INB 446L Test 4

Cardiovascular, Immune + Lymph, GI

Cardiovascular System Overview

Transports blood, nutrients, oxygen, and waste throughout the body.

• consists of heart, blood vessels (arteries, veins, capillaries), and lymphatic system.

• plays a key role in maintaining homeostasis and immune function

Pulmonary Circulation

Right heart → lungs → left heart

• carries deoxygenated blood from right ventricle to lungs for oxygenation

Systemic Circulation

Left heart → Body → Right heart

• delivers oxygenated blood from left ventricle to body and returns deoxygenated blood to heart

Portal Circulatory Systems

Blood travels through 2 capillary beds before returning to heart

• venous portal systems:

  • Hepatic portal system carries blood from intestines to liver

  • hypophyseal portal system connects hypothalamus and anterior pituitary gland

• Arterial portal system includes efferent arteriole in kidney that carries blood between two capillary networks in nephrons

Azygos Vein

Vein that drains the right side of thoracic cavity, receiving venous return from the intercostal spaces and forms a connection between the superior and inferior vena cava, allowing alternative blood return to the heart

• empties into the superior vena cava, near the right atrium

• provides collateral circulation if there’s obstruction in the superior or inferior vena cava

• enlarges in cases of superior vena cava syndrome, causing venous congestion

Cardiac Tamponade

Blood or fluid accumulates in the pericardial sac, restricting heart expansion and the heart cannot fill properly, leading to decreased stroke volume and cardiac output.

• Decreased arterial pressure & pulse pressure → due to limited ventricular filling

• elevated venous pressure → blood backs up into the venous system

• jugular venous distention (JVD swelling) → sign of impaired venous return

• shock → reduced cardiac output leads to systemic hypoperfusion (tissues and organs don’t receive enough oxygen and nutrients, leading to metabolic failure)

Mediastinum

The central compartment of the thorax

• Boundaries:

  • superior: thoracic inlet

  • inferior: diaphragm

  • anterior: sternum

  • posterior: vertebral column

  • lateral: lungs (pleural cavities)

• Subdivisions:

  • superior mediastinum: contains the greatest vessels, trachea, esophagus

  • inferior mediastinum: divided into 3 parts

    • anterior: thymus, lymph nodes, fat

    • middle: heart, pericardium, great vessels

    • posterior: esophagus, descending aorta, thoracic duct, sympathetic chain

Location & orientation of the Heart

Lies between the sternal angle and the 5th intercostal space

• positioned anteriorly and slightly to the left within the mediastinum

• 2/3 of heart sits to left of midline

Key anatomical landmarks of the heart

• Apex of the heart is located at left 5th intercostal space, near the midclavicular line

• Base of heart sits at level of 2nd rib, primarily formed by left atrium

• Right border formed by right atrium

• left border formed by left ventricle

• inferior border formed by right ventricle

Atrioventricular Valves

control blood filling of ventricles

• Tricuspid valves (right AV valve) has 3 cusps to prevent backflow from the right ventricle into the right atrium

  • chordae tendinae are fibrous cords that anchor cusps to papillary muscles (contract during systole to prevent valve prolapse)

• Mitral (bicuspid valve) is between left atrium and ventricle

Semilunar valves

control blood ejection from ventricles

• pulmonary valve is between right ventricle and pulmonary trunk

  • opens during systole to allow blood flow into the pulmonary artery, prevents backflow into the right ventricle during diastole

• Aortic valve is between left ventricle and ascending aorta

  • Opens during systole, allowing blood ejection and closes during diastole preventing backflow nad enabling coronary artery perfusion

Valves are operated based on…

a pressure-dependent mechanism

Diastole

relaxation and filling phase

• AV valves are open, blood fills the ventricles

• atria contract to push remaining blood into ventricles, ventricular pressure decreases

Systole

Contraction and Ejection phase

• AV valves close (first heart sound - aligns with QRS complex and AV valve closure)

• ventricles contract, pushing blood through aortic and pulmonary valves, ventricular pressure rises

• semilunar valves close (second heart sound - follows T wave)

Murmurs

abnormal heart sounds that can indicate valve diseases (stenosis or regurgitation are 2 examples)

Auricle

Small muscular pouch that increases atrial volume

Cristae Terminalis

ridge separating smooth and rough atrial surfaces (pectinate muscles)

Pectinate muscles

parallel ridges in the atrial wall aiding contraction and strengthens the atrial wall

Fossa Ovalis

Remnant of fetal foramen ovale, which allowed blood shunting between atria

Tricuspid valve

regulates blood flow into the right ventricle

Superior vena cava

Returns deoxygenated blood from upper body

Inferior Vena cava

Returns deoxygenated blood from lower body

Coronary Sinus

Drains venous blood from the heart’s own circulation

Right Ventricle

pumps deoxygenated blood to lungs via pulmonary valve

Blood flow through heart

Aortic sinuses

contain openings for right and left coronary arteries.

