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Human Structure > Histology: Endocrine > Flashcards

Histology: Endocrine Flashcards

1
Q

Endocrine Glands

A

Secrete into bloodstream (no ducts)

  • Pituitary Gland
  • Pineal Gland
  • Thyroid Gland
  • Parathyroid Gland
  • Adrenal Glands
  • Testes/Ovaries

Diffuse neuroendocrine system

  • Scattered, hormone producing cells within organs (pancreatic islets, enteroendocrine cells in gut)
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2
Q

Hypothalamus & Pituitary Gland

A

“Master regulators of endocrine system”

  • Hypothalamus regulates pituitary gland
  • Pituitary secretions regulate other endocrine glands

Examples:

  • Blood pressure
  • Body Temp
  • Fluid/Electrolyte Balance
  • Body Weight
  • Appetite
  • Reproductive System
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3
Q

Pituitary Gland

A

below hypothalamus

  • Anterior Lobe (adenohypophysis)
    • _​_Glandular epithelium
    • Three Regions:
      • Pars Distalis
      • Pars Intermedia
      • Pars Tuberalis (wraps around infundibulum, attached to hypothalamus)
  • Posterior lobe (neuohypophysis)
    • _​_Neurosecretory tissue
    • Two Regions:
      • Infundibular Stalk
      • Pars Nervosa
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4
Q

Development of Pituitary Gland

A

Anterior Lobe:

  • Derives from ectoderm from oropharynx roof (Rathke’s Pouch)

Posterior Lobe:

  • Neuroectoderm from floor 3rd ventricle
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5
Q

Regulation of Pituitary Gland (via Hypothalamus)

A

Neurosecretory Cells

  • Produce and secrete releasing and inhibitory hormones and act on cells in pars distalis (anterior lobe)

Paraventricular Nucleus***

  • Produce oxytocin

Supraoptic Nucleus***

  • Produce anti-diuretic hormone (ADH)

***Axons project through infundibular stalk to posterior lobe (pars nervosa)

  • Hormones accumulate here and will be released from posterior pituitary when appropriately stimulated
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6
Q

Blood Supply to Pituitary Gland

A
  • Hypophysial arteries from internal carotid artery
    • ​Superior Hypohysial a. supples upper portions: pars tuberalis, median eminence (floor hypothalamus), infundibulum
    • Inferior Hypophysial a.
      • ​Supples pars nervosa
    • *****No direct arterial supply to pars distalis
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7
Q

Hypothalamo-Hypophyseal Portal System

A
  • Carries hypothalamic neuroendocrine secretions (from neurosecretory cells)
    • Primary Capillary Plexus picks up inhibitory/releasing hormones
      • Fenestrated/Sinusoidal
    • Hypophyseal Portal Veins travel along pars tuberalis from primary capillary plexus to secondary capillary plexus
      • _​_Surrounds pars distalis
  • Blood leaves pituitary gland via hypophyseal veins
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8
Q

Pars Distalis

A
  • Main portion of anterior lobe (75%)
  • 3 Cell Types:
    • Acidiphils (bright pink)
    • Basophils (purple)
    • Chromophobes
      • Either undifferentiated stem cells (haven’t yet formed acidiphils or basophils) or recently degranulated cells
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9
Q

Acidophils

A

Somatotrophs

  • 50% Cells in anterior lobe
  • Secrete Growth Hormone (GH)
    • ​Acts on growth plates/skeletal muscle
  • Stimulated by GHRH and Ghrelin (coordinates growth with meal consumption)
  • Inhibited by somatostatin

Lactotrophs

  • Secrete prolactin
    • Acts on mammary glands during pregnancy (stimulates milk production)
  • Stimulated by thyrotropin releasing hormone and vasoactive inhibitory peptide
  • Inhibited by dopamine
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10
Q

