LECTURE 3: HISTOLOGY: The study of tissuesdrmagrann.com/Anatomy/3 Tissues NU lecture.docx · Web viewHISTOLOGY: The study of tissues Cells Tissues Organs Organ systems Organism Cells

HISTOLOGY: The study of tissues

Cellsà Tissuesà Organsà Organ systemsà Organism

Cells are not found by themselves; they’re with others. These are called tissues.TISSUE: A group of cells, usually similar, which share a particular function.ORGAN A group of tissues which share a particular function.ORGAN SYSTEM: A group of organs which share a particular function (digestive system, nervous system).

Cell Differentiation Through the process of cell differentiation, each cell develops a characteristic set

of structural features. Each cell has to contribute one piece toward the overall function of the organism,

so that all the vital functions can be covered. During differentiation, cells in nearby locations become able to work together. After differentiation, cells do not change their function throughout their life cycle

Specialized Structures on EpitheliumMicrovilli

The presence of large numbers of microvilli on the exposed surfaces of epithelial cells indicates that this is the area where absorption and secretion take place.

These cells are transportation specialists. They are probably located along portions of the digestive and urinary tracts

CiliaHair-like structures that wave back and forth to move substances along the top of the cell They are smaller than microvilli.

TYPES OF TISSUES EPITHELIUM: a sheet of cells that makes up the surface of the skin and also

lines tubes in the body. CONNECTIVE TISSUE: deep to the epithelium; supplies oxygen and nutrients

to epithelium. Fibrous (Proper) Connective Tissue Special Connective Tissue (cartilage, bone, blood, muscles, nerves)

SIMPLE EPITHELIUM has only one cell layer. SIMPLE SQUAMOUS EPITHELIUM: SIMPLE CUBOIDAL EPITHELIUM SIMPLE COLUMNAR EPITHELIUM PSEUDOSTRATIFIED EPITHELIUM

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STRATIFIED EPITHELIUM has more than one cell layer. The type of epithelium is named by the APICAL layer. STRATIFIED SQUAMOUS EPITHELIUM:

1) Keratinized stratified squamous epithelium 2) Non-keratinized stratified squamous epithelium  

STRATIFIED CUBOIDAL EPITHELIUM STRATIFIED COLUMNAR EPITHELIUM TRANSITIONAL EPITHELIUM

FIBROUS (PROPER) Connective tissues ADIPOSE (fat) RETICULAR (lymph nodes) LOOSE (aka AREOLAR; upper dermis) DENSE

REGULAR (tendons and ligaments) IRREGULAR (lower dermis and joint capsules)

Special Connective Tissue Cartilages

Hyaline cartilage (most joints) Elastic cartilage (ear) Fibrocartilage (intervertebral discs)

Bone tissues Compact bone (shaft of long bones) Spongy bone (ends of long bones)

Blood Muscles (discussed more in later lectures) Nerves (discussed more in later lectures)

Disorders of Adipose Lipoma (benign tumor) Liposarcoma (malignant tumor)

COLLAGEN This is a type of fiber that is found in all connective tissues (other than blood). It gives connective tissues an elastic consistency. It has very little blood supply, so it does not regenerate well. It does not interfere with diffusion of materials from one area to another; it just

provides support for connective tissues.

NOTE: If you get injured, you’d rather break a bone than tear a ligament, why? The number of fibroblasts is the same, but the ligament has a lot more collagen to

be made by each fibroblast. And the blood supply to bone is much better than a ligament.

Collagen Disorder: Scleroderma: Collagen becomes hard

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Another Tissue Disorder: Granuloma A granuloma is an inflammation found in many diseases. It is a collection of

immune cells known as macrophages. Granulomas form when the immune system attempts to wall off substances that it

perceives as foreign but is unable to eliminate. Such substances include infectious organisms such as bacteria and fungi as well

as other materials such as keratin and suture fragments.

Types of Membranes Synovial Membranes: This membrane lines the inside of fluid-filled joints. The

cellular layers are incomplete, with gaps between adjacent cells to allow the fluid to escape into the joint to serve as a cushion.

Mucous Membranes: Mucous membranes are covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs. They are located at the nostrils, the mouth, the lips, the eyelids, the ears, the genital area, and the anus.

Serous Membranes: secrete a watery fluid. The fluid reduces friction from muscles or organs rubbing against each other. Its major function is to produce tiny amounts of transudate on their opposing surfaces to reduce friction. The serous membrane covering the heart is the pericardium. Inflammation here is called pericarditis. The serous membrane surrounding the lungs is the pleura. Inflammation here is called pleuritis. The serous membrane lining the abdominal cavity is the peritoneum. Inflammation here is called peritonitis.

Another way to classify epithelium is by whether it is moist or dry.

1. MOIST EPITHELIUM: there are two types:a. MUCOSA is the cell type that produces mucous. Therefore, pseudo-stratified

epithelium is a mucous epithelium, or a mucosa.b. SEROSA is an epithelium that has watery secretions on the surface. This is

found in sweat glands.

2. DRY EPITHELIUM is keratinized stratified squamous epithelium.

TYPES OF GLANDS• Exocrine Gland

• Secretes substances into a duct and then excretes it onto the skin (e.g. sweat, oil)

• Endocrine Gland• Secretes substances into the blood to be transported to another part of

the body, where it is used (e.g. hormones). We will discuss endocrine glands in a separate lecture.

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EXOCRINE GLANDSThese are glands that produce a secretion which empties into a duct (tube). There are many different types and many ways to classify exocrine glands.

1. Classified based on the type of secretiona. SEROUS GLANDS secrete sweat.b. MUCOUS GLANDS secrete mucous, as found in goblet cellsc. MIXED GLANDS secrete mucous and sweat, as found in salivary glands.d. OIL GLANDS secrete waxy and oily substances, as found in sebaceous glands.

2. Classified by the method of secretiona. MEROCRINE (Eccrine) GLANDS produce a secretion by a process called

EXOCYTOSIS. The secretion vesicle moves to the plasma membrane, where it fuses and the material is released outside the cell. This is the process of most sweat glands and mucous glands.

b. APOCRINE GLANDS accumulate material in the apical section, the top of the cell breaks off, and the material is released. The cells that broke down will grow again. An example is the mammary gland. Apocrine glands are also considered to be a type of sweat gland.

c. HOLOCRINE GLANDS are those where the entire cell breaks off with all the contents inside, such as sebaceous glands. After the cell breaks off, the other cells move in quickly and close up the gap.

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Functions of Merocrine glands Thermoregulation Inhibiting the growth of

bacteria on the skin Excretion of water,

electrolytes, and some drugs They do not function as a

lubricant for the skin.

3. Classified by their structure (what they look like)a. UNICELLULAR GLANDS, for example a goblet cell

Goblet cells are found in the trachea and secrete mucous to trap debris; then you cough it up.

b. MULTICELLULAR GLANDS Alveolar

Simple alveolarCompound alveolar (mammary glands)

Tubular Simple tubular (sweat glands) Compound tubular

ALVEOLAR TUBULAR

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Goblet cell