Lymphatic System

Question 1

describe spleen, its location, structures related to the spleen, functions and vasculature

Answer 1

spleen
- lymphoid organ
- left hypochondrium, posterior to stomach
- purple, variable in size and shape
- cannot be palpated in living subjects
- intraperitoneal
- small bare area by the hilum to give attachment to peritoneal ligaments
- splenorenal ligament - left kidney
- gastrosplenic ligament - greater curvature of the stomach

related structures
- long axis is parallel to the left tenth rib
- hilum is perforated by many blood vessels, nerves and lymphatics
- left dome of the diaphragm is responsible for movement of the organ during ventilation

vasculature
- splenic artery is a branch of the coeliac trunk
- crosses along upper pancreas and gives pancreatic branches, as well as short gastric arteries and left gastroomental arterys to go to the stomach
- veins accompany terminal branches of the splenic artery and unit to form splenic vein. unites with superior mesenteric to form portal vein
- if there is portal hypertension, the spleen can become enlarged, called splenomegaly

function
- primary site of b cell maturation after they leave the bone marrow
- major filtration unit to clear blood of damaged RBC and bacteria

Question 2

describe bone marrow, and the differences between red and yellow

Answer 2

• red marrow has great number of RBC being produced
• by 20, diaphysis has only yellow marrow because of fat infiltration
• red marrow can be found in flat bones, short bones, irregular bones and the epiphyses of long bones

vasculature
- bone marrow receives from nutrient arteries that pierce the diaphysis via the nutrient foramina

Question 3

describe the structure, function and location of the thymus

Answer 3

function
- maturation and education of t lymphocytes via positive and negative selection
- primary lymphoid organ
- cortex and medulla

location
- anterior mediastinum

structure
- cortex and medualla
- enclosed by a capsular membrane that fuses with connective tissue joining the left and right lobes
- left lobe is thicker than the right
- atrophies at the start of puberty

vasculature
- inferior thyroid and internal thoracic vessels
- superior thyroid provides a branch
- vessels enter at interlobular septa through thymic parenchyma via corticomedullary junction

Question 4

describe the microscopic structure of the spleen

Answer 4

• covered by an outer dense irregular connective tissue capsule which sends radiating trabeculae into the organs trabeculae
• red and white pulp inside

white pulp
- grayish white islands of lymphoid tissue surrounding a central arteriole to form periarteriolar lymphatic sheaths.
- t cells are found in PALS
- lymphoid nodules are in the peripheral white pulp, where b cellsare found.
- the marginal zone is cellular lymphoid tissue that surrounds the white pulp, and this contains macrophages and b cells.

red pulp
- makes up most of the spleen
- abundant erythrocytes
- found around white pulp
- many thin walled venous sinusoids

vasculature of the white pulp and red pulp is different.
white - central arterioles from the splenic artery at the hilum, two layers of smooth muscle in the walls.
red - 90% capillaries drain into venous sinusoids in a closed system. remaining open ended capillaries discharge blood freely into the intersinusoidal meshwork
- sinusoids merge to form trabecular veins which merge to form the splenic vein that leaves at the hilum.

how it filters old RBC
- they are worn out and lack pliability, cannot squeeze out of the sinusoids and are therefore taken out of circulation

Question 5

describe the features of the different tonsils

Answer 5

tubal
- surround eustachian tube
- nasopharynx
- shorter and straighter in young children so nasal and throat infections can reach the middle ear more easily

palatine
- circumpharayngeal lymphoid ring
- ovoid mass of lymphoid tissue in the lateral wall of the oropharynx
- supported internally by collagen type III
- free surface mucosa invaginates to form 10-20 crypts that can contain calcified bacteria
- has 4 lymphoid compartments
- max size at puberty, then atrophy

lingual
- dorsal surface of posterior one third of the tongue

adenoids
- nasopharynx

Question 6

describe the innervation of the tongue

Answer 6

sensory

anterior two thirds
- general sensation - lingual nerve of mandibular trigeminal
- taste - facial nerve via chordae tympani

posterior third
- general sensation - glossopharyngeal
- taste - glossopharyngeal nerve

motor

palatoglossus - vagus nerve
intrinsic muscle - hypoglossal
genioglossus, hypoglossus, styloglossus - hypoglossal nerve

Question 7

describe the thoracic duct

Answer 7

• transport lymph into circulation
• lymph capillaries to vessels to ducts

course
- arises from cisterna chyli (confluence of instestinal vessels), passes into thorax between azygous and descending aorta, ascends through posterior mediastinum and enters superior mediastinum on the left of the oesophagus.
- crosses apex of the left lung and enters at the root of the neck to terminate in the confluence of the left internal jugular and subclavian veins at pirgoffs angle