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214 Cards in this Set

  • Front
  • Back
respiratory portion
site of O2 and CO2 exchange b/w air and blood; includes respiratory bronchioles and alveoli
conducting portion
pipes air to and from lungs; warms, moistens, and cleanses air - includes nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles – lines w/ciliated pseudostratified columnar ep.
nasal cavity
region of the skull where air enters, and is conditioned and cleaned
anterior portion of nasal cavity; ep. changes from keratinized to respiratory ep.
nasal fossae
2 regions of the nasal cavity divided by nasal septum
olfactory region
olfactory chemoreceptors are found in the olfactory epithelium in the superior conchae
olfactory epithelium
contains basal cells, supporting cells, and olfactory cells – bipolar neurons (apex = dendrite w/afferent axons below basement membrane)
tube connecting pharynx to trachea; contains supporting cartilaginous plates, both hyaline and elastic
avascular, dense regular CT, branched bundles of skeletal tissue
vestibular folds
very vascular, loose CT, adipose, stratified ep.
flap at trachea that protects the larynx – stratified sq. ep., loose CT, elastic cartilage. Contains many lymphocytes.
airway that extends from larynx to bronchi; lined with respiratory mucosa; contains thickest basement membrane in body
tracheal cartilage
horseshoe shaped bands of hyaline cartilage that keep the tracheal lumen open
tracheal muscle
smooth muscle attaches to the perichondrium, bridging open Cs of cartilage; muscle contraction involved in cough reflex
respiratory epithelium
pseudostratified ciliated ep. lining the conducting portion of the respiratory system
ciliated cells
most abundant cell in respiratory ep.; ~ 300 cilia on apical surface of each cell which sweep mucus toward pharynx to be swallowed or expelled
goblet cells
2nd most abundant cells in respiratory epithelium; secrete mucus
basal cells
mitotic cells which adhere to the basement membrane via hemidesmosomes and do not extend to the lamina
submucosal cells
glandular tubes/asini located in the CT below respiratory ep. Connected to lumen via duct. Aid in generation of “sticky carpet”
respiratory organ
distinct sections of an organ, 3 R lobes and 2 L lobes in the lung
visceral pleura
thin inner layer of the pleura; elastic fibers are continuous with pulmonary parenchyma
parietal pleura
thick outer layer of the pleura
serous membrane covering lung; mesothelial cells on CT containing collagen and elastic fibers
cartilage plates replace rings of trachea, fewer goblets and glands, abundant elastic fibers, spiral bundles of smooth muscle
cartilage is absent, no glands, abundant elastic fiber and smooth muscle; diameter  5mm
Terminal bronchioles
lined w/ciliated simple columnar ep. w/interspersed Clara cells
clara cells
plump cuboidal protein producing cells, protect against oxidative pollutants and inflammation
respiratory bronchioles
transition b/w conducting and respiratory portions; ciliated simple columnar and Clara cells become continuous with simple squamous near alveolar interruptions
alveolar ducts
– continuation of resp. bronchiole; walls contain only alveoli and smooth muscle
alveolar sac
alveolar space at duct terminals, no smooth muscle
saclike protrusions of the resp. bronchioles, alveolar ducts, and alveolar sacs lined with squamous alveolar cells – spongy structure of lungs. Site of O2 and CO2 exchange b/w air and blood – held together by reticular and elastic fibers
interalveolar septum
alveolar wall that lies b/w 2 neighboring alveoli – 2 thin squamous layers on either side of a capillary
squamous alveolar cells type I
attenuated squamous cells making up 97% of alveolar lining – readily permeable to gas
great alveolar cells type II (septal cells)
rounded mitotic cells that give rise to type I cells. produce surfactant. Attached to type I via occluding and desmosomal junctions
multi lamellar bodies
vesicles w/in type II cells, continuously released @ apical surface
aqueous coat of lamellar bodies lining alveolar surface, reduces surface tension which reduces effort of breathing and keeps alveoli open
alveolar macrophages
dust cells – brownish deposits found w/in interalveolar septum, often seen in smokers’ lungs
alveolar pores
spaces in interalveolar septum linking neighboring alveoli; equalize air pressure and promote air circulation
blood air barrier
separation between air in the alveoli and blood in the capillaries provided by a) surface lining/cytoplasm of alveolar squamous, b) fused basal laminae of alveolar & endothelial cells, and c) endothelial cytoplasm
The endocrine system is an integrating system that coordinates the activities of cells and organs by sending chemical signals
occurs when the hormones act locally whithout the need for transport by the blood. (ex. Islets of Langerhans are inhibited by hormones secreted by cells on the same islet.)
