- secretory product that is carried by the bloodstream to target cells

- includes paracrine and autocrine

- relatively long-lasting effects

- 3 categories: steroids, small peptides/proteins, amino acid derivatives

Hormones

- cholesterol-derived compounds

- secreted by the adrenal cortex and gonads

- require carrier/binding proteins for transport in plasma

- producing cells contain large quantities of smooth ER and mitochondria often have a tubular-shaped cristae

(not the plate-like shape)

Steroids

- secreted by hypothalamus, pituitary, (para)thyroid, & neuroendocrine system

- water-soluble but require carriers

- producing cells look like protein producing cells, but with basal granules (vs apical), lots of rough ER

Small peptide, polypeptide, protein hormones

- includes catecholamines, thyroid, prostaglandins, prostacyclins and leukotrienes

Amino acid- and arachidonic acid- derivate hormones

- activate second messenger cascades following hormone stimulus

- most have stimulatory effects on cell metabolism

Cell surface receptors

- generally influence gene expression following hormone stimulus without the help of a second messenger

- most are in nucleus

Intracellular receptors

- type of feedback more common regarding hormone control and production

Negative feedback

- type of feedback that occurs during childbirth

Positive feedback

- Classic endocrine architecture includes groups of glandular epithelial cells and cords & clumps with fenestrated capillaries

- but NONE of these

Ducts

- consists of two lobes, anterior & posterior

- derived from ectoderm of oropharynx (Rathke's pouch) and neuroectoderm of the floor of the 3rd ventricle respectively

- produces tropic and non-tropic hormones and ADH/oxytocin

Pituitary Gland

- made up of Pars distalis, intermedia and tuberalis

- also called the adenohypophysis

- produce ACTH, TSH, FSH, LH, GH, PRL

- contain Somatotropes, Lactotropes, Corticotropes, Gonadotropes, and Thyrotropes

Anterior Lobe of Pituitary Gland

- bulk of the anterior lobe's structure

- most inferior/anterior portion of pituitary gland

Pars distalis

- located between the anterior and posterior lobes of the pituitary gland

- has small follicles of unknown significance

Pars intermedia

- surrounds the infundibulum (connecting stalk) of the pituitary gland

Pars tuberalis

- derived from the neuroectoderm of the floor of the 3rd ventricle

- consists of the pars nervosa and infundibulum & median eminence

- also called the neurohypophysis

- primarily secrete ADH and oxytocin

- contains pituicytes that interact with its blood supply

Posterior lobe of the Pituitary gland

- surrounded by pars tuberalis

- connects hypothalamus to posterior lobe of the pituitary

- where hypothalamic inhibitory & releasing factors are discharged into the primary capillary plexus to perfuse the anterior pituitary

Infundibulum & median eminence

superior hypophysial arteries --> primary capillary plexus (pars tuberalis, median eminence & infundibulum)

--> hypophysial portal veins

--> secondary capillary plexus perfuses pars distalis of anterior lobe

--> dural sinuses

Hypophyseal Portal System

(Blood supply to adenohypophysis/infundibulum)

- Pars nervosa (neurohypophysis) supplied directly by a capillary plexus from thiese arteries

Inferior hypophysial arteries

target cells = other endocrine glands

Examples:

Adrenocorticotrophic hormone (ACTH)

Thyroid stimulating hormone (TSH, thyrotropin)

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Tropic hormones

Target cells = NOT endocrine cells

Examples:

Growth hormone (GH)

Prolactin (PRL)

Non-tropic hormones

- acidophils (stain redish)

- produce growth hormone

- synthesis increased by hypothalamic growth hormone-releasing hormone (GHRH), thyroid hormone and cortisol

- release inhibited by hypothalamic somatostatin

Somatotropes (GH cells)

- acidophil (stains red)

- secrete prolactin

- production stimulated by hypothalamic TRH and other factors associated with pregnancy/nursing

- production inhibited by hypothalamic dopamine

Lactotropes (PRL cells, Mammotrophs)

- Basophilic (stain purple)

- produce proopiomelancortin (POMC), which is then cleaved to ACTH, beta-lipotrophic hormone, melanocyte-stimulating hormone, and beta-endorphin

- Stimulated by corticotropin-releasing hormone (CRH)

Corticotropes (ACTH cells)

- basophilic (stain purple)

- produce FSH and/or LH

- FSH/LH act on gonads, both ovaries & testes

- stimulated by gonadotropin-releasing hormone (GnRH)

Gonadotropes (FSH & LH cells)

- basophilic (stain purple)

- stimulated by hypothalamic thyrotropin-releasing hormone (TRH)

Thyrotropes (TSH cells)

- posterior pituitary contains non-myelinated axons and nerve endings from hypothalamus that release hormones near capillary network (from inferior hypophysial arteries)

- the secretory nerve endings have swellings called

Herring bodies

- ADH and oxytocin are produced here

Hypothalamus NOT posterior pituitary

- acts on distal convoluted tubule & collecting ducts to reabsorb water

- release is controlled through hypothalamic osmoreceptors and feedback from sensory bodies

(carotid body, juxtaglomerular apparatus)

ADH (arginine vasopressin)

- promotes smooth muscle contraction

(uterine & myoepithelial cells of mammary gland)

- feedback from cervix, vagina and nipple promote its release

Oxytocin

- specialized glial cells associated with posterior lobe capillaries

Pituicytes