Lymphatic drainage pathways

Lymphatic drainage pathways US Medical PG Question 1: A 49-year-old woman presents to her physician with complaints of breast swelling and redness of the skin over her right breast for the past 1 month. She also mentions that the skin above her right breast appears to have thickened. She denies any pain or nipple discharge. The past medical history is significant for a total abdominal hysterectomy at 45 years of age. Her last mammogram 1 year ago was negative for any pathologic changes. On examination, the right breast was diffusely erythematous with gross edema and tenderness and appeared larger than the left breast. The right nipple was retracted and the right breast was warmer than the left breast. No localized mass was palpated. Which of the following statements best describes the patient’s most likely condition?

• A. It shows predominant lymphatic spread.
• B. The lesion expresses receptors for estrogen and progesterone.
• C. The lesion is due to Streptococcal infection.
• D. It is a benign lesion.
• E. The inflammation is due to obstruction of dermal lymphatic vessels. (Correct Answer)

Lymphatic drainage pathways Explanation: ***The inflammation is due to obstruction of dermal lymphatic vessels.*** - The presentation of **rapid-onset breast swelling, redness, thickening of the skin, warmth, and nipple retraction** without a palpable mass is highly suggestive of **inflammatory breast cancer (IBC)**. - IBC is characterized by the **obstruction of dermal lymphatic vessels by tumor cells**, leading to the classic inflammatory signs and **peau d'orange** appearance. *It shows predominant lymphatic spread.* - While IBC does involve **lymphatic spread**, this statement alone does not fully encompass the characteristic pathology of the condition causing the observed symptoms. - The obstruction of the **dermal lymphatic vessels** is a more precise description of the immediate cause of the clinical presentation. *The lesion expresses receptors for estrogen and progesterone.* - Although some breast cancers are **hormone receptor-positive (ER/PR positive)**, there is no direct information in the vignette to suggest this specificity for the patient's condition. - This statement refers to a **molecular characteristic** that is not a defining feature of the clinical presentation of IBC. *The lesion is due to Streptococcal infection.* - While a **bacterial infection** (like **streptococcal cellulitis**) can cause redness, swelling, and warmth, it typically presents with more acute symptoms, fever, and often a clearer response to antibiotics. - The **thickening of the skin** and **nipple retraction** point away from a simple infection and towards a malignant process. *It is a benign lesion.* - The rapid progression of symptoms, pronounced skin changes, and nipple retraction are all **red flags for malignancy**, specifically inflammatory breast cancer. - **Benign lesions** rarely cause such diffuse, severe, and rapidly progressing inflammatory signs.

Lymphatic drainage pathways US Medical PG Question 2: A 43-year-old man comes to the physician because of weight loss and swelling on the left side of his neck. Physical examination shows a firm, enlarged left upper cervical lymph node that is immobile. Immunohistochemical testing performed on a biopsy specimen from the lymph node stains positive for cytokeratin. Which of the following is the most likely site of the primary neoplasm in this patient?

• A. Nerve sheath
• B. Bone
• C. Muscle
• D. Skin
• E. Nasopharynx (Correct Answer)

Lymphatic drainage pathways Explanation: ***Nasopharynx*** - A **firm, enlarged, immobile cervical lymph node** in the upper neck (Level II) with **cytokeratin positivity** indicates metastatic carcinoma of epithelial origin. - **Nasopharyngeal carcinoma** classically presents with **cervical lymphadenopathy as the initial manifestation** in up to 90% of cases, often before other symptoms develop. - The **left upper cervical location** is characteristic of nasopharyngeal primary tumors, which have a strong predilection for Level II nodal metastasis. - **Weight loss** suggests systemic disease consistent with advanced carcinoma. - Nasopharyngeal carcinoma is **cytokeratin-positive** (epithelial origin) and frequently presents with isolated neck mass **without nasal symptoms** in early stages. *Skin* - While cutaneous squamous cell carcinoma can metastasize to cervical nodes, it would require a **visible primary skin lesion** on the head, neck, or scalp, which would be evident on physical examination. - Skin primaries more commonly metastasize to **posterior cervical nodes (Level V)** from scalp lesions, not upper anterior cervical nodes. - This presentation is **far less common** than mucosal head and neck primaries for isolated cervical metastasis. *Nerve sheath* - Nerve sheath tumors such as **schwannomas** or **neurofibromas** are of mesenchymal origin and stain positive for **S-100 protein**, not cytokeratin. - These tumors are typically **benign and mobile**, not firm and immobile like metastatic carcinoma. *Bone* - Primary bone tumors (e.g., osteosarcoma) do not express **cytokeratin** and would not present with isolated cervical lymphadenopathy. - Bone tumors would show characteristic imaging findings and typically metastasize to lungs, not regional lymph nodes. *Muscle* - Muscle-derived tumors such as **rhabdomyosarcoma** or **leiomyosarcoma** are mesenchymal in origin. - These tumors stain positive for **desmin** and **actin**, not cytokeratin, which is specific to epithelial cells.

