TISSUE

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Laurie Francis laurie @lauriefrancis.ca





TISSUE



The cells in our bodies make up tissues, groups of the same kind of cells with a

common structure and function. Tissues are often organized into organs and for this

example I’ve chosen the digestive system to illustrate.



In animals there are four main types of tissue:

1) Epithelial Tissue

This type of tissue is found covering the body, lining cavities and within hollow

organs and glands. It is made up of layers of cells and its function is to protect the

interior from outside influences such as chemicals, physical damage and

dehydration. Epithelial tissue is seen in either simple (only one cell layer thick) or

stratified (many cells in thickness) arrangements. Simple epithelial tissue is found

on absorptive or secretory surfaces and Stratified epithelial tissue is found

wherever underlying structures need protection from physical wear and tear.



2) Connective Tissue

This is the most abundant type of tissue in the body and comes in many different

forms and configurations throughout the body. The function of connective tissue is to

provide structural support, protection, transport and insulation. The two main types of

ordinary connective tissue are seen as Loose Areolar Connective Tissue and

Dense Connective Tissue. Loose connective tissue is found just about everywhere

in the body, as it provides support for structures passing through it, such as blood

and lymph vessels and nerves. It also serves to bind together other tissues,

including organs and their components. Dense connective tissue differs from loose

connective tissue in that there are more fibres, and fewer fibroblasts. These occur in

structures requiring high strength in one direction (i.e. tendons).



3) Muscle Tissue

Muscle has both the ability to contract and the ability to conduct electrical impulses.

Muscles are classified functionally as either voluntary (because it requires

conscious thought ie. bicep) or involuntary (because it contracts and relaxes without

conscious thought ie. intestines) and structurally as either striated or smooth.

Smooth muscle tissue is found in the walls of the digestive tract, uterus, bladder,

blood vessels and other internal organs and they contract as a single unit. Striated

muscle tissue is seen are a result of the orderly arrangement of filaments within the

muscle cell. Skeletal muscle cells are arranged into bundles surrounded by thin

layers of connective tissue. The connective tissue surrounding these bundles

extends as dense connective tissue to anchor the muscle to the bone in the form of a

tendon. There is a third type of unique muscle tissue called Cardiac Muscle Tissue

found only in the heart and appears as a sheet of muscle rather than as fibres. It

shows some features of skeletal muscle and some features of smooth muscle. The

cardiac muscle cells are stacked end to end which gives it the ability to conduct

electrical impulses causing wave contractions.









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P.O. 1368, Bradford, ON L3Z 2B7

Tel: 905-778-8787

Laurie Francis signlady@sympatico.ca

4) Nervous Tissue

Nervous tissue is what forms the communicative pathways and is composed of two

types of tissue: excitable cells that initiate, conduct, transmit and receive information

and non-excitable cells that support the excitable cells (called neurons)









Photo courtesy of http://health.allrefer.com/pictures-images/tissue-types.html









ORGANS

Groups of different types of tissues are arranged together to form organs. Each organ

works together with other organs to keep the body in homeostasis. For example one

organ of the digestive system is the stomach which is made up of four layers of tissue:

three layers of muscle tissue and mucosa.



SYSTEMS

The organs that make up the systems of the body are found within four main cavities:

cranial, thoracic, abdominal and pelvic.



Cranial Cavity

Located in the cranial cavity is the brain, the organ of thought. It is made up of nerve

tissue and is protected by the skull. It communicates to the rest of the body through the

spinal cord. The brain controls a wide variety of functions. It is the site of reason and

intelligence, controls posture and movement and performs a variety of automatic

functions (heart rate, body temperature, digestive processes). In addition to neurons,

the brain contains glial cells which form a support system for neurons. The brain is

surrounded by connective tissues called the Meninges that separate the skull from the

brain. The brain receives signals through nerves from the sensors of the body.









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P.O. 1368, Bradford, ON L3Z 2B7

Tel: 905-778-8787

Laurie Francis signlady@sympatico.ca

Thoracic Cavity

The thoracic cavity is located in the upper trunk of the body and contains the lungs and

heart along with many other structures such as the trachea, bronchi, lymph nodes and

vessels and nerves and blood vessels. The lungs are the respiration organs that allow

air breathers to exchange gases necessary to the rest of the body. Oxygen is taken in

from the air we breathe and passed on to the blood. The heart pumps the blood

throughout the body which carries the gas to the cells. The cells can then exchange

their waste product (CO2) to the blood for transport back to the lungs where the lungs

exhale the carbon dioxide.