when the hormone acts on the secreting cell.
when neurons send chemical signals into the blood stream.
process of release of adenohypophysis hormones via nervous impulse passing down axons of the hypothalamus
molecules that function as the chemical signals (messages that transmit regulatory signals). They are released by specialized endocrine cells. They are secreted into the interstitial space then enter capillaries (no ducts are involved). Most act at a distance from site of secretion. Only small quantities needed (pf or ng range).
secretory granule
hormones for release into interstitial space and tehn into capillaries for circulation in blood.
target cell
tissues and organs on which the hormones act. They react because there are receptor sites that recognize the hormones. This initiates intracellular second messengers. Thus hormones will not influence all cells of the body. Endocrine glands are also target organs, providing hormone control through a feedback mechanism.
protein that accepts hormone and initiates secondary messenger.
steroid binding protein
cytoplasmic receptor involved in the mechanism of action of a steroid hormone. Steroid hormones are hydrophobic and enter target cells freely and THEN bind to receptor in cytpoplasm.
second messenger
activates hormonal cascade.
secondary messenger involved in protein and peptide hormone activity.
signal transduction
game of telephone for hormones, e.g., sending the message down the line.
protein kinase
links nervous system to endocrine system via pituitary gland. Regulates metabolic processes and other autonomic activities.
hypophyseal portal system
Portal system between hypothalamus and hypophysis that carries low MW polypeptide hormones from the hypothalamus to the endocrine cells of the pars distalis to regulate secretory activity of adenohypophysis.
hypothalamo-hypophyeal tract
System of 3 known sites of production of hormones that frees 3 groups of hormones. 1)hormones made in hypothalamus and released in p.n., 2) stimulating / inhibiting hormones made in hypothalamus, 3) hormones made in pars distalis
median eminance
a neurohemal organ containing the primary capillary bed of the hypophyseal portal system
paraventricular nucleus
Site in the hypothalamus where oxytocin is produced
supraoptic nucleus
Site in the hypothalamus where ADH is produced
releasing and inhibiting hormones
hypothalamic hormones stored in median eminence, released and transported to P.D. to inhibit / release of hormons
Growth hormone releasing hormone from hypothalamu
Gonadotropin releasing hormone from hypothalamus
local inhibition of other endocrine glands from hypothalamus
prolactin inhibiting hormone to balance prolactin production from hypothalamus
thyrotropin releasing hormone from hypothalamus
corticotropin releasing hormone from hypothalamus
Epiphysis (pinneal)
gland that mediates day length information through secretion of melatonin at night. Found in brain in the midline above diencephalon.
main cells of epiphysis (pineal gland). Interstitial astrocytes.
hormone that affects sleep wake cycles and gonadal function.
Hypophsis (pituitary gland)
lies in sella turcica, develops from oral ectoderm and from nerve tissue. Consists of 2 glands, neurohypophysis and adenohypophysis. Secretes numerous hormones controlling targets.
rathke's pouch
adenohypophysis formed from ectoderm of primitive mouth. This fissure is caused from separation of the base from oral cavity.
sella turcica
location in skull of pituitary gland
portion of hypophysis originating from ectoderm of primitive mouth. Has 3 regions: pas distalis, pars tuberalis and pars intermedia.
porion of hypophysis originating from nerve tissue. Has 2 parts: pars nervosa and infundibulum (neural stalk). Secretes ADH and oxytocin. 2 cell types: pituicytes (glial) and axons from neuronal cell bodies
pars distalis (anterior lobe)
largest portion of adenohypophysis. 3 cell types: Acidophil, Basophil and chromophobes. Pars distalis cells secrete FLAT PEG
secreted by acidophils of Pars distalis. Includes GH or STH
secreted by acidophils of Pars distalis. Includes prolactin
secreted by basophils of Pars distalis. Includes LH and FSH
secreted by basophils of Pars distalis. Includes TSH
secreted by basophils of Pars distalis. Includes ACTH and MSH
pars tuberalis
funnel shaped region surrounding the infundibulum of the neurohypophysis
pars intermedia
middle part of the adenohypophysis that has unknown function in humans. Developed from dorsal portion of rathke's pouch.
