Endo Histo Flashcards
Paracrine signaling
Short-distance communication between cells via substances released, shed, or presented by cells to affect specific targets on other cells in the vicinity, within a tissue or organ [somatostatin in pancreatic and stomach d-cells]
Autocrine signaling
Substances are released by a cell and affect the cell of origin itself [interleukins, growth factors]
Juxtacrine signaling
Substances expressed/anchored to the cell membrane bind to receptors on adjacent cells [delta/notch signaling in the developing nervous system and immune system]
Endocrine signaling
Communication between cells involving substances released through interstitial space and carried by the vascular system
Hormones
Factors synthesized from amino acids, cholesterol or phospholipids that use endocrine routes to induce distal cellular changes through specific binding to receptors …non-endocrine signaling substances are called “factors”
Other types of signaling
synaptic, intracellular
Epithelial info about endocrine glands and organs
Epithelial/epitheloid
Lacks a free surface, embedded in connective tissue
Fenestrated capillaries and lymphatic capillaries surround secretory tissue
Hormones are released into interstitial space
DUCTLESS (vs. exocrine)
Secretory cells are organized in follicles, anastamosing cords, nests, or clusters
Hypothalamus
Hypothalamus is the central regulator of the endocrine system
Nuclei of the hypothalamus
11 ‘major’ nuclei of the hypothalamus with diverse functions, release diverse substances
For the neuroendocrine system, we care about the PV (paraventricular) and SO (supraoptic) nuclei, in particular
Some release neurotransmitters
Some release neurohormones
Both can have indirect or direct effects on glands
Two major types of neurohormones in the neuroendocrine system
Releasing/Inhibiting Hormones
Direct hormones
Hypothalamic Connection to the pituitary gland
Below the hypothalamus is neural tissue transitioning into the pituitary gland, called the median eminence, which is surrounded by capillary beds
The median eminence lacks a blood-brain barrier
Hypothalamus network with pituitary
Hypothalamus: median eminence: infundibulum (posterior pituitary)
Below infundibulum (“pituitary stalk” )is pars nervosa
Axons from both the PV Hypothalamus and SO Hypothalamus project through infundibulum into pars nervosa, release oxytocin or vasopressin into pars nervosa
Called the neurohypophysis
Below the median emenince is hypothalamo-hypophyseal portal system
Arteries from internal carotid artery varry neurohormones (releasing and inhibiting) to anterior pituitary, called adenohypophysis
Pars tuberalis- Mostly vascularized area, wraps around infundibulum
Pars intermedia- Transitional area
Pars distalis
Posterior pituitary embryological origins
Posterior Pituitary from neuroectoderm, extension of the same structure of developing hypothalamus
Anterior pituitary embryological origins
Anterior Pituitary from oral ectoderm, develops from Rathke’s Pouch
Pituitary gland tissue and location
Pituitary gland is heterogenuous, pea-sized gland sitting in the sella turcica of the sphenoid bone
What’s in the anterior pitutitary (histological)
Cell bodies of secretory cells
What’s in the posterior pituitary
Axon terminals of neurons
if you see cell bodies, they’re most likely specialized glial cells: pituicytes
Two major components of neurohypophysis (posterior):
(hypophysis = pituitary gland)
Axons of hypothalamic neurons from PV and SO
Pituicytes
Herring Bodies
Unmyelinated Axons have dilations called “Herring Bodies”
Release either Vasopressin (AVP/ADH) or Oxytocin (+others) from neuroscretory vesicles
Along with neurophysin and ATP
Pituicytes
Pituicytes = astrocytes of the pituitary gland Will stain with GFAP - marker for astrocytes [*Think about immunocytochemistry]
Oxytocin