Basophils

A

Corticotrophs

  • Produce precursor of adrenocorticotropic hormone (POMC)
    • POMC cleaved to form ACTH
  • Stimulated by CRH
  • Inhibited by Cortisol
  • Results in release of cortisol from adrenal cortex

Gondaotrophs

  • Secrete FSH and LH
  • Stimulated by GnRH

Thyrotrophs (least populous cell type)

  • Secrete thyroid stimulating hormone
  • Stimulated by TRH
  • Inhibited by somatostatin
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11
Q

Pars Intermedia

A
  • Between pars distalis and posterior lobe
  • Unclear function
  • Contains colloid-filled cysts
    • Remnants of Rathke’s Pouch
  • Contains basophils and chromophobes
    • Basophils here secrete POMC (cleaved differently into Melanocye Stimulating Hormone & beta-endorphin)
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12
Q

Pars Tuberalis

A
  • Surrounds infundibular stalk
  • Contains vessles of hypothalamo-hypophyseal portal system
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13
Q

Pituitary Adenoma

A
  • Benign, slow-growing
  • Affect on somatotroph:
    • ​Growth hormone secreting tumor
    • In children –> Gigantism (longer bones)
    • In adults –> Acromegaly (thicker bones)
      • Usually in forehead/jaw, hands/feet
  • Affect on corticotroph:
    • Cushing’s Disease
      • Overproduction of ACTH, too much cortisol
  • Affect on Lactotrophs
    • Prolactinomas
      • ​Milk production in non-lactating females
      • Amenorrhea
      • Erectile dysfunction
      • Infertility
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14
Q

Posterior Pituitary

A
  • Not a true endocrine gland
  • Contains unmyelinated axons of secretory neurons
    • Cell bodies exist in suproptic and paraventricular nuclei of hypothalamus
  • Pituicytes
    • _​_Glial cells in postioter pituitary
    • Support axons

NB: neurosecreotry bodies/Herring Bodies (dilations of axon terminals)

  • Storing hormones released from posterior pituitary
  • In close association with fenestrated capillaries
  • Two Hormones:
    • ​ADH (vasopressin)
      • Produced in supraoptic nucleus
      • Released in response to low blood volume, or increased osmolality
      • Acts on aquaporin channels of collecting ducts to promote water reabsorption
      • Can stimulate vascular smooth muscle contraction at high concentrations
    • Oxytocin
      • ​Produced in paraventricular nucleus
      • Released in responsed to distenstion cervix/vagina during childbirth or nipple stimulation
      • Stimulates contraction of uterine smooth muscle or myoepithelial cells in mammary gland to faciliate milk ejection
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15
Q

Adrenal Gland

A

Adrenal Cortex

  • From intermediate mesoderm
  • Produces steroid hormones
  • Three regions:
    • Zona glomerulosa
    • Zona fasciculata
    • Zona reticularis

Adrenal Medulla

  • From neural crest cells
  • Produces catecholamines (epinephrine and norepinephrine)
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16
Q

Zona Glomerulosa

A
  • Just deep to connective tissue capsule
  • Small, densely-packed basophilic cells arranged in glomeruli
  • Secrete mineralicorticoids (Aldosterone)
    • Stimulates Na+ reabsorption in DCT
    • Stimulated by angiotensin II (part of RAAS)
    • Weekly stimulated by ACTH
17
Q

Zona Fasciulata

A
  • Larger polyhedral cells
    • Lots of lipid droplets within cytoplasm
    • Arranged in long cords, 1-2 cells thick separated by fenestrated sinusoidal capillaries
  • Secretes glucocorticoids (primarily cortisol)
    • ​Released in response to ACTH
    • Cortisol works in negative feedback loop

Cortisol:

  • Releases energy (breaks down fat/glycogen)
18
Q

Zona Reticularis

A
  • Small cells in anastomosing cord network
    • Separated by capillaries
    • Cells contain lipofuscin (stain darker)
  • Secrete weak androgens (DHEA)
    • Converted to testosterone in both sexes
    • Secretes small amounts of glucocorticoids
    • Stimulated by ACTH
19
Q

Adrenal Medulla

A
  • Chromaffin Cells (stain with chromium dyes)
    • Large, pale-staining
    • Granules that store epinephrine and norepinephrine
    • Modified postganglionic sympathetic neuron
      • Innervation from preganglionic sympathetic neuron causes release of granules
20
Q

Blood Supply of Adrenal Gland

A
  • Suprarenal arteries form subcapsular capillary plexus
    • Cortical Arterioles
      • _​_Form adreno-cortico sinusoid that goes to medulla (venous blood)
    • Medullary Arterioles
      • Passing blood straight to medulla (arterial blood)
  • Central Adrenomedullar veins collect blood in medulla
    • Longitudinal smooth muscle to faciliate efflux of hormones
21
Q

Thyroid Gland

A
  • Surrounded by thin connective tissue capsule, extend septa that separate gland into lobules
  • Comprised of epithelial follicles filled with colloid
    • Gelatinous storage form of inactive thyroud hormones

Follicular Cells

  • Darker-staining; cuboidal when active, squamous when inactive
  • Line lumens of follicles
  • Secrete thryoglobulin; stimulated by TSH
    • This is converted to T3, T4

Parafollicular cells (C-Cells)

  • Larger, pale-staining
  • At periphery of follicles or between follicles
  • Secrete calcitonin in response to elevated blood Ca2+ levels
    • Promotes Ca2+ deposition into bones by suppressing osteoclasts
22
Q

Follilcular Cell EM

A
  • Short microvilli on apical surface
  • Abundant RER, golgi, lysozomes (break down colloid to secrete thyroid hormones)
23
Q

Parafollicular Cells EM

A
  • Indented nucleus
  • Secretory granules (calcitonin) within the cytoplasm
24
Q

T3 and T4

A
  • Produced via iodination of tyrosine residues in thryoglobulin
  • Stored as colloid in inactive form bound to thyroglobulin
    • Stores product outside cell
  • T4 is more abundant; T3 is more potent
    • Regulate basal metabolism, heat production, contributes to growth and development
25
Q

Thyroid Disease

A
  • Goiter
    • Enlargement of thyroid gland
    • Indicates hyper or hypoactive gland
  • Hyperthyroidism (Grave’s Disease)
    • Increased metabolism/weight loss, excessive sweating
    • Protrusion of eyes due to increased CT deposition behind eyeballs
  • Hypothyroidism (Myxedema)
    • Mental/physical sluggishness, weight gain, chills
    • Insufficient dietary iodine, Hashimoto’s disease (autoimmune disease that destroys follicular cells)
26
Q

Parathyroid Gland

A
  • Embedded in posterior aspect of thyroid gland
  • Surrounded by CT capsule
    • Septa form irregular lobules
  • Cells in cords:
    • Principal Cells (purple)
      • Most numerous
      • Small cells, secrete Parathyroid Hormone
        • ​Regulates blood calcium, secreted in response to low blood calcium levels
        • Stimulates resorption of bone, increased absorption of Ca2+ in gut
        • Stimulates Kidneys to convert vitamin D to active form
        • Absense leads to decreased blood Ca2+ levels (tetany can result)
    • Oxyphil Cells
      • Larger, eosinophilic
      • No known secretory roll
    • Adipose Cells
27
Q

Pineal Gland

A
  • Regulates circadian rhythms
    • Secrete melatonin in response to darkness
    • Light inhibits melatonin secretion
  • Also secretes serotonin, norepinephrine and dopamine
  • Derived from neuroectoderm

Pinealocytes

  • Most of cells
  • Secrete melatonin and serotonin

Interstitial Glial Cells (less than 5%)

  • Supporting cells, resemble astrocytes

Corpora Arenacea

  • “Brain Sand”
  • Unknown function
  • More numerous with age

Human Structure (30 decks)

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