Tissues and organs

Epithelial tissue is necessary for protection, diffusion, filtration, secretion, absorption and others. Simple epithelium with its single layer of cells is found in organs in which the principal functions are diffusion (lungs), filtration (kidneys), secretion (glands), or absorption (intestines). The selective movement of materials through epithelium would be hindered by a stratified epithelium, which is found in areas where protection is a major function. The multiple layers of cells in stratified epithelium are well adapted for a protective role. Damaged cells are replaced by cells from deeper layers and a continuous barrier of epithelial cells is maintained in the tissue. Stratified squamous epithelium is found in areas of the body where abrasion can occur such as the skin, mouth, throat, esophagus, and anus. Cells involved in diffusion and filtration are normally flat and thin. For example, simple squamous epithelium forms blood and lymph capillaries, the alveoli of the lungs, and parts of the kidney tubules.

Connective tissue is found in tendons, ligaments, cartilages, bones, dermis of skin, arteries, spleen and others. This tissue produces new blood cells, allows growth of long bones, connects different structures, provides great strength and support for bones, transports oxygen, carbon dioxide, hormones, nutrients, waste products and has some other functions.

Muscular tissue has the ability to contract. Muscles contract to move the entire body, to pump blood through the heart and blood vessels, and to decrease the size of hollow organs such as the stomach. Skeletal muscles represent a large portion of the human body's total weight. Skeletal muscle attaches to the skeleton and by contracting causes the major body movements. Cardiac muscle is the muscle of the heart. The contraction of the cardiac muscle is responsible for pumping blood. Smooth muscles are widespread throughout the body and are responsible for a wide range of functions such as movements in the digestive, urinary, and reproductive systems.

Nervous tissue conducts impulses all over the body. Nerve cells, or neurons, located in the brain, spinal cord, and cell processes, conduct not only impulses and store "information", and in some ways integrate and evaluate data. Neuroglia support neurons and form a selectively permeable barrier between neurons and other cell types.

Ex. 24. Answer the following questions:

1. What is the function of epithelial tissue? 2. Where is connective tissue located? 3. What is the function of connective tissue? 4. What is cardiac muscle? 5. Where are nervous cells located? 6. What is the function of nervous tissue?

Ex. 25. Read the data of the following table and speak on the location and functions of different tissues:

Functions and Location of Tissues.

Tissue	Location
Epithelial tissue
Simple squmous epithelium	Blood and lymph capillaries, alveoli of lungs, the inner part of the eardrum, smallest ducts of glands
Simple cuboidal epithelium	Part of kidney tubule, many glands, pancreatic duct, inside lining of eye, ducts of glands
Simple columnar epithelium	Stomach, small intestine, large intestine, uterus, bronchioles of lungs, auditory tubes, bile duct, gallbladder, ducts of glands
Stratified squmous epithelium	Skin, mouth and throat, epiglottis, larynx, esophagus, anus, vagina
Stratified cuboidal epithelium	Sweat gland ducts
Stratified columnar epithelium	Mammary gland ducts
Pseudostratified columnar epithelium	Larynx, nasal cavity, paranasal sinus, nasopharynx, trachea, salivary gland ducts
Transitional epithelium	Urinary bladder
Connective tissue
Loose (alveolar) connective tissue	Muscles, nerves
Dense regular connective tissue	Tendons, ligaments between the vertebrae
Dense irregular connective tissue	Dermis of the skin, elastic arteries
Adipose tissue	Subcutaneous areas, renal pelvis, around kidneys
Bone marrow	Within marrow cavities of bone; yellow marrow in the shafts of long bones and red marrow in the ends of long bones and in short, flat, and irregularly shaped bones.
Muscular tissue
Skeletal muscle	Attached to bones
Cardiac muscle	Heart
Smooth muscle	Walls of hollow organs, blood vessels, eyes, glands, skin
Nervous tissue Neuron Neuroglia	In the brain, spinal cord. Cell processes are located in all parts of the body. In the brain, spinal cord, ganglia, nerves

OVERVIEW

Cells are grouped into tissues. The four basic tissue types are epithelial, connective, muscular, and nervous tissue. Epithelium consists of cells that have very little extracellular material between them. Epithelium covers surfaces, e.g., the outside of the body and the lining of the digestive tract, the vessels and many body cavities. Connective tissue consists of cells separated from each other by nonliving extracellular matrix. Connective tissue is classified according to the type of protein and proportions of protein and fluid in the matrix. Connective tissue is subdivided into adipose tissue, fibrous connective tissue, bone, and blood. Connective tissue forms the dermis of the skin, inner portion of the skin, bones, tendons, ligaments, the walls of large arteries, bone marrow, liver and others. Muscular tissue has the ability to contract. The three types of muscular tissue – skeletal, cardiac, and smooth muscle – are classified according to both structure and function. Nervous tissue is characterized by the ability to conduct electrical signals. It consists of neurons, or nerve cells, which are responsible for conductive ability, and support cells (neuroglia).

LESSON 20

(additional)

SYSTEMS OF THE HUMAN BODY