anatomy test 3.3

the superior mediastinum is located

superior to transverse thoracic plane passing through the sternal angle and the T4/5 IV discs

contents of superior mediastinum from anterior to posterior

thymus

great vessels (brachiocephalic veins and shit like that)

phrenic nerves and vagus nerves

cardiac nerve plexus

left recurrent laryngeal nerve

trachea and esophagus with nerves

thoracic duct and lymphatic trunks

thymus

after puberty it gradually degrades and is replaced by fat

blood supply is from branches of the internal thoracic artery

brachiocephalic veins are formed by the union of

subclavian and internal jugular veins bilaterally

they unite at the 1st costal cartilage to form the SVC

left brachiocephalic veins vs right

L: is twice as long as right and passes anterior to the arch of aorta and great vessels

superior vena cava syndrome is caused by obstruction

the vessels with subsequent head, neck and upper limb edema

lung cancer is a potential cause

aortic arch begins posterior to the

2nd right sternocostal joint (sternal angle)

it arches superiorly, posteriorly to the left and then inferiorly

in 65% of people the typical branches arising from the aortic arch are

brachiocephalic trunk, left common carotid and left subclavian arteries

6 pairs of aortic arches intially develop

4th aortic arch contribute to the right subclavian artery and the arch of the aorta

6th arches become ductus arteriosus and proximal part of pulmonary arteries

during development the neural crest cells migrate

toward the heart via the aortic arches

neural crest cells migrate and enter paired

truncal and bulbar ridges

ridges grow and divide outflow tract in spiral manner and fuse to form the aorticopulmonary septum (AP)

the ap septum now divides

truncus arteriosus and bulbus cordis into the aorta and pulmonary trunk

persistent truncus arteriosus is caused by

abnormal neural crest cell migration

only partial AP septum develops

one large vessel leaves the heart

usually have VSD marked cyanosis from right-left shunting

location of brachiocephalic trunk

anterior to trachea

posterior to left brachiocephalic vein

left common carotid artery location

ascends into the neck posterior to the left sternoclavicular joint

left subclavian artery location

most posterior

ascends lateral to the trachea

the phrenic nerve lies on the anterior surface

of the anterior scalene muscles as they pass inferiorly into thorax

the vagus and sympathetic nerves form the

carotid, pulmonary and esophageal plexuses

left recurrent laryngeal nerve arises from

the vagus nerve and wraps underneath the aortic arch just lateral to the ligamentum arteriosum then ascends to the larynx between the trachea and esophagus

aortic aneurysm, bronchogenic or esophageal carcinoma may com press

the recurrent laryngeal nerve causing a hoarse voice

the left recurrent larnygeal nerve is located in the

superior mediastinum

the right recurrent larnygeal nerve arises form the

right vagus nerve and wraps underneath the right subclavian artery before ascending to the larynx

it does not descend to the superior mediastinum

the anterior mediastinum contains

inferior portion of thymus gland in infants and children

it is anterior to the pericardium and posterior to the body of the sternum

contents of posterior mediastinum

thoracic aorta

thoracic duct

posterior mediastinal lymph nodes

azygos and hemiazygos veins

esophagus and plexus

thoracic aorta beings at lower border of

T4 body on left side

approaching median plane as it descends to T12 vertebrae and passes through aortic hiatus

coarctation

abnormal narrowing of the aorta which obstructs blood flow to the inferior part of the body

most common site is postductal (after the ductus arteriosus)

in coarctation collateral vessels become so large they

erode the surfaces of the ribs and pulsation is noted in the intercostal spaces

blood flow direction in ribs

internal thoracic arteries-> anterior intercostal arteries-> posterior intercostal arteries-> distal thoracic aorta

this provides blood flow to abdomen, pelvis and lower limbs

esophagus

fibromuscular tube from pharynx to stomach

lies anterior to vertebral bodies

passes through superior to posterior mediastinum

esophageal plexus

branching fibers from both left and right vagus nerves mix in the esophageal plexus to then form trunks