• When the aortic valve closes during diastole, backflow of blood fills the coronary arteries, supplying the heart muscle.

Coronary Circulation

First branches off the aorta are coronary arteries that supply oxygenated blood to the myocardium

• travel in the coronary sulcus, encircling the heart

• divided into the left and right coronary arteries, each with critical branches

Coronary Artery Disease

narrowing of coronary arteries leads to angina, myocardial infarction, or heart faillure.

Left Anterior Descending Blockage

Causes fatal heart attacks due to its role in supplying the left ventricle and septum

Right Coronary Artery Blockage

Can affect SA & AV node function, leading to bradycardia or heart block

Coronary Venous System

Returns deoxygenated blood from the myocardium to the right atrium

• Main veins converge into the coronary sinus (largest cardiac vein)

• runs posteriorly in the coronary sulcus between the left atrium and ventricle.

Ascending Aorta

First branches are the right and left coronary arteries → supply oxygenated blood to heart muscle

Aortic Arch

3 major branches:

• Brachiocephalic trunks supplies right side, divides into:

  • right common carotid artery → supplies right head and neck

  • right subclavian artery → supplies right upper limb

• Left common carotid artery → supplies left head and neck

• left subclavian artery → supplies left upper limb and thoracic structures

Fibrous Skeleton

• provides structural support for heart valves

• maintains valve positioning and prevents excessive stretch

• serves as an electrical insulator, preventing random electrical impulses from passing between atria and ventricles

• forms attachment points for cardiac muscle fibers

Cardiac Muscle’s unique ability

heart muscle contracts rhythmically on its own without direct nervous stimulation (autorhythmicity)

• conduction system components are modified cardiac muscle cells that initiate and regulate heartbeat

Electrical conduction pathway

1. SA node: natural pacemaker located at junction of SVC and right atrium, sets heart rate of 60-100 bpm by generating impulses (P wave)

2. AV node, located in interatrial septum and receives impulses from SA node, delays conduction by 0.1 sec to allow atrial contraction before ventricular contraction (PR interval)

3. Buncle of His (AV bundle) conducts impulses from AV node to ventricles

4. Right and left buncle branches carry signals down interventricular septum towards apex

5. Purkinje Fibers distribute impulses throughout the ventricles, triggering contraction (QRS complex)

Electrical impulses depolarize and repolarize myocardium (T wave is ventricular repolarization)

Baroreceptors

Blood pressure regulation, detect arterial blood pressure changes by sensing vessel wall stretch

• high pressure baroreceptors are located in the aortic arch and carotid sinus (detect systemic BP)

• low pressure ones are located in the walls of pulmonary vessesl adn atria (detecting venous return)

• increased BP activates glossopharyngeal nerve (CN 9) from the carotid sinus and brainstem as well as Vagus nerve (CN 10) to decrease Heart rate (parasympathetic)

• decreased BP reduces baroreceptor firing and increases HR and BP via sympathetic activation (T1-T5)

Chemoreceptors

Oxygen, CO2, and pH level changes detected to regulate respiration and circulation

• located in aortic and carotid bodies (near baroreceptors)

• low O2, high CO2, or acidosis triggers increased sympathetic activity and raises HR and BP to improve oxygenation

Epicardium

visceral pericardium; outer protective layer

• mesothelial cells (simple squamous epithelium) and underlying connective tissue

• contains blood vessels, lymphatics, and adipose tissue

Myocardium

contractile muscle layer that is composed of cardiac muscle fibers arranged in spirals

• intercalated discs (gap junctions & desmosomes) allow coordinated contraction

Endocardium

Inner lining of the heart made from endothelial layer (simple squamous epithelium) and thin subendothelial Connective tissue

• subendocardial layer houses purkinje fibers (conducting system)

Purkinje fibers

Specialized cardiac muscle fibers located in the subendocardial layer

• pale staining cells due to high glycogen content & fewer myofibrils

• found in ventricular walls, conducting impulses rapidly for synchronized contraction

• Final component of the conduction system → ensures rapid depolarization of ventricles

