Download 2. atomic. Formed by atoms. The atoms that can be found in living

UNIT 3: Organization of human body
1- Organization levels of the human body
There are different levels of organization:
There are five levels of organization of living beings:.
1. Subatomic. It consists of subatomic particles, ie, protons, electrons and neutrons (and
also its subparticles: eons, quarks, leptons,…)
2. atomic. Formed by atoms. The atoms that can be found in living beings are called
bioelements. There are three types:
 Primary Bioelements: are indispensable elements for forminfvorganic
biomolecules (carbohydrates, lipids, proteins and nucleic acids). Constitute 96% of
dry living matter. Are carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur
(C, H, O, N, P, S, respectively).
 Secondary bioelements. Constitute 3% of dry living matter. Calcium (Ca),
sodium (Na), potassium (K), magnesium (Mg) and chlorine (Cl). .
 Trace elements They are present in very small amounts in living things (<0,1%)
but their absence makes us get ill. Copper (Cu), iron (Fe), iodine (I), etc.
3. Molecular. Molecules are formed by grouping two or more atoms. Molecules found
in living beings are called biomolecules. We distinguish two types of biomolecules:


Inorganic: Water and mineral salts
Organic: Carbohydrates, lipids, proteins and nucleic acids.
4. Cells. Molecules may join to form cells. Examples- blood cells, nerve cells, ova, etc.
5. Tissues. A tissue is a group of similar cells working together to perform a function.
(i.e. Skin)
6. Organ. An organ is a group of tissues that perform a specific function (i.e. heart,
brain, spleen, kidney...).
7. System. is a collection of organs that perform a specific function- the circulatory
system or digestive system for example.
8. Organism. All the systems of the body form an organism (a human being).
9.Population: Is a group of human beings living in a given area.
10. Community: Is a group formed by human beings and other living beings living in a
given area.
11. Ecosystem. Is the relation with living and non-living matter.
2-Cell Theory
Leewenhoek used a simple microscope to observe tiny unicellular organisms.
The cell was discovered by Robert Hooke in 1665. He examined (under a compound
microscope) very thin slices of cork and saw a multitude of tiny pores that he remarked
looked like the walled compartments a monk would live in. He called them cells.
We can summarize the principles of cell theory as:
1) Every organism is made of one or more cells.
2)The cell is the anatomical and physiological unit of living matter,
3) All cells come from preexisting cells by division of these, that is, all cells
arise from previous cells
3- Characteristic of human cells
Structure: human cells are eucariotic and heterotroph.
Shape:Human cells can be Spheroid (leucocyte), Stellate (neuron); Discoid (blood cell);
Fusiform (muscle cell),...
Number of cells: There are billions of about 250 different types of cells in the human
body.
Size: The smallest cell in the human being is the spermatozoa and the biggest one is the
egg cell and the neuron.
4- Cell structure
Light microscope reveals three main parts in any cell: cell membrane, nucleus, and
cytoplasm:
 Cell membrane
Function: Surrounds the cell and protects it.
(nutrients) and out of cell (waste products).
It controls passage of materials in
Is made of a double layer of lipids.
 Nucleus
Is an organelle that controlsw the cell activity. It consists of:
Nuclear envelope (membrane that surrounds the nucleus) perforated by nuclear pores.
Nucleoplasm, liquid inside the nucleus.
Chromatin (DNA when cell is not dividing). When the cell is going to start the cell
division, chromatin turns into chromosomes.
Nucleoli, dark structure where ribosomes are produced.
 Cytoplasm
Is the fluid between the nucleus and the cell membrane.
It consists of: water, cytoskeleton, organelles (membranous and nonmembranous)
Membranous organelles
 Endoplasmic reticulum- is a network of flattened membranous sacs. There are
two types:
Rough endoplasmic reticulum- Connected to the membrane of the
nuclear envelope and is covered with ribosomes. It synthesizes proteins.
Smooth endoplasmic reticulum-It lacks ribosomes. It synthesizes
lipids.
 Golgi complex- network of membranous sacs with dilated ends. A pile of these
sacs forms a dictiosome. It produces lysosomes.
 Mitochondria-Are rod-shaped cells surrounded by a double membrane (inner
and outer membrane). The inner membrane has folds called cristae. The space
inside the mitochondria is called matrix. These organelles specialize in
synthesizing energy through a mechanism called cell respiration.
 Lyssomes: Small bags containing digestive enzymes to digest subtances.
Nonmembranous organelles
 Ribosomes- Are small organelles made of protein and RNA. They consist of
two subunits: a large subunit and a small subunit. They are synthesized in
nucleoli and they can be located in cytoplasm and on the outer surfaces of the
rough endoplasmic reticulum. They “read” RNA (which is a copy made from
DNA) and synthesize proteins.
5- Types of tissues
-Epithelial tissue. There two types:
Coating tissues: cover and protect the body surface (epidermis in skin) and
internal cavities (blood vessels).
Glands: synthesizes substances. According to the substance synthesized, we can
find three types of glands:
-Exocrine gland: releases substances into cavities inside the body or its
outer surface (sweat glands produce sweat, sebaceous glands produce
fats).
-Endocrine gland: secretes hormones into the bloodstream (testis
release testosterone, ovaries produce progesterone, adrenal gland
produces adrenaline).
-Exocrine and endocrine glands: these glands consist of an endocrine
part and an exocrine part (the pancreas secretes the hormone insulin and
pancreatic juice).
-Connective tissue: is made up of cells, extracellular substance and fibers (i.e., collagen
fibers…). There are different types:
-Conjunctive tissue: connects different types of tissues and organs in the
body. Its cells are called fibroblasts.
-Fat tissue: is a reservoir of energy. Its cells are called adipocytes which
are full of fats.
-Cartilaginous tissue: is an elastic tissue and structural component of the
rib cage, the ear and the nose. Cartilage consists of cells called
chondrocytes.
-Bone tissue: its cells are called osteocytes. This tissue has a high
extracellular content of calcium.
-Blood: It’s a liquid tissue, made up of cells (red cells, leucocytes and
platelets) in a liquid medium (plasma). It transports nutrients and waste
products.
-Muscular tissue: is formed by cells called muscular fibers or myocytes. There are
three types of muscular tissues:
-Striated skeletal muscle tissue: is called "striated" because of its
appearance consisting of light and dark bands which are visible using
a light microscope. A single skeletal muscle cell is long with many
nuclei located at the periphery of the cell. Its function is the
movement of the skeleton under conscious control.
-Cardiac muscle tissue: are striated, and have a single central
nucleus. They are involved in pumping blood through the heart:
-Smooth muscle tissue: Unlike Skeletal and Cardiac muscle tissue,
Smooth muscle is not striated. It has a single centrally located
nucleus. They surround the vessels and in the digestive system move
food along the gastrointestinal tract.
-Nervous tissue: is composed of neurons (which transmit impulses), and glial cells
(which help neurons in the propagation of the nerve impulse).
6- Organs and systems
Organs: brain, heart, kidney, spleen, stomach, lungs,...
-Systems involved in nutrition: circulatory system, respiratory system, digestive
system and excretory system
-Systems involved in reproduction: reproductive system
-Systems involved in relationships: Nervous system, muscular system, skeletal
system, endocrine system