Lymphatic drainage pathways US Medical PG Question 3: A 32-year-old man comes to the physician because of a 3-week history of cough, weight loss, and night sweats. He migrated from Sri Lanka 6 months ago. He appears emaciated. His temperature is 38.1°C (100.5°F). Physical examination shows enlargement of the right supraclavicular lymph node. Chest and abdominal examination show no abnormalities. An interferon-gamma assay is positive. A biopsy specimen of the cervical lymph node is most likely to show the causal organism in which of the following locations?

• A. Mantle zone
• B. Medullary sinus
• C. Germinal center
• D. Subcapsular sinus
• E. Paracortex (Correct Answer)

Lymphatic drainage pathways Explanation: ***Paracortex*** - The patient's symptoms (cough, weight loss, night sweats, fever), recent migration from an endemic area (Sri Lanka), **supraclavicular lymphadenopathy**, and positive **interferon-gamma release assay (IGRA)** strongly suggest **tuberculosis**. - In tuberculous lymphadenitis, **caseating granulomas** containing *Mycobacterium tuberculosis* organisms characteristically form in the **paracortex** (T-cell zone). - The **paracortex** is where **cell-mediated immunity** occurs, with T cells interacting with infected macrophages and dendritic cells to form the **epithelioid granulomas** with **Langhans giant cells** that are pathognomonic for TB. - The organisms are found within these **granulomas**, which predominantly occur in the paracortical (interfollicular) region. *Mantle zone* - The **mantle zone** primarily contains **naïve B cells** surrounding germinal centers. - This is a B-cell area not typically involved in granuloma formation or mycobacterial infection. *Germinal center* - **Germinal centers** are sites of B cell proliferation, somatic hypermutation, and antibody class switching. - TB is a disease of **cell-mediated immunity** (T cells and macrophages), not humoral immunity, so granulomas do not form in germinal centers. *Medullary sinus* - The **medullary sinuses** are channels in the medulla of the lymph node through which lymph flows toward the efferent lymphatic vessels. - While macrophages line these sinuses and may contain some organisms in acute infections, the characteristic **caseating granulomas** of chronic tuberculous lymphadenitis form in the **paracortex**, not in the sinuses. *Subcapsular sinus* - The **subcapsular sinus** is the initial entry point for afferent lymph into the lymph node. - While this is where pathogens first enter, chronic granulomatous infections like TB develop their characteristic pathology deeper in the node, specifically in the **paracortex** where T-cell-mediated granuloma formation occurs.

Lymphatic drainage pathways US Medical PG Question 4: A 39-year-old man presents with painless swelling of the right testis and a sensation of heaviness. The physical examination revealed an intra-testicular solid mass that could not be felt separately from the testis. After a thorough evaluation, he was diagnosed with testicular seminoma. Which of the following group of lymph nodes are most likely involved?

• A. Superficial inguinal lymph nodes (lateral group)
• B. Deep inguinal lymph nodes
• C. Superficial inguinal lymph nodes (medial group)
• D. Para-rectal lymph nodes
• E. Para-aortic lymph nodes (Correct Answer)

