Lymph Node

ball-shaped organ of the immune system; garrisons of B, T, and other immune cells. filters lymph; site of lymphocyte proliferation and differentiation; usually in series along lymph channels

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Thymus -

paired lobes, subdivided into lobules, and thin capsule is present, with incomplete septa

Embryonic deriv: 3rd pharyngeal pouch and part of 4th

Cortex: (1) densely packed lymphocytes undergoing selection, differentiation, & maturation

(2) several populations of thymic epithelial cells

(3) macrophages (busily phagocytosing apoptotic lymphocytes)

Medulla: (1) antigen-presenting dendritic cells

(2) more populations of thymic epithelial cells

(3) hassall's corpuscles

(4) mature T-cells, undergoing more selection, not as densely packed as in the cortex

Thymus -

paired lobes, subdivided into lobules, and thin capsule is present, with incomplete septa

Functions: T-cell production and produce humoral factors (thymosin) which affect the maturation of lympocytes in other lymphatic organs

Embryonic deriv: 3rd pharyngeal pouch and part of 4th

Cortex: (1) densely packed lymphocytes undergoing selection, differentiation, & maturation

(2) several populations of thymic epithelial cells

(3) macrophages (busily phagocytosing apoptotic lymphocytes)

Medulla: (1) antigen-presenting dendritic cells

(2) more populations of thymic epithelial cells

(3) hassall's corpuscles

(4) mature T-cells, undergoing more selection, not as densely packed as in the cortex

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Spleen

Functions: filters blood; produces lymphocytes, w/ B-cells producing Abs; Destroys worn-out cells; hematopoiesis in the embryo; blood storage - only a minor function in healthy humans (enlarged spleens may sequester clinically significant volumes of platelets)

White pulp - fresh state appearance, staining dark blue in H&E due to lymphocytes; central arteries (follicular arteries) are present; they are surrounded by a periarterial lymphocytic sheath (PALS). T-lymphocytes are most abundant in the PALS. Nodules are present at intervals along the course of the central arteries and here B-lymphocytes prevail.

Red pulp (75% of volume) - consists of splenic cords (tissue between the sinusoids and contains many macrophages and erythrocytes) and venous sinusoids; elongated endothelial cells line the sinusoids and are enclosed by circular reticular fibers (the barrel analogy with staves surrounded by hoops).

Blood supply  - (1) Trabecular arteries - larger arteries in fibrous trabecule

(2) central arteries in white pulp - the PALS and lymph nodules surround these

(3) Penicillar (straight arteries) - These are branches of the central arteries; Near their ends these vessels (really arterioles) are ensheated by a layer of macrophages, reticular cells, and lymphatic cells. At their ends the penicillar arteries are called arterial capillaries.

Open circulation - arterial capillaries emptying into splenic cord spaces; blood passing between endothelial cells of sinusoids to get back to circulation (as opp. to closed circulation)

Venous sinusoids - elongated endothelial cells; from them, the blood courses to pulp (connecting) venules and veins which then enter the trabecular veins

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Palatine tonsils

- - Largest of the tonsils
- - Covered by stratified squamous mucosa
- - Deep crypts

All tonsils are...

(1) covered with mucosa and consist of aggregates of nodules with efferent lyph vessels only. The epithelium is often infiltrated with lymphocytes

(2) MALT organs and are part of a collection of MALT tissues collectively called Waldeyer's ring, because they are in a vaguely ring-like arrangement around the superior portion of the pharynx

Pharyngeal tonsils (adenoid)

- - Small, shallow crypts
- - Pseudostratified ciliated columnar
(respiratory epithelium) –squamous metaplasia is common

All tonsils are...

(1) covered with mucosa and consist of aggregates of nodules with efferent lyph vessels only. The epithelium is often infiltrated with lymphocytes

(2) MALT organs and are part of a collection of MALT tissues collectively called Waldeyer's ring, because they are in a vaguely ring-like arrangement around the superior portion of the pharynx

Lingual Tonsils

- - Small, shallow crypts
- - Covered by stratified squamous mucosa with underlying tongue muscle

All tonsils are...

(1) covered with mucosa and consist of aggregates of nodules with efferent lyph vessels only. The epithelium is often infiltrated with lymphocytes

(2) MALT organs and are part of a collection of MALT tissues collectively called Waldeyer's ring, because they are in a vaguely ring-like arrangement around the superior portion of the pharynx

Where on the larynx is respiratory epithelium NOT found?

Where on the larynx are mucous glands NOT found in the lamina propria?

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Respiratory epithelium: upper surface of epiglottis and true vocal folds (stratified squamous)

Mucous glands: true vocal folds, vocalis ligament, and vocalis muscle

What two distinguishing factors does this structure have?

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Bronchus

Smooth muscle: bundles spiral around the lumen in the lamina propria

Cartilage (hyaline): discontinuous plates; plates get smaller peripherally, where they tend to be found at bifurcations

What two distinguishing factors does this structure have?

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Bronchus

Smooth muscle: bundles spiral around the lumen in the lamina propria

Cartilage (hyaline): discontinuous plates; plates get smaller peripherally, where they tend to be found at bifurcations

What two distinguishing factors does this structure have?

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Bronchus

Smooth muscle: bundles spiral around the lumen in the lamina propria

Cartilage (hyaline): discontinuous plates; plates get smaller peripherally, where they tend to be found at bifurcations

Respiratory acinus

Composed of Respiratory bronchioles (RB), Aveolar Ducts (AD), Alveolar sacs (cluster of aveoli with common opening), alveoli - the functional part of gas exchange

Alveolar wall, thick wall

separate basal lamina for alveolar epithelim and endothelium

forms a tissue space containing many elastic fibers (elastin), important in the elastic recoil of the normal lung, allowing the lung to stretch to accomodate inhaled air; becomes like a string-like tether supporting bronchioles by attachment to lung parechyma (alveoli).

Collagen fibers, macrophages, and other connective tissue cells are also present here.

(silver stain highlights the elastin in alveolar walls)

Alveoli (air space)

Air space: Macrophages (or dust cells)

Surfactant: lowers surface tension

Walls have thick and thin parts.

Alveolar pores: equalize interalveolar air pressure