Anat - Endocrine System Flashcards
What is the role of the endocrine system?
Communication and regulation in response to normal physiologic changes in the body and alterations in the external environment
=> to ensure homeostasis (regulates functions such as growth, development, reproduction)
Involves hormones that can stimulate change in metabolic activity by binding to receptors on target cells
What are the main endocrine glands in the body?
- Hypothalamus
- Pituitary
- Thyroid
- Parathyroid
- Adrenal
- Pancreas
*Organs can secrete hormones as well: GIT, heart, skin, bone etc.
What are the 4 types of hormones?
List some examples.
- Peptide/protein (hydrophilic)
- Pituitary: FSH, LH, TSH
- Pancreas: Insulin, glucagon - Steroids (lipophilic)
- Gonads: Testosterone, estrogen
- Adrenal cortex: Cortisol - Tyrosine/amino derived - amines (lipophilic)
- Thyroid: T3, T4
- Adrenal medulla: catecholamines, epinephrine (hydrophilic) - Fatty acid derived
Describe the structure of the endocrine gland
- Rich blood supply with fenestrated capillaries
- Cuboidal/columnar epithelium - secretory cells
- Cells arranged in cords or clusters
- Supportive framework (connective tissue)
Which two endocrine glands make up the neuroendocrine unit?
Hypothalamus and pituitary
[PITUITARY]
What are the structures in the anterior pituitary (adenohypophysis)?
Top to bottom:
1. Pars Tuberalis
2. Pars intermedia (lies b/w pars distalis and pars nervosa)
3. Pars distalis
[PITUITARY]
Describe the Pars Distalis of the anterior pituitary (adenohypophysis)
- Structure
- Cells
- Hormones produced (majority of hormones produced by pituitary occurs here)
Pars Distalis contains:
- Continuous cords of cells
- Chromophils - secretory cells in which hormone is stored in cytoplasmic granules
- Chromophobe cells - degranulated chromophil cells
- Sinusoidal capillaries
2 types of Chromophils:
- Acidophils (alpha cells) *more lightly stained and pink
They produce:
- Somatotrophs (GH)
- Mammotrophs (prolactin) - Basophils (beta cells) *more darkly stained and purple
They produce:
- Gonadotrophs (FSH, LH)
- Corticotrophs (ACTH or corticotropin)
- Thyrotrophs (TSH)
[PITUITARY]
Describe the Pars Intermedia of the anterior pituitary (adenohypophysis)
Lies b/w the anterior pars distalis and the posterior pars nervosa
Exist in follicles
Produces Melanotrophs (Melanocyte stimulating hormone) - to produce melanin, protect skin from UV rays
[PITUITARY]
Describe the Pars Tuberalis of the anterior pituitary (adenohypophysis)
- Structure
- Cells
- Hormones produced (majority of hormones produced by pituitary occurs here)
Wraps the pituitary stalk in a highly vascularized sheath
- Undifferentiated cells (gonadotrophs)
- Many cells appear to be chromophobes
- Some acidophils and basophils present
[PITUITARY]
Explain the functions of the hormones secreted by the anterior pituitary
- Somatotrophs (GH) - act on bones, muscle, adipose tissues
- Mammotrophs (prolactin) - act on mammary glands and testes, breast for milk production
- Gonadotrophs (FSH, LH) - act on gonads
- Corticotrophs (ACTH or corticotropin) - act on adrenal cortex
- Thyrotrophs (TSH) - act on thyroid gland
- Melanotrophs (MSH) - act on melanocytes in the epidermis
[PITUITARY]
When are hormones in the anterior pituitary secreted?
Hormones in anterior pituitary only secreted when regulated by regulatory hormones from the hypothalamus
E.g.,
- GnRH => Gonadotrophs (FSH, LH) => testosterone, progesterone, estrogen, inhibin
- CRH => Corticotrophs (ACTH or corticotropin) => cortisol
- TRH => Thyrotrophs (TSH) => T3, T4
[PITUITARY]
What are the structures in the posterior pituitary (neurohypophysis)?
Top to bottom:
- Neural stalk
- Pars Nervosa
[PITUITARY]
Describe the posterior pituitary (neurohypophysis)
- Function
- Content
Extension from hypothalamus, hormones made in the hypothalamus are secreted by posterior pituitary
Consists of:
- Axons of neurosecretory cells in supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus
- Pituicytes (glial cells/supporting cells) that assist in storage + release of hormones and ensheath the axons to regular hormone secretion
- Herring bodies (neurosecretory bodies) that are the extension/terminal end of the axons, contain GRANULES of hormones that eventually get exocytosis and released into the capillaries
- Capillaries
[PITUITARY]
What are the hormones made by the hypothalamus that are secreted from the posterior pituitary? What are their functions?
