A&P II Chapters 19 & 20: Blood Vessels and Lymphatic System

Comprehensive vocabulary flashcards covering cardiovascular blood vessel structure, hemodynamics, blood pressure regulation, and the lymphatic system based on A&P II Chapters 19 and 20.

Tunica intima

The innermost vessel layer consisting of simple squamous endothelium, underlying connective tissue, and an internal elastic membrane in many arteries, providing a smooth, low-friction blood-contacting surface.

Tunica media

The middle vessel layer containing smooth muscle and elastic fibers; it is especially thick in arteries and controls vasoconstriction and vasodilation to regulate blood flow and resistance.

Tunica externa (adventitia)

The outer collagen-rich connective tissue layer that anchors and protects blood vessels, containing vasa vasorum to supply the walls of large vessels.

Elastic arteries (conducting)

Large arteries, such as the aorta and pulmonary trunk, with abundant elastic lamellae that stretch during systole and recoil during diastole to smooth pulsatile flow.

Muscular arteries (distributing)

Medium-sized arteries, such as the brachial and femoral arteries, characterized by a smooth muscle-rich media that adjusts the delivery of blood to specific organs.

Arterioles (resistance vessels)

Small arteries with one or a few smooth-muscle layers that serve as the major controllers of peripheral resistance and regulate blood delivery to capillary beds.

Continuous capillaries

The most common and least permeable capillaries, characterized by an uninterrupted endothelial lining, intact basement membrane, and small intercellular clefts; found in the skin, muscle, lungs, and central nervous system.

Fenestrated capillaries

Capillaries with an intact basement membrane and endothelial pores (fenestrations) that provide increased permeability for filtration and absorption in tissues such as the kidneys, small intestine, and endocrine glands.

Sinusoid capillaries

The most permeable capillaries, featuring large gaps, an incomplete basement membrane, irregular wide lumens, and slow flow, permitting the passage of large proteins and cells in the liver, spleen, bone marrow, and adrenal medulla.

Vascular shunt

A bypass channel formed by the metarteriole and thoroughfare channel that allows blood to travel directly from a terminal arteriole to a postcapillary venule when precapillary sphincters are closed.

Precapillary sphincters

Cuffs of smooth muscle surrounding the root of each true capillary; their relaxation increases true capillary perfusion, while contraction diverts blood through the vascular shunt.

Capacitance vessels

Veins that serve as blood reservoirs due to their thin walls and large lumens, holding approximately $60\%$ of systemic blood volume at low pressure.

Pulse pressure (PP)

The difference between systolic pressure and diastolic pressure, calculated using the formula $\text{PP} = \text{systolic pressure} - \text{diastolic pressure}$.

Mean arterial pressure (MAP)

The average pressure driving blood forward into tissues, calculated at typical resting heart rates as $\text{MAP} \approx \text{diastolic pressure} + \frac{1}{3}(\text{pulse pressure})$ or $\frac{\text{systolic} + 2 \times \text{diastolic}}{3}$.

Skeletal muscle pump

A mechanism promoting venous return in which contracting skeletal muscles compress veins, forcing blood forward past one-way venous valves that prevent reflux.

Respiratory pump

A venous return mechanism where inspiration increases thoracic volume, lowering intrathoracic pressure and raising abdominal pressure to draw blood toward the heart.

Baroreceptors

Arterial stretch receptors located in the carotid sinuses and aortic arch that detect blood pressure fluctuations and signal the cardiovascular centers in the medulla oblongata.

Angiotensin-converting enzyme (ACE)

An enzyme primarily located in pulmonary vascular endothelium that converts angiotensin I to the potent vasoconstrictor angiotensin II.

Atrial natriuretic peptide (ANP)

A hormone secreted by atrial muscle cells in response to high blood volume and stretch that promotes renal sodium and water excretion, suppresses renin and aldosterone, and lowers blood pressure.

Net filtration pressure (NFP)

The net driving force for capillary fluid movement, defined by the formula $\text{NFP} = (\text{capillary hydrostatic} + \text{interstitial osmotic}) - (\text{capillary osmotic} + \text{interstitial hydrostatic})$.

Lymph

Clear interstitial fluid once it enters lymphatic capillaries, containing water, electrolytes, small amounts of protein, lymphocytes, cellular debris, and sometimes pathogens.

Chyle

Milky, fatty lymph absorbed from the small intestine containing dietary lipids packaged into chylomicrons.

Right lymphatic duct

A large lymphatic vessel that drains lymph from the right upper quadrant (right side of head, neck, thorax, and right upper limb) into the junction of the right internal jugular and right subclavian veins.

Thoracic duct

The main lymphatic vessel that drains lymph from the left side of the head, neck, and thorax, the left upper limb, and the entire lower body into the left internal jugular and subclavian vein junction.

Cisterna chyli

An enlarged lymphatic sac at the base of the thoracic duct that collects fatty lymph from the intestinal trunk and fluid from the lumbar trunks.

Primary lymphoid organs

Organs where lymphocytes are formed and mature, specifically the red bone marrow (site of hematopoiesis and B-cell maturation) and the thymus (site of T-cell maturation).

Secondary lymphoid organs

Peripheral structures where mature lymphocytes encounter antigens and mount immune responses, including lymph nodes, the spleen, tonsils, Peyer's patches, appendix, and MALT.

Hassall's corpuscles

Concentric epithelial reticular structures situated in the thymic medulla that participate in regulatory signaling during T lymphocyte maturation.

Lymph nodes

Small, encapsulated bean-shaped secondary lymphoid organs arranged along lymphatic vessels that filter lymph via macrophages and activate B and T cells.

White pulp

Lymphocyte-rich immune regions of the spleen clustered around central arteries that detect and respond to blood-borne antigens.

Red pulp

Splenic tissue composed of blood-filled sinusoids and splenic cords where resident macrophages phagocytose aged or damaged red blood cells and recycle hemoglobin iron.

Peyer's patches

Aggregated clusters of lymphoid follicles located predominantly in the ileum of the small intestine that monitor luminal antigens and provide mucosal immunity.

Lymphedema

Tissue swelling caused by inadequate lymphatic drainage and subsequent accumulation of protein-rich interstitial fluid, frequently following lymph node resection or obstruction.