A & P Exam 4

Autonomic Nervous System (involuntary nervous system)

motor neurons that innervate smooth muscle, cardiac muscle, and glands subconsciously making adjustments to ensure optimal support for body activities

Examples of ANS adjustments

shunts blood to areas that need it and adjusts heart rate, blood pressure, digestive processes, etc.

Two arms of ANS

Parasympathetic and Sympathetic divisions

Parasympathetic “Rest-and-Digest”

promotes maintenance functions, conserves energy, ex. blood pressure, heart rate, and respiratory rates are low and GI tract is high

Sympathetic “Fight or Flight”

mobilizes body during activity; During physical activity: shunts blood to skeletal muscles and heart, dilates bronchioles, causes liver to release glucose

* More complex and innervates more organs than parasympathetic

Some structures are innervated only by the sympathetic:

adrenal medulla, sweat glands, kidneys, and almost all blood vessels

Dual innervation

divisions cause opposite effects; Dynamic antagonism maintains homeostasis

Sites of origin

Parasympathetic fibers originate from brain stem and sympathetic fibers originate in spinal cord

Relative lengths of Fibers

Parasympathetic: long preganglionic & Sympathetic: short preganglionic

Location of Ganglia

Parasympathetic → in or near effector organ & Sympathetic → near spinal cord

Vagus Nerves

90% parasympathetic fibers in body and in ganglia in walls of target organs

Cardiac plexus

slow heart rate

Pulmonary plexus

serves lungs and bronchi

Esophageal plexus

form anterior and posterior vagal trunks that sends branches to stomach, liver, gallbladder, pancreas, small intestine, and part of the large intestine

Sympathetic division unique roles

thermoregulatory responses to heat (skin blood vessels dilate), release of renin from kidneys (increases blood pressure), metabolic effects

Parasympathetic & Sympathetic Interactions

dual innervation; both ANS divisions are partially active, resulting in a basal sympathetic and parasympathetic tone

Sympathetic tone - constriction of blood vessels

If blood pressure drops → sympathetic __fibers fire faster__ and increase __constriction__ of blood vessels

If blood pressure rises → __fibers fire__ causing less constriction (__dilation__) blood vessels

Parasympathetic division dominates…

heart (slows), (activates) smooth muscle of the digestive and urinary tract & activates most glands (except adrenal and sweat)

Sympathetic division can override the effects of parasympathetic…

during times of stress

Parasympathetic & Sympathetic - localized vs. diffuse effects

Parasympathetic → short-lived and highly localized (ACh is quickly destroyed

Sympathetic → longer-lasting and has body-wide prolonged effects even after signal stops (NE inactivates slower than ACh)

Hypothalamus is…

main integrative center of ANS activity

Chambers: Atria - The receiving chambers

Small, thin-walled chambers; contribute little to propulsion of blood

Right atrium

receives deoxygenated blood from body

Left atrium

receives oxygenated blood from lungs

Super vena cava

returns blood from body regions above the diaphragm

Inferior vena cava

returns blood from body regions below the diaphragm

Coronary sinus

returns blood from coronary veins

Chambers: Ventricles - The Discharging Chambers

Actual pumps of the heart

Right venticle

pumps deoxygenated blood into the pulmonary trunk

Left ventricle

pumps oxygenated blood into aorta

Papillary muscles

project into ventricular cavity

* anchor and attach to heart valves

Heart valves

ensure uni-directional blood flow through heart & open and close in response to pressure changes

* No valves are found between major veins and atria

Tricuspid Valve

3 cusps and lies between right atria and ventricle

Mitral Valve

2 cusps and lies between left atria and ventricle

Chordae tendineae

anchor cusps of the atrioventricular valves (mitral and tricuspid) to papillary muscles; holds flaps closed

Semilunar valve

Pulmonary and aortic; each valve consists of 3 cusps that roughly resemble a half moon

Pulmonary Semilunar Valve

located between right ventricle and pulmonary trunk

Aortic Semilunar Valve

located between left ventricle and aorta

Pathway of Blood Flow

equal volumes of blood are pumped to pulmonary and systematic circuits

Pulmonary circuit

short, low-pressure circulation

Systematic circuit

long, high-pressure circulation

Anatomy differences in ventricles

left ventricle walls are 3x thicker than right and pumps with greater pressure

Coronary Circulation

supplies blood to the myocardium and flow occurs during diastole

Cardiac muscles

branched, fat and interconnected; contains large mitochondria to resist fatigue

Intercalated Discs

connective tissue matrix (endomysium) contains numerous capilaries

Desmosomes

hold cells together & prevent cells from separating during contraction

Gap Junctions

allow ions to pass from cell to cell & electrically couple adjacent cells and allows the hear to be a single coordinated unit

Pacemaker cells

set the basic rhythm; sequence of excitation: sinoatrial (SA) node (pacemaker) → atrioventricular (AV) node → AV bundle → interventricular septum → subendocardial conducting network

