Hematopoietic & Lymphatic Systems – Comprehensive Study Notes

Two major body fluids
- Blood
- Lymph
Shared purpose: distribution of protective factors, nutrients, O $_2$ , electrolytes, & removal of wastes.
Parallel flow: blood in cardiovascular vessels; lymph in lymphatic vessels that ultimately re-enters blood at the subclavian veins.

General functions of blood
- Transportation: nutrients, waste products, respiratory gases, hormones
- Regulation: fluid–electrolyte balance, acid–base balance, body temperature
- Protection: WBC-mediated immunity & platelet-mediated hemostasis.
Physical composition
- $91\%$ – $92\%$ liquid (plasma)
- $8\%$ – $9\%$ solids (formed elements).
Plasma as a solvent & transport medium
- Dissolved nutrients: glucose, amino acids, lipids
- Electrolytes: Na $^+$ , K $^+$ , Ca $^{2+}$ , Cl $^-$
- Hormones, vitamins, antibodies, metabolic wastes
- CO $<em>2$ carried mainly as bicarbonate (HCO $</em>3^-$ ).
Major plasma proteins
- Albumin (most abundant): maintains colloid osmotic pressure, thus helping regulate blood volume & pressure.
- Fibrinogen group: prothrombin, fibrinogen, other clotting factors that circulate in inactive form until needed.
- Globulins
- Transport globulins: move lipids & fat-soluble vitamins
- $\gamma$ -globulins: antibodies that confer immunity.

Life span ≈ $120\text{ days}$ ; continuous production required.
Site of formation: red bone marrow → stem cells undergo mitosis.
Requirements for erythropoiesis
- DNA synthesis: vitamin $B_{12}$ , folic acid
- Cytoplasmic maturation / Hb synthesis: adequate protein & iron.
Destruction & recycling
- Senescent RBCs removed by reticuloendothelial cells in spleen, liver, red marrow.
- Iron recycled for new Hb; excess stored in liver (ferritin/hemosiderin).
- Heme → bilirubin → liver → bile → duodenum → gives stool its brown color.
Pathologic note: ↑RBC destruction or liver dysfunction → ↑bilirubin → jaundice (yellow sclera & skin in light-skinned individuals).

Protective roles: destroy damaged tissue, detoxify foreign proteins, fight infection, participate in immune response.
Sites of production: spleen, lymph nodes, thymus, red marrow.
Five types
- Neutrophils
- Eosinophils
- Basophils
- Lymphocytes
- Monocytes.

Components: lymph vessels, lymph fluid, nodes, nodules, spleen, thymus.
Primary functions
- Returns interstitial fluid & proteins to bloodstream.
- Produces lymphocytes & antibodies for immune defense against pathogens, malignant cells, foreign proteins.

Permeable capillaries in most tissues absorb excess fluid/proteins.
One-way flow aided by skeletal muscle compression.
Fluid passes through sequential lymph nodes/nodules → phagocytosis & immune surveillance.
Nodes also generate lymphocytes & monocytes.

Hematopoietic & immunologic roles
- Produces lymphocytes & monocytes that enter circulation.
- Fixed plasma cells → antibody production.
- Fixed macrophages → phagocytize blood-borne pathogens/foreign substances.
Clinical note: post-splenectomy → ↑susceptibility to encapsulated bacteria (e.g., pneumococci → pneumonia).

Location: posterior to thyroid.
Large in fetus/infant; involutes with age.
Site of T-lymphocyte maturation (recognition of antigens; cell-mediated immunity).
Once T cells colonize spleen & nodes, population self-perpetuates despite thymic shrinkage.

B cells (humoral immunity)
- Originate in embryonic bone marrow.
- Recognize extracellular antigens; differentiate into plasma cells → produce antibodies (appear in $\gamma$ -globulin fraction of plasma).
T cells (cell-mediated immunity)
- Two cooperative reactions:
- Helper T cells activate B cells (humoral) & orchestrate overall response.
- Suppressor T cells down-regulate helper T activity once antigen cleared.
- Cell-mediated pathway: activated T cells → memory T cells (future recognition) + killer/cytotoxic T cells (destroy pathogen via membrane disruption).
Interactive paradigm: Humoral & cellular arms often synergize for full immunity.

Plasma viscosity: slight ↑, often reflecting total-body-fluid ↓.
Bone marrow output: mild ↓ in RBCs & WBCs, though counts remain within normal limits unless stressed.
T-cell profile
- Absolute number unchanged, but higher proportion immature.
- Helper:suppressor ratio ↑ → overall immune response ↓.
- Result: ↑ susceptibility to infections, esp. respiratory & urinary; ↑ risk of nosocomial infections.
Altered clinical presentations
- Blunted fever response; classic infection symptoms (pain, chills) may be absent.
- Examples:
1. Pneumonia without fever/chills.
2. UTIs without dysuria.
3. Silent peritonitis/appendicitis despite severe illness.
4. Delayed/attenuated reaction to tuberculosis skin test.
Humoral immunity note: Women > $55$ yrs show lower tetanus-toxoids antibody titers → potential need to reconsider immunization schedules.

General definition: inadequate RBC number or insufficient hemoglobin.
Types & typical etiologies
- Iron-deficiency anemia: poor intake, chronic blood loss, malabsorption, ↑ demand.
- Pernicious anemia: ↓ intake/absorption of vitamin $B_{12}$ .
- Folic-acid-deficiency anemia: poor nutrition, chronic alcoholism, malabsorptive disorders (e.g., Crohn disease).

Pathophysiology: uncontrolled proliferation of immature WBCs; can be acute or chronic; further classified by cell lineage.
Clinical associations: anemia & hemorrhage (due to thrombocytopenia) common.
Older-adult prevalence: Chronic lymphocytic leukemia (CLL) most common; mean diagnosis age $72\text{ yrs}$ .
Prognosis: life expectancy spans few to $\approx20$ yrs depending on disease stage & overall health.

Blood donation & transfusion: understanding plasma proteins & formed elements key for safe transfusion practices and volume replacement therapy.
Elder care: clinicians must adapt assessment strategies – monitor infections without relying solely on fever/pain; evaluate immunization status.
Surgical considerations: splenectomy patients require vaccination & prophylactic antibiotics due to compromised splenic function.
Nutrition/public health: highlight need for adequate iron, $B_{12}$ , folate intake in aging populations to mitigate anemia risk.