1

18-1

Chp. 18Endocrine System

Functions:

• Metabolism and tissue maturation

• Ion regulation

• Water balance

• Immune system regulation

• Heart rate and blood pressure regulation

• Control of blood glucose and other nutrients

• Control of reproductive functions

• Uterine contractions and milk release

18-2

Pituitary Gland and

Hypothalamus• Where nervous and

endocrine systems interact

• Hypothalamus regulates secretions of anterior pituitary

• Posterior pituitary is an extension of the hypothalamus

• Anterior pituitary produces nine major hormones that– Regulate body functions

– Regulate the secretions of other endocrine glands

2

18-3

Hypothalamus, Anterior Pituitary,

and Target Tissues

18-4

Releasing and Inhibiting Hormones

• Tropins or tropic hormones: hormones that regulate the hormone secretions of target endocrine tissues. All anterior pituitary hormones are tropins.

• Releasing hormones:

– GHRH. Growth hormone-releasing hormone. Causes the anterior pituitary to release growth hormone.

– TRH. Thyrotropin-releasing hormone. Causes the anterior pituitary to release thyroid-stimulating hormone (TSH).

– CRH. Corticotropin-releasing hormone. Causes anterior pituitary to produce adrenocorticotropic hormone.

– GnRH. Gonadotropin-releasing hormone. Causes anterior pituitary to produce FSH (follicle stimulating hormone) and LH (luteinizing hormone).

– PRH. Prolactin-releasing hormone. Causes the anterior pituitary to release prolactin.

• Inhibiting hormones:

– GHIH. Growth hormone-inhibiting hormone, somatostatin. Causes the anterior pituitary to decrease release of growth hormone.

– PIH. Prolactin-inhibiting hormone. Causes the anterior pituitary to decrease release of prolactin.

3

18-5

Hypothalamus, Posterior Pituitary,

and Target Tissues

18-6

Hormones of Posterior Pituitary: ADH

• Antidiuretic hormone (ADH). Also called vasopressin.

A. Osmoreceptors (specialized neurons of

hypothalamus monitor changes in intercellular

osmolality (relative concentrations of electrolytes and

water). If the concentration of electrolytes increases

or if the concentration of water decreases, then ADH

secretion is stimulated.

B. Baroreceptors (specialized neurons found in walls of

atria of heart, large veins, carotid arteries, aortic arch)

sense changes in blood pressure (BP). If BP

decreases, then ADH secretion is stimulated.

4

18-7

Control of ADH Secretion

18-8

Control of Oxytocin Secretion

5

18-9

Anterior Pituitary Hormones

• Growth hormone (GH) or somatotropin

• Thyroid-stimulating hormone (TSH)

• Adrenocorticotropic hormone (ACTH)

• Melanocyte-stimulating hormone (MSH)

• Beta endorphins

• Lipotropins

• Luteinizing hormone (LH)

• Follicle-stimulating hormone (FSH)

• Prolactin

18-10

Growth Hormone

(GH or somatotropin)

• Stimulates uptake of amino acids; protein synthesis

• Stimulates breakdown of fats to be used as an energy source but stimulates synthesis of glycogen: glucose sparing

• Promotes bone and cartilage growth

• Regulates blood levels of nutrients after a meal and during periods of fasting

6

18-11

Thyroid Gland• One of largest endocrine glands; Highly vascular. Iodine enters follicular cells

by active transport. Only gland that stores hormone.

• Histology

– Composed of follicles: follicular cells surrounding thyroglobulin/thyroid hormones

– Parafollicular cells: between follicles

• Physiology

–Follicular cells secrete thyroglobulin into lumen of follicle. Iodine and tyrosine necessary for production of T3 and T4. Hormones stored here attached to the thyroglobulin then absorbed into follicular cells; hormones detached from thyroglobulin and released into circulation.

–Parafollicular cells. Secrete calcitoninwhich reduces [Ca2+] in body fluids when Ca levels are elevated.

18-12

Biosynthesis of Thyroid

Hormones

7

18-13

18-14

Regulation of

Calcitonin Secretion• Produced by parafollicular cells

• Secretion triggered by high Ca2+ concentration in

blood; acts to decrease Ca2+ concentration

• Primary target tissue: bone. Decreases osteoclast

activity, lengthens life span of osteoblasts.

