Functional Anatomy and Microanatomy of Endocrine Organs - pituitary, hypothalamus and pineal glands

endocrine vs exocrine

exocrine - long ducts with substances secreted externally

endocrine - no ducts, substances are secreted into bloodstream then lymph or tissue fluid

2 sections of the hypophysis

neurohypophysis

adenohypophysis

location of the hypophysis

Rostral to it is the optic chiasm and caudally are the mamillary bodies of the hypothalamus

it sits in the stella turcica or hypophyseal fossa which is a bony cavity of the sphenoid bone

3 sections of the adenohypophysis

pars distalis

pars intermedia

pars tuberalis

pars distalis cells

chromophils

• acidophils - somatotrophs and lactotrophs

• basophils - thyrotrophs, gonadotrophs and corticotrophs

chromophobes - postsecretory cells or stem cells

what do somatotrophs secrete?

growth hormone and somatotropin

what do lactotrophs secrete

prolactin

what do thyrotrophs secrete

thyroid stimulating hormonew

what do gonadotrophs secrete

follicle stimulating hormone

luteinizing hormone

what do corticotrophs secrete

adrenocortocotrophic hormone

function of the pars intermedia

thin section of basophilic cells which are melanotrophs to produce alpha melanocyte stimulating hormone and found close to the pars nervosa

function of pars tuberalis

provides a scaffold for the capillary network of the hypophyseal portal systemho

how are hormones from the adenohypophysis secreted?

the hypothalamus produces hormones in neurosecretory cells of nuclei (peptides and amines) which are released into the bloodstream (hypophyseal portal system) and carried to the pars distalis through the pars tuberalis and then bind to receptors on the endocrine cells and have a stimulatory or inhibitory action

• connected to the hypothalamus via a vascular connection

three sections of the neurohypophysis

median eminence

infundibular stalk

pars nervosa

cells found in the neurohypophysis

pituicytes/neuroglial cells, endothelial cells of the capillaries, nerves, herring bodies

how is the neurohypophysis controlled by the hypothalamus?

the hypothalamus neurosecretory cells in nuclei secrete amines and peptides and these travel along the axons to the neurohypophysis and are stored in herring bodies and are then secreted via the action of pituicytes which are neuroglial cells and placed in the bloodstream to be sent to the rest of the bodyho

hormones from the neurohypophysis

ADH/vasopressin

oxytocin

development of the pituitary gland

adenohypophysis - rathke’s pouch from the oral ectoderm and stomadeum

neurohypophysis - outpouching of the diencephalon

both meet and leave rathke’s cleft which closes in some species, but not in the cow

what is the function of the hypothalamus

It regulates the endocrine and nervous system by regulating temperature, hunger, sex, blood volume and so on, to maintain homeostasis - part of the limbic system

where is the epiphysial gland

this is part of the epithalamus in the mid-brain.

• dorsal to the hypophysis and corpora quadrigemina

• attached to the dorsocaudal end of the third ventricle

  • tumour or cyst of the pineal gland would press on the cerebral aqueduct

function of the pineal gland

it is influenced by the external environment via the retina and optic nerve or vestigial eye and pineal nerves to produce and secrete melatonin

how is melatonin produced

trypophan is converted to serotonin by the pinealocytes, and then the pinealocytes produce an enzyme to converte serotonin to melatonin

which cells are found in the pineal gland

astrocytes and pinealocytes

retino-pineal pathway

1.       Light enters the retina

2.       It then travels to the hypothalamus to the Suprachiasmatic (above the chiasm of two optic nerves) and paraventricular nuclei of the hypothalamus – as in neurone in the hypothalamus

3.       It then goes down to the spinal cord and synapses with the cranial cervical ganglia

4.       It sends its fibres back to the pineal gland to produce melatonin in the pinealocytes