Cells and Tissues: Some Insights

Cells and Tissues: Some Insights

Cells

Protein Packaging by the Golgi body

Golgi apparatus are the cell organelles that transport proteins and lipids. They process the proteins manufactured by the rough endoplasmic reticulum before they are sent out of the cell. Proteins enter the Golgi apparatus through the opposite side of the stack that faces the plasma membrane (Rushworth, 2011). The organization, shape, and number of cristae of Golgi apparatus vary in different cell types.

Lysosomes: Its Structure and Functions

The lysosome, a specialized vesicle found only within animal cells, participates in the digestion of large molecules through the use of hydrolytic enzymes and helps the cell to eliminate its waste products. There are over sixty different enzymes that ensure the operation of these processes.

Structure. Lysosomes are small in size ranging from 0.1 to 0.5 micrometer though some may reach 1.2 micrometers. They have a simple structure made up of a phospholipid bilayer that encloses a fluid containing a variety of hydrolytic enzymes.

Functions. Lysosomes are involved in the formation of complex molecules like carbohydrates, lipids, proteins, and nucleic acids. Since the hydrolytic enzymes they enclose express optimum function at acidic pH levels, lysosomes have an acidic pH. Lysosomes break down  and digest different kinds of molecules using these enzymes; they also participate in the digestion of food molecules entering the cell after fusing with the endocytic vesicle. Lysosomes destroy malfunctioning organelles through a process called autophagy and also perform phagocytosis, a the process through which a cell engulfs a molecule to break it down.

Autolysis

Autolysis refers to the enzymatic digestion of cells by the enzymes found within them; it also refers to the destruction of cells and tissues of an organism by the enzymes which these cells self-produce. Dead cells are mostly susceptible to autolysis. The lysosomes play a central role in autolysis and hence, are called as “suicide sacs” of a cell.

The Structure and Origin of Mitochondria

Structure. Mitochondria are made up of two membranes—the outer and the inner. The two membranes have different structures and create distinct components within the organelle. The outer membrane consists of a simple phospholipids bilayer with a pore-forming protein structure known as “porins” (Kühlbrandt, 2015); this layer makes it permeable to molecules of approximately ten kilodaltons or less in size.  The inner membrane—permeable only to water, oxygen, and carbon dioxide—has a highly complex structure. It is folded into layers called the cristae that increase its surface area. The arrangement of both the outer and inner membranes create a component called the intermembrane space which performs the function of oxidative phosphorylation. The inner membrane encloses a fluid-filled matrix that contains enzymes for the  citric acid cycle reactions, and also provides media for dissolution of oxygen, water, and carbon dioxide.

Origin. According to the endosymbiotic theory, mitochondria originated from early bacteria and later became incorporated into our cells. That mitochondria have their own DNA and can reproduce through binary fission and their only function in our cells is to provide the energy necessary for biological functions substantiates that mitochondria were not originally a part of our cells.

Nucleus: Outer Membrane and Inner Contents

Outer membrane. The outer membrane of the nucleus faces the cytoplasm, is continuous in various regions with the rough endoplasmic reticulum, and bears ribosomes on its surface.

Inner contents. Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include the building blocks of nucleic acids and it surrounds the nucleolus Threads of chromatin are also found in this inner part..

Tissues

Fluid Tissue

Blood is the only fluid tissue and is found throughout the body. It is a connective tissue which consists of cells—red blood cells, white blood cells, and platelets—that circulate in a fluid called plasma.

Significance of the Relationship Among Cells, Tissues, and Organs

Cells form the structural and functional unit of organisms. Groups of cells forms tissues and many tissues combine to form organs that perform specific functions. Examples of organs include the lungs, kidneys, and the stomach.

Human Tissues—Their Types and Functions

Epithelial tissue, connective tissue, nervous tissue, and muscle tissue are the main types of tissues found in humans. Epithelial tissue protects the body from loss of moisture, bacterial entry, and internal injury while connective tissue provides structure and support to the body (Brelje & Sorenson, n.d.). Nervous tissue forms the nervous system, which coordinates the activities and movements of the body through a network of nerves. Muscle tissue are of three types: cardiac muscle, which is involved in the contraction of the heart and assists pumping of blood; smooth muscle, which forms organs such as the stomach; and, skeletal muscle that facilitates movement of bones and other structures.

Functions of Five Organs Analyzed in the Lab

Heart, Stomach, Skin, Lungs and Eyes were five among the various organs analyzed in the lab. The heart pumps blood throughout the body and is part of the cardiovascular system. The stomach, part of the gastrointestinal tract, digests food by proteolysis and acidification. The skin acts as a barrier against bacterial entry and also protects the body from mechanical injury, pressure, and temperature variations. The lungs are vital organs and are part of the respiratory system that performs the function of respiration. The eye is a special sense organ for visual perception.

References

Andersen, P. [Bozeman Science]. (2012, February 24). A tour of the cell [Video file]. Retrieved from https://www.youtube.com/watch?v=1Z9pqST72is

Brelje, T. C. and Sorenson, R. L. (n.d.). Histology guide: Virtual histology laboratory. Retrieved from http://www.histologyguide.com/slidebox/slidebox.html

Kühlbrandt, W. (2015). Structure and function of mitochondrial membrane protein complexes. BMC Biology, 13, 89. https://doi.org/10.1186/s12915-015-0201-x

Rushworth, G. (2011). Body systems: Human cells. New Rochelle, NY: Benchmark Education Company.