neurosecretory cells
cells that secrete the hormones of the neurohypophysis
anti-diurectic hormone, aka vasopressin. Increases water permeability of kidney collecting ducts and promotes smooth muscle contraction. Secreted by neurohypophysis.
hormone released by neurohyphysis, a nona aa cyclic polypeptide. In females, responsible for contraction of uterine smooth muscle and myoepithelial cells of mammary glands
herring bodies
clusters of granules in axonal swellings
type of branched glial cell found in neurohypophysis
Adrenal Gland
mixed gland located above the kidneys
adrenal cortex
outer edge of the adrenal gland, derived from the genital ridge mesoderm
Zona glomerulosa
"zone of cells in rounded clusters located in adrenal cortex, Secrete mineralocorticoids & aldosterone, Regulated by kidney & lung: renin-angiotensin system
Secreted in the zona glomerulosa, stimulates resorption of Na by epithelia cells in kidney, salivary and sweat glands
Secreted in the zona glomerulosa, stimulates absorption of Na and Cl ions in kidney, which leads to increase in bp
Zona fasciculate
middle layer of polygonal cells in adrenal cortex, arranged in cords, secretes glucocorticoids, main target of ACTH
secreted in the zona fasciculate, stimulate the production of glucose and the conversion of glucose to glycogen
secreted in the zona fasciculate, decreases the uptake of glycogen
zona reticularis
zone in adrenal cortex that is closest to the medulla, secretes weak androgens
androgen secreted by the zona reticularis in the adrenal cortex, Tumor: masculinization of women, gynecomastia in men
adrenal medulla
located in center of adrenal gland and derived from neural crest, Cords of cells surrounded by an extensive network of fenestrated capillaries that drain into the adrenal vein, secretes sex steroids
chromaffin cells
located in adrenal medulla, produces catecholamines,: name given to cells which are responsive to dichromate dye
include epinephrine and norepinephrine, produced in chromaffin cells, mimics the action of the sympathetic nervous system - ”fight or flight” response.
represents 80% of catecholamine output, increased metabolism and O2 consumption, heat production
catecholamine output, "fight or flight" response
ganglion cells
cells of the adrenal medulla, accentuating its function as a modified post-ganglionic sympathetic neuron, able to receive neural input, but with no axon or dendrites
Endocrine pancreas
entire pancreas derived from ENDODERM (like thyroid), cords of epithelial cells supported by reticular fibers, serous acini (exocrine part of pancreas) surround the islet and their secretions are collected by a network of ducts
Islets of Langerhans
located in the pancreas, roughly spherical aggregate of endocrine cells surround by a fenestrated capillary network
beta cells
basophilic cells in islets of langerhans, produce insulin
made by beta cells in Islets of Langerhans, stimulates glucose uptake in many cell types, stimulates liver to convert glucose to glycogen, stimulates adipose cells to convert glucose to triglycerides
alpha cells
adicophilic cells in Islets of Langershans, produce glucagon
made by alpha cells in Islets of Langerhans, produce glucagon and store it in cytoplasmic granules, stimulates conversion of glycogen to glucose in LIVER
delta cells
located in the Islets of Langerhans, produce somatostatin
produced by delta cells in Islets of Langerhans, inhibits release of glucagon and insulin (dampens effects of Islet functions)
F cells
located in the islets of Langerhans, secrete pancreatic polypeptide (PP)
pancreatic polypeptide, produced by F cells in the Islets of Langerhans, blocks secretion of stomatostatin and exocrine pancreatic enzymes
thyroid gland
Bilobed organ, lies across 2nd & 3rd cartilaginous rings of trachea, below the larynx, derived from endoderm,
lined by cuboidal epithelium, polarized cells with basement membrane on outside and apical side toward the follicle center, surrounded by extensive fenestrated capillary network, joined by junctional complexes
jelly-like filling of follicles in thyroid gland, contains thyroglobulin which is linked to iodine
Large protein made by follicle cells in thyroid gland that fill sphere of follicle, have tyrosines that can be iodinated to make MIT or DIT (precursors of T4,T3)
T4 (thyroxine)