Milk letdown reflex
Uterine smooth muscle contraction during orgasm, menstruation and parturition Oxytocin injections
Vasopressin (ADH)
Increase water permeability in kidneys
Diabetes insipidus
Central Nephrogenic
Adenohypophysis histology
Cells are in clumps or cords with sinusoidal spaces
Classical staining of acidophils (lighter), basophils (purple/blue), and chromophobes (no stain)
Basic histology of the adenohypophysis tells relatively little compared to immunocytochemistry
Lactotrophs (PRL, VIP), somatotrophs (GH), corticotrophs (ACTH), gonadotrophs (FSH and LH), thyrotrophs (TSH)
Receptors for Releasing Hormones
Folliculo-stellate cells (supportive functions, might be stem cells)
The pars distalis has majority of the endocrine cells
The other aspects of the adenohypophysis (pars intermedia and pars tuberalis)
The pars intermedia contains colloid-filled spaces and MSH
The pars tuberalis surrounds the infundibulum, mostly vascularized region of the pituitary
Hormone categories of the adenohypophysis
somatotrophs, lactotrophs, gonadotrophs, thyrotrophs, coricotrophs
somatotrophs
somatotropin (Growth hormone, GH), A
cidophil
major functions: stimulates growth in epiphysial plates of long bones via IGF (insulin growth factors) produced in the liver
lactotrophs
Prolactin. acidophil, promotes milk secretion
gonadotrophs
FSH and LH, basophilic
FSH promotes ovarian follicle development and estrogen secretion in women, spermatogenesis in men
LH promotes ovarian follicle maturation and progesterone secretion in women, interstitial cell androgen secretion in men
Thyrotrophs
Thyrotropn (TSH), basophilic
Stimulates thyroid hormone synthesis, storage and liberation
Corticotrophs
Adreno corticotropin (ACTH), Lipotropin (LPH), Basophilic
ACTH stimulates secretion of adrenal cortex hormones
LPH helps regulate lipid metabolism
Kallmann syndrome
DSD “Differences in Sexual Development”
Hypogonadatropic
Hypogonadism
Delayed or absent puberty
Impaired sense of smell
Mutations in genes regulating migration of GnRH-containing neurons Also regulate migration of olfactory neurons
Review the basic organization of the hypothalamic-pituitary system
Pineal Gland- the other major neuroendocrine tissue source
•“Photo-neuroendocrine system”
–Retina, hypothalamus, pineal gland all derived from the same source (diencephalon).
–Neuroectoderm
- Part of the epithalamus
- Two major cell types:
–Pinealocytes (modified neurons)
•Release melatonin
–interstitial cells (glia)
- Unmyelinated nerve axons from superior cervical ganglia
- Brain sand in CT scans show “brain sand” or corpora arenacaea
–Calcium phosphate
–Midline of brain in CT
neurons vs glial cells
neurons usually larger, rounder
What does melatonin do?
- There are 3 types of melatonin receptors (MT1-3)
- It’s synthesis is inhibited by light
–Signals night-time to the body
- In many animals, the day length coding determines lengths of reproductive cycles, affecting activity of GnRH neurons (not so in humans)
- Not entirely necessary * for humans, although tumors = early onset puberty
Melatonin synthesis is regulated by the sympathetic nervous system. Pathway from hypothalamus to spinal cord to SCV back up to pineal gland
Thyroid gland - Follicles (hormones stored in inactive form here)
•Follicular epithelium
–Surround the big colloid-containing follicles (thryoglobulin…precursor to the stuff released)
–Follicular cells (thyrocytes)
•Easier to identify…going to be darker (more basophilic) and make contact with follicles themselves. Make T3 and T4. These cells transport iodide.
–Parafollicular cells (calcitonin)
- In light microscopy, actually paler staining, solitary, not abutting the follicles
- Supposed to oppose the actions of PTH
T cells vs C cells
T cells come into direct contact with the follicle, C cells usually have some layers in between.
