Endocrine Organs

Endocrine organs 

Produce hormones in small amounts 

  



Chemical signals

Secrete into the bloodstream Distributed throughout the body Affects target cells/organs where ever they are in the body What determines what the targets are?

Hypophysis   

Pituitary gland Found in the sella turcica Derived from oral ectoderm (Rathke’s pouch) and nervous tissue growing together

Hypophysis 

Actually composed of two glands 

The anterior pituitary/lobe or the adenohypophysis or the pars distalis 



Pars tuberalis and pars intermedia

The posterior pituitary/lobe or the neurohypophysis or the pars nervosa 

Infundibulum/neural stalk

Difference between lobes 



The anterior lobe actually synthesizes the hormones that it releases The posterior lobe simply releases the hormones that are produced by neurons in the brain (the hypothalamus) 

Essentially the pars nervosa is releasing __________.

Adenohypophysis 

3 cells types are apparent  

Chromophobes Chromophiles  

Acidophils basophils

Neurohypophysis 



Composed of 100,000 neurons that arise in the paraventricular (oxytocin) and supraoptic (vasopressin) nuclei Cells end on a neurohemal organ 

A structure where neurons end on blood vessels not other neurons, muscles or glands

Actions of the hormones 

The pituitary gland affects more organs and tissues than any other organ in the body, hence 

The Master Gland

Other glands 

Adrenals  

  

Medulla Cortex

Islets of Langerhans Thyroid Parathyroids

Adrenals 

Besides the standard location of the adrenals (on top of the kidneys) adrenal tissue is sometimes also found in other locations in the abdomen

A ball, of yarn

A bundle or band

A network

Adrenal medulla 



Essentially a sympathetic ganglion where the postganglionic cells have lost their axons and dendrites They store epinephrine (80%) and norepinephrine which is released upon sympathetic stimulation

Epi vs Norepi cells 



Epinephrine secreting cells have smaller granules that are less electron dense and fill the vacuoles Norepinephrine secreting cells have larger granules that are more electron dense and are irregularly shaped.

Islets of Langerhans of Pancreas 

The endocrine part of the pancreas   

Alpha cells -> glucagon Beta cells -> insulin Delta cells -> somatostatin

Thyroid 

Peculiar organ structurally  

Composed of follicles Follicles filled with colloid 



thyroglobulin

Parafollicular cells produce another hormone 

Calcitonin – increase blood calcium and stimulates osteogenesis

Colloid contains thyroglobulin which when needed for secretion is converted to T3 and T4 forms of thyroxin.

Parathyroid 

Chief cells produce 

Parathormone 

Raises blood calcium and stimulates osteoclastic activity

Chief Cells (Parathormone)

Oxyphil cells (?)