Endocrine System (Ch. 18)
Human Anatomy lecture
I. Overview – KNOW Fig. 18.1
A. Review endocrine - vs. - exocrine glands
- secrete hormones (chemical messengers) into blood stream:
endocrine cell  interstitial fluid  capillary  through blood vessels to target tissue 
“picked up” only by target tissue w/specific receptor
 NOTE: No duct involved
B. More a physiological system than an anatomical system
- essentially every body tissue and organ secretes chemical messengers affecting
other tissues
C. Controls more slowly than nervous system, but lasts longer.
II. Central Endocrine organs
A. Hypothalamus
1. Interface between nervous and endocrine systems
2. Different nuclei (review Fig. 15.11) secrete at least 8 different hormones
3. Most (6) diffuse into the hypophyseal portal veins into the anterior pituitary,
where they stimulate or inhibit release of other hormones
4. Two travel down axons to the posterior pituitary, where they are stored until
released
B. Pituitary gland (hypophysis) – Fig. 18.2
- sits in sella turcica
- 2 anatomically distinct glands
1. Anterior pituitary (adenohypophysis) or “anterior lobe”
- embryologically derived from the roof of the mouth
- 5 different cell types secrete 6 major hormones
- blood supply via hypophyseal portal system
2. Posterior pituitary (neurohypophysis) or “posterior lobe”
- derived from brain outgrowth
- physically connected to hypothalamus via infundibulum
- has axon terminals from hypothalamic neurons, supported by neuroglia
- separate blood supply from anterior lobe
C. Pineal gland
- in epithalamus, attached to roof of 3rd ventricle
- largest in children (1-5 yrs), atrophied by end of puberty
- secretes melatonin
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III. Peripheral endocrine organs
A. Thymus – Fig. 18.5
- several hormones involved in T cell maturation
B. Thyroid gland - Fig. 18.6
- largest endocrine gland in adults, inferior to larynx
- left and right lateral lobes connected by isthmus
- thyroid hormone uniquely contains iodine
- produced and stored in microscopic sacs called follicles
C. Parathyroid glands – Fig. 18.7
- 4 small masses embedded in posterior surface of the thyroid
D. Adrenal (suprarenal) glands –Fig. 18.8
- structurally and functionally 2 distinct glands
1. adrenal cortex - 3 histological zones that secrete 3 types of steroid hormones
(corticosteroids)
2. adrenal medulla - consists of anaxonic chromaffin cells: essentially
sympathetic postganglionic cells
- secrete epinephrine and norepinephrine
* adrenal medulla = sympathetic ganglion
E. Pancreas
- pancreatic islets (of Langerhans) are endocrine portions
- 5 different cell types produce 5 different hormones, including insulin
F. Gonads
- ovaries (follicular cells) and testes (interstitial [Leydig] cells) produce several
reproductive hormones, all of which are steroid hormones
G. Other tissues  See Table 18.3 (NRF details)
heart
kidneys
placenta
liver
gut
bone
skin
adipose tissue
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