Extrinsic Conduction System

heartbeat modified by ANS via cardiac centers in medulla oblongata

Cardio-acceleratory center

sends signals through sympathetic trunk to increase both rate and force

* stimulates SA and AV nodes, heart muscle, and coronary arteries

Cardio-inhibitory center

Parasympathetic signals via vagus nerve to decrease rate

* inhibits SA and AV nodes

Cardiac muscle fibers - Action potential

Contractile muscle cells make up bulk of heart and responsible for pumping action; cardiac muscles AP’s have plateau

Cardiac vs skeletal muscle fiber contractions:

Skeletal muscle AP lasts 1-2 ms while cardiac muscle AP lasts 200 ms

Benefit of longer AP and contraction:

Sustained contraction ensures efficient ejection of blood and longer refractory period prevents tetanic contractions

Electrocardiograph

detects electrical currents generated by heart

Electrocardiogram (ECG or EKG)

graphic recording of electrical activity

* Composite of all action potentials at given time
* 12 lead ECG is most typical

P wave

depolarization of SA node and atria node

QRS complex

ventricular depolarization and atrial repolarization

T wave

ventricular repolarization

P-R interval

beginning of atrial excitation to beginning of ventricular excitation

S-T segment

entire ventricular myocardium depolarized

Q-T interval

beginning of ventricular depolarization through ventricular repolarization

Systole

period of heart contraction

Distiole

Period of heart relaxation

Cardiac cycle

blood flows through heart during one complete heartbeat; cycle represents series of pressure and blood volume changes

Cardia Output (CO)

CO = heart rate (HR) x stroke volume (SV)

* flow for entire vascular system

Stroke volume

volume of blood pumped out by one ventricle with each beat & correlates with force of contraction

cardiac reserve

difference between resting and maximal CO

Stroke Volume

SV = EDV - ESV

EDV

is affected by length of ventricular diastole and venous pressure (\~120ml/beat)

ESV

is affected by arterial BP and force of ventricular contraction

Three main factors that affect SV

1. Preload
2. Contractibility
3. Afterload

Preload

degree to which cardiac muscles are stretched just before they contract

* increased preload → increased EDV → Increased SV

Frank-Starling Law of the Heart

cardiac muscle exhibit a length-tension relationship

* at rest cardiac muscle cells are shorter than optimal length → dramatic increase in contractile force

Preload (EDV) can be increased by:

increased filling time (slower heart beat) and increased venous return

Afterload

Pressure that ventricles must overcome to eject blood (peripheral resistance)

* Back pressure from arterial blood pushing on semilunar valves is major pressure


* Aortic pressure 

\
Hypertension increases afterload…

resulting in increased end-systolic volume (ESV) and reduced stroke volume (SV)

Contractility

Contractile strength at given muscle length & increased contractility lowers ESV, caused by:

* Positive inotropic agents
* increased Ca2+ influx

Cardiac Output - heart rate

Affected by ANS; increased sympathetic activity → increased HR and increased parasympathetic activity (vagal nerve) → decreased HR

Blood vessels structure & function

delivery system of dynamic structures that begin and end at the heart & works with lymphatic system to circulate fluids

Arteries

carry blood away from the heart

Capillaries

direct contact with tissue cells to serve cellular needs; endothelium with sparse basal lamina

Veins

carry blood toward the heart

Lumen

central blood-containing space

Walls of all vessels (except capillaries) have three layers

1. Tunica intima
2. Tunica media
3. Tunica externa

Tunica Intima

Innermost layer that is “intimate” contact with blood

Endothelium

simple squamous epithelium that lines lumen of all vessels; slick surface reduces friction

Tunica Media

Middle layer composed mostly of smooth muscle and sheets of elastin (protein/fiber); sympathetic vasomotor nerve fibers innervate this layer

Vasoconstriction

decreased lumen diameter

Vasodialation

increased lumen diameter

Tunica Externa

Outermost layer of wall composed mostly of loose collagen fibers and infiltrated with nerve fibers, lymphatic vessels

Vas vasorum

system of tiny blood vessels found in larger vessels nourish outermost external layer

Arteries are divide into three groups based on…

size and function

Elastic Arteries

large, low-resistance lumen & acts as pressure reservoirs that expand and recoil as blood is ejected from the heart

* Aorta and its major branches
* called conducting arteries b/c they conduct blood from heart to medium sized vessels
* substantial smooth muscle

Muscular Arteries (AKA distributing arteries)

deliver blood to organs, have thickest tunica media with more smooth muscle and active in vasoconstriction

Arterioles (AKA resistance arteries)

change diameter to change resistance to blood flow and leads to capillary beds

Capillaries

these microscopic vessels are so small only a single RBC can pass through at a time; they exchange gases, nutrients, waste, hormones, etc., between blood and interstitial fluids

* supply almost every cell
* All capillary endothelium cells are joined by tight junctions that are incomplete

Capillary bed

capillaries for a network between arteriole and venule

Vascular shunt (metarteriole)

directly connects arteriole and venule

True capillary

actual exchange vessel