Ch 14: Blood vessels

Skeletal muscle fibers vary in their content of myoglobin (an O2 binding protein). Red muscle fibers vs. White muscle fibers

Red muscle fibres -> high myoglobin content White muscle fibres -> low myoglobin content

The _ band contains thin filaments but no thick filaments.

I

Plasma membrane of a muscle fibre

sarcolemma

Elastic arteries

- Largest arteries in the body - The largest diameter among arteries - Elastic lamellae - Includes aorta and pulmonary trunk (plus subclavian, brachiocephalic, and common carotid arteries) - Pressure reservoir (blood is ejected from the heart into the arteries, the walls stretch/momentarily store mechanical energy, then eject the blood as kinetic energy)

Electrical excitability

- Muscle tissue responds to stimuli by producing electrical signals called action potentials (impulses) - muscle action potentials stimulated by electrical and chemical stimuli

Anastomoses

- Union of the branches of two or more arteries supplying the same body region - Most tissues of the body receive blood from more than one artery. - Alternate routes for blood to reach tissue or organ (collateral circulation) - end arteries = arteries that don't anastomose (alternate blood routes may also be provided by non-anastomosing vessels that supply the same region of the body)

Venules

- Venules drain the capillary blood and begin flow of blood back to the heart - Postcapillary venules (initially receive blood from capillaries) - Muscular venules (as venules move away from capillaries they increase in size and acquire 1 or 2 layers of smooth muscle; can no longer exchange with interstitial fluid but hold blood ->good reservoir)

Slow oxidative fibres aka type 1 fibres

- appear dark red (lots of myoglobin) - generate ATP by aerobic cellular respiration - use ATP at a slow rate; slow contraction speed - maintain posture; aerobic, endurance-type activities

Fenestrated capillary

- contains fenestrations (small pores/holes) - found in kidneys, villi or SI, endocrine glands etc.

Veins: VALVES

- folds of tunica interna that form flaplike cusps - project into the lumen toward the heart - prevent backflow

Cardiac muscle tissue

- found only in the heart (forms most of the heart wall) - striated - involuntary action

Fast oxidative glycolytic fibres aka type IIa fibres

- largest - lots of myoglobin - dark red - generate ATP by aerobic cellular respiration and anaerobic cellular respiration - use ATP at a fast rate; fast contraction speed - walking, sprinting

Fast glycolytic fibres aka type IIb fibres

- low myoglobin content - white - generate ATP mainly by anaerobic cellular respiration - use ATP at fast rate; contract quickly - weight lifting, throwing a ball (intense, short movements)

Continuous capillary

- most common type (CNS, lungs, skin, smooth muscle/connective tissue) - intercellular clefts (gaps between neighbouring endothelial cells)

Skeletal muscle tissue

- move bones of the skeleton - striated - primarily voluntarily controlled

Sliding filament mechanism

- myosin heads attach to thin filaments on both ends of a sarcomere and pull them towards the M line - thin filaments slide inward and meet at centre of sarcomere - Z discs come closer together and sarcomere shortens - lengths of thin/thick filaments don't change but the whole muscle fibre/muscle shortens

Arterioles

- regulate flow of blood into capillary networks of tissues - 400 million with diameter ranging from 15 um to 30 um - The tunica media consists of one to two layers of smooth muscle cells having a circular (rather than longitudinal) orientation in the vessel wall. - Metarteriole (terminal end of arteriole) tapers toward the capillary junction (metarteriole-capillary junction); most distal muscle cell forms precapillary sphincter which monitors blood flow into capillary - the rest are resistance vessels (regulate resistance)

Tunica media

- smooth muscle/connective tissue - regulates diameter of lumen wall - limits loss of blood in damaged vessels 1. External elastic lamina - separates from tunica externa

Veins: VASCULAR (VENOUS) SINOUS

- vein with thin endothelial wall with no smooth muscle to alter diameter - dense connective tissue instead

Smooth muscle tissue

- walls of hollow internal structures (ie. blood vessels, airways, hair follicles in skin) - nonstriated - involuntary (some have autorhythmicity)

Sinusoid (capillary)

- wider - large fenestrations - incomplete/absent basement membrane - large intercellular clefts (allow proteins/blood to pass from tissue into bloodstream) - specialized lining cells adapted to function of the tissue

Four steps of the contraction cycle

1. ATP HYDROLYSIS: Myosin heads break down ATP and become reoriented and energized 2. Myosin head attaches to myosin-binding site on actin and releases phosphate group (cross-bridges) 3. POWER STROKE: Myosin cross-bridges release ADP, rotate toward centre of the sarcomere (slides thin filament past thick filament toward M line) 4. As myosin heads bind ATP the myosin head detaches from actin

Myofibrils are built from what 3 proteins?

