HUMAN BIOLOGY

What kinds of bodily activities do

hormones typically regulate?

• Hormones generally regulate slower, often long-term changes
  in the growth or functioning of body parts.

taKe-home message

hormones as Long-term Controllers

n Hormones typically regulate activities that occur over an

extended period.

Nervous system signals control rapid-fire reflexes and

speedy responses to changing conditions inside or outside

the body. By contrast, the endocrine system specializes in

slower, often long-term bodily changes such as growth,

sexual maturation, production of red blood cells, and the

like. Some of these functions involve hormones from the

hypothalamus and pituitary, while others depend on other

sources (Table 15.4).

We’ve now completed our overview of hormones and

general information about how they function. The rest of

the chapter looks at how some major hormones operate

in the body and how disorders arise when those key sub-

stances don’t function properly.

Source Secretion(s) Main Targets Primary actions

Pancreatic islets Insulin Muscle, adipose tissue Lowers blood-sugar level

Glucagon Liver Raises blood-sugar level

Somatostatin Insulin-secreting cells Influences carbohydrate metabolism

Adrenal Glucocorticoids Most cells Promote protein breakdown and conversion to glucose

cortex (including cortisol)

Mineralocorticoids Kidney Promote sodium reabsorption; control salt–water balance

(including aldosterone)

Adrenal Epinephrine Liver, muscle, adipose Raises blood level of sugar, fatty acids; increases heart rate,

medulla (adrenaline) tissue force of contraction

Norepinephrine Smooth muscle of Promotes constriction or dilation of blood vessel diameter

blood vessels

Thyroid Triiodothyronine, Most cells Regulate metabolism; have roles in growth, development

thyroxine

Calcitonin Bone Lowers calcium levels in blood

Parathyroids Parathyroid hormone Bone, kidney Elevates levels of calcium and phosphate ions in blood

Thymus Thymosins, etc. Lymphocytes Have roles in immune responses

Gonads:

Testes Androgens (including General Required in sperm formation, development of genitals,

(in males) testosterone) maintenance of sexual traits; influence growth, development

Ovaries Estrogens General Required in egg maturation and release; prepare uterine

(in females) lining for pregnancy; required in development of genitals,

maintenance of sexual traits; influence growth, development

Progesterone Uterus, breasts Prepares, maintains uterine lining for pregnancy; stimulates

breast development

Pineal Melatonin Hypothalamus Influences daily biorhythms

Endocrine cells Gastrin, secretin, etc. Stomach, pancreas, Stimulate activity of stomach, pancreas, liver, gallbladder

of stomach, gut gallbladder

Liver IGFs (insulin-like Most cells Stimulate cell growth and development

growth factors)

Kidneys Erythropoietin Bone marrow Stimulates red blood cell production

Angiotensin* Adrenal cortex, Helps control blood pressure, aldosterone secretion

arterioles

Vitamin D* Bone, gut Enhances calcium resorption and uptake

Heart Atrial natriuretic Kidney, blood vessels Increases sodium excretion; lowers blood pressure

peptide

Table 15.4 Hormone Sources Other Than the Hypothalamus and Pituitary

15.4

292 Chapter 15

*These hormones are not produced in the kidneys but are formed when enzymes produced in kidneys activate specific substances in the blood.

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