Muscle tissue and blood vessel walls.

Premed II HISTOLOGY OF MUSCLES AND BLOOD VESSELS WALLS.

Muscle tissue

-Muscle tissue is composed of differentiated cells containing

contractile proteins.

• Muscle Overview• The three types of muscle tissue are • skeletal,

cardiac, and smooth• These types differ in structure,

location, function,and means of activation

• Muscle Similarities• Skeletal and smooth muscle cells are

elongated and are called muscle fibers• Muscle contraction depends on two kinds of

myofilaments –• actin and myosin• Muscle terminology is similar• Sarcolemma – muscle plasma membrane• Sarcoplasm – cytoplasm of a muscle cell

SKELETAL MUSCLE LONGITUDINAL AND CROSS

• The oval nuclei are usually found at the periphery of the cell under cell membrane.

• This helps to distinguish skeletal muscle from cardiac and smooth muscle with a centrally placed nuclei.

• Cardiac Muscle Tissue• Occurs only in the heart• Is striated like skeletal muscle but is not

voluntary• Contracts at a fairly steady rate set by the

heart’s pacemaker• Neural controls allow the heart to

respond to changes in bodily needs

CARDIAC MUSCLE WITH INTERCALATED DISCS

• Cardiac muscle has cross striations composed of elongated,branched individual cells that lie parallel to each other.

• At sides of end to end contact are intercalated disks,structures found only in cardiac muscle.

• Smooth Muscle Tissue• Found in blood vessel walls, and the

walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages

• Forces food and other substances through internal body channels

• It is not striated and is involuntary

• Consists of collection of fusiform cells that do not show cross striations,contraction is slow and not subject to voluntary control.

• Sarcoplasm>>>> consists of the cytoplasm of the muscle cell excluding the myofibrils.

• The SER,is called the sarcolplasmic reticulum.• Sarcolemma.

SMOOTH MUSCLE LONGITUDINAL AND CROSS SECTIONS

• Muscle Function• Skeletal muscles are responsible for all locomotion• Cardiac muscle is responsible for coursing the

blood through the body• Smooth muscle helps maintain blood pressure

(blood vessel walls), and squeezes or propelssubstances (i.e., food, feces) through organs

• Muscles also maintain posture, stabilize joints, and generate heat

• Muscle cells are mesodermal in origin,and they are differentiated by a gradual process with simultaneous synthesis of myofibrils.

• Skeletal Muscle• Each muscle is a discrete organ composed of

muscle tissue, blood vessels, nerve fibers, andconnective tissue

• The three connective tissue sheaths are:• Endomysium – fine sheath of loose connective tissue

composed of reticular fibers surrounding each muscle fiber

• Perimysium – fibrous connective tissue thatsurrounds groups of muscle fibers called fascicles

• Epimysium – an overcoat of dense regularconnective tissue that surrounds the entire muscle

• The endomysium is composed mainly of BL and the reticular fibres.

• One important role of connective tissue is to mechanically transmit the forces generated by contracting muscle cells,because in most instances,individual cells do not extend from one end of a muscle to the other.

• Laminin is protein component of the endomysium.

Blood Vessel

Why circulatory system?

-cell function varies- hence difference in the requirement of nutrients, oxygen, ions, metabolites, signaling molecules

-Precisely -

- a “properly functioning” tubular system is essential for the delivery of goods at appropriate time/amount /site for a harmonious interaction between billions of cells – so a separate system- THE VASCULAR SYSTEM

--

Prelude

1. Is a closed system

2. Has a central pump (heart) and peripheral tubular system for transport of blood

3. Tubular system is

a). blood vessels – active system to deliver blood at different levels with different amount and pressure and re-circulate it against gravity to the central pump

b). lymph vessels- passive system ; just to carry excess extracellular fluid that could not normally go back to the blood vessel.

Basic histology:

1. Tubes of even lumen with a wall formed of three tunics

Tunica intima : endothelium (simple squamous epithelium), subendothelial tissue of loose tissue formed by fine collagen & elastic fibers and internal elastic lamina formed by elastic sheets with fenestrae in it

Tunica media: has concentric layers of helically arranged elastic, collagen and smooth muscle fibers. Components vary in different types of vessel depending on the function. elastic laminae are fenestrated;

Also has external elastic lamina – demarcation between tunica media and adventitia;

Tunica adventitia: a connective tissue layer; contains mainly collagen fibers coursing in longitudinal direction; also has elastic fibers.

Thickness varied in different vessels.

Basic histology:

Basic histology:

Blood supply to vessel:

1. Inner part of the vessel is nourished by diffusion from the lumen

2. Peripheral part by a small vessel – vasa vasorum –derived from the same artery or from neighboring arteries.

3.Vasa vasorum are more numerous in veins???

Nerve supply:

1. By sympathetic adrenergic fibers for vasoconstriction

2. By para –sympathetic cholinergic fibers for vasodilatation- “action is through release of nitrous oxide from the endothelium that causes relaxation of muscle”

nerves usually do not penetrate for into the muscle coat; hence releases neurotransmitter substance which cause ion permeability changes in the superficial muscles which is transmitted to deep muscles through gap junctions.

T.adventitia is thin ; has collagen , elastic; (predominantly collagen ) irregularly arranged

Vasa vasorum and vasa nervorum & lymphatics are present

Large artery

Elastic lamina

Medium sized artery - muscular artery

-1.Tunica intima: has all three components

- well defined internal elastic lamina

-few elastic, collagen and reticular fibers

- - the number of smooth muscle fibers diminishes as the artery becomes smaller

-external elastic lamina is seen in large muscular artery & absent in small muscular artery

3. Tunica adventitia: collagen, elastic and reticular fibers

(Vasa vasorum and vasa nervorum & lymphatics are present

2. Tunica media : is thick with circularly oriented smooth muscle fibers ( 40 layers)

Muscular artery – medium sized artery

Note the cross section of smooth muscle fibers

Capillary

Structure;

-single layer of endothelium resting on basal lamina

-surrounded by perivascular cells (pericytes)

Venous system

General information:

1. Are capacitance vessels – 70% of blood in normal conditions; low pressure collecting system

2. Change in relative volume of blood leads to resizing of the lumen by contraction of smooth muscle fibers

3. Wall is thinner relative to the size of the lumen

4. Three tunics – thinner than that in corresponding sized arteries

T. intima:

-endothelial lining

internal elastic lamina is absent

-thin subendothelial tissue

T. media:

-thinner than adventitia

- mainly cicularly arranged smooth muscle fibers, elastic fibers and reticular fibers

-external elastic lamina is absent

T. adventitia:

-

-thicker; mainly collagen

- larger vessels (below the level of the heart) have bundles of longitudinally oriented smooth muscle fibers- for peristaltic pumping of blood against gravity

-vasa vasorum, nerves and lymph vessels are present; numerous than in corresponding sized artery

-small and medium sized veins have valves to prevent back flow

Three types of vessels based on size

- Venules, small veins & large veins

:

Lymphatics - a picture

Neurovascular bundle – a common feature in many areas; medium sized vessels supplying a particular area is usually accompanied by nerve of that region; surround by a sheath of collagen tissue