplasmic
reticulum

Nucleus

Nucleolus

Centriole

Secretory
vesicle

Granular

endoplasmic

reticulum