1. Biology 322 Human Anatomy
Endocrine System

2. Endocrine System
Isolated organs & tissues (“endocrine glands”) which secrete chemical messages (“hormones”) into the blood which cause changes in cells and tissues (“targets”) elsewhere in the body.
Endocrine glands are ductless: they have a rich network of capillaries, and hormones are carried to target tissues & organs by the blood.

3. Endocrine System
Target cells & tissues respond to hormones relatively slowly (seconds, minutes, days) compared to much more rapid (milliseconds) responses to nervous stimulation

4. A specific hormone can only affect cells which have specific receptors for it on their plasma membranes.

5. Any single hormone can have only one effect on any specific target cells, but it may affect different types of target cells in different ways.
For example, epinephrine can:
Stimulate contraction of smooth muscle cells in
arterioles of intestines
Inhibit contraction of smooth muscle cells in
arterioles of leg muscles
Stimulate cardiac muscle cells to contract more quickly
Stimulate sweat glands to secrete sweat
Stimulate liver cells to release glucose into the blood
Stimulate fat cells to break down and release
fats into the blood

7. Hypothalamus
Inferior part of brain,
inferior and anterior
to thalamus.
Right and left halves.
Nuclei in the hypothalamus send 6 hormones to regulate the hormones produced by the anterior pituitary gland:
Growth hormone releasing hormone
Growth hormone inhibiting hormone
Thyrotropin releasing hormone
Corticotropin releasing hormone
Gonadotropin releasing hormone
Prolactin inhibiting hormone

8. Hypothalamus
Inferior part of brain,
inferior and anterior
to thalamus.
Right and left halves.
Nuclei in the hypothalamus synthesize 2 hormones, then transport them down their axons to be released from the posterior pituitary gland as hormones:
Antidiuretic hormone
Oxytocin

9. Pituitary Gland
also called Hypophysis
Located in sella turcica of sphenoid bone
Two developmentally and functionally distinct parts, both under control of hypothalamus of brain

10. Anterior pituitary or adenohypophysis
Secretes 6 hormones
Secretory cells regulated (stimulated or inhibited) by hormones produced in the hypothalamus and carried to it by hypothalamic – hypophyseal portal veins

11. 1) Growth Hormone (GH):
Stimulates growth of many organs
2) Thyroid Stimulating Hormone (TSH):
Stimulates thyroid gland to secrete its hormones
3) Adrenocorticotropic Hormone (ACTH):
Stimulates adrenal cortex to secrete its hormones
4) Prolactin (PRL):
Stimulates milk production by breast
5) Follicle Stimulating Hormone (FSH):
Stimulates development or eggs / sperm
6) Luteinizing Hormone (LH):
Stimulates testes to produce testosterone
Stimulates follicle of ovary to change to corpus luteum

12. Posterior pituitary or neurohypophysis
Secretes 2 hormones
Secretory cells are really the axons whose cell bodies are located in the hypothalamus and whose axons pass through the hypothalamic-hypophyseal tract

13. 1) Oxytocin (OT):
Stimulates contraction of smooth muscle in breast
(lactation) and uterus (labor)
2) Antidiuretic Hormone (ADH):
Increases absorption of water in the kidney to
concentrate urine and decrease its volume

14. Thyroid Gland:
Located in neck, anterior to trachea.
Secretes Triiodothyronine
Tetraiodothyronine
Calcitonin

15. Thyroid Gland:
Located in neck, anterior to trachea.
Secretes Triiodothyronine (T3)
Tetraiodothyronine (T4)
Calcitonin
Secretory cells for T3 and T4
arranged in hollow spheres
called follicles; Stimulated
by thyroid-stimulating hormone
from adenohypophysis.
Secretory cells for calcitonin
located between follicles;
Regulated by concentration of calcium in blood

16. Triiodothyronine (T3) & tetraiodothyronine (T4) increase metabolic rates of cells throughout the body by stimulating energy production by mitochondria.
Calcitonin (CT) stimulates osteoblasts to store additional calcium in the extracellular matrix of bone, thus lowering calcium levels in the blood