• transmits impulses from AV bundle of His to ventricular myocardium

• allows near-simultaneous contraction of the ventricles for efficient blood ejection

Arteries

carry blood away from the heart

• aorta and arteries have highest pressure, large fluctuations between systole and diastole

• rounder, thicker wall, prominent tunica media

Veins

carry blood toward the heart

• irregular shape, thinner wall, larger lumen, thicker tunica externa relative to wall thickness

• contain 65-70% of blood volume at a time

• act as blood reservoirs due to high compliance and large lumens

• thinner walls and less smooth muscle than arteries

• valves in medium and large veins prevent backflow

• skeletal muscle pump, muscle contractions compress veins to aid venous return (especially in legs)

arterioles

regulate blood flow into capillary networks, smaller vessels

• major drop in pressure due to resistance, they act as pressure regulators

• few layers of smooth muscle in tunica media and major role in resistance and blood pressure regulation

capillaries

allow exchange of nutrients, gases, and waste between blood and tissues, smaller vessesl

• only composed of endothelium and a basement membrane, allowing efficient exchange of materials

• 5-10 um diameters (just enough for RBCs to squeeze through)

• slow blood flow for maximized exchange time

• supported by pericytes - contractile cells that stabilize capillary walls and help with repair

• use pinocytotic vesicles for large molecule transport, especially in continuous capillaries

postcapillary venules

return most fluids to blood, excess fluid drains into lymphatic system. Also allow WBCs to migrate into tissues (diapedesis), smaller vessels

• decrease in pressure from capillaries, very low in venae cavae

• composed of endothelium and pericytes

Muscular venules

Venules that have 1-2 layers of smooth muscle and begin to show a distinct tunica media

• pressure is still low and structure is thinner than arterioles

Blood vessel arrangement in series

Elastic arteries → muscular arteries → arterioles → capillaries → venules → small and large veins → venae cavae and pulmonary veins

blood flows in one direction due to pressure gradients generated by the heart and vessel structure

Structure of blood vessels

All have smooth muscle and connective tissue, lined by endothelium (simple squamous epithelium)

• tunica intima (inner layer) is made of the endothelium and loose connective tissue with perforated internal elastic lamina

• tunica media (middle smooth muscle layer) made of smooth muscle, elastic fibers, Type 3 collagen, proteoglycans, glycoproteins, and external elastic lamina

• tunica adventitia (outer connective tissue) is made of type 1 collagen and elastic fibers, contains vasa vasorum (small blood vessels that nourish large vessel walls)

Elastic artery

Type of artery that has a thick tunica media filled with elastic fibers and dampens pressure fluctuations from the heartbeat (aorta)

• thick wall accomodates high pressure from the heart

• MA: atherosclerotic lesions are common in elastic arteries like the aorta

Muscular artery

Type of artery that has a prominent internal and external elastic lamina and smooth muscle that dominates the tunica media

• directs blood to specific organs (femoral artery example)

Continuous capillaries

type of capillary that is the most common and found in muscle, skin, lungs, and brain

• has tight junctions, small intercellular clefts, pinocytosis

Fenestrated capillaries

type of capillary that has pores in its endothelium (for rapid exchange) and is found in kidneys, intestines, and endocrine glands

Sinusoidal capillaries

type of capillary that has large gaps and discontinuous basement membrane, found in liver, spleen, bone marrow

Simple pathway flow

type of capillary flow that uses one arteriole, one capillary bed, and one venule and is the most common (skin, muscles)

Arteriovenous shunt (bypass)

Type of capillary flow where blood flows directly from arteriole to venule and is used in thermoregulation (skin in cold temp)

Portal system

type of capillary flow where two capillary beds are connected by a portal vein

• enhances exchange between two regions

• hepatic portal system and hypophyseal portal system

Immune System

monitors the body’s external and internal environments, responds to potentially harmful substances like pathogens and toxins

• composed of cells (lymphocytes, main effector cells), tissues (mucosa associated lymphoid tissues), and organs (lymph nodes, thymus, red bone marrow, spleen)

• lymphatic vessles transport lymph and connect with cardiovascular system

Lymph

fluid in immune system that is made up of WBC’s and plasma like fluid (interstitial fluid)

• lymph capillaries → lymph vessels → nodes → ducts → veins

• valves ensure one-way flow of lymph

right lymphatic duct

drains right upper limb, right side of head/neck and right thorax

Thoracic duct

drains the rest of the body, empties into the left subclavian vein