8

18-15

Parathyroid Glands

• Embedded in thyroid

• Two glands on each side

• Secrete PTH: target tissues are bone, kidneys and intestines.– Increases blood calcium and phosphate

levels

– Stimulates osteoclasts

– Promotes calcium reabsorption by kidneys and PO4 excretion

– Increases synthesis of vitamin D which, in turn, increases absorption of Ca and PO4 by intestines. Net loss of PO4 under influence of PTH.

• Regulation depends on calcium levels.

18-16

Adrenocorticotrophic Hormone (ACTH)

• CRH from hypothalamus causes release of

ACTH from anterior pituitary which

– Causes cortisol secretion from the adrenal cortex (a glucocorticoid from the zona fasciculata)

– Causes aldosterone secretion from the adrenal cortex (a mineralocorticoid from the zona glomerulosa)

– Binds directly to melanocytes of the skin; causes increase in production of melanin.

9

18-17

Adrenal Glands

• Near superior poles of kidneys; retroperitoneal

• Inner medulla; outer cortex

• Medulla: formed from neural crest; sympathetic. Secretes epinephrine and norepinephrine

• Cortex: three zones from superficial to deep

– Zona glomerulosa

– Zona fasciculata

– Zona reticularis

18-18

10

18-19

Pancreas

• Located along small intestine and

stomach; retroperitoneal

• Exocrine gland

– Produces pancreatic digestive juices

• Endocrine gland

– Consists of pancreatic islets

– Composed of

• Alpha cells; secrete glucagon

• Beta cells; secrete insulin

• Delta cells; secrete somatostatin

18-20

Insulin and Glucagon

Insulin

• Target tissues: liver,

adipose tissue, muscle,

and satiety center of

hypothalamus

• Increases uptake of

glucose and amino

acids by cells

Glucagon

• Target tissue is liver

• Causes breakdown of

glycogen and fats for

energy

11

18-21

Hormones of the Reproductive System

Male: Testes

• Testosterone– Regulates production of

sperm cells and development and maintenance of male reproductive organs and secondary sex characteristics

• Inhibin– Inhibits FSH secretion

Female: Ovaries

• Estrogen and Progesterone– Uterine and mammary

gland development and function, external genitalia structure, secondary sex characteristics, menstrual cycle

• Inhibin– Inhibits FSH secretion

• Relaxin– Increases flexibility of

symphysis pubis

18-22

LH, FSH, Prolactin• Gonadotropins: glycoprotein hormones that promote

growth and function of the gonads

• LH and FSH

– Both hormones regulate production of gametes and reproductive hormones

• Testosterone in males

• Estrogen and progesterone in females

• GnRH from hypothalamus stimulates LH and FSH secretion

• Prolactin: role in milk production

– Regulation of secretion: prolactin-releasing hormone (PRH) and prolactin-inhibiting hormones (PIH)

12

18-23

Melanocyte Stimulating Hormone,

Endorphins, and Lipotropins

• ACTH, MSH, endorphins and lipotropins all

derived from the same large precursor molecule

when stimulated by CRH

• MSH causes melanocytes to produce more

melanin

• Endorphins act as an analgesic; produced during

times of stress.

• Lipotropins cause adipose cells to catabolize fat

18-24

Pineal Body

• In epithalamus; produces melatonin and argininevasotocin

13

18-25

Thymus Gland, GI Tract

• Thymosin. Development of the immune

system.

• GI tract: several hormones regulate

digestion and enzyme secretion. Studied

with digestive system.

18-26

Hormone-like Substances

• Autocrines: chemical signals released by a cell

and the substance affects that same cell.

– Chemical mediators of inflammation which are

modified fatty acids: eicosanoids such as

prostaglandins, thromboxanes, prostacyclins, and

leukotrienes

• Paracrines: chemical signals released into

intercellular fluid and affecting nearby cells.

– Endorphins and enkephalins modulate sensation of pain

– Several growth factors

14

18-27

Effects of Aging on

Endocrine System

• Gradual decrease in secretory activity of some

glands

– GH as people age except in people who exercise

regularly

– Melatonin

– Thyroid hormones

– Kidneys secrete less renin

• Familial tendency to develop type II diabetes