Mediastinum Anatomy & Physiology PA 481 C Tony Serino, Ph.D. Biology Department Misericordia Univ.
Dec 29, 2015
Mediastinum
Anterior
Superior
Middle
Posterior
Superior and anterior are continuous with each other; both may bereferred to as the superior mediastinum
Esophagus• Function: Deglutition• Two sphincters: upper
and lower esophageal sphincters (lower is physiological only)
• Retropleural position (therefore, covered by adventitia)
• Mucosa: stratified squamous with many mucus glands (esophageal glands)
• Muscularis: changes from skeletal to smooth muscle
Thymus Gland• Bilobed organ that is largest in children, but begins to regress sharply at the onset of puberty (around age 11)
• It is the site of T-cell lymphocyte production and produces hormones (such as, thymosin) that modifies their physiology
General Circulatory System
1. Cardiovascular– Consists of a closed
system of vessels which transport blood
– Two circuits: Systemic and Pulmonary
– Arteries move blood away from the heart
– Veins move blood toward the heart
General Circulatory System2. Lymphvascular –
moves lymph– Consist of blind end
tubes which collect interstitial fluid (now called lymph) and returns it to circulation
– The lymph is cleaned before returned to the blood vessels
Heart as a Dual Pump
• Cardiac muscle arranged as whorls that squeeze the blood
• Twin pumps: systemic and pulmonary
• Four chambers: 2 atria and 2 ventricles
Most Common Coronary Arterial Pattern
Fig. 1.51
Ant. Desc. a. (LAD)
Post. Desc. a.
R. Marginal a.
L. Marginal a.
Circumflex a.
Coronary Variation
15% LCA dominant
Single CA
Most people right dominant.
Circumflex from right aortic sinus
(4% have an accessory coronary artery)
(note: which branch gives rise to posterior descending a.determines dominance)
Coronary Veins
Fig. 1.52
Coronary sinus
Great Cardiac v.
Small Cardiac v. Middle Cardiac v.
Ant. Cardiac veins
Factors Affecting SV• Stroke Volume (SV) =
End Diastolic Volume – End Systolic Volume• SV = EDV – ESV (ml/beat)• EDV affected by:
– Venous return which is dependent on venous tone, skeletal muscle pumps, etc.
• ESV– As the heart fills it is stretched which allows for better overlap of
the contractile proteins which will affect the force of contraction and the ESV (Starling’s Law of the Heart)
– Increasing the force of contraction at any EDV will decrease the ESV and increase the SV (sympathetic stimulation and epinephrine)
Sympathetic Stimulation
• Leads to increase HR• Increases in Ca++
release from SR, increase Ca++ through membrane and increase myosin crossbridge cycling
• Increases force of contraction
Heart Rate Control• Sinus Rhythm = normal SA node control• Autonomic Activity
– Sympathetic (thoracic trunk) = accelerator (induces tachycardia)
– Parasympathetic (vagus n.)= brake (induces bradycardia)
• Hormones– epinephrine
• Drugs-caffeine, nicotine, atropine, etc.
Posterior Mediastinum
Thoracic aorta
Sympathetic trunk
Vagus n.
Azygous v.
Trachea
Esophagus
Phrenic n.
Intercostal a., v., & n.
Hemiazygous v.
Lung root
Thoracic duct