Topic #2: The Structure of the Human Body
Structure of the Human Body
4 Levels of Organization
organ systems , organs,  tissues,  cells
Organ systems are composed of organs
Organ systems are a group of organs that perform a common function
Define each level of organization by level below it
Organs are a group of tissues that perform a common function
Definition of Tissues
Tissues are a group of cells that perform a common function
Digestive System: An Example of an Organ System
Organs Systems of Our Body
Organs are a group of tissues that perform a common function
Example of an Organ:The Stomach
Definition of Tissues
Tissues are a group of cells that perform a common function
Cells with a common structure, function
Structure is suited to function
4 major types: epithelial, connective, muscular, nervous
 Epithelial Tissue
Cover body surface and line organs and cavities
Connective Tissue
Diversity of form, function
Muscle Tissue
Contractile tissue
Nervous Tissue
 Send nervous impulses
What are cells?
Cells are the fundamental structural and functional unit of the body
The Cell Doctrine
All living things are composed of cells
A single cell is the smallest unit that exhibits all the characteristics of life
All cells come from preexisting life
Cells are specialized for their function
Muscle cells:  long thin, contractile fibers
Cell Structure Reflects Cell Function
Nerve cells: have long and thin extensions to carry impulses over distance
Basic Units of a human cell
The cell is surrounded with a plasma membrane
The fluid within membrane is called cytoplasm
Complex solution
Nucleus contains the genetic material (DNA)
organelles: membrane-bound structures with specialized functions
Internal Structures of an Animal Cell
Structural Features of the Plasma Membrane
Lipid bilayer with chunks of protein floating in it
Phospholipids: polar head and nonpolar tail
Proteins: provide means of transportation through membrane
Carbohydrates attached to proteins: recognition patterns for cells and organisms (glycoproteins, antigens)
Internal Membranes Create Compartments
organelles: membrane-bound structures with specialized functions
Molecules are transported across membranes
Membranes control chemical environment in organelles
Nucleus is a specialized compartment containing DNA
DNA is a large organic molecule
double helix
Consists of nucleotides containing bases A, T, G, C
DNA molecules linked together to form chromatin
Chromatin coils up during cell division to form chromosomes
On Chromosomes are the genes
DNA has three separate but related functions
An information molecule (blueprint for creating a protein)
The genetic molecule (blueprint are copied and passed on to new cells)
Controls activities of cells (directs production of proteins which control all chemical reactions in the cell)
Organelles also form compartments: Endoplasmic Reticulum (ER) and Ribosome
Some Organelles: Endoplasmic Reticulum (ER) and Ribosome
Golgi Apparatus
Receives substances from ER, refines and packages them
Vesicles Ship and Store Cellular Products
Vesicles: storage, secretory membrane-bound spheres
Mitochondria: Provide Energy to the Cell
Malfunctioning organelles
can cause disease
Zellweger’s syndrome
peroxisome malfunction
Cannot produces hydrogen peroxide
Necessary for breakdown of various toxins e.g. alcohol
I-cell disease (lysosome malfunction)
Lysosomes contain powerful digestive enzymes
Digest bacteria, cellular debris
Result in build up of inclusions
Abnormal cell structure
Seriously affect muscle , skeletal tissue
Death in first decade
Genetic disorder (recessive gene)
Is skin an organ or an organ system?
Texts are divided
Some call it the largest organ
Others such as your text group it in the integumentary system with hair and finger nails
If organ: it consists of tissues
If system: must be different organs
Skin has Multitude of Functions :
 prevent dehydration
 protect from injury
 defense against microorganisms
 regulate body temperature
 make vitamin D
Skin has three layers
Epidermis, Dermis, Hypodermis
Are they tissue layers or organs?
Skin: Structure: Epidermis
Epidermis: outer layer, stratified squamous epithelial tissue,
Specialized keratinocytes and melanocytes ,
no blood vessels
Is epidermis a tissue or an organ?
Only type of tissue
Epithelial tissue
keratinocytes and melanocytes  are specialized epithelial tissue
Therefore tissue???
Skin: Structure: Dermis
deeper layer
 primarily connective tissues
Containing fibers which give the skin  its elasticity
Also contains accessory
Structures, e.g. blood vessels, nerves
Connective tissue contains collagen (tight skin of youth)
As we age produce less collagen: causes wrinkles
Accessory Structures of Dermis: Are these organs?
Hair: shaft, follicle
Smooth muscle: attached to hair follicle, raises hair to upright position
Oil glands/sebaceous glands: secretion moistens and softens skin
Sweat glands: secrete sweat, help in temperature regulation
Blood vessels: supply nutrients, remove waste, assist in temperature regulation
Sensory nerve endings: for heat, cold, touch, deep pressure, vibration
Is the dermis an organ or an organ system?
Accessory structures are made of different tissues
Therefore dermis is an organ system ???
loose connective tissue and adipose tissue
“subcutaneous fat”
Fat storage, insulation
Melanocytes near base of epidermis produce melanin
Exposure to sun increases melanin production: protect dividing cells, dermis,
Produces suntan
Prolonged Exposure to Sun Can damage
 dividing cells  skin cancer
collagen in dermis (wrinkles)
keratinocytes  rough skin (alligator skin)
melanocytes  uneven melanin
liver spots
Both UVA (once thought to be safe) and UVB cause damage
Protect Yourself
Skin cancer is increasing
Holes in the ozone increase UV rays
Cover up
Wear suntan lotion with a high SPF
Wear sunglasses
Smoking causes damage to skin
Thickens collagen fibers in dermis  wrinkles
Dehydrates keratinocytes  rough skin
Narrows blood vessels in dermis slower to heal