Abdominal Cavity

This is the largest cavity of the body and is located in the main part of the trunk. It

contains the majority of the organs of digestion: stomach, small intestine, most of the

large intestine, liver, gall bladder, and pancreas. It also contains the spleen,

kidneys and other structures such as the adrenal glands, blood vessels, lymph nodes

and vessels, and the nerves. The stomach is located on the left side of the body just

above the diaphragm. The stomach’s function is to break down large food molecules into

smaller ones using hydrochloric acid which is produced in the stomach. Once the

contents are liquefied they are released to the small intestine. The small intestine

needs to have its contents in the liquid form in order for nutrient absorption to occur. It

is a 6 metre long tube where the most extensive part of digestion occurs. Most food

products are absorbed in the small intestine. It also secretes a hormone that stimulates

the pancreas to produce digestive enzymes. Sitting underneath the stomach and

attached to the small intestine is the pancreas. This is a glandular organ that secretes

digestive enzymes and hormones and produces the body's most important enzymes

designed to digest foods and break down starches.



The liver is the largest glandular organ of the body and it lies on the right side of the

abdomen beneath the diaphragm. Blood is carried to the liver via two large vessels; the

hepatic artery and the portal vein. The hepatic artery carries oxygen-rich blood from the

aorta and the portal vein carries blood containing digested food from the small intestine.

The liver breaks down fats, converts glucose to glycogen, produces urea (the main

substance of urine), makes certain amino acids (the building blocks of proteins), filters

harmful substances from the blood (such as alcohol), stores vitamins and minerals and

maintains a proper level of glucose in the blood. It also produces about 80% of the

cholesterol in the body. The gallbladder is a small pear-shaped organ that stores and

concentrates bile. It is connected to the liver (which produces the bile) by the hepatic

duct. Bile is a digestive liquid continually secreted by the liver that emulsifies fats and

neutralizes acids in partly digested food.



The spleen creates lymphocytes for the destruction and recycling of old red-blood cells.

The most important functions of the spleen are mechanical filtration, which

removes senescent red blood cells and control of infection. It is also a blood

reservoir to supply the body with blood in emergencies such as a bad cut. The spleen is

also the location where white blood cells trap organisms.



The large intestine is responsible for absorption of water to be recycled again

throughout the body and excretion of solid waste material. Waste material is moved

along the length of the intestine by rhythmic contractions of intestinal muscles

(peristalsis). Impaired peristaltic action can contribute many conditions such as Irritable

Bowel Syndrome, Crohn’s disease, colitis, etc. The kidneys are a pair of organs





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P.O. 1368, Bradford, ON L3Z 2B7

Tel: 905-778-8787

Laurie Francis signlady@sympatico.ca

located in the abdominal cavity. They have a couple of different functions. Their main

purpose is to separate urea, mineral salts, toxins, and other waste products from the

blood. They also conserve water, salts, and electrolytes.



Pelvic Cavity

The pelvic cavity is located in the lower part of the trunk and contains the rest of the

large intestine, rectum, some of the small intestine, bladder and internal

reproductive organs. The rectum is the final straight portion of the large intestine and

acts as a temporary storage facility for feces. The bladder collects urine from the

kidneys and stores it until it is full enough to empty through the urethra. The

reproductive organs in the female are the uterus, uterine tubes, ovaries and vagina. In

the male the organs are the prostrate gland, seminal vesicles, spermatic cords, deferent

ducts, ejaculatory ducts and urethra.









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P.O. 1368, Bradford, ON L3Z 2B7

Tel: 905-778-8787

Laurie Francis signlady@sympatico.ca





The Digestive System









Mouth - the first part of the digestive system. The teeth, tongue

salivary glands, are all involved in the digestive system.



Esophagus - uses peristalsis to force food from the throat into the

stomach



Liver - filters toxins from blood, makes bile & blood proteins

Stomach – food is churned in acid bath and broken down

Gall bladder – stores and releases bile into small intestine

Pancreas - an enzyme-producing gland

Duodenum – first part of small intestine Transverse colon – horizontal portion of large intestine

Ascending colon – part of large intestine that runs upwards

Ileum - last part of the small intestine. Descending colon – part of large intestine that runs downwards

Cecum – first part of large intestine Jejunum – long coiled mid-section of small intestine

Appendix – attached to cecum (function is controversial) Sigmoid colon – part of large intestine just before rectum.



Anus – opening at end of digestive system where feces is voided. Rectum – last part of large intestine that stores feces for

evacuation.









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