17. Parathyroid Glands:
Four small glands on
posterior surface of thyroid
Secretes one hormone: Parathyroid Hormone (PTH)
PTH increases concentration of calcium in blood:
- Stimulates osteocytes & osteoclasts to reabsorb calcium
from bone
- Inhibits kidneys from losing calcium through urine

18. Adrenal Glands:
Located in abdomen
Superior to kidneys
Each adrenal actually two
functionally distinct glands,
one (adrenal cortex)
wrapped around the other
(adrenal medulla)

19. Adrenal Medulla:
Actually a ganglion of the
sympathetic division of the
autonomic nervous system
Secretory cells stimulated by
preganglionic sympathetic neurons
and
Secrete two related hormones
called catecholamines

20. Since epinephrine and
norepinephrine are the
neurotransmitters normally
secreted by postganglionic
sympathetic neurons, they
produce all of the effects of
sympathetic nerve stimulation
on various organs

21. Adrenal Cortex:
Secretes more than twenty
different steroid hormones,
collectively called the
corticosteroids
Secretory cells arranged in three concentric layers, each of which secretes a specific group of corticosteroids.
From superficial to deep:
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis

22. Cells in zona glomerulosa secrete mineralocorticoids
which
regulate concentrations of various minerals (ions, electrolytes) in the blood by controlling their retention and removal by the kidneys.
Most common mineralocorticoid = Aldosterone

23. Cells in zona fasciculata secrete glucocorticoids
which
Regulate metabolism in many cells by:
a) stimulating breakdown of fat
b) stimulating breakdown of proteins
c) increasing concentrations of fatty acids, amino acids,
and glucose in the blood
Stimulate repair of damaged tissue
Most common glucocorticoids = cortisol & corticosterone

24. Cells in zona reticularis secrete gonadocorticoids, or
sex hormones, which supplement those secreted by testes and ovaries.
Mostly androgens (male hormones)
Some estrogens and progesterone (female hormones)
Most common = dehydroepiandrosterone & testosterone

25. Pancreas:
Located in abdomen
Posterior & inferior to stomach
Body of pancreas anterior to
aorta & inferior vena cava
Tail of pancreas extends left

26. Pancreas:
Primarily an exocrine gland
99% of cells secretes digestive enzymes into small intestine
but
1% = groups of endocrine
cells called pancreatic islets
or islets of Langerhans
Secrete two hormones
Insulin
Glucagon
which are antagonistic to each
other in regulating blood glucose

27. Pancreatic Islets:
Alpha cells produce glucagon
Stimulated by low blood sugar
Causes increased blood sugar
by glycogen breakdown
gluconeogenesis
Beta cells produce insulin
Stimulated by high blood sugar
Causes decreased blood sugar
by glycogen synthesis

28. Gonads:
Produce most of the steroid sex hormones

29. Gonads:
Produce most of the steroid sex hormones
Testes:
Interstitial (Leydig) cells
produce androgens
mostly testosterone
Stimulated by luteinizing
hormone from adenohypophysis
Causes development of male
sexual characteristics & their
maintenance

30. Gonads:
Produce most of the steroid sex hormones
Ovaries:
As oocyte develops, it is
surrounded by follicular cells
which produce estrogens,
primarily estradiol
Stimulated by Follicle
Stimulating Hormone from
adenohypophysis.
Causes development of female sexual characteristics
Prepares uterus for pregnancy
Prepares breast for lactation

31. Gonads:
Produce most of the steroid sex hormones
Ovaries:
After ovulation, follicle changes
to corpus luteum, secretes
progesterone.
Stimulated by luteinizing
hormone from adenohypophysis
Maintains thick lining with uterus for pregnancy

32. Many other organs also contain cells & tissues
which secrete hormones.
Examples:
Kidney: Renin (blood pressure)
Erythropoietin (erythrocyte development)
Calciferol (blood calcium)
Heart: Atrial natriuretic hormone (blood sodium)
Liver: Angiotensin (blood pressure)
Thymus: Thymopoietin (lymphocyte development)
Stomach: Cholecystokinin (gall bladder contraction)
& Secretin (pancreas secretion)
Intestine: Gastrin (stomach function)