the anterior vagal trunk arises from the

left vagus nerve

the right vagus nerve gives rise to

posterior vagal trunk

parasympathetic vs sympathetic innervation for esophagus

P- vagus

S- upper thoracic ganglia

typical places esophagus can become compressed

origin of esophagus at junction with pharynx

arch of aorta, left main bronchus

esophageal hiatus

contriction of aorta and bronchus are often grouped

together so that 3 constriction sites are cited instead of 4

azygos vein forms the

collateral pathway between SVC and IVC and drains the posterior wall of abdomen

azygos vein forms from

junction of subcostal and ascending lumbar vein at the L1 or L2 vertebral level

receives intercostal, accessory and hemiazygos veins

arch over root of right lung and drains to the SVC

accessory hemiazygos crosses at

T8 to empty into azygos

hemiazygos crosses at

T9 to empty into the azygos

azygos vein can provide a route for

venous return to the heart if either SVC or IVC are blocked

thoracic duct

largest lymphatic vessel and begins at cisterna chyli (L2)

appears beaded due to valves

path of thoracic duct

ascends to the right midline between azygos vein and root of aorta

traverses the diaphragm via aortic hiatus

at T4,5,6 it crosses to the left midline and enters the superior mediastinum

empties on the left side at the junction of the internal jugular and left subclavian veins

thoracic duct injury can lead to

chylothorax (lymph in pleural cavity)

the right lymphatic duct empties into the

junction of internal jugular and subclavian

the right lymphatic duct drains

right upper limb, head, neck and thorax

thoracic duct carries lymph from

the rest of the body

splanchnic nerves pass into the

abdominal cavity carrying preganglionic sympathetic fibers to prevertebral ganglia

sympathetic ganglia and trunks are not in

the posterior mediastinum

cells of lymphocytic tissue

B cells

T cells

NK cells

supporting cells in lymphatic tissue

monocytes and macrophages

basophils, eosinophils, neutrophils and mast cells

reticular cells

dendritic cells

langerhan cells (found in epidermis and other stratified squamous epithelia)

epithelioreticular cells (thymus only)

cluster of differentiation molecules

cell surface molecules that can be visualized by immuno-histochemical techniques using monoclonal antibodies

approximately 70% of lymphocytes are

immuno-competent cells circulating in the blood or lymph

these cells participate in a cycle in which they exit the systemic circulation to enter lymphatic tissue where they are responsible for immunologic surveillance

these cells are mainly long-lived, mature lymphocytes (mostly T cells) which have developed the ability to recognize and respond to foreign antigens

the other 30% of lymphocytes in the blood are

short lived immature or activated cells destined for specific tissues

these cells leave the capillaries and enter the LCT that lies beneath epithelia such as that of the gut

T lymphocytes

called T cells bc they differentiate in the thymus

involved in cell mediated immunity

account for 60-80% of lymphocytes

all T cells express

CD3,5 and 7 as well as T-cell receptors

subclasses of T-cells are identified by whether or not they express

CD4 or CD8

helper T-cells express CD4

cytotoxic T cells express CD8 (kill virus-infected cells, cancer cells and transplanted cells)

suppressor T-cells regulate

T-cell activity

gamma/ delta reside at

interfaces of external and internal environment

HIV binds to

CD4 on helper t cells

injects single-stranded RNS into the cell

RNA incorporated into T-cell genome

Langerhan cells may serve as reservoir for HIV

B lymphocytes

called B-cells bc first recognized as a distinct population of lymphocytes in the bursa or fabricius of birds

involved in production of antibodies

responsible for humoral immunity

make up 20-30% of circulating lymphocytes

bursa equivalent in humans is

Gut-associated lymphoid tissue (GALT) and bone marrow

B-cells express membrane bound immunoglobulin called

B-cell receptors

these serve as antigen-specific binding sites

NK cells

neither B or T cells

they are specialized to kill certain types of target cells

genetically programed to kill cells that are transformed either by viruses or neoplasia

NK cells release

perforins and granzymes that form channels in targeted cells

causes targeted cells to undergo apoptosis

antigen presenting cells (APCs)

these interact with CD4+ T helper cells

APCs of mononuclear phagocytic system (MPS)

macrophages

perisinusoidal macrophages (kupffer cells)

langerhans cells of epidermis, oral mucosa and vagina

dendritic cells of the spleen and lymph nodes

APCs not of the MPS

B lymphocytes

Epithelioreticular cells (Type II and III)

APCs endocytose antigen

break it down into peptides that bind to MHC-II and the MHC-II/peptide complex is inserted into the plasma membrane

Major histocampatability complex (MHC)

display molecules on the surfaces of cells that are recognized by T lymphocytes

these display molecules contain short peptide sequences (8-10) of self or non-self antigens