Steps of T3 and T4 production and transport
- Production of thyroglobulin
- Uptake of iodide from blood
- Iodination of tyrosyl residues in thryoglobulin in the colloid
- Formation of T3 and T4
- Endocytosis of iodinated thyroglobulin by thryrocytes
Secretion of T4 and T3
Parathyroid gland
- Gross structure: 2 pairs of small ovoid, superior and inferior (in connective tissue, in posterior surface of thyroid gland)
- Septa from connective tissue divide into lobules
–Fat cells in connective tissue of adults, easier to see
•Blood from inferior thyroid arteries—lots of fenestrated capillaries and lymphatic capillaries
Parathyroid gland Main Actors: Principal/Chief cells
- More of the parenchyma, tangled curvilinear cords of chief cells
- Regulate synthesis, storage and secretion of PTH
- Small, polygonal, centrally located nucleus
- Acidophilic
- Replicate when they are stimulated by changes in blood calcium levels
Oxyphil cells: the other type of parathyroid cell
- Not secretory, fewer
- More rounded, larger than principal cells, distinctly acidophilic cytoplasm
- Derived from Chief cells
- Found increases in CKD, tumors
- Possible paracrine action on chief cells
Adrenal Glands: gross anatomy
•
–Glands are both embedded in perirenal fat superior t okidney
–Covered in a thick connective tissue capsule
–2 divisions of secretory tissue: medulla (catecholamine-secreting) and cortex (steroid-secreting)
adrenal glands: blood supply
–Capsular arteries supply capsule,
–Fenestrated cortical sinusoidal capillaries supply cortex and drain into fenestrated medullary capillary sinusoids,
–Medullary arterioles that traverse the cortex, travel within the trabeculae and bring arterial blood to the medullary capillary sinusoids
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–The medulla has a dual blood supply, arterial blood from the medullary arterioles and venous blood from the cortex
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–Lymphatic vessels in the capsule around larger blood vessels and in the medulla,
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Adrenal medulla
- Pale staining, epitheloid (from neural crest) chromaffin cells.
- Will aslo see sinusoidal blood capillaries , connective tissue, and nerves (stroma)
- Chromaffin cells are modified neurons (neural crest derivatives)
Chromaffin cells
–Glucocorticoids released by the adrenal cortex are thought to have inhibited axonal growth from the chromaffin cells
–Chromogranins present
–Chromaffin cells organized in ovoid clusters
–Presynaptic, myelinated sympathetic nerve fibers synapse on chromaffin cells.
–Chromaffin cells secrete either norepinephrine or epinephrine (80:20 ratio) [“catecholamines”]
- Cell type determined by proximity to cortex
- Cell type determined by type of dense core vesicle
Pheochromocytoma
- Excessive catecholamines produced
- Symptoms of over-active sympathetic nervous system
- Large, loose clusters of chromaffin cells enveloped by thin, vascular channels (zellballen)
Adrenal Cortex: zona glomerulosa
–cells are closely packed in ovoid clusters and curved columns continuous with the cellular cords in the fasciculata.
–Small and columnar or pyramidal. Spherical nuclei.
–Rich network of fenestrated sinusoidal capillaries around each cluster. Lots of smooth ER (think about the lipid nature…)
–Secretes aldosterone, which controls BP (a mineralocorticoid in fluid and electrolyte balance).
–Product of cholesterol, synthesis controlled by actions of angiotensin II
–Aldosterone synthase is only found in glomerulosa cells.
Adrenal Cortex: Zona fasciculata
–Most of cortical volume
–large and polyhedral cells
–arranged in long, straight cords, one or two cells thick and separated by sinuosoidal capillaries.
–Spherical nucleus. May see binucleate cells.
–Developed sEr (because steroid secreting)
–Produce glucocorticoids and gonadocorticoids. Cortisol acts across body and brain.
–“HPA-axis” From ACTH
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Adrenal Cortex: Zona Reticularis
–Smaller cells than in fasciculata. Nuclei are more deeply stained.
–Anastamosing cords separated by fenestrated capillaries. Large lipofuscin.
–Mostly secrete gonadocorticoids DHEA, DHEAS, and androstenedione.
lipofuscin
brownish stain in the middle of a cell that indicates it is older…
Congenital Adrenal hyperplasia
- Collection of genetic conditions, usually causes DSD
- Androgenizing phenotype
- May lack aldosterone
- May lack cortisol
What would an XY male with CAH look like? Very male. Lots of hair, but also lots of problems and will die with messed up levels of aldosterone/ cortisol etc.
An XX female would have a “psuedopenis,” large clitoris
What would an XY female with CAH look like?
Endocrine Pancreas
•Pancreas is both exocrine and endocrine
–Islets of Langerhans scattered throughout exocrine tissue, mostly in tail of pancreas
–Islet cells secrete: glucagon, insulin, or somatostatin
–α, β or δ-cells, respectively