Lymphatic drainage pathways Explanation: ***Para-aortic lymph nodes*** - The **testes** develop in the abdomen and descend into the scrotum, retaining their original lymphatic drainage. Therefore, **testicular cancer** typically metastasizes to the **para-aortic** (or retroperitoneal) lymph nodes, which are located near the renal veins at the level of L1-L2. - This is the primary lymphatic drainage pathway for the testes. *Superficial inguinal lymph nodes (lateral group)* - These lymph nodes primarily drain the skin of the **scrotum**, perineum, and lower limbs, but not the **testes** themselves. - Involvement would suggest spread to the scrotal skin or compromised lymphatic flow due to prior scrotal surgery or infection, which is not indicated here. *Deep inguinal lymph nodes* - **Deep inguinal lymph nodes** drain structures deeper in the leg and gluteal region, as well as receiving efferent vessels from the superficial inguinal nodes. - They are not the primary drainage site for the **testes**. *Superficial inguinal lymph nodes (medial group)* - Similar to the lateral group, the **medial superficial inguinal lymph nodes** primarily drain the external genitalia (excluding the testes), perineum, and lower abdominal wall. - They are not the direct drainage route for **testicular cancer**. *Para-rectal lymph nodes* - **Para-rectal lymph nodes** are located near the rectum and are involved in the drainage of the rectum and lower sigmoid colon. - They have no direct connection to the lymphatic drainage of the **testes**.

Lymphatic drainage pathways US Medical PG Question 5: A 59-year-old woman presents to her primary care provider with a 6-month history of progressive left-arm swelling. Two years ago she had a partial mastectomy and axillary lymph node dissection for left breast cancer. She was also treated with radiotherapy at the time. Upon further questioning, she denies fever, pain, or skin changes, but reports difficulty with daily tasks because her hand feels heavy and weak. She is bothered by the appearance of her enlarged extremity and has stopped playing tennis. On physical examination, nonpitting edema of the left arm is noted with hyperkeratosis, papillomatosis, and induration of the skin. Limb elevation, exercise, and static compression bandaging are started. If the patient has no improvement, which of the following will be the best next step?

• A. Diethylcarbamazine
• B. Low molecular weight heparin
• C. Endovascular stenting
• D. Vascularized lymph node transfer (Correct Answer)
• E. Antibiotics

Lymphatic drainage pathways Explanation: ***Vascularized lymph node transfer*** - This patient presents with **secondary lymphedema** due to axillary dissection and radiotherapy, which has not responded to conservative management. - **Vascularized lymph node transfer** is a surgical option that involves transplanting healthy lymph nodes to the affected area to re-establish lymphatic drainage pathways, offering a more definitive solution for refractory cases. *Diethylcarbamazine* - **Diethylcarbamazine** is an anti-filarial drug used to treat lymphedema caused by **parasitic infections**, specifically filariasis. - The patient's lymphedema is secondary to breast cancer treatment, not parasitic infection, making this a **misdirected treatment**. *Low molecular weight heparin* - **Low molecular weight heparin** is an anticoagulant used to prevent or treat **venous thromboembolism (VTE)**. - While patients with cancer are at increased risk for VTE, her symptoms are consistent with lymphedema and not thrombosis, which would typically present with more acute pain and swelling, making this an inappropriate treatment. *Endovascular stenting* - **Endovascular stenting** is a procedure used to open blocked or narrowed **blood vessels**, such as in peripheral artery disease or venous obstruction. - Her condition is specifically lymphedema, a lymphatic circulation issue, not a vascular obstruction, so stenting would not address the underlying problem. *Antibiotics* - **Antibiotics** are used to treat **bacterial infections**, which can complicate lymphedema (e.g., cellulitis). - While chronic lymphedema causes skin changes (hyperkeratosis, papillomatosis, induration), the patient shows no signs of **acute infection** such as fever, pain, erythema, or warmth, making empirical antibiotics unnecessary at this stage.

Lymphatic drainage pathways US Medical PG Question 6: A 35-year-old woman volunteers for a study on respiratory physiology. Pressure probes A and B are placed as follows: Probe A: between the parietal and visceral pleura Probe B: within the cavity of an alveolus The probes provide a pressure reading relative to atmospheric pressure. To obtain a baseline reading, she is asked to sit comfortably and breathe normally. Which of the following sets of values will most likely be seen at the end of inspiration?