MHC I is expressed on the surfaces of

all nucleated cells and platelets

CD8+ cytotoxic T lymphocytes detect whether the displayed peptides are self or whether they are transformed by viral infection or cancer

MHC II is only expressed on the surface of

APCs

MHC II presents endocytosed and digested foreign peptides on APC surface to CD4+ helper T cells

diffuse lymphatic tissue is found in

the LCT that underlies epithelia (lamina propria)

also called mucosa-associated lymphatic tissue (MALT)

contains numerous plasma cells

often can identify numerous eosinophils

nodular lymphatic tissue

nodules or follicles are sharply delineated, but not encapsulated

primary nodules contain small lymphocytes

secondary nodules (most numerous) contain a lightly-stained germinal center with numerous large lymphoblasts and plasmablasts

also contain follicular dendritic cells

GALt

is a type of MALT

specialized accumulations of lymphatic nodules are found in

tonsils (pharyngeal, palatine, lingual)

Ileum ( peyers patches)

vermiform appendix

tonsils form a

protective ring (waldeyer's ring) of lymphatic tissue around the posterior aspect of the oral cavity

palatine tonsils lie on either side of

the posterior oral cavity between the palatoglossal and palatopharyngeal arches

lingual tonsils are in the

base of the tongue (posterior tongue)

pharyngeal tonsils are in the roof

of the pharynx

called adenoids

when enlarged can block the eustachain tubes and result in nasal voice

lymph nodes

small, bean-shaped encapsulated organs

located along lymphatic vessels

act as filters along the lymphatics through which lymph percolates

traps antigens in the lymph where they are processed by APCs

afferent vs efferent lymphatics

A: enter through the capsule of the node

E: exit the hilum of the node

lymph node structure

thin connective tissue

beneath capsule is subcapsular sinus

cortex with 2 regions

medulla

hilum

thin connective tissue of lymph node

extending into node are trabeculae of CT

2 regions of cortex

outer cortex has nodules

deep cortex (paracortex) has no nodules: contains most of the T-cells in node

called thymic dependent cortex

medulla or lymph node

contains cords of cells

cords separated by medullary sinuses

hilum of lymph node is where

artery enters

vein and efferent lymphatics exit

the stroma or supportive connective tissue of lymph node is made up of

reticular fibers

lymph flow through lymph node

1. Lymph enters via afferent lymphatics

along the convex capsular surface.

2. Enter subcapsular sinus.

3. Percolates along trabecular sinuses.

4. Enters medullary sinus.

5. Exits via efferent lymphatic at hilum

of the node

distribution of lymphocytes in cortex

T-cells mainly in deep cortex

B-cells accumulate predominantly in germinal centers

High endothelial venules (HEVs)

most lymphatics enter node via HEVs

they function to draw water out of the lymph into the bloodstream

high concentration of aquaporin-1

have receptors that bind antigen-primed lymphocytes in the blood stream

lymphadenitis (catch scratch fever)

bacteria infection caused hyperplasia of lymphatic nodules and enlargement of lymph nodes

thymus

site of T-cell education

in development the endothelium of third pharyngeal pouch grows caudally into the thorax and becomes disconnected from pouch

it becomes populated with multipotential lymph stem cells

microanatomy of thymus

•has thin capsule with trabecular extending into organ

•Capsule and trabeculae have blood vessels, nerves and efferent

lymphatics (no afferents).

• Has a medullary deep to a cortex that does not normally have

lymphatic nodules.

• Developing T-cells (thymocytes) are in a meshwork formed by

epithelioreticular cells, which are derived from pharyngeal pouch

endoderm.

blood thymus barrier

a physical barrier to prevent antigens from reaching the developing T-cells in the cortex

blood thymus barrier made up of

endothelium

basal lamina

pericytes

macrophages

type I epithelioreticular cells with tight junctions

t-cell education

Complex process by which cells that recognize self-antigens displayed by self-MHC are eliminated

positive selection occurs in the

cortex. cell that recognizes MHC II and self peptides survive

Non-reacting cells die by apoptosis

negative selection occurs in

medulla. cells that are highly reactive to self antigens are eliminated

thymic follicular hyperplasia

happens in autoimmune diseases, follicles with germinal centers appear in the thymus

spleen

largest lymphatic organ

located in upper left quadrant of the abdomen deep to ribs 9,10,11

filters blood

has a dense CT capsule from which trabeculae extend into the organ

medially located hilum