introduction to the human body

organization of the human body

The basic building blocks of the human body are cells. Human cells are organized into tissues, tissues are organized into organs, and organs are organized into organ systems.

human cells

The average human adult consists of an incredible 100 trillion cells! Cells are the basic units of structure and function in the human body, as they are in all living things. Each cell must carry out basic life processes in order to survive and help keep the body alive. Most human cells also have characteristics for carrying out other, special functions. For example, muscle cells have extra mitochondria to provide the energy needed to move the body. You can see examples of these and some other specialized human cells in Figure 16.1. To learn more about specialized human cells and what they do, watch this video: . MEDIA Click image to the left or use the URL below. URL:

textbook_image

human tissues

Specialized cells are organized into tissues. A tissue is a group of specialized cells of the same kind that perform the same function. There are four basic types of human tissues: connective, epithelial, muscle, and nervous tissues. The four types are shown in Figure 16.2. Connective tissue consists of cells that form the bodys structure. Examples include bone and cartilage, which protect and support the body. Blood is also a connective tissue. It circulates and connects cells throughout the body. Epithelial tissue consists of cells that cover inner and outer body surfaces. Examples include skin and the linings of internal organs. Epithelial tissue protects the body and its internal organs. It also secretes substances such as hormones and absorbs substances such as nutrients. Muscle tissue consists of cells that can contract, or shorten. Examples include skeletal muscle, which is attached to bones and makes them move. Other types of muscle include cardiac muscle, which makes the heart beat, and smooth muscle, which is found in other internal organs. Nervous tissue consists of nerve cells, or neurons, which can send and receive electrical messages. Nervous tissue makes up the brain, spinal cord, and other nerves that run throughout the body.

human organs

The four types of tissues make up all the organs of the human body. An organ is a structure composed of two or more types of tissues that work together to perform the same function. Examples of human organs include the skin, brain, lungs, kidneys, and heart. Consider the heart as an example. Figure 16.3 shows how all four tissue types work together to make the heart pump blood.

textbook_image

textbook_image

human organ systems

Human organs are organized into organ systems. An organ system is a group of organs that work together to carry out a complex function. Each organ of the system does part of the overall job. For example, the heart is an organ in the circulatory system. The circulatory system also includes the blood vessels and blood. There are many different human organ systems. Figure 16.4 shows six of them and gives their functions.

textbook_image

how human organ systems work together

The organ systems of the body work together to carry out life processes and maintain homeostasis. The body is in homeostasis when its internal environment is kept more-or-less constant. For example, levels of sugar, carbon dioxide, and water in the blood must be kept within narrow ranges. This requires continuous adjustments. For example: After you eat and digest a sugary snack, the level of sugar in your blood quickly rises. In response, the endocrine system secretes the hormone insulin. Insulin helps cells absorb sugar from the blood. This causes the level of sugar in the blood to fall back to its normal level. When you work out on a hot day, you lose a lot of water through your skin in sweat. The level of water in the blood may fall too low. In response, the excretory system excretes less water in urine. Instead, the water is returned to the blood to keep water levels from falling lower. What happens if homeostasis is not maintained? Cells may not get everything they need, or toxic wastes may build up in the body. If homeostasis is not restored, it may cause illness or even death.

instructional diagrams

No diagram descriptions associated with this lesson

questions

Functions of epithelial tissue include

a. secreting hormones.

b. absorbing substances.

c. protecting internal organs.

-->  d. all of the above

__type of tissue that includes bone and cartilage

a. nervous

b. muscle

c. cell

d. organ

e. epithelial

f. tissue

-->  g. connective

__structure composed of two or more types of tissues that work together to do the same task

a. nervous

b. muscle

c. cell

-->  d. organ

e. epithelial

f. tissue

g. connective

The brain and spinal cord consist mainly of

a. connective tissue.

b. muscle tissue.

-->  c. nervous tissue.

d. epithelial tissue.

Which human organ system carries wastes away from cells?

a. respiratory system

b. nervous system

c. digestive system

-->  d. circulatory system

__type of tissue that consists of cells that can contract

a. nervous

-->  b. muscle

c. cell

d. organ

e. epithelial

f. tissue

g. connective

__one of the basic building blocks of the human body

a. nervous

b. muscle

-->  c. cell

d. organ

e. epithelial

f. tissue

g. connective

The human organ system that controls virtually all body activities is the

a. skeletal system.

b. muscular system.

-->  c. nervous system.

d. none of the above

__type of tissue that can send and receive electrical messages

-->  a. nervous

b. muscle

c. cell

d. organ

e. epithelial

f. tissue

g. connective

The condition in which the bodys internal environment is kept stable is called

a. organization.

b. specialization.

-->  c. homeostasis.

d. maintenance.

__any group of specialized cells of the same type that perform the same function

a. nervous

b. muscle

c. cell

d. organ

e. epithelial

-->  f. tissue

g. connective

__type of tissue that covers inner and outer body surfaces

a. nervous

b. muscle

c. cell

d. organ

-->  e. epithelial

f. tissue

g. connective

The basic units of structure and function of the human body are organs.

a. true

-->  b. false

Most human cells are specialized for specific functions.

-->  a. true

b. false

A tissue consists of four basic types of cells.

a. true

-->  b. false

The heart is an organ in the circulatory system.

-->  a. true

b. false

The average human adult consists of about a billion cells.

a. true

-->  b. false

Each cell of the body carries out basic life processes.

-->  a. true

b. false

Most human cells have specialized functions.

-->  a. true

b. false

There are a total of five basic types of human tissues.

a. true

-->  b. false

The skin consists mainly of muscle tissue.

a. true

-->  b. false

Neurons are cells that can send and receive electrical messages.

-->  a. true

b. false

Smooth muscle tissue is found in the heart.

a. true

-->  b. false

Connective tissues are found in the walls of blood vessels.

-->  a. true

b. false

Which of the following is a human connective tissue?

a. skin

b. muscle

-->  c. blood

d. none of the above

The type of tissue that secretes hormones and absorbs nutrients is

a. muscle tissue.

b. nerve tissue.

-->  c. epithelial tissue.

d. connective tissue.

Types of muscle tissue include

a. skeletal muscle.

b. cardiac muscle.

c. smooth muscle.

-->  d. all of the above

Nervous tissue makes up most of the

a. lungs.

b. kidneys.

-->  c. brain.

d. stomach.

How does the hormone insulin help maintain homeostasis in the human body?

-->  a. It helps cells absorb sugar from the blood after you eat and digest food.

b. It stimulates the production of sweat on a hot day to cool the body.

c. It controls the contractions of cardiac muscles when you work out.

d. It keeps the level of carbon dioxide in the blood within a narrow range.

What is the basic function of the circulatory system?

-->  a. transporting substances

b. taking in oxygen

c. controlling sensations

d. allowing movement

Type(s) of tissue found in the human heart and blood vessels include

a. nervous tissue.

b. epithelial tissue.

c. connective tissue.

-->  d. all of the above

diagram questions

No diagram questions associated with this lesson