(2 DIT combined) acts on all cells to increase metabolism and O2 consumption, heat production
T3 (triiodothyronin)
(1 DIT + 1 MIT) acts on all cells to increase metabolism and O2 consumption, heat production
parafollicular cells
(C or clear cells) larger and clear cells found between thyroid follicles, derived from neural crest, contain eosinophilic granules, produce calcitonin
protein hormone produced by the parafollicular cells, lowers levels of calcium in blood by inhibiting osteoclasts
Parathyroid Gland
Dorsal (posterior) side of thyroid gland, derived from the endoderm of the 3rd and 4th pharyneal pouches, has a capsule of reticular CT
Chief Cells
The dominant cells in the parathyroid gland, cuboidal, round nuclei, produce parathyroid hormone (PTH)
Oxyphil Cells
located in the parathyroid gland, larger cell than chief cell but same size nucleus, unknown function
Renal Capsule
a tough fibrous layer surrounding the kidney
the concave medial border; nerves enter, blood and lymph vessels enter and exit, ureter exits
outer portion of the kidney
inner portion of kidney
Medullar pyramids
the medulla consists of 10 -18 conical or pyramidal structures
Medullary rays
parallel arrays of tubules leaving the base of each pyramid, entering cortex (medullary tissue that extends into the cortex)
Renal Lobe
portion of a kidney consisting of a renal pyramid and the renal cortex above it.
Renal Lobule
part of a renal lobe. It consists of the nephrons grouped around a single medullary ray, and draining into a single collecting duct
Renal Papilla
the tip of the renal pyramid; location where the kidneys converge at a traffic intersection. Transitional epithelium begins to be seen.
Minor calyces
Major calyces
collects urine from multiple minor calyces before passing it through the renal pelvis into the ureter.
Renal Column
a medullary extension of the renal cortex in between the renal pyramids. It allows the cortex to be better anchored. Each column consists of lines of blood vessels and urinary tubes and a fibrous material.
Renal sinus
a cavity within the kidney which is occupied by the renal pelvis, renal calices, blood vessels, nerves and fat.
Area Cribosa
where large collecting ducts enter the minor calyx in the renal papilla
functional unit of the kidney. Consists of: renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and—depending on who you ask—collecting tubules and ducts.
Juxtamedullary nephrons
1/7 of all nephrons; extra long Loop of Henle critical to establishment of a gradient of hypertonicity in the medullary interstitium
Cortical Nephrons
have shorter loops of Henle, don’t extend into medulla
Renal Corpuscle
a glomerulus surrounded by a double-walled epithelial capsule (Bowman’s capsule)
capillary tuft surrounded by Bowman's capsule. Unlike most other capillary beds, the glomerulus drains into an efferent arteriole rather than a venule. The resistance of the arterioles results in high pressure in the glomerulus aiding the process of ultrafiltration where fluids and soluble materials in the blood are forced out of the capillaries and into Bowman's space.
Bowman’s Capsule
Double-walled epithelial capsule; internal (visceral) layer covers the capillaries of the glomerulus, external (parietal) layer forms outer limit of renal corpuscle. The urinary space is the lumen between.
Vascular Pole
where afferent artery enters and the efferent artery exits the renal corpuscle
Afferent arteriole
provides blood supply to each glomerulus
Efferent Arteriole
sends filtered blood through the vasa recta, collecting capillaries intertwined with the convoluted tubules that reabsorb substances before combing with efferent venules from other nephrons to form the renal vein, which rejoins the main bloodstream.
Urinary pole
where the proximal distal tubule begins
specialized cells of the visceral layer, from which arise primary processes, which in turn give rise to numerous foot processes (pedicles, secondary processes), that embrace the capillaries of the glomerulus. Basement membrane fused with basement membrane of the visceral layer.
Foot processes
form a barrier to the urinary space; interdigitate to define elongated spaces, the filtration slits, which work together with the fenestrated capillaries of the glomerulus to allow fluid and particles smaller than albumin to migrate into the urinary space.
