Principles of Endocrinology; The Central Endocrine Glands

Human Physiology – From Cells to Systems | 9e Lauralee Sherwood Chapter 18

Hypothalamus, pituitary gland, and pineal gland

What are the central endocrine glands?

Endocrine system

consists of the ductless endocrine glands scattered throughout the body

Endocrinology

study of homeostatic chemical adjustments and other activities that hormones accomplish

Hydrophilic

Hydrophilic or lipophilic?

peptide hormones, catecholamines, and indoleamines

lipophilic

Hydrophilic or lipophilic?

steroid hormones and thyroid hormone

Tropic hormones

primary function is regulated by hormone secretion by an endocrine gland

True

True or false?

A single endocrine gland may produce multiple hormones. A single hormone may be secreted by more than one endocrine gland. A single hormone has more than one target.

Effective plasma concentration

Influenced by these factors:

• hormone secretion

• peripheral conversion

• transport

• inactivation

• excretion

Negative-feedback control

output of a system counteracts a change in output

Neuroendocrine reflexes

produce sudden increase in hormone secretion in response to a specific stimulus

Diurnal rhythms

repetitive oscillations in hormone levels that cycle every 24 hours

Hyposecretion

too little hormone is secreted

hypersecretion

too much hormone is secreted

• causes: tumors & immunologic factors

Down regulation

prevents the target cells from overreacting to a prolonged high concentration of insulin

Permissiveness

the situation in which a hormone cannot exert its full effects without the presence of another hormone

Synergism

occurs when two or more hormones combine to produce effects greater than the sum of their individual effects

Antagonism

a pair of hormones that have opposing effects of one another

Pituitary gland

This structure is located in a bony cavity at the brain base.

hypothalamus and posterior pituitary

Which two structures act as a unit to secrete vasopressin and oxytocin?

Vasopressin

conserves H2O during urine formation and causes contraction of arteriolar smooth muscle

Oxytocin

stimulates contraction of uterine smooth muscle

Somatotropes

anterior pituitary cells that secrete growth hormone

Thyrotropes

secrete thyroid-stimulating hormone

Corticotropes

produce and release adrenocorticotropic hormone

Thyrotropin-releasing hormone (TRH)

stimulates release of TSH (thyrotropin) & prolactin

Corticotropin-releasing hormone (CRH)

stimulates release of ACTH (corticotropin)

Gonadotropin-releasing hormone (GnRH)

stimulates release of FSH and LH (gonadotropins)

Dopamine (prolactin-inhibiting hormone; PIH)

inhibits release of PRL

Prolactin-releasing peptide (PrRP)

stimulates release of PRL

GH

hormone that stimulates growth

• directly exerts metabolic effects not related to growth

Hypertrophy

increase in cell size

hyperplasia

increase in number of cells

thickness and length

Bone grows in what two mechanisms?

Mature, nongrowing bone

osteocytes retire from active bone-forming duty

IGF-I

GH causes bones to grow in both length and in thickness via what?

GH deficiency

may be caused by a pituitary defect (lack of GH) or may occur secondary to hypothalamic dysfunctions (lack of GHRH)

Hyposecretion

as a child is one cause of dwarfism

GH excess

most often caused by a tumor of the GH-producing cells of the anterior pituitary

hypersecretion

one cause of gigantism

Thyroid hormone

role in normal endochondral ossification and is essential for skeletal development, linear growth, maintenance of bone mass, and efficient fracture healing

Insulin

alter cellular nutrition to increase nutrient uptake and utilization

Sex steroids

modulate cell sensitivity to GH

• androgens and estrogens

Melatonin

What does the pineal gland secrete?

Suprachiasmatic nucleus

master biological clock that regulates circadian rhythms and sleep-wake cycles.

Melatonin

helps keep the body’s circadian rhythms in time with the light-dark cycle

Melanopsin

protein found in a special type of retinal ganglion cell

• receptor molecule for light that keeps body in tune with external time

melatonin

What is the hormone of darkness?