The structure, function and organization of the human body

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Unit 3

The Structure, Function and Organisation of The Human Body

Outcome 1 Handout



The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. It is usually a microscopic structure containing nuclear and cytoplasmic material enclosed by a semi-permeable membrane. Some organisms, such as most bacteria, are unicellular(consist of a single cell). Other organisms, such as humans, are multicellular.

Each cell is at least somewhat self-contained and self-maintaining: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Each cell stores its own set of instructions for carrying out each of these activities.

Comparison of structures between animal and plant cells

Typical animal cell

Typical plant cell



Nucleolus (within nucleus)

Rough endoplasmic reticulum (ER)

Smooth ER



Golgi apparatus








Nucleolus (within nucleus)

Rough ER

Smooth ER



Golgi apparatus (dictiosomes)




Cell wall


Nucleus- Controls the cell. It consists of the nuclear envelope, nucleolus, chromatin, and nucleoplasm.

Nucleolus- are non-membraneous matrix of RNA (ribonucleic acid) and protein. found in the nucleus. Instructions in DNA are copied here. It works with ribosomes in the synthesis of protein.

Chromosomes- Determines what traits a living thing will have,
passes information from parent to offspring.

Cell Membrane- same as unit membrane. Gives the cell shape, holds the cytoplasm, and controls what moves into and out of the cell. acts as a boundary layer to contain the cytoplasm (fluid in cell) interlocking surfaces bind cells together.

Cytoplasm- Jellylike material (cytosol and organelles), most of the
cell's chemical reactions take place there, and made
up of mostly water and some chemicals.

Vacuoles- Liquid-filled, may store food, water, minerals, or wastes. There maybe more than one. In plants it takes up a lot of space, produce turgor pressure against cell wall for support.

Mitochondria- Produce energy when food is broken down, often
called the "powerhouse of the cell". It's structure is composed of modified double unit membrane (protein, lipid). Its inner membrane infolded to form cristae. It is the site of cellular respiration i.e. the release of chemical energy from food

Glucose + Oxygen ------> Carbon Dioxide + Water + Energy (ATP)

Ribosomes- Where proteins are made, and often connected to the endoplasmic reticulum. A cell may have as many as 500,000. They are non-membraneous, spherical bodies composed of RNA (ribonucleic acid) and protein enzymes. They are the site of protein synthesis.

Endoplasmic Reticulum- The "transportation system" in the cell, connects the nuclear membrane with the cell membrane. Used in detoxification of the cell. "ER".   Forms a tubular network throughout the cell. Provides a large surface area for the organization of chemical reactions and synthesis.

Centrioles- Found only in animal cells, is used in cell reproduction to
help the chromosomes arrange before cell division. They are nine triplets of microtubules form one centriole. Two centrioles form one centrosome. They form spindle fibres to separate chromosomes during cell division.

Golgi apparatus(bodies)- Stacks of flattened sacs of unit membrane (cisternae) vesicles pinch off the edges. Modifies chemicals to make them functional. Secretes chemicals in tiny vesicles. Stores chemicals. May produce endoplasmic reticulum.

Lysosomes- digests food particles with enzymes, pinched of pieces of golgi apparatus. Are membrane bound bag containing hydrolytic enzymes. Are hydrolytic enzyme = (water split biological catalyst) i.e. using water to split chemical bonds.

They  break large molecules into small molecules by inserting a molecule of water into the chemical bond.

Cell Wall- Found only in plant cells. Forms a thick outer covering outside the cell membrane, gives the plant support and shape. Is a non-living secretion of the cell membrane, composed of cellulose. They are cellulose fibrils deposited in alternating layers for strength. Cell wall contains pits (openings) that make it totally permeable.  It  provides protection from physical injury and together with vacuole, provides skeletal support.

Chloroplasts- Found only in plant cells. Found in the cytoplasm of green plant
cells, contain chlorophyll, traps the energy from light, and is where photosynthesis takes place. It is composed of a double layer of modified membrane (protein,chlorophyll, lipid). The inner membrane invaginates to form layers called "grana" (sing., granum) where chlorophyll is concentrated. It is the site of photosynthesis

Carbon Dioxide + Water ---------------> Glucose + Oxygen
radiant energy (food).