Proximal Convoluted Tubule
at the urinary pole, the squamous epithelium of the parietal layer is continuous with the cuboidal epithelium of the PCT. These cells line the lumen with a brush border of microvilli and have apical canaliculi.
Loop of Henle
U-shaped structure consisting of thick and thin descending and ascending limbs.
Distal Convoluted Tubule
thick ascending limb penetrates the cortex to become the DCT. Simple cuboidal epithelium, no brush border, no apical canaliculi.
Collecting Tubules & Ducts
urine passes from DCT into collecting tubules that join up to form larger, straight collecting ducts
Papillary Ducts
Juxtaglomerular Apparatus
=Macula Densa + Juxtaglomerular cells; plays a role in the maintenance of blood pressure in the body
Juxtaglomerular cells
modified smooth muscle cells of the afferent arteriole; detect blood pressure, release renin when stimulated by nerve or macula densa
Macula Densa
portion of the DCT that abuts the afferent arteriole; can detect the ionic strength of the filtrate, signals JG to release renin
Mesangial cells
reside in the matrix between the capillaries of the glomerulus. Function unknown
Interlobular arteries (and veins)
run in between the lobes of the kidney
Arcuate arteries (and veins)
form an arc in the cortex, define boundary between the medulla and cortex
Intralobular arteries (and veins)
run between medullary rays, give rise to afferent arteries, define boundaries between renal lobules
Vasa Recta
(straight vessels) follow the descending limb of the loop of Henle down into the medulla and return with the ascending limb.
Transitional Epithelium
multi-layered cells that can contract and expand, unlike a stratified epithelium, when distended you don’t see a layer of “squamous” nuclei below the luminal layer (i.e. there is no corneum or lucida)
Facet cells
AKA pillow cells. Large, round superficial cells of transitional epithelium. Have special membrane of thick plates that provide osmotic barrier between urine and tissue fluids.
Carries urine from the bladder to the exterior. Apparently, there’s nothing interesting about the female urethra, except that it’s short, only deals with urine, and isn’t that great for keeping pathogens out of the bladder.
Prostatic (urethra)
portion of the male urethra that passes through the prostrate
Membranous (urethra)
stratified or pseudo stratified columnar epithelium. Surrounded by external (voluntary) sphincter.
Bulbous (urethra)
located in the corpus spongiosum, pseudo stratified columnar with stratified and squamous areas.
Pendulous (urethra)
located in the corpus spongiosum pseudo stratified columnar with stratified and squamous areas.
Filtration Barrier
Separates the urinary space and the blood in the capillaries of the glomerulus; consists of the fused basement membrane between podocytes and the fenestrated endothelial cells of the capillaries.
Counter Current Systems
a mechanism used to transfer some property of a fluid from one flowing current of fluid to another across a Semipermeable membrane
originates as blood plasma that leaks from the capillaries of the circulatory system, becoming interstitial fluid, and filling the space between individual cells of tissue. Plasma is forced out of the capillaries and forced back in due to interactions of hydrostatic pressure (favoring movement out of the capillaries) and colloidal osmotic pressure(favoring movement into the capillaries). While out of the capillaries, the fluid mixes with the interstitial fluid, causing a gradual increase in the volume of fluid. Most of the fluid is returned to the capillaries. The excess interstitial fluid is collected by the lymphatic system and is processed by lymph nodes prior to being returned to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid.
secondary/peripheral lymphatic tissue= lymphocyte reactions, diffuse-epithelial surfaces, lymph node-lymph borne antigens, spleen-blood borne antigens

Primary/central lymphatic tissue= lymphocyte production and differentiation, bone marrow, thymus
Diffuse lymphatic tissue
Lymphocytes accumulated in connective tissue
associated with non-keratinizing epithelium with little or incomplete connective tissue capsule, considerable variability in cellularity and organization, stratified squamous epithelium of vagina/esophagus, respiratory epithelium-Bronchus-Associated Lymphatic Tissue (BALT), transitional epithelium, Mucosal-Associated-Lymphatic-Tissue (MALT): tonsils and gut, elements of diffuse lymphatic tissue organization also found in nodules and follicles. Follicles are adynamic collection of B cells. Follicles reflect B cell response to antigen stimulation. Primary (1o ) follicle-accumulation of B cells resulting from antigen-driven B cell proliferation. Secondary (2o) follicle-actively producing B cells-region with mitotic lymphocytes in center=germinal center.