• A. Probe A: -6 mm Hg; Probe B: 0 mm Hg (Correct Answer)
• B. Probe A: 0 mm Hg; Probe B: -1 mm Hg
• C. Probe A: -4 mm Hg; Probe B: 0 mm Hg
• D. Probe A: -4 mm Hg; Probe B: -1 mm Hg
• E. Probe A: -6 mm Hg; Probe B: -1 mm Hg

Lymphatic drainage pathways Explanation: ***Probe A: -6 mm Hg; Probe B: 0 mm Hg*** - At the **end of inspiration**, the **intrapleural pressure (Probe A)** is at its most negative, typically around -6 to -8 cm H2O (equivalent to -4 to -6 mmHg), reflecting the maximum expansion of the thoracic cavity. - At the **end of inspiration**, just before exhalation begins, there is **no airflow**, so the **intrapulmonary pressure (Probe B)** equalizes with atmospheric pressure, resulting in a 0 mm Hg reading. *Probe A: 0 mm Hg; Probe B: -1 mm Hg* - An **intrapleural pressure of 0 mm Hg** would indicate a **pneumothorax** since it should always be negative to prevent lung collapse. - An **intrapulmonary pressure of -1 mm Hg** would indicate that **inspiration is still ongoing**, as air would be flowing into the lungs. *Probe A: -4 mm Hg; Probe B: 0 mm Hg* - While an **intrapulmonary pressure of 0 mm Hg** is correct at the end of inspiration, an **intrapleural pressure of -4 mm Hg** is typical for the **end of expiration (Functional Residual Capacity)** during quiet breathing, not the end of inspiration. - The **intrapleural pressure becomes more negative** during inspiration due to increased thoracic volume, so -4 mm Hg would be insufficient. *Probe A: -4 mm Hg; Probe B: -1 mm Hg* - An **intrapleural pressure of -4 mm Hg** is the normal pressure at the **end of expiration**, not the end of inspiration, where it becomes more negative. - An **intrapulmonary pressure of -1 mm Hg** indicates that **inspiration is still in progress**, not at its end, as air would still be flowing into the lungs. *Probe A: -6 mm Hg; Probe B: -1 mm Hg* - While an **intrapleural pressure of -6 mm Hg** is consistent with the end of inspiration, an **intrapulmonary pressure of -1 mm Hg** means that **airflow is still occurring into the lungs**. - At the **very end of inspiration**, just before the start of exhalation, airflow momentarily ceases, and intrapulmonary pressure becomes zero relative to the atmosphere.

Lymphatic drainage pathways US Medical PG Question 7: An otherwise healthy 39-year-old woman presents to her primary care provider because of right-leg swelling, which started 4 months ago following travel to Kenya. The swelling has been slowly progressive and interferes with daily tasks. She denies smoking or alcohol use. Family history is irrelevant. Vital signs include: temperature 38.1°C (100.5°F), blood pressure 115/72 mm Hg, and pulse 99/min. Physical examination reveals non-pitting edema of the entire right leg. The overlying skin is rough, thick and indurated. The left leg is normal in size and shape. Which of the following is the most likely cause of this patient condition?

• A. Obstruction of lymphatic channels (Correct Answer)
• B. Hypoalbuminemia
• C. Lymphatic hypoplasia
• D. Venous thromboembolism
• E. Persistent elevation of venous pressures

Lymphatic drainage pathways Explanation: ***Obstruction of lymphatic channels*** - The patient's history of travel to **Kenya**, along with **progressive, non-pitting edema** of the entire right leg and **rough, thick, indurated skin**, strongly suggests **filariasis**, a parasitic infection that obstructs lymphatic channels. - **Obstruction of lymphatic channels** leads to **lymphedema**, which characteristically presents with the described symptoms and skin changes (e.g., **elephantiasis**). *Hypoalbuminemia* - **Hypoalbuminemia** typically causes **generalized, pitting edema** due to decreased plasma oncotic pressure, not localized, non-pitting edema in a single limb. - There are no clinical signs to suggest **hepatic** or **renal dysfunction** that would cause significant hypoalbuminemia. *Lymphatic hypoplasia* - **Lymphatic hypoplasia** (primary lymphedema) is usually congenital or develops in early life and would not typically manifest acutely after travel in a 39-year-old. - While it causes lymphedema, the travel history points to an acquired cause rather than a congenital defect. *Venous thromboembolism* - **Venous thromboembolism** (DVT) typically presents with acute onset of **painful, edematous** limb, often with **pitting edema**, and can be associated with warmth and erythema. - The **slowly progressive** nature of the swelling over 4 months and **non-pitting edema** are less consistent with acute DVT. *Persistent elevation of venous pressures* - **Persistent elevation of venous pressures** (e.g., chronic venous insufficiency) leads to **pitting edema**, skin discoloration (**hyperpigmentation**), and **ulcerations**, not the rough, thick, indurated skin seen in this case. - This condition is also typically associated with factors like prolonged standing or obesity, which are not mentioned here.

