Histology Flashcards
Does the endocrine system have ducts?
No - secretes directly into the vascular channels (highly vascularized with rich blood supply)
Specific molecules secreted into the bloodstream that elicit selective responses from organs, tissues or cells
Hormones
How are hormones often regulated?
via feedback loops
What do cells need to have in order for hormones to be effective on them?
Complementary receptor molecules
Give examples of amino acid derived hormones in the body (includes proteins, glycoproteins, peptides or modified AA)
Pituitary
Parathyroid
Thyroid
Pancreatic islet cells
Steroid hormones are derived from ___________
cholesterol
Amino acid derived hormones are from what embryonic tissue layer?
endoderm or ectoderm
Steroid hormones are derived from what embryonic layer?
Mesoderm
What type of hormone will be derived from cells with abundant SER?
Steroids
In order for a hormone to target an intracellular receptor, the hormone must be _____ _______
lipid soluble
All amino acid derived hormones (except thyroid) target this receptor location
Cell surface receptors (on plasma membrane of target cells)
What are the differences in action between cell surface and intracellular receptors
Cell surface receptors activate secondary messenger cascades
Intracellular receptors target nucleus and activate gene expression
Discrete gland examples
Pituitary Pineal Thyroid Parathyroid Adrenals
Glands with endocrine and exocrine function
Kidney
Pancreas
Gonads
Placenta
Do paracrine secretions involve the vascular system?
No
Endocrine secretions
hormones secreted into the blood to target distant cells
paracrine secretions
neighboring cells
autocrine
Target sites on the same cell
How is the pituitary linked to the hypothalamus?
Via the infundibulum
What type of tissue is the anterior lobe (adenohypophysis) or the pituitary?
glandular epithelial
What type of tissue is the posterior lobe (neurohypophysis) or the pituitary?
neural secretory
Why does the posterior pituitary stain lighter than the anterior?
Neurons. They don’t stain well.
What is the embryologic origin of the anterior pituitary?
Oropharynx ectoderm
Rathke’s pouch
What is the embryologic origin of the posterior pituitary?
Neuroectoderm
What is the fancy vascular system that supplies the pituitary gland?
Hypothalamohypophyseal Portal system
What 2 sets of vessels make up the hypothalamohypophyseal portal system
Superior hyophyseal arteries
Inferior hypophyseal arteries
What arteries make up the superior hypophyseal arteries and what area is supplied by this?
Arise from the internal carotid arteries and posterior communicating arteries of circle of willis
Supplies pars tuberalis, median eminence and infundibulum
What makes up the inferior hypophyseal arteries and what are is supplied by this?
Arise from internal carotids
Supply pars nervosa
Does the anterior lobe of the pituitary have arterial blood supply?
No, not directly
Route of pituitary blood supply?
Arteries - fenestrated capillaries - portal veins - hypophyseal portal veins - second fenestrated sinusoidal capillary network
How does the anterior pituitary stain?
Dark - makes hormones so lots of RER and ribosomes
How does the posterior pituitary stain?
Lighter - nonmyelinated axons, nerve ending and blood vessels stain faintly
Which region of pituitary will you wind vesicles with colloid?
pars intermedia
3 division of the anterior pituitary
Pars distalis (75%) Pars intermedia Pars tuberalis
What types of cells are in the pars distalis?
Chromophobes (light)
Chromophils (dark)
Two types of chromophils?
Acidophils (stain pink)
Basophils (stain purple)
Somatotropes (GH, STH) and Mammotropes (PRL) are this type of chromophil
Acidophil
Thyrotropes (TSH), Gonadotropes (FSH, LH, ICSH), Corticotropes (ACTH, MSH) are this type of chromophil
Basophil
What types of hormones are made from basophils?
TSH (thyrotropes)
FSH, LH, ICSH (gonadotropes)
ACTH, MSH (corticotropes)
What types of hormones are made from acidophils?
GH, STH (somatotropes)
PRL (mammotropes)
The pars intermedia is lined by _____ _____ and filled with _____
Cuboidal epithelium
Colloid
what is produced in the pars intermedia?
MSH and corticotropes
The superior hypophyseal arteries terminate here (forming primary portal system plexus)
Pars tuberalis
The cells of the pars tuberalis contain these two hormones
FSH and LH
This neural track passes through the infundibular stalk
Hypothalamic hypophyseal tract
Hormones of the pars nervosa? (2)
Oxytocin
ADH
Where would you find pituicytes and herring bodies?
pars nervosa
Oxytocin functions?
Suckling, uterine contractions
Diabetes insipidus pathology?
Lack of ADH (or mutated receptor)
Location of the pineal gland?
Attached by stalk to roof of 3rd ventricle between 2 hemispheres
Not separated by BBB
What innervates the pineal gland?
SNS (from superior cervical ganglion)
PNS
Epinephrine
Cell types of the pineal gland
Pinealocytes (produce melatonin)
Glial cells
What do pinealocytes do?
Produce melatonin
Radiologic marker for the pineal gland?
Brain sand (corpora arenacea) -concentration of calcium phosphate and carbonate on carrier proteins
Melatonin function
- Suppresses gonadotrophin (FSH and LH) via hypothalamus inhibition
- Retards gonadal growth and function
- Alters emotional responses to changes in day length
Embryologic origin of thyroid?
Pharyngeal endoderm (same as tongue)
Structure of thyroid
Two lateral lobes connected by isthmus
CT capsule
adjacent to larynx and upper trachea
Functional unit of the thyroid?
Follicles, surrounded by fenestrated capillaries
2 cell types of the thyroid
Follicular cells (principal) Parafollicular cells (c cells)
Histology of the thyroid follicle?
Simple epithelium (cuboidal, squamous and columnar)
What types of cells synthesize thyroid hormones?
Follicular cells
Basal end of follicular cells face which direction?
Towards the basement membrane, away from colloid
Physiology of inactive follicular cells?
"resting" Basal levels of thyroglobulin Low cuboidal to squamous Few mito, small golgi some RER
Physiology of active follicular cells?
Stimulated by TSH (from pit.) Columnar Lots of mito, big golgi Lots of RER Lipid droplets/PAS pos. Apical lysosomes T3 and T4 release - basal surface
Where are parafollicular cells found
between follicular cells and basement membrane (not on lumen)
What is the function of parafollicular (c cells)?
Synthesize calcitonin
Calcitonin function?
Lowers blood calcium by inhibiting bone resorption
Decreases osteoclast motility and numbers
Promotes excretion of calcium and phosphate from kidneys
What is necessary for the synthesis of T3 and T4
Synthesis Thyroglobulin
Resorption, diffusion and oxidation of Iodide
Where is thyroglobulin found?
Colloid (3 month supply stored)
If you see vacuoles in the thyroid what does that mean?
the gland is active
What AA is a large component of colloid?
Tyrosine
What produces TSH?
thyrotropes (basophil) that are found in the pars distalis
How is T3 and T4 produced?
Pinocytosis of thyroglobulin in colloid
- fusion with lysosomes and thyroglobulin proteolysis
- Formation and release of T3 and T4 to cytoplasm and diffusion (binds to carrier proteins)
Where do you find the parathyroid glands?
Two pairs. Located on posterior surface of each lateral lobe.
Embryologic origin of parathyroid?
Pharyngeal endoderm
What separates parathyroid from thyroid?
CT capsules
Name the three cell types of the parathyroid
Chief (principal)
Oxyphil
Fat
Active Chief cell of Parathyroid
More RER, big golgi, vesicles
Depleted glycogen
Secreting PTH
PTH function
Regulate circulating calcium
How doe PTH increase blood calcium?
Increase osteoclast numbers indirectly by stimulating osteoblasts to produce osteoclast stimulating factor (RANKL)
Osteoclasts DO NOT have PTH receptor
Osteoclasts have PTH receptor
What type of bone cell has a PTH receptor
Osteoblasts - makes osteoclast stimulating factor (RANKL)