Peyer’s patches
Lymphoid organs located in the sub mucosal tissue of the mammalian gut containing very high proportions of IgA secreting precursor cells. The patches have B and T dependent regions and germinal centres. A specialised epithelium lies between the patch and the intestine. Involved in gut associated immunity.
A worm-shaped process projecting from the blind end of the caecum.
Lymph node
Effective Filters of Lymph, Sites for responses to lymph-borne antigens.
Lymphocyte compartments in the lymph node are Cortex->B-cells, Paracortex->T cells and dendritic cells and Medulla-> mixture B cells, plasma cells & macrophages> T cells.
Lymphocytes enter the lymph node via the blood (high endothelial venules)and via afferent lymph from tissues. Lymphocytes leave the lymph node via efferent lymphatics. Lymph drains back into venous blood (thoracic duct). If lymphocytes encounter appropriate antigen in the lymph node, they proliferate and differentiate. If antigen is not encountered, lymphocytes pass through the lymph node and enter the lymph. Since lymph enters the venous circulation, lymph-borne cells can re-enter lymph nodes or other secondary lymphatic tissue via the blood. This process is called lymphocyte recirculation. Lymph node structure brings together antigen, antigen presenting cells, and lymphocytes to facilitate immune responses. 70% T-cells, 30% B-cells.
Lymph node capsule
Lymph node trabeculae
bundles of dense connective tissue
Lymph node cortex
Antigen/T cell/B cell interactions first occur in the paracortex, antigen-activated B cells form follicles in cortex. The cortex contains the outer cortex, inner cortex, and paracortical region.
Lymph node medulla
mixture B cells, plasma cells & macrophages, contains medullary cords and mudellary sinuses
Afferent Lymphatics
A lymphatic vessel entering, or bringing lymph to a node
lymph node Subscapular sinuses
areas of loose lymphoid tissue (whose reticular fibril meshes are wide) situated immediately beneath the capsule. They are composed of a loose network of reticular cells and fibers. Lymph, containing antigens, lymphocytes, and APCs, circulates around the wide spaces of these sinuses after being delivered into these channels by the afferent lymphatic vessels.
Lymph node Peritrabecular sinuses
The part of the subscapular sinus that follows the oiuter edges of the trabeculae
Lymph node Medullary sinuses
dilated spaces that separate the medullary cords, bridged by reticular cells and fibers. They contain lymph, lymphocytes, often many macrophages, and sometimes even granulocytes if the lymph node is draining an infected region. These sinuses (which arise from the intermediate sinuses) join at the hilum delivering the lymph to the efferent lymph vessel of the lymph node.
Lymph node Medullary cords
branched, cordlike extensions of dense lymphoid tissue that arise in the inner cortex and separate the sinuses. They contain primarily B lymphocytes and often plasma cells and macrophages.
Efferent lymphatics
high endothelial venules
High endothelial venules- Lymphocytes enter the lymph node via the blood (high endothelial venules) and via afferent lymph from tissues.
Lymph node Hilus
concave depression of lymph node through which arteries and nerves enter and veins and lymphatic vessels leave.
the spleen is responsible for immune responses to blood borne antigens, blood filtration, removal of senescent RBC and platelets. The spleen is compartmentalized into red pulp and white pulp. The framework+ mesenchymal stromal cells make reticular fibers (type III collagen). NO LYMPHATIC SINUSES IN THE SPLEEN! 30% T-cells, 70% B-cells.
Spleen Capsule
dense connective tissue that surrounds the spleen from which emerges trabeculae which divide the splenic pulp into compartments.
White pulp
in spleen- T cell zone (associated with central artery,30% of splenic lymphocytes are T cells) and B cell zone(surrounds the T cell zone, ~70% of spenic lymphocytes are B cells), aggregates of lymphocytes, site of immune responses to blood-borne antigens, looks blue when stained, more dense than red pulp.
Red pulp
in spleen- network of venous sinuses suspended by framework of reticular cells and reticular fibers with bundles of dense connective tissue (trabeculae). Site of blood fitration, extensive system of venous sinuses; NO lymphatic vessels or lymphatic sinuses. Cords contains all formed elements of the blood and numerous macrophages. Repeating bands of reticular fiber represent strips of basement
membrane that hold the venous sinuses together.