Lymphatic drainage pathways US Medical PG Question 8: A pathologist receives a patient sample for analysis. Cells in the sample are first labeled with fluorescent antibodies and then passed across a laser beam in a single file of particles. The light scatter and fluorescent intensity of the particles are plotted on a graph; this information is used to characterize the sample. This laboratory method would be most useful to establish the diagnosis of a patient with which of the following?

• A. Ventricular septal defect and facial dysmorphism with low T-lymphocyte count
• B. Painless generalized lymphadenopathy with monomorphic cells and interspersed benign histiocytes on histology
• C. Pancytopenia and deep vein thrombosis with intermittent hemoglobinuria (Correct Answer)
• D. Multiple opportunistic infections with decreased CD4 counts
• E. Vesicular lesions with dermatomal distribution and dendritic corneal ulcers

Lymphatic drainage pathways Explanation: ***Pancytopenia and deep vein thrombosis with intermittent hemoglobinuria*** - The described laboratory method is **flow cytometry**, which is the **gold standard for diagnosing paroxysmal nocturnal hemoglobinuria (PNH)** by detecting the absence of **CD55** and **CD59** on red blood cells due to impaired GPI anchor synthesis. - PNH classically presents with **pancytopenia**, **hemolytic anemia** (leading to hemoglobinuria), and a high risk of **thrombosis** (e.g., deep vein thrombosis). *Ventricular septal defect and facial dysmorphism with low T-lymphocyte count* - This clinical picture suggests **DiGeorge syndrome**, which involves a developmental defect of the **third and fourth pharyngeal pouches**, leading to thymic hypoplasia and **T-cell deficiency**. - While flow cytometry is used to quantify T-lymphocyte subsets (e.g., CD3, CD4, CD8), the primary method for diagnosing DiGeorge syndrome is **fluorescent in situ hybridization (FISH)** for a **22q11 deletion**, making it less ideal for flow cytometry diagnosis. *Painless generalized lymphadenopathy with monomorphic cells and interspersed benign histiocytes on histology* - This description with "**monomorphic cells**" is more consistent with certain **non-Hodgkin lymphomas** (e.g., Burkitt lymphoma) rather than Hodgkin lymphoma, which typically shows a **polymorphic** cellular infiltrate. - While flow cytometry can be useful in characterizing lymphomas by identifying cell surface markers, the diagnosis is primarily established by **lymph node biopsy and histopathology** with **immunohistochemistry**, making flow cytometry a supplementary rather than primary diagnostic tool. *Multiple opportunistic infections with decreased CD4 counts* - This presentation is highly suggestive of **HIV infection leading to AIDS**. The "decreased CD4 counts" are a key diagnostic and prognostic marker. - While flow cytometry is used to **monitor CD4 cell counts** in HIV patients, the initial diagnosis of HIV is established via **antibody/antigen combination tests** and confirmed by **Western blot** or **PCR for viral load**, not by flow cytometry. *Vesicular lesions with dermatomal distribution and dendritic corneal ulcers* - This clinical presentation points to **herpes zoster ophthalmicus** (shingles affecting the eye due to **varicella-zoster virus** reactivation). - Diagnosis is primarily **clinical** based on the characteristic rash and eye findings, although **PCR** of vesicular fluid can confirm VZV infection. Flow cytometry has no role in this diagnosis.

Lymphatic drainage pathways US Medical PG Question 9: A 23-year-old woman presents to her primary care physician with 3 days of fatigue and back pain after she started a drug for malaria prophylaxis. She says that her urine has also been darker over the same time period. Her past medical history is significant for allergies as well as a broken elbow that was treated in a cast 10 years ago. She does not take any medications, does not smoke, and drinks socially. Peripheral blood smear reveals both red blood cells with dark intracellular inclusions as well as abnormally shaped red blood cells. The immune cells responsible for the shape of these red blood cells are located in which of the following places?