There are many different types of cells in the human body. None of these cells function well on there own, they are part of the larger organism that is called - you.

Tissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. Organsare then formed by the functional grouping together of multiple tissues.

Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialized function. There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue.

    1. Epithelial Tissue- The cells of epithelial tissue pack tightly together and form continuous sheets that serve as linings in different parts of the body. Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.

    2. Connective Tissue- There are many types of connective tissue in the body. Generally speaking, connective tissue adds support and structure to the body. Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue. Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue. In addition to these more recognizable forms of connective tissue, blood is also considered a form of connective tissue.

    3. Muscle Tissue- Muscle tissue is a specialized tissue that can contract. Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement. Examples of muscle tissue are contained in the muscles throughout your body.

    4. Nerve Tissue- Nerve tissue contains two types of cells: neurons and glial cells. Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body.


Organs are the next level of organization in the body. An organ is a structure that contains at least two different types of tissue functioning together for a common purpose. There are many different organs in the body: the liver, kidneys, heart, even your skin is an organ. In fact, the skin is the largest organ in the human body and provides us with an excellent example for explanation purposes. The skin is composed of three layers: the epidermis, dermis and subcutaneous layer.

The epidermis is the outermost layer of skin. It consists of epithelial tissue in which the cells are tightly packed together providing a barrier between the inside of the body and the outside world. Below the epidermis lies a layer of connective tissue called the dermis. In addition to providing support for the skin, the dermis has many other purposes. The dermis contains blood vessels that nourish skin cells. It contains nerve tissue that provides feeling in the skin. And it contains muscle tissue that is responsible for giving you 'goosebumps' when you get cold or frightened.

The subcutaneous layer is beneath the dermis and consists mainly of a type of connective tissue called adipose tissue. Adipose tissue is more commonly known as fat and it helps cushion the skin and provide protection from cold temperatures.

Nervous tissue: is one of four major classes of vertebrate tissue.

Nervous tissue is the main component of the nervous system-the brain, spinal cord, and nerves-which regulates and controls body functions. It is composed of neurones, which transmit impulses, and the neuroglia, which assist propagation of the nerveimpulse as well as provide nutrientsto the neuron. Every time you get pinched, part of your nerve tissue is damaged.

Nervous tissue is made of nerve cells that come in many varieties, all of which are distinctly characteristic by the axon or long stem like part of the cell that sends action potential signals to the next cell.

Functions of the nervous system are sensory input, integration, controls of muscles and glands, homeostasis, and mental activity.

All living cells have the ability to react to stimuli. Nervous tissue is specialized to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. Nerve tissue (as in the brain, spinal cord and peripheral nerves that branch throughout the body) are all made up of specialized nerve cells called neurons. Neurons are easily stimulated and transmit impulses very rapidly. A nerve is made up of many nerve cell fibres (neurons) bound together by connective tissue. A sheath of dense connective tissue, the epineurium surrounds the nerve. This sheath penetrates the nerve to form the perineurium which surrounds bundles of nerve fibres. Blood vessels of various sizes can be seen in the epineurium. The endoneurium, which consists of a thin layer of loose connective tissue, surrounds the individual nerve fibres.

The cell body is enclosed by a cell (plasma) membrane and has a central nucleus. Granules called Nissl bodies are found in the cytoplasm of the cell body. Within the cell body, extremely fine neurofibrils extend from the dendrites into the axon. The axon is surrounded by the myelin sheath, which forms a whitish, non-cellular, fatty layer around the axon. Outside the myelin sheath is a cellular layer called the neurilemma or sheath of Schwann cells. The myelin sheath together with the neurilemma is also known as the medullary sheath. This medullary sheath is interrupted at intervals by the nodes of Ranvier.

Neuronal Communication

Nerve cells are functionally made to each other at a junction known as a synapse, where the terminal branches of an axon and the dendrites of another neuron lie in close proximity to each other but normally without direct contact. Information is transmitted across the gap by chemical secretions called neurotransmitters. It causes activation in the post-synaptic cell. All cells possess the ability to respond to stimuli.