1. Contractile proteins - generate force during contraction - actin and myosin (which makes muscle fibres red) 2. Regulatory proteins - help switch contraction process on/off - tropomyosin and troponin 3. Structural proteins - contribute to alignment, stability, elasticity, and extensibility of myofibrils - pg 292 for summary

3 components of the tunica interna

1. Endothelium 2. Basement membrane - deep to endothelium; provides physical support 3. Internal elastic lamina - openings facilitate diffusion through tunica interna to tunica media

Four key functions of muscular tissue

1. Producing body movements 2. Stabilizing body positions 3. Storing and moving substances within the body - ie. sphincters (storage of urine/poop) 4. Producing heat - thermogenesis: as muscular tissue contracts it also produces heat (ie. shivering = increase in body temp)

Between the ages of 30 and 50, an estimated __% of muscle mass is lost. Another __% is lost by age 80. Relative number of SO fibres increases.

10% 40%

Muscular tissue accounts for __ to __% of total body mass.

40 to 50

The _ band extends the entire length of the thick filaments. Towards each end of the A band is a zone of overlap.

A

Structure of a skeletal muscle

A skeletal muscle bundle consists of a body (belly) connected by tendons to the skeleton. • Tendons (minimally vascular; regular connective tissue and collagen fibres) • Aponeuroses (tendons arranged in flat sheet)

Extensibility

Ability of muscle to stretch without being damaged. - connective tissue limits extensibility; smooth muscle subject to greatest amount of stretching

Contractility

Ability of muscular tissue to contract forcefully when stimulated by an action potential (ie. when skeletal muscle contracts it generates tension and pulls on attachment points)

Elasticity

Ability of muscular tissue to return to its original length and shape after contraction/extension

Large, elastic arteries leave the heart and divide into medium-sized, muscular arteries that branch out into the body and divide into small arteries, which divide into still smaller arteries called __________.

Arterioles

Tunica externa

Contains vasa vasorum which supply blood to tissues of the vessel wall

The _ zone in the centre of each A band contains thick filaments only. Supporting proteins that hold the thick filaments together at the centre of this zone form the _ line.

H zone M line

Each skeletal muscle fiber arises from the fusion of a hundred or more small mesodermal cells called _________.

Myoblasts

Thoracic aorta scheme of distribution

Thoracic: 1. Visceral branches (pericardial, bronchial, esophageal, mediastinal) 2. Parietal branches (posterior intercostal, subcostal, superior phrenic)

_________ tubules are filled with interstitial fluid and allow action potential to go through them and spread throughout the muscle fibre.

Transverse

Anastomotic veins

Veins paired with mid-to small-sized arteries connect with one another through channels called anastomotic veins (most in the free limbs)

What is the role of skeletal muscle contractions and venous valves in returning blood to the heart?

When skeletal muscles contract the proximal valve opens and blood is forced towards the heart

As arterioles enter a tissue they branch into numerous tiny vessels called __________ which allow exchange of substances between blood and body tissues.

capillaries

Veins that travel below the fascia between the skeletal muscles and form connections (anastomoses) with superficial veins

deep veins

The dramatic muscle growth that occurs after birth occurs by enlargement of existing muscle fibres called __________. They fuse lengthwise to form _________ cells which retain the capacity to fuse with each other or damaged muscle fibres to regenerate functional muscle fibres.

hypertrophy satellite cells

In some parts of the body, blood passes from one capillary network to another through the ______ vessel.

portal vessel (such circulation of blood is called portal system)

Veins that course through the subcutaneous layer deep to the skin unaccompanied by parallel arteries

superficial veins

Isometric contraction

tension generated is not enough to exceed the resistance of the object to be moved and the muscle does not change its length - ie. holding book in outstretched hand - important for posture

Groups of capillaries within a tissue reunite to form small veins called ________ which merge to form veins.

venules

Medium-sized arteries

• Capable of greater vasoconstriction and vasodilation (adjust blood flow) • Have a well-defined internal elastic lamina • Called distributing arteries (bc they branch/deliver blood to each of the organs) • Vascular tone (ability of muscle to contract and maintain partial contraction)

Circulatory routes

• Circulatory routes for blood flow are parallel. • Each organ receives its own supply of freshly oxygenated blood. • There are two basic routes for blood flow: • Systemic circulation • Pulmonary circulation

Isotonic contraction

Tension in muscle remains almost constant while muscle changes length 1. Concentric isotonic contraction - if the tension generated is great enough to overcome resistance of the object being moved, the muscle shortens and pulls on its tendon to produce movement/reduce angle at a joint (ie. picking up book from a table) 2. Eccentric isotonic contraction - length of a muscle increases during contraction - ie. putting down a book