Chp 4

From Cells to Organ Systems

Outline

4-1. Tissues

4-2. Epithelia

4-3. Connective tissues

4-4. Muscle tissue

4-5. Nervous tissue

4-6. Organs and organ systems

4-7. The skin

4-8. Homeostasis in multicellular organisms

4-1. Tissues

Multicellular organisms are made of group of specialized cells responsible for a defined function. These groups of cells are the tissues, themselves forming organs.

4-2. Epithelia

- Sheets of cells covering organs and cavities. Some are specialized in secreting substances (sweat gland, digestive gland, endocrine glands)

- They are made of 1 or more layer of cells. These cells are attached to the underlying connective tissue by a basement membrane. The cells are attached to each other by tight, adhesion or gap junctions.

- no blood vessels supply, only the tip of sensory neurons present in epithelial tissues.

4-3. Connective tissues

- most abundant and widely distributed

- binds, strengthens, protects, insulates

- fat is major site of stored energy reserves

A- Characteristics:

1- consists of 3 basic elements: cells, ground substance and fibers

matrix = fibers + ground substance

2- does not occur on free surface

3- has a nerve supply, except for cartilage

4- highly vascular, except cartilage and tendons and ligaments

5- matrix is secreted by cells from the connective tissue.

a- Cells:

a1- Fibroblasts: large, flat, spindle shaped, produce the matrix

a2- Macrophages: large, phagocytic cells, develop from blood monocytes

a3- Mast cells: produce histamine, responsible for allergic reactions

b- Fibers:

b1- Collagen: tough, resistant, occur in bundles, give to the tissues their

strength.

b2- Elastin: provide some strength but are able to recoil

b3- Reticulin (also reticular fibers): thin, more fragile than other, form

network in organs, common in lymphatic system.

c- Matrix:

Can be gelatinous, fluid or calcified. Its texture gives the tissues their hardness.

B- Types of tissues

b1- Loose connective tissue: fx: strength, elasticity, support, found in

subcutaneous layer of the skin.

b2- Adipose tissue: fx: store triglycerides, formed by adipocytes

b3- Fibrous connective tissue: rich in collagen fibers: tendons, ligaments

b4- Elastic connective tissue: rich in elastin, in vocal cord, arterial wall.

b5- Reticular connective tissue: rich in reticulin. in lympatic system.

b6- Cartilage: secreted by chondroblasts. the matrix is semirigid.

b7- Bone: matrix is calcified, secreted by osteocytes. unit = osteon.

b8- Blood: fluid matrix. consists of plasma and formed elements red, white blood cells and platelets

4-4. Muscle tissue

- consists of contracting fibers able to generate a force.

- 3 types:

Skeletal Cardiac Visceral

Location: Along bones heart viscera

Activity: Voluntary involuntary involuntary

Striation: Present present no striation

Nucleus at periphery center center

Appearance: long fiber long fiber spindled shape cell

Features: intercalated disc

4-5. Nervous tissue

Typical cell is neuron. Can generate and send an impulse. Neurons are supported by other cells, the neuroglial cells.

4-6. Organs and organ systems

- Organs are formed by more than one tissue. They have a specialized function. Several organs performing complementary functions are part of an organ system.s (look at them in the book and know which organs are within them).

The body is divided in 3 planes:

- Sagittal: right and left sides (median plane if in the middle)

- Frontal: anterior and posterior

- Transverse: superior and inferior

The body is divided into 2 major cavities, dorsal and ventral.

The ventral cavity is divided into 2 cavities, thoracic and abdominopelvic cavities which are separated by a muscle, the diaphragm. The space between the lungs is the mediastinum which contains the heart, great vessels, esophagus, trachea, bronchi and thymus.

Four types of membranes line the body and body cavities:

- Serous membranes: line and lubricate body cavities à decrease friction (pleura..)

- Mucous membranes: secretes mucus to lubricate tracts, such as airways, digestive tract..

- Synovial membranes: lubricate, line movables joints

- Cutaneous membranes: skin, protect body from dehydration, injury.

4-7. The skin

a- Role:

1- Protects against infection, mechanical shock, chemical injury

2- Prevents fluid loss

3- Sensor for touch, pain, temperature

4- Excretion of sweat

5- Immunity

6- Synthesis of vitamin D

b- Structure:

Formed by 3 major layers: the epidermis (an epithelium), the dermis (connective tissue + adipose tissue + other tissues (muscles, nerves..)) and subcutaneous layer or hypodermis (same as dermis but with more adipose tissue).

http://www.homestead.com/doctorderm/skinanatomy.html

http://www.safetyline.wa.gov.au/institute/level2/course16/lecture129/l129_02.asp

a- Epidermis:

The cells in the first layer are the keratinocytes, or cells synthesizing keratin. They divide rapidly and displace the more superficial layers. Cells in the upper layers are far from the nutrients supplied by the blood vessels and slowly die. The last layer is formed from keratin. Melanocytes are located toward the base. They secrete melanin, a pigment responsible for skin color and playing a role in protection against UV. As with all epithelia, the epidermis is attached by the basement membrane to the underlying connective tissue.

b- Dermis:

Formed by connective tissue. Contains most of the organs of the skin. Surface under the epidermis is uneven, forming the dermal papilla which are responsible for the fingerprints.

c- Organs of the skin:

Hairs: originate from keratocytes embedded into the dermis. Formed by a hair shaft, hair root. Several layers of cells at the base of the hair, the follicle, divide to form the hair root

Arrector pili: muscle attached to hair root, triggers raising of the hair and goose bumps (plays a role in protection against cold in furry animals, also helps frighten predators by making them appear larger).

Sensory nerve endings: - Touch:

- temperature

- Pain nerve endings

Sweat glands: secrete sweat which help with body temperature regulation

Sebaceous glands: secrete an oily secretion, sebum, which maintains moisture

and soupleness of the skin

4-8. Homeostasis in multicellular organisms

Homeostasis is the ability of an organism to maintain a constant internal environment. Ex: constant temperature, blood pressure, oxygen, calcium, potassium levels, pH in the blood…

Homeostatic regulation is possible because of :

1- a set of receptors which senses conditions outside the cell

2- a regulatory center which analyses incoming information, integrates them and send a response

3- effectors, organs or cells responding to the orders from the regulatory center.

http://lsvl.la.asu.edu/bio100/ghofmann/5apr.h3.jpg

The most important mechanism of homeostasis is negative feedback.

If a parameter increases too much above the normal range, the receptors send a message to the regulatory center which sends orders for effectors to cause a drop in the value.

Ex: Temperature

Normal body temperature is around 37^o C or 98.6^o F. Heat is a by-product of cellular (especially muscle) metabolism and the skin plays a key role in the homeostatic maintenance of body temperature. Excess heat can be lost by radiation, conduction, convection and evaporation. Too high or low body temperatures are sensed by thermoreceptors located in the hypothalamus. In response to too low temperature, blood vessels vasoconstrict, the respiratory and cardiac rates decrease, muscles shiver. In response to too high temperatures, blood vessels vasodilate, the respiratory and cardiac rates increase, sweat formation greatly increases