Histology Flashcards
Describe the islets of Langerhans.
Insulo-acinar portal system, capillary plexus & anastomosing cords of cells
Cells can only be differentiated via immunostaining.
Fewer proteins in comparison to acinar hence stain pale.
Surrounded by delicate fibrous capsule
a-cells- usually surround the periphery and in a single layer, secretes glucagon.
b-cells- clusters in the center, produce insulin.
delta-cells- produces somatostatin.
Pancreatic Polypeptide cells- secretes PP
How are islets of Langerhans secretions regulated?
Neural: ANS, Cholinergic P- insulin, adrenergic S- glucagon (b-adrenergic)
Cell-cell communication through gap junctions
Hormonal: can stimulater or inhibit each other
-Delta cells - Somatostatin & gastrin –– SS inhibits glucagon & insulin release (paracrine – intra-islet signaling)
F / PP cells - Pancreatic polypeptide –– inhibits somatostatin secretion– paracrine (also inhibits the secretion of pancreatic enzymes and bile
from gall bladder - endocrine)
Blood glucose (vascular)
Describe and state the function of C cells in the thyroid.
They are found between follicles, and secrete calcitonin, which downregulates osteoclast activity hence no bone resorption.
What are the features of steroid-secreting cells under a microscope?
They polyhedral shaped
Lipid droplets- stores cholesterol backbone of steroids
Prominent sER- enzymes
Mitochondrial-tubular cristae and enzyme functions
associated with fenestrated capillaries, with short microvilli projection
golgi close to the nucleus
What are the steroid hormones that are secreted?
Zona:
Glomerulosa: mineralocorticoids- aldosterone (salt and potassium regulation DCT)
Fasciculata: glucocorticoids- cortisol (glucose homeostasis)
Reticularis: Androgens and glucocorticoids
what does the adrenal medulla secrete?
E and NE in chromaffin granules
Why is the adrenal medulla neurohormone secretion?
ls:
Modified sympathetic post ganglionic neurons
Origin – Neural crest
Adreno-cortico medullary capillary axis - Glucocorticoids - epinephrine
Release is stimulated by preganglionic sympathetic nerves (cholinergic)
What are the embryological origin of the Pituitary gland?
Anterior- upgrowth from the roof the primitive oral cavity Rathkes Pouch and wraps around the anterior aspect of the Posterior.
Posterior- down growth of hypothalamus (nervous tissue)- connected via Pituitary Stalk
What are chromophobes?
The undifferentiated cells found in the Anterior and is resistant to stain
Which class of hormones are secreted by the Anterior Pituitary?
Peptide hormones
Which hormones are secreted by the anterior pituitary?
GH- whole body
Prolactin- breast in females (mammary glands)
ACTH- adrenal cortex
FSH/LH- gonads
TSH- Thyroid
State the location of the neuronal cell bodies that give rise to the axons in the neurohypophysis.
Hypothalamus
Supraoptic nucleus- ADH
Paraventricular nucleus- oxytocin
What are Pituicytes?
Glial cells, support axons unmyelinated axons of neurosecretory cells of the SON or PVN
Pituicytes contact the basal lamina of the fenestrated capillaries
Blood-brain barrier
Explain what Herring bodies are.
Neurosecretory granule containing the neurophysin-hormone complex
Where axon comes into contact with capillaries
Define Neurohormone.
is a chemical substance that is produced by neurons and released into the bloodstream, where it can act as a hormone to affect the function of distant cells or organs.