• A. Lymph nodes
• B. Red pulp of the spleen (Correct Answer)
• C. Bone marrow
• D. White pulp of the spleen
• E. Blood vessels

Lymphatic drainage pathways Explanation: ***Red pulp of the spleen*** - The patient's symptoms (fatigue, back pain, dark urine after malaria prophylaxis) and lab findings (**dark intracellular inclusions** and abnormally shaped red blood cells) suggest **G6PD deficiency**, leading to **hemolytic anemia**. - The **red pulp of the spleen** is where old or damaged red blood cells, including those with Heinz bodies (intracellular inclusions) or abnormal shapes, are **phagocytosed** by macrophages, thus "shaping" them or removing severely affected cells. *Lymph nodes* - **Lymph nodes** are primarily involved in filtering lymph and are major sites for adaptive immune responses, housing B and T lymphocytes. - They are not the primary sites for the destruction or "shaping" of red blood cells. *Bone marrow* - The **bone marrow** is the primary site of **hematopoiesis**, where red blood cells are produced, not where they are destroyed or undergo physical shaping due to immune cell action in hemolysis. - While macrophages are present, their main role in marrow is related to erythropoiesis (e.g., central macrophage in erythroblastic islands) and debris clearance, not erythrocyte shaping in peripheral circulation. *White pulp of the spleen* - The **white pulp of the spleen** is rich in lymphocytes and is the site of immune responses, similar to lymph nodes. - It is involved in adaptive immunity and not directly engaged in the physical destruction or "shaping" of red blood cells during hemolysis. *Blood vessels* - **Blood vessels** are conduits for blood transport and are not primary sites for the physical destruction or shaping of red blood cells by immune cells. - While some hemolysis can occur intravascularly, the immune cells responsible for removing and "shaping" damaged red blood cells (like macrophages) are predominantly organ-resident.

Lymphatic drainage pathways US Medical PG Question 10: Arrange in sequence the structures involved in the direct pathway (1=Striatum, 2=GPi, 3=Thalamus, 4=Cortex output, 5=Cortex input):-

• A. 1,3,4,2,5
• B. 5,1,2,3,4 (Correct Answer)
• C. 1,2,3,4,5
• D. 5,4,2,3,1
• E. 5,1,3,2,4

Lymphatic drainage pathways Explanation: ***5,1,2,3,4*** - The direct pathway of the basal ganglia begins with the **cortex** (5) sending excitatory signals to the **striatum** (1). - The striatum then inhibits the **internal globus pallidus (GPi)** (2), which disinhibits the **thalamus** (3), leading to excitation of the **cortex** (4). - This is the correct sequence: **Cortex input → Striatum → GPi → Thalamus → Cortex output**. *1,3,4,2,5* - This sequence is incorrect as it starts with the striatum instead of cortical input. - The direct pathway does not begin with striatal activity; the cortex must first activate the striatum. *1,2,3,4,5* - This order is incorrect because it implies the pathway starts at the striatum rather than the cortex. - The cortex should be the starting point (5) and the ending point (4) of the motor loop. *5,4,2,3,1* - This sequence is incorrect as it places cortex output (4) before the striatum receives input. - This reverses the functional flow and does not follow the **disinhibitory mechanism** of the direct pathway. *5,1,3,2,4* - This sequence incorrectly places the thalamus (3) before the GPi (2). - In the direct pathway, the striatum must first inhibit the GPi before the thalamus can be disinhibited.

Lymphatic drainage pathways Flashcard 1 of 7

Question: The CD8+ T-cell response in infectious mononucleosis leads to lymphadenopathy, especially in the _____ nodes

Answer: posterior cervical (specific)

Lymphatic drainage pathways Flashcard 2 of 7

Question: Which lymph node cluster drains the skin above the umbilicus? _____

Answer: Axillary

Lymphatic drainage pathways Flashcard 3 of 7

Question: The _____ duct drains lymph from the right side of the body above the diaphragm

Answer: right lymphatic

Lymphatic drainage pathways Flashcard 4 of 7

Question: Which lymph node cluster drains the posterior calf? _____

Answer: Popliteal

Lymphatic drainage pathways Flashcard 5 of 7

Question: What lymph node cluster drains the nasal cavity, nasopharynx, and auditory tubes?_____

Answer: Retropharyngeal lymph nodes

Lymphatic drainage pathways Flashcard 6 of 7

Question: Medullary sinuses within lymph nodes communicate with the _____ lymphatics

Answer: efferent

Lymphatic drainage pathways Flashcard 7 of 7

Question: lymphatics

Answer: mesoderm