Major Endocrine Glands

Essentials of Anatomy and Physiology, Seventh Edition
Valerie C. Scanlon and Tina Sanders
Copyright © F.A. Davis Company 2015
Chapter 10
The Endocrine System

Endocrine Glands—ductless glands that secrete
hormones into the blood
Hormones—chemicals that exert their effects on target organs
or tissues
Chemistry of hormones—Amines:
Proteins:
Steroids:
Question: Can you name the major endocrine glands?

Answer
The major endocrine glands are the pituitary gland (anterior
and posterior), thyroid gland, parathyroid glands,
pancreas, adrenal glands (cortex and medulla in each),
ovaries, and testes.

Regulation of Secretion of Hormones
Hormones are secreted when there is a need for their effects;
each hormone has a specific stimulus for secretion.
The secretion of most hormones is regulated by negative
feedback mechanisms.
Question: Describe the basic sequence or steps of a negative feedback
mechanism.

Answer
The basic sequence of a negative feedback mechanism for
hormone secretion is as follows:
A stimulus increases secretion of the hormone.
The hormone exerts its effects; the effects decrease the
stimulus.
The secretion of the hormone decreases until the
stimulus recurs.

Pituitary Gland (hypophysis)—within the sella
turcica, below the hypothalamus (see Tables 10–1 and 10–2)
Posterior pituitary gland (neurohypophysis)—stores
hormones produced by the hypothalamus: ADH and
oxytocin
Antidiuretic hormone (ADH)—increases water reabsorption
by the kidneys; in large amounts, causes vasoconstriction
Result:
Stimulus for secretion:

Posterior Pituitary (continued)
Oxytocin—stimulates contraction of the myometrium during
labor; stimulates release of milk from mammary glands.

Anterior Pituitary Gland (adenohypophysis)—regulated
by releasing hormones from the hypothalamus
Growth hormone (GH)—increases amino acid transport into
cells:
Increases protein synthesis:
Increases mitosis:
Increases use of fats for energy:

Anterior Pituitary (continued)
Thyroid stimulating hormone (TSH)—increases secretion of
thyroxine and T3
Adrenocorticotropic hormone (ACTH)—increases secretion
of cortisol
Prolactin—stimulates milk production

Anterior Pituitary (continued)
Gonadotropic hormones (stimulus: GnRH): FSH and LH
Follicle-stimulating hormone (FSH)
In women: initiates development of ovarian follicles and
secretion of estrogen
In men: initiates sperm development
Luteinizing hormone (LH)
In women: stimulates ovulation and secretion of
progesterone
In men: stimulates secretion of testosterone

Thyroid Gland—on the front of the trachea below
the larynx (see Table 10–3)
Thyroxine and T3 (iodine is part of both hormones)—increase
use of all three food types for energy and increase protein
synthesis
Result:
Calcitonin—decreases reabsorption of calcium from bones
Effect on blood calcium level:

Parathyroid Glands—two on the back of each lobe of
the thyroid (see Table 10–4)
Parathyroid hormone (PTH)
Effect on bones:
Effect on small intestine:
Effect on kidneys:
Effect on blood calcium level:

Pancreas—between the duodenum and the spleen; islets
of Langerhans are the endocrine part (see Table 10–5)
Glucagon—alpha cells
Increases conversion of glycogen to glucose by the
liver
Increases use of fats and amino acids for energy
Effect on blood glucose level:

Pancreas (continued)
Insulin—beta cells
Increases use of glucose by cells
Increases conversion of glucose to glycogen in the
liver and muscles
Increases cellular intake of fatty acids and amino
acids and use for synthesis
Effect on blood glucose level:

Adrenal Glands—on top of the kidneys (see Tables
10–6 and 10–7); each has a medulla and a cortex.
Adrenal medulla—secretes catecholamines in stressful
situations: epinephrine and norepinephrine
Stimulus for secretion (of both):
Norepinephrine—stimulates vasoconstriction:
Effect on blood pressure:
Questions: State the relative positions of the adrenal cortex and medulla.
The effects of epinephrine are much the same as the responses brought
about by which division of the nervous system?

Answers
The adrenal cortex is the outer layer of the gland; the
medulla is the inner layer.
The effects of epinephrine are very much like the effects of
the sympathetic division of the autonomic nervous
system.

Adrenal Medulla (continued)
Epinephrine—effect on:
Heart rate and force:
Blood vessels in skin and viscera:
Blood vessels in skeletal muscle:
Peristalsis:
Bronchioles:
Liver:
Cell respiration:
Use of fats for energy:

Adrenal Cortex
Produces: Mineralocorticoids (aldosterone)
Glucocorticoids (cortisol)
Very small amounts of sex hormones (male
androgens and female estrogens)

Adrenal Cortex (continued)
Aldosterone—increases the reabsorption of Na+
ions by the
kidneys and the excretion of K+
ions,
Results (indirect effects)—
Hydrogen ions:
Chloride and bicarbonate ions:
Water:
Blood pH:
Blood volume and blood pressure :

Adrenal Cortex (continued)
Cortisol—increases the use of amino acids and fats for
energy:
Decreases the use of glucose to conserve glucose:
Has an anti-inflammatory effect:
Lysosomes:
Effects of histamine:

Ovaries—on either side of the uterus in the pelvic cavity
Estrogen—produced by follicle cells
Initiates growth of ova:
Stimulates growth of the endometrium:
Promotes growth of ducts of mammary glands:
Stimulates development of secondary sex characteristics:
Question: What effect does estrogen have on the epiphyseal discs of long bones?

Answer
Estrogen promotes closure of the epiphyseal discs of long
bones; this means that all of the cartilage has been
replaced by bone matrix.

Ovaries (continued)
Progesterone—produced by the corpus luteum:
Growth of endometrium:
Growth of secretory cells of mammary glands:
Inhibin—inhibits secretion of FSH:

Testes—in the scrotum between the upper thighs
Testosterone—produced by interstitial cells
Promotes maturation of sperm
Stimulates growth of reproductive organs:
Stimulates development of secondary sex characteristics:
Increases protein synthesis:
Epiphyseal discs—
Inhibin—inhibits secretion of FSH:

Mechanisms of Hormone Action—target cells
have receptors for specific hormones
The two-messenger model (for protein hormones):
First messenger—a hormone bonds to a cell membrane
receptor  synthesis of cyclic AMP
Second messenger—cyclic AMP activates the cell’s
enzymes:

Mechanisms of Hormone Action (continued)
Mechanism for steroid hormones:
Steroid hormone—diffuses into the cell and bonds to a
cytoplasmic receptor
Steroid-protein complex—enters the cell’s nucleus 
activates genes:
Result:

Wrap-Up Question
Blood chemistry affects hormone secretion; name the
hormone for each stimulus.
1. Hyperglycemia
2. Hypercalcemia
3. Hyperkalemia
4. Hyponatremia
5. Hypocalcemia
6. Hypoglycemia
7. Increased TSH
8. Increased ACTH

Answers
1. Hyperglycemia—insulin
2. Hypercalcemia—calcitonin
3. Hyperkalemia—aldosterone
4. Hyponatremia—aldosterone
5. Hypocalcemia—PTH
6. Hypoglycemia—glucagon
7. Increased TSH—thyroxine
8. Increased ACTH—cortisol

Major Endocrine Glands

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