Splenic cords
in red pulp. They contain T and B cells, macrophages, plasma cells, and many blood cells. They are separated by irregularly shaped wide sinusoids.
Spleen Marginal sinus
marginal venous sinusoid separates white from red pulp and is often difficult to see.
Spleen- Trabecular arteries
The splenic artery divides as it penetrates the hilum, branching into trabecular arteries of various sizes that follow the course of the CT trabeculae.
periarterial lymphatic sheath, part of the white pulp
Spleen- Central arteries
When the trabecular arteries leave the trabeculae to enter the parenchyma, they are enveloped by a sheath of T lymphocytes, the PALS. Also called white pulp arteries.
Spleen Sinusoids
in the red pulp. Lined by elongated endothelial cells with the long axes parallel to the long axes of the sinusoids. Sinusoids are surrounded by an incomplete basal lamina, with spaces 2-3 micrometers in diameter or smaller, thus, only flexible cells can pass from the red pulp cords to the lumen of the sinusoids.
Open vs. closed splenic circulation
There are two proposed methods of the manner in which blood flows from the arterial capillaries of the red pulp to the interior of the sinusoids. In open circulation, formed elements of the blood are just dropped off into the parenchyma of the spleen. In closed circulation, the capillaries open directly into the sinusoids and the blood always remains in the vessels.
thymus-derived Lymphocytes include HELPER/REGULATORY CD4+ cells and CYTOTOXIC CD8+ cells. The thymus is a primary lymphatic tissue which attains its peak development during youth. It has dual embryonic origin: lymphocytes arise in the boine marrow from cells of mesenchymal origin and these cells invade an epithelium primordium that has developed from the endoderm of the third and fourth pharyngeal pouches.
Thymic cortex
the peripheral dark zone of thymic lobules that contains antigen activated B-cells that have formed follicles. Stains darkly because of high density of lymphocytes. There are reticular fibers (type III collagen) in lymph node cortex.
Thymic medulla
mixture B cells, plasma cells & macrophages that contains a low density of lymphocytes (thymocytes) and predominance of epithelial cells. This is responsible for lighter staining. Medulla contains Hassall bodies.
Hassal’s corpuscles (bodies)
characteristic of the thymic medulla. They are of unknown function and contain flattened epithelial reticular cells that are arranged concentrically and are filled with keratin filaments. They sometimes calcify.
Epithelial reticular cells in thymus
Epithelial reticular cells are pleomorphic, stellate, non-phagocytic cells which seem to be supportive in function and are held together by desmosomes. They replace the fibroblastoid reticular cells found in other lymphoid organs. Other epithelial cells in the medulla have the ultrastructure of secretory cells. Although different epithelial cells throughout the thymus appear alike by light microscopy their ultrastructure and function varies.
Thymic Septae
interlobular connective tissue of thymus (?????)
Thymic Lobules
The thymus has a connective tissue capsule that penetrates the parenchyma and divides is into incomplete lobules, so that there is continuity between the cortex and the medulla of adjoining lobules. Each lobule has a peripheral dark zone (cortex) and inner light zone (medulla).
Humoral immune response
an adaptive immune response characterized by the production of antibodies produced by plasma cells derived from clones of activated B cells.
Cellular immune response
an adaptive immune response mediated by T-cells that (1) secrete cytokines that act on B cells, T cells, and on inflammatory cells such as macrophages and neutrophils, and (2) attack foreign cells or cells that exhibit foreign epitopes on their surfaces, such as cells infected by bacteria of viruses, and tumor cells.
Filtration of blood
accomplished by the spleen removing senescent RBCs in red pulp.
Filtration of lymph
occurs in the lymph node. Lymph percolates through lymphatic channels (sinuses) that are studded with macrophages.Lymphocytes enter the lymph node via the blood (high endothelial venules) and via afferent lymph from tissues. Lymphocytes leave the lymph node via efferent lymphatics. Lymph drains back into venous blood (thoracic duct). If lymphocytes encounter appropriate antigen in the lymph node, they proliferate and differentiate.

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