- Oxytocin
- lactation in breast, contraction of uterus smooth muscle in childbirth
- also known as the love hormone or social hormone, activated during interactions - ADH (antidiuretic hormone)
- water retention in kidney tubules
- reduce urinary flow, incr water absorption
*These hormones are stored in the neurohypophysis as granules in the axons
[PITUITARY]
Explain the blood supply of the hypothalamus and the pituitary gland
Internal carotid artery branches - innervated the hypothalamus
PRIMARY capillary plexus (SUPERIOR hypophyseal arteries) [stalk and medium eminence] - supplies PITUITARY gland
SECONDARY capillary plexus - supplied the ANTERIOR PITUITARY gland
INFERIOR hypophyseal arteries - supplies the POSTERIOR PITUITARY gland
Veins:
Hypophyseal portal veins - drains from PITUITARY gland
Hypophyseal veins
[PITUITARY]
Anterior pituitary control is supplied by _________
Anterior is supplied by the hypothalamic hypophyseal portal system (which consist of the PRIMARY and SECONDARY CAPILLARY PLEXUS)
[PITUITARY]
Posterior pituitary control is supplied by _________
Posterior is supplied by the hypothalamic hypophyseal tract (axons) (INFERIOR hypophyseal arteries)
[PITUITARY]
What are the 2 functional groups of hormones?
- Directly acting on non-endocrine tissues (e.g., GH, prolactin, ADH)
- Modulating the activity of other endocrine glands (TSH, ACTH, FSH, LH)
[PITUITARY]
What endocrine glands are under pituitary control?
What endocrine glands are NOT under pituitary control?
- Thyroid gland
- Gonads
- Adrenal gland (adrenal cortex)
NOT under pituitary control:
- Pancreas
- Adrenal medulla
- Parathyroid
[PITUITARY]
List some examples of pituitary disorders
- Adenomas of adenohypohysis
- High GH: gigantism in children, acromegaly in adults
- High ACTH => cortisol: Cushing’s disease - moon face, buffalo hump, skin thinning
- Damage to neurohypophysis by head trauma can cause diabetes insipidus (ADH or vasopressin insufficiency)
[THYROID GLAND]
Where is the thyroid gland located?
What is the structure of thyroid gland?
Located anterior and inferior the larynx in the neck
Butterfly shaped gland with two lobes connected by an isthmus
Develops from foregut endoderm near the base of the developing tongue
[THYROID GLAND]
Blood supply of the thyroid gland
Covered by capsule, richly supplied by superior and inferior thyroid arteries
[THYROID GLAND]
What are the cell types and structure in the thyroid gland?
What are their functions
- Thyroid/epithelial follicles (round)
- Functional unit for TH production - under control of TSH
- Consist of follicular cells and colloid space
- Follicular cells: cuboidal to tall columnar cells
- Colloid contains tyrosine-containing thyroglobulin
- Secrete T3, T4 that regular BMR, influence growth and maturation of nervous tissue - Parafollicular cells (C cells)
- Parafollicular cells develop from the neural crest
- Located in b/w the thyroid follicles
- Larger than follicular cells, lighter stain
- Secrete calcitonin (dcr calcium levels)
[THYROID GLAND]
What are some thyroid gland disorders?
- Over/underproduction of thyroid hormones
- Overstimulation of thyroid gland by TSH/TSI - goiter, bulging eyes
- Thyroid nodules
- Thyroiditis
- Thyroid neoplasms
- Cretinism (lack of thyroxine T4) - stunted growth, mental retardation in children
[PARATHYROID GLAND]
Describe the structure of the parathyroid gland
4 ovoid masses lying on the posterior surface of the thyroid gland, within its capsule
*Seen under microscope
[PARATHYROID GLAND]
What is the function of the parathyroid gland?
It secretes parathyroid hormone (PTH) which raises calcium level
[PARATHYROID GLAND]
What are the two cell types in parathyroid gland and what are their functions?
- Oxyphil cells
- larger cells
- darker cytoplasm
- more acidophilic - Chief cells
- small polygonal cells with round nuclei
- pale staining cytoplasm
- more abundant
- older people may have degenerated chief cells
- manage the secretion of PTH
[ADRENAL GLAND]
What are the 3 broad layers in the adrenal gland?
- External capsule
- Adrenal cortex
- Adrenal medulla
[ADRENAL GLAND]
The adrenal cortex develops from the ______
The adrenal medulla develops from the ________
The adrenal cortex develops from the mesoderm
The adrenal medulla develops from the neural crest
[ADRENAL GLAND]
What is the function of adrenal gland?
Maintain constancy of the internal environment of the body and make appropriate physiological changes in response to acute stress
[ADRENAL CORTEX]
What are the structures (cells, organelles) in the adrenal cortex that help it carry out its function?
- Steroid secreting cells that have acidophilic cytoplasm rich in lipid droplets with central nuclei
- Abundant smooth endoplasmic reticulum and mitochondria that has enzymes for cholesterol synthesis
- Steroids are not stored in granules, but DIFFUSED through the plasma membrane
[ADRENAL CORTEX]
What are the 3 layers in the adrenal cortex?
Top to bottom:
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
[ADRENAL CORTEX]
Describe the zona glomerulosa
- what cells, and structures are found?
- what hormone does it secrete?
- what is it controlled by?
- Columnar or pyramidal cells, rounded or arched cords
- Secretes mineralocorticoids (aldosterone) - control water and electrolyte balance (retain sodium and water)
- Controlled by renin angiotensin (kidneys)
[ADRENAL CORTEX]
Describe the zona fasciculata
- what cells, and structures are found?
- what hormone does it secrete?
- what is it controlled by?
- Long cords of polyhedral cells with vacuolated appearance
- Secrete glucocorticoids (cortisol) - that has effect on carbohydrate, protein, and lipid metabolism, and suppresses immune function
- Secrete some adrenal androgens
- Controlled by ACTH secreted from the pituitary gland
[ADRENAL CORTEX]
Describe the zona reticularis
- what cells, and structures are found?
- what hormone does it secrete?
- what is it controlled by?
- Smaller cells with irregular cords, heavily stained (darker)
- Secretes dehydroepiandrosterone (androgens) that supplement the gonadal sex hormone secretion
- Secretes glucocorticoid (cortisol) in small amounts
[ADRENAL MEDULLA]
What cells are present in the adrenal medulla?
What is its structure and function?
- Chromaffin cells
- Large pale staining polyhedral cells (in cords or clumps)
- Have electron dense GRANULES containing catecholamines (epinephrine, norepinephrine)
- These cells are innervated by preganglionic sympathetic neurons (mediated flight or fight response)
- These cells are considered to be modified postsynaptic sympathetic neurons - Some ganglion cells
[ADRENAL MEDULLA]
What is the function of the hormones released by the adrenal medulla?
- Epinephrine: incr HR, dilate bronchioles, dilate arteries of cardiac and skeletal muscles
- Norepinephrine: constrict vessels of digestive system and skin, incr blood flow to the heart, muscles, and brain
Both these hormone cause glycogenolysis (break down of glycogen into glucose for energy)
[ADRENAL GLAND]
What are some disorders of the adrenal gland?
- Adrenal cortical insufficiency/Addison’s disease (hypoadrenalism due to damage of adrenal cortex, due to long-term corticosteroids)
=> symptoms: fatigue, muscle weakness, LOA, weight loss, abdominal pain, low blood sodium, hypovolemia, low BP - Adrenal cortical tumors (hyperadrenalism)
=> excess glucocorticoids - cushing’s disease
=> excess mineralocorticoids - conn’s syndrome: can cause severe high BP - Adrenal medullary tumor
=> pheochromocytoma (grows from the chromaffin cells)
[PANCREAS]
What is the structure and histology of the pancreas?
- Endocrine cells
- Exocrine cells
Islet of Langerhans (endocrine cells)
- Compact spherical or ovoid masses of endocrine cells embedded within acinar cells
- Endocrine cells appear rounded or polygonal, smaller and lightly stained than exocrine cells
- The islets may be acidophilic or basophilic with cytoplasmic granules
- Arranged in cords separated by fenestrated capillaries
Exocrine cells
- Acinar cells
=> Form a thin reticular capsule surrounding each islet
=> Secrete digestive enzymes into the gut - Endocrine cells appear rounded or polygonal, smaller and lightly stained than exocrine cells
- Duct cells
=> Secrete aq NaHCO3 solution into the gut
[PANCREAS]
What are the 4 cell types in the pancreatic islet cells?
- Alpha cells (20%)
- Beta cells (70%)
3 Delta cells (5-10%) - F cells (1-2%)
*All secrete hydrophilic peptide hormones
[PANCREAS]
What do the alpha cells secrete?
alpha cells secrete glucagon
- incr blood glucose, glycogenolysis, lipolysis, proteolysis
[PANCREAS]
What do the beta cells secrete?
beta cells secrete insulin
- dcr blood glucose by promoting uptake into cells, glycogenesis, lipogenesis, proteogenesis
- B cell malfunction causes DM
[PANCREAS]
What do the delta cells secrete?
delta cells secrete somatostatin
- inhibit release of other islet cell hormones (insulin, glucagon)
- inhibit GH and TSH from anterior pituitary
- inhibit HCl secretion from gastric parietal cells
[PANCREAS]
What do the F cells secrete?
F cells/PP cells secrete pancreatic polypeptide
- stimulates action of gastric chief cells to secrete pepsinogen
- dcr pancreatic enzyme secretion*
- dcr bile secretion
- dcr bicarbonate secretion
